Purpose: Active immunotherapy is emerging as a potential therapeutic approach for prostate cancer. We conducted the first phase I trial of an Ii-Key/HER-2/neu(776-790) hybrid peptide vaccine (AE37) with recombinant granulocyte macrophage colony-stimulating factor as adjuvant in patients with HER-2/neu(+) prostate cancer. The primary end points of the study were to evaluate toxicity and monitor patients' immune responses to the vaccine.
Experimental design: Thirty-two HER-2/neu(+), castrate-sensitive, and castrate-resistant prostate cancer patients were enrolled. Of these, 29 patients completed all six vaccination cycles with AE37. Immunologic responses in the total patient population were monitored by delayed-type hypersensitivity and IFN-gamma ELISPOT and intracellular staining. Regulatory T-cell (Treg) frequency and plasma HER-2/neu and transforming growth factor-beta levels were also determined. Immunologic responses were also analyzed among groups of patients with different clinical characteristics. Local/systemic toxicities were monitored throughout the study.
Results: Toxicities beyond grade 2 were not observed. Seventy-five percent of patients developed augmented immunity to the AE37 vaccine and 65% to the unmodified AE36 peptide as detected in the IFN-gamma-based ELISPOT assay. Intracellular IFN-gamma analyses revealed that AE37 elicited both CD4(+) and CD8(+) T-cell responses. Eighty percent of the patients developed a positive delayed-type hypersensitivity reaction to AE36. Additionally, significant decreases could be detected in circulating Treg frequencies, plasma HER-2/neu, and serum transforming growth factor-beta levels. Patients with less extensive disease developed better immunologic responses on vaccination.
Conclusion: AE37 vaccine is safe and can induce HER-2/neu-specific cellular immune responses in patients with castrate-sensitive and castrate-resistant prostate cancer, thus emphasizing the potential of AE37 to target HER-2/neu for the immunotherapy of prostate cancer.