Exhibit 4.3

$200,000,000

ABGENIX, INC.

31/2%
Convertible Subordinated Notes Due 2007

REGISTRATION RIGHTS AGREEMENT

March 4,
2002

CREDIT SUISSE FIRST BOSTON CORPORATION
BANC OF AMERICA SECURITIES LLC
ROBERTSON STEPHENS, INC.,
    C/O CREDIT SUISSE FIRST BOSTON CORPORATION,
        ELEVEN MADISON AVENUE,
        NEW YORK, N.Y. 10010-3629

Dear Sirs:

Abgenix, Inc.,
a Delaware corporation (the "Company") proposes to issue and sell to Credit Suisse First Boston Corporation, Banc of
America Securities LLC and Robertson Stephens, Inc. (collectively, the "Initial Purchasers"), upon the terms set forth in a purchase agreement
dated as of February 27, 2002 (the "Purchase Agreement"), $200,000,000 aggregate principal amount (plus up to an additional $50,000,000 principal
amount) of its 31/2% Convertible Subordinated Notes due 2007 (the "Initial Securities"). The Initial Securities will be convertible into
shares of common stock, par value $0.0001 per share, of the Company (the "Common Stock") at the conversion price set forth in the Offering Circular
dated February 27, 2002 (the "Offering Circular"). The Initial Securities will be issued pursuant to an Indenture, dated as of the date hereof
(the "Indenture"), between the Company and State Street Bank and Trust Company of California, N.A., as trustee (the
"Trustee"). As an inducement to the Initial Purchasers to enter into the Purchase Agreement, the Company agrees with the Initial Purchasers, for the
benefit of (i) the Initial Purchasers and (ii) the holders of the Initial Securities and the Common Stock issuable upon conversion of the Initial Securities (collectively, the
"Securities") from time to time until such time as such Securities have been sold pursuant to a Shelf Registration Statement (as defined below) (each of
the forgoing a "Holder" and collectively the "Holders"), as follows:

1.Shelf Registration.(a) The Company shall, at its cost, prepare and, as promptly as practicable (but
in no event more than 90 days after the date of this Agreement) file with the Securities and Exchange Commission (the "Commission") and
thereafter use its commercially reasonable efforts to cause to be declared effective as soon as practicable after it has filed a registration statement on Form S-3 or, if
Form S-3 is not available, on an appropriate form under the Securities Act (the "Shelf Registration Statement") relating to the offer
and sale of the Transfer Restricted Securities (as defined in Section 5 hereof) by the Holders thereof from time to time in accordance with the methods of distribution set forth in the Shelf
Registration Statement and Rule 415 under the Securities Act of 1933, as amended (the "Securities Act") (hereinafter, the
"Shelf Registration");provided, however, that no Holder (other than an Initial Purchaser) shall be
entitled to have the Securities held by it covered by such Shelf Registration Statement unless such Holder agrees in writing to be bound by all the provisions of this Agreement applicable to such
Holder.

(b)  The
Company shall use its commercially reasonable efforts to keep the Shelf Registration Statement continuously effective in order to permit the prospectus included
therein (the "Prospectus") to be lawfully delivered by the Holders of the relevant Securities, for a period of two years (or for such longer period if
extended pursuant to Section 2(h) below) from the date of this Agreement or such shorter period that will terminate when all the Securities covered by the Shelf Registration Statement
(i) have been sold pursuant thereto or (ii) are no longer restricted securities (as defined in Rule 144(k)

---

under the Securities Act, or any successor rule thereof), assuming for this purpose that the Holders thereof are not affiliates of the Company (in any such case, such period being called the
"Shelf Registration Period"). The Company shall be deemed not to have used its commercially reasonable efforts to keep the Shelf Registration Statement
effective during the requisite period if it voluntarily takes any action that would result in Holders of Securities covered thereby not being able to offer and
sell such Securities during that period, unless such action is (i) required by applicable law or (ii) taken by the Company in good faith and contemplated by
Section 2(b)(v) below, and the Company thereafter complies with the requirements of Section 2(h).

(c)  Notwithstanding
any other provisions of this Agreement to the contrary, the Company shall cause the Shelf Registration Statement and the Prospectus and any amendment or
supplement thereto, as of the effective date of the Shelf Registration Statement, amendment or supplement, (i) to comply in all material respects with the applicable requirements of the
Securities Act and the rules and regulations of the Commission and (ii) not to contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or
necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading.

(d)  Each
Holder of Transfer Restricted Securities agrees, by its acquisition of Transfer Restricted Securities, that if such Holder wishes to sell Transfer Restricted
Securities pursuant to a Shelf Registration Statement and related Prospectus, it will do so only in accordance with this Section 1(d) and Section 2(h). Each Holder of Transfer Restricted
Securities wishing to sell Transfer Restricted Securities pursuant to a Shelf Registration Statement and related Prospectus agrees to deliver a written notice, substantially in the form of Annex A to
the Offering Circular (a "Notice and Questionnaire") to the Company at least five (5) Business Days prior to any intended distribution of
Transfer Restricted Securities under the Shelf Registration Statement. Any Holder who does not complete and deliver a Notice and Questionnaire to the Company will not be permitted to sell Transfer
Restricted Securities pursuant to the Shelf Registration Statement.

2.Registration Procedures.In connection with the Shelf Registration contemplated by Section 1 hereof,
the following provisions shall apply:

(a)  The
Company shall (i) furnish to each Initial Purchaser, prior to the filing thereof with the Commission, a copy of the Shelf Registration Statement and each
amendment thereof and each supplement, if any, to the prospectus included therein and, in the event that an Initial Purchaser (with respect to any portion of an unsold allotment from the original
offering) is participating in the Shelf Registration Statement, shall use its commercially reasonable efforts to reflect in each such document, when so filed with the Commission, such comments as such
Initial Purchaser reasonably may propose; (ii) include in the Shelf Registration Statement at the time it is first declared effective, the name of each Holder that provided a written notice to
the Company on or prior to the date five (5) Business Days prior to such time of effectiveness containing substantially the information called for by the Notice and Questionnaire; and
(iii) from and after the date the Shelf Registration Statement is initially declared effective, use its commercially reasonable efforts, as promptly as practicable after the date a Notice and
Questionnaire is delivered, if required by applicable law, to file with the Commission a post-effective amendment to the Shelf Registration Statement or prepare and, if required by
applicable law, file a supplement to the related Prospectus or a supplement or amendment to any document incorporated therein by reference or file any other document required under the
Securities Act so that the Holder delivering such Notice and Questionnaire is named as a selling security holder in the Shelf Registration Statement and the related Prospectus in such a manner as to
permit such Holder to deliver such Prospectus to purchasers of the Transfer Restricted Securities in accordance with applicable law and, if the Company shall file a post-effective
amendment to the Shelf Registration Statement, use reasonable
efforts to cause such post-effective amendment to be declared effective under the Securities Act as promptly as is practicable.

2

---

(b)  The
Company shall give written notice to the Initial Purchasers and the Holders of the Securities (which notice pursuant to clauses (ii)-(v) hereof shall be
accompanied by an instruction to suspend the use of the Prospectus pursuant to the terms of Section 2(b)(v) and is referred to herein as a "Deferral
Notice"):



(c)  The
Company shall make every reasonable effort to obtain the withdrawal at the earliest possible time, of any order suspending the effectiveness of the Shelf
Registration Statement.

(d)  The
Company shall furnish to each Holder of Securities included within the coverage of the Shelf Registration, without charge, at least one copy of the Shelf
Registration Statement and any post-effective amendment thereto, including financial statements and schedules, if any, and, if the Holder so requests in writing, all exhibits thereto
(including those, if any, incorporated by reference).

(e)  The
Company shall, during the Shelf Registration Period, deliver to each Holder of Securities included within the coverage of the Shelf Registration, without charge, as
many copies of the Prospectus (including each preliminary prospectus) included in the Shelf Registration Statement and any amendment or supplement thereto as such person may reasonably request. The
Company consents, subject to the provisions of this Agreement, to the use of the Prospectus or any amendment or supplement thereto by each of the selling Holders of the Securities in connection with
the offering and sale of the Securities covered by the Prospectus, or any amendment or supplement thereto, included in the Shelf Registration Statement.

(f)    Prior
to any public offering of the Securities pursuant to the Shelf Registration Statement, the Company shall register or qualify or cooperate with the Holders of the
Securities included therein and their respective counsel in connection with the registration or qualification of the Securities for offer

3

---

and sale under the securities or "blue sky" laws of such states of the United States as any Holder of the Securities reasonably requests in writing and do any and all other acts or things necessary
or advisable to enable the offer and sale in such jurisdictions of the Securities covered by such Registration Statement; provided, however, that the Company shall not be required to
(i) qualify generally to do business in any jurisdiction where it is not then so qualified or (ii) take any action which would subject it to general service of process or to taxation in
any jurisdiction where it is not then so subject.

(g)  The
Company shall cooperate with the Holders of the Securities to facilitate the timely preparation and delivery of certificates, if any, representing the Securities to
be sold pursuant to any Registration Statement free of any restrictive legends and in such denominations and registered in such names as the Holders may reasonably request a reasonable period of time
prior to sales of the Securities pursuant to the Shelf Registration Statement.

(h)  Upon
the occurrence of any event contemplated by paragraphs (ii) through (v) of Section 2(b) above during the period for which the Company is
required to maintain an effective Shelf Registration Statement, the Company shall promptly prepare and file a post-effective amendment to the Shelf Registration Statement or an
amendment or supplement to the Prospectus and any other required document so that, as thereafter delivered to Holders or purchasers of the Securities, the Prospectus will not contain an untrue
statement of a material fact or omit to state any material fact required to be
stated therein or necessary to make the statements therein, in light of the circumstances under which they were made, not misleading; provided, that if the Company has delivered a Deferral Notice,
then the Company shall have no obligation to file any such amendment, supplement or other document until the 45th or 90th day, as the case may be, after the delivery of the
Deferral Notice. If the Company notifies the Initial Purchasers and the Holders in accordance with paragraphs (ii) through (v) of Section 2(b) above to suspend the use of the
Prospectus until the end of the Deferral Period, then the Initial Purchasers and the Holders shall suspend use of such prospectus, and the period of effectiveness of the Shelf Registration Statement
provided for in Section 1(b) above shall be extended by the number of days from and including the date of the giving of such notice to and including the date when the Initial Purchasers and the
Holders shall have received such amended or supplemented prospectus pursuant to this Section 2(h), unless the Securities covered by the Shelf Registration Statement are no longer restricted
securities as defined in Rule 144(k) of the Securities Act.

(i)    Not
later than the effective date of the Shelf Registration Statement, the Company will provide CUSIP numbers for the Initial Securities and the Common Stock registered
under the Shelf Registration Statement, and provide the Trustee with printed certificates for the Initial Securities, in a form eligible for deposit with The Depository Trust Company.

(j)    The
Company will comply with all rules and regulations of the Commission to the extent and so long as they are applicable to the Shelf Registration and will make
generally available to its security holders (or otherwise provide in accordance with Section 11(a) of the Securities Act) an earnings statement satisfying the provisions of Section 11(a)
of the Securities Act, no later than 45 days after the end of a 12-month period (or 90 days, if such period is a fiscal year) beginning with the first month of the Company's
first fiscal quarter commencing after the effective date of the Shelf Registration Statement, which statement shall cover such 12-month period; provided, that if the Company files the
reports required by this Section 3(j) with the SEC and such reports are publicly available, it shall be deemed to have satisfied its obligation to furnish reports to its security holders
pursuant to this Section 3(j).

(k)  The
Company shall cause the Indenture to be qualified under the Trust Indenture Act of 1939, as amended, (the "Trust Indenture
Act") in a timely manner and containing such changes, if any, as shall be necessary for such qualification. In the event that such qualification would require the

4

---

appointment of a new trustee under the Indenture, the Company shall appoint a new trustee thereunder pursuant to the applicable provisions of the Indenture.

(l)    The
Company may require each Holder of Securities to be sold pursuant to the Shelf Registration Statement to furnish to the Company such information regarding the Holder
and the distribution of the Securities as the Company may from time to time reasonably require for inclusion in the Shelf Registration Statement, and the Company may exclude from such registration the
Securities of any Holder that unreasonably fails to furnish such information within a reasonable time after receiving such request.

(m)  The
Company shall enter into such customary agreements and take all such other actions, if any, as any Holder shall reasonably request in order to facilitate the
disposition of the Securities pursuant to the Shelf Registration.

(n)  The
Company shall (i) make reasonably available for inspection by the Holders and any attorney, accountant or other agent retained by the Holders, all relevant
financial and other records, pertinent corporate documents and properties of the Company and (ii) cause the Company's officers, directors, employees, accountants and auditors to supply all
relevant information reasonably requested by the Holders or any such attorney, accountant or agent in connection with the Shelf Registration Statement, in each case, as shall be reasonably necessary
to enable such persons, to conduct a reasonable investigation within the meaning of Section 11 of the Securities Act;provided, however, that the
foregoing inspection and information gathering shall be coordinated on behalf of the Initial Purchasers by you and on behalf of the other parties, by one counsel designated by and on behalf of such
other parties as described in Section 3 hereof; provided, further, that no person shall be granted the rights set forth in (i) and (ii) above unless and until such person shall
have executed and delivered a confidentiality agreement in favor of the Company with respect to any information received pursuant to the exercise of such rights in a customary form reasonably
acceptable to the Company prior to the receipt of any such information.

(o)  The
Company will use its commercially reasonable efforts to cause the Securities covered by a Registration Statement to be rated with the appropriate rating agencies, if
so requested by holders of a majority in aggregate principal amount of Securities covered by the Shelf Registration Statement.

(p)  The
Company shall use its commercially reasonable efforts, subject to the terms and conditions of this Agreement, to take all other steps necessary to effect the
registration of the Securities covered by a Registration Statement contemplated hereby.

3.Registration Expenses.(a) All expenses incident to the Company's performance of and compliance with
this Agreement will be borne by the Company, regardless of whether a Registration Statement is ever filed or becomes effective, including without limitation;



5

---



The
Company will bear its internal expenses (including, without limitation, all salaries and expenses of its officers and employees performing legal or accounting duties), the expenses of any annual
audit and the fees and expenses of any person, including special experts, retained by the Company.

(b)  In
connection with the Shelf Registration Statement required by this Agreement, the Company will reimburse the Initial Purchasers and the Holders of Securities covered
by the Shelf Registration Statement, for the reasonable fees and disbursements of not more than one counsel, designated by the Holders of a majority in principal amount of the Securities covered by
the Shelf Registration Statement (provided that Holders of Common Stock issued upon the conversion of the Initial Securities shall be deemed to be Holders of the aggregate principal amount of Initial
Securities from which such Common Stock was converted) to act as counsel for the Holders in connection therewith.

4.Indemnification.(a) The Company agrees to indemnify and hold harmless each Holder and each person,
if any, who controls such Holder within the meaning of the Securities Act or the Securities Exchange Act of 1934, as amended (the "Exchange Act") (each
Holder, and such controlling persons are referred to collectively as the "Indemnified Parties") from and against any losses, claims, damages or
liabilities, joint or several, or any actions in respect thereof (including, but not limited to, any losses, claims, damages, liabilities or actions relating to purchases and sales of the Securities)
to which each Indemnified Party may become subject under the Securities Act, the Exchange Act or otherwise, insofar as such losses, claims, damages, liabilities or actions arise out of or are based
upon any untrue statement or alleged untrue statement of a material fact contained in the Shelf Registration Statement or prospectus including any document incorporated by reference therein, or in any
amendment or supplement thereto or in any preliminary prospectus relating to the Shelf Registration, or arise out of, or are based upon, the omission or alleged omission to state therein a material
fact required to be stated therein or necessary to make the statements therein not misleading, and shall reimburse, as incurred, the Indemnified Parties for any legal or other expenses reasonably
incurred by them in connection with investigating or defending any such loss, claim, damage, liability or action in respect thereof;provided, however,
that (i) the Company shall not be liable in any such case to the extent that such loss, claim, damage or liability arises out of or is based upon any untrue statement or alleged untrue
statement or omission or alleged omission made in the Shelf Registration Statement or prospectus or in any amendment or supplement thereto or in any preliminary prospectus relating to the Shelf
Registration in reliance upon and in conformity with written information pertaining to such
Holder and furnished to the Company by or on behalf of such Holder specifically for inclusion therein and (ii) with respect to any untrue statement or omission or alleged untrue statement or
omission made in any preliminary prospectus relating to the Shelf Registration Statement, the indemnity agreement contained in this subsection (a) shall not inure to the benefit of any Holder
from whom the person asserting any such losses, claims, damages or liabilities purchased the Securities concerned, to the extent that a prospectus relating to such Securities was required to be
delivered by such Holder under the Securities Act in connection with such purchase and any such loss, claim, damage or liability of such Holder results from the fact that there was not sent or given
to such person, at or prior to the written confirmation of the sale of such Securities to such person, a copy of the final prospectus if the Company had previously furnished copies thereof to such
Holder;provided further, however, that this indemnity agreement will be in addition to any liability which the Company may otherwise have to such
Indemnified Party.

(b)  Each
Holder, severally and not jointly, will indemnify and hold harmless the Company, its officers and directors and each person, if any, who controls the Company within
the meaning of the Securities Act or the Exchange Act from and against any losses, claims, damages or liabilities or any actions in respect thereof, to which the Company or any such controlling person
may become subject under the Securities Act, the Exchange Act or otherwise, insofar as such losses, claims, damages, liabilities or actions arise out of or are based upon any untrue statement or
alleged untrue statement of a material fact contained in the Shelf Registration Statement or prospectus including any document

6

---

incorporated by reference therein, or in any amendment or supplement thereto or in any preliminary prospectus relating to the Shelf Registration, or arise out of or are based upon the omission or
alleged omission to state therein a material fact necessary to make the statements therein not misleading, but in each case only to the extent that the untrue statement or omission or alleged untrue
statement or omission was made in reliance upon and in conformity with written information pertaining to such Holder and furnished to the Company by or on behalf of such Holder specifically for
inclusion therein; and, subject to the limitation set forth immediately preceding this clause, shall reimburse, as incurred, the Company for any legal or other expenses reasonably incurred by the
Company or any such controlling person in connection with investigating or defending any loss, claim, damage, liability or action in respect thereof. This indemnity agreement will be in addition to
any liability which such Holder may otherwise have to the Company or any of its officers, directors or controlling persons.

(c)  Promptly
after receipt by an indemnified party under this Section 4 of notice of the commencement of any action or proceeding (including a governmental
investigation), such indemnified party will, if a claim in respect thereof is to be made against the indemnifying party under this Section 4, notify the indemnifying party of the commencement
thereof; but the omission so to notify the indemnifying party will not, in any event, relieve the indemnifying party from any obligations to any indemnified party other than the indemnification
obligation provided in paragraph (a) or (b) above. In case any such action is brought against any indemnified party, and it notifies the indemnifying party of the commencement thereof,
the indemnifying party will be entitled to participate therein and, to the extent that it may wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with
counsel reasonably satisfactory to such indemnified party (who shall not, except with the consent of the indemnified party, be counsel to the indemnifying party), and after notice from the
indemnifying party to such indemnified party of its election so to assume the defense thereof the indemnifying party will not be liable to such indemnified party under this Section 4 for any
legal or other expenses, other than reasonable costs of investigation, subsequently incurred by such indemnified party in connection with the defense thereof. No indemnifying party shall, without the
prior written consent of the indemnified
party, effect any settlement of any pending or threatened action in respect of which any indemnified party is or could have been a party and indemnity could have been sought hereunder by such
indemnified party unless such settlement (i) includes an unconditional release of such indemnified party from all liability on any claims that are the subject matter of such action, and
(ii) does not include a statement as to or an admission of fault, culpability or a failure to act by or on behalf of any indemnified party.

(d)  If
the indemnification provided for in this Section 4 is unavailable or insufficient to hold harmless an indemnified party under subsections (a) or
(b) above, then each indemnifying party shall contribute to the amount paid or payable by such indemnified party as a result of the losses, claims, damages or liabilities (or actions in respect
thereof) referred to in subsection (a) or (b) above (i) in such proportion as is appropriate to reflect the relative benefits received by the indemnifying party or parties on the
one hand and the indemnified party on the other from the sale of the Securities, pursuant to the Shelf Registration, or (ii) if the allocation provided by the foregoing clause (i) is not
permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also in such proportion as is appropriate to
reflect the relative fault of the indemnifying party or parties on the one hand and the indemnified party on the other in connection with the statements or omissions that resulted in such losses,
claims, damages or liabilities (or actions in respect thereof) as well as any other relevant equitable considerations. The relative fault of the parties shall be determined by reference to, among
other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company on the one
hand or such Holder or such other indemnified party, as the case may be, on the other, and the parties' relative intent, knowledge, access to information and opportunity to correct or prevent such
statement or omission. The amount paid by an indemnified party as a result of the losses, claims, damages or liabilities referred to in the first sentence

7

---

of this subsection (d) shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any action or claim
which is the subject of this subsection (d). Notwithstanding any other provision of this Section 4(d), the Holders shall not be required to contribute any amount in excess of the amount by
which the net proceeds received by such Holders from the sale of the Securities pursuant to the Shelf Registration Statement exceeds the amount of damages which such Holders have otherwise been
required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of
the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. For purposes of this paragraph (d), each person, if any, who
controls such indemnified party within the meaning of the Securities Act or the Exchange Act shall have the same rights to contribution as such indemnified party and each person, if any, who controls
the Company within the meaning of the Securities Act or the Exchange Act shall have the same rights to contribution as the Company.

(e)  The
agreements contained in this Section 4 shall survive the sale of the Securities pursuant to the Shelf Registration Statement and shall remain in full force
and effect, regardless of any termination or cancellation of this Agreement or any investigation made by or on behalf of any indemnified party.

5.Additional Interest Under Certain Circumstances.(a) Additional interest (the
"Additional Interest") with respect to the Transfer Restricted Securities shall be assessed as follows if any of the following events occur (each such
event in clauses (i) through (iii) below being herein called a "Registration Default"):



Each
of the foregoing will constitute a Registration Default whatever the reason for any such event and whether it is voluntary or involuntary or is beyond the control of the Company or pursuant to
operation of law or as a result of any action or inaction by the Commission.

Additional
Interest shall accrue on the Transfer Restricted Securities (in addition to the interest set forth in the title of the Initial Securities) from and including the date on which
any such Registration Default shall occur to but excluding the date on which all such Registration Defaults have been cured, at (x) in respect of any Initial Securities, a rate of 0.50% per
annum of the principal amount thereof to the Damages Payment Date (as defined below), and (y) in respect of any shares of Common Stock issued upon conversion of each $1,000 principal amount of
Initial Securities, a rate of 0.50% per annum of the principal amount of such Initial Securities so converted, to the Damages Payment Date, divided by the Conversion Price (as defined in the
Indenture), in each case determined as of the Business Day immediately preceding the next Damages Payment Date;provided, that any Additional Interest
accrued with respect to any Initial Security or portion thereof called for redemption on a redemption date or converted into shares of Common Stock on a conversion date prior to the Damages Payment
Date, shall, in any such event, be paid instead to the Holder who submitted such Security or portion thereof for redemption or conversion on the applicable redemption date or conversion date, as the
case may be, on such date (or promptly following the conversion date in the case of conversion). The rate of accrual of the Additional Interest with respect to any period shall not

8

---

exceed 0.50% per annum notwithstanding the occurrence of multiple concurrent Registration Defaults until all Registration Defaults have been cured.

(b)  Notwithstanding
Section 5(a)(iii), a Registration Default referred to in Section 5(a)(iii) hereof shall be deemed not to have occurred and be
continuing in relation to the Shelf Registration Statement or the
related Prospectus if the Company has delivered a Deferral Notice pursuant to Section 2(b) of this Agreement and the Deferral Period shall not have extended past the periods permitted by
Section 2(b)(v).

(c)  Any
amounts of Additional Interest due pursuant to Section 5(a) will be payable in cash on the regular interest payment dates with respect to the Initial
Securities (each a "Damages Payment Date"), except in the case of an Initial Security or portion thereof called for redemption on a redemption date or
converted into shares of Common Stock on a conversion date prior to a Damages Payment Date. The amount of Additional Interest will be determined on the basis of a 360-day year comprised of
twelve 30-day months and the actual number of days on which Additional Interest accrued during such period.

(d)  "Transfer Restricted Securities" means each Security until the earliest of (i) the date on which such Security has
been effectively registered under the Securities Act and disposed of in accordance with the Shelf Registration Statement, or (ii) the date on which such Security is distributed to the public
pursuant to Rule 144 under the Securities Act or (iii) the date on which such Security would be saleable pursuant to Rule 144(k) under the Securities Act were it not held by an
affiliate of the Company.

6.Rules 144 and 144A.The Company shall use its best efforts to file the reports required to be filed by
it under the Securities Act and the Exchange Act in a timely manner and, if at any time the Company is not required to file such reports, it will, upon the request of any Holder, make publicly
available other information so long as necessary to permit sales of their securities pursuant to Rules 144 and 144A. The Company covenants that it will take such further action as any Holder
may reasonably request, all to the extent required from time to time to enable such Holder to sell Transfer Restricted Securities without registration under the Securities Act within the limitation of
the exemptions provided by Rules 144 and 144A (including the requirements of Rule 144A(d)(4)). The Company will provide a copy of this Agreement to prospective purchasers of Securities
identified to the Company by the Initial Purchasers upon request. Upon the request of any Holder, the Company shall deliver to such Holder a written statement as to whether it has complied with such
requirements. Notwithstanding the foregoing, nothing in this Section 6 shall be deemed to require the Company to register any of its securities pursuant to the Exchange Act.

7.Miscellaneous.

(a)Remedies.The Company acknowledges and agrees that any failure by the Company to comply with its obligations
under Section 1 hereof may result in material irreparable injury to the Initial Purchasers or the Holders for which there is no adequate remedy at law, that it will not be possible to measure
damages for such injuries precisely and that, in the event of any such failure, the Initial Purchasers or any Holder may obtain such relief as may be required to specifically enforce the Company's
obligations under Sections 1 hereof. The Company further agrees to waive the defense in any action for specific performance that a remedy at law would be adequate. Notwithstanding the forgoing, in the
event of a Registration Default as described in Section 5(a)(ii), Holders agree to waive the remedy of specific performance with respect to such Registration Default only if it would be
commercially unreasonable for the Company to have the Shelf Registration Statement declared effective by the Commission. In the case of an action for specific performance pursuant to the preceding
sentence of this paragraph, the
Company's waiver of the defense that an adequate remedy at law would be adequate shall not apply, notwithstanding anything to the contrary in this Agreement.

9

---

(b)No Inconsistent Agreements.The Company will not on or after the date of this Agreement enter into any
agreement with respect to its securities that is inconsistent with the rights granted to the Holders in this Agreement or otherwise conflicts with the provisions hereof. The rights granted to the
Holders hereunder do not in any way conflict with and are not inconsistent with the rights granted to the holders of the Company's securities under any agreement in effect on the date hereof.

(c)Amendments and Waivers.The provisions of this Agreement may not be amended, modified or supplemented, and
waivers or consents to departures from the provisions hereof may not be given, except by the Company and the written consent of the holders of a majority in principal amount of the Securities affected
by such amendment, modification, supplement, waiver or consent (provided that holders of Common Stock issued upon conversion of Initial Securities shall not be deemed holders of Common Stock, but
shall be deemed to be holders of the aggregate principal amount of Initial Securities from which such Common Stock was converted). Without the consent of the Holder of each Initial Security, however,
no modification may change the provisions relating to the payment of Additional Interest.

(d)Notices.All notices and other communications provided for or permitted hereunder shall be made in writing
by hand delivery, first-class mail, facsimile transmission, or air courier which guarantees overnight delivery:



All
such notices and communications shall be deemed to have been duly given: at the time delivered by hand, if personally delivered; three business days after being deposited in the
mail, postage

10

---

prepaid, if mailed; when receipt is acknowledged by recipient's facsimile machine operator, if sent by facsimile transmission; and on the day delivered, if sent by overnight air courier guaranteeing
next day delivery.

(e)Third Party Beneficiaries.The Holders shall be third party beneficiaries to the agreements made hereunder
between the Company, on the one hand, and the Initial Purchasers, on the other hand, and shall have the right to enforce such agreements directly to the extent they may deem such enforcement necessary
or advisable to protect their rights or the rights of Holders hereunder.

(f)Successors and Assigns.This Agreement shall be binding upon the Company and its successors and assigns.

(g)Counterparts.This Agreement may be executed in any number of counterparts and by the parties hereto in
separate counterparts, each of which when so executed shall be deemed to be an original and all of which taken together shall constitute one and the same agreement.

(h)Headings.The headings in this Agreement are for convenience of reference only and shall not limit or
otherwise affect the meaning hereof.

(i)Governing Law.THIS AGREEMENT SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE
OF NEW YORK.

By
the execution and delivery of this Agreement, the Company submits to the nonexclusive jurisdiction of any federal or state court in the State of New York.

(j)Severability.If any one or more of the provisions contained herein, or the application thereof in any
circumstance, is held invalid, illegal or unenforceable, the validity, legality and enforceability of any such provision in every other respect and of the remaining provisions contained herein shall
not be affected or impaired thereby.

(k)Securities Held by the Company.Whenever the consent or approval of Holders of a specified percentage of
principal amount of Securities is required hereunder, Securities held by the Company or its affiliates (other than subsequent Holders of Securities if such subsequent Holders are deemed to be
affiliates solely by reason of their holdings of such Securities) shall not be counted in determining whether such consent or approval was given by the Holders of such required percentage.

[Signature Page Follows]

11

---

If the foregoing is in accordance with your understanding of our agreement, please sign and return to the Company a counterpart hereof, whereupon this instrument,
along with all counterparts, will become a binding agreement among the several Initial Purchasers and the Company in accordance with its terms.

| | Very truly yours,
| | -----------------
| | ABGENIX, INC.    
| | by               

The
foregoing Registration
Rights Agreement is hereby confirmed
and accepted as of the date first
above written.

CREDIT SUISSE FIRST BOSTON CORPORATION
BANC OF AMERICA SECURITIES LLC
ROBERTSON STEPHENS, INC.

BY: CREDIT SUISSE FIRST BOSTON CORPORATION

|by |  | /s/RENEE COMPTON RYANName: Renee Compton Ryan Title: Director | 
|-- |  | ------------------------------------------------------------- | 

12

---

QuickLinks