Clinical Trial Results of a HER2/neu Peptide Vaccine for the Prevention of PSA Recurrence in High-risk Prostate Cancer Patients

Thomas E. Novak, Matthew T. Hueman*, Zia A. Dehqanzada*, David G. McLeod, George E. Peoples*
Walter Reed Army Medical Center, Washington, DC

Introduction: Early prostate cancer vaccine trials have primarily targeted patients with advanced, hormone-refractory disease. The authors seek to investigate the safety, immunogenic response to and clinical efficacy of a purified peptide vaccine in prostate cancer patients with adverse clinical parameters that predict a high rate of biochemical recurrence following radical prostatectomy.
Methods: Patients undergoing radical prostatectomy were prospectively identified at high risk for recurrence by the validated CPDR/CaPSURE equation. From these high-risk patients, twenty-six eligible patients with HER2/neu expressing tumors were enrolled. Sixteen HLA-A2(+) patients were vaccinated with purified preparations of the E75 epitope of the HER2/neu protein while ten HLA-A2(-) patients were followed as clinical controls. Toxicities, immunologic responses, and time to recurrence were measured.
Results: Only minor toxicities occurred. All vaccinated patients demonstrated some degree of peptide-specific immune response using both in vitro and in vivo assays. The vaccinated HLA-A2+ patients were noted to have larger tumors, higher post-operative Gleason scores, more positive margins and higher CPDR recurrence risk scores. Despite this, preliminary data identified comparable disease-free survival between the vaccinated and control patients (logrank p =0.3547) at a median follow-up of 23 months.
Conclusion: The E75 prostate cancer vaccine is safe and effective at generating an immune response against the E75 epitope of the HER2/neu protein. This immunity may confer some protection against biochemical failure in patients at high-risk for recurrence following radical prostatectomy.

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