To Our Clients:

Enclosed for your consideration are the Offer to Purchase dated August 6, 2026 (the “Offer to Purchase”), the related Letter of Transmittal (as it may be amended or supplemented from time to time, the “Letter of Transmittal” and, together with the Offer to Purchase, the “Offer”) in connection with the offer by Avena Merger Sub Inc., a Delaware corporation (“Purchaser”), and a wholly owned subsidiary of argenx BV, a private company with limited liability (besloten vennootschap) organized under Belgian law (“Parent”), to acquire all of the outstanding shares of common stock, par value $0.001 per share (the “Shares”), of Forte Biosciences, Inc., a Delaware corporation (“Forte”), for $77.00 per Share in cash, without interest (the “Offer Price”), subject to any applicable withholding of taxes, upon the terms and subject to the conditions set forth in the Offer. Also enclosed is Forte’s Tender Offer Solicitation/Recommendation Statement on Schedule 14D-9.

We or our nominees are the holder of record of Shares held for your account. A tender of such Shares can be made only by us or our nominees as the holder of record and pursuant to your instructions. The enclosed Letter of Transmittal is furnished to you for your information only and cannot be used by you to tender Shares held by us or our nominees for your account.

We request instructions as to whether you wish us to tender any or all of the Shares held by us or our nominees for your account, upon the terms and subject to the conditions set forth in the Offer.

Your attention is directed to the following:

corporation and a wholly owned subsidiary of Parent. At the effective time of the Merger (being such date and at such time as the certificate of merger in respect of the Merger is duly filed with the Secretary of State of the State of Delaware or at such later time and date as may be agreed upon by the parties to the Merger Agreement in writing and specified in the certificate of merger in accordance with the DGCL, the “Effective Time”), each outstanding Share (other than (i) Shares held owned both as of the Offer Commencement Date and immediately prior to the Effective Time by Forte (including those held in Forte’s treasury), Parent, Purchaser or any direct or indirect wholly owned subsidiary of Forte or Parent (other than Shares held on behalf of third parties), (ii) Shares irrevocably accepted for purchase in the Offer and (iii) Shares issued and outstanding immediately prior to the Effective Time that are held by holders who are entitled to appraisal rights under Section 262 of the DGCL and have properly exercised and perfected their respective demands for appraisal of such Shares in the time and manner provided in Section 262 of the DGCL and, as of the Effective Time, have neither validly withdrawn nor lost their rights to such appraisal and payment under the DGCL) will be automatically converted into the right to receive the Offer Price, in cash, without interest, subject to any applicable withholding of taxes. No appraisal rights are available in connection with the Offer. However, if the Offer is successful and the Merger is consummated, any Shares issued and outstanding as of immediately prior to the Effective Time that are held of record or beneficially owned by holders who (A) did not tender their Shares in the Offer (or, if tendered, validly and subsequently withdrew such Shares prior to the Offer Acceptance Time), (B) follow the procedures set forth in Section 262 of the DGCL, (C) do not thereafter withdraw their demand for appraisal of such Shares or otherwise lose their appraisal rights, in each case in accordance with Section 262 of the DGCL, and (D) in the case of a beneficial owner, have submitted a demand that (x) reasonably identifies the holder of record of the shares for which the demand is made, (y) is accompanied by documentary evidence of such beneficial owner’s beneficial ownership of stock and a statement that such documentary evidence is a true and correct copy of what it purports to be, and (z) provides an address at which such beneficial owner consents to receive notices given by Forte and to be set forth on the verified list to be filed with the Delaware Register in the Delaware Court of Chancery, will be entitled to receive appraisal rights for the “fair value” of their Shares in accordance with Section 262 of the DGCL. The “fair value” of such Shares as of the Effective Time could be more than, the same as or less than the consideration to be received pursuant to the Merger and Forte may argue in any appraisal proceeding that, for purposes of such proceeding, the fair value of such Shares is less than the Offer Price. The Merger Agreement is more fully described in Section 13 of the Offer to Purchase.

If you wish to have us or our nominees tender any or all of your Shares, please complete, sign, detach and return the instruction form below. An envelope to return your instructions to us is enclosed. If you authorize tender of your Shares, all such Shares will be tendered unless otherwise specified on the instruction form. Your prompt action is requested. Your instructions should be forwarded to us in ample time to permit us to submit a tender on your behalf by the Expiration Time.

The Offer is not being made to holders in any jurisdiction in which the making of the Offer or acceptance thereof would not be in compliance with the laws of such jurisdiction. We are not aware of any jurisdiction where the making of the Offer or acceptance thereof would be prohibited by securities, blue sky or other valid laws of such jurisdiction. If we become aware of any U.S. state in which the making of the Offer or acceptance of Shares pursuant thereto would not be in compliance with an administrative or judicial action pursuant to a valid state statute, we will make a good faith effort to comply with that state statute. If, after a good faith effort, we cannot comply with the state statute, the Offer will not be made to (nor will tenders be accepted from or on behalf of) the holders of Shares in that state. In those jurisdictions where applicable laws or regulations require that the Offer be made by a licensed broker or dealer, the Offer will be deemed to be made on behalf of Purchaser by one or more registered brokers or dealers licensed under the laws of such jurisdiction to be designated by Purchaser.

The undersigned acknowledge(s) receipt of your letter and the enclosed Offer to Purchase dated August 6, 2026 and the related Letter of Transmittal (together, as may be amended or supplemented from time to time, the “Offer”), in connection with the offer by Avena Merger Sub Inc., a Delaware corporation (“Purchaser”), and a wholly owned subsidiary of argenx BV, a private company with limited liability (besloten vennootschap) organized under Belgian law (“Parent”), to acquire all of the outstanding shares of common stock, par value $0.001 per share (the “Shares”), of Forte Biosciences, Inc., a Delaware corporation (“Forte”), for $77.00 per Share, in cash, without interest, subject to any applicable withholding of taxes and upon the terms and subject to the conditions set forth in the Offer.

The undersigned hereby instruct(s) you to tender to Purchaser the number of Shares indicated below (or if no number is indicated below, all Shares) held by you or your nominees for the account of the undersigned, upon the terms and subject to the conditions set forth in the Offer furnished to the undersigned. The undersigned understands and acknowledges that all questions as to the validity, form and eligibility (including time of receipt) and acceptance for payment of any tender of Shares made on my behalf will be determined by Purchaser in its sole discretion.

The method of delivery of this Instruction Form is at the election and risk of the tendering stockholder. This Instruction Form should be delivered to us in ample time to permit us to submit the tender on your behalf prior to the expiration of the Offer.