Document:

EX-10.2

 Exhibit 10.2 

ALECTOR, INC. 
 2017 STOCK
OPTION AND GRANT PLAN 
 (as amended on November 15, 2018) 

 

	SECTION 1.	 GENERAL PURPOSE OF THE PLAN; DEFINITIONS 

The name of the plan is the Alector, Inc. 2017 Stock Option and Grant Plan (the “Plan”). The purpose of the Plan is to encourage and
enable the officers, employees, directors, Consultants and other key persons of Alector, Inc., a Delaware corporation (including any successor entity, the “Company”) and its Subsidiaries, upon whose judgment, initiative and efforts the
Company largely depends for the successful conduct of its business, to acquire a proprietary interest in the Company. 
 The following terms
shall be defined as set forth below: 
 “Affiliate” of any Person means a Person that directly or indirectly, through one or
more intermediaries, controls, is controlled by or is under common control with the first mentioned Person. A Person shall be deemed to control another Person if such first Person possesses directly or indirectly the power to direct, or cause the
direction of, the management and policies of the second Person, whether through the ownership of voting securities, by contract or otherwise. 

“Award” or “Awards,” except where referring to a particular category of grant under the Plan, shall include
Incentive Stock Options, Non-Qualified Stock Options, Restricted Stock Awards, Unrestricted Stock Awards, Restricted Stock Units or any combination of the foregoing. 

“Award Agreement” means a written or electronic agreement setting forth the terms and provisions applicable to an
Award granted under the Plan. Each Award Agreement may contain terms and conditions in addition to those set forth in the Plan; provided, however, in the event of any conflict in the terms of the Plan and the Award Agreement, the terms of the
Plan shall govern. 
 “Board” means the Board of Directors of the Company. 

“Cause” shall have the meaning as set forth in the Award Agreement(s). In the case that any Award Agreement does not contain
a definition of “Cause,” it shall mean (i) the grantee’s dishonest statements or acts with respect to the Company or any Affiliate of the Company, or any current or prospective customers, suppliers vendors or other third parties
with which such entity does business; (ii) the grantee’s commission of (A) a felony or (B) any misdemeanor involving moral turpitude, deceit, dishonesty or fraud; (iii) the grantee’s failure to perform his assigned
duties and responsibilities to the reasonable satisfaction of the Company which failure continues, in the reasonable judgment of the Company, after written notice given to the grantee by the Company; (iv) the grantee’s gross negligence,
willful misconduct or insubordination with respect to the Company or any Affiliate of the Company; or (v) the grantee’s material violation of any provision of any agreement(s) between the grantee and the Company relating to noncompetition,
nonsolicitation, nondisclosure and/or assignment of inventions. 

 “Chief Executive Officer” means the Chief Executive Officer of the
Company or, if there is no Chief Executive Officer, then the President of the Company. 
 “Code” means the Internal Revenue
Code of 1986, as amended, and any successor Code, and related rules, regulations and interpretations. 
 “Committee” means
the Committee referred to in Section 2. 
 “Consultant” means any natural person that provides bona fide
services to the Company (including a Subsidiary), and such services are not in connection with the offer or sale of securities in a capital-raising transaction and do not directly or indirectly promote or maintain a market for the Company’s
securities. 
 “Disability” means “disability” as defined in Section 422(c) of the Code. 

“Effective Date” means the date on which the Plan is adopted as set forth on the final page of the Plan. 

“Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations thereunder. 

“Exchange Program” means a program under which (i) outstanding Awards are surrendered or cancelled in exchange for
awards of the same type (which may have higher or lower exercise prices and different terms), awards of a different type, and/or cash, (ii) holders of Awards would have the opportunity to transfer any outstanding Awards to a financial
institution or other person or entity selected by the Committee, and/or (iii) the exercise price of an outstanding Award is reduced or increased. The Committee will determine the terms and conditions of any Exchange Program in its sole
discretion. 
 “Fair Market Value” of the Stock on any given date means the fair market value of the Stock determined in
good faith by the Committee based on the reasonable application of a reasonable valuation method not inconsistent with Section 409A of the Code. If the Stock is admitted to trade on a national securities exchange, the determination shall be
made by reference to the closing price reported on such exchange. If there is no closing price for such date, the determination shall be made by reference to the last date preceding such date for which there is a closing price. If the date for which
Fair Market Value is determined is the first day when trading prices for the Stock are reported on a national securities exchange, the Fair Market Value shall be the “Price to the Public” (or equivalent) set forth on the cover page for the
final prospectus relating to the Company’s Initial Public Offering. 
 “Good Reason” shall have the meaning as
set forth in the Award Agreement(s). In the case that any Award Agreement does not contain a definition of “Good Reason,” it shall mean (i) a material diminution in the grantee’s base salary except for across-the-board salary reductions similarly affecting all or substantially all similarly situated employees of the Company or (ii) a change of more than 50 miles in the
geographic location at which the grantee provides services to the Company, so long as the grantee provides at least 90 days notice to the Company following the initial occurrence of any such event and the Company fails to cure such event within 30
days thereafter. 
 “Grant Date” means the date that the Committee designates in its approval of an Award in
accordance with applicable law as the date on which the Award is granted, which date may not precede the date of such Committee approval. 

“Holder” means, with respect to an Award or any Shares, the Person holding such Award or Shares, including the initial
recipient of the Award or any Permitted Transferee. 

  
 -2- 

 “Incentive Stock Option” means any Stock Option designated and qualified as
an “incentive stock option” as defined in Section 422 of the Code. 
 “Initial Public Offering” means the
consummation of the first firm commitment underwritten public offering pursuant to an effective registration statement under the Securities Act covering the offer and sale by the Company of its equity securities, as a result of or following which
the Stock shall be publicly held. 
 “Non-Qualified Stock Option” means any Stock
Option that is not an Incentive Stock Option. 
 “Option” or “Stock Option” means any option to purchase
shares of Stock granted pursuant to Section 5. 
 “Permitted Transferees” shall mean any of the following to whom a
Holder may transfer Shares hereunder (as set forth in Section 9(a)(ii)(A)): the Holder’s child, stepchild, grandchild, parent, stepparent, grandparent, spouse, former spouse, sibling, niece, nephew, mother-in-law, father-in-law, son-in-law, daughter-in-law, brother-in-law, or sister-in-law, including adoptive relationships, any person sharing the Holder’s household (other than a tenant or employee), a trust in which these persons have more than fifty percent of the beneficial
interest, a foundation in which these persons control the management of assets, and any other entity in which these persons own more than fifty percent of the voting interests; provided, however, that any such trust does not require or permit
distribution of any Shares during the term of the Award Agreement unless subject to its terms. Upon the death of the Holder, the term Permitted Transferees shall also include such deceased Holder’s estate, executors, administrators, personal
representatives, heirs, legatees and distributees, as the case may be. 
 “Person” shall mean any individual, corporation,
partnership (limited or general), limited liability company, limited liability partnership, association, trust, joint venture, unincorporated organization or any similar entity. 

“Restricted Stock Award” means Awards granted pursuant to Section 6 and “Restricted Stock”
means Shares issued pursuant to such Awards. 
 “Restricted Stock Unit” means an Award of phantom stock units to
a grantee, which may be settled in cash or Shares as determined by the Committee, pursuant to Section 8. 
 “Sale
Event” means the consummation of (i) the dissolution or liquidation of the Company, (ii) the sale of all or substantially all of the assets of the Company on a consolidated basis to an unrelated person or entity,
(iii) a merger, reorganization or consolidation pursuant to which the holders of the Company’s outstanding voting power immediately prior to such transaction do not own a majority of the outstanding voting power of the surviving or
resulting entity (or its ultimate parent, if applicable), (iv) the acquisition of all or a majority of the outstanding voting stock of the Company in a single transaction or a series of related transactions by a Person or group of Persons, or
(v) any other acquisition of the business of the Company, as determined by the Board; provided, however, that the Company’s Initial Public Offering, any subsequent public offering or another capital raising event, or a merger
effected solely to change the Company’s domicile shall not constitute a “Sale Event.” 

  
 -3- 

 “Section 409A” means Section 409A of the
Code and the regulations and other guidance promulgated thereunder. 
 “Securities Act” means the Securities Act of 1933,
as amended, and the rules and regulations thereunder. 
 “Service Relationship” means any relationship as a
full-time employee, part-time employee, director or other key person (including Consultants) of the Company or any Subsidiary or any successor entity (e.g., a Service Relationship shall be deemed to continue without interruption in the event an
individual’s status changes from full-time employee to part-time employee or Consultant). 
 “Shares” means
shares of Stock. 
 “Stock” means the Common Stock, par value $0.0001 per share, of the Company. 

“Subsidiary” means any corporation or other entity (other than the Company) in which the Company has more than a
50 percent interest, either directly or indirectly. 
 “Ten Percent Owner” means an employee who owns or is
deemed to own (by reason of the attribution rules of Section 424(d) of the Code) more than 10 percent of the combined voting power of all classes of stock of the Company or any parent of the Company or any Subsidiary. 

“Termination Event” means the termination of the Award recipient’s Service Relationship with the Company and its
Subsidiaries for any reason whatsoever, regardless of the circumstances thereof, and including, without limitation, upon death, disability, retirement, discharge or resignation for any reason, whether voluntarily or involuntarily. The following
shall not constitute a Termination Event: (i) a transfer to the service of the Company from a Subsidiary or from the Company to a Subsidiary, or from one Subsidiary to another Subsidiary or (ii) an approved leave of absence for military
service or sickness, or for any other purpose approved by the Committee, if the individual’s right to re-employment is guaranteed either by a statute or by contract or under the policy pursuant to which
the leave of absence was granted or if the Committee otherwise so provides in writing. 
 “Unrestricted Stock Award”
means any Award granted pursuant to Section 7 and “Unrestricted Stock” means Shares issued pursuant to such Awards. 
  

	SECTION 2.	 ADMINISTRATION OF PLAN; COMMITTEE AUTHORITY TO SELECT GRANTEES AND DETERMINE AWARDS

 (a) Administration of Plan. The Plan shall be administered by the Board, or at the discretion of the Board, by a
committee of the Board or a committee of Board members or of other individuals satisfying applicable laws appointed by the Board. All references herein to the “Committee” shall be deemed to refer to the individual(s) then responsible for
administration of the Plan at the relevant time (i.e., either the Board of Directors or such a committee or committees, as applicable). 

  
 -4- 

 (b) Powers of Committee. The Committee shall have the power and authority to grant
Awards consistent with the terms of the Plan, including the power and authority: 
 (i) to select the individuals to whom Awards may from
time to time be granted; 
 (ii) to determine the time or times of grant, and the amount, if any, of Incentive Stock Options, Non-Qualified Stock Options, Restricted Stock Awards, Unrestricted Stock Awards, Restricted Stock Units, or any combination of the foregoing, granted to any one or more grantees; 

(iii) to determine the number of Shares to be covered by any Award and, subject to the provisions of the Plan, the price, exercise price,
conversion ratio or other price relating thereto; 
 (iv) to determine and, subject to Section 12, to modify from time to time the
terms and conditions, including restrictions, not inconsistent with the terms of the Plan, of any Award, which terms and conditions may differ among individual Awards and grantees, and to approve the form of Award Agreements; 

(v) to institute and determine the terms and conditions of an Exchange Program; 

(vi) to accelerate at any time the exercisability or vesting of all or any portion of any Award; 

(vii) to impose any limitations on Awards, including limitations on transfers, repurchase provisions and the like, and to exercise repurchase
rights or obligations; 
 (viii) subject to Section 5(a)(ii) and any restrictions imposed by Section 409A, to extend at any time
the period in which Stock Options may be exercised; and 
 (ix) at any time to adopt, alter and repeal such rules, guidelines and practices
for administration of the Plan and for its own acts and proceedings as it shall deem advisable; to interpret the terms and provisions of the Plan and any Award (including Award Agreements); to make all determinations it deems advisable for the
administration of the Plan; to decide all disputes arising in connection with the Plan; and to otherwise supervise the administration of the Plan. 
 All
decisions and interpretations of the Committee shall be binding on all persons, including the Company and all Holders. 
 (c) Award
Agreement. Awards under the Plan shall be evidenced by Award Agreements that set forth the terms, conditions and limitations for each Award. 

(d) Indemnification. Neither the Board nor the Committee, nor any member of either or any delegate thereof, shall be liable for any
act, omission, interpretation, construction or determination made in good faith in connection with the Plan, and the members of the Board and the Committee (and any delegate thereof) shall be entitled in all cases to indemnification and
reimbursement by the Company in respect of any claim, loss, damage or expense (including, without limitation, reasonable attorneys’ fees) arising or resulting therefrom to the fullest extent permitted by law and/or under the Company’s
governing documents, including its certificate of incorporation or bylaws, or any directors’ and officers’ liability insurance coverage which may be in effect from time to time and/or any indemnification agreement between such individual
and the Company. 

  
 -5- 

 (e) Foreign Award Recipients. Notwithstanding any provision of the Plan to the
contrary, in order to comply with the laws in other countries in which the Company and any Subsidiary operate or have employees or other individuals eligible for Awards, the Committee, in its sole discretion, shall have the power and authority to:
(i) determine which Subsidiaries, if any, shall be covered by the Plan; (ii) determine which individuals, if any, outside the United States are eligible to participate in the Plan; (iii) modify the terms and conditions of any Award
granted to individuals outside the United States to comply with applicable foreign laws; (iv) establish subplans and modify exercise procedures and other terms and procedures, to the extent the Committee determines such actions to be necessary
or advisable (and such subplans and/or modifications shall be attached to the Plan as appendices); provided, however, that no such subplans and/or modifications shall increase the share limitation contained in Section 3(a) hereof;
and (v) take any action, before or after an Award is made, that the Committee determines to be necessary or advisable to obtain approval or comply with any local governmental regulatory exemptions or approvals. 

 

	SECTION 3.	 STOCK ISSUABLE UNDER THE PLAN; MERGERS AND OTHER TRANSACTIONS; SUBSTITUTION 

(a) Stock Issuable. The maximum number of Shares reserved and available for issuance under the Plan shall be 5,275,666 Shares, subject
to adjustment as provided in Section 3(b). For purposes of this limitation, the Shares underlying any Awards that are forfeited, canceled, reacquired by the Company prior to vesting, satisfied without the issuance of Stock or otherwise
terminated (other than by exercise) and Shares that are withheld upon exercise of an Option or settlement of an Award to cover the exercise price or tax withholding shall be added back to the Shares available for issuance under the Plan. Subject to
such overall limitations, Shares may be issued up to such maximum number pursuant to any type or types of Award, and no more than 18,000,000 Shares may be issued pursuant to Incentive Stock Options. The Shares available for issuance under the Plan
may be authorized but unissued Shares or Shares reacquired by the Company. Beginning on the date that the Company becomes subject to Section 162(m) of the Code, Options with respect to no more than 5,275,666 Shares shall be granted to any one
individual in any calendar year period. For the avoidance of doubt, Shares issued by the Company as a result of equity awards granted pursuant to any equity incentive plan sponsored by any predecessor to the Company shall be treated as Shares
granted under the Plan for purposes of determining the number of Shares available for issuance under the Plan. 
 (b) Changes in
Stock. Subject to Section 3(c) hereof, if, as a result of any reorganization, recapitalization, reclassification, stock dividend, stock split, reverse stock split or other similar change in the Company’s capital stock, the outstanding
Shares are increased or decreased or are exchanged for a different number or kind of shares or other securities of the Company, or additional Shares or new or different shares or other securities of the Company or other non-cash assets are distributed with respect to such Shares or other securities, in each case, without the receipt of consideration by the Company, or, if, as a result of any merger or consolidation, or sale of all
or substantially all of the assets of the Company, the outstanding Shares are converted into or exchanged for other securities of the Company or any successor entity (or a parent or subsidiary thereof), the Committee shall make an appropriate and
proportionate adjustment in (i) the maximum number of Shares reserved for issuance under the Plan, (ii) the number and kind of Shares or other securities subject to any then outstanding Awards under the Plan, (iii) the repurchase
price, if any, 

  
 -6- 

 
per Share subject to each outstanding Award, and (iv) the exercise price for each Share subject to any then outstanding Stock Options under the Plan, without changing the aggregate exercise
price (i.e., the per share exercise price multiplied by the number of Shares underlying such Stock Options) as to which such Stock Options remain exercisable. The Committee shall in any event make such adjustments as may be required by
Section 25102(o) of the California Corporation Code and the rules and regulations promulgated thereunder. The adjustment by the Committee shall be final, binding and conclusive. No fractional Shares shall be issued under the Plan resulting from
any such adjustment, but the Committee in its discretion may make a cash payment in lieu of fractional shares. 
 (c) Sale Events.

 (i) Options. 

(A) In the case of and subject to the consummation of a Sale Event, the Plan and all outstanding Options issued hereunder shall
terminate upon the effective time of any such Sale Event unless assumed or continued by the successor entity, or new stock options or other awards of the successor entity or parent thereof are substituted therefor, with an equitable or proportionate
adjustment as to the number and kind of shares and, if appropriate, the per share exercise prices, as such parties shall agree (after taking into account any acceleration hereunder and/or pursuant to the terms of any Award Agreement). 

(B) In the event of the termination of the Plan and all outstanding Options issued hereunder pursuant to Section 3(c),
each Holder of Options shall be permitted, within a period of time prior to the consummation of the Sale Event as specified by the Committee, to exercise all such Options which are then exercisable or will become exercisable as of the effective time
of the Sale Event; provided, however, that the exercise of Options not exercisable prior to the Sale Event shall be subject to the consummation of the Sale Event. 

(C) Notwithstanding anything to the contrary in Section 3(c)(i)(A), in the event of a Sale Event, the Company shall have
the right, but not the obligation, to make or provide for a cash payment to the Holders of Options, without any consent of the Holders, in exchange for the cancellation thereof, in an amount equal to the difference between (A) the value as
determined by the Committee of the consideration payable per share of Stock pursuant to the Sale Event (the “Sale Price”) times the number of Shares subject to outstanding Options being cancelled (to the extent then vested and exercisable,
including by reason of acceleration in connection with such Sale Event, at prices not in excess of the Sale Price) and (B) the aggregate exercise price of all such outstanding vested and exercisable Options. 

(ii) Restricted Stock and Restricted Stock Unit Awards. 

(A) In the case of and subject to the consummation of a Sale Event, all unvested Restricted Stock and unvested Restricted Stock
Unit Awards (other than those becoming vested as a result of the Sale Event) issued hereunder shall be forfeited immediately prior to the effective time of any such Sale Event unless assumed or continued by the successor entity, or awards of the
successor entity or parent thereof are substituted therefor, with an equitable or proportionate adjustment as to the number and kind of shares subject to such awards as such parties shall agree (after taking into account any acceleration hereunder
and/or pursuant to the terms of any Award Agreement). 

  
 -7- 

 (B) In the event of the forfeiture of Restricted Stock pursuant to
Section 3(c)(ii)(A), such Restricted Stock shall be repurchased from the Holder thereof at a price per share equal to the original per share purchase price paid by the Holder (subject to adjustment as provided in Section 3(b)) for such
Shares. 
 (C) Notwithstanding anything to the contrary in Section 3(c)(ii)(A), in the event of a Sale Event, the
Company shall have the right, but not the obligation, to make or provide for a cash payment to the Holders of Restricted Stock or Restricted Stock Unit Awards, without consent of the Holders, in exchange for the cancellation thereof, in an amount
equal to the Sale Price times the number of Shares subject to such Awards, to be paid at the time of such Sale Event or upon the later vesting of such Awards. 
  

	SECTION 4.	 ELIGIBILITY 

Grantees under the Plan will be such full or part-time officers and other employees, directors, Consultants and key persons of the Company and
any Subsidiary who are selected from time to time by the Committee in its sole discretion; provided, however, that Awards shall be granted only to those individuals described in Rule 701(c) of the Securities Act. 

 

	SECTION 5.	 STOCK OPTIONS 

Upon the grant of a Stock Option, the Company and the grantee shall enter into an Award Agreement. The terms and conditions of each such Award
Agreement shall be determined by the Committee, and such terms and conditions may differ among individual Awards and grantees. 
 Stock
Options granted under the Plan may be either Incentive Stock Options or Non-Qualified Stock Options. Incentive Stock Options may be granted only to employees of the Company or any Subsidiary that is a
“subsidiary corporation” within the meaning of Section 424(f) of the Code. To the extent that any Option does not qualify as an Incentive Stock Option, it shall be deemed a Non-Qualified Stock
Option. 
 (a) Terms of Stock Options. The Committee in its discretion may grant Stock Options to those individuals who meet the
eligibility requirements of Section 4. Stock Options shall be subject to the following terms and conditions and shall contain such additional terms and conditions, not inconsistent with the terms of the Plan, as the Committee shall deem
desirable. 
 (i) Exercise Price. The exercise price per share for the Shares covered by a Stock Option shall be determined by the
Committee at the time of grant but shall not be less than 100 percent of the Fair Market Value on the Grant Date. In the case of an Incentive Stock Option that is granted to a Ten Percent Owner, the exercise price per share for the Shares
covered by such Incentive Stock Option shall not be less than 110 percent of the Fair Market Value on the Grant Date. 

  
 -8- 

 (ii) Option Term. The term of each Stock Option shall be fixed by the Committee, but
no Stock Option shall be exercisable more than ten years from the Grant Date. In the case of an Incentive Stock Option that is granted to a Ten Percent Owner, the term of such Stock Option shall be no more than five years from the Grant Date. 

(iii) Exercisability; Rights of a Stockholder. Stock Options shall become exercisable and/or vested at such time or times, whether or
not in installments, as shall be determined by the Committee at or after the Grant Date. The Award Agreement may permit a grantee to exercise all or a portion of a Stock Option immediately at grant; provided that the Shares issued upon such exercise
shall be subject to restrictions and a vesting schedule identical to the vesting schedule of the related Stock Option, such Shares shall be deemed to be Restricted Stock for purposes of the Plan, and the optionee may be required to enter into an
additional or new Award Agreement as a condition to exercise of such Stock Option. An optionee shall have the rights of a stockholder only as to Shares acquired upon the exercise of a Stock Option and not as to unexercised Stock Options. An optionee
shall not be deemed to have acquired any Shares unless and until a Stock Option shall have been exercised pursuant to the terms of the Award Agreement and this Plan and the optionee’s name has been entered on the books of the Company as a
stockholder. 
 (iv) Method of Exercise. Stock Options may be exercised by an optionee in whole or in part, by the optionee giving
written or electronic notice of exercise to the Company, specifying the number of Shares to be purchased. Payment of the purchase price may be made by one or more of the following methods (or any combination thereof) to the extent provided in the
Award Agreement: 
 (A) In cash, by certified or bank check, by wire transfer of immediately available funds, or other
instrument acceptable to the Committee; 
 (B) If permitted by the Committee, by the optionee delivering to the Company a
promissory note, if the Board has expressly authorized the loan of funds to the optionee for the purpose of enabling or assisting the optionee to effect the exercise of his or her Stock Option; provided, that at least so much of the exercise
price as represents the par value of the Stock shall be paid in cash if required by state law; 
 (C) If permitted by the
Committee and the Initial Public Offering has occurred (or the Stock otherwise becomes publicly-traded), through the delivery (or attestation to the ownership) of Shares that have been purchased by the optionee on the open market or that are
beneficially owned by the optionee and are not then subject to restrictions under any Company plan. To the extent required to avoid variable accounting treatment under ASC 718 or other applicable accounting rules, such surrendered Shares if
originally purchased from the Company shall have been owned by the optionee for at least six months. Such surrendered Shares shall be valued at Fair Market Value on the exercise date; 

(D) If permitted by the Committee and the Initial Public Offering has occurred (or the Stock otherwise becomes
publicly-traded), by the optionee delivering to the Company a properly executed exercise notice together with irrevocable instructions to a broker to promptly deliver to the Company cash or a check payable and acceptable to the

  
 -9- 

 
Company for the purchase price; provided that in the event the optionee chooses to pay the purchase price as so provided, the optionee and the broker shall comply with such procedures and
enter into such agreements of indemnity and other agreements as the Committee shall prescribe as a condition of such payment procedure; or 

(E) If permitted by the Committee, and only with respect to Stock Options that are not Incentive Stock Options, by a “net
exercise” arrangement pursuant to which the Company will reduce the number of Shares issuable upon exercise by the largest whole number of Shares with a Fair Market Value that does not exceed the aggregate exercise price. 

Payment instruments will be received subject to collection. No certificates for Shares so purchased will be issued to the optionee or, with
respect to uncertificated Stock, no transfer to the optionee on the records of the Company will take place, until the Company has completed all steps it has deemed necessary to satisfy legal requirements relating to the issuance and sale of the
Shares, which steps may include, without limitation, (i) receipt of a representation from the optionee at the time of exercise of the Option that the optionee is purchasing the Shares for the optionee’s own account and not with a view to
any sale or distribution of the Shares or other representations relating to compliance with applicable law governing the issuance of securities, (ii) the legending of the certificate (or notation on any book entry) representing the Shares to
evidence the foregoing restrictions, (iii) obtaining from the optionee payment or provision for all withholding taxes due as a result of the exercise of the Option and (iv) if required by the Company, the optionee’s execution and
delivery of any stockholders’ agreements or other agreements with the Company and/or certain other stockholders of the Company relating to the Shares. The delivery of certificates representing the shares of Stock (or the transfer to the
optionee on the records of the Company with respect to uncertificated Stock) to be purchased pursuant to the exercise of a Stock Option will be contingent upon (A) receipt from the optionee (or a purchaser acting in his or her stead in
accordance with the provisions of the Stock Option) by the Company of the full purchase price for such Shares and the fulfillment of any other requirements contained in the Award Agreement or applicable provisions of laws and (B) if required by
the Company, the optionee shall have entered into any stockholders agreements or other agreements with the Company and/or certain other of the Company’s stockholders relating to the Stock. In the event an optionee chooses to pay the purchase
price by previously-owned Shares through the attestation method, the number of Shares transferred to the optionee upon the exercise of the Stock Option shall be net of the number of Shares attested to. 

(b) Annual Limit on Incentive Stock Options. To the extent required for “incentive stock option” treatment under
Section 422 of the Code, the aggregate Fair Market Value (determined as of the Grant Date) of the Shares with respect to which Incentive Stock Options granted under the Plan and any other plan of the Company or its parent and any Subsidiary
that become exercisable for the first time by an optionee during any calendar year shall not exceed $100,000 or such other limit as may be in effect from time to time under Section 422 of the Code. To the extent that any Stock Option exceeds
this limit, it shall constitute a Non-Qualified Stock Option. 
 (c) Termination. Any portion
of a Stock Option that is not vested and exercisable on the date of termination of an optionee’s Service Relationship shall immediately expire and be null and void. Once any portion of the Stock Option becomes vested and exercisable, the
optionee’s right to exercise such portion of the Stock Option (or the optionee’s representatives and legatees as 

  
 -10- 

 
applicable) in the event of a termination of the optionee’s Service Relationship shall continue until the earliest of: (i) the date which is: (A) 12 months following the date on which
the optionee’s Service Relationship terminates due to death or Disability (or such longer period of time as determined by the Committee and set forth in the applicable Award Agreement), or (B) three months following the date on which the
optionee’s Service Relationship terminates if the termination is due to any reason other than death or Disability (or such longer period of time as determined by the Committee and set forth in the applicable Award Agreement), or (ii) the
Expiration Date set forth in the Award Agreement; provided that notwithstanding the foregoing, an Award Agreement may provide that if the optionee’s Service Relationship is terminated for Cause, the Stock Option shall terminate
immediately and be null and void upon the date of the optionee’s termination and shall not thereafter be exercisable. 
  

	SECTION 6.	 RESTRICTED STOCK AWARDS 

(a) Nature of Restricted Stock Awards. The Committee may, in its sole discretion, grant (or sell at par value or such other purchase
price determined by the Committee) to an eligible individual under Section 4 hereof a Restricted Stock Award under the Plan. The Committee shall determine the restrictions and conditions applicable to each Restricted Stock Award at the time of
grant. Conditions may be based on continuing employment (or other Service Relationship), achievement of pre-established performance goals and objectives and/or such other criteria as the Committee may
determine. Upon the grant of a Restricted Stock Award, the Company and the grantee shall enter into an Award Agreement. The terms and conditions of each such Award Agreement shall be determined by the Committee, and such terms and conditions may
differ among individual Awards and grantees. 
 (b) Rights as a Stockholder. Upon the grant of the Restricted Stock Award and payment
of any applicable purchase price, a grantee of Restricted Stock shall be considered the record owner of and shall be entitled to vote the Restricted Stock if, and to the extent, such Shares are entitled to voting rights, subject to such conditions
contained in the Award Agreement. The grantee shall be entitled to receive all dividends and any other distributions declared on the Shares; provided, however, that the Company is under no duty to declare any such dividends or to make
any such distribution. Unless the Committee shall otherwise determine, certificates evidencing the Restricted Stock shall remain in the possession of the Company until such Restricted Stock is vested as provided in subsection (d) below of this
Section, and the grantee shall be required, as a condition of the grant, to deliver to the Company a stock power endorsed in blank and such other instruments of transfer as the Committee may prescribe. 

(c) Restrictions. Restricted Stock may not be sold, assigned, transferred, pledged or otherwise encumbered or disposed of except as
specifically provided herein or in the Award Agreement. Except as may otherwise be provided by the Committee either in the Award Agreement or, subject to Section 12 below, in writing after the Award Agreement is issued, if a grantee’s
Service Relationship with the Company and any Subsidiary terminates, the Company or its assigns shall have the right, as may be specified in the relevant instrument, to repurchase some or all of the Shares subject to the Award at such purchase price
as is set forth in the Award Agreement. 

  
 -11- 

 (d) Vesting of Restricted Stock. The Committee at the time of grant shall specify in
the Award Agreement the date or dates and/or the attainment of pre-established performance goals, objectives and other conditions on which the substantial risk of forfeiture imposed shall lapse and the
Restricted Stock shall become vested, subject to such further rights of the Company or its assigns as may be specified in the Award Agreement. 
  

	SECTION 7.	 UNRESTRICTED STOCK AWARDS 

The Committee may, in its sole discretion, grant (or sell at par value or such other purchase price determined by the Committee) to an eligible
person under Section 4 hereof an Unrestricted Stock Award under the Plan. Unrestricted Stock Awards may be granted in respect of past services or other valid consideration, or in lieu of cash compensation due to such grantee. 

 

	SECTION 8.	 RESTRICTED STOCK UNITS 

(a) Nature of Restricted Stock Units. The Committee may, in its sole discretion, grant to an eligible person under Section 4 hereof
Restricted Stock Units under the Plan. The Committee shall determine the restrictions and conditions applicable to each Restricted Stock Unit at the time of grant. Vesting conditions may be based on continuing employment (or other Service
Relationship), achievement of pre-established performance goals and objectives and/or other such criteria as the Committee may determine. Upon the grant of Restricted Stock Units, the grantee and the Company
shall enter into an Award Agreement. The terms and conditions of each such Award Agreement shall be determined by the Committee and may differ among individual Awards and grantees. On or promptly following the vesting date or dates applicable to any
Restricted Stock Unit, but in no event later than March 15 of the year following the year in which such vesting occurs, such Restricted Stock Unit(s) shall be settled in the form of cash or shares of Stock, as specified in the Award Agreement.
Restricted Stock Units may not be sold, assigned, transferred, pledged, or otherwise encumbered or disposed of. 
 (b) Rights as a
Stockholder. A grantee shall have the rights of a stockholder only as to Shares, if any, acquired upon settlement of Restricted Stock Units. A grantee shall not be deemed to have acquired any such Shares unless and until the Restricted Stock
Units shall have been settled in Shares pursuant to the terms of the Plan and the Award Agreement, the Company shall have issued and delivered a certificate representing the Shares to the grantee (or transferred on the records of the Company with
respect to uncertificated stock), and the grantee’s name has been entered in the books of the Company as a stockholder. 
 (c)
Termination. Except as may otherwise be provided by the Committee either in the Award Agreement or in writing after the Award Agreement is issued, a grantee’s right in all Restricted Stock Units that have not vested shall automatically
terminate upon the grantee’s cessation of Service Relationship with the Company and any Subsidiary for any reason. 

  
 -12- 

	SECTION 9.	 TRANSFER RESTRICTIONS; COMPANY RIGHT OF FIRST REFUSAL; COMPANY REPURCHASE RIGHTS 

(a) Restrictions on Transfer. 

(i) Non-Transferability of Stock Options. Stock Options and, prior to exercise, the Shares
issuable upon exercise of such Stock Option, shall not be transferable by the optionee otherwise than by will, or by the laws of descent and distribution, and all Stock Options shall be exercisable, during the optionee’s lifetime, only by the
optionee, or by the optionee’s legal representative or guardian in the event of the optionee’s incapacity. Notwithstanding the foregoing, the Committee, in its sole discretion, may provide in the Award Agreement regarding a given Stock
Option that the optionee may transfer by gift, without consideration for the transfer, his or her Non-Qualified Stock Options to his or her family members (as defined in Rule 701 of the Securities Act), to
trusts for the benefit of such family members, or to partnerships in which such family members are the only partners (to the extent such trusts or partnerships are considered “family members” for purposes of Rule 701 of the Securities
Act), provided that the transferee agrees in writing with the Company to be bound by all of the terms and conditions of this Plan and the applicable Award Agreement, including the execution of a stock power upon the issuance of Shares. Stock
Options, and the Shares issuable upon exercise of such Stock Options, shall be restricted as to any pledge, hypothecation, or other transfer, including any short position, any “put equivalent position” (as defined in the Exchange Act) or
any “call equivalent position” (as defined in the Exchange Act) prior to exercise. 
 (ii) Shares. No Shares shall be sold,
assigned, transferred, pledged, hypothecated, given away or in any other manner disposed of or encumbered, whether voluntarily or by operation of law, unless (i) the transfer is in compliance with the terms of the applicable Award Agreement,
all applicable securities laws (including, without limitation, the Securities Act), and with the terms and conditions of this Section 9, (ii) the transfer does not cause the Company to become subject to the reporting requirements of the
Exchange Act, and (iii) the transferee consents in writing to be bound by the provisions of the Plan and the Award Agreement, including this Section 9. In connection with any proposed transfer, the Committee may require the transferor to
provide at the transferor’s own expense an opinion of counsel to the transferor, satisfactory to the Committee, that such transfer is in compliance with all foreign, federal and state securities laws (including, without limitation, the
Securities Act). Any attempted transfer of Shares not in accordance with the terms and conditions of this Section 9 shall be null and void, and the Company shall not reflect on its records any change in record ownership of any Shares as a
result of any such transfer, shall otherwise refuse to recognize any such transfer and shall not in any way give effect to any such transfer of Shares. The Company shall be entitled to seek protective orders, injunctive relief and other remedies
available at law or in equity including, without limitation, seeking specific performance or the rescission of any transfer not made in strict compliance with the provisions of this Section 9. Subject to the foregoing general provisions, and
unless otherwise provided in the applicable Award Agreement, Shares may be transferred pursuant to the following specific terms and conditions (provided that with respect to any transfer of Restricted Stock, all vesting and forfeiture provisions
shall continue to apply with respect to the original recipient): 
 (A) Transfers to Permitted Transferees. The Holder
may transfer any or all of the Shares to one or more Permitted Transferees; provided, however, that following such transfer, such Shares shall continue to be subject to the terms of this Plan (including this Section 9) and such Permitted
Transferee(s) shall, as a condition to any such transfer, deliver a written acknowledgment to that effect to the Company and shall deliver a stock power to the Company with respect to the Shares. Notwithstanding the foregoing, the Holder may not
transfer any of the Shares to a Person whom the Company reasonably determines is a direct competitor or a potential competitor of the Company or any of its Subsidiaries. 

  
 -13- 

 (B) Transfers Upon Death. Upon the death of the Holder, any Shares
then held by the Holder at the time of such death and any Shares acquired after the Holder’s death by the Holder’s legal representative shall be subject to the provisions of this Plan, and the Holder’s estate, executors,
administrators, personal representatives, heirs, legatees and distributees shall be obligated to convey such Shares to the Company or its assigns under the terms contemplated by the Plan and the Award Agreement. 

(b) Right of First Refusal. In the event that a Holder desires at any time to sell or otherwise transfer all or any part of his or her
Shares (other than shares of Restricted Stock which by their terms are not transferrable), the Holder first shall give written notice to the Company of the Holder’s intention to make such transfer. Such notice shall state the number of Shares
that the Holder proposes to sell (the “Offered Shares”), the price and the terms at which the proposed sale is to be made and the name and address of the proposed transferee. At any time within 30 days after the receipt of such notice by
the Company, the Company or its assigns may elect to purchase all or any portion of the Offered Shares at the price and on the terms offered by the proposed transferee and specified in the notice. The Company or its assigns shall exercise this right
by mailing or delivering written notice to the Holder within the foregoing 30-day period. If the Company or its assigns elect to exercise its purchase rights under this Section 9(b), the closing for such
purchase shall, in any event, take place within 45 days after the receipt by the Company of the initial notice from the Holder. In the event that the Company or its assigns do not elect to exercise such purchase right, or in the event that the
Company or its assigns do not pay the full purchase price within such 45-day period, the Holder shall be required to pay a transaction processing fee of $10,000 to the Company (unless waived by the Committee)
and then may, within 60 days thereafter, sell the Offered Shares to the proposed transferee and at the same price and on the same terms as specified in the Holder’s notice. Any Shares not sold to the proposed transferee shall remain subject to
the Plan. If the Holder is a party to any stockholders agreements or other agreements with the Company and/or certain other of the Company’s stockholders relating to the Shares, (i) the transferring Holder shall comply with the
requirements of such stockholders agreements or other agreements relating to any proposed transfer of the Offered Shares, and (ii) any proposed transferee that purchases Offered Shares shall enter into such stockholders agreements or other
agreements with the Company and/or certain of the Company’s stockholders relating to the Offered Shares on the same terms and in the same capacity as the transferring Holder. 

(c) Company’s Right of Repurchase. 

(i) Right of Repurchase for Unvested Shares Issued Upon the Exercise of an Option. Upon a Termination Event, the Company or its assigns
shall have the right and option to repurchase from a Holder of Shares acquired upon exercise of a Stock Option which are still subject to a risk of forfeiture as of the Termination Event. Such repurchase rights may be exercised by the Company within
the later of (A) six months following the date of such Termination Event or (B) seven months after the acquisition of Shares upon exercise of a Stock Option. The repurchase price shall be equal to the lower of the original per share price
paid by the Holder, subject to adjustment as provided in Section 3(b) of the Plan, or the current Fair Market Value of such Shares as of the date the Company elects to exercise its repurchase rights. 

  
 -14- 

 (ii) Right of Repurchase With Respect to Restricted Stock. Upon a Termination Event,
the Company or its assigns shall have the right and option to repurchase from a Holder of Shares received pursuant to a Restricted Stock Award any Shares that are still subject to a risk of forfeiture as of the Termination Event. Such repurchase
right may be exercised by the Company within six months following the date of such Termination Event. The repurchase price shall be the lower of the original per share purchase price paid by the Holder, subject to adjustment as provided in
Section 3(b) of the Plan, or the current Fair Market Value of such Shares as of the date the Company elects to exercise its repurchase rights. 

(iii) Procedure. Any repurchase right of the Company shall be exercised by the Company or its assigns by giving the Holder written
notice on or before the last day of the repurchase period of its intention to exercise such repurchase right. Upon such notification, the Holder shall promptly surrender to the Company, free and clear of any liens or encumbrances, any certificates
representing the Shares being purchased, together with a duly executed stock power for the transfer of such Shares to the Company or the Company’s assignee or assignees. Upon the Company’s or its assignee’s receipt of the certificates
from the Holder, the Company or its assignee or assignees shall deliver to him, her or them a check for the applicable repurchase price; provided, however, that the Company may pay the repurchase price by offsetting and canceling any
indebtedness then owed by the Holder to the Company. 
 (d) Escrow Arrangement. 

(i) Escrow. In order to carry out the provisions of this Section 9 of this Plan more effectively, the Company shall hold any
Shares issued pursuant to Awards granted under the Plan in escrow together with separate stock powers executed by the Holder in blank for transfer. The Company shall not dispose of the Shares except as otherwise provided in this Plan. In the event
of any repurchase by the Company (or any of its assigns), the Company is hereby authorized by the Holder, as the Holder’s attorney-in-fact, to date and complete the
stock powers necessary for the transfer of the Shares being purchased and to transfer such Shares in accordance with the terms hereof. At such time as any Shares are no longer subject to the Company’s repurchase and first refusal rights, the
Company shall, at the written request of the Holder, deliver to the Holder a certificate representing such Shares with the balance of the Shares to be held in escrow pursuant to this Section. 

(ii) Remedy. Without limitation of any other provision of this Plan or other rights, in the event that a Holder or any other Person is
required to sell a Holder’s Shares pursuant to the provisions of Sections 9(b) or (c) hereof and in the further event that he or she refuses or for any reason fails to deliver to the Company or its designated purchaser of such Shares the
certificate or certificates evidencing such Shares together with a related stock power, the Company or such designated purchaser may deposit the applicable purchase price for such Shares with a bank designated by the Company, or with the
Company’s independent public accounting firm, as agent or trustee, or in escrow, for such Holder or other Person, to be held by such bank or accounting firm for the benefit of and for delivery to him, her, them or it, and/or, in its discretion,
pay such purchase 

  
 -15- 

 
price by offsetting any indebtedness then owed by such Holder as provided above. Upon any such deposit and/or offset by the Company or its designated purchaser of such amount and upon notice to
the Person who was required to sell the Shares to be sold pursuant to the provisions of Sections 9(b) or (c), such Shares shall at such time be deemed to have been sold, assigned, transferred and conveyed to such purchaser, such Holder shall have no
further rights thereto (other than the right to withdraw the payment thereof held in escrow, if applicable), and the Company shall record such transfer in its stock transfer book or in any appropriate manner. 

(e) Lockup Provision. If requested by the Company, a Holder shall not sell or otherwise transfer or dispose of any Shares (including,
without limitation, pursuant to Rule 144 under the Securities Act) held by him or her for such period following the consummation of, or the effective date of a registration statement pertaining to, a public offering by the Company of Shares as the
Company shall specify reasonably and in good faith. If requested by the underwriter engaged by the Company, each Holder shall execute a separate letter confirming his or her agreement to comply with this Section. 

(f) Adjustments for Changes in Capital Structure. If, as a result of any reorganization, recapitalization, reclassification, stock
dividend, stock split, reverse stock split or other similar change in the Common Stock, the outstanding Shares are increased or decreased or are exchanged for a different number or kind of securities of the Company, the restrictions contained in
this Section 9 shall apply with equal force to additional and/or substitute securities, if any, received by Holder in exchange for, or by virtue of his or her ownership of, Shares. 

(g) Termination. The terms and provisions of Section 9(b) and (c) (except for the Company’s right to repurchase Shares still
subject to a risk of forfeiture upon a Termination Event) shall terminate upon the closing of the Company’s Initial Public Offering or upon consummation of any Sale Event, in either case as a result of which Shares are registered under
Section 12 of the Exchange Act and publicly-traded on any national security exchange. 
  

	SECTION 10.	 TAX WITHHOLDING 

(a) Payment by Grantee. Each grantee shall, no later than the date as of which the value of an Award or of any Shares or other amounts
received thereunder first becomes includable in the gross income of the grantee for income tax purposes, pay to the Company, or make arrangements satisfactory to the Committee regarding payment of, any Federal, state, or local taxes of any kind
required by law to be withheld by the Company with respect to such income. The Company and any Subsidiary shall, to the extent permitted by law, have the right to deduct any such taxes from any payment of any kind otherwise due to the grantee. The
Company’s obligation to deliver stock certificates (or evidence of book entry) to any grantee is subject to and conditioned on any such tax withholding obligations being satisfied by the grantee. 

(b) Payment in Stock. The Company’s minimum required tax withholding obligation may be satisfied, in whole or in part, by the
Company withholding from Shares to be issued pursuant to an Award a number of Shares having an aggregate Fair Market Value (as of the date the withholding is effected) that would satisfy the minimum withholding amount due. 

  
 -16- 

	SECTION 11.	 SECTION 409A AWARDS. 

To the extent that any Award is determined to constitute “nonqualified deferred compensation” within the meaning of Section 409A
(a “409A Award”), the Award shall be subject to such additional rules and requirements as may be specified by the Committee from time to time. In this regard, if any amount under a 409A Award is payable upon a “separation from
service” (within the meaning of Section 409A) to a grantee who is considered a “specified employee” (within the meaning of Section 409A), then no such payment shall be made prior to the date that is the earlier of
(i) six months and one day after the grantee’s separation from service, or (ii) the grantee’s death, but only to the extent such delay is necessary to prevent such payment from being subject to interest, penalties and/or
additional tax imposed pursuant to Section 409A. The Company makes no representation or warranty and shall have no liability to any grantee under the Plan or any other Person with respect to any penalties or taxes under Section 409A that
are, or may be, imposed with respect to any Award. 
  

	SECTION 12.	 AMENDMENTS AND TERMINATION 

The Board may, at any time, amend or discontinue the Plan and the Committee may, at any time, amend or cancel any outstanding Award for the
purpose of satisfying changes in law or for any other lawful purpose, but no such action shall adversely affect rights under any outstanding Award without the consent of the holder of the Award. The Committee may exercise its discretion to institute
and determine the terms and conditions of an Exchange Program. To the extent determined by the Committee to be required either by the Code to ensure that Incentive Stock Options granted under the Plan are qualified under Section 422 of the Code
or otherwise, Plan amendments shall be subject to approval by the Company stockholders entitled to vote at a meeting of stockholders. Nothing in this Section 12 shall limit the Board’s or Committee’s authority to take any action
permitted pursuant to Section 3(c). The Board reserves the right to amend the Plan and/or the terms of any outstanding Stock Options to the extent reasonably necessary to comply with the requirements of the exemption pursuant to paragraph
(f)(4) of Rule 12h-1 of the Exchange Act. 
  

	SECTION 13.	 STATUS OF PLAN 

With respect to the portion of any Award that has not been exercised and any payments in cash, Stock or other consideration not received by a
grantee, a grantee shall have no rights greater than those of a general creditor of the Company unless the Committee shall otherwise expressly so determine in connection with any Award. 

 

	SECTION 14.	 GENERAL PROVISIONS 

(a) No Distribution; Compliance with Legal Requirements. The Committee may require each person acquiring Shares pursuant to an Award to
represent to and agree with the Company in writing that such person is acquiring the Shares without a view to distribution thereof. No Shares shall be issued pursuant to an Award until all applicable securities law and other legal and stock exchange
or similar requirements have been satisfied. The Committee may require the placing of such stop-orders and restrictive legends on certificates for Stock and Awards as it deems appropriate. 

  
 -17- 

 (b) Delivery of Stock Certificates. Stock certificates to grantees under the Plan
shall be deemed delivered for all purposes when the Company or a stock transfer agent of the Company shall have mailed such certificates in the United States mail, addressed to the grantee, at the grantee’s last known address on file with the
Company; provided that stock certificates to be held in escrow pursuant to Section 9 of the Plan shall be deemed delivered when the Company shall have recorded the issuance in its records. Uncertificated Stock shall be deemed delivered for all
purposes when the Company or a stock transfer agent of the Company shall have given to the grantee by electronic mail (with proof of receipt) or by United States mail, addressed to the grantee, at the grantee’s last known address on file with
the Company, notice of issuance and recorded the issuance in its records (which may include electronic “book entry” records). 

(c) No Employment Rights. The adoption of the Plan and the grant of Awards do not confer upon any Person any right to continued
employment or Service Relationship with the Company or any Subsidiary. 
 (d) Trading Policy Restrictions. Option exercises and other
Awards under the Plan shall be subject to the Company’s insider trading policy-related restrictions, terms and conditions as may be established by the Committee, or in accordance with policies set by the Committee, from time to time. 

(e) Designation of Beneficiary. Each grantee to whom an Award has been made under the Plan may designate a beneficiary or beneficiaries
to exercise any Award on or after the grantee’s death or receive any payment under any Award payable on or after the grantee’s death. Any such designation shall be on a form provided for that purpose by the Committee and shall not be
effective until received by the Committee. If no beneficiary has been designated by a deceased grantee, or if the designated beneficiaries have predeceased the grantee, the beneficiary shall be the grantee’s estate. 

(f) Legend. Any certificate(s) representing the Shares shall carry substantially the following legend (and with respect to
uncertificated Stock, the book entries evidencing such shares shall contain the following notation): 
 The transferability of this
certificate and the shares of stock represented hereby are subject to the restrictions, terms and conditions (including repurchase and restrictions against transfers) contained in the Alector, Inc. 2017 Stock Option and Grant Plan and any agreements
entered into thereunder by and between the company and the holder of this certificate (a copy of which is available at the offices of the company for examination). 

  
 -18- 

 (g) Information to Holders of Options. In the event the Company is relying on the
exemption from the registration requirements of Section 12(g) of the Exchange Act contained in paragraph (f)(1) of Rule 12h-1 of the Exchange Act, the Company shall provide the information described in
Rule 701(e)(3), (4) and (5) of the Securities Act to all holders of Options in accordance with the requirements thereunder. The foregoing notwithstanding, the Company shall not be required to provide such information unless the optionholder has
agreed in writing, on a form prescribed by the Company, to keep such information confidential. 
  

	SECTION 15.	 EFFECTIVE DATE OF PLAN 

The Plan shall become effective upon adoption by the Board and shall be approved by stockholders in accordance with applicable state law and
the Company’s certificate of incorporation and bylaws within 12 months thereafter. If the stockholders fail to approve the Plan within 12 months after its adoption by the Board of Directors, then any Awards granted or sold under the Plan shall
be rescinded and no additional grants or sales shall thereafter be made under the Plan. Subject to such approval by stockholders and to the requirement that no Shares may be issued hereunder prior to such approval, Stock Options and other Awards may
be granted hereunder on and after adoption of the Plan by the Board. No grants of Stock Options and other Awards may be made hereunder after the tenth anniversary of the date the Plan is adopted by the Board or the date the Plan is approved by the
Company’s stockholders, whichever is earlier. 
  

	SECTION 16.	 GOVERNING LAW 

This Plan, all Awards and any controversy arising out of or relating to this Plan and all Awards shall be governed by and construed in
accordance with the General Corporation Law of the State of Delaware as to matters within the scope thereof, and as to all other matters shall be governed by and construed in accordance with the internal laws of the State of California, without
regard to conflict of law principles that would result in the application of any law other than the law of the State of California. 
  

			
	DATE ORIGINALLY ADOPTED BY THE BOARD OF DIRECTORS:	  	October 11, 2017
		
	DATE ORIGINALLY APPROVED BY THE STOCKHOLDERS:	  	October 13, 2017
		
	DATE AMENDMENT APPROVED BY THE BOARD OF DIRECTORS:	  	August 15, 2018
		
	DATE AMENDMENT APPROVED BY THE BOARD OF DIRECTORS:	  	November 15, 2018

  
 -19- 

 INCENTIVE STOCK OPTION GRANT NOTICE 

UNDER THE ALECTOR, INC. 

2017 STOCK OPTION AND GRANT PLAN 

Pursuant to the Alector, Inc. 2017 Stock Option and Grant Plan (the “Plan”), Alector, Inc., a Delaware corporation (together
with any successor, the “Company”), has granted to the individual named below, an option (the “Stock Option”) to purchase on or prior to the Expiration Date, or such earlier date as is specified herein, all or any
part of the number of shares of Common Stock, par value $0.0001 per share (“Common Stock”), of the Company indicated below (the “Shares”), at the Option Exercise Price per share, subject to the terms and conditions
set forth in this Incentive Stock Option Grant Notice (the “Grant Notice”), the attached Incentive Stock Option Agreement (the “Agreement”) and the Plan. This Stock Option is intended to qualify as an
“incentive stock option” as defined in Section 422(b) of the Internal Revenue Code of 1986, as amended from time to time (the “Code”). To the extent that any portion of the Stock Option does not so qualify, it shall
be deemed a non qualified stock option. 
 Name of Optionee: __________________ (the “Optionee”) 

No. of Shares: __________ Shares of Common Stock 
 Grant Date:
__________________ 
 Vesting Commencement Date: __________________ (the “Vesting Commencement Date”) 

Expiration Date: __________________ (the “Expiration Date”) 

Option Exercise Price/Share: $_________________ (the “Option Exercise Price”) 

 

			
	Vesting Schedule:	  	25 percent of the Shares shall vest and become exercisable on the first anniversary of the Vesting Commencement Date; provided that the Optionee continues to have a Service Relationship with the Company at such time.
Thereafter, the remaining 75 percent of the Shares shall vest and become exercisable in 36 equal monthly installments following the first anniversary of the Vesting Commencement Date, provided the Optionee continues to have a Service
Relationship with the Company on each vesting date. Notwithstanding anything in the Agreement to the contrary, in the case of a Sale Event, this Stock Option and the Shares shall be treated as provided in Section 3(c) of the Plan.

 Attachments: Incentive Stock Option Agreement, 2017 Stock Option and Grant Plan 

  
 -20- 

 INCENTIVE STOCK OPTION AGREEMENT 

UNDER THE ALECTOR, INC. 

2017 STOCK OPTION AND GRANT PLAN 

All capitalized terms used herein and not otherwise defined shall have the respective meanings set forth in the Grant Notice and the Plan.

 1. Vesting, Exercisability and Termination. 

(a) No portion of this Stock Option may be exercised until such portion shall have vested and become exercisable. 

(b) Except as set forth below, and subject to the determination of the Committee in its sole discretion to accelerate the vesting schedule
hereunder, this Stock Option shall be vested and exercisable on the respective dates indicated below: 
 (i) This Stock
Option shall initially be unvested and unexercisable. 
 (ii) This Stock Option shall vest and become exercisable in
accordance with the Vesting Schedule set forth in the Grant Notice. 
 (c) Termination. Except as may otherwise be provided by the
Committee, if the Optionee’s Service Relationship is terminated, the period within which to exercise this Stock Option will be subject to earlier termination as set forth below (and if not exercised within such period, shall thereafter
terminate subject, in each case, to Section 3(c) of the Plan): 
 (i) Termination Due to Death or Disability. If
the Optionee’s Service Relationship terminates by reason of such Optionee’s death or Disability, this Stock Option may be exercised, to the extent exercisable on the date of such termination, by the Optionee, the Optionee’s legal
representative or legatee for a period of 12 months from the date of death or Disability or until the Expiration Date, if earlier. 

(ii) Other Termination. If the Optionee’s Service Relationship terminates for any reason other than death or
Disability, and unless otherwise determined by the Committee, this Stock Option may be exercised, to the extent exercisable on the date of termination, for a period of 90 days from the date of termination or until the Expiration Date, if earlier;
provided however, if the Optionee’s Service Relationship is terminated for Cause, this Stock Option shall terminate immediately upon the date of such termination. 

For purposes hereof, the Committee’s determination of the reason for termination of the Optionee’s Service Relationship shall be
conclusive and binding on the Optionee and his or her representatives or legatees. Any portion of this Stock Option that is not vested and exercisable on the date of termination of the Service Relationship shall terminate immediately and be null and
void. 

  
 -21- 

 (d) It is understood and intended that this Stock Option is intended to qualify as an
“incentive stock option” as defined in Section 422 of the Code to the extent permitted under applicable law. Accordingly, the Optionee understands that in order to obtain the benefits of an incentive stock option under
Section 422 of the Code, no sale or other disposition may be made of Shares for which incentive stock option treatment is desired within the one year period beginning on the day after the day of the transfer of such Shares to him or her, nor
within the two year period beginning on the day after Grant Date of this Stock Option and further that this Stock Option must be exercised within three months after termination of employment as an employee (or 12 months in the case of death or
disability) to qualify as an incentive stock option. If the Optionee disposes (whether by sale, gift, transfer or otherwise) of any such Shares within either of these periods, he or she will notify the Company within 30 days after such disposition.
The Optionee also agrees to provide the Company with any information concerning any such dispositions required by the Company for tax purposes. Further, to the extent this Stock Option and any other incentive stock options of the Optionee having an
aggregate Fair Market Value in excess of $100,000 (determined as of the Grant Date) first become exercisable in any year, such options will not qualify as incentive stock options. 

2. Exercise of Stock Option. 

(a) The Optionee may exercise this Stock Option only in the following manner: Prior to the Expiration Date, the Optionee may deliver a Stock
Option exercise notice (an “Exercise Notice”) in the form of Appendix A hereto indicating his or her election to purchase some or all of the Shares with respect to which this Stock Option is then exercisable. Such notice shall
specify the number of Shares to be purchased. Payment of the purchase price may be made by one or more of the methods described in Section 5 of the Plan, subject to the limitations contained in such Section of the Plan, including the
requirement that the Committee specifically approve in advance certain payment methods. 
 (b) Notwithstanding any other provision hereof or
of the Plan, no portion of this Stock Option shall be exercisable after the Expiration Date. 
 3. Incorporation of Plan.
Notwithstanding anything herein to the contrary, this Stock Option shall be subject to and governed by all the terms and conditions of the Plan. 

4. Transferability of Stock Option. This Stock Option is personal to the Optionee and is not transferable by the Optionee in any manner
other than by will or by the laws of descent and distribution. The Stock Option may be exercised during the Optionee’s lifetime only by the Optionee (or by the Optionee’s guardian or personal representative in the event of the
Optionee’s incapacity). The Optionee may elect to designate a beneficiary by providing written notice of the name of such beneficiary to the Company, and may revoke or change such designation at any time by filing written notice of revocation
or change with the Company; such beneficiary may exercise the Optionee’s Stock Option in the event of the Optionee’s death to the extent provided herein. If the Optionee does not designate a beneficiary, or if the designated beneficiary
predeceases the Optionee, the legal representative of the Optionee may exercise this Stock Option to the extent provided herein in the event of the Optionee’s death. 

5. Restrictions on Transfer of Shares. The Shares acquired upon exercise of the Stock Option shall be subject to certain transfer
restrictions and other limitations including, without limitation, the provisions contained in Section 9 of the Plan. 

  
 -22- 

 6. Miscellaneous Provisions. 

(a) Equitable Relief. The parties hereto agree and declare that legal remedies may be inadequate to enforce the provisions of this
Agreement and that equitable relief, including specific performance and injunctive relief, may be used to enforce the provisions of this Agreement. 

(b) Adjustments for Changes in Capital Structure. If, as a result of any reorganization, recapitalization, reincorporation,
reclassification, stock dividend, stock split, reverse stock split or other similar change in the Common Stock, the outstanding shares of Common Stock are increased or decreased or are exchanged for a different number or kind of securities of the
Company, the restrictions contained in this Agreement shall apply with equal force to additional and/or substitute securities, if any, received by the Optionee in exchange for, or by virtue of his or her ownership of, this Stock Option or Shares
acquired pursuant thereto. 
 (c) Change and Modifications. This Agreement may not be orally changed, modified or terminated, nor
shall any oral waiver of any of its terms be effective. This Agreement may be changed, modified or terminated only by an agreement in writing signed by the Company and the Optionee. 

(d) Governing Law. This Agreement shall be governed by and construed in accordance with the General Corporation Law of the State of
Delaware as to matters within the scope thereof, and as to all other matters shall be governed by and construed in accordance with the internal laws of the State of California, without regard to conflict of law principles that would result in the
application of any law other than the law of the State of California. 
 (e) Headings. The headings are intended only for convenience
in finding the subject matter and do not constitute part of the text of this Agreement and shall not be considered in the interpretation of this Agreement. 

(f) Saving Clause. If any provision(s) of this Agreement shall be determined to be illegal or unenforceable, such determination shall
in no manner affect the legality or enforceability of any other provision hereof. 
 (g) Notices. All notices, requests, consents and
other communications shall be in writing and be deemed given when delivered personally, by telex or facsimile transmission or when received if mailed by first class registered or certified mail, postage prepaid. Notices to the Company or the
Optionee shall be addressed as set forth underneath their signatures below, or to such other address or addresses as may have been furnished by such party in writing to the other. 

(h) Benefit and Binding Effect. This Agreement shall be binding upon and shall inure to the benefit of the parties hereto, their
respective successors, assigns, and legal representatives. The Company has the right to assign this Agreement, and such assignee shall become entitled to all the rights of the Company hereunder to the extent of such assignment. 

(i) Counterparts. For the convenience of the parties and to facilitate execution, this Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which shall constitute one and the same document. 

  
 -23- 

 (j) Integration. This Agreement constitutes the entire agreement between the parties
with respect to this Stock Option and supersedes all prior agreements and discussions between the parties concerning such subject matter. 

7. Dispute Resolution. 

(a) Except as provided below, any dispute arising out of or relating to the Plan or this Stock Option, this Agreement, or the breach,
termination or validity of the Plan, this Stock Option or this Agreement, shall be finally settled by binding arbitration conducted expeditiously in accordance with the J.A.M.S./Endispute Comprehensive Arbitration Rules and Procedures (the
“J.A.M.S. Rules”). The arbitration shall be governed by the United States Arbitration Act, 9 U.S.C. Sections 1 16, and judgment upon the award rendered by the arbitrators may be entered by any court having jurisdiction thereof. The
place of arbitration shall be San Francisco, California. 
 (b) The arbitration shall commence within 60 days of the date on which a written
demand for arbitration is filed by any party hereto. In connection with the arbitration proceeding, the arbitrator shall have the power to order the production of documents by each party and any third-party witnesses. In addition, each party may
take up to three depositions as of right, and the arbitrator may in his or her discretion allow additional depositions upon good cause shown by the moving party. However, the arbitrator shall not have the power to order the answering of
interrogatories or the response to requests for admission. In connection with any arbitration, each party to the arbitration shall provide to the other, no later than seven business days before the date of the arbitration, the identity of all
persons that may testify at the arbitration and a copy of all documents that may be introduced at the arbitration or considered or used by a party’s witness or expert. The arbitrator’s decision and award shall be made and delivered within
six months of the selection of the arbitrator. The arbitrator’s decision shall set forth a reasoned basis for any award of damages or finding of liability. The arbitrator shall not have power to award damages in excess of actual compensatory
damages and shall not multiply actual damages or award punitive damages, and each party hereby irrevocably waives any claim to such damages. 

(c) The Company, the Optionee, each party to the Agreement and any other holder of Shares issued pursuant to this Agreement (each, a
“Party”) covenants and agrees that such party will participate in the arbitration in good faith. This Section 7 applies equally to requests for temporary, preliminary or permanent injunctive relief, except that in the case of
temporary or preliminary injunctive relief any party may proceed in court without prior arbitration for the limited purpose of avoiding immediate and irreparable harm. 

(d) Each Party (i) hereby irrevocably submits to the jurisdiction of any United States District Court of competent jurisdiction for the
purpose of enforcing the award or decision in any such proceeding, (ii) hereby waives, and agrees not to assert, by way of motion, as a defense, or otherwise, in any such suit, action or proceeding, any claim that it is not subject personally
to the jurisdiction of the above named courts, that its property is exempt or immune from attachment or execution (except as protected by applicable law), that the suit, action or proceeding is brought in an inconvenient forum, that the venue of the
suit, action or proceeding is improper or that this Agreement or the subject matter hereof may not be enforced in or by such court, and (iii) hereby waives and agrees not to seek any review by any court of any other jurisdiction which may be
called 

  
 -24- 

 
upon to grant an enforcement of the judgment of any such court. Each Party hereby consents to service of process by registered mail at the address to which notices are to be given. Each Party
agrees that its, his or her submission to jurisdiction and its, his or her consent to service of process by mail is made for the express benefit of each other Party. Final judgment against any Party in any such action, suit or proceeding may be
enforced in other jurisdictions by suit, action or proceeding on the judgment, or in any other manner provided by or pursuant to the laws of such other jurisdiction. 

8. Waiver of Statutory Information Rights. The Optionee understands and agrees that, but for the waiver made herein, the Optionee would
be entitled, upon written demand under oath stating the purpose thereof, to inspect for any proper purpose, and to make copies and extracts from, the Company’s stock ledger, a list of its stockholders, and its other books and records, and the
books and records of subsidiaries of the Company, if any, under the circumstances and in the manner provided in Section 220 of the General Corporation Law of Delaware (any and all such rights, and any and all such other rights of the Optionee
as may be provided for in Section 220, the “Inspection Rights”). In light of the foregoing, until the first sale of Stock of the Company to the general public pursuant to a registration statement filed with and declared
effective by the Securities and Exchange Commission under the Securities Act, the Optionee hereby unconditionally and irrevocably waives the Inspection Rights, whether such Inspection Rights would be exercised or pursued directly or indirectly
pursuant to Section 220 or otherwise, and covenants and agrees never to directly or indirectly commence, voluntarily aid in any way, prosecute, assign, transfer, or cause to be commenced any claim, action, cause of action, or other proceeding
to pursue or exercise the Inspection Rights. The foregoing waiver shall not affect any rights of a director, in his or her capacity as such, under Section 220. The foregoing waiver shall not apply to any contractual inspection rights of the
Optionee under any other written agreement between the Optionee and the Company. 
 9. Stockholders’ Agreements. The Grantee
understands and agrees as a condition to the Grantee’s receipt of the Shares, the Grantee is required to execute adoption agreements (substantially in the forms attached hereto as Exhibits A and B) to that certain Voting Agreement, dated
October 13, 2017, by and among the Company and the stockholders listed as parties thereto, as the same may be amended and/or restated from time to time (the “Voting Agreement”) and that certain Right of First Refusal and Co-Sale Agreement, dated October 13, 2017, by and among the Company and the stockholders listed as parties thereto, as the same may be amended and/or restated from time to time (the “ROFR
Agreement”), as a Key Holder (as such term is defined in the Voting Agreement or the ROFR Agreement, as the case may be), and the Grantee will thereby be bound by, and subject to, all terms and provisions of the Voting Agreement and the
ROFR Agreement applicable to a Key Holder thereunder. 
 [SIGNATURE PAGE FOLLOWS] 

  
 -25- 

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby
agreed to by the undersigned as of the date first above written. 
  

			
	ALECTOR, INC.
		
	By:	 	 
		 	Name:
		 	Title:
	
	Address:
	
	 
	
	 
	
	 

 The undersigned hereby acknowledges receiving and reviewing a copy of the Plan, including, without limitation,
Section 9 thereof, and understands that this Stock Option is subject to the terms of the Plan and of this Agreement. This Agreement is hereby accepted, and the terms and conditions of the Plan, the Grant Notice and this Agreement, SPECIFICALLY
INCLUDING THE ARBITRATION PROVISIONS SET FORTH IN SECTION 7 AND THE WAIVER OF STATUTORY INFORMATION RIGHTS SET FORTH IN SECTION 8 OF THIS AGREEMENT, are hereby agreed to, by the undersigned as of the date first above written. 

 

			
	OPTIONEE:
		
	By:	 	 
		 	Name:
		 	Title:
	
	Address:
	
	 
	
	 
	
	 

  
 -26- 

 SPOUSE’S CONSENT 

I acknowledge that I have read the 
 foregoing Incentive Stock
Option Agreement 
 and understand the contents thereof. 
  

                          
                                         
              

  
 -27- 

 
			
	DESIGNATED BENEFICIARY:
		
		 	 
		
		 	Beneficiary’s Address:
		
		 	 
		
		 	 
		
		 	 

  
 -28- 

 Appendix A 

STOCK OPTION EXERCISE NOTICE 
 Alector,
Inc. 
 Attention: [____________________] 
  

                          
                                       

 

                          
                                       

Pursuant to the terms of the grant notice and stock option agreement between the undersigned and Alector, Inc. (the “Company”) dated
__________ (the “Agreement”) under the Alector, Inc. 2017 Stock Option and Grant Plan, I, [Insert Name] ________________, hereby [Circle One] partially/fully exercise such option by including herein payment in the amount of $______
representing the purchase price for [Fill in number of Shares] _______ Shares. I have chosen the following form(s) of payment: 
  

					
	 ☐
	  	1.	  	Cash
			
	 ☐
	  	2.	  	Certified or bank check payable to Alector, Inc.
			
	 ☐
	  	3.	  	Other (as referenced in the Agreement and described in the Plan (please describe))              
                                         
                     .

 In connection with my exercise of the option as set forth above, I hereby represent and warrant to the Company
as follows: 
 (i) I am purchasing the Shares for my own account for investment only, and not for resale or with a view to
the distribution thereof. 
 (ii) I have had such an opportunity as I have deemed adequate to obtain from the Company such
information as is necessary to permit me to evaluate the merits and risks of my investment in the Company and have consulted with my own advisers with respect to my investment in the Company. 

(iii) I have sufficient experience in business, financial and investment matters to be able to evaluate the risks involved in
the purchase of the Shares and to make an informed investment decision with respect to such purchase. 
 (iv) I can afford a
complete loss of the value of the Shares and am able to bear the economic risk of holding such Shares for an indefinite period of time. 

  
 -29- 

 (v) I understand that the Shares may not be registered under the Securities
Act of 1933 (it being understood that the Shares are being issued and sold in reliance on the exemption provided in Rule 701 thereunder) or any applicable state securities or “blue sky” laws and may not be sold or otherwise transferred or
disposed of in the absence of an effective registration statement under the Securities Act of 1933 and under any applicable state securities or “blue sky” laws (or exemptions from the registration requirement thereof). I further
acknowledge that certificates representing Shares will bear restrictive legends reflecting the foregoing and/or that book entries for uncertificated Shares will include similar restrictive notations. 

(vi) I have read and understand the Plan and acknowledge and agree that the Shares are subject to all of the relevant terms of
the Plan, including without limitation, the transfer restrictions set forth in Section 9 of the Plan. 
 (vii) I
understand and agree that the Company has a right of first refusal with respect to the Shares pursuant to Section 9(b) of the Plan. 

(viii) I understand and agree that the Company has certain repurchase rights with respect to the Shares pursuant to
Section 9(c) of the Plan. 
 (ix) I understand and agree that I may not sell or otherwise transfer or dispose of the
Shares for a period of time following the effective date of a public offering by the Company as described in Section 9(f) of the Plan. 

(x) I understand and agree to the waiver of statutory information rights as set forth in Section 8 of the Agreement. 

 

	
	Sincerely yours,
	
	   

	Name:
	
	Address:
	
	   

	
	   

	
	   

	
	Date:
                                         
                                         
      

  
 -30- 

 EXHIBIT A 

ADOPTION AGREEMENT 
 This
Adoption Agreement (“Adoption Agreement”) is executed on ___________________, 20__, by the undersigned (the “Holder”) pursuant to the terms of that certain Voting Agreement of Alector, Inc. (the
“Company”) dated as of October 13, 2017 (the “Agreement”), by and among the Company and certain of its Stockholders, as such Agreement may be amended or amended and restated hereafter. Capitalized terms used
but not defined in this Adoption Agreement shall have the respective meanings ascribed to such terms in the Agreement. By the execution of this Adoption Agreement, the Holder agrees as follows. 

1.1 Acknowledgement. Holder acknowledges that Holder is acquiring certain shares of the capital stock of the Company (the
“Stock”), for one of the following reasons (Check the correct box): 
  

	 	☐	 As a transferee of Shares from a party in such party’s capacity as an “Investor” bound by
the Agreement, and after such transfer, Holder shall be considered an “Investor” and a “Stockholder” for all purposes of the Agreement. 

 

	 	☐	 As a transferee of Shares from a party in such party’s capacity as a “Key Holder” bound
by the Agreement, and after such transfer, Holder shall be considered a “Key Holder” and a “Stockholder” for all purposes of the Agreement. 

 

	 	☐	 As a new Investor in accordance with Subsection 7.1(a) of the Agreement, in which case Holder will be an
“Investor” and a “Stockholder” for all purposes of the Agreement. 

  

	 	☐	 In accordance with Subsection 7.1(b) of the Agreement, as a new party who is not a new Investor, in which case
Holder will be a “Stockholder” for all purposes of the Agreement. 

 1.2 Agreement. Holder hereby
(a) agrees that the Stock, and any other shares of capital stock or securities required by the Agreement to be bound thereby, shall be bound by and subject to the terms of the Agreement and (b) adopts the Agreement with the same force and
effect as if Holder were originally a party thereto. 
 1.3 Notice. Any notice required or permitted by the Agreement shall be given
to Holder at the address or facsimile number listed below Holder’s signature hereto. 

  
 -31- 

									
	HOLDER:	 		 	ACCEPTED AND AGREED:
				
	By:	 	                                     
                                         
              	 		 	ALECTOR, INC.
	Name and Title of Signatory	 		 	
				
	Address:
                                         
                                         
	 		 	By:	 	                                      
                                         
                                    
				
	                               
                                         
                          	 		 		 	                                 
                                         
                                         

			
		 		 	Title:                              
                                         
                                         

				
	Facsimile Number:
                                         
                         	 		 		 	

  
 -32- 

 EXHIBIT B 

ROFR AND CO-SALE AGREEMENT ADOPTION AGREEMENT 

This Adoption Agreement (“Adoption Agreement”) is executed on ________________, 20__, by the undersigned (the
“Holder”) pursuant to the terms of that certain Right of First Refusal and Co-Sale Agreement dated as of October 13, 2017 (the “Agreement”), by and among the Company and
certain parties listed therein as Investors and Key Holders, as such Agreement may be amended or amended and restated hereafter. Capitalized terms used but not defined in this Adoption Agreement shall have the respective meanings ascribed to such
terms in the Agreement. By the execution of this Adoption Agreement, the Holder agrees as follows. 

1.1    Acknowledgement. Holder acknowledges that Holder is acquiring certain shares of the capital stock of the Company
(the “Stock”) in accordance with Section 6.14 of the Agreement, as a new party who is not a new Investor, in which case Holder will be a “Key Holder” for all purposes of the Agreement. 

1.2    Agreement. Holder hereby (a) agrees that the Stock, and any other shares of capital stock or securities
required by the Agreement to be bound thereby, shall be bound by and subject to the terms of the Agreement and (b) adopts the Agreement with the same force and effect as if Holder were originally a party thereto as a Key Holder. 

1.3    Notice. Any notice required or permitted by the Agreement shall be given to Holder at the address or facsimile
number listed below Holder’s signature hereto. 
  

									
	HOLDER:	 		 	ACCEPTED AND AGREED:
				
	By:	 	                                     
                                         
              	 		 	ALECTOR, INC.
	Name and Title of Signatory	 		 	
				
	Address:
                                         
                                         
	 		 	By:	 	                                      
                                         
                                    
				
	                               
                                         
                          	 		 		 	                                 
                                         
                                         

			
		 		 	Title:                              
                                         
                                         

				
	Facsimile Number:
                                         
                         	 		 		 	

  
 -33- 

 NON-QUALIFIED STOCK OPTION GRANT NOTICE 

UNDER THE ALECTOR, INC. 

STOCK OPTION AND GRANT PLAN 

Pursuant to the Alector, Inc. 2017 Stock Option and Grant Plan (the “Plan”), Alector, Inc., a Delaware corporation (together
with any successor, the “Company”), has granted to the individual named below, an option (the “Stock Option”) to purchase on or prior to the Expiration Date, or such earlier date as is specified herein, all or any
part of the number of shares of Common Stock, par value $0.0001 per share (“Common Stock”), of the Company indicated below (the “Shares”), at the Option Exercise Price per share, subject to the terms and conditions
set forth in this Non-Qualified Stock Option Grant Notice (the “Grant Notice”), the attached Non-Qualified Stock Option Agreement (the
“Agreement”) and the Plan. This Stock Option is not intended to qualify as an “incentive stock option” as defined in Section 422(b) of the Internal Revenue Code of 1986, as amended from time to time (the
“Code”). 
 Name of Optionee:    __________________ (the “Optionee”) 

No. of Shares:    __________ Shares of Common Stock 

Grant Date:    __________________ 
 Vesting
Commencement Date:    __________________ (the “Vesting Commencement Date”) 
 Expiration Date:
    __________________ (the “Expiration Date”) 
 Option Exercise Price/Share:  $_________________ (the
“Option Exercise Price”) 
  

			
	Vesting Schedule:	  	25 percent of the Shares shall vest and become exercisable on the first anniversary of the Vesting Commencement Date; provided that the Optionee continues to have a Service Relationship with the Company at such time.
Thereafter, the remaining 75 percent of the Shares shall vest and become exercisable in 36 equal monthly installments following the first anniversary of the Vesting Commencement Date, provided the Optionee continues to have a Service
Relationship with the Company on each vesting date. Notwithstanding anything in the Agreement to the contrary, in the case of a Sale Event, this Stock Option and the Shares shall be treated as provided in Section 3(c) of the Plan.

 Attachments: Non-Qualified Stock Option Agreement, 2017 Stock Option and Grant
Plan 

  
 -34- 

 NON-QUALIFIED STOCK OPTION AGREEMENT 

UNDER THE ALECTOR, INC. 

STOCK OPTION AND GRANT PLAN 

All capitalized terms used herein and not otherwise defined shall have the respective meanings set forth in the Grant Notice and the Plan.

  

	 	1.	 Vesting, Exercisability and Termination. 

(a) No portion of this Stock Option may be exercised until such portion shall have vested and become exercisable. 

(b) Except as set forth below, and subject to the determination of the Committee in its sole discretion to accelerate the vesting schedule
hereunder, this Stock Option shall be vested and exercisable on the respective dates indicated below: 
 (i) This Stock
Option shall initially be unvested and unexercisable. 
 (ii) This Stock Option shall vest and become exercisable in
accordance with the Vesting Schedule set forth in the Grant Notice. 
 (c) Termination. Except as may otherwise be provided by the
Committee, if the Optionee’s Service Relationship is terminated, the period within which to exercise this Stock Option will be subject to earlier termination as set forth below (and if not exercised within such period, shall thereafter
terminate subject, in each case, to Section 3(c) of the Plan): 
 (i) Termination Due to Death or Disability. If
the Optionee’s Service Relationship terminates by reason of such Optionee’s death or Disability, this Stock Option may be exercised, to the extent exercisable on the date of such termination, by the Optionee, the Optionee’s legal
representative or legatee for a period of 12 months from the date of death or Disability or until the Expiration Date, if earlier. 

(ii) Other Termination. If the Optionee’s Service Relationship terminates for any reason other than death or
Disability, and unless otherwise determined by the Committee, this Stock Option may be exercised, to the extent exercisable on the date of termination, for a period of 90 days from the date of termination or until the Expiration Date, if earlier;
provided however, if the Optionee’s Service Relationship is terminated for Cause, this Stock Option shall terminate immediately upon the date of such termination. 

For purposes hereof, the Committee’s determination of the reason for termination of the Optionee’s Service Relationship shall be
conclusive and binding on the Optionee and his or her representatives or legatees and any Permitted Transferee. Any portion of this Stock Option that is not vested and exercisable on the date of termination of the Service Relationship shall
terminate immediately and be null and void. 

  
 -35- 

 2. Exercise of Stock Option. 

(a) The Optionee may exercise this Stock Option only in the following manner: Prior to the Expiration Date, the Optionee may deliver a Stock
Option exercise notice (an “Exercise Notice”) in the form of Appendix A hereto indicating his or her election to purchase some or all of the Shares with respect to which this Stock Option is then exercisable. Such notice
shall specify the number of Shares to be purchased. Payment of the purchase price may be made by one or more of the methods described in Section 5 of the Plan, subject to the limitations contained in such Section of the Plan, including the
requirement that the Committee specifically approve in advance certain payment methods. 
 (b) Notwithstanding any other provision hereof or
of the Plan, no portion of this Stock Option shall be exercisable after the Expiration Date. 
 3. Incorporation of Plan.
Notwithstanding anything herein to the contrary, this Stock Option shall be subject to and governed by all the terms and conditions of the Plan. 

4. Transferability of Stock Option. This Stock Option is personal to the Optionee and is not transferable by the Optionee in any manner
other than by will or by the laws of descent and distribution. The Stock Option may be exercised during the Optionee’s lifetime only by the Optionee (or by the Optionee’s guardian or personal representative in the event of the
Optionee’s incapacity). The Optionee may elect to designate a beneficiary by providing written notice of the name of such beneficiary to the Company, and may revoke or change such designation at any time by filing written notice of revocation
or change with the Company; such beneficiary may exercise the Optionee’s Stock Option in the event of the Optionee’s death to the extent provided herein. If the Optionee does not designate a beneficiary, or if the designated beneficiary
predeceases the Optionee, the legal representative of the Optionee may exercise this Stock Option to the extent provided herein in the event of the Optionee’s death. 

5. Restrictions on Transfer of Shares. The Shares acquired upon exercise of the Stock Option shall be subject to certain transfer
restrictions and other limitations including, without limitation, the provisions contained in Section 9 of the Plan. 
 6.
Miscellaneous Provisions. 
 (a) Equitable Relief. The parties hereto agree and declare that legal remedies may be inadequate
to enforce the provisions of this Agreement and that equitable relief, including specific performance and injunctive relief, may be used to enforce the provisions of this Agreement. 

(b) Adjustments for Changes in Capital Structure. If, as a result of any reorganization, recapitalization, reincorporation,
reclassification, stock dividend, stock split, reverse stock split or other similar change in the Common Stock, the outstanding shares of Common Stock are increased or decreased or are exchanged for a different number or kind of securities of the
Company, the restrictions contained in this Agreement shall apply with equal force to additional and/or substitute securities, if any, received by the Optionee in exchange for, or by virtue of his or her ownership of, this Stock Option or Shares
acquired pursuant thereto. 

  
 -36- 

 (c) Change and Modifications. This Agreement may not be orally changed, modified or
terminated, nor shall any oral waiver of any of its terms be effective. This Agreement may be changed, modified or terminated only by an agreement in writing signed by the Company and the Optionee. 

(d) Governing Law. This Agreement shall be governed by and construed in accordance with the General Corporation Law of the State of
Delaware as to matters within the scope thereof, and as to all other matters shall be governed by and construed in accordance with the internal laws of the State of California, without regard to conflict of law principles that would result in the
application of any law other than the law of the State of California. 
 (e) Headings. The headings are intended only for convenience
in finding the subject matter and do not constitute part of the text of this Agreement and shall not be considered in the interpretation of this Agreement. 

(f) Saving Clause. If any provision(s) of this Agreement shall be determined to be illegal or unenforceable, such determination shall
in no manner affect the legality or enforceability of any other provision hereof. 
 (g) Notices. All notices, requests, consents and
other communications shall be in writing and be deemed given when delivered personally, by telex or facsimile transmission or when received if mailed by first class registered or certified mail, postage prepaid. Notices to the Company or the
Optionee shall be addressed as set forth underneath their signatures below, or to such other address or addresses as may have been furnished by such party in writing to the other. 

(h) Benefit and Binding Effect. This Agreement shall be binding upon and shall inure to the benefit of the parties hereto, their
respective successors, assigns, and legal representatives. The Company has the right to assign this Agreement, and such assignee shall become entitled to all the rights of the Company hereunder to the extent of such assignment. 

(i) Counterparts. For the convenience of the parties and to facilitate execution, this Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which shall constitute one and the same document. 
 (j)
Integration. This Agreement constitutes the entire agreement between the parties with respect to this Stock Option and supersedes all prior agreements and discussions between the parties concerning such subject matter. 

7. Dispute Resolution. 

(a) Except as provided below, any dispute arising out of or relating to the Plan or this Stock Option, this Agreement, or the breach,
termination or validity of the Plan, this Stock Option or this Agreement, shall be finally settled by binding arbitration conducted expeditiously in accordance with the J.A.M.S./Endispute Comprehensive Arbitration Rules and Procedures (the
“J.A.M.S. Rules”). The arbitration shall be governed by the United States Arbitration Act, 9 U.S.C. Sections 1-16, and judgment upon the award rendered by the arbitrators may be entered by any
court having jurisdiction thereof. The place of arbitration shall be [San Francisco, California]. 

  
 -37- 

 (b) The arbitration shall commence within 60 days of the date on which a written demand for
arbitration is filed by any party hereto. In connection with the arbitration proceeding, the arbitrator shall have the power to order the production of documents by each party and any third-party witnesses. In addition, each party may take up to
three depositions as of right, and the arbitrator may in his or her discretion allow additional depositions upon good cause shown by the moving party. However, the arbitrator shall not have the power to order the answering of interrogatories or the
response to requests for admission. In connection with any arbitration, each party to the arbitration shall provide to the other, no later than seven business days before the date of the arbitration, the identity of all persons that may testify at
the arbitration and a copy of all documents that may be introduced at the arbitration or considered or used by a party’s witness or expert. The arbitrator’s decision and award shall be made and delivered within six months of the selection
of the arbitrator. The arbitrator’s decision shall set forth a reasoned basis for any award of damages or finding of liability. The arbitrator shall not have power to award damages in excess of actual compensatory damages and shall not multiply
actual damages or award punitive damages, and each party hereby irrevocably waives any claim to such damages. 
 (c) The Company, the
Optionee, each party to the Agreement and any other holder of Shares issued pursuant to this Agreement (each, a “Party”) covenants and agrees that such party will participate in the arbitration in good faith. This Section 7
applies equally to requests for temporary, preliminary or permanent injunctive relief, except that in the case of temporary or preliminary injunctive relief any party may proceed in court without prior arbitration for the limited purpose of avoiding
immediate and irreparable harm. 
 (d) Each Party (i) hereby irrevocably submits to the jurisdiction of any United States District
Court of competent jurisdiction for the purpose of enforcing the award or decision in any such proceeding, (ii) hereby waives, and agrees not to assert, by way of motion, as a defense, or otherwise, in any such suit, action or proceeding, any
claim that it is not subject personally to the jurisdiction of the above named courts, that its property is exempt or immune from attachment or execution (except as protected by applicable law), that the suit, action or proceeding is brought in an
inconvenient forum, that the venue of the suit, action or proceeding is improper or that this Agreement or the subject matter hereof may not be enforced in or by such court, and (iii) hereby waives and agrees not to seek any review by any court
of any other jurisdiction which may be called upon to grant an enforcement of the judgment of any such court. Each Party hereby consents to service of process by registered mail at the address to which notices are to be given. Each Party agrees that
its, his or her submission to jurisdiction and its, his or her consent to service of process by mail is made for the express benefit of each other Party. Final judgment against any Party in any such action, suit or proceeding may be enforced in
other jurisdictions by suit, action or proceeding on the judgment, or in any other manner provided by or pursuant to the laws of such other jurisdiction. 

8. Waiver of Statutory Information Rights. The Optionee understands and agrees that, but for the waiver made herein, the Optionee would
be entitled, upon written demand under oath stating the purpose thereof, to inspect for any proper purpose, and to make copies and extracts from, the Company’s stock ledger, a list of its stockholders, and its other books and records, and the
books and records of subsidiaries of the Company, if any, under the circumstances and in the manner provided in Section 220 of the General Corporation Law of Delaware (any and all such rights, and

  
 -38- 

 
any and all such other rights of the Optionee as may be provided for in Section 220, the “Inspection Rights”). In light of the foregoing, until the first sale of Stock of
the Company to the general public pursuant to a registration statement filed with and declared effective by the Securities and Exchange Commission under the Securities Act, the Optionee hereby unconditionally and irrevocably waives the Inspection
Rights, whether such Inspection Rights would be exercised or pursued directly or indirectly pursuant to Section 220 or otherwise, and covenants and agrees never to directly or indirectly commence, voluntarily aid in any way, prosecute, assign,
transfer, or cause to be commenced any claim, action, cause of action, or other proceeding to pursue or exercise the Inspection Rights. The foregoing waiver shall not affect any rights of a director, in his or her capacity as such, under
Section 220. The foregoing waiver shall not apply to any contractual inspection rights of the Optionee under any other written agreement between the Optionee and the Company. 

9. Stockholders’ Agreements. The Grantee understands and agrees as a condition to the Grantee’s receipt of the Shares, the
Grantee is required to execute adoption agreements (substantially in the forms attached hereto as Exhibits A and B) to that certain Voting Agreement, dated October 13, 2017, by and among the Company and the stockholders listed as parties
thereto, as the same may be amended and/or restated from time to time (the “Voting Agreement”) and that certain Right of First Refusal and Co-Sale Agreement, dated October 13, 2017, by
and among the Company and the stockholders listed as parties thereto, as the same may be amended and/or restated from time to time (the “ROFR Agreement”), as a Key Holder (as such term is defined in the Voting Agreement or the ROFR
Agreement, as the case may be), and the Grantee will thereby be bound by, and subject to, all terms and provisions of the Voting Agreement and the ROFR Agreement applicable to a Key Holder thereunder. 

[SIGNATURE PAGE FOLLOWS] 

  
 -39- 

 The foregoing Agreement is hereby accepted and the terms and conditions thereof hereby
agreed to by the undersigned as of the date first above written. 
  

			
	ALECTOR, INC.
		
	By:	 	 
		 	Name:
		 	Title:
	
	Address:
	
	 
	
	 
	
	 

 The undersigned hereby acknowledges receiving and reviewing a copy of the Plan, including, without
limitation, Section 9 thereof, and understands that this Stock Option is subject to the terms of the Plan and of this Agreement. This Agreement is hereby accepted, and the terms and conditions of the Plan, the Grant Notice and this Agreement,
SPECIFICALLY INCLUDING THE ARBITRATION PROVISIONS SET FORTH IN SECTION 7 AND THE WAIVER OF STATUTORY INFORMATION RIGHTS SET FORTH IN SECTION 8 OF THIS AGREEMENT, are hereby agreed to, by the undersigned as of the date first above written. 

 

			
	OPTIONEE:
	
	 
	Name:
	
	Address:
	
	 
	
	 
	
	 

  
 -40- 

	
	SPOUSE’S CONSENT
	
	 I acknowledge that I have read the
 foregoing Non-Qualified Stock Option Agreement
 and understand the contents thereof.

	
	 

  
 -41- 

 
	
	DESIGNATED BENEFICIARY:
	
	Beneficiary’s Address:
	
	 
	
	 
	
	 

  
 -42- 

 Appendix A 

STOCK OPTION EXERCISE NOTICE 
 Alector,
Inc. 
  

	
	
	Attention:
[                                         
                                   ]
	
	   

	
	   

 Pursuant to the terms of the grant notice and stock option agreement between the undersigned and Alector, Inc. (the
“Company”) dated                      (the “Agreement”) under the Alector, Inc. 2017 Stock Option and Grant
Plan, I, [Insert Name]                             , hereby [Circle One] partially/fully exercise such
option by including herein payment in the amount of $                 representing the purchase price for [Fill in number of Shares]
                     Shares. I have chosen the following form(s) of payment: 

☐    1. Cash 

☐    2. Certified or bank check payable to Alector, Inc. 

☐    3. Other (as referenced in the Agreement and described in the Plan (please describe))
                                         
                                   . 

In connection with my exercise of the option as set forth above, I hereby represent and warrant to the Company as follows: 

(i) I am purchasing the Shares for my own account for investment only, and not for resale or with a view to the distribution
thereof. 
 (ii) I have had such an opportunity as I have deemed adequate to obtain from the Company such information as is
necessary to permit me to evaluate the merits and risks of my investment in the Company and have consulted with my own advisers with respect to my investment in the Company. 

(iii) I have sufficient experience in business, financial and investment matters to be able to evaluate the risks involved in
the purchase of the Shares and to make an informed investment decision with respect to such purchase. 
 (iv) I can afford a
complete loss of the value of the Shares and am able to bear the economic risk of holding such Shares for an indefinite period of time. 

  
 -43- 

 (v) I understand that the Shares may not be registered under the Securities
Act of 1933 (it being understood that the Shares are being issued and sold in reliance on the exemption provided in Rule 701 thereunder) or any applicable state securities or “blue sky” laws and may not be sold or otherwise
transferred or disposed of in the absence of an effective registration statement under the Securities Act of 1933 and under any applicable state securities or “blue sky” laws (or exemptions from the registration requirement thereof). I
further acknowledge that certificates representing Shares will bear restrictive legends reflecting the foregoing and/or that book entries for uncertificated Shares will include similar restrictive notations. 

(vi) I have read and understand the Plan and acknowledge and agree that the Shares are subject to all of the relevant terms of
the Plan, including without limitation, the transfer restrictions set forth in Section 9 of the Plan. 
 (vii) I
understand and agree that the Company has a right of first refusal with respect to the Shares pursuant to Section 9(b) of the Plan. 

(viii) I understand and agree that the Company has certain repurchase rights with respect to the Shares pursuant to
Section 9(c) of the Plan. 
 (ix) I understand and agree that I may not sell or otherwise transfer or dispose of the
Shares for a period of time following the effective date of a public offering by the Company as described in Section 9(f) of the Plan. 

(x) I understand and agree to the waiver of statutory information rights as set forth in Section 8 of the Agreement. 

 

			
	Sincerely yours,
	
	   

	Name:
	
	Address:
	
	   

	
	   

	
	   

		
	Date:	 	 

  
 -44- 

 EXHIBIT A 

ADOPTION AGREEMENT 
 This
Adoption Agreement (“Adoption Agreement”) is executed on
                            , 20        , by the
undersigned (the “Holder”) pursuant to the terms of that certain Voting Agreement of Alector, Inc. (the “Company”) dated as of October 13, 2017 (the “Agreement”), by and among the Company and
certain of its Stockholders, as such Agreement may be amended or amended and restated hereafter. Capitalized terms used but not defined in this Adoption Agreement shall have the respective meanings ascribed to such terms in the Agreement. By the
execution of this Adoption Agreement, the Holder agrees as follows. 
 1.1 Acknowledgement. Holder acknowledges that Holder is
acquiring certain shares of the capital stock of the Company (the “Stock”), for one of the following reasons (Check the correct box): 

☐ As a transferee of Shares from a party in such party’s capacity as an “Investor” bound by the Agreement, and after such
transfer, Holder shall be considered an “Investor” and a “Stockholder” for all purposes of the Agreement. 
 ☐ As
a transferee of Shares from a party in such party’s capacity as a “Key Holder” bound by the Agreement, and after such transfer, Holder shall be considered a “Key Holder” and a “Stockholder” for all purposes of the
Agreement. 
 ☐ As a new Investor in accordance with Subsection 7.1(a) of the Agreement, in which case Holder will be an
“Investor” and a “Stockholder” for all purposes of the Agreement. 
 ☐ In accordance with Subsection 7.1(b) of the
Agreement, as a new party who is not a new Investor, in which case Holder will be a “Stockholder” for all purposes of the Agreement. 

1.2 Agreement. Holder hereby (a) agrees that the Stock, and any other shares of capital stock or securities required by the
Agreement to be bound thereby, shall be bound by and subject to the terms of the Agreement and (b) adopts the Agreement with the same force and effect as if Holder were originally a party thereto. 

1.3 Notice. Any notice required or permitted by the Agreement shall be given to Holder at the address or facsimile number listed below
Holder’s signature hereto. 

  
 -45- 

					
	HOLDER:                                    
                                         
       	 		 	ACCEPTED AND AGREED:
			
	By:                                     
                                         
                  	 		 	ALECTOR, INC.
	Name and Title of Signatory	 		 	
			
	Address:                                     
                                         
          	 		 	By:                                     
                                         
                  
			
	                                      
                                         
                         	 		 	Title:                                    
                                         
                 
			
	Facsimile
Number:                                        
                                	 		 	

  
 -46- 

 EXHIBIT B 

ROFR AND CO-SALE AGREEMENT ADOPTION AGREEMENT 

This Adoption Agreement (“Adoption Agreement”) is executed on
                            , 20      , by the undersigned (the
“Holder”) pursuant to the terms of that certain Right of First Refusal and Co-Sale Agreement dated as of October 13, 2017 (the “Agreement”), by and among the Company and
certain parties listed therein as Investors and Key Holders, as such Agreement may be amended or amended and restated hereafter. Capitalized terms used but not defined in this Adoption Agreement shall have the respective meanings ascribed to such
terms in the Agreement. By the execution of this Adoption Agreement, the Holder agrees as follows. 
 1.1 Acknowledgement. Holder
acknowledges that Holder is acquiring certain shares of the capital stock of the Company (the “Stock”) in accordance with Section 6.14 of the Agreement, as a new party who is not a new Investor, in which case Holder will be a
“Key Holder” for all purposes of the Agreement. 
 1.2 Agreement. Holder hereby (a) agrees that the Stock, and any other
shares of capital stock or securities required by the Agreement to be bound thereby, shall be bound by and subject to the terms of the Agreement and (b) adopts the Agreement with the same force and effect as if Holder were originally a party
thereto as a Key Holder. 
 1.3 Notice. Any notice required or permitted by the Agreement shall be given to Holder at the address or
facsimile number listed below Holder’s signature hereto. 
  

					
	HOLDER:                                    
                                         
                 	 		 	ACCEPTED AND AGREED:
			
	By:                                     
                                         
                              	 		 	ALECTOR, INC.
	Name and Title of Signatory	 		 	
			
	Address:                                     
                                         
                    	 		 	By:                                     
                                         
                  
			
	                                      
                                         
                                 	 		 	Title:                                    
                                         
               
			
	Facsimile
Number:                                        
                                        
  	 		 	

  
 -47-EX-10.3

 Exhibit 10.3 

ALECTOR, INC. 
 2019
EQUITY INCENTIVE PLAN 
 1. Purposes of the Plan. The purposes of this Plan are: 

 

	 	•	 	 to attract and retain the best available personnel for positions of substantial responsibility,

  

	 	•	 	 to provide additional incentive to Employees, Directors and Consultants, and 

 

	 	•	 	 to promote the success of the Company’s business. 

The Plan permits the grant of Incentive Stock Options, Nonstatutory Stock Options, Restricted Stock, Restricted Stock Units, Stock
Appreciation Rights, Performance Units and Performance Shares. 
 2. Definitions. As used herein, the following definitions will
apply: 
 (a) “Administrator” means the Board or any of its Committees as will be administering the Plan, in accordance with
Section 4 of the Plan. 
 (b) “Applicable Laws” means the legal and regulatory requirements relating to the
administration of equity-based awards and the related issuance of Shares thereunder, including but not limited to U.S. federal and state corporate laws, U.S. federal and state securities laws, the Code, any stock exchange or quotation system on
which the Common Stock is listed or quoted and the applicable laws of any non-U.S. country or jurisdiction where Awards are, or will be, granted under the Plan. 

(c) “Award” means, individually or collectively, a grant under the Plan of Options, Stock Appreciation Rights, Restricted
Stock, Restricted Stock Units, Performance Units or Performance Shares. 
 (d) “Award Agreement” means the written or
electronic agreement setting forth the terms and provisions applicable to each Award granted under the Plan. The Award Agreement is subject to the terms and conditions of the Plan. 

(e) “Board” means the Board of Directors of the Company. 

(f) “Change in Control” means the occurrence of any of the following events: 

(i) A change in the ownership of the Company which occurs on the date that any one person, or more than one person acting as a group
(“Person”), acquires ownership of the stock of the Company that, together with the stock held by such Person, constitutes more than fifty percent (50%) of the total voting power of the stock of the Company; provided, however,
that for purposes of this subsection, (A) the acquisition of additional stock by any one Person, who is considered to own more than fifty percent (50%) of the total voting power of the stock of the Company

 
will not be considered a Change in Control, and (B) if the stockholders of the Company immediately before such change in ownership continue to retain immediately after the change in
ownership, in substantially the same proportions as their ownership of shares of the Company’s voting stock immediately prior to the change in ownership, the direct or indirect beneficial ownership of fifty percent (50%) or more of the total
voting power of the stock of the Company or of the ultimate parent entity of the Company, such event will not be considered a Change in Control under this subsection (i). For this purpose, indirect beneficial ownership will include, without
limitation, an interest resulting from ownership of the voting securities of one or more corporations or other business entities which own the Company, as the case may be, either directly or through one or more subsidiary corporations or other
business entities; or 
 (ii) A change in the effective control of the Company which occurs on the date that a majority of members of the
Board is replaced during any twelve (12)-month period by Directors whose appointment or election is not endorsed by a majority of the members of the Board prior to the date of the appointment or election. For purposes of this subsection (ii), if any
Person is considered to be in effective control of the Company, the acquisition of additional control of the Company by the same Person will not be considered a Change in Control; or 

(iii) A change in the ownership of a substantial portion of the Company’s assets which occurs on the date that any Person acquires (or
has acquired during the twelve (12)-month period ending on the date of the most recent acquisition by such person or persons) assets from the Company that have a total gross fair market value equal
to or more than fifty percent (50%) of the total gross fair market value of all of the assets of the Company immediately prior to such acquisition or acquisitions; provided, however, that for purposes of this subsection (iii), the following
will not constitute a change in the ownership of a substantial portion of the Company’s assets: (A) a transfer to an entity that is controlled by the Company’s stockholders immediately after the transfer, or (B) a transfer of
assets by the Company to: (1) a stockholder of the Company (immediately before the asset transfer) in exchange for or with respect to the Company’s stock, (2) an entity, fifty percent (50%) or more of the total value or
voting power of which is owned, directly or indirectly, by the Company, (3) a Person, that owns, directly or indirectly, fifty percent (50%) or more of the total value or voting power of all the outstanding stock of the Company, or
(4) an entity, at least fifty percent (50%) of the total value or voting power of which is owned, directly or indirectly, by a Person described in this subsection (iii)(B)(3). For purposes of this subsection (iii), gross fair market value
means the value of the assets of the Company, or the value of the assets being disposed of, determined without regard to any liabilities associated with such assets. 

For purposes of this definition, persons will be considered to be acting as a group if they are owners of a corporation that enters into a
merger, consolidation, purchase or acquisition of stock, or similar business transaction with the Company. 
 Notwithstanding the
foregoing, a transaction will not be deemed a Change in Control unless the transaction qualifies as a change in control event within the meaning of Section 409A. 

  
 -2- 

 Further and for the avoidance of doubt, a transaction will not constitute a Change in
Control if: (i) its sole purpose is to change the state of the Company’s incorporation, or (ii) its sole purpose is to create a holding company that will be owned in substantially the same proportions by the persons who held the
Company’s securities immediately before such transaction. 
 (g) “Code” means the Internal Revenue Code of 1986, as
amended. Reference to a specific section of the Code or regulation thereunder will include such section or regulation, any valid regulation promulgated under such section, and any comparable provision of any future legislation or regulation
amending, supplementing or superseding such section or regulation. 
 (h) “Committee” means a committee of Directors or of
other individuals satisfying Applicable Laws appointed by the Board, or a duly authorized committee of the Board, in accordance with Section 4 hereof. 

(i) “Common Stock” means the Common Stock of the Company. 

(j) “Company” means Alector, Inc., a Delaware corporation, or any successor thereto. 

(k) “Consultant” means any natural person, including an advisor, engaged by the Company or a Parent or Subsidiary to render
bona fide services to such entity, provided the services (i) are not in connection with the offer or sale of securities in a capital-raising transaction, and (ii) do not directly promote or maintain
a market for the Company’s securities, in each case, within the meaning of Form S-8 promulgated under the Securities Act, and provided, further, that a Consultant will include only those persons to whom
the issuance of Shares may be registered under Form S-8 promulgated under the Securities Act. 
 (l)
“Director” means a member of the Board. 
 (m) “Disability” means total and permanent disability as defined
in Section 22(e)(3) of the Code, provided that in the case of Awards other than Incentive Stock Options, the Administrator in its discretion may determine whether a permanent and total disability exists in accordance with uniform and non-discriminatory standards adopted by the Administrator from time to time. 
 (n)
“Employee” means any person, including Officers and Directors, employed by the Company or any Parent or Subsidiary of the Company. Neither service as a Director nor payment of a director’s fee by the Company will be sufficient
to constitute “employment” by the Company. 
 (o) “Exchange Act” means the Securities Exchange Act of 1934, as
amended. 
 (p) “Exchange Program” means a program under which (i) outstanding Awards are surrendered or cancelled in
exchange for awards of the same type (which may have higher or lower exercise prices and different terms), awards of a different type, and/or cash, (ii) Participants would have the opportunity to transfer any outstanding Awards to a financial
institution or other person or entity selected by the Administrator, and/or (iii) the exercise price of an outstanding Award is increased or reduced. The Administrator will determine the terms and conditions of any Exchange Program in its sole
discretion. 

  
 -3- 

 (q) “Fair Market Value” means, as of any date, the value of Common Stock
determined as follows: 
 (i) For purposes of any Awards granted on the Registration Date, the Fair Market Value will be the initial price
to the public as set forth in the final prospectus included within the registration statement in Form S-1 filed with the Securities and Exchange Commission for the initial public offering of the Company’s
Common Stock. 
 (ii) For purposes of any Awards granted on any other date, the Fair Market Value will be the closing sales price for Common
Stock as quoted on any established stock exchange or national market system (including without limitation the New York Stock Exchange, NASDAQ Global Select Market, the NASDAQ Global Market or the NASDAQ Capital Market of The NASDAQ Stock Market) on
which the Common Stock is listed on the date of determination (or the closing bid, if no sales were reported), as reported in The Wall Street Journal or such other source as the Administrator deems reliable. If the determination date for the
Fair Market Value occurs on a non-trading day (i.e., a weekend or holiday), the Fair Market Value will be such price on the immediately preceding trading day, unless otherwise determined by the Administrator.
In the absence of an established market for the Common Stock, the Fair Market Value thereof will be determined in good faith by the Administrator. 

The determination of fair market value for purposes of tax withholding may be made in the Administrator’s discretion subject to
Applicable Laws and is not required to be consistent with the determination of Fair Market Value for other purposes. 
 (r) “Fiscal
Year” means the fiscal year of the Company. 
 (s) “Incentive Stock Option” means an Option intended to qualify as
an incentive stock option within the meaning of Section 422 of the Code and the regulations promulgated thereunder. 
 (t)
“Nonstatutory Stock Option” means an Option that by its terms does not qualify or is not intended to qualify as an Incentive Stock Option. 

(u) “Officer” means a person who is an officer of the Company within the meaning of Section 16 of the Exchange Act and
the rules and regulations promulgated thereunder. 
 (v) “Option” means a stock option granted pursuant to the Plan. 

(w) “Outside Director” means a Director who is not an Employee. 

(x) “Parent” means a “parent corporation,” whether now or hereafter existing, as defined in
Section 424(e) of the Code. 
 (y) “Participant” means the holder of an outstanding Award. 

(z) “Performance Share” means an Award denominated in Shares which may be earned in whole or in part upon attainment of
performance goals or other vesting criteria as the Administrator may determine pursuant to Section 10. 

  
 -4- 

 (aa) “Performance Unit” means an Award which may be earned in whole or in
part upon attainment of performance goals or other vesting criteria as the Administrator may determine and which may be settled for cash, Shares or other securities or a combination of the foregoing pursuant to Section 10. 

(bb) “Period of Restriction” means the period during which the transfer of Shares of Restricted Stock are subject to
restrictions and therefore, the Shares are subject to a substantial risk of forfeiture. Such restrictions may be based on the passage of time, the achievement of target levels of performance, or the occurrence of other events as determined by the
Administrator. 
 (cc) “Plan” means this 2019 Equity Incentive Plan. 

(dd) “Registration Date” means the effective date of the first registration statement that is filed by the Company and
declared effective pursuant to Section 12(b) of the Exchange Act, with respect to any class of the Company’s securities. 

(ee) “Restricted Stock” means Shares issued pursuant to a Restricted Stock award under Section 7 of the Plan, or issued
pursuant to the early exercise of an Option. 
 (ff) “Restricted Stock Unit” means a bookkeeping entry representing an
amount equal to the Fair Market Value of one Share, granted pursuant to Section 8. Each Restricted Stock Unit represents an unfunded and unsecured obligation of the Company. 

(gg) “Rule 16b-3” means Rule 16b-3 of the Exchange Act or any successor to Rule 16b-3, as in effect when discretion is being
exercised with respect to the Plan. 
 (hh) “Section 16(b)” means Section 16(b) of the Exchange
Act. 
 (ii) “Section 409A” means Code Section 409A, as it has been and may be amended from time to
time, and any proposed or final Treasury Regulations and Internal Revenue Service guidance that has been promulgated or may be promulgated thereunder from time to time. 

(jj) “Securities Act” means the Securities Act of 1933, as amended. 

(kk) “Service Provider” means an Employee, Director or Consultant. 

(ll) “Share” means a share of the Common Stock, as adjusted in accordance with Section 14 of the Plan. 

(mm) “Stock Appreciation Right” means an Award, granted alone or in connection with an Option, that pursuant to Section 9
is designated as a Stock Appreciation Right. 
 (nn) “Subsidiary” means a “subsidiary corporation,” whether now or
hereafter existing, as defined in Section 424(f) of the Code. 

  
 -5- 

 3.
Stock Subject to the Plan. 
 (a)
Stock Subject to the Plan. Subject to the provisions of Section 14 of the Plan and the automatic increase set forth in Section 3(b) of the Plan, the maximum
aggregate number of Shares that may be issued under the Plan is                     Shares, plus (i) any Shares that, as of the date of
stockholder approval of this Plan, have been reserved but not issued pursuant to any awards granted under the Company’s 2017 Stock Option and Grant Plan (the “Existing Plan”) and are not subject to any awards granted thereunder, and
(ii) any Shares subject to stock options or similar awards granted under the Existing Plan that, after the date of stockholder approval of this Plan, expire or otherwise terminate without having been exercised in full and Shares issued pursuant
to awards granted under the Existing Plan that, after the date of stockholder approval of this Plan, are forfeited to or repurchased by the Company, with the maximum number of Shares to be added to the Plan pursuant to clauses (i) and (ii)
equal to                     Shares. The Shares may be authorized, but unissued, or reacquired Common Stock. 

(b) Automatic Share Reserve Increase. Subject to the provisions of Section 14 of the Plan, the number of Shares available for
issuance under the Plan will be increased on the first day of each Fiscal Year beginning with the 2020 Fiscal Year, in an amount equal to the least of
(i)                     Shares, (ii) five percent (5%) of the outstanding Shares on the last day of the immediately preceding Fiscal Year or
(iii) such number of Shares determined by the Board. 
 (c) Lapsed Awards. If an Award expires or becomes unexercisable without
having been exercised in full, is surrendered pursuant to an Exchange Program, or, with respect to Restricted Stock, Restricted Stock Units, Performance Units or Performance Shares, is forfeited to or repurchased by the Company due to failure to
vest, the unpurchased Shares (or for Awards other than Options or Stock Appreciation Rights the forfeited or repurchased Shares), which were subject thereto will become available for future grant or sale under the Plan (unless the Plan has
terminated). With respect to Stock Appreciation Rights, only Shares actually issued (i.e., the net Shares issued) pursuant to a Stock Appreciation Right will cease to be available under the Plan; all remaining Shares under Stock Appreciation
Rights will remain available for future grant or sale under the Plan (unless the Plan has terminated). Shares that have actually been issued under the Plan under any Award will not be returned to the Plan and will not become available for future
distribution under the Plan; provided, however, that if Shares issued pursuant to Awards of Restricted Stock, Restricted Stock Units, Performance Shares or Performance Units are repurchased by the Company or are forfeited to the Company, such Shares
will become available for future grant under the Plan. Shares used to pay the exercise price of an Award or to satisfy the tax withholding obligations related to an Award will become available for future grant or sale under the Plan. To the extent
an Award under the Plan is paid out in cash rather than Shares, such cash payment will not result in reducing the number of Shares available for issuance under the Plan. Notwithstanding the foregoing and, subject to adjustment as provided in
Section 14, the maximum number of Shares that may be issued upon the exercise of Incentive Stock Options will equal the aggregate Share number stated in Section 3(a), plus, to the extent allowable under Section 422 of the Code and the
Treasury Regulations promulgated thereunder, any Shares that become available for issuance under the Plan pursuant to Sections 3(b) and 3(c). 

(d) Share Reserve. The Company, during the term of this Plan, will at all times reserve and keep available such number of Shares as will
be sufficient to satisfy the requirements of the Plan. 

  
 -6- 

 4. Administration of the Plan. 

(a) Procedure. 
 (i)
Multiple Administrative Bodies. Different Committees with respect to different groups of Service Providers may administer the Plan. 

(ii) Rule 16b-3. To the extent desirable to qualify transactions hereunder as exempt under Rule 16b-3, the transactions contemplated
hereunder will be structured to satisfy the requirements for exemption under Rule 16b-3. 
 (iii) Other Administration. Other than as
provided above, the Plan will be administered by (A) the Board or (B) a Committee, which committee will be constituted to satisfy Applicable Laws. 

(b) Powers of the Administrator. Subject to the provisions of the Plan, and in the case of a Committee, subject to the specific duties
delegated by the Board to such Committee, the Administrator will have the authority, in its discretion: 
 (i) to determine the Fair Market
Value; 
 (ii) to select the Service Providers to whom Awards may be granted hereunder; 

(iii) to determine the number of Shares to be covered by each Award granted hereunder; 

(iv) to approve forms of Award Agreements for use under the Plan; 

(v) to determine the terms and conditions, not inconsistent with the terms of the Plan, of any Award granted hereunder. Such terms and
conditions include, but are not limited to, the exercise price, the time or times when Awards may be exercised (which may be based on performance criteria), any vesting acceleration or waiver of forfeiture restrictions, and any restriction or
limitation regarding any Award or the Shares relating thereto, based in each case on such factors as the Administrator will determine; 

(vi) to institute and determine the terms and conditions of an Exchange Program; 

(vii) to construe and interpret the terms of the Plan and Awards granted pursuant to the Plan; 

(viii) to prescribe, amend and rescind rules and regulations relating to the Plan, including rules and regulations relating to sub-plans established for the purpose of satisfying applicable non-U.S. laws or for qualifying for favorable tax treatment under applicable
non-U.S. laws; 

  
 -7- 

 (ix) to modify or amend each Award (subject to Section 19 of the Plan), including but
not limited to the discretionary authority to extend the post-termination exercisability period of Awards (subject to Section 6(b) of the Plan regarding Incentive Stock Options); 

(x) to allow Participants to satisfy tax withholding obligations in such manner as prescribed in Section 15 of the Plan; 

(xi) to authorize any person to execute on behalf of the Company any instrument required to effect the grant of an Award previously granted by
the Administrator; 
 (xii) to allow a Participant to defer the receipt of the payment of cash or the delivery of Shares that would
otherwise be due to such Participant under an Award; and 
 (xiii) to make all other determinations deemed necessary or advisable for
administering the Plan. 
 (c) Effect of Administrator’s Decision. The Administrator’s decisions,
determinations and interpretations will be final and binding on all Participants and any other holders of Awards. 
 5. Eligibility.
Nonstatutory Stock Options, Stock Appreciation Rights, Restricted Stock, Restricted Stock Units, Performance Shares and Performance Units may be granted to Service Providers. Incentive Stock Options may be granted only to Employees. 

6. Stock Options. 
 (a)
Limitations. Each Option will be designated in the Award Agreement as either an Incentive Stock Option or a Nonstatutory Stock Option. However, notwithstanding such designation, to the extent that the aggregate fair market value of the shares
with respect to which incentive stock options are exercisable for the first time by the Participant during any calendar year (under all plans of the Company and any Parent or Subsidiary) exceeds one hundred thousand dollars ($100,000), such
options will be treated as nonstatutory stock options. For purposes of this Section 6(a), incentive stock options will be taken into account in the order in which they were granted. The fair market value of the shares will be determined as of
the time the option with respect to such shares is granted. 
 (b) Term of Option. The term of each Option will be stated in the Award
Agreement. In the case of an Incentive Stock Option, the term will be ten (10) years from the date of grant or such shorter term as may be provided in the Award Agreement. Moreover, in the case of an Incentive Stock Option granted to a
Participant who, at the time the Incentive Stock Option is granted, owns stock representing more than ten percent (10%) of the total combined voting power of all classes of stock of the Company or any Parent or Subsidiary, the term of the Incentive
Stock Option will be five (5) years from the date of grant or such shorter term as may be provided in the Award Agreement. 

  
 -8- 

 (c) Option Exercise Price and Consideration. 

(i) Exercise Price. The per share exercise price for the Shares to be issued pursuant to exercise of an Option will be determined by
the Administrator, subject to the following: 
 (1) In the case of an Incentive Stock Option 

(A) granted to an Employee who, at the time the Incentive Stock Option is granted, owns stock representing more than ten percent (10%) of the
voting power of all classes of stock of the Company or any Parent or Subsidiary, the per Share exercise price will be no less than one hundred ten percent (110%) of the Fair Market Value per Share on the date of grant. 

(B) granted to any Employee other than an Employee described in paragraph (A) immediately above, the per Share exercise price will be no
less than one hundred percent (100%) of the Fair Market Value per Share on the date of grant. 
 (2) In the case of a Nonstatutory Stock
Option, the per Share exercise price will be no less than one hundred percent (100%) of the Fair Market Value per Share on the date of grant. 

(3) Notwithstanding the foregoing, Options may be granted with a per Share exercise price of less than one hundred percent (100%) of the Fair
Market Value per Share on the date of grant pursuant to a transaction described in, and in a manner consistent with, Section 424(a) of the Code. 

(ii) Waiting Period and Exercise Dates. At the time an Option is granted, the Administrator will fix the period within which the Option
may be exercised and will determine any conditions that must be satisfied before the Option may be exercised. 
 (iii) Form of
Consideration. The Administrator will determine the acceptable form of consideration for exercising an Option, including the method of payment. In the case of an Incentive Stock Option, the Administrator will determine the acceptable form of
consideration at the time of grant. Such consideration may consist entirely of: (1) cash; (2) check; (3) promissory note, to the extent permitted by Applicable Laws, (4) other Shares, provided that such Shares have a Fair Market
Value on the date of surrender equal to the aggregate exercise price of the Shares as to which such Option will be exercised and provided that accepting such Shares will not result in any adverse accounting consequences to the Company, as the
Administrator determines in its sole discretion; (5) consideration received by the Company under a broker-assisted (or other) cashless exercise program (whether through a broker or otherwise) implemented by the Company in connection
with the Plan; (6) by net exercise; (7) such other consideration and method of payment for the issuance of Shares to the extent permitted by Applicable Laws; or (8) any combination of the foregoing methods of payment. 

(d) Exercise of Option. 

(i) Procedure for Exercise; Rights as a Stockholder. Any Option granted hereunder will be exercisable according to the terms of the
Plan and at such times and under such conditions as determined by the Administrator and set forth in the Award Agreement. An Option may not be exercised for a fraction of a Share. 

  
 -9- 

 An Option will be deemed exercised when the Company receives: (i) a notice of exercise
(in such form as the Administrator may specify from time to time) from the person entitled to exercise the Option, and (ii) full payment for the Shares with respect to which the Option is exercised (together with applicable withholding
taxes). Full payment may consist of any consideration and method of payment authorized by the Administrator and permitted by the Award Agreement and the Plan. Shares issued upon exercise of an Option will be issued in the name of the Participant or,
if requested by the Participant, in the name of the Participant and his or her spouse. Until the Shares are issued (as evidenced by the appropriate entry on the books of the Company or of a duly authorized transfer agent of the Company), no right to
vote or receive dividends or any other rights as a stockholder will exist with respect to the Shares subject to an Option, notwithstanding the exercise of the Option. The Company will issue (or cause to be issued) such Shares promptly after the
Option is exercised. No adjustment will be made for a dividend or other right for which the record date is prior to the date the Shares are issued, except as provided in Section 14 of the Plan. 

Exercising an Option in any manner will decrease the number of Shares thereafter available, both for purposes of the Plan and for sale under
the Option, by the number of Shares as to which the Option is exercised. 
 (ii) Termination of Relationship as a Service Provider.
If a Participant ceases to be a Service Provider, other than upon the Participant’s termination as the result of the Participant’s death or Disability, the Participant may exercise his or her Option within such period of time as is
specified in the Award Agreement to the extent that the Option is vested on the date of termination (but in no event later than the expiration of the term of such Option as set forth in the Award Agreement). In the absence of a specified time in the
Award Agreement, the Option will remain exercisable for three (3) months following the Participant’s termination. Unless otherwise provided by the Administrator, if on the date of termination the Participant is not vested as to his or her
entire Option, the Shares covered by the unvested portion of the Option will revert to the Plan. If after termination the Participant does not exercise his or her Option within the time specified by the Administrator, the Option will terminate, and
the Shares covered by such Option will revert to the Plan. 
 (iii) Disability of Participant. If a Participant ceases to be a
Service Provider as a result of the Participant’s Disability, the Participant may exercise his or her Option within such period of time as is specified in the Award Agreement to the extent the Option is vested on the date of termination (but in
no event later than the expiration of the term of such Option as set forth in the Award Agreement). In the absence of a specified time in the Award Agreement, the Option will remain exercisable for twelve (12) months following the
Participant’s termination. Unless otherwise provided by the Administrator, if on the date of termination the Participant is not vested as to his or her entire Option, the Shares covered by the unvested portion of the Option will revert to the
Plan. If after termination the Participant does not exercise his or her Option within the time specified herein, the Option will terminate, and the Shares covered by such Option will revert to the Plan. 

  
 -10- 

 (iv) Death of Participant. If a Participant dies while a Service Provider, the
Option may be exercised following the Participant’s death within such period of time as is specified in the Award Agreement to the extent that the Option is vested on the date of death (but in no event may the option be exercised later than the
expiration of the term of such Option as set forth in the Award Agreement), by the Participant’s designated beneficiary, provided such beneficiary has been designated prior to Participant’s death in a form acceptable to the Administrator.
If no such beneficiary has been designated by the Participant, then such Option may be exercised by the personal representative of the Participant’s estate or by the person(s) to whom the Option is transferred pursuant to the
Participant’s will or in accordance with the laws of descent and distribution. In the absence of a specified time in the Award Agreement, the Option will remain exercisable for twelve (12) months following Participant’s death. Unless
otherwise provided by the Administrator, if at the time of death Participant is not vested as to his or her entire Option, the Shares covered by the unvested portion of the Option will immediately revert to the Plan. If the Option is not so
exercised within the time specified herein, the Option will terminate, and the Shares covered by such Option will revert to the Plan. 
 (v)
Tolling Expiration. A Participant’s Award Agreement may also provide that: 
 (1) if the exercise of the Option following the
termination of Participant’s status as a Service Provider (other than upon the Participant’s death or Disability) would result in liability under Section 16(b), then the Option will terminate on the earlier of (A) the expiration
of the term of the Option set forth in the Award Agreement, or (B) the tenth (10th) day after the last date on which such exercise would result in liability under Section 16(b); or 

(2) if the exercise of the Option following the termination of the Participant’s status as a Service Provider (other than upon the
Participant’s death or Disability) would be prohibited at any time solely because the issuance of Shares would violate the registration requirements under the Securities Act, then the Option will terminate on the earlier of (A) the
expiration of the term of the Option or (B) the expiration of a period of thirty (30)-day period after the termination of the Participant’s status as a Service Provider during which the exercise of
the Option would not be in violation of such registration requirements. 
 7. Restricted Stock. 

(a) Grant of Restricted Stock. Subject to the terms and provisions of the Plan, the Administrator, at any time and from time to time,
may grant Shares of Restricted Stock to Service Providers in such amounts as the Administrator, in its sole discretion, will determine. 

(b) Restricted Stock Agreement. Each Award of Restricted Stock will be evidenced by an Award Agreement that will specify the Period of
Restriction, the number of Shares granted, and such other terms and conditions as the Administrator, in its sole discretion, will determine. Unless the Administrator determines otherwise, the Company as escrow agent will hold Shares of Restricted
Stock until the restrictions on such Shares have lapsed. 
 (c) Transferability. Except as provided in this Section 7 or the
Award Agreement, Shares of Restricted Stock may not be sold, transferred, pledged, assigned, or otherwise alienated or hypothecated until the end of the applicable Period of Restriction. 

  
 -11- 

 (d) Other Restrictions. The Administrator, in its sole discretion, may impose such
other restrictions on Shares of Restricted Stock as it may deem advisable or appropriate. 
 (e) Removal of Restrictions. Except as
otherwise provided in this Section 7, Shares of Restricted Stock covered by each Restricted Stock grant made under the Plan will be released from escrow as soon as practicable after the last day of the Period of Restriction or at such other
time as the Administrator may determine. The Administrator, in its discretion, may accelerate the time at which any restrictions will lapse or be removed. 

(f) Voting Rights. During the Period of Restriction, Service Providers holding Shares of Restricted Stock granted hereunder may exercise
full voting rights with respect to those Shares, unless the Administrator determines otherwise. 
 (g) Dividends and Other
Distributions. During the Period of Restriction, Service Providers holding Shares of Restricted Stock will be entitled to receive all dividends and other distributions paid with respect to such Shares, unless the Administrator provides
otherwise. If any such dividends or distributions are paid in Shares, the Shares will be subject to the same restrictions on transferability and forfeitability as the Shares of Restricted Stock with respect to which they were paid. 

(h) Return of Restricted Stock to Company. On the date set forth in the Award Agreement, the Restricted Stock for which restrictions
have not lapsed will revert to the Company and again will become available for grant under the Plan. 
 8. Restricted Stock Units.

 (a) Grant. Restricted Stock Units may be granted at any time and from time to time as determined by the Administrator. After the
Administrator determines that it will grant Restricted Stock Units under the Plan, it will advise the Participant in an Award Agreement of the terms, conditions, and restrictions related to the grant, including the number of Restricted Stock Units.

 (b) Vesting Criteria and Other Terms. The Administrator will set vesting criteria in its discretion, which, depending on the extent
to which the criteria are met, will determine the number of Restricted Stock Units that will be paid out to the Participant. The Administrator may set vesting criteria based upon the achievement of Company-wide, divisional, business unit, or
individual goals (including, but not limited to, continued employment or service), applicable federal or state securities laws or any other basis determined by the Administrator in its discretion. 

(c) Earning Restricted Stock Units. Upon meeting the applicable vesting criteria, the Participant will be entitled to receive a payout
as determined by the Administrator. Notwithstanding the foregoing, at any time after the grant of Restricted Stock Units, the Administrator, in its sole discretion, may reduce or waive any vesting criteria that must be met to receive a payout. 

(d) Form and Timing of Payment. Payment of earned Restricted Stock Units will be made as soon as practicable after the
date(s) determined by the Administrator and set forth in the Award Agreement. The Administrator, in its sole discretion, may only settle earned Restricted Stock Units in cash, Shares, or a combination of both. 

  
 -12- 

 (e) Cancellation. On the date set forth in the Award Agreement, all unearned
Restricted Stock Units will be forfeited to the Company. 
 9. Stock Appreciation Rights. 

(a) Grant of Stock Appreciation Rights. Subject to the terms and conditions of the Plan, a Stock Appreciation Right may be granted to
Service Providers at any time and from time to time as will be determined by the Administrator, in its sole discretion. 
 (b) Number of
Shares. The Administrator will have complete discretion to determine the number of Stock Appreciation Rights granted to any Service Provider. 

(c) Exercise Price and Other Terms. The per share exercise price for the Shares to be issued pursuant to exercise of a Stock
Appreciation Right will be determined by the Administrator and will be no less than one hundred percent (100%) of the Fair Market Value per Share on the date of grant. Otherwise, the Administrator, subject to the provisions of the Plan, will have
complete discretion to determine the terms and conditions of Stock Appreciation Rights granted under the Plan. 
 (d) Stock Appreciation
Right Agreement. Each Stock Appreciation Right grant will be evidenced by an Award Agreement that will specify the exercise price, the term of the Stock Appreciation Right, the conditions of exercise, and such other terms and conditions as the
Administrator, in its sole discretion, will determine. 
 (e) Expiration of Stock Appreciation Rights. A Stock Appreciation Right
granted under the Plan will expire ten (10) years from the date of grant or such shorter term as may be provided in the Award Agreement, as determined by the Administrator, in its sole discretion. Notwithstanding the foregoing, the rules of
Section 6(d) relating to exercise also will apply to Stock Appreciation Rights. 
 (f) Payment of Stock Appreciation Right
Amount. Upon exercise of a Stock Appreciation Right, a Participant will be entitled to receive payment from the Company in an amount determined by multiplying: 

(i) The difference between the Fair Market Value of a Share on the date of exercise over the exercise price; times 

(ii) The number of Shares with respect to which the Stock Appreciation Right is exercised. 

At the discretion of the Administrator, the payment upon Stock Appreciation Right exercise may be in cash, in Shares of equivalent value, or
in some combination thereof. 
 10. Performance Units and Performance Shares. 

(a) Grant of Performance Units/Shares. Performance Units and Performance Shares may be granted to Service Providers at any time and from
time to time, as will be determined by the Administrator, in its sole discretion. The Administrator will have complete discretion in determining the number of Performance Units and Performance Shares granted to each Participant. 

  
 -13- 

 (b) Value of Performance Units/Shares. Each Performance Unit will have an initial
value that is established by the Administrator on or before the date of grant. Each Performance Share will have an initial value equal to the Fair Market Value of a Share on the date of grant. 

(c) Performance Objectives and Other Terms. The Administrator will set performance objectives or other vesting provisions (including,
without limitation, continued status as a Service Provider) in its discretion which, depending on the extent to which they are met, will determine the number or value of Performance Units/Shares that will be paid out to the Service Providers.
The time period during which the performance objectives or other vesting provisions must be met will be called the “Performance Period.” Each Award of Performance Units/Shares will be evidenced by an Award Agreement that will specify the
Performance Period, and such other terms and conditions as the Administrator, in its sole discretion, will determine. The Administrator may set performance objectives based upon the achievement of Company-wide, divisional, business unit or
individual goals (including, but not limited to, continued employment or service), applicable federal or state securities laws, or any other basis determined by the Administrator in its discretion. 

(d) Earning of Performance Units/Shares. After the applicable Performance Period has ended, the holder of Performance Units/Shares will
be entitled to receive a payout of the number of Performance Units/Shares earned by the Participant over the Performance Period, to be determined as a function of the extent to which the corresponding performance objectives or other vesting
provisions have been achieved. After the grant of a Performance Unit/Share, the Administrator, in its sole discretion, may reduce or waive any performance objectives or other vesting provisions for such Performance Unit/Share. 

(e) Form and Timing of Payment of Performance Units/Shares. Payment of earned Performance Units/Shares will be made as soon as
practicable after the expiration of the applicable Performance Period. The Administrator, in its sole discretion, may pay earned Performance Units/Shares in the form of cash, in Shares (which have an aggregate Fair Market Value equal to the value of
the earned Performance Units/Shares at the close of the applicable Performance Period) or in a combination thereof. 
 (f)
Cancellation of Performance Units/Shares. On the date set forth in the Award Agreement, all unearned or unvested Performance Units/Shares will be forfeited to the Company, and again will be available for grant under the Plan. 

11. Outside Director Limitations. No Outside Director may be paid, issued or granted, in any Fiscal Year, cash compensation and equity
awards (including any Awards issued under this Plan) with an aggregate value greater than $750,000, increased to $1,000,000 in the Fiscal Year of his or her initial service as an Outside Director (with the value of each equity award based on its
grant date fair value (determined in accordance with U.S. generally accepted accounting principles)). Any cash compensation paid or Awards granted to an individual for his or her services as an Employee, or for his or her services as a Consultant
(other than as an Outside Director), will not count for purposes of the limitation under this Section 11. 

  
 -14- 

 12. Leaves of Absence/Transfer Between Locations. Unless the Administrator provides
otherwise, vesting of Awards granted hereunder will be suspended during any unpaid leave of absence. A Participant will not cease to be an Employee in the case of (i) any leave of absence approved by the Company or (ii) transfers between
locations of the Company or between the Company, its Parent, or any Subsidiary. For purposes of Incentive Stock Options, no such leave may exceed three (3) months, unless reemployment upon expiration of such leave is guaranteed by statute or
contract. If reemployment upon expiration of a leave of absence approved by the Company is not so guaranteed, then six (6) months following the first (1st) day of such leave any Incentive Stock Option held by the Participant will cease to
be treated as an Incentive Stock Option and will be treated for tax purposes as a Nonstatutory Stock Option. 
 13. Transferability of
Awards. Unless determined otherwise by the Administrator, an Award may not be sold, pledged, assigned, hypothecated, transferred, or disposed of in any manner other than by will or by the laws of descent or distribution and may be exercised,
during the lifetime of the Participant, only by the Participant. If the Administrator makes an Award transferable, such Award will contain such additional terms and conditions as the Administrator deems appropriate. 

14. Adjustments; Dissolution or Liquidation; Merger or Change in Control. 

(a) Adjustments. In the event that any dividend or other distribution (whether in the form of cash, Shares, other securities, or other
property), recapitalization, stock split, reverse stock split, reorganization, merger, consolidation, split-up, spin-off, combination, repurchase, or exchange of Shares
or other securities of the Company, or other change in the corporate structure of the Company affecting the Shares occurs, the Administrator, in order to prevent diminution or enlargement of the benefits or potential benefits intended to be made
available under the Plan, will adjust the number and class of Shares that may be delivered under the Plan and/or the number, class, and price of Shares covered by each outstanding Award, and the numerical Share limits in Section 3 of the Plan.

 (b) Dissolution or Liquidation. In the event of the proposed dissolution or liquidation of the Company, the Administrator will
notify each Participant as soon as practicable prior to the effective date of such proposed transaction. To the extent it has not been previously exercised, an Award will terminate immediately prior to the consummation of such proposed action. 

(c) Change in Control. In the event of a merger of the Company with or into another corporation or other entity or a Change in Control,
each outstanding Award will be treated as the Administrator determines subject to the restriction in the following paragraph, including, without limitation, that each Award be assumed or an equivalent option or right substituted by the successor
corporation or a Parent or Subsidiary of the successor corporation. The Administrator will not be required to treat all Awards or Participants similarly in the transaction. 

In the event that the successor corporation does not assume or substitute for the Award, the Participant will fully vest in and have the right
to exercise all of his or her outstanding Options and Stock Appreciation Rights, including Shares as to which such Awards would not otherwise be vested or exercisable, all restrictions on Restricted Stock and Restricted Stock Units will lapse, and,
with respect to Awards with performance-based vesting, unless specifically provided otherwise under the applicable Award Agreement, a Company policy applicable to the Participant, or other written agreement between the Participant and the Company,
all performance goals or other vesting criteria 

  
 -15- 

 
will be deemed achieved at one hundred percent (100%) of target levels and all other terms and conditions met. In addition, if an Option or Stock Appreciation Right is not assumed or
substituted in the event of a Change in Control, the Administrator will notify the Participant in writing or electronically that the Option or Stock Appreciation Right will be exercisable for a period of time determined by the Administrator in its
sole discretion, and the Option or Stock Appreciation Right will terminate upon the expiration of such period. 
 For the purposes of this
subsection (c), an Award will be considered assumed if, following the Change in Control, the Award confers the right to purchase or receive, for each Share subject to the Award immediately prior to the Change in Control, the consideration (whether
stock, cash, or other securities or property) received in the Change in Control by holders of Common Stock for each Share held on the effective date of the transaction (and if holders were offered a choice of consideration, the type of
consideration chosen by the holders of a majority of the outstanding Shares); provided, however, that if such consideration received in the Change in Control is not solely common stock of the successor corporation or its Parent, the Administrator
may, with the consent of the successor corporation, provide for the consideration to be received upon the exercise of an Option or Stock Appreciation Right or upon the payout of a Restricted Stock Unit, Performance Unit or Performance Share, for
each Share subject to such Award, to be solely common stock of the successor corporation or its Parent equal in fair market value to the per share consideration received by holders of Common Stock in the Change in Control. 

Notwithstanding anything in this Section 14(c) to the contrary, an Award that vests, is earned or
paid-out upon the satisfaction of one or more performance goals will not be considered assumed if the Company or its successor modifies any of such performance goals without the Participant’s consent;
provided, however, a modification to such performance goals only to reflect the successor corporation’s post-Change in Control corporate structure will not be deemed to invalidate an otherwise valid Award assumption. 

(d) Outside Director Awards. With respect to Awards granted to an Outside Director, in the event of a Change in Control, the Participant
will fully vest in and have the right to exercise Options and/or Stock Appreciation Rights as to all of the Shares underlying such Award, including those Shares which would not otherwise be vested or exercisable, all restrictions on Restricted Stock
and Restricted Stock Units will lapse, and, with respect to Awards with performance-based vesting, unless specifically provided otherwise under the applicable Award Agreement, a Company policy applicable to the Participant, or other written
agreement between the Participant and the Company, all performance goals or other vesting criteria will be deemed achieved at one hundred percent (100%) of target levels and all other terms and conditions met. 

  
 -16- 

 15. Tax. 

(a) Withholding Requirements. Prior to the delivery of any Shares or cash pursuant to an Award (or exercise thereof) or such
earlier time as any tax withholding obligations are due, the Company will have the power and the right to deduct or withhold, or require a Participant to remit to the Company, an amount sufficient to satisfy U.S. federal, state, or local taxes, non-U.S. taxes, or other taxes (including the Participant’s FICA obligation) required to be withheld with respect to such Award (or exercise thereof). 

(b) Withholding Arrangements. The Administrator, in its sole discretion and pursuant to such procedures as it may specify from time to
time, may permit a Participant to satisfy such tax withholding obligation, in whole or in part by (without limitation) (i) paying cash, (ii) electing to have the Company withhold otherwise deliverable cash or Shares having a fair
market value not in excess of the maximum statutory amount required to be withheld, or (iii) delivering to the Company already-owned Shares having a fair market value not in excess of the maximum statutory amount required to be withheld. The
fair market value of the Shares to be withheld or delivered will be determined as of the date that the taxes are required to be withheld. 

(c) Compliance With Section 409A. Awards will be designed and operated in such a manner that they are either exempt
from the application of, or comply with, the requirements of Section 409A such that the grant, payment, settlement or deferral will not be subject to the additional tax or interest applicable under Section 409A, except as otherwise
determined in the sole discretion of the Administrator. The Plan and each Award Agreement under the Plan is intended to meet the requirements of Section 409A and will be construed and interpreted in accordance with such intent, except as
otherwise determined in the sole discretion of the Administrator. To the extent that an Award or payment, or the settlement or deferral thereof, is subject to Section 409A the Award will be granted, paid, settled or deferred in a manner that
will meet the requirements of Section 409A, such that the grant, payment, settlement or deferral will not be subject to the additional tax or interest applicable under Section 409A. In no event will the Company (or any Parent or Subsidiary
of the Company, as applicable) reimburse a Participant for any taxes imposed or other costs incurred as a result of Section 409A. 
 16.
No Effect on Employment or Service. Neither the Plan nor any Award will confer upon a Participant any right with respect to continuing the Participant’s relationship as a Service Provider, nor will they interfere in any way with the
Participant’s right or the right of the Company (or any Parent or Subsidiary of the Company) to terminate such relationship at any time, with or without cause, to the extent permitted by Applicable Laws. 

17. Date of Grant. The date of grant of an Award will be, for all purposes, the date on which the Administrator makes the determination
granting such Award, or such other later date as is determined by the Administrator. Notice of the determination will be provided to each Participant within a reasonable time after the date of such grant. 

18. Term of Plan. Subject to Section 23 of the Plan, the Plan will become effective upon the later to occur of (i) its
adoption by the Board or (ii) the business day immediately prior to the Registration Date. It will continue in effect for a term of ten (10) years from the date adopted by the Board, unless terminated earlier under Section 19
of the Plan. 

  
 -17- 

 19. Amendment and Termination of the Plan. 

(a) Amendment and Termination. The Administrator may at any time amend, alter, suspend or terminate the Plan. 

(b) Stockholder Approval. The Company will obtain stockholder approval of any Plan amendment to the extent necessary and desirable to
comply with Applicable Laws. 
 (c) Effect of Amendment or Termination. No amendment, alteration, suspension or termination of the
Plan will materially impair the rights of any Participant, unless mutually agreed otherwise between the Participant and the Administrator, which agreement must be in writing and signed by the Participant and the Company. Termination of the Plan will
not affect the Administrator’s ability to exercise the powers granted to it hereunder with respect to Awards granted under the Plan prior to the date of such termination. 

20. Conditions Upon Issuance of Shares. 

(a) Legal Compliance. Shares will not be issued pursuant to an Award unless the exercise of such Award and the issuance and delivery of
such Shares will comply with Applicable Laws and will be further subject to the approval of counsel for the Company with respect to such compliance. 

(b) Investment Representations. As a condition to the exercise of an Award, the Company may require the person exercising such Award to
represent and warrant at the time of any such exercise that the Shares are being purchased only for investment and without any present intention to sell or distribute such Shares if, in the opinion of counsel for the Company, such a representation
is required. 
 21. Inability to Obtain Authority. The inability of the Company to obtain authority from any regulatory body having
jurisdiction or to complete or comply with the requirements of any registration or other qualification of the Shares under any U.S. federal or state law, any non-U.S. law, or the rules and regulations of the
Securities and Exchange Commission, the stock exchange on which Shares of the same class are then listed, or any other governmental or regulatory body, which authority, registration, qualification or rule compliance is deemed by the Company’s
counsel to be necessary or advisable for the issuance and sale of any Shares hereunder, will relieve the Company of any liability in respect of the failure to issue or sell such Shares as to which such requisite authority, registration,
qualification or rule compliance will not have been obtained. 
 22. Clawback. The Administrator may specify in an Award Agreement
that the Participant’s rights, payments, and/or benefits with respect to an Award will be subject to reduction, cancellation, forfeiture, and/or recoupment upon the occurrence of certain specified events, in addition to any applicable vesting,
performance or other conditions and restrictions of an Award. Notwithstanding any provisions to the contrary under this Plan, an Award granted under the Plan shall be subject to the Company’s clawback policy (if any) as may be established
and/or amended from time to time. The Board may require a Participant to forfeit or return to and/or reimburse the Company 

  
 -18- 

 
all or a portion of the Award and/or Shares issued under the Award, any amounts paid under the Award, and any payments or proceeds paid or provided upon disposition of the Shares issued under the
Award, pursuant to the terms of such Company policy or as necessary or appropriate to comply with Applicable Laws. 
 23. Stockholder
Approval. The Plan will be subject to approval by the stockholders of the Company within twelve (12) months after the date the Plan is adopted by the Board. Such stockholder approval will be obtained in the manner and to the degree required
under Applicable Laws. 

  
 -19- 

 ALECTOR, INC. 

2019 EQUITY INCENTIVE PLAN 

STOCK OPTION AGREEMENT 

Unless otherwise defined herein, the terms defined in the Alector, Inc. 2019 Equity Incentive Plan (the “Plan”) will have the
same defined meanings in this Stock Option Agreement, which includes the Notice of Stock Option Grant (the “Notice of Grant”), the Terms and Conditions of Stock Option Grant attached hereto as Exhibit A, the Exercise Notice attached
hereto as Exhibit B, and all other exhibits and appendices attached hereto (all together, the “Option Agreement”). 
 NOTICE OF STOCK
OPTION GRANT 
 Participant: 

Address: 
 The
undersigned Participant has been granted an Option to purchase Common Stock of Alector, Inc. (the “Company”), subject to the terms and conditions of the Plan and this Option Agreement, as follows: 

 

							
	        	 	Grant Number:	  	  
	  	        
				
		 	Date of Grant:	  	  
	  	
				
		 	Vesting Commencement Date:	  	  
	  	
				
		 	Number of Shares Granted:	  	  
	  	
				
		 	Exercise Price per Share (in U.S. Dollars): 	  	 $
	  	
				
		 	Total Exercise Price(in U.S. Dollars): 	  	 $
	  	
				
		 	Type of Option:	  	         Incentive Stock Option	  	
				
		 		  	         Nonstatutory Stock Option	  	
				
		 	Term/Expiration Date:	  	  
	  	
				
		 	Vesting Schedule:	  		  	

 Subject to accelerated vesting as set forth below or in the Plan, this Option will be exercisable, in whole or
in part, in accordance with the following schedule: 
 [Twenty-five percent (25%) of the Shares subject to the Option shall vest on the one
(1) year anniversary of the Vesting Commencement Date, and one forty-eighth (1/48th) of the Shares subject to the Option shall vest each month thereafter on the same day of the month as the
Vesting Commencement Date (and if there is no corresponding day, on the last day of the month), subject to Participant continuing to be a Service Provider through each such date.]  

 Termination Period: 

This Option will be exercisable for [three (3) months] after Participant ceases to be a Service Provider, unless such termination is due
to Participant’s death or Disability, in which case this Option will be exercisable for [twelve (12) months] after Participant ceases to be a Service Provider. Notwithstanding the foregoing sentence, in no event may this Option be
exercised after the Term/Expiration Date as provided above and this Option may be subject to earlier termination as provided in Section 14 of the Plan. 

By Participant’s signature and the signature of the representative of the Company below, Participant and the Company agree that this
Option is granted under and governed by the terms and conditions of the Plan and this Option Agreement, including the Terms and Conditions of Stock Option Grant, attached hereto as Exhibit A, all of which are made a part of this document.
Participant acknowledges receipt of a copy of the Plan. Participant has reviewed the Plan and this Option Agreement in their entirety, has had an opportunity to obtain the advice of counsel prior to executing this Option Agreement, and fully
understands all provisions of the Plan and this Option Agreement. Participant hereby agrees to accept as binding, conclusive, and final all decisions or interpretations of the Administrator upon any questions relating to the Plan and the Option
Agreement. Participant further agrees to notify the Company upon any change in the residence address indicated below. 
  

					
	PARTICIPANT	  	        	  	ALECTOR, INC.
			
	  
 Signature
	  		  	  
 Signature

			
	  
 Print Name
	  		  	  
 Print Name

			
		  		  	  
 Title

			
	Address:	  		  	
			
	  
	  		  	
			
	  
	  		  	

  
 - 2 - 

 EXHIBIT A 

TERMS AND CONDITIONS OF STOCK OPTION GRANT 

1. Grant of Option. 
 (a)
The Company hereby grants to the individual (“Participant”) named in the Notice of Stock Option Grant of this Option Agreement (the “Notice of Grant”) an option (the “Option”) to purchase the number of Shares set forth
in the Notice of Grant, at the exercise price per Share set forth in the Notice of Grant (the “Exercise Price”), subject to all of the terms and conditions in this Option Agreement and the Plan, which is incorporated herein by this
reference. Subject to Section 19(c) of the Plan, in the event of a conflict between the terms and conditions of the Plan and the terms and conditions of this Option Agreement, the terms and conditions of the Plan will prevail. 

(b) For U.S. taxpayers, the Option will be designated as either an Incentive Stock Option (“ISO”) or a Nonstatutory Stock Option
(“NSO”). If designated in the Notice of Grant as an ISO, this Option is intended to qualify as an ISO under Section 422 of the Internal Revenue Code of 1986, as amended (the “Code”). However, if this Option is intended to be
an ISO, to the extent that it exceeds the $100,000 rule of Code Section 422(d) it will be treated as an NSO. Further, if for any reason this Option (or portion thereof) will not qualify as an ISO, then, to the extent of such nonqualification,
such Option (or portion thereof) shall be regarded as a NSO granted under the Plan. In no event will the Administrator, the Company or any Parent or Subsidiary or any of their respective employees or directors have any liability to Participant (or
any other person) due to the failure of the Option to qualify for any reason as an ISO. 
 (c) For
non-U.S. taxpayers, the Option will be designated as an NSO. 
 2. Vesting Schedule. Except as
provided in Section 3, the Option awarded by this Option Agreement will vest in accordance with the vesting provisions set forth in the Notice of Grant. Shares subject to this Option that are scheduled to vest on a certain date or upon the
occurrence of a certain condition will not vest in accordance with any of the provisions of this Option Agreement, unless Participant will have been continuously a Service Provider from the Date of Grant until the date such vesting occurs. 

3. Administrator Discretion. The Administrator, in its discretion, may accelerate the vesting of the balance, or some lesser portion of
the balance, of the unvested Option at any time, subject to the terms of the Plan. If so accelerated, such Option will be considered as having vested as of the date specified by the Administrator. 

4. Exercise of Option. 

(a) Right to Exercise. This Option may be exercised only within the term set out in the Notice of Grant, and may be exercised during
such term only in accordance with the Plan and the terms of this Option Agreement. 

 (b) Method of Exercise. This Option is exercisable by delivery of an exercise notice
(the “Exercise Notice”) in the form attached as Exhibit B to the Notice of Grant or in a manner and pursuant to such procedures as the Administrator may determine, which will state the election to exercise the Option, the number of
Shares in respect of which the Option is being exercised (the “Exercised Shares”), and such other representations and agreements as may be required by the Company pursuant to the provisions of the Plan. The Exercise Notice will be
completed by Participant and delivered to the Company. The Exercise Notice will be accompanied by payment of the aggregate Exercise Price as to all Exercised Shares and of any Tax Obligations (as defined in Section 6(a)). This Option will be
deemed to be exercised upon receipt by the Company of such fully executed Exercise Notice accompanied by the aggregate Exercise Price. 
 5.
Method of Payment. Payment of the aggregate Exercise Price will be by any of the following, or a combination thereof, at the election of Participant: 

(a) cash in U.S. dollars; 
 (b)
check designated in U.S. dollars; 
 (c) consideration received by the Company under a formal cashless exercise program adopted by the
Company in connection with the Plan; or 
 (d) if Participant is a U.S. employee, surrender of other Shares which have a Fair Market Value on
the date of surrender equal to the aggregate Exercise Price of the Exercised Shares and that are owned free and clear of any liens, claims, encumbrances, or security interests, provided that accepting such Shares, in the sole discretion of the
Administrator, will not result in any adverse accounting consequences to the Company. 
 6. Tax Obligations. 

(a) Responsibility for Taxes. Participant acknowledges that, regardless of any action taken by the Company or, if different,
Participant’s employer (the “Employer”) or Parent or Subsidiary to which Participant is providing services (together, the Company, Employer and/or Parent or Subsidiary to which the Participant is providing services, the “Service
Recipient”), the ultimate liability for any tax and/or social insurance liability obligations and requirements in connection with the Option, including, without limitation, (i) all federal, state, and local taxes (including the
Participant’s Federal Insurance Contributions Act (FICA) obligation) that are required to be withheld by the Company or the Service Recipient or other payment of tax-related items related to
Participant’s participation in the Plan and legally applicable to Participant, (ii) the Participant’s and, to the extent required by the Company (or Service Recipient), the Company’s (or Service Recipient’s) fringe benefit
tax liability, if any, associated with the grant, vesting, or exercise of the Option or sale of Shares, and (iii) any other Company (or Service Recipient) taxes the responsibility for which the Participant has, or has agreed to bear, with
respect to the Option (or exercise thereof or issuance of Shares thereunder) (collectively, the “Tax Obligations”), is and remains Participant’s responsibility and may exceed the amount actually withheld by the Company or the Service
Recipient. Participant further acknowledges that the Company and/or the Service Recipient (A) make no representations or undertakings regarding the treatment of any Tax Obligations in connection with any aspect of the

  
 - 2 - 

 
Option, including, but not limited to, the grant, vesting or exercise of the Option, the subsequent sale of Shares acquired pursuant to such exercise and the receipt of any dividends or other
distributions, and (B) do not commit to and are under no obligation to structure the terms of the grant or any aspect of the Option to reduce or eliminate Participant’s liability for Tax Obligations or achieve any particular tax result.
Further, if Participant is subject to Tax Obligations in more than one jurisdiction between the Date of Grant and the date of any relevant taxable or tax withholding event, as applicable, Participant acknowledges that the Company and/or the Service
Recipient (or former employer, as applicable) may be required to withhold or account for Tax Obligations in more than one jurisdiction. If Participant fails to make satisfactory arrangements for the payment of any required Tax Obligations hereunder
at the time of the applicable taxable event, Participant acknowledges and agrees that the Company may refuse to issue or deliver the Shares. 

(b) Tax Withholding. When the Option is exercised, Participant generally will recognize immediate U.S. taxable income if Participant is
a U.S. taxpayer. If Participant is a non-U.S. taxpayer, Participant will be subject to applicable taxes in his or her jurisdiction. Pursuant to such procedures as the Administrator may specify from time to
time, the Company and/or Service Recipient shall withhold the amount required to be withheld for the payment of Tax Obligations. The Administrator, in its sole discretion and pursuant to such procedures as it may specify from time to time, may
permit Participant to satisfy such Tax Obligations, in whole or in part (without limitation), if permissible by applicable local law, by (i) paying cash, (ii) electing to have the Company withhold otherwise deliverable Shares having a fair
market value equal to the minimum amount that is necessary to meet the withholding requirement for such Tax Obligations (or such greater amount as Participant may elect if permitted by the Administrator, if such greater amount would not result in
adverse financial accounting consequences), (iii) withholding the amount of such Tax Obligations from Participant’s wages or other cash compensation paid to Participant by the Company and/or the Service Recipient, (iv) delivering to the
Company already vested and owned Shares having a fair market value equal to such Tax Obligations, or (v) selling a sufficient number of such Shares otherwise deliverable to Participant through such means as the Company may determine in its sole
discretion (whether through a broker or otherwise) equal to the minimum amount that is necessary to meet the withholding requirement for such Tax Obligations (or such greater amount as Participant may elect if permitted by the Administrator, if such
greater amount would not result in adverse financial accounting consequences). To the extent determined appropriate by the Company in its discretion, it will have the right (but not the obligation) to satisfy any Tax Obligations by reducing the
number of Shares otherwise deliverable to Participant. Further, if Participant is subject to tax in more than one jurisdiction between the Date of Grant and a date of any relevant taxable or tax withholding event, as applicable, Participant
acknowledges and agrees that the Company and/or the Service Recipient (and/or former employer, as applicable) may be required to withhold or account for tax in more than one jurisdiction. If Participant fails to make satisfactory arrangements for
the payment of any required Tax Obligations hereunder at the time of the Option exercise, Participant acknowledges and agrees that the Company may refuse to honor the exercise and refuse to deliver the Shares if such amounts are not delivered at the
time of exercise. 
 (c) Notice of Disqualifying Disposition of ISO Shares. If the Option granted to Participant herein is an ISO, and
if Participant sells or otherwise disposes of any of the Shares acquired pursuant to the ISO on or before the later of (i) the date two (2) years after the Date of Grant, or (ii) the date one (1) year after the date of exercise,
Participant will immediately notify the Company in writing of such disposition. Participant agrees that Participant may be subject to income tax withholding by the Company on the compensation income recognized by Participant. 

  
 - 3 - 

 (d) Code Section 409A. Under Code Section 409A, a stock right
(such as the Option) that vests after December 31, 2004 (or that vested on or prior to such date but which was materially modified after October 3, 2004) that was granted with a per share exercise price that is determined by the Internal
Revenue Service (the “IRS”) to be less than the fair market value of an underlying share on the date of grant (a “discount option”) may be considered “deferred compensation.” A stock right that is a “discount
option” may result in (i) income recognition by the recipient of the stock right prior to the exercise of the stock right, (ii) an additional twenty percent (20%) federal income tax, and (iii) potential penalty and interest
charges. The “discount option” may also result in additional state income, penalty and interest tax to the recipient of the stock right. Participant acknowledges that the Company cannot and has not guaranteed that the IRS will agree that
the per Share exercise price of this Option equals or exceeds the fair market value of a Share on the date of grant in a later examination. Participant agrees that if the IRS determines that the Option was granted with a per Share exercise price
that was less than the fair market value of a Share on the date of grant, Participant shall be solely responsible for Participant’s costs related to such a determination. 

7. Rights as Stockholder. Neither Participant nor any person claiming under or through Participant will have any of the rights or
privileges of a stockholder of the Company in respect of any Shares deliverable hereunder unless and until certificates representing such Shares (which may be in book entry form) will have been issued, recorded on the records of the Company or its
transfer agents or registrars, and delivered to Participant (including through electronic delivery to a brokerage account). After such issuance, recordation, and delivery, Participant will have all the rights of a stockholder of the Company with
respect to voting such Shares and receipt of dividends and distributions on such Shares. 
 8. No Guarantee of Continued Service.
PARTICIPANT ACKNOWLEDGES AND AGREES THAT THE VESTING OF SHARES PURSUANT TO THE VESTING SCHEDULE HEREOF IS EARNED ONLY BY CONTINUING AS A SERVICE PROVIDER, WHICH UNLESS PROVIDED OTHERWISE UNDER APPLICABLE LAW IS AT THE WILL OF THE COMPANY (OR THE
SERVICE RECIPIENT) AND NOT THROUGH THE ACT OF BEING HIRED, BEING GRANTED THIS OPTION OR ACQUIRING SHARES HEREUNDER. PARTICIPANT FURTHER ACKNOWLEDGES AND AGREES THAT THIS OPTION AGREEMENT, THE TRANSACTIONS CONTEMPLATED HEREUNDER AND THE VESTING
SCHEDULE SET FORTH HEREIN DO NOT CONSTITUTE AN EXPRESS OR IMPLIED PROMISE OF CONTINUED ENGAGEMENT AS A SERVICE PROVIDER FOR THE VESTING PERIOD, FOR ANY PERIOD, OR AT ALL, AND WILL NOT INTERFERE IN ANY WAY WITH PARTICIPANT’S RIGHT OR THE RIGHT
OF THE COMPANY (OR THE SERVICE RECIPIENT) TO TERMINATE PARTICIPANT’S RELATIONSHIP AS A SERVICE PROVIDER, SUBJECT TO APPLICABLE LAW, WHICH TERMINATION, UNLESS PROVIDED OTHERWISE UNDER APPLICABLE LAW, MAY BE AT ANY TIME, WITH OR WITHOUT CAUSE.

 9. Nature of Grant. In accepting the Option, Participant acknowledges, understands and agrees that: 

  
 - 4 - 

 (a) the grant of the Option is voluntary and occasional and does not create any contractual
or other right to receive future grants of options, or benefits in lieu of options, even if options have been granted in the past; 
 (b) all
decisions with respect to future option or other grants, if any, will be at the sole discretion of the Company; 
 (c) Participant is
voluntarily participating in the Plan; 
 (d) the Option and any Shares acquired under the Plan are not intended to replace any pension
rights or compensation; 
 (e) the Option and Shares acquired under the Plan and the income and value of same, are not part of normal or
expected compensation for purposes of calculating any severance, resignation, termination, redundancy, dismissal, end-of-service payments, bonuses, long-service awards,
pension or retirement or welfare benefits or similar payments; 
 (f) the future value of the Shares underlying the Option is unknown,
indeterminable, and cannot be predicted with certainty; 
 (g) if the underlying Shares do not increase in value, the Option will have no
value; 
 (h) if Participant exercises the Option and acquires Shares, the value of such Shares may increase or decrease in value, even below
the Exercise Price; 
 (i) for purposes of the Option, Participant’s engagement as a Service Provider will be considered terminated as
of the date Participant is no longer actively providing services to the Company or any Parent or Subsidiary (regardless of the reason for such termination and whether or not later found to be invalid or in breach of employment laws in the
jurisdiction where Participant is a Service Provider or the terms of Participant’s employment or service agreement, if any), and unless otherwise expressly provided in this Option Agreement (including by reference in the Notice of Grant to
other arrangements or contracts) or determined by the Administrator, (i) Participant’s right to vest in the Option under the Plan, if any, will terminate as of such date and will not be extended by any notice period (e.g.,
Participant’s period of service would not include any contractual notice period or any period of “garden leave” or similar period mandated under employment laws in the jurisdiction where Participant is a Service Provider or
Participant’s employment or service agreement, if any, unless Participant is providing bona fide services during such time); and (ii) the period (if any) during which Participant may exercise the Option after such termination of
Participant’s engagement as a Service Provider will commence on the date Participant ceases to actively provide services and will not be extended by any notice period mandated under employment laws in the jurisdiction where Participant is
employed or terms of Participant’s engagement agreement, if any; the Administrator shall have the exclusive discretion to determine when Participant is no longer actively providing services for purposes of his or her Option grant (including
whether Participant may still be considered to be providing services while on a leave of absence and consistent with local law);  

(j) unless otherwise provided in the Plan or by the Copmpany in its discretion, the Option and the benefits evidenced by this Option Agreement
do not create any entitlement to have the Option or any such benefits transferred to, or assumed by, another company nor to be exchanged, cashed out or substituted for, in connection with any corporate transaction affecting the Shares; and 

  
 - 5 - 

 (k) the following provisions apply only if Participant is providing services outside the
United States: 
 (i) the Option and the Shares subject to the Option are not part of normal or expected compensation or salary for any
purpose; 
 (ii) Participant acknowledges and agrees that no Service Recipient shall be liable for any foreign exchange rate fluctuation
between Participant’s local currency and the United States Dollar that may affect the value of the Option or of any amounts due to Participant pursuant to the exercise of the Option or the subsequent sale of any Shares acquired upon exercise;
and 
 (iii) no claim or entitlement to compensation or damages shall arise from forfeiture of the Option resulting from the termination of
Participant’s engagement as a Service Provider (for any reason whatsoever, whether or not later found to be invalid or in breach of employment laws in the jurisdiction where Participant is a Service Provider or the terms of Participant’s
employment or service agreement, if any), and in consideration of the grant of the Option to which Participant is otherwise not entitled, Participant irrevocably agrees never to institute any claim against any Service Recipient, waives his or her
ability, if any, to bring any such claim, and releases each Service Recipient from any such claim; if, notwithstanding the foregoing, any such claim is allowed by a court of competent jurisdiction, then, by participating in the Plan, Participant
shall be deemed irrevocably to have agreed not to pursue such claim and agrees to execute any and all documents necessary to request dismissal or withdrawal of such claim. 

10. No Advice Regarding Grant. The Company is not providing any tax, legal or financial advice, nor is the Company making any
recommendations regarding Participant’s participation in the Plan, or Participant’s acquisition or sale of the underlying Shares. Participant is hereby advised to consult with his or her own personal tax, legal and financial advisors
regarding his or her participation in the Plan before taking any action related to the Plan. 
 11. Data Privacy.
Participant hereby explicitly and unambiguously consents to the collection, use and transfer, in electronic or other form, of Participant’s personal data as described in this Option Agreement and any other Option grant materials by and
among, as applicable, the Employer or other Service Recipient, the Company and any Parent or Subsidiary for the exclusive purpose of implementing, administering and managing Participant’s participation in the Plan.  

Participant understands that the Company and the Employer may hold certain personal information about Participant, including, but not
limited to, Participant’s name, home address and telephone number, date of birth, social insurance number or other identification number, salary, nationality, job title, any Shares or directorships held in the Company, details of all Options or
any other entitlement to Shares awarded, canceled, exercised, vested, unvested or outstanding in Participant’s favor (“Data”), for the exclusive purpose of implementing, administering and managing the Plan. 

  
 - 6 - 

 Participant understands that Data will be transferred to a stock plan service provider
as may be selected by the Company in the future, which is assisting the Company with the implementation, administration, and management of the Plan. Participant understands that the recipients of the Data may be located in the United States or
elsewhere, and that the recipient’s country of operation (e.g., the United States) may have different data privacy laws and protections than Participant’s country. Participant understands that if he or she resides outside the United
States, he or she may request a list with the names and addresses of any potential recipients of the Data by contacting his or her local People representative. Participant authorizes the Company and any other possible recipients which may assist the
Company (presently or in the future) with implementing, administering and managing the Plan to receive, possess, use, retain and transfer the Data, in electronic or other form, for the sole purposes of implementing, administering and managing
Participant’s participation in the Plan. Participant understands that Data will be held only as long as is necessary to implement, administer and manage Participant’s participation in the Plan. Participant understands that if he or she
resides outside the United States, he or she may, at any time, view Data, request additional information about the storage and processing of Data, require any necessary amendments to Data or refuse or withdraw the consents herein, in any case
without cost, by contacting in writing his or her local People representative. Further, Participant understands that he or she is providing the consents herein on a purely voluntary basis. If Participant does not consent, or if Participant later
seeks to revoke his or her consent, his or her engagement as a Service Provider and career with the Employer will not be adversely affected; the only adverse consequence of refusing or withdrawing Participant’s consent is that the Company would
not be able to grant Participant Options or other equity awards or administer or maintain such awards. Therefore, Participant understands that refusing or withdrawing his or her consent may affect Participant’s ability to participate in the
Plan. For more information on the consequences of Participant’s refusal to consent or withdrawal of consent, Participant understands that he or she may contact his or her local People representative. 

12. Address for Notices. Any notice to be given to the Company under the terms of this Option Agreement will be addressed to the Company
at Alector, Inc., 151 Oyster Point Blvd., Suite 300, South San Francisco, CA 94080, or at such other address as the Company may hereafter designate in writing. 

13. Non-Transferability of Option. This Option may not be transferred in any manner otherwise
than by will or by the laws of descent or distribution and may be exercised during the lifetime of Participant only by Participant. 
 14.
Successors and Assigns. The Company may assign any of its rights under this Option Agreement to single or multiple assignees, and this Option Agreement shall inure to the benefit of the successors and assigns of the Company. Subject to the
restrictions on transfer herein set forth, this Option Agreement shall be binding upon Participant and his or her heirs, executors, administrators, successors and assigns. The rights and obligations of Participant under this Option Agreement may
only be assigned with the prior written consent of the Company. 

  
 - 7 - 

 15. Additional Conditions to Issuance of Stock. If at any time the Company will
determine, in its discretion, that the listing, registration, qualification or rule compliance of the Shares upon any securities exchange or under any state, federal or non-U.S. law, the tax code and related
regulations or under the rulings or regulations of the United States Securities and Exchange Commission or any other governmental regulatory body or the clearance, consent or approval of the United States Securities and Exchange Commission or any
other governmental regulatory authority is necessary or desirable as a condition to the purchase by, or issuance of Shares, to Participant (or his or her estate) hereunder, such purchase or issuance will not occur unless and until such listing,
registration, qualification, rule compliance, clearance, consent or approval will have been completed, effected or obtained free of any conditions not acceptable to the Company. Subject to the terms of the Option Agreement and the Plan, the Company
shall not be required to issue any certificate or certificates for Shares hereunder prior to the lapse of such reasonable period of time following the date of exercise of the Option as the Administrator may establish from time to time for reasons of
administrative convenience. 
 16. Language. If Participant has received this Option Agreement or any other document related to the
Plan translated into a language other than English and if the meaning of the translated version is different than the English version, the English version will control. 

17. Interpretation. The Administrator will have the power to interpret the Plan and this Option Agreement and to adopt such rules for
the administration, interpretation and application of the Plan as are consistent therewith and to interpret or revoke any such rules (including, but not limited to, the determination of whether or not any Shares subject to the Option have vested).
All actions taken and all interpretations and determinations made by the Administrator in good faith will be final and binding upon Participant, the Company and all other interested persons. Neither the Administrator nor any person acting on behalf
of the Administrator will be personally liable for any action, determination, or interpretation made in good faith with respect to the Plan or this Option Agreement. 

18. Electronic Delivery and Acceptance. The Company may, in its sole discretion, decide to deliver any documents related to the Option
awarded under the Plan or future options that may be awarded under the Plan by electronic means or request Participant’s consent to participate in the Plan by electronic means. Participant hereby consents to receive such documents by electronic
delivery and agrees to participate in the Plan through any on-line or electronic system established and maintained by the Company or a third party designated by the Company. 

19. Captions. Captions provided herein are for convenience only and are not to serve as a basis for interpretation or construction of
this Option Agreement. 
 20. Agreement Severable. In the event that any provision in this Option Agreement will be held invalid or
unenforceable, such provision will be severable from, and such invalidity or unenforceability will not be construed to have any effect on, the remaining provisions of this Option Agreement. 

21. Amendment, Suspension or Termination of the Plan. By accepting this Option, Participant expressly warrants that he or she has
received an Option under the Plan, and has received, read, and understood a description of the Plan. Participant understands that the Plan is discretionary in nature and may be amended, suspended or terminated by the Company at any time. 

  
 - 8 - 

 22. Governing Law and Venue. This Option Agreement will be governed by the laws of
California, without giving effect to the conflict of law principles thereof. For purposes of litigating any dispute that arises under this Option or this Option Agreement, the parties hereby submit to and consent to the jurisdiction of the State of
California, and agree that such litigation will be conducted in the courts of San Mateo County, California, or the United States federal courts for the Northern District of California, and no other courts, where this Option is made and/or to be
performed. 
 23. Country Addendum. Notwithstanding any provisions in this Option Agreement, this Option shall be subject to any
special terms and conditions set forth in an appendix (if any) to this Option Agreement for any country whose laws are applicable to Participant and this Option (as determined by the Administrator in its sole discretion) (the “Country
Addendum”). Moreover, if Participant relocates to one of the countries included in the Country Addendum (if any), the special terms and conditions for such country will apply to Participant, to the extent the Company determines that the
application of such terms and conditions is necessary or advisable for legal or administrative reasons. The Country Addendum (if any) constitutes a part of this Option Agreement. 

24. Modifications to the Agreement. This Option Agreement constitutes the entire understanding of the parties on the subjects covered.
Participant expressly warrants that he or she is not accepting this Option Agreement in reliance on any promises, representations, or inducements other than those contained herein. Modifications to this Option Agreement or the Plan can be made only
in an express written contract executed by a duly authorized officer of the Company. Notwithstanding anything to the contrary in the Plan or this Option Agreement, the Company reserves the right to revise this Option Agreement as it deems necessary
or advisable, in its sole discretion and without the consent of Participant, to comply with Code Section 409A or to otherwise avoid imposition of any additional tax or income recognition under Section 409A of the Code in connection with
the Option. 
 25. No Waiver. Either party’s failure to enforce any provision or provisions of this Option Agreement shall not in
any way be construed as a waiver of any such provision or provisions, nor prevent that party from thereafter enforcing each and every other provision of this Option Agreement. The rights granted both parties herein are cumulative and shall not
constitute a waiver of either party’s right to assert all other legal remedies available to it under the circumstances. 
 26. Tax
Consequences. Participant has reviewed with his or her own tax advisors the U.S. federal, state, local and non-U.S. tax consequences of this investment and the transactions contemplated by this Option
Agreement. With respect to such matters, Participant relies solely on such advisors and not on any statements or representations of the Company or any of its agents, written or oral. Participant understands that Participant (and not the Company)
shall be responsible for Participant’s own tax liability that may arise as a result of this investment or the transactions contemplated by this Option Agreement. 

  
 - 9 - 

 ALECTOR, INC. 

2019 EQUITY INCENTIVE PLAN 

STOCK OPTION AGREEMENT 

COUNTRY ADDENDUM 
 TERMS AND
CONDITIONS 
 This Country Addendum includes additional terms and conditions that govern the Option granted to Participant under the Plan if
Participant works in one of the countries listed below. If Participant is a citizen or resident of a country (or is considered as such for local law purposes) other than the one in which he or she is currently working or if Participant relocates to
another country after receiving the Option, the Company will, in its discretion, determine the extent to which the terms and conditions contained herein will be applicable to Participant. 

Certain capitalized terms used but not defined in this Country Addendum shall have the meanings set forth in the Plan, and/or the Stock Option Agreement to
which this Country Addendum is attached. 
 NOTIFICATIONS 

This Country Addendum also includes notifications relating to exchange control and other issues of which Participant should be aware with respect to his or her
participation in the Plan. The information is based on the exchange control, securities and other laws in effect in the countries listed in this Country Addendum, as of
                . Such laws are often complex and change frequently. As a result, the Company strongly recommends that Participant not rely on the notifications
herein as the only source of information relating to the consequences of his or her participation in the Plan because the information may be outdated when Participant exercises the Option or sells Shares acquired under the Plan. 

In addition, the notifications are general in nature and may not apply to Participant’s particular situation, and the Company is not in a position to
assure Participant of any particular result. Accordingly, Participant is advised to seek appropriate professional advice as to how the relevant laws in Participant’s country may apply to Participant’s situation. 

Finally, if Participant is a citizen or resident of a country other than the one in which Participant is currently working (or is considered as such for local
law purposes) or if Participant moves to another country after the Option is granted, the information contained herein may not be applicable to Participant. 

 EXHIBIT B 

ALECTOR, INC. 
 2019
EQUITY INCENTIVE PLAN 
 EXERCISE NOTICE 

Alector, Inc. 
 151 Oyster Point Blvd., Suite 300 

South San Francisco, CA 94080 
 Attention: Stock Administration

 1. Exercise of Option. Effective as of today,
                        ,             , the undersigned
(“Purchaser”) hereby elects to purchase                          shares (the “Shares”) of the Common Stock of
Alector, Inc. (the “Company”) under and pursuant to the 2019 Equity Incentive Plan (the “Plan”) and the Stock Option Agreement, dated              and including the
Notice of Grant, the Terms and Conditions of Stock Option Grant, and exhibits attached thereto (the “Option Agreement”). The purchase price for the Shares will be
$                        , as required by the Option Agreement. 

2. Delivery of Payment. Purchaser herewith delivers to the Company the full purchase price of the Shares and any Tax Obligations (as
defined in Section 6(a) of the Option Agreement) to be paid in connection with the exercise of the Option. 
 3. Representations of
Purchaser. Purchaser acknowledges that Purchaser has received, read and understood the Plan and the Option Agreement and agrees to abide by and be bound by their terms and conditions. 

4. Rights as Stockholder. Until the issuance (as evidenced by the appropriate entry on the books of the Company or of a duly authorized
transfer agent of the Company) of the Shares, no right to vote or receive dividends or any other rights as a stockholder will exist with respect to the Shares subject to the Option, notwithstanding the exercise of the Option. The Shares so acquired
will be issued to Purchaser as soon as practicable after exercise of the Option. No adjustment will be made for a dividend or other right for which the record date is prior to the date of issuance, except as provided in Section 14 of the Plan.

 5. Tax Consultation. Purchaser understands that Purchaser may suffer adverse tax consequences as a result of Purchaser’s
purchase or disposition of the Shares. Purchaser represents that Purchaser has consulted with any tax consultants Purchaser deems advisable in connection with the purchase or disposition of the Shares and that Purchaser is not relying on the Company
for any tax advice. 

 6. Entire Agreement; Governing Law. The Plan and Option Agreement are incorporated
herein by reference. This Exercise Notice, the Plan and the Option Agreement constitute the entire agreement of the parties with respect to the subject matter hereof and supersede in their entirety all prior undertakings and agreements of the
Company and Purchaser with respect to the subject matter hereof, and may not be modified adversely to the Purchaser’s interest except by means of a writing signed by the Company and Purchaser. This Option Agreement is governed by the internal
substantive laws, but not the choice of law rules, of California. 
  

					
	Submitted by:	  	        	  	Accepted by:
			
	PURCHASER	  		  	ALECTOR, INC.
			
	  
 Signature
	  		  	  
 Signature

			
	  
 Print Name
	  		  	  
 Print Name

			
	Address:	  		  	  
 Title

			
	  
	  		  	
			
	  
	  		  	
			
		  		  	
			
		  		  	  
 Date Received

  
 - 2 - 

 ALECTOR, INC. 

2019 EQUITY INCENTIVE PLAN 

RESTRICTED STOCK UNIT AGREEMENT 

NOTICE OF RESTRICTED STOCK UNIT GRANT 

Unless otherwise defined herein, the terms defined in the Alector, Inc. 2019 Equity Incentive Plan (the “Plan”) will have the
same defined meanings in this Restricted Stock Unit Agreement, which includes the Notice of Restricted Stock Unit Grant (the “Notice of Grant”), the Terms and Conditions of Restricted Stock Unit Grant attached hereto as Exhibit A,
and all other exhibits and appendices attached hereto (all together, the “Award Agreement”). 

Participant:     

Address: 
 The
undersigned Participant has been granted the right to receive an Award of Restricted Stock Units, subject to the terms and conditions of the Plan and this Award Agreement, as follows: 

 

							
	        	 	Grant Number:	 	  
	 	
				
		 	Date of Grant:	 	  
	 	
				
		 	Vesting Commencement Date:	 	  
	 	
				
		 	Number of Restricted Stock Units:	 	  
	 	

 Vesting Schedule: 

Subject to any acceleration provisions contained in the Plan or set forth below, the Restricted Stock Units will vest in accordance with the
following schedule: 
 [Twenty-five percent (25%) of the Restricted Stock Units will vest on the one (1) year anniversary of the
Vesting Commencement Date, and one sixteenth (1/16th) of the Restricted Stock Units will vest quarterly thereafter on the same day as the Vesting Commencement Date, subject to Participant
continuing to be a Service Provider through each such date.] 
 In the event Participant ceases to be a Service Provider for any or
no reason before Participant vests in the Restricted Stock Units, the Restricted Stock Units and Participant’s right to acquire any Shares hereunder will immediately terminate. 

By Participant’s signature and the signature of the representative of Alector, Inc. (the “Company”) below, Participant and
the Company agree that this Award of Restricted Stock Units is granted under and governed by the terms and conditions of the Plan and this Award Agreement, including the Terms and Conditions of Restricted Stock Unit Grant, attached hereto as
Exhibit A, all of which are made a part of this document. Participant acknowledges receipt of a copy of the Plan. Participant has reviewed the Plan and this Award Agreement in their entirety, has had an opportunity

 
to obtain the advice of counsel prior to executing this Award Agreement, and fully understands all provisions of the Plan and this Award Agreement. Participant hereby agrees to accept as binding,
conclusive, and final all decisions or interpretations of the Administrator upon any questions relating to the Plan and the Award Agreement. Participant further agrees to notify the Company upon any change in the residence address indicated below.

 By accepting this Award Agreement, Participant expressly consents to the sale of Shares to cover the Tax Withholding Obligations (as
defined in the Terms and Conditions of Restricted Stock Unit Grant) arising from the Restricted Stock Units and any associated broker or other fees and agrees and acknowledges that Participant may not satisfy them by any means other than such sale
of Shares, unless required to do so by the Administrator or pursuant to the Administrator’s express written consent.
  

					
	PARTICIPANT:	 	    	  	ALECTOR, INC.
			
	  
	 		  	  

	Signature	 		  	Signature
			
	  
	 		  	  

	Print Name	 		  	Print Name
			
		 		  	  

		 		  	Title

 Address: 

  
 - 2 - 

 EXHIBIT A 

TERMS AND CONDITIONS OF RESTRICTED STOCK UNIT GRANT 

1. Grant of Restricted Stock Units. The Company hereby grants to the individual (the “Participant”) named in the Notice of
Grant of Restricted Stock Units of this Award Agreement (the “Notice of Grant”) under the Plan an Award of Restricted Stock Units, subject to all of the terms and conditions in this Award Agreement and the Plan, which is incorporated
herein by reference. Subject to Section 19(c) of the Plan, in the event of a conflict between the terms and conditions of the Plan and this Award Agreement, the terms and conditions of the Plan shall prevail. 

2. Company’s Obligation to Pay. Each Restricted Stock Unit represents the right to receive a Share on the date it vests. Unless and
until the Restricted Stock Units will have vested in the manner set forth in Section 3 or 4, Participant will have no right to payment of any such Restricted Stock Units. Prior to actual payment of any vested Restricted Stock Units, such
Restricted Stock Unit will represent an unsecured obligation of the Company, payable (if at all) only from the general assets of the Company. 

3. Vesting Schedule. Except as provided in Section 4, and subject to Section 5, the Restricted Stock Units awarded by this
Award Agreement will vest in accordance with the vesting schedule set forth in the Notice of Grant, subject to Participant continuing to be a Service Provider through each applicable vesting date. 

4. Payment after Vesting. 

(a) General Rule. Subject to Section 8, any Restricted Stock Units that vest will be paid to Participant (or in the event of
Participant’s death, to his or her properly designated beneficiary or estate) in whole Shares. Subject to the provisions of Section 4(b), such vested Restricted Stock Units shall be paid in whole Shares as soon as practicable after
vesting, but in each such case within sixty (60) days following the vesting date. In no event will Participant be permitted, directly or indirectly, to specify the taxable year of payment of any Restricted Stock Units payable under this Award
Agreement. 
 (b) Acceleration. 

(i) Discretionary Acceleration. The Administrator, in its discretion, may accelerate the vesting of the balance, or some lesser portion
of the balance, of the unvested Restricted Stock Units at any time, subject to the terms of the Plan. If so accelerated, such Restricted Stock Units will be considered as having vested as of the date specified by the Administrator. If Participant is
a U.S. taxpayer, the payment of Shares vesting pursuant to this Section 4(b) shall in all cases be paid at a time or in a manner that is exempt from, or complies with, Section 409A. The prior sentence may be superseded in a future
agreement or amendment to this Award Agreement only by direct and specific reference to such sentence. 

 (ii) Notwithstanding anything in the Plan or this Award Agreement or any other agreement
(whether entered into before, on or after the Date of Grant), if the vesting of the balance, or some lesser portion of the balance, of the Restricted Stock Units is accelerated in connection with Participant’s termination as a Service Provider
(provided that such termination is a “separation from service” within the meaning of Section 409A, as determined by the Company), other than due to Participant’s death, and if (x) Participant is a U.S. taxpayer and a
“specified employee” within the meaning of Section 409A at the time of such termination as a Service Provider and (y) the payment of such accelerated Restricted Stock Units will result in the imposition of additional tax under
Section 409A if paid to Participant on or within the six (6) month period following Participant’s termination as a Service Provider, then the payment of such accelerated Restricted Stock Units will not be made until the date six
(6) months and one (1) day following the date of Participant’s termination as a Service Provider, unless Participant dies following his or her termination as a Service Provider, in which case, the Restricted Stock Units will be paid
in Shares to Participant’s estate as soon as practicable following his or her death. 
 (c) Section 409A. It is the intent
of this Award Agreement that it and all payments and benefits to U.S. taxpayers hereunder be exempt from, or comply with, the requirements of Section 409A so that none of the Restricted Stock Units provided under this Award Agreement or Shares
issuable thereunder will be subject to the additional tax imposed under Section 409A, and any ambiguities herein will be interpreted to be so exempt or so comply. Each payment payable under this Award Agreement is intended to constitute a
separate payment for purposes of Treasury Regulation Section 1.409A-2(b)(2). However, in no event will the Company reimburse Participant, or be otherwise responsible for, any taxes or costs that may be imposed on Participant as a result of
Section 409A. For purposes of this Award Agreement, “Section 409A” means Section 409A of the Code, and any final Treasury Regulations and Internal Revenue Service guidance thereunder, as each may be amended from time to
time. 
 5. Forfeiture Upon Termination as a Service Provider. Notwithstanding any contrary provision of this Award Agreement, if
Participant ceases to be a Service Provider for any or no reason, the then-unvested Restricted Stock Units awarded by this Award Agreement will thereupon be forfeited at no cost to the Company and Participant will have no further rights thereunder.

 6. Tax Consequences. Participant has reviewed with his or her own tax advisors the U.S. federal, state, local and non-U.S. tax consequences of this investment and the transactions contemplated by this Award Agreement. With respect to such matters, Participant relies solely on such advisors and not on any statements or
representations of the Company or any of its agents, written or oral. Participant understands that Participant (and not the Company) shall be responsible for Participant’s own tax liability that may arise as a result of this investment or the
transactions contemplated by this Award Agreement. 
 7. Death of Participant. Any distribution or delivery to be made to Participant
under this Award Agreement will, if Participant is then deceased, be made to Participant’s designated beneficiary, or if no beneficiary survives Participant, the administrator or executor of Participant’s estate. Any such transferee must
furnish the Company with (a) written notice of his or her status as transferee, and (b) evidence satisfactory to the Company to establish the validity of the transfer and compliance with any laws or regulations pertaining to said transfer.

  
 -2- 

 8. Tax Obligations 

(a) Responsibility for Taxes. Participant acknowledges that, regardless of any action taken by the Company or, if different,
Participant’s employer (the “Employer”) or Parent or Subsidiary to which Participant is providing services (together, the Company, Employer and/or Parent or Subsidiary to which the Participant is providing services, the “Service
Recipient”), the ultimate liability for any tax and/or social insurance liability obligations and requirements in connection with the Restricted Stock Units, including, without limitation, (i) all federal, state, and local taxes (including
the Participant’s Federal Insurance Contributions Act (FICA) obligation) that are required to be withheld by the Company or the Employer or other payment of tax-related items related to Participant’s
participation in the Plan and legally applicable to Participant, (ii) the Participant’s and, to the extent required by the Company (or Service Recipient), the Company’s (or Service Recipient’s) fringe benefit tax liability, if
any, associated with the grant, vesting, or settlement of the Restricted Stock Units or sale of Shares, and (iii) any other Company (or Service Recipient) taxes the responsibility for which the Participant has, or has agreed to bear, with
respect to the Restricted Stock Units (or settlement thereof or issuance of Shares thereunder) (collectively, the “Tax Obligations”), is and remains Participant’s responsibility and may exceed the amount actually withheld by the
Company or the Service Recipient. Participant further acknowledges that the Company and/or the Service Recipient (A) make no representations or undertakings regarding the treatment of any Tax Obligations in connection with any aspect of the
Restricted Stock Units, including, but not limited to, the grant, vesting or settlement of the Restricted Stock Units, the subsequent sale of Shares acquired pursuant to such settlement and the receipt of any dividends or other distributions, and
(B) do not commit to and are under no obligation to structure the terms of the grant or any aspect of the Restricted Stock Units to reduce or eliminate Participant’s liability for Tax Obligations or achieve any particular tax result.
Further, if Participant is subject to Tax Obligations in more than one jurisdiction between the Date of Grant and the date of any relevant taxable or tax withholding event, as applicable, Participant acknowledges that the Company and/or the Service
Recipient (or former employer, as applicable) may be required to withhold or account for Tax Obligations in more than one jurisdiction. If Participant fails to make satisfactory arrangements for the payment of any required Tax Obligations hereunder
at the time of the applicable taxable event, Participant acknowledges and agrees that the Company may refuse to issue or deliver the Shares. 

(b) Tax Withholding and Default Sell-to-Cover Method of Tax
Withholding. When Shares are issued as payment for vested Restricted Stock Units, Participant generally will recognize immediate U.S. taxable income if Participant is a U.S. taxpayer. If Participant is a
non-U.S. taxpayer, Participant will be subject to applicable taxes in his or her jurisdiction. Subject to Section 8(c), the minimum amount of Tax Obligations which the Company determines must be withheld
with respect to this Award (“Tax Withholding Obligation”) will be satisfied by Shares being sold on Participant’s behalf at the prevailing market price pursuant to such procedures as the Company may specify from time to time,
including through a broker-assisted arrangement (it being understood that the Shares to be sold must have vested pursuant to the terms of this Award Agreement and the Plan) (the
“Sell-to-Cover Method”). The proceeds from the Sell-to-Cover Method will be
used to satisfy Participant’s Tax Withholding Obligation arising with respect to this Award. In addition to Shares sold to satisfy the Tax Withholding Obligation, additional Shares will be sold to satisfy any associated broker or other fees.
Only whole Shares will be sold through the Sell-to-Cover Method to satisfy any Tax Withholding Obligation and any associated broker or other fees. Any proceeds from the
sale of Shares in excess of the Tax Withholding Obligation and any associated broker or other fees generated 

  
 -3- 

 
through the Sell-to-Cover Method will be paid to Participant in accordance with procedures the Company may specify
from time to time. By accepting this Award, Participant expressly consents to the sale of Shares to cover the Tax Withholding Obligation (and any associated broker or other fees) through the Sell-to-Cover Method and agrees and acknowledges that Participant may not satisfy them by any means other than such sale of Shares, unless required to do so by the Administrator or pursuant to the
Administrator’s express written consent. 
 (c) Administrator Discretion. Notwithstanding the foregoing Sections 8(a) and
8(b), if the Administrator determines it is in the best interests of the Company for Participant to satisfy Participant’s Tax Withholding Obligation by a method other than through the default Sell-to-Cover Method described in Section 8(b), it may permit or require Participant to satisfy Participant’s Tax Withholding Obligation, in whole or in part (without limitation), if permissible by
Applicable Laws, by (i) paying cash, (ii) withholding the amount of such Tax Withholding Obligation from Participant’s wages or other cash compensation paid to Participant by the Company and/or the Service Recipient,
(iii) delivering to the Company Shares that Participant owns and that have vested with a fair market value equal to the amount required to be withheld (or such greater amount up to the maximum statutory rate applicable to the Participant if
permitted by the Administrator and provided such greater amount would not result in adverse financial accounting consequences to the Company as determined by the Administrator), (iv) by having the Company withhold otherwise deliverable Shares having
a fair market value equal to the amount required to be withheld (or such greater amount up to the maximum statutory rate applicable to the Participant if permitted by the Administrator and provided such greater amount would not result in adverse
financial accounting consequences to the Company as determined by the Administrator) or (v) such other means as the Administrator deems appropriate. 

(d) Company’s Obligation to Deliver Shares. For clarification purposes, in no event will the Company issue Participant any Shares
unless and until arrangements satisfactory to the Administrator have been made for the payment of Participant’s Tax Withholding Obligation. If Participant fails to make satisfactory arrangements for the payment of such Tax Withholding
Obligations hereunder at the time any applicable Restricted Stock Units otherwise are scheduled to vest pursuant to Sections 3 or 4 or Participant’s Tax Withholding Obligations otherwise become due, Participant will permanently forfeit such
Restricted Stock Units to which Participant’s Tax Withholding Obligation relates and any right to receive Shares thereunder and such Restricted Stock Units will be returned to the Company at no cost to the Company. Participant acknowledges and
agrees that the Company may refuse to issue or deliver the Shares if such Tax Obligations are not delivered at the time they are due. 
 9.
Rights as Stockholder. Neither Participant nor any person claiming under or through Participant will have any of the rights or privileges of a stockholder of the Company in respect of any Shares deliverable hereunder unless and until
certificates representing such Shares (which may be in book entry form) will have been issued, recorded on the records of the Company or its transfer agents or registrars, and delivered to Participant (including through electronic delivery to a
brokerage account). After such issuance, recordation, and delivery, Participant will have all the rights of a stockholder of the Company with respect to voting such Shares and receipt of dividends and distributions on such Shares. 

  
 -4- 

 10. No Guarantee of Continued Service. PARTICIPANT ACKNOWLEDGES AND AGREES THAT THE
VESTING OF THE RESTRICTED STOCK UNITS PURSUANT TO THE VESTING SCHEDULE HEREOF IS EARNED ONLY BY CONTINUING AS A SERVICE PROVIDER, WHICH UNLESS PROVIDED OTHERWISE UNDER APPLICABLE LAW IS AT THE WILL OF THE COMPANY (OR THE SERVICE RECIPIENT) AND NOT
THROUGH THE ACT OF BEING HIRED, BEING GRANTED THIS RESTRICTED STOCK UNIT AWARD OR ACQUIRING SHARES HEREUNDER. PARTICIPANT FURTHER ACKNOWLEDGES AND AGREES THAT THIS AWARD AGREEMENT, THE TRANSACTIONS CONTEMPLATED HEREUNDER AND THE VESTING SCHEDULE SET
FORTH HEREIN DO NOT CONSTITUTE AN EXPRESS OR IMPLIED PROMISE OF CONTINUED ENGAGEMENT AS A SERVICE PROVIDER FOR THE VESTING PERIOD, FOR ANY PERIOD, OR AT ALL, AND SHALL NOT INTERFERE IN ANY WAY WITH PARTICIPANT’S RIGHT OR THE RIGHT OF THE
COMPANY (OR THE SERVICE RECIPIENT) TO TERMINATE PARTICIPANT’S RELATIONSHIP AS A SERVICE PROVIDER, SUBJECT TO APPLICABLE LAW, WHICH TERMINATION, UNLESS PROVIDED OTHERWISE UNDER APPLICABLE LAW, MAY BE AT ANY TIME, WITH OR WITHOUT CAUSE. 

11. Grant is Not Transferable. Except to the limited extent provided in Section 7, this grant and the rights and privileges
conferred hereby will not be transferred, assigned, pledged or hypothecated in any way (whether by operation of law or otherwise) and will not be subject to sale under execution, attachment or similar process. Upon any attempt to transfer, assign,
pledge, hypothecate or otherwise dispose of this grant, or any right or privilege conferred hereby, or upon any attempted sale under any execution, attachment or similar process, this grant and the rights and privileges conferred hereby immediately
will become null and void. 
 12. Nature of Grant. In accepting the grant, Participant acknowledges, understands, and agrees that:

 (a) the grant of the Restricted Stock Units is voluntary and occasional and does not create any contractual or other right to receive
future grants of Restricted Stock Units, or benefits in lieu of Restricted Stock Units, even if Restricted Stock Units have been granted in the past; 

(b) all decisions with respect to future Restricted Stock Units or other grants, if any, will be at the sole discretion of the Company; 

(c) Participant is voluntarily participating in the Plan; 

(d) the Restricted Stock Units and the Shares subject to the Restricted Stock Units are not intended to replace any pension rights or
compensation; 
 (e) the Restricted Stock Units and the Shares subject to the Restricted Stock Units, and the income and value of same, are
not part of normal or expected compensation for purposes of calculating any severance, resignation, termination, redundancy, dismissal, end-of-service payments, bonuses,
long-service awards, pension or retirement or welfare benefits or similar payments; 
 (f) the future value of the underlying Shares is
unknown, indeterminable and cannot be predicted; 

  
 -5- 

 (g) for purposes of the Restricted Stock Units, Participant’s status as a Service
Provider will be considered terminated as of the date Participant is no longer actively providing services to the Company or any Parent or Subsidiary (regardless of the reason for such termination and whether or not later to be found invalid or in
breach of employment laws in the jurisdiction where Participant is a Service Provider or the terms of Participant’s employment or service agreement, if any), and unless otherwise expressly provided in this Award Agreement (including by
reference in the Notice of Grant to other arrangements or contracts) or determined by the Administrator, Participant’s right to vest in the Restricted Stock Units under the Plan, if any, will terminate as of such date and will not be extended
by any notice period (e.g., Participant’s period of service would not include any contractual notice period or any period of “garden leave” or similar period mandated under employment laws in the jurisdiction where Participant is a
Service Provider or the terms of Participant’s employment or service agreement, if any, unless Participant is providing bona fide services during such time); the Administrator shall have the exclusive discretion to determine when Participant is
no longer actively providing services for purposes of the Restricted Stock Units grant (including whether Participant may still be considered to be providing services while on a leave of absence and consistent with local law); 

(h) unless otherwise provided in the Plan or by the Company in its discretion, the Restricted Stock Units and the benefits evidenced by this
Award Agreement do not create any entitlement to have the Restricted Stock Units or any such benefits transferred to, or assumed by, another company nor be exchanged, cashed out or substituted for, in connection with any corporate transaction
affecting the Shares; and 
 (i) the following provisions apply only if Participant is providing services outside the United States: 

(i) the Restricted Stock Units and the Shares subject to the Restricted Stock Units are not part of normal or expected compensation or salary
for any purpose; 
 (ii) Participant acknowledges and agrees that none of the Company, the Employer or any Parent or Subsidiary shall be
liable for any foreign exchange rate fluctuation between Participant’s local currency and the United States Dollar that may affect the value of the Restricted Stock Units or of any amounts due to Participant pursuant to the settlement of the
Restricted Stock Units or the subsequent sale of any Shares acquired upon settlement; and 
 (iii) no claim or entitlement to compensation
or damages shall arise from forfeiture of the Restricted Stock Units resulting from the termination of Participant’s status as a Service Provider (for any reason whatsoever whether or not later found to be invalid or in breach of employment
laws in the jurisdiction where Participant is a Service Provider or the terms of Participant’s employment or service agreement, if any), and in consideration of the grant of the Restricted Stock Units to which Participant is otherwise not
entitled, Participant irrevocably agrees never to institute any claim against the Company, any Parent or Subsidiary or the Service Recipient, waives his or her ability, if any, to bring any such claim, and releases the Company, any Parent or
Subsidiary and the Service Recipient from any such claim; if, notwithstanding the foregoing, any such claim is allowed by a court of competent jurisdiction, then, by participating in the Plan, Participant shall be deemed irrevocably to have agreed
not to pursue such claim and agrees to execute any and all documents necessary to request dismissal or withdrawal of such claim. 

  
 -6- 

 13. No Advice Regarding Grant. The Company is not providing any tax, legal or
financial advice, nor is the Company making any recommendations regarding Participant’s participation in the Plan, or Participant’s acquisition or sale of the underlying Shares. Participant is hereby advised to consult with his or her own
personal tax, legal and financial advisors regarding his or her participation in the Plan before taking any action related to the Plan. 

14. Data Privacy. Participant hereby explicitly and unambiguously consents to the collection, use and transfer, in
electronic or other form, of Participant’s personal data as described in this Award Agreement and any other Restricted Stock Unit grant materials by and among, as applicable, the Employer or other Service Recipient, the Company and any Parent
or Subsidiary for the exclusive purpose of implementing, administering and managing Participant’s participation in the Plan. 

Participant understands that the Company and the Service Recipient may hold certain personal information about Participant, including,
but not limited to, Participant’s name, home address and telephone number, date of birth, social insurance number or other identification number, salary, nationality, job title, any Shares or directorships held in the Company, details of all
Restricted Stock Units or any other entitlement to Shares awarded, canceled, exercised, vested, unvested or outstanding in Participant’s favor (“Data”), for the exclusive purpose of implementing, administering and managing the Plan.

 Participant understands that Data will be transferred to a stock plan service provider as may be selected by the Company in
the future, which is assisting the Company with the implementation, administration, and management of the Plan. Participant understands that the recipients of the Data may be located in the United States or elsewhere, and that the recipients’
country of operation (e.g., the United States) may have different data privacy laws and protections than Participant’s country. Participant understands that if he or she resides outside the United States, he or she may request a list with the
names and addresses of any potential recipients of the Data by contacting his or her local People representative. Participant authorizes the Company, any stock plan service provider selected by the Company and any other possible recipients which may
assist the Company (presently or in the future) with implementing, administering and managing the Plan to receive, possess, use, retain and transfer the Data, in electronic or other form, for the sole purpose of implementing, administering and
managing his or her participation in the Plan. Participant understands that Data will be held only as long as is necessary to implement, administer and manage Participant’s participation in the Plan. Participant understands if he or she resides
outside the United States, he or she may, at any time, view Data, request additional information about the storage and processing of Data, require any necessary amendments to Data or refuse or withdraw the consents herein, in any case without cost,
by contacting in writing his or her local People representative. Further, Participant understands that he or she is providing the consents herein on a purely voluntary basis. If Participant does not consent, or if Participant later seeks to revoke
his or her consent, his or her status as a Service Provider and career with the Service Recipient will not be adversely affected; the only adverse consequence of refusing or withdrawing Participant’s consent is that the Company would not be
able to grant Participant Restricted Stock Units or other equity awards or administer or maintain such awards. Therefore, Participant understands that refusing or withdrawing his or her consent may affect Participant’s ability to participate in
the Plan. For more information on the consequences of Participant’s refusal to consent or withdrawal of consent, Participant understands that he or she may contact his or her local People representative. 

  
 -7- 

 15. Address for Notices. Any notice to be given to the Company under the terms of
this Award Agreement will be addressed to the Company at Alector, Inc., 151 Oyster Point Blvd., Suite 300, South San Francisco, CA 94080 or at such other address as the Company may hereafter designate in writing. 

16. Electronic Delivery and Acceptance. The Company may, in its sole discretion, decide to deliver any documents related to the
Restricted Stock Units awarded under the Plan or future Restricted Stock Units that may be awarded under the Plan by electronic means or request Participant’s consent to participate in the Plan by electronic means. Participant hereby consents
to receive such documents by electronic delivery and agrees to participate in the Plan through any on-line or electronic system established and maintained by the Company or a third party designated by the
Company. 
 17. No Waiver. Either party’s failure to enforce any provision or provisions of this Award Agreement shall not in any
way be construed as a waiver of any such provision or provisions, nor prevent that party from thereafter enforcing each and every other provision of this Award Agreement. The rights granted both parties herein are cumulative and shall not constitute
a waiver of either party’s right to assert all other legal remedies available to it under the circumstances. 
 18. Successors and
Assigns. The Company may assign any of its rights under this Award Agreement to single or multiple assignees, and this Award Agreement shall inure to the benefit of the successors and assigns of the Company. Subject to the restrictions on
transfer herein set forth, this Award Agreement shall be binding upon Participant and his or her heirs, executors, administrators, successors and assigns. The rights and obligations of Participant under this Award Agreement may only be assigned with
the prior written consent of the Company. 
 19. Additional Conditions to Issuance of Stock. If at any time the Company will
determine, in its discretion, that the listing, registration, qualification or rule compliance of the Shares upon any securities exchange or under any state, federal or non-U.S. law, the tax code and related
regulations or under the rulings or regulations of the United States Securities and Exchange Commission or any other governmental regulatory body or the clearance, consent or approval of the United States Securities and Exchange Commission or any
other governmental regulatory authority is necessary or desirable as a condition to the issuance of Shares to Participant (or his or her estate) hereunder, such issuance will not occur unless and until such listing, registration, qualification, rule
compliance, clearance, consent or approval will have been completed, effected or obtained free of any conditions not acceptable to the Company. Subject to the terms of the Award Agreement and the Plan, the Company shall not be required to issue any
certificate or certificates for Shares hereunder prior to the lapse of such reasonable period of time following the date of vesting of the Restricted Stock Units as the Administrator may establish from time to time for reasons of administrative
convenience. 
 20. Language. If Participant has received this Award Agreement or any other document related to the Plan translated
into a language other than English and if the meaning of the translated version is different than the English version, the English version will control. 

21. Interpretation. The Administrator will have the power to interpret the Plan and this Award Agreement and to adopt such rules for the
administration, interpretation and application of the Plan as are consistent therewith and to interpret or revoke any such rules (including, but not limited to, the determination of whether or not any Restricted Stock Units have vested). All actions
taken and 

  
 -8- 

 
all interpretations and determinations made by the Administrator in good faith will be final and binding upon Participant, the Company and all other interested persons. Neither the Administrator
nor any person acting on behalf of the Administrator will be personally liable for any action, determination, or interpretation made in good faith with respect to the Plan or this Award Agreement. 

22. Captions. Captions provided herein are for convenience only and are not to serve as a basis for interpretation or construction of
this Award Agreement. 
 23. Amendment, Suspension or Termination of the Plan. By accepting this Award, Participant expressly warrants
that he or she has received an Award of Restricted Stock Units under the Plan, and has received, read, and understood a description of the Plan. Participant understands that the Plan is discretionary in nature and may be amended, suspended or
terminated by the Company at any time. 
 24. Modifications to the Award Agreement. This Award Agreement constitutes the entire
understanding of the parties on the subjects covered. Participant expressly warrants that he or she is not accepting this Award Agreement in reliance on any promises, representations, or inducements other than those contained herein. Modifications
to this Award Agreement or the Plan can be made only in an express written contract executed by a duly authorized officer of the Company. Notwithstanding anything to the contrary in the Plan or this Award Agreement, the Company reserves the right to
revise this Award Agreement as it deems necessary or advisable, in its sole discretion and without the consent of Participant, to comply with Section 409A or to otherwise avoid imposition of any additional tax or income recognition under
Section 409A in connection with this Award of Restricted Stock Units. 
 25. Governing Law; Venue; Severability. This Award
Agreement and the Restricted Stock Units are governed by the internal substantive laws, but not the choice of law rules, of California. For purposes of litigating any dispute that arises under these Restricted Stock Units or this Award Agreement,
the parties hereby submit to and consent to the jurisdiction of the State of California, and agree that such litigation will be conducted in the courts of San Mateo County, California, or the United States federal courts for the Northern District of
California, and no other courts, where this Award Agreement is made and/or to be performed. In the event that any provision hereof becomes or is declared by a court of competent jurisdiction to be illegal, unenforceable or void, this Award Agreement
shall continue in full force and effect. 
 26. Entire Agreement. The Plan is incorporated herein by reference. The Plan and this
Award Agreement (including the appendices and exhibits referenced herein) constitute the entire agreement of the parties with respect to the subject matter hereof and supersede in their entirety all prior undertakings and agreements of the Company
and Participant with respect to the subject matter hereof, and may not be modified adversely to the Participant’s interest except by means of a writing signed by the Company and Participant. 

27. Country Addendum. Notwithstanding any provisions in this Award Agreement, the Restricted Stock Unit grant shall be subject to any
special terms and conditions set forth in an appendix (if any) to this Award Agreement for any country whose laws are applicable to Participant and this Award of Restricted Stock Units (as determined by the Administrator in its sole discretion) (the
“Country Addendum”). Moreover, if Participant relocates to one of the countries included in the 

  
 -9- 

 
Country Addendum (if any), the special terms and conditions for such country will apply to Participant, to the extent the Company determines that the application of such terms and conditions is
necessary or advisable for legal or administrative reasons. The Country Addendum constitutes part of this Award Agreement. 

  
 -10- 

 ALECTOR, INC. 

2019 EQUITY INCENTIVE PLAN 

RESTRICTED STOCK UNIT AGREEMENT 

COUNTRY ADDENDUM 
 TERMS AND
CONDITIONS 
 This Country Addendum includes additional terms and conditions that govern the Award of Restricted Stock Units granted to Participant
under the Plan if Participant works in one of the countries listed below. If Participant is a citizen or resident of a country (or is considered as such for local law purposes) other than the one in which he or she is currently working or if
Participant relocates to another country after receiving the Award of Restricted Stock Units, the Company will, in its discretion, determine the extent to which the terms and conditions contained herein will be applicable to Participant. 

Certain capitalized terms used but not defined in this Country Addendum shall have the meanings set forth in the Plan, and/or the Restricted Stock Unit
Agreement to which this Country Addendum is attached. 
 NOTIFICATIONS 

This Country Addendum also includes notifications relating to exchange control and other issues of which Participant should be aware with respect to his or her
participation in the Plan. The information is based on the exchange control, securities and other laws in effect in the countries listed in this Country Addendum, as of [DATE]. Such laws are often complex and change frequently. As a result, the
Company strongly recommends that Participant not rely on the notifications herein as the only source of information relating to the consequences of his or her participation in the Plan because the information may be outdated when Participant vests
in the Restricted Stock Units and acquires Shares, or when Participant subsequently sell Shares acquired under the Plan. 
 In addition, the notifications
are general in nature and may not apply to Participant’s particular situation, and the Company is not in a position to assure Participant of any particular result. Accordingly, Participant is advised to seek appropriate professional advice as
to how the relevant laws in Participant’s country may apply to Participant’s situation. 
 Finally, if Participant is a citizen or resident of a
country other than the one in which Participant is currently working (or is considered as such for local law purposes) or if Participant moves to another country after receiving the Award of Restricted Stock Units, the information contained herein
may not be applicable to Participant.

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00290-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00290-of-00352.parquet"}]]