TENDER AND SUPPORT AGREEMENT This TENDER AND SUPPORT AGREEMENT (this " Agreement "), dated as of

TENDER AND SUPPORT AGREEMENT

This TENDER AND SUPPORT AGREEMENT (this "Agreement"), dated as of March 31, 2026, is by and among Biogen

Inc., a Delaware corporation ("Parent"), Aspen Purchaser Sub, Inc., a Delaware corporation and a wholly owned subsidiary of Parent ("Purchaser"), and each stockholder listed on the signature pages hereto

(each, a "Stockholder").

WHEREAS, each Stockholder is, as of the date hereof, the record or beneficial

owner (as defined in Rule 13d-3 under the Securities Exchange Act of 1934, as amended (the "Exchange Act")) of the number of outstanding shares of common stock, par value $0.0001 per share

(the "Shares"), of Apellis Pharmaceuticals, Inc., a Delaware corporation (the "Company"), set forth opposite the name of such Stockholder on Schedule I hereto;

WHEREAS, contemporaneously with the execution of this Agreement, Parent, Purchaser and the Company are entering into that certain Agreement

and Plan of Merger, dated as of the date hereof (as it may be amended or supplemented from time to time pursuant to the terms thereof, the "Merger Agreement"), pursuant to which, among other things, (a) Parent has agreed to

cause Purchaser to commence a tender offer (as it may be extended, amended or supplemented from time to time in accordance with the Merger Agreement, the "Offer") to acquire all of the outstanding Shares and (b) as soon as

practicable following the consummation of the Offer, Purchaser will merge with and into the Company (the "Merger") in accordance with Section 251(h) of the General Corporation Law of the State of Delaware (the

"DGCL"), with the Company surviving the Merger as a wholly owned subsidiary of Parent, all upon the terms and subject to the conditions set forth in the Merger Agreement; and

WHEREAS, as a condition of and inducement to the willingness of Parent and Purchaser to enter into the Merger Agreement, each Stockholder,

severally and not jointly (and solely in such Stockholder's capacity as a holder of the Subject Shares (as defined below)), has agreed to enter into this Agreement.

NOW, THEREFORE, in consideration of the foregoing and the mutual covenants and agreements set forth herein, and intending to be legally bound

hereby, the parties hereto agree as follows:

SECTION 1. Representations and Warranties of each Stockholder.

Each Stockholder hereby represents and warrants to Parent and Purchaser as follows:

(a) As of the date hereof, such Stockholder (together with such Stockholder's spouse if such Stockholder is an individual and is

married, and the Subject Shares constitute community property under applicable law) (i) is the beneficial owner of the Shares set forth opposite such Stockholder's name on Schedule I to this Agreement (such Shares, together with

any Shares described in Section 10, the "Subject Shares") and (ii) except as set forth in Schedule I to this Agreement, does not have any record or beneficial ownership interest in any other

Shares or hold any shares of restricted stock, performance-based stock units, deferred stock units, options to acquire Shares, warrants or other rights or securities convertible into or exercisable or exchangeable for Shares.

(b) If such Stockholder is an individual, such Stockholder has the legal capacity, right and authority to execute, deliver and perform this

Agreement and to consummate the transactions contemplated hereby. If such Stockholder is an entity, such Stockholder (i) is duly organized, validly existing and in good standing (to the extent such concepts are applicable) under the laws of the

jurisdiction of its organization and (ii) has all requisite corporate (or similar, in the case of a non-corporate entity) power and authority to enter into this Agreement, to perform its obligations

hereunder and to consummate the transactions contemplated hereby, and the execution and delivery by such Stockholder of this Agreement, the performance by such Stockholder of its obligations hereunder and the consummation by such Stockholder of the

transactions contemplated hereby have been duly and validly authorized by all necessary corporate (or similar, in the case of a non-corporate entity) action on the part of such Stockholder, and no additional

corporate (or similar, in the case of a

non-corporate entity) proceedings or actions on the part of such Stockholder are necessary to authorize the execution and delivery by such Stockholder of

this Agreement, the performance by such Stockholder of its obligations hereunder or the consummation of the transactions contemplated hereby.

(c) This Agreement has been duly and validly executed and delivered by such Stockholder and, assuming the due authorization, execution and

delivery by Parent and Purchaser, constitutes a valid and binding obligation of such Stockholder, enforceable against such Stockholder in accordance with its terms, subject to the Bankruptcy and Equity Exception.

(d) The execution and delivery of this Agreement by such Stockholder does not, and the consummation by such Stockholder of the transactions

contemplated by this Agreement shall not, (i) in the event that such Stockholder is an entity, conflict with, or result in any violation or breach of, any provision of the certificate of incorporation, bylaws, limited liability company

agreement or partnership agreement (or similar governing documents) of such Stockholder, (ii) conflict with, or result in any violation or breach of, or constitute a default (or give rise to a right of termination, cancellation or acceleration

of any obligation or loss of any material benefit) under, or require a notice, consent or waiver under, any of the terms, conditions or provisions of any contract to which such Stockholder is a party or by which any of its properties or assets

(including such Stockholder's Subject Shares) are bound, or result in the loss of a material benefit or rights under any such contract, (iii) result in the creation or imposition of any Lien on any asset of such Stockholder (including

such Stockholder's Subject Shares), other than Stockholder Permitted Liens (as defined below) or a Lien created by Parent or Purchaser, or (iv) conflict with or violate any permit, concession, franchise, license, judgment, injunction,

order, decree, statute, law, ordinance, rule or regulation applicable to such Stockholder or any of its properties or assets (including such Stockholder's Subject Shares), except in the case of clauses (ii) through (iv) as, individually

or in the aggregate, would not reasonably be expected to prevent, materially delay or materially impair the ability of such Stockholder to fulfill its obligations under this Agreement or consummate the transactions contemplated by this Agreement.

(e) Such Stockholder's Subject Shares are now, and at all times during the term hereof will be (except for Subject Shares

transferred in accordance with Section 4(b)), held beneficially and either as of record by such Stockholder or by a nominee or custodian for the benefit of such Stockholder, free and clear of all Liens, except for

(i) any such Liens created and expressly contemplated by this Agreement (in connection therewith any restrictions on transfer or any other Liens have been waived by appropriate consent) and (ii) Liens imposed by federal or state

securities laws (collectively, "Stockholder Permitted Liens").

(f) Other than as provided in this Agreement and

except to the extent limited or restricted with respect to Subject Shares for which such Stockholder is the beneficial owner but not the holder of record as a result of such Stockholder being the beneficial owner but not the holder of record, such

Stockholder has full voting power with respect to all such Stockholder's Subject Shares, and full power of disposition, full power to issue instructions with respect to the matters set forth herein and full power to agree to all of the matters

set forth in this Agreement, in each case with respect to all such Stockholder's Subject Shares. None of such Stockholder's Subject Shares are subject to any stockholders' agreement, proxy, voting trust or other agreement or

arrangement with respect to the voting of such Subject Shares, except as created and expressly contemplated by this Agreement.

Stockholder understands and acknowledges that Parent and Purchaser are entering into the Merger Agreement in reliance upon such Stockholder's execution, delivery and performance of this Agreement.

(h) As of the date hereof, there are no Legal Proceedings pending or, to such Stockholder's actual knowledge, threatened against such

Stockholder before or by any Governmental Entity, that, individually or in the aggregate, would reasonably be expected to prevent, materially delay or materially impair the ability of such Stockholder to fulfill its obligations under this Agreement

or consummate the transactions contemplated by this Agreement. As of the date hereof, there are no judgments, orders or decrees by any Governmental Entity outstanding against such Stockholder that, individually or in the aggregate, would reasonably

be expected to prevent, materially delay or materially impair the ability of such Stockholder to fulfill its obligations under this Agreement or consummate the transactions contemplated by this Agreement.

(i) No agent, broker, investment banker, financial advisor or other firm or Person is or

shall be entitled to any broker's, finder's, financial advisor's or other similar fee or commission from the Company or any of its Subsidiaries in connection with such Stockholder tendering the Subject Shares based upon any

agreement made by or on behalf of the Stockholder in its capacity as such.

SECTION 2. Representations and Warranties of Parent and

Purchaser. Each of Parent and Purchaser hereby represents and warrants to each Stockholder as follows:

(a) Each of Parent and

Purchaser is a corporation duly organized, validly existing and in good standing under the laws of the State of Delaware.

Parent and Purchaser has the corporate power and authority to execute and deliver and perform its obligations under this Agreement.

This Agreement has been duly executed and delivered by each of Parent and Purchaser and, assuming due authorization, execution and delivery by the Stockholders, this Agreement constitutes the valid and binding obligation of each of Parent and

Purchaser and is enforceable against each of Parent and Purchaser in accordance with its terms, subject to the Bankruptcy and Equity Exception.

(d) The execution and delivery of this Agreement by each of Parent and Purchaser does not, and the consummation by Parent and Purchaser of

the transactions contemplated by this Agreement shall not, (i) conflict with, or result in any violation or breach of, any provision of the certificate of incorporation, bylaws or other organizational documents of Parent or Purchaser,

(ii) conflict with, or result in any violation or breach of, or constitute a default (or give rise to a right of termination, cancellation or acceleration of any obligation or loss of any material benefit) under, or require a notice, consent or

waiver under, any of the terms, conditions or provisions of any contract to which Parent or Purchaser is a party or by which any of Parent's or Purchaser's properties or assets are bound, or result in the loss of a material benefit or

rights under any such contract, (iii) result in the creation or imposition of any Lien on any asset of Parent or Purchaser, other than Permitted Liens, or (iv) conflict with or violate any permit, concession, franchise, license, judgment,

injunction, order, decree, statute, law, ordinance, rule or regulation applicable to Parent or Purchaser or any of Parent's or Purchaser's properties or assets, except in the case of clauses (ii) through (iv) as, individually or in

the aggregate, would not reasonably be expected to prevent, materially delay or materially impair the ability of Parent or Purchaser to fulfill its obligations under this Agreement or consummate the transactions contemplated by this Agreement.

(e) As of the date hereof, there are no Legal Proceedings pending or, to Parent's knowledge, threatened against Parent or Purchaser

before or by any Governmental Entity, that, individually or in the aggregate, would reasonably be expected to prevent, materially delay or materially impair the ability of Parent or Purchaser to fulfill its obligations under this Agreement or

consummate the transactions contemplated by this Agreement. As of the date hereof, there are no judgments, orders or decrees by any Governmental Entity outstanding against Parent or Purchaser that, individually or in the aggregate, would reasonably

be expected to prevent, materially delay or materially impair the ability of Parent or Purchaser to fulfill its obligations under this Agreement or consummate the transactions contemplated by this Agreement.

SECTION 3. Tender of Subject Shares; Agreement to Vote; Irrevocable Proxy.

(a) Tender of Subject Shares.

(i) Subject to the terms of this Agreement, each Stockholder agrees to tender or cause to be tendered in the Offer all of such

Stockholder's Subject Shares pursuant to and in accordance with the terms of the Offer, free and clear of all Liens, except for Stockholder Permitted Liens. Without limiting the generality of the foregoing, each Stockholder hereby agrees that

promptly following, and in any event no later than ten (10) Business Days after, the commencement (within the meaning of Rule 14d-2 under the Exchange Act) of the Offer (or, if such Stockholder has not

received the Offer Documents by such time, within five (5) Business Days following receipt of the Offer Documents), such Stockholder shall (x) deliver pursuant to the terms of the Offer

(A) a letter of transmittal covering all of such Stockholder's Subject Shares complying with the terms of the Offer, (B) a Certificate or Certificates (or affidavits of loss in

lieu thereof) representing such Shares or an "agent's message" (or such other evidence, if any, of transfer as the Paying Agent may reasonably request) in the case of any Uncertificated Shares, and (C) all other documents or

instruments required to be delivered by stockholders of the Company pursuant to the terms of the Offer, and (y) use reasonable best efforts to instruct such Stockholder's broker or such other Person that is the holder of record of any

Shares beneficially owned by such Stockholder to tender such Shares free and clear of all Liens (other than Stockholder Permitted Liens) in accordance with this Section 3(a) and the terms of the Offer. In the case of any

Shares acquired by such Stockholder subsequent to the date hereof, within three (3) Business Days after such Stockholder acquires beneficial ownership of such Shares free and clear of all Liens that would prevent, interfere with or impede the

transfer of such Shares, such Stockholder shall take the actions specified in this Section 3(a) with respect to such Shares.

(ii) Each Stockholder agrees that, once any of such Stockholder's Subject Shares are tendered in the Offer, such Stockholder will not

withdraw such Subject Shares from the Offer, unless and until this Agreement has been terminated in accordance with Section 7.

(iii) Each Stockholder acknowledges and agrees that Purchaser's obligation to accept for payment Shares tendered into the Offer,

including any Subject Shares tendered by such Stockholder, is subject to the terms and conditions of the Merger Agreement.

Offer is terminated or withdrawn by Purchaser, or the Merger Agreement is validly terminated in accordance with its terms prior to the Acceptance Time, Purchaser shall, and Parent shall cause Purchaser to, promptly return or cause to be returned all

tendered Subject Shares to the applicable Stockholder no later than five (5) Business Days after the applicable termination or withdrawal.

(b) Agreement to Vote. Each Stockholder agrees that:

(i) at any annual or special meeting of the stockholders of the Company, and at any adjournment or postponement thereof, or in connection with

any action proposed to be taken by written consent of the stockholders of the Company or circumstances where a vote, consent or other approval of such Stockholder with respect to the Merger Agreement, the CVR Agreement, the Merger or any of the

other Transactions is sought, such Stockholder shall (or shall cause the applicable holder of record to) be present (in person or by proxy) for purposes of constituting a quorum and vote, or cause to be voted, or exercise its right to consent with

respect to, including by executing a written consent if requested by the Company, all of its Subject Shares in favor of any matter presented to the stockholders of the Company that are necessary to the consummation of the Merger or any of the other

Transactions, including in favor of any proposal to adjourn or postpone to a later date any meeting of the stockholders of the Company at which any of the foregoing matters are submitted for consideration and a vote of the stockholders of the

(ii) at any annual or special meeting of the stockholders of the Company, and at any adjournment or postponement thereof,