A Pilot Study to Assess the Immunogenicity of Candidate PSA Peptides for a Prostate Cancer Vaccine

The goal of this project is to collect information in regards to the immunogenicity of PSA peptides in order to develop a novel therapeutic vaccine. This vaccine will consist of prostate specific antigen (PSA) peptide and Candida skin test reagent. Candida has recently been shown to be a promising new vaccine adjuvant for promoting T-cell responses. It can induce interleukin-12 (promotes T-cell response) secretion by Langerhans cells, the main antigen presenting cells in skin. In a Phase I clinical trial treating women with biopsy-proven high-grade squamous intraepithelial lesions (HSILs), precursors of cervical cancer, a combination of human papillomavirus peptides with Candida was demonstrated to be safe, to induce immune responses to human papillomavirus, and to promote T-helper type 1 (Th-1) response (promotes cellmediated immunity) in vaccine recipients.

For treating prostate cancer, PSA is an ideal antigen as it is expressed in prostate cancer but not in any other organs. The characteristics of peptides that can effectively be used in therapeutic vaccines are their solubility in a single solution, immunogenicity in terms of containing large number of T-cell epitopes (so the vaccine can be used for all patients and not just a few that express certain Human Leukocyte Antigen (HLA) tissue types), and ability to mature Langerhans cells which in turn promotes T-cell activity.

In this protocol the investigators focus on the immunogenicity of candidate peptides.