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Phase I Clinical Trial of a HER-2/neu Peptide (E75) Vaccine for the Prevention of Prostate-Specific Antigen Recurrence in High-Risk Prostate Cancer Patients

Authors' Affiliations: ¹ Clinical Breast Care Project, Department of Surgery and ² Center for Prostate Disease Research, Department of Urology, Walter Reed Army Medical Center, Washington, District of Colombia; ³ Clinical Breast Care Project, Immunology and Research Center, Uniformed Services University of the Health Sciences, Bethesda, Maryland; and ⁴ University of Texas M.D. Anderson Cancer Center, Houston, Texas

Requests for reprints: George E. Peoples, Clinical Breast Care Project, Immunology and Research Center, Uniformed Services University of the Health Sciences, 4301 Jones Bridge Road, Building 139, Bethesda, MD 20814. Phone: 202-782-9692; Fax: 301-493-6840; E-mail: george.peoples{at}na.amedd.army.mil.

Purpose: The E75 peptide is an immunogenic peptide from the HER-2/neu protein that is substantially expressed in prostate cancer. We are conducting a clinical trial of an E75/granulocyte macrophage colony-stimulating factor vaccine to prevent post-prostatectomy prostate-specific antigen (PSA) recurrences in high-risk prostate cancer (HRPC) patients.

Experimental Design: Prostate cancer patients at high risk for recurrence were prospectively evaluated and identified by the validated Center for Prostate Disease Research (CPDR)/CaPSURE high-risk equation. From these high-risk equation patients, 27 HER-2/neu-expressing prostate cancer patients were enrolled. HLA-A2⁺ patients (n = 17) were vaccinated, whereas HLA-A2^– patients (n = 10) were followed as clinical controls. Local/systemic toxicities, immunologic responses, and time to recurrence were measured.

Results: This vaccine is safe with only minor toxicities observed. Additionally, the vaccine is immunogenic with all patients showing both in vivo and in vitro phenotypic and functional immune responses, although variable. HLA-A2⁺ patients were found to have larger tumors, higher postoperative Gleason scores, and more high-risk CPDR scores than HLA-A2^– patients. Despite these differences, disease-free survival was not different between the vaccinated HLA-A2⁺ patients and the HLA-A2^– controls at a median follow up of 23 months. Three of the four vaccinated patients that recurred had rising PSAs at the initiation of the trial. Ex vivo phenotypic assays were predictive of recurrences and correlated in general with functional assays.

Conclusions: The E75 vaccine strategy is safe and effective in eliciting an immune response against the HER-2/neu protein in HRPC patients and may be useful as a preventive strategy against disease recurrence. Vaccination in response to a rising PSA may be too late.

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