RAPT Therapeutics, Inc.

1. Represents the annual grant of restricted stock units ("RSUs") under the Issuer's Amended & Restated Non-Employee Director Compensation Policy, previously granted to the Reporting Person and reported on Form 4 dated February 2, 2026, which were scheduled to fully vest on the first anniversary of the grant date. Each RSU represents a contingent right to receive one share of common stock upon vesting.

2. The Issuer entered into an Agreement and Plan of Merger, dated January 19, 2026 (the "Merger Agreement") with GlaxoSmithKline LLC, a Delaware limited liability company ("Parent"), Redrose Acquisition Co., a Delaware corporation and a wholly owned subsidiary of Parent ("Purchaser") and solely for purposes of providing a guaranty pursuant to Section 8.11 of the Merger Agreement, GSK plc, a public limited company organized under the laws of England and Wales. Pursuant to the Merger Agreement, Purchaser completed a tender offer to acquire all of the issued and outstanding shares of common stock of the Issuer, for $58.00 per share (the "Offer Price"), in cash, without interest and subject to any applicable withholding of taxes. On March 3, 2026, Purchaser merged with and into the Issuer, with the Issuer surviving as an indirect wholly owned subsidiary of Parent (the effective time of such merger, the "Effective Time").

3. Pursuant to the Merger Agreement, each RSU award that was outstanding as of immediately prior to the Effective Time, whether vested or unvested, was cancelled and converted into the right to receive cash in an amount equal to (i) the total number of Shares issuable in settlement of such RSU immediately prior to the Effective Time without regard to vesting, multiplied by (ii) the Offer Price, which amount shall be paid in accordance with the Merger Agreement.

4. This Form 4 reports securities transacted pursuant to the Merger Agreement.

5. The number of shares underlying this option and the exercise price were adjusted to reflect the 1-for-8 reverse stock split effected by the Issuer on June 16, 2025.

6. Pursuant to the terms of the Merger Agreement, each stock option that was outstanding as of immediately prior to the Effective Time, whether vested or unvested, was accelerated and became fully vested and exercisable as of immediately prior to the Effective Time. At the Effective Time, each stock option that was outstanding and unexercised as of immediately before the Effective Time and which had a per share exercise price that was (a) less than Offer Price, was cancelled and converted solely into the right to receive cash in an amount equal to the product of (i) the total number of shares subject to such stock option immediately prior to the Effective Time, multiplied by (ii) the excess of (x) the Offer Price, over (y) the exercise price payable per share under such stock option, and (b) greater than the Offer Price, was cancelled for no consideration.