UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the Securities

Exchange Act of 1934 (Amendment No.           )

Filed by the Registrant ☒

Filed by a Party other than the Registrant ☐

Check the appropriate box:

☐ Preliminary Proxy Statement

☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material Pursuant to §240.14a-12

Poseida Therapeutics, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check all boxes that apply):

☒ No fee required.

☐ Fee paid previously with preliminary materials.

☐ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11.

Poseida Therapeutics P.O. BOX 8016, CARY, NC 27512-9903 Poseida Therapeutics, Inc. Important Notice Regarding the Availability of Proxy Materials Stockholders Meeting to be held on June 16, 2022 For Stockholders of record as of April 20, 2022 This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. This is not a ballot. You cannot use this notice to vote your shares. We encourage you to access and review all of the important information contained in the proxy materials before voting. To view the proxy materials, and to obtain directions to attend the meeting, go to: www.proxydocs.com/PSTX To vote your proxy while visiting this site, you will need the 12 digit control number in the box below. Under United States Securities and Exchange Commission rules, proxy materials do not have to be delivered in paper. Proxy materials can be distributed by making them available on the internet. For a convenient way to view proxy materials and VOTE go to www.proxydocs.com/PSTX Have the 12 digit control number located in the shaded box above available when you access the website and follow the instructions. If you want to receive a paper or e-mail copy of the proxy material, you must request one. There is no charge to you for requesting a copy. In order to receive a paper package in time for this year's meeting, you must make this request on or before June 06, 2022. To order paper materials, use one of the following methods. INTERNET www.investorelections.com/PSTX TELEPHONE (866) 648-8133 * E-MAIL paper@investorelections.com When requesting via the Internet or telephone you will need the 12 digit control number located in the shaded box above. * If requesting material by e-mail, please send a blank e-mail with the 12 digit control number (located above) in the subject line. No other requests, instructions OR other inquiries should be included with your e-mail requesting material. Poseida Therapeutics, Inc. Meeting Type: Annual Meeting of Stockholders Date: Thursday, June 16, 2022 Time: 01:00 PM, Pacific Time Place: Annual Meeting to be held live via the Internet. Please visit www.proxydocs.com/PSTX for more details. You must register to attend the meeting online and/or participate at www.proxydocs.com/PSTX SEE REVERSE FOR FULL AGENDA

Poseida Therapeutics, Inc. Annual Meeting of Stockholders THE BOARD OF DIRECTORS RECOMMENDS A VOTE: FOR ON PROPOSALS 1 AND 2 PROPOSAL 1. To elect the Board of Directors’ three nominees named below to serve as Class II directors to hold office until the 2025 Annual Meeting of Stockholders. 1.01 Luke Coming 1.02 Mark J. Gergen, J.D 1.03 Marcea B. Lloyd, J.D. 2. To ratify the selection by the Audit Committee of the Board of Directors of PricewaterhouseCoopers LLP as the independent registered public accounting firm of Poseida Therapeutics for its fiscal year ending December 31, 2022. 3. To conduct any other business properly brought before the meeting.