Poseida Therapeutics Presents Encouraging Preclinical Data Highlighting P-ckit-ALLO1 at the ASGCT 2022 Annual Meeting

Preclinical data supports potential of P-ckit-ALLO1 as a less toxic preconditioning agent for hematopoietic stem cell (HSC) transplants

P-ckit-ALLO1 eliminates >95% of hematopoietic stem and progenitor cells (HSPCs) and prolongs survival in mouse models of acute myeloid leukemia (AML)

SAN DIEGO, May 17, 2022 /PRNewswire/ -- Poseida Therapeutics, Inc. (Nasdaq: PSTX), a clinical-stage biopharmaceutical company utilizing proprietary genetic engineering platform technologies to create cell and gene therapeutics with the capacity to cure, today will present preclinical data at the American Society of Gene and Cell Therapy (ASGCT) 2022 Annual Meeting highlighting the use of anti-c-kit CAR-T cells as a preconditioning agent to enable hematopoietic stem cell (HSC) transplants. The ASGCT Annual Meeting is being held in Washington, D.C. and virtually May 16-19, 2022.

"We are pleased to present preclinical data from our anti-c-kit CAR-T program demonstrating the broad capabilities of our platform technologies to potentially improve patient outcomes," said Devon Shedlock, Ph.D., Chief Scientific Officer, Cell Therapies at Poseida Therapeutics. "P-ckit-ALLO1 is an allogeneic or 'off-the-shelf' adoptive cell therapy comprised of early memory T cells expressing key bone marrow homing markers that enable it to effectively eliminate hematopoietic stem cells (HSC) and robustly inhibit growth of acute myeloid leukemia (AML) cells in animal models. The data presented today show that P-ckit-ALLO1 could be an ideal treatment as both a safer HSC transplantation approach as well as an anti-tumor therapy."

Presentation details:

Poster Presentation: Anti-c-kit CAR-T Cells Enable HSC Engraftment in a Humanized Model of Stem Cell Transplant Conditioning
Session Title: Cell Therapies II
Session Date/Time: Tuesday, May 17, 2022, 5:30 – 6:30 PM ET
Poster Board Number: Tu-239
Location: Walter E. Washington Convention Center, Hall D
Abstract Number: 734

P-ckit-ALLO1 leverages the Company's proprietary piggyBac^® Gene Delivery System, Cas-CLOVER™ Site-specific Gene Editing System, and a proprietary "Booster Molecule" to develop fully allogeneic CAR-T cells targeting human c-kit, which is highly expressed on HSCs as well as on myeloid malignancies such as AML, meaning the treatment can be used for either HSC transplant conditioning or as a treatment for AML. In addition to the CAR gene, the piggyBac transposon includes a selection marker for generation of a pure CAR+ product and a proprietary fast-acting safety switch enabling rapid clearance of the reactive CAR-T cells prior to donor HSC transplant.

Data demonstrated that P-ckit-ALLO1 was able to eliminate 95% of HSCs in bone marrow within four days, which was sufficient to enable HSC transplant in a humanized mouse model with reduced acute myelotoxicity compared to busulfan. In addition, data demonstrated that P-ckit-ALLO1 was able to significantly inhibit growth of AML cells in animal models and significantly prolong survival. These encouraging data support the potential of anti-c-kit CAR-T cells for use as an alternative and less toxic conditioning regimen to facilitate HSC transplantation as well as a potential anti-tumor therapy.

Poseida Therapeutics is a clinical-stage biopharmaceutical company dedicated to utilizing our proprietary genetic engineering platform technologies to create next generation cell and gene therapeutics with the capacity to cure. We have discovered and are developing a broad portfolio of product candidates in a variety of indications based on our core proprietary platforms, including our non-viral piggyBac® DNA Delivery System, Cas-CLOVER™ Site-specific Gene Editing System and nanoparticle- and AAV-based gene delivery technologies. Our core platform technologies have utility, either alone or in combination, across many cell and gene therapeutic modalities and enable us to engineer our portfolio of product candidates that are designed to overcome the primary limitations of current generation cell and gene therapeutics. To learn more, visit www.poseida.com and connect with us on Twitter and LinkedIn.

Statements contained in this press release regarding matters that are not historical facts are "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995. Such forward-looking statements include statements regarding, among other things, the potential benefits of Poseida's technology platforms and product candidates, Poseida's plans and strategy with respect to developing its technologies and product candidates, and anticipated timelines and milestones with respect to Poseida's development programs and manufacturing activities. Because such statements are subject to risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. These forward-looking statements are based upon Poseida's current expectations and involve assumptions that may never materialize or may prove to be incorrect. Actual results could differ materially from those anticipated in such forward-looking statements as a result of various risks and uncertainties, which include, without limitation, risks and uncertainties associated with development and regulatory approval of novel product candidates in the biopharmaceutical industry and the other risks described in Poseida's filings with the Securities and Exchange Commission. All forward-looking statements contained in this press release speak only as of the date on which they were made. Poseida undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date on which they were made, except as required by law.

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