Phase I study of a vaccine using recombinant vaccinia virus expressing PSA (rV-PSA) in patients with metastatic androgen-independent prostate cancer

Abstract

Background: A Phase I trial of recombinant vaccinia prostate specific antigen (rV-PSA) in patients with advanced metastatic prostate cancer was conducted. This report describes 42 patients who were treated with up to three monthly vaccinations.

Methods: All patients were entered on a dose-escalation phase I study of recombinant vaccinia containing the gene for PSA (rV-PSA). The primary objective of this study was to determine the safety of this vaccine in metastatic androgen-independent prostate cancer patients. A secondary objective was to assess evidence of anti-tumor activity by PSA measurements, radiologic findings, and immunologic methods.

Results: There was no significant treatment-related toxicity apart from erythema, tenderness, and vesicle formation that lasted several days at the site of injection in some patients. There were immunologic responses, in selected patients, as evidenced by an increase in the proportion of PSA-specific T cells after vaccination. Furthermore, we show that these patients' T cells can lyse PSA-expressing tumor cells in vitro.

Conclusion: Given the low toxicity profile and the evidence of immunologic activity, we believe future study is warranted with PSA-based vaccines in prostate cancer. New PSA-based vaccines and vaccine strategies are currently being evaluated.