Nearly a week after filing for a $115 million IPO that it had put off for more than a year, and two months after dosing the first patient in its phase I trial in metastatic castration-resistant prostate cancer, Poseida Therapeutics Inc. has closed on a $110 million series D to continue its CAR T-cell therapy programs.

The series D financing was led by funds advised by Fidelity Management Research Co. LLC, with participation by Adage Capital Management and Schonfeld Strategic Advisors. A number of current investors also participated. BofA Securities was the sole placement agent.

On June 19, Poseida filed to raise up to $115 million from an IPO and plans to list shares on Nasdaq under the symbol PSTX. The company filed for a $115 million IPO in January 2019 but pulled the request in the wake of a federal government shutdown that slowed the process.

In the interim, the company raised a $142 million series C in April 2019, which turned out to be the biggest series C fundraiser of the year. Novartis AG leapt in to invest $75 million while other investors included Malin Corp. plc, Longitude Capital, Vivo Capital and Boxer Capital LLC. New investors included Aisling Capital Management, Pentwater Capital Management, Perceptive Advisors as well as additional undisclosed institutional investors.

In May, Poseida reported the first patient had been dosed in its phase I trial evaluating P-PSMA-101, an autologous CAR T therapeutic candidate comprising self-renewing stem cell memory T cells, in treating metastatic castration-resistant prostate cancer (mCRPC). Preclinical data showed P-PSMA-101 eliminated tumor cells to undetectable levels in 100% of the animals it tested, with one incidence of relapse in the low-dose cohort. Those data were generated in a preclinical model of mCRPC in which immuno-deficient mice were implanted with solid tumors composed of a human mCRPC cell line, the company said.

“To our knowledge, based on published literature, no other product candidate has shown complete solid tumor elimination in this preclinical model,” the company noted in its SEC S-1 filing of June 19.

The phase I, open-label, multicenter, dose-escalating trial includes cohorts receiving single and multiple doses of P-PSMA-101, which targets prostate-specific membrane antigen that is expressed on metastatic castration-resistant prostate cancer cells, to determine which dose has the fewest side effects. The company said there is a strong correlation between the percentage of TSCM cells in the product candidate and best clinical response. The primary outcome measures are assessing P-PSMA-101’s safety, determining the maximum tolerated dose and accessing its efficacy. The study’s estimated primary completion date is September 2023.

Also in May, the FDA granted P-BCMA-101 orphan designations for treating relapsed and/or refractory multiple myeloma and for multiple myeloma. P-BCMA-101 cells targets B-cell maturation antigen (BCMA). Poseida is evaluating P-BCMA-101 in a potentially registrational phase II trial and an expanded phase I trial for treating patients with relapsed/refractory multiple myeloma in the outpatient setting. Interim results from the phase I show favorable tolerability with low levels of cytokine release syndrome and almost no neurotoxicity. Based on those results, the company initiated its phase II study on a fully outpatient basis.

The company’s allogeneic programs, using well-characterized cells from a healthy donor and then modified from Poseida’s piggyBac and Cas-CLOVER gene editing technology to reduce or eliminate reactivity, includes P-BCMA-ALL01 for treating relapsed/refractory multiple myeloma patients. An IND may be filed later this year or sometime in 2021. Another of its allogeneic programs is P-MUC1C-ALL01, which is in preclinical development for multiple solid tumor indications. The company has said it could treat a range of solid tumors derived from epithelial cells such as breast, colorectal, lung, ovarian, pancreatic and renal cancers, and cancers expressing a cancer-specific form of the Mucin 1 protein.

Also in the past year, San Diego-based Poseida cut a deal with Aro Biotherapeutics Co., of Philadelphia, that involved licensing CAR T-cell therapies.

In May 2019, Be The Match Biotherapies, a subsidiary of the National Marrow Donor Program/Be The Match that offers integrated services and software to manage the collection and delivery of cellular therapies, signed on to provide end-to-end support services for clinical development of Poseida's BCMA and PSMA CAR T-cell programs. No financial terms were released.

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