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Abstract CT061: Interim results of a phase Ia clinical trial of a PSA, IL-2, GM-CSF containing prostate cancer therapeutic vaccine in PSA defined biochemical recurrent prostate cancer patients

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 lower cost and easy to administer therapeutic vaccine with the combination of tumor antigen (PSA) and biologic adjuvants (IL-2 and GM-CSF). This study is a Phase 1a clinical trial of a PSA/IL-2/GM-CSF vaccine in 20 biochemically recurrent hormone-naive 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 a 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. Four of 20 patients have progressed (3 PSA progression and 1 radiological progression) at 31 weeks follow-up. Citation Format: Jonathan F. Head, Gregory A. Daniels, Michelle A. McKinney, Weg M. Ongkeko, Kyoko Sakamoto, Jessica Wang-Rodriguez. Interim results of a phase Ia 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 American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT061.