14570 Background: Prostatic acid phosphatase (PAP) is a tumor antigen in prostate cancer. Clinical trials conducted in patients with metastatic prostate cancer targeting PAP by means of antigen presenting-cell vaccines have suggested clinical benefit in terms of disease progression and overall survival. Ultimately, tumor vaccines may be most effective in the setting of minimal residual disease. We have been investigating plasmid DNA vaccines encoding PAP in rodent models. We found these to be safe and effective in eliciting PAP-specific CD8 T cells and saw evidence of anti-tumor efficacy. We report here the initial immunological results from a dose-escalation portion of a phase I trial testing a DNA vaccine encoding PAP in patients with minimal residual stage D0 prostate cancer. Methods: Patients with clinical stage D0 prostate cancer with rising PSA were vaccinated over a 12-week period, 6 times at 14-day intervals, with a plasmid DNA vaccine encoding PAP (pTVG-HP). Vaccinations were administered intradermally with 100 mcg, 500 mcg, or 1500 mcg doses, and with 200 mcg of GM-CSF co-administered as a vaccine adjuvant. Immunological responses were evaluated by antigen-specific T cell proliferation and IFNγ secretion, and by ELISA for PAP-specific IgG. Results: At present 9 patients have been enrolled in a dose-escalation portion of the trial, and 6 have completed all immunizations. No serious adverse events have been observed, and no patients have discontinued treatment. To date, immunological analysis has been performed for the first, lowest dose cohort. PAP-specific CD4 and CD8 T cell responses, measured by antigen-specific T cell proliferation, were elicited following immunization in 2 of 3 patients. PAP-specific IgG antibodies were not detectable in these patients following vaccination. Conclusions: Intradermal immunization of patients with stage D0 prostate cancer with pTVG-HP has been without evidence of adverse events in doses up to 500 mcg. CD4 and CD8 T cell responses have been observed, consistent with a predominantly cellular immune response, at even the lowest dose of vaccine. Immunological analysis will be performed for patients completing the other dose levels, and all patients will be followed for changes in serum PSA levels. No significant financial relationships to disclose.
Safety and Immunological Efficacy of a DNA Vaccine Encoding Prostatic Acid Phosphatase in Patients With Stage D0 Prostate Cancer