DNA vaccine with pembrolizumab to elicit antitumor responses in patients with metastatic, castration-resistant prostate cancer (mCRPC).

168Background: We have previously investigated a DNA vaccine encoding prostatic acid phosphatase (PAP, pTVG-HP) in patients with PSA-recurrent prostate cancer, and have demonstrated that this can be safely administered over many months and can elicit PAP-specific T cells. A phase 2 trial is currently underway. In preclinical models, we have found that blockade of regulatory receptors, including PD-1, at the time of T cell activation with vaccination produced anti-tumor responses in vivo. Similarly, we have recently found that patients with prostate cancer previously immunized with a DNA vaccine develop PD-1-regulated T cells. These findings suggested that combined PD-1 blockade with vaccination should elicit superior anti-tumor responses in patients with prostate cancer. Methods: A clinical trial was designed to evaluate the immunological and clinical efficacy of pTVG-HP when delivered in combination or in sequence with pembrolizumab, in patients with mCRPC. Serial biopsies, blood draws, and exploratory F...