Document:

EX-4.1

 Exhibit 4.1 

ALECTOR, INC. 
 AMENDED
AND RESTATED REGISTRATION RIGHTS AGREEMENT 
 April 26, 2018 

 TABLE OF CONTENTS 

 

									
	 	  	 	  	 	  	Page	 
	 1.
	  	Definitions	  	 	1	 
	 2.
	  	Registration Rights	  	 	4	 
		  	2.1	  	Demand Registration	  	 	4	 
		  	2.2	  	Company Registration	  	 	6	 
		  	2.3	  	Underwriting Requirements	  	 	6	 
		  	2.4	  	Obligations of the Company	  	 	8	 
		  	2.5	  	Furnish Information	  	 	9	 
		  	2.6	  	Expenses of Registration	  	 	9	 
		  	2.7	  	Delay of Registration	  	 	9	 
		  	2.8	  	Indemnification	  	 	10	 
		  	2.9	  	Reports Under Exchange Act	  	 	12	 
		  	2.10	  	Limitations on Subsequent Registration Rights	  	 	13	 
		  	2.11	  	“Market Stand-off” Agreement	  	 	13	 
		  	2.12	  	Restrictions on Transfer	  	 	13	 
		  	2.13	  	Termination of Registration Rights	  	 	15	 
			
	 3.
	  	Miscellaneous	  	 	15	 
		  	3.1	  	Successors and Assigns	  	 	15	 
		  	3.2	  	Governing Law	  	 	15	 
		  	3.3	  	Counterparts; Facsimile	  	 	16	 
		  	3.4	  	Titles and Subtitles	  	 	16	 
		  	3.5	  	Notices	  	 	16	 
		  	3.6	  	Amendments and Waivers	  	 	16	 
		  	3.7	  	Severability	  	 	17	 
		  	3.8	  	Aggregation of Shares	  	 	17	 
		  	3.9	  	Entire Agreement	  	 	17	 
		  	3.10	  	Delays or Omissions	  	 	17	 
		  	3.11	  	Prior Agreement Superseded	  	 	17	 
		  	3.12	  	Consent to Jurisdiction	  	 	17	 

 Schedule A - Schedule of Investors 

Schedule B - Schedule of Key Holders 

  
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 AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT 

THIS AMENDED AND RESTATED REGISTRATION RIGHTS AGREEMENT (“Agreement”) is made as of April 26, 2018, by and among
Alector, Inc., a Delaware corporation (the “Company”), and each of the investors listed on Schedule A hereto, each of which is referred to in this Agreement as an “Investor”, and each of
the stockholders listed on Schedule B hereto, each of whom is referred to herein as a “Key Holder”. Capitalized terms used herein without definition shall, unless otherwise indicated, have the meaning
specified in the Company’s Certificate of Incorporation, as may be amended or restated from time to time. 
 RECITALS 

WHEREAS, the Company and certain of the Investors are parties to the Series E Preferred Stock Purchase Agreement of even date herewith
(the “Purchase Agreement”); 
 WHEREAS, the Company, certain of the Investors and Key Holders have previously
entered into that certain Registration Rights Agreement dated as of October 13, 2017 (the “Prior Agreement”); 

WHEREAS, the parties hereto constitute the requisite parties to amend and restate the Prior Agreement; and 

WHEREAS, to induce certain Investors to enter into the Purchase Agreement and purchase shares of Series E Preferred Stock thereunder,
the Company and the undersigned Investors and Key Holders desire to amend and restate the Prior Agreement and to accept the rights and obligations created pursuant hereto in lieu of the rights and obligations created under the Prior Agreement. 

NOW, THEREFORE, the parties hereby agree as follows: 

1. Definitions. For purposes of this Agreement: 

1.1 “Affiliate” means, with respect to any specified Person, any other Person who or which, directly or indirectly, controls,
is controlled by, or is under common control with such specified Person, including without limitation any general partner, officer, director, or manager of such Person and any venture capital fund now or hereafter existing that is controlled by one
or more general partners or managing members of, or shares the same management company with, such Person. 
 1.2 “Board of
Directors” means the Board of Directors of the Company. 
 1.3 “Damages” means any loss, damage, or liability
(joint or several) to which a party hereto may become subject under the Securities Act, the Exchange Act, or other federal or state law, insofar as such loss, damage, or liability (or any action in respect thereof) arises out of or is based upon:
(i) any untrue statement or alleged untrue statement of a material fact contained in any registration statement of the Company, including any preliminary prospectus or final prospectus contained therein or any amendments or supplements thereto;
(ii) an omission or alleged omission to state therein a material fact required to be stated therein, 

 
or necessary to make the statements therein not misleading; or (iii) any violation or alleged violation by the indemnifying party (or any of its agents or Affiliates) of the
Securities Act, the Exchange Act, any state securities law, or any rule or regulation promulgated under the Securities Act, the Exchange Act, or any state securities law. 

1.4 “Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated
thereunder. 
 1.5 “Excluded Registration” means: (i) a registration relating to the sale of securities to employees
of, or other individuals providing services to, the Company or a subsidiary pursuant to a stock option, stock purchase, or similar plan; (ii) a registration relating to an SEC Rule 145 transaction; (iii) a registration on any form that
does not include substantially the same information as would be required to be included in a registration statement covering the sale of the Registrable Securities; or (iv) a registration in which the only Common Stock being registered is
Common Stock issuable upon conversion of debt securities that are also being registered. 
 1.6 “Form S-1” means such registration form under the Securities Act as in effect on the date hereof or any successor registration form under the Securities Act subsequently adopted by the SEC. 

1.7 “Form S-3” means such registration form under the Securities Act as in
effect on the date hereof or any registration form under the Securities Act subsequently adopted by the SEC that permits incorporation of substantial information by reference to other documents filed by the Company with the SEC. 

1.8 “Holder” means any holder of Registrable Securities who is a party to this Agreement. 

1.9 “Immediate Family Member” means a child, stepchild, grandchild, parent, stepparent, grandparent, spouse, sibling, mother-in-law, father-in-law,
son-in-law, daughter-in-law, brother-in-law, or sister-in-law, including adoptive relationships, of a natural person referred to herein. 

1.10 “Initiating Holders” means, collectively, Holders who properly initiate a registration request under this Agreement.

 1.11 “IPO” means the Company’s first underwritten public offering of its Common Stock under the Securities Act.

 1.12 “Key Holder Registrable Securities” means (i) the Common Stock now owned or subsequently acquired by the Key
Holders, and (ii) any Common Stock issued as (or issuable upon the conversion or exercise of any warrant, right, or other security that is issued as) a dividend or other distribution with respect to, or in exchange for or in replacement of such
stock. 
 1.13 “Person” means any individual, corporation, partnership, trust, limited liability company, association or
other entity. 

  
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 1.14 “Preferred Registrable Securities” means Registrable Securities
exclusive of Key Holder Registrable Securities. 
 1.15 “Preferred Stock” means the Company’s Series A-1 Preferred Stock, Series A-2 Preferred Stock, Series B Preferred Stock, Series C Preferred Stock, Series D Preferred Stock and Series E Preferred Stock. 

1.16 “Registrable Securities” means: (i) any stock issued or issuable (directly or indirectly) upon
conversion and/or exercise of any other securities of the Company, acquired by the Investors prior to or after the date hereof; (ii) the Key Holder Registrable Securities, provided, however, that such Holders shall not be
deemed Holders for the purposes of Sections 2.10 and 3.6; and (iii) any Common Stock issued as (or issuable upon the conversion or exercise of any warrant, right, or other security that is issued as) a dividend
or other distribution with respect to, or in exchange for or in replacement of, the stock referenced in clause (i) above; excluding in all cases, however, any Registrable Securities sold by a Person in a transaction in which the applicable
rights under this Agreement are not assigned pursuant to Section 3.1, and excluding for purposes of Section 2 any stock for which registration rights have terminated pursuant to
Section 2.13 of this Agreement. 
 1.17 “Registrable Securities then outstanding” means the
number of shares of stock determined by adding the number of outstanding Common Stock that are Registrable Securities and the number of Common Stock issuable (directly or indirectly) pursuant to then exercisable and/or convertible securities that
are Registrable Securities. 
 1.18 “Requisite Holders” means Holders of a majority of the Registrable Securities then
outstanding that comprise shares of Common Stock issued or issuable upon the conversion of shares of Series A-1 Preferred Stock, Series A-2 Preferred Stock, Series B
Preferred Stock, Series C Preferred Stock, Series D Preferred Stock and Series E Preferred Stock, together with any Common Stock issued as (or issuable upon the conversion or exercise of any warrant, right, or other security that is issued as)
a dividend or other distribution with respect to, or in exchange for, or in replacement of, the foregoing shares. 
 1.19
“Restricted Securities” means the securities of the Company required to bear the legend set forth in Section 2.12(b) hereof. 

1.20 “SEC” means the Securities and Exchange Commission. 

1.21 “SEC Rule 144” means Rule 144 promulgated by the SEC under the Securities Act. 

1.22 “SEC Rule 145” means Rule 145 promulgated by the SEC under the Securities Act. 

1.23 “Securities Act” means the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder.

 1.24 “Selling Expenses” means all underwriting discounts, selling commissions, and stock transfer taxes applicable to
the sale of Registrable Securities, and fees and disbursements of counsel for any Holder, except for the fees and disbursements of one counsel to the selling Holders borne and paid by the Company as provided in Section 2.6.

  
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 1.25 “Securities Act” means the Securities Act of 1933, as amended, and the
rules and regulations promulgated thereunder. 
 1.26 “Series A-1 Preferred Stock”
means shares of the Company’s Series A-1 Preferred Stock, par value $0.0001 per share. 
 1.27
“Series A-2 Preferred Stock” means shares of the Company’s Series A-2 Preferred Stock, par value $0.0001 per share. 

1.28 “Series B Preferred Stock” means shares of the Company’s Series B Preferred Stock, par value $0.0001 per share.

 1.29 “Series C Preferred Stock” means shares of the Company’s Series C Preferred Stock, par value $0.0001 per
share. 
 1.30 “Series D Preferred Stock” means shares of the Company’s Series D Preferred Stock, par value $0.0001
per share. 
 1.31 “Series E Preferred Stock” means shares of the Company’s Series E Preferred Stock, par value
$0.0001 per share. 
 2. Registration Rights. The Company covenants and agrees as follows: 

2.1 Demand Registration. 

(a) Form S-1 Demand. If at any time after the earlier of (i) three (3) years after
the date of this Agreement or (ii) one hundred eighty (180) days after the effective date of the registration statement for the IPO, the Company receives a request from the Requisite Holders that the Company file a Form S-1 registration statement with respect to at least 25% of the Registrable Securities then outstanding (or a lesser percent for which the anticipated aggregate offering price, net of Selling Expenses, would
be at least $15 million), then the Company shall: (i) within ten (10) days after the date such request is given, give notice thereof (the “Demand Notice”) to all Holders other than the Initiating Holders; and (ii) as
soon as practicable, and in any event within sixty (60) days after the date such request is given by the Initiating Holders, file a Form S-1 registration statement under the Securities Act covering all
Registrable Securities that the Initiating Holders requested to be registered and any additional Registrable Securities requested to be included in such registration by any other Holders, as specified by notice given by each such Holder to the
Company within twenty (20) days of the date the Demand Notice is given, and in each case, subject to the limitations of Section 2.1(c) and Section 2.3. 

(b) Form S-3 Demand. If at any time when it is eligible to use a Form S-3 registration statement, the Company receives a request from Holders of at least thirty percent (30%) of the Preferred Registrable Securities then outstanding that the Company file a Form S-3 registration statement with respect to outstanding Registrable Securities for which the 

  
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anticipated aggregate offering price, net of Selling Expenses, would be at least $3 million, then the Company shall: (i) within ten (10) days after the date such request is given,
give a Demand Notice to all Holders other than the Initiating Holders; and (ii) as soon as practicable, and in any event within sixty (60) days after the date such request is given by the Initiating Holders, file a Form S-3 registration statement under the Securities Act covering all Registrable Securities that the Initiating Holders requested to be registered and any additional Registrable Securities requested to be included in
such registration by any other Holders, as specified by notice given by each such Holder to the Company within twenty (20) days of the date the Demand Notice is given, and in each case, subject to the limitations of Section 2.1(c)
and Section 2.3. 
 (c) Notwithstanding the foregoing obligations, if the Company furnishes to Holders requesting a
registration pursuant to this Section 2.1 a certificate signed by the Company’s chief executive officer stating that in the good faith judgment of the Board of Directors it would be materially detrimental to the Company and its
stockholders for such registration statement to either become effective or remain effective for as long as such registration statement otherwise would be required to remain effective, because such action would (i) materially interfere
with a significant acquisition, corporate reorganization, or other similar transaction involving the Company; (ii) require premature disclosure of material information that the Company has a bona fide business purpose for preserving as
confidential; or (iii) render the Company unable to comply with requirements under the Securities Act or Exchange Act, then the Company shall have the right to defer taking action with respect to such filing for a period of not more than
sixty (60) days after the request of the Initiating Holders is given; provided, however, that the Company may not invoke this right more than once in any twelve (12) month period; and provided further that the
Company shall not register any securities for its own account or that of any other Holder during such sixty (60) day period other than pursuant to a registration relating to the sale of securities to employees of the Company or a
subsidiary pursuant to a stock option, stock purchase, or similar plan; a registration on any form that does not include substantially the same information as would be required to be included in a registration statement covering the sale of the
Registrable Securities; or a registration in which the only Common Stock being registered are Common Stock issuable upon conversion of debt securities that are also being registered. 

(d) The Company shall not be obligated to effect, or to take any action to effect, any registration pursuant to Section 2.1(a):
(i) during the period that is sixty (60) days before the Company’s good faith estimate of the date of filing of, and ending on a date that is one hundred eighty (180) days after the effective date of, a
Company-initiated registration, provided, that the Company is actively employing in good faith commercially reasonable efforts to cause such registration statement to become effective; (ii) after the Company has effected two
(2) registrations pursuant to Section 2.1(a); or (iii) if the Initiating Holders propose to dispose of Registrable Securities that may be immediately registered on Form S-3
pursuant to a request made pursuant to Section 2.1(b). The Company shall not be obligated to effect, or to take any action to effect, any registration pursuant to Section 2.1(b): (A) during the period that is thirty
(30) days before the Company’s good faith estimate of the date of filing of, and ending on a date that is ninety (90) days after the effective date of, a Company-initiated registration, provided, that the Company is actively employing
in good faith commercially reasonable efforts to cause such registration statement to become effective; or (B) if the Company has effected two registrations pursuant to Section 2.1(b) within the twelve (12) month period
immediately 

  
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preceding the date of such request. A registration shall not be counted as “effected” for purposes of this Section 2.1(d) until such time as the applicable registration
statement has been declared effective by the SEC, unless the Initiating Holders withdraw their request for such registration, elect not to pay the registration expenses therefor, and forfeit their right to one demand registration statement pursuant
to Section 2.6, in which case such withdrawn registration statement shall be counted as “effected” for purposes of this Section 2.1(d).  

2.2 Company Registration. If the Company proposes to register (including, for this purpose, a registration effected by the Company for
stockholders other than the Holders) any of its securities under the Securities Act in connection with the public offering of such securities solely for cash (other than in an Excluded Registration), the Company shall, at such time, promptly give
each Holder notice of such registration. Upon the request of each Holder given within twenty (20) days after such notice is given by the Company, the Company shall, subject to the provisions of Section 2.3, cause to be
registered all of the Registrable Securities that each such Holder has requested to be included in such registration. The Company shall have the right to terminate or withdraw any registration initiated by it under this Section 2.2
before the effective date of such registration, whether or not any Holder has elected to include Registrable Securities in such registration. The expenses (other than Selling Expenses) of such withdrawn registration shall be borne by the Company in
accordance with Section 2.6. 
 2.3 Underwriting Requirements. 

(a) If, pursuant to Section 2.1, the Initiating Holders intend to distribute the Registrable Securities covered by
their request by means of an underwriting, they shall so advise the Company as a part of their request made pursuant to Section 2.1, and the Company shall include such information in the Demand Notice. The underwriter(s) will be selected
by the Company and shall be reasonably acceptable to a majority in interest of the Initiating Holders. In such event, the right of any Holder to include such Holder’s Registrable Securities in such registration shall be conditioned upon such
Holder’s participation in such underwriting and the inclusion of such Holder’s Registrable Securities in the underwriting to the extent provided herein. All Holders proposing to distribute their securities through such underwriting shall
(together with the Company as provided in Section 2.4(e)) enter into an underwriting agreement in customary form with the underwriter(s) selected for such underwriting. Notwithstanding any other provision of this Section 2.3,
if the managing underwriter(s) advise(s) the Initiating Holders in writing that marketing factors require a limitation on the number of shares to be underwritten, then the Initiating Holders shall so advise all Holders of Registrable Securities that
otherwise would be underwritten pursuant hereto, and the number of Registrable Securities that may be included in the underwriting shall be allocated among such Holders of Registrable Securities, including the Initiating Holders, in proportion (as
nearly as practicable) to the number of Registrable Securities owned by each Holder or in such other proportion as shall mutually be agreed to by all such selling Holders; provided, however, that the number of Registrable Securities held by
the Holders to be included in such underwriting shall not be reduced unless all other securities are first entirely excluded from the underwriting. To facilitate the allocation of shares in accordance with the above provisions, the Company or the
underwriters may round the number of shares allocated to any Holder to the nearest one hundred (100) shares. 

  
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 (b) In connection with any offering involving an underwriting of the securities of the
Company pursuant to Section 2.2, the Company shall not be required to include any of the Holders’ Registrable Securities in such underwriting unless the Holders accept the terms of the underwriting as agreed upon between the Company
and its underwriters, and then only in such quantity as the underwriters in their sole discretion determine will not jeopardize the success of the offering by the Company. If the total number of securities, including Registrable Securities,
requested by stockholders to be included in such offering exceeds the number of securities to be sold (other than by the Company) that the underwriters in their reasonable discretion determine is compatible with the success of the offering, then the
Company shall be required to include in the offering only that number of such securities, including Registrable Securities, which the underwriters and the Company in their sole discretion determine will not jeopardize the success of the offering. If
the underwriters determine that less than all of the Registrable Securities requested to be registered can be included in such offering, then the Registrable Securities that are included in such offering shall be allocated among the selling Holders
in proportion (as nearly as practicable to) the number of Registrable Securities owned by each selling Holder or in such other proportions as shall mutually be agreed to by all such selling Holders. To facilitate the allocation of shares in
accordance with the above provisions, the Company or the underwriters may round the number of shares allocated to any Holder to the nearest one hundred (100) shares. Notwithstanding the foregoing, in no event shall (i) the
number of Registrable Securities included in the offering be reduced unless all other securities (other than securities to be sold by the Company) are first entirely excluded from the offering, (ii) the number of Registrable Securities
included in the offering be reduced below thirty percent (30%) of the total number of securities included in such offering, unless such offering is the IPO, in which case the selling Holders may be excluded further if the underwriters make the
determination described above and no other stockholder’s securities are included in such offering, or (iii) notwithstanding (ii) above, any Preferred Registrable Securities be excluded from underwriting unless all Key Holder
Registrable Securities are first excluded from such offering. For purposes of the provisions in this Section 2.3(b) and Section 2.3(a) concerning apportionment, for any selling Holder that is a partnership, limited liability
company, or corporation, the partners, members, retired partners, retired members, members, and Affiliates of such Holder, or the estates and Immediate Family Members of any such partners, retired partners, members, and retired members and any
trusts for the benefit of any of the foregoing Persons, shall be deemed to be a single “selling Holder,” and any pro rata reduction with respect to such “selling Holder” shall be based upon the aggregate number of Registrable
Securities owned by all Persons included in such “selling Holder,” as defined in this sentence. 
 (c) For purposes of
Section 2.1, a registration shall not be counted as “effected” if, as a result of an exercise of the underwriter’s cutback provisions in Section 2.3(a), fewer than fifty percent (50%) of the total number of
Registrable Securities that Holders have requested to be included in such registration statement are actually included. 

  
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 2.4 Obligations of the Company. Whenever required under this Section 2 to
effect the registration of any Registrable Securities, the Company shall, as expeditiously as reasonably possible: 
 (a) prepare and file
with the SEC a registration statement with respect to such Registrable Securities and use its commercially reasonable efforts to cause such registration statement to become effective and, upon the request of the Holders of a majority of the
Registrable Securities registered thereunder, keep such registration statement effective for a period of up to one hundred twenty (120) days or, if earlier, until the distribution contemplated in the registration statement has been
completed; provided, however, that (i) such one hundred twenty (120) day period shall be extended for a period of time equal to the period the Holder refrains, at the request of an underwriter of Common Stock (or other
securities) of the Company, from selling any securities included in such registration, and (ii) in the case of any registration of Registrable Securities on Form S-3 that are intended to be offered
on a continuous or delayed basis, subject to compliance with applicable SEC rules, such one hundred twenty (120) day period shall be extended for up to sixty (60) days, if necessary, to keep the registration statement
effective until all such Registrable Securities are sold; 
 (b) prepare and file with the SEC such amendments and supplements to such
registration statement, and the prospectus used in connection with such registration statement, as may be necessary to comply with the Securities Act in order to enable the disposition of all securities covered by such registration statement; 

(c) furnish to the selling Holders such numbers of copies of a prospectus, including a preliminary prospectus, as required by the Securities
Act, and such other documents as the Holders may reasonably request in order to facilitate their disposition of their Registrable Securities; 

(d) use its commercially reasonable efforts to register and qualify the securities covered by such registration statement under other
securities or blue-sky laws of such jurisdictions as shall be reasonably requested by the selling Holders; provided that the Company shall not be required to qualify to do business in any such states or
jurisdictions, except as may be required by the Securities Act; 
 (e) in the event of any underwritten public offering, enter into and
perform its obligations under an underwriting agreement, in usual and customary form, with the underwriter(s) of such offering; 
 (f) use
its commercially reasonable efforts to cause all such Registrable Securities covered by such registration statement to be listed on a national securities exchange or trading system and each securities exchange and trading system (if any) on which
similar securities issued by the Company are then listed; 
 (g) provide a transfer agent and registrar for all Registrable Securities
registered pursuant to this Agreement and provide a CUSIP number for all such Registrable Securities, in each case not later than the effective date of such registration; 

(h) promptly make available for inspection by the selling Holders, any managing underwriter(s) participating in any disposition pursuant to
such registration statement, and any attorney or accountant or other agent retained by any such underwriter or selected by the selling Holders, all financial and other records, pertinent limited liability company documents, and properties of the
Company, and cause the Company’s officers, directors, employees, and independent accountants to supply all information reasonably requested by any such seller, underwriter, attorney, accountant, or agent, in each case, as necessary or advisable
to verify the accuracy of the information in such registration statement and to conduct appropriate due diligence in connection therewith; 

  
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 (i) notify each selling Holder, promptly after the Company receives notice thereof, of the
time when such registration statement has been declared effective or a supplement to any prospectus forming a part of such registration statement has been filed; and 

(j) after such registration statement becomes effective, notify each selling Holder of any request by the SEC that the Company amend or
supplement such registration statement or prospectus. 
 2.5 Furnish Information. It shall be a condition precedent to the
obligations of the Company to take any action pursuant to this Section 2 with respect to the Registrable Securities of any selling Holder that such Holder shall furnish to the Company such information regarding itself, the Registrable
Securities held by it, and the intended method of disposition of such securities as is reasonably required to effect the registration of such Holder’s Registrable Securities. 

2.6 Expenses of Registration. All expenses (other than Selling Expenses) incurred in connection with registrations, filings, or
qualifications pursuant to Section 2, including all registration, filing, and qualification fees; printers’ and accounting fees; fees and disbursements of counsel for the Company; and the reasonable fees and disbursements, not to
exceed $50,000, of one counsel for the selling Holders, shall be borne and paid by the Company; provided, however, that the Company shall not be required to pay for any expenses of any registration proceeding begun pursuant to
Section 2.1 if the registration request is subsequently withdrawn at the request of the Requisite Holders to be registered (in which case all selling Holders shall bear such expenses pro rata based upon the number of
Registrable Securities that were to be included in the withdrawn registration), unless the Requisite Holders agree to forfeit their right to one registration pursuant to Section 2.1(a) or Section 2.1(b),
as the case may be; provided further that if, at the time of such withdrawal, the Holders have learned of a material adverse change in the condition, business, or prospects of the Company from that known to the Holders at the time of their
request and have withdrawn the request with reasonable promptness after learning of such information, then the Holders shall not be required to pay any of such expenses and shall not forfeit their right to one registration pursuant to
Section 2.1(a) or Section 2.1(b). All Selling Expenses relating to Registrable Securities registered pursuant to this Section 2 shall be borne and paid by the Holders pro rata on the basis of the number of
Registrable Securities registered on their behalf. 
 2.7 Delay of Registration. No Holder shall have any right to obtain or seek an
injunction restraining or otherwise delaying any registration pursuant to this Agreement as the result of any controversy that might arise with respect to the interpretation or implementation of this Section 2. 

  
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 2.8 Indemnification. If any Registrable Securities are included in a registration
statement under this Section 2: 
 (a) To the extent permitted by law, the Company will indemnify and hold harmless: each
selling Holder, and the partners, members, officers, directors, and members of each such Holder; legal counsel and accountants for each such Holder; any underwriter (as defined in the Securities Act) for each such Holder; and each Person, if any,
who controls such Holder or underwriter within the meaning of the Securities Act or the Exchange Act, against any Damages, and the Company will pay to each such Holder, underwriter, controlling Person, or other aforementioned Person any legal or
other expenses reasonably incurred thereby in connection with investigating or defending any claim or proceeding from which Damages may result, as such expenses are incurred; provided, however, that the indemnity agreement contained in this
Section 2.8(a) shall not apply to amounts paid in settlement of any such claim or proceeding if such settlement is effected without the consent of the Company, which consent shall not be unreasonably withheld, nor shall the Company be
liable for any Damages to the extent that they arise out of or are based upon actions or omissions made in reliance upon and in conformity with written information furnished by or on behalf of any such Holder, underwriter, controlling Person, or
other aforementioned Person expressly for use in connection with such registration. 
 (b) To the extent permitted by law, each selling
Holder, severally and not jointly, will indemnify and hold harmless the Company, and each of its directors, each of its officers who has signed the registration statement, each Person (if any), who controls the Company within the meaning of the
Securities Act, legal counsel and accountants for the Company, any underwriter (as defined in the Securities Act), any other Holder selling securities in such registration statement, and any controlling Person of any such underwriter or other
Holder, against any Damages, in each case only to the extent that such Damages arise out of or are based upon actions or omissions made in reliance upon and in conformity with written information furnished by or on behalf of such selling Holder
expressly for use in connection with such registration; and each such selling Holder will pay to the Company and each other aforementioned Person any legal or other expenses reasonably incurred thereby in connection with investigating or defending
any claim or proceeding from which Damages may result, as such expenses are incurred; provided, however, that the indemnity agreement contained in this Section 2.8(b) shall not apply to amounts paid in settlement of any such claim
or proceeding if such settlement is effected without the consent of the Holder, which consent shall not be unreasonably withheld; and provided further that in no event shall the aggregate amounts payable by any Holder by way of indemnity or
contribution under this Section 2.8(b) exceed the proceeds from the offering received by such Holder (net of any Selling Expenses paid by such Holder), except in the case of fraud or willful misconduct by such Holder. 

(c) Promptly after receipt by an indemnified party under this Section 2.8 of notice of the commencement of any action (including
any governmental action) for which a party may be entitled to indemnification hereunder, such indemnified party will, if a claim in respect thereof is to be made against any indemnifying party under this Section 2.8, give the
indemnifying party notice of the commencement thereof. The indemnifying party shall have the right to participate in such action and, to the extent the indemnifying party so desires, participate jointly with any other indemnifying party to which
notice has been given, and to 

  
 10 

 
assume the defense thereof with counsel mutually satisfactory to the parties; provided, however, that an indemnified party (together with all other indemnified parties that may be
represented without conflict by one counsel) shall have the right to retain one separate counsel, with the fees and expenses to be paid by the indemnifying party, if representation of such indemnified party by the counsel retained by the
indemnifying party would be inappropriate due to actual or potential differing interests between such indemnified party and any other party represented by such counsel in such action. The failure to give notice to the indemnifying party within a
reasonable time of the commencement of any such action shall relieve such indemnifying party of any liability to the indemnified party under this Section 2.8 to the extent that such failure materially prejudices the indemnifying
party’s ability to defend such action. The failure to give notice to the indemnifying party will not relieve it of any liability that it may have to any indemnified party otherwise than under this Section 2.8. 

(d) Notwithstanding anything else herein to the contrary, the foregoing indemnity agreements of the Company and the selling
Holders are subject to the condition that, insofar as they relate to any Damages arising from any untrue statement or alleged untrue statement of a material fact contained in, or omission or alleged omission of a material fact from, a preliminary
prospectus (or necessary to make the statements therein not misleading) that has been corrected in the form of prospectus included in the registration statement at the time it becomes effective, or any amendment or supplement thereto filed with the
SEC pursuant to Rule 424(b) under the Securities Act (the “Final Prospectus”), such indemnity agreement shall not inure to the benefit of any Person if a copy of the Final Prospectus was furnished to the indemnified party and such
indemnified party failed to deliver, at or before the confirmation of the sale of the shares registered in such offering, a copy of the Final Prospectus to the Person asserting the loss, liability, claim, or damage in any case in which such delivery
was required by the Securities Act. 
 (e) To provide for just and equitable contribution to joint liability under the Securities Act in
any case in which either (i) any party otherwise entitled to indemnification hereunder makes a claim for indemnification pursuant to this Section 2.8 but it is judicially determined (by the entry of a final judgment or decree
by a court of competent jurisdiction and the expiration of time to appeal or the denial of the last right of appeal) that such indemnification may not be enforced in such case, notwithstanding the fact that this Section 2.8 provides for
indemnification in such case, or (ii) contribution under the Securities Act may be required on the part of any party hereto for which indemnification is provided under this Section 2.8, then, and in each such case, such
parties will contribute to the aggregate losses, claims, damages, liabilities, or expenses to which they may be subject (after contribution from others) in such proportion as is appropriate to reflect the relative fault of each of the indemnifying
party and the indemnified party in connection with the statements, omissions, or other actions that resulted in such loss, claim, damage, liability, or expense, as well as to reflect any other relevant equitable considerations. The relative fault of
the indemnifying party and of the indemnified party shall be determined by reference to, among other things, whether the untrue or allegedly untrue statement of a material fact, or the omission or alleged omission of a material fact, relates to
information supplied by the indemnifying party or by the indemnified party and the parties’ relative intent, knowledge, access to information, and opportunity to correct or prevent such statement or omission; provided, however, that, in
any such case, (x) no Holder will be required to contribute any amount in excess of the public offering price of all such 

  
 11 

 
Registrable Securities offered and sold by such Holder pursuant to such registration statement, and (y) no Person guilty of fraudulent misrepresentation (within the meaning of
Section 11(f) of the Securities Act) will be entitled to contribution from any Person who was not guilty of such fraudulent misrepresentation; and provided further that in no event shall a Holder’s liability pursuant to this
Section 2.8(e), when combined with the amounts paid or payable by such Holder pursuant to Section 2.8(b), exceed the proceeds from the offering received by such Holder (net of any Selling Expenses paid by such Holder), except
in the case of willful misconduct or fraud by such Holder. 
 (f) Notwithstanding the foregoing, to the extent that the provisions on
indemnification and contribution contained in the underwriting agreement entered into in connection with the underwritten public offering are in conflict with the foregoing provisions, the provisions in the underwriting agreement shall control. 

(g) Unless otherwise superseded by an underwriting agreement entered into in connection with the underwritten public offering, the
obligations of the Company and Holders under this Section 2.8 shall survive the completion of any offering of Registrable Securities in a registration under this Section 2, and otherwise shall survive the termination of this
Agreement. 
 2.9 Reports Under Exchange Act. With a view to making available to the Holders the benefits of SEC Rule 144 and any
other rule or regulation of the SEC that may at any time permit a Holder to sell securities of the Company to the public without registration or pursuant to a registration on Form S-3, the Company shall: 

(a) make and keep available adequate current public information, as those terms are understood and defined in SEC Rule 144, at all times after
the effective date of the registration statement filed by the Company for the IPO; 
 (b) use commercially reasonable efforts to file with
the SEC in a timely manner all reports and other documents required of the Company under the Securities Act and the Exchange Act (at any time after the Company has become subject to such reporting requirements); and 

(c) furnish to any Holder, so long as the Holder owns any Registrable Securities, forthwith upon request: (i) to the extent accurate, a
written statement by the Company that it has complied with the reporting requirements of SEC Rule 144 (at any time after ninety (90) days after the effective date of the registration statement filed by the Company for the IPO), the
Securities Act, and the Exchange Act (at any time after the Company has become subject to such reporting requirements), or that it qualifies as a registrant whose securities may be resold pursuant to Form S-3
(at any time after the Company so qualifies); (ii) a copy of the most recent annual or quarterly report of the Company and such other reports and documents so filed by the Company; and (iii) such other information as may be
reasonably requested in availing any Holder of any rule or regulation of the SEC that permits the selling of any such securities without registration (at any time after the Company has become subject to the reporting requirements under the Exchange
Act) or pursuant to Form S-3 (at any time after the Company so qualifies to use such form). 

  
 12 

 2.10 Limitations on Subsequent Registration Rights. From and after the date of this
Agreement, the Company shall not, without the prior written consent of the Requisite Holders, enter into any agreement with any holder or prospective holder of any securities of the Company that would allow such holder or prospective holder
(i) to include such securities in any registration unless, under the terms of such agreement, such holder or prospective holder may include such securities in any such registration only to the extent that the inclusion of such securities
will not reduce the number of the Registrable Securities of the Holders that are included or (ii) to initiate a demand registration of any securities held by such holder or prospective holder. 

2.11 “Market Stand-off” Agreement. Each Holder hereby
agrees that it will not, without the prior written consent of the managing underwriter, during the period commencing on the date of the final prospectus relating to the IPO, and ending on the date specified by the Company and the managing
underwriter (such period not to exceed one hundred eighty (180) days, or such other period as may be reasonably requested by the Company or an underwriter to accommodate regulatory restrictions on (1) the publication or other
distribution of research reports and (2) analyst recommendations and opinions, including, but not limited to, the restrictions contained in FINRA Rule 2711(f)(4) or NYSE Rule 472(f)(4), or any successor provisions or amendments thereto),
(i) lend, offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right, or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly,
any Common Stock or any securities convertible into or exercisable or exchangeable (directly or indirectly) for Common Stock held immediately before the effective date of the registration statement for such offering or (ii) enter into
any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of such securities, whether any such transaction described in clause (i) or (ii) above is to be settled by
delivery of Common Stock or other securities, in cash, or otherwise. The foregoing provisions of this Section 2.11 shall not apply to the sale of any shares to an underwriter pursuant to an underwriting agreement, and shall
be applicable to the Holders of Preferred Registrable Securities only if all officers, directors and stockholders individually owning more than one percent (1%) of the outstanding Common Stock (after giving effect to conversion into Common Stock of
all outstanding Preferred Stock) are subject to the same restrictions. The underwriters in connection with such registration are intended third party beneficiaries of this Section 2.11 and shall have the right, power, and authority to
enforce the provisions hereof as though they were a party hereto. Each Holder further agrees to execute such agreements as may be reasonably requested by the underwriters in connection with such registration that are consistent with this
Section 2.11 or that are necessary to give further effect thereto. Any discretionary waiver or termination of the restrictions of any or all of such agreements by the Company or the underwriters shall apply pro rata to all Holders of
Preferred Registrable Securities subject to such agreements, based on the number of shares subject to such agreements. 
 2.12
Restrictions on Transfer. 
 (a) The Preferred Stock and the Registrable Securities shall not be sold, pledged, or otherwise
transferred, and the Company shall not recognize any such sale, pledge, or transfer, except upon the conditions specified in this Agreement, which conditions are intended to ensure compliance with the provisions of the Securities Act. A transferring
Holder will cause any proposed purchaser, pledgee, or transferee of the Preferred Stock and the Registrable Securities held by such Holder to agree to take and hold such securities subject to the provisions and upon the conditions specified in this
Agreement. 

  
 13 

 (b) Each certificate or instrument representing (i) the Preferred Stock,
(ii) the Registrable Securities, and (iii) any other securities issued in respect of the securities referenced in clauses (i) and (ii), upon any stock split, stock dividend, recapitalization, merger,
consolidation, or similar event, shall (unless otherwise permitted by the provisions of Section 2.12(c)) be stamped or otherwise imprinted with a legend substantially in the following form: 

THE SECURITIES REPRESENTED HEREBY HAVE BEEN ACQUIRED FOR INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933. SUCH STOCK
MAY NOT BE SOLD, PLEDGED, OR TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR A VALID EXEMPTION FROM THE REGISTRATION AND PROSPECTUS DELIVERY REQUIREMENTS OF SAID ACT. 

THE SECURITIES REPRESENTED HEREBY MAY BE TRANSFERRED ONLY IN ACCORDANCE WITH THE TERMS OF AN AGREEMENT BETWEEN THE COMPANY AND THE HOLDERS, A
COPY OF WHICH IS ON FILE WITH THE SECRETARY OF THE COMPANY. 
 The Holders consent to the Company making a notation in its records and giving instructions
to any transfer agent of the Restricted Securities in order to implement the restrictions on transfer set forth in this Section 2.12. 

(c) The holder of each certificate representing Restricted Securities, by acceptance thereof, agrees to comply in all respects with the
provisions of this Section 2. Before any proposed sale, pledge, or transfer of any Restricted Securities, unless there is in effect a registration statement under the Securities Act covering the proposed transaction, the Holder thereof
shall give notice to the Company of such Holder’s intention to effect such sale, pledge, or transfer. Each such notice shall describe the manner and circumstances of the proposed sale, pledge, or transfer in sufficient detail and, if reasonably
requested by the Company, shall be accompanied at such Holder’s expense by either: (i) a written opinion of legal counsel who shall, and whose legal opinion shall, be reasonably satisfactory to the Company, addressed to the Company,
to the effect that the proposed transaction may be effected without registration under the Securities Act; (ii) a “no action” letter from the SEC to the effect that the proposed sale, pledge, or transfer of such Restricted
Securities without registration will not result in a recommendation by the staff of the SEC that action be taken with respect thereto; or (iii) any other evidence reasonably satisfactory to counsel to the Company to the effect that the
proposed sale, pledge, or transfer of the Restricted Securities may be effected without registration under the Securities Act, whereupon the Holder of such Restricted Securities shall be entitled to sell, pledge, or transfer such Restricted
Securities in accordance with the terms of the notice given by the Holder to the Company. The Company will not require such a legal opinion or “no action” letter (x) in any transaction in compliance with SEC Rule 144 or
(y) in any transaction in which such Holder distributes Restricted Securities to an Affiliate of such Holder for no consideration; 

  
 14 

 
provided that each transferee agrees in writing to be subject to the terms of this Section 2.12. Each certificate or instrument evidencing the Restricted Securities transferred as
above provided shall bear, except if such transfer is made pursuant to SEC Rule 144, the appropriate restrictive legend set forth in Section 2.12(b), except that such certificate shall not bear such restrictive legend if, in
the opinion of counsel for such Holder and the Company, such legend is not required in order to establish compliance with any provisions of the Securities Act. 

2.13 Termination of Registration Rights. The right of any Holder to request registration or inclusion of Registrable Securities in any
registration pursuant to Section 2.1 or Section 2.2 shall terminate upon the earlier to occur of: 
 (a) the closing
of a Deemed Liquidation Event; and 
 (b) on the fifth (5th) anniversary of the IPO.

 3. Miscellaneous. 

3.1 Successors and Assigns. The rights under this Agreement may be assigned (but only with all related obligations) by a
Holder to a transferee of Registrable Securities that: (i) is an Affiliate, partner, member, limited partner, retired partner, retired member, or member of a Holder; (ii) is a Holder’s Immediate Family Member or trust
for the benefit of an individual Holder or one or more of such Holder’s Immediate Family Members; or (iii) after such transfer, holds at least 500,000 shares of Registrable Securities (subject to appropriate adjustment for stock
splits, stock dividends, combinations, and other recapitalizations); provided, however, that (x) the Company is, within a reasonable time after such transfer, furnished with written notice of the name and address of such transferee and
the Registrable Securities with respect to which such rights are being transferred; and (y) such transferee agrees in a written instrument delivered to the Company to be bound by and subject to the terms and conditions of this Agreement,
including the provisions of Section 2.11. For the purposes of determining the number of shares of Registrable Securities held by a transferee, the holdings of a transferee: (1) that is an Affiliate, limited partner, retired
partner, member, retired member, or member of a Holder; (2) who is a Holder’s Immediate Family Member; or (3) that is a trust for the benefit of an individual Holder or such Holder’s Immediate Family Member shall be
aggregated together and with those of the transferring Holder; provided further that all transferees who would not qualify individually for assignment of rights shall have a single attorney-in-fact for the purpose of exercising any rights, receiving
notices, or taking any action under this Agreement. The terms and conditions of this Agreement inure to the benefit of and are binding upon the respective successors and permitted assignees of the parties. Nothing in this Agreement, express or
implied, is intended to confer upon any party other than the parties hereto or their respective successors and permitted assignees any rights, remedies, obligations or liabilities under or by reason of this Agreement, except as expressly provided
herein. 
 3.2 Governing Law. This Agreement and any controversy arising out of or relating to this Agreement shall be governed by,
and construed in accordance with, the laws of the State of Delaware, without giving effect to any principles of conflicts of law that would require the application of the laws of any other jurisdiction. 

  
 15 

 3.3 Counterparts; Facsimile. This Agreement may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument. This Agreement may also be executed and delivered by facsimile signature and in two or more counterparts, each of which
shall be deemed an original, but all of which together shall constitute one and the same instrument. 
 3.4 Titles and Subtitles. The
titles and subtitles used in this Agreement are for convenience only and are not to be considered in construing or interpreting this Agreement. 

3.5 Notices. All notices and other communications given or made pursuant to this Agreement shall be in writing and shall be deemed
effectively given: (a) upon personal delivery to the party to be notified, (b) when sent by confirmed electronic mail or facsimile if sent during normal business hours of the recipient, and if not so confirmed, then on the
next business day, (c) five (5) days after having been sent by registered or certified mail, return receipt requested, postage prepaid, or (d) one (1) business day after deposit with a nationally
recognized overnight courier, specifying next business day delivery, with written verification of receipt. All communications shall be sent to the respective parties at their address as set forth on Schedule A hereto,
Schedule B hereto, or to the principal office of the Company and to the attention of the Chief Executive Officer, in the case of the Company, or to such email address, facsimile number, or address as subsequently modified by
written notice given in accordance with this Section 3.5. If notice is given to the Company, a copy (which shall not constitute notice) shall also be sent to Kingsley L. Taft, Esq., Goodwin Procter LLP, 100 Northern Avenue, Boston, MA
02210, email: ktaft@goodwinlaw.com. 
 3.6 Amendments and Waivers. Any term of this Agreement may be amended and the observance of
any term of this Agreement may be waived (either generally or in a particular instance, and either retroactively or prospectively) only with the written consent of the Company and the Requisite Holders; provided that the Company may in its
sole discretion waive compliance with Section 2.12(c) (and the Company’s failure to object promptly in writing after notification of a proposed assignment allegedly in violation of Section 2.12(c) shall be deemed to be a
waiver); and provided further that any provision hereof may be waived by any waiving party on such party’s own behalf, without the consent of any other party. Notwithstanding the foregoing, this Agreement may not be amended or terminated and
the observance of any term hereof may not be waived with respect to any Investor without the written consent of such Investor, unless such amendment, termination, or waiver applies to all Investors in the same fashion. Further, this Agreement may
not be amended, and no provision hereof may be waived, in each case, in any way which would adversely affect the rights of the Key Holders hereunder in a manner disproportionate to any adverse effect such amendment or waiver would have on the rights
of the Investors hereunder, without also the written consent of the holders of at least a majority of the Key Holder Registrable Securities which shall not be unreasonable withheld, conditioned or delayed. The Company shall give prompt notice of any
amendment or termination hereof or waiver hereunder to any party hereto that did not consent in writing to such amendment, termination, or waiver. Any amendment, termination, or waiver effected in accordance with this
Section 3.6 shall be binding on all parties hereto, regardless of whether any such party has consented thereto. No waivers of or exceptions to any term, condition, or provision of this Agreement, in any one or more
instances, shall be deemed to be or construed as a further or continuing waiver of any such term, condition, or provision. 

  
 16 

 3.7 Severability. In case any one or more of the provisions contained in this
Agreement is for any reason held to be invalid, illegal or unenforceable in any respect, such invalidity, illegality, or unenforceability shall not affect any other provision of this Agreement, and such invalid, illegal, or unenforceable provision
shall be reformed and construed so that it will be valid, legal, and enforceable to the maximum extent permitted by law. 
 3.8
Aggregation of Shares. All Registrable Securities held or acquired by Affiliates shall be aggregated together for the purpose of determining the availability of any rights under this Agreement. 

3.9 Entire Agreement. This Agreement (including any Schedules and Exhibits hereto) constitutes the full and entire understanding and
agreement among the parties with respect to the subject matter hereof, and any other written or oral agreement relating to the subject matter hereof existing between the parties is expressly canceled. 

3.10 Delays or Omissions. Except as set forth in Section 3.6 with respect to the Company’s failure to object promptly
in writing after notification of a proposed assignment allegedly in violation of Section 2.12(c), no delay or omission to exercise any right, power, or remedy accruing to any party under this Agreement, upon any breach or default of any
other party under this Agreement, shall impair any such right, power, or remedy of such nonbreaching or nondefaulting party, nor shall it be construed to be a waiver of or acquiescence to any such breach or default, or to any similar breach or
default thereafter occurring, nor shall any waiver of any single breach or default be deemed a waiver of any other breach or default theretofore or thereafter occurring. All remedies, whether under this Agreement or by law or otherwise afforded to
any party, shall be cumulative and not alternative. 
 3.11 Prior Agreement Superseded. Pursuant to Section 3.6 of the Prior
Agreement, the undersigned parties who are parties to such Prior Agreement hereby amend and restate the Prior Agreement to read in its entirety as set forth in this Agreement, all with the intent and effect that the Prior Agreement shall hereby be
terminated and entirely replaced and superseded by this Agreement. 
 3.12 Consent to Jurisdiction. For any action brought by a Key
Holder or Investor against the Company, or by the Company against any Key Holder or Investor, each of the parties hereto hereby consents to the non-exclusive jurisdiction of the courts of the State of
California in connection with any matter or dispute arising under this Agreement regarding the affairs of the Company. 
 [REMAINDER OF
PAGE INTENTIONALLY LEFT BLANK] 

  
 17 

 IN WITNESS WHEREOF, the parties have executed this Agreement as of the date first written
above. 
  

			
	COMPANY:
	
	ALECTOR, INC.
		
	By:	 	/s/ Arnon Rosenthal
	Name:	 	Arnon Rosenthal
	Title:	 	President and CEO

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	PVP VI (AIV) FEEDER CORP. HOLDING PARTNERSHIP, L.P.
		
	By:	 	Polaris Venture Management Co. VI, L.L.C.
		 	Its General Partner
		
	By:	 	/s/ Max Eisenberg
	Name:	 	Max Eisenberg
	Title:	 	Attorney-in-fact

  

			
	POLARIS VENTURE PARTNERS VI (AIV), L.P.
		
	By:	 	Polaris Venture Management Co. VI, L.L.C.
		 	Its General Partner
		
	By:	 	/s/ Max Eisenberg
	Name:	 	Max Eisenberg
	Title:	 	Attorney-in-fact

  

			
	POLARIS VENTURE PARTNERS VI, L.P.
		
	By:	 	Polaris Venture Management Co. VI, L.L.C.
		 	Its General Partner
		
	By:	 	/s/ Max Eisenberg
	Name:	 	Max Eisenberg
	Title:	 	Attorney-in-fact

  

			
	POLARIS VENTURE PARTNERS FOUNDERS’ FUND VI, L.P.
		
	By:	 	Polaris Venture Management Co. VI, L.L.C.
		 	Its General Partner
		
	By:	 	/s/ Max Eisenberg
	Name:	 	Max Eisenberg
	Title:	 	Attorney-in-fact

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	 INVESTORS:

	
	ORBIMED PRIVATE INVESTMENTS IV—AL
	(FEEDER), LP
		
	By:	 	OrbiMed Capital GP IV LLC, its General Partner
		
	By:	 	OrbiMed Advisors LLC, its Managing Member
		
	By:	 	/s/ Carl Gordon
	Name:	 	Carl Gordon
	Title:	 	Member
	
	ORBIMED PRIVATE INVESTMENTS IV—AL, LP
		
	By:	 	OrbiMed Capital GP IV LLC, its General Partner
		
	By:	 	OrbiMed Advisors LLC, its Managing Member
		
	By:	 	/s/ Carl Gordon
	Name:	 	Carl Gordon
	Title:	 	Member

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	 INVESTORS:
  

DEMENTIA DISCOVERY, L.P.

		
	By:	 	Dementia Discovery GP, LP, its sole General Partner
		
	By:	 	Dementia Discovery General Partner, LLP,
		 	its sole General Partner
		
	By:	 	/s/ Nick Coleman
	Name:	 	Nick Coleman
	Title:	 	Member
	
	DDF PARALLEL LLP
		
	By:	 	Dementia Discovery General Partner LLP,
		 	Its Managing Member
		
	By:	 	/s/ Nick Coleman
	Name:	 	Nick Coleman
	Title:	 	Member

 [Signature Page to Series E Registration Rights Agreement] 

			
	INVESTORS:
	
	GV 2014, L.P.
	By:	 	GV 2014 GP, L.L.C., its General Partner
		
	By:	 	/s/ Daphne M. Chang
	Name:	 	Daphne M. Chang
	Title:	 	Authorized Signatory
	
	GV 2017, L.P.
	By:	 	GV 2017 GP, L.P., its General Partner
	By:	 	GV 2017 GP, L.L.C., its General Partner
		
	By:	 	/s/ Daphne M. Chang
	Name:	 	Daphne M. Chang
	Title:	 	Authorized Signatory

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	TOPSPIN BIOTECH FUND II, LP
	By:	 	L.G. MANAGEMENT, LLC,
	its General Partner
		
	By:	 	/s/ Steven J. Winick
	Name:	 	Steven J. Winick
	Title:	 	Managing Director

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	BANNER LLC
		
	By:	 	/s/ Joseph Cosmai
	Name:	 	Joseph Cosmai
	Title:	 	Vice President
	Name:	 	
	Title:	 	

 
			
	
	SYMMETRY GROUP LTD.
		
	By:	 	/s/ Joseph Cosmai
	Name:	 	Joseph Cosmai
	Title:	 	Vice President and Treasurer

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	MISSION BAY CAPITAL II, LP
		
	By:	 	/s/ Douglas Crawford
	Name:	 	Douglas Crawford
	Title:	 	Managing Director

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	AMGEN VENTURES LLC
		
	By:	 	/s/ David W. Meline
	Name:	 	David W. Meline
	Title:	 	Executive Vice President and
Chief Financial Officer

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	ABBVIE INC.
		
	By:	 	/s/ [illegible]
	Name:	 	[illegible]
	Title:	 	

 
			
	
	ABBVIE BIOTECHNOLOGY LTD
		
	By:	 	/s/ Stephen P. Muldoon
	Name:	 	Stephen P. Muldoon
	Title:	 	Director

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	MRL VENTURES FUND LLC
		
	By:	 	/s/ Christine Brennan, Ph.D.
	Name:	 	Christine Brennan, Ph.D.
	Title:	 	Partner

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	THE EBERSMAN FAMILY TRUST UA DTD 05/29/2002
		
	By:	 	/s/ David Ebersman
	Name:	 	David Ebersman
	Title:	 	Trustee

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	PRESTON FAMILY TRUST
		
	By:	 	/s/ Heather Preston
	Name:	 	Heather Preston
	Title:	 	Trustee

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	THE DE SAUVAGE FAMILY TRUST, DTD
10/18/2000
		
	By:	 	/s/ Frederic de Sauvage
	Name:	 	Frederic de Sauvage
	Title:	 	Trustee

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	SECTION 32 FUND 2, LP
	By:	 	Section 32 GP 2, LLC, its general partner
		
	By:	 	/s/ Jennifer L. Kercher
	Name:	 	Jennifer L. Kercher
	Title:	 	Chief Operating Officer

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	
	INVESTORS:
	
	FEDERATED KAUFMANN FUND, A PORTFOLIO OF FEDERATED EQUITY FUNDS
	
	FEDERATED KAUFMANN SMALL CAP FUND, A PORTFOLIO OF FEDERATED EQUITY FUNDS
	
	FEDERATED KAUFMANN FUND II, A PORTFOLIO OF FEDERATED EQUITY FUNDS
		
	By:	 	Federated Equity Management Company of Pennsylvania, investment advisor
		
	By:	 	/s/ Hans P. Utsch
	Name:	 	Hans P. Utsch
	Title:	 	
		 	Vice President, Federated Global Investment Management, as attorney-in-fact for Federated Kaufmann Fund, a portfolio of Federated Equity
Funds
		
		 	Vice President, Federated Global Investment Management, as attorney-in-fact for Federated Kaufmann Small Cap Fund, a portfolio of Federated Equity
Funds
		
		 	Vice President, Federated Global Investment Management, as attorney-in-fact for Federated Kaufmann Fund II, a portfolio of Federated Equity
Funds

 [Signature Page to Series E Registration Rights Agreement] 

			
	
	INVESTORS:
	
	SHREWSBURY CAPITAL PARTNERS LLC
		
	By:	 	/s/ Jonathan Gold
	Name:	 	Jonathan Gold
	Title:	 	Managing Member

 [Signature Page to Series E Registration Rights Agreement] 

 
	
	INVESTORS:
	
	/s/ Tillman Gerngross
	Tillman Gerngross

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	LEERRINK HOLDINGS LLC
		
	By: 	 	/s/ Joseph R. Gentile
		 	Name: Joseph R. Gentile
		 	Title: CAO

  

			
	LEERRINK PARTNERS CO-INVESTMENT FUND, LLC
		
	By:	 	/s/ Joseph R. Gentile
		 	Name: Joseph R. Gentile
		 	Title: Manager

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	HCM CURE II, LLC
		
	By:	 	Highline Capital Management, L.P.
		
	By:	 	Highline Capital GP, Inc., its General Partner
		
	By: 	 	/s/ Howard M. Singer
		 	Name: Howard M. Singer
		 	Title: Chief Operating Officer

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	FORESITE CAPITAL FUND IV, L.P.
		
	By:	 	Foresite Capital Management IV, LLC,
its General Partner
		
	By: 	 	/s/ Dennis D. Ryan
		 	Name: Dennis D. Ryan
		 	Title: Chief Financial Officer

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	PERCEPTIVE LIFE SCIENCES MASTER FUND LTD.
		
	By:	 	/s/ James H. Mannix
		 	Name: James H. Mannix
		 	Title: Chief Operating Officer

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	DEERFIELD SPECIAL SITUATIONS FUND, L.P.
	By:	 	Deerfield Mgmt, L.P.
General Partner
	By:	 	J.E. Flynn Capital, LLC
General Partner
		
	By:	 	/s/ David J. Clark
		 	Name: David J. Clark
		 	Title: Authorized Signatory

  

			
	DEERFIELD PRIVATE DESIGN FUND III, L.P.
	By:	 	Deerfield Mgmt, L.P.
General Partner
	By:	 	J.E. Flynn Capital, LLC
General Partner
		
	By:	 	/s/ David J. Clark
		 	Name: David J. Clark
		 	Title: Authorized Signatory

  

			
	DEERFIELD PRIVATE DESIGN FUND IV, L.P.
	By:	 	Deerfield Mgmt, L.P.
General Partner
	By:	 	J.E. Flynn Capital, LLC
General Partner
		
	By:	 	/s/ David J. Clark
		 	Name: David J. Clark
		 	Title: Authorized Signatory

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	NEW LEAF BIOPHARMA OPPORTUNITIES II, L.P.
		
	By:	 	New Leaf BPO Associates II, L.P.
	Its:	 	General Partner
		
	By:	 	New Leaf BPO Management II, L.L.C.
	Its:	 	General Partner
		
	By:	 	/s/ Craig L. Slutzkin
		 	Name: Craig L. Slutzkin
		 	Title: Chief Financial Officer

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	CASDIN PARTNERS MASTER FUND, L.P.
	By:	 	Casdin Partners GP, LLC, its General Partner
		
	By:	 	/s/ Eli Casdin
		 	Name: Eli Casdin
		 	Title: Managing Member

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	LAV AGATE LIMITED
		
	By: 	 	 /s/ Yu Luo

		 	Name: Yu Luo
		 	Title: Authorized Signatory

 [Signature Page to Series E Registration Rights Agreement] 

 
			
	INVESTORS:
	
	LAVRITE, LLC
		
	By:	 	 /s/ Lou Lavigne

		 	Name: Lou Lavigne
		 	Title: Managing Director

 [Signature Page to Series E Registration Rights Agreement] 

 
	
	KEY HOLDERS:
	
	/s/ Arnon Rosenthal
	Arnon Rosenthal

  

	
	THE ROSENTHAL FAMILY REVOCABLE TRUST DATED NOVEMBER 4, 1994, AS RESTATED ON JUNE 9, 1999
	
	/s/ Arnon Rosenthal
	Name: Arnon Rosenthal
	Title: Trustee

  

	
	ADI ROSENTHAL 2007 TRUST DATED MARCH 27, 2007
	
	/s/ Arnon Rosenthal
	Name: Arnon Rosenthal
	Title: Trustee

  

	
	NOAM ROSENTHAL 2007 TRUST DATED MARCH 27, 2007
	
	/s/ Arnon Rosenthal
	Name: Arnon Rosenthal
	Title: Trustee

  

	
	SHANI ROSENTHAL 2007 TRUST DATED MARCH 27, 2007
	
	/s/ Arnon Rosenthal
	Name: Arnon Rosenthal
	Title: Trustee

 [Signature Page to Series E Registration Rights Agreement] 

 
	
	KEY HOLDERS:
	
	/s/ Asa Abeliovich
	Asa Abeliovich

  

	
	/s/ Tillman Gerngross
	Tillman Gerngross

  

			
	ULYSSES CONSOLIDATED LLC
		
	By:	 	/s/ Errik Anderson
	Name: Errik Anderson
	Title: President

  

	
	/s/ Jonathan Sheller
	Jonathan Sheller

  

	
	/s/ Kelly Hackett
	Kelly Hackett

  

	
	/s/ Ryan McGovern
	Ryan McGovern

 [Signature Page to Series E Registration Rights Agreement] 

 
	
	KEY HOLDERS:
	
	/s/ Sabah Oney
	Sabah Oney
	
	/s/ Robert Paul
	Robert Paul
	
	/s/ Calvin Yu
	Calvin Yu
	
	/s/ Robert King
	Robert King
	
	/s/ Stephanie Yonker
	Stephanie Yonker

 [Signature Page to Series E Registration Rights Agreement] 

 SCHEDULE A 

INVESTORS 
 Name and Address

 Polaris Venture Partners VI (AIV), L.P. 

Polaris Venture Partners VI, L.P. 
 Polaris Venture
Partners Founders’ Fund VI, L.P. 
 PVP VI (AIV) Feeder Corp Holding Partnership, L.P. 

OrbiMed Private Investments IV—AL, LP 
 OrbiMed
Private Investments IV—AL (Feeder), LP 
 MRL Ventures Fund LLC 

GV 2014, L.P. 
 GV 2017, L.P. 

Topspin Biotech Fund II, LP 
 Banner LLC 

Symmetry Group Ltd. 
 Mission Bay Capital II, LP

 Dementia Discovery LP 
 DDF Parallel LLP

 AbbVie Inc. 
 AbbVie Biotechnology Ltd 

Amgen Ventures LLC 
 Tillman Gerngross 

The Ebersman Family Trust UA DTD 05/29/2002 
 Preston
Family Trust 

 The de Sauvage Family Trust, DTD 10/18/2000 

Section 32 Fund 2, LP 
 Federated Kaufmann Fund

 Federated Kaufmann Small Cap Fund 
 Federated
Kaufmann Fund II 
 Shrewsbury Capital Partners LLC 

Casdin Partners Master Fund VI, L.P. 
 New Leaf
Biopharma Opportunities II, L.P. 
 HCM Cure II, LLC (Highline Capital) 

Deerfield Special Situations Fund, L.P. 
 Deerfield
Private Design Fund III, L.P. 
 Deerfield Private Design Fund IV, L.P. 

LAV Agate Limited 
 Leerink Holdings LLC 

Leerink Partners Co-Investment Fund, LLC 

Perceptive Life Sciences Master Fund LTD 
 Foresite
Capital Fund IV, L.P. 
 Lavrite, LLC 

 SCHEDULE B 

KEY HOLDERS 
 Name and Address

 Arnon Rosenthal 
 The Rosenthal Family
Revocable Trust Dated November 4, 1994, 
 as restated on June 9, 1999 

Adi Rosenthal 2007 Trust dated March 27, 2007 

Noam Rosenthal 2007 Trust dated March 27, 2007 

Shani Rosenthal 2007 Trust dated March 27, 2007 

Asa Abeliovich 
 Tillman Gerngross 

Ulysses Consolidated LLC (Errik Anderson) 
 Jon Sheller

 Kelly Hackett 
 Ryan McGovern 

Sabah Oney 
 Robert Paul 

Calvin Yu 
 Robert King 

Stephanie YonkerEX-10.2

 Exhibit 10.2 

ALECTOR, INC. 
 2017 STOCK
OPTION AND GRANT PLAN 
 (as amended on August 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. 

“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 accelerate at any time the exercisability or vesting of all or any portion of any Award; 

(vi) to impose any limitations on Awards, including limitations on transfers, repurchase provisions and the like, and to exercise repurchase
rights or obligations; 
 (vii) 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 
 (viii) 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

  
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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. 

  
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 (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. 

  
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	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. 

  
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 (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. 

  
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 (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 

  
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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. 

  
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	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 reduce
the exercise price of outstanding Stock Options or effect repricing through cancellation of outstanding Stock Options and by granting such holders new Awards in replacement of the cancelled Stock Options. 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). 

  
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 (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

  
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 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]. 

  
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 (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-

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