HLA-associated multipeptide vaccination in biochemically relapsed prostate cancer patients

Abstract

5134 Background: We conduct a phase I/II monocenter clinical trial using multi peptide vaccination in patients with hormone naive, biochemically relapsed prostate cancer. The synthetic peptides applied are MHC-class I (HLA-A2) and -class II binders for activating CD4+ and CD8+ T- effector cells in vivo. Study endpoints are side effects as well as PSA- and T-cell response. Methods: Patients (pts) with rising PSA after primary curative surgical treatment without metastatic imageable lesions receive 14 peptides emulsified in Montanide ISA51 subcutaneously, combined with one of four T-cell stimulatory adjuvants versus no adjuvant for 18 months (mo) or until progression. PSA doubling time (DT) and clinical performance are monitored. T-cell activity and specifity are assessed with Elispot assay, tetramer staining and intracellular cytokine stainings. Results: 25 out of 35 pts have terminated the study treatment so far. During the vaccination period, geometric mean PSA DT increased from 7.8 mo (range 1.5 - 44.8 mo, 25 pts) to 11.8 months (range 2.2 - 571.3 mo, 24pts) whereas 1 pt showed a decreasing PSA value. Overall 8/25 pts (32%) had a mean rise of PSA DT of 81.6 mo and four of them did not receive any further treatment and were evaluable for follow-up (FU) after peptide vaccination (FU median 16 mo, range 5–33). These four pts raised their mean geometric PSA DT from 8.2 mo prior study treatment to 51.9 mo at treatment end and 52.5 mo at end of FU. PSA progressed unchanged in 10 patients (40%) or increased intermittently only in 4 pts. Two pts had PSA decline or DT increase during FU but not during the treatment period. Four patients (16%) exhibited an allergic reaction CTCAE II°. All pts reacted to at least one of the tumor antigen-derived HLA-class I epitopes after the fourth vaccine injection and up to six peptides were recognized simultaneously by CD8+ T cells in some individuals. Conclusions: Multi peptide vaccination stabilized or slowed down PSA progress in 11 of 25 cases. Stimulation of specific T-cell response is observed. Rise of PSA DT delaying standard treatment up to 33 mo and thus, delaying disease specific mortality is feasible. No significant financial relationships to disclose.