While progress has occurred in both cellular and immune checkpoint therapy, the benefit of therapeutic cancer vaccines has been difficult to demonstrate. Prostate cancer may be an exception with the modest activity of Sipuleucel T. We have developed a potentially low cost and easy to administer therapeutic vaccine with the combination of tumor antigen (PSA) and biologic adjuvants (IL2 and GM-CSF). This study is a phase 1a clinical trial of a PSA/IL-2/GM-CSF vaccine in biochemically recurrent hormone-naïve and hormone-independent prostate cancer patients. Major inclusion criteria include adenocarcinoma of the prostate, rising serum PSA and no measurable disease. Phase 1a examines the rate of serious adverse events (SAEs) and dose limiting adverse events (DLAEs) in an initial course of 6 vaccinations (“induction vaccination”). Twenty patients enrolled and nineteen patients completed all six intradermal injections (one patient received 5 vaccines, missed week 11 vaccine) of the PSA/IL-2/GM-CSF vaccine at weeks 1, 2, 3, 7, 11 and 15. None of the patients vaccinated in the phase 1a portion had an SAE or DLAE with the most common AE relating to grade 1 injection site reactions. Fifteen of the 18 patients who received vaccines had immune responses to PSA as demonstrated in a lymphocyte blastogenesis assay by week 31. Interestingly, after vaccination 14 of 20 patients had an increase in the doubling time of their serum PSA, suggesting a slowing of the growth of the prostate cancer. Five of 20 patients have progressed (3 PSA progression and 2 radiologic progression) at 43 weeks’ follow-up.

Citation Format: Jonathan F. Head, Gregory A. Daniels, Michelle McKinney, Jessica Wang-Rodriguez. Forty-three week follow-up of a phase 1a clinical trial of a PSA, IL-2, GM-CSF containing prostate cancer therapeutic vaccine in PSA defined biochemical recurrent prostate cancer patients [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A009.