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

To measure antigen-specific interferon-secretion by enzyme-linked immunospot (ELISPOT) assay, which measures antigen-specific interferon-secretion.

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.

One time blood draw at time of consent. Blood will be stored until all subjects have been enrolled and then the enzyme-linked immunospot (ELISPOT) assay will be done to measure the antigen-specific interferon secretion.

Number of Participants With Antigen-specific Interferon- Secretion as Measured by Enzyme-linked Immunospot (ELISPOT) Assay

The spots formed by interferon-gamma-secreting T-cells will be counted with an automated ELISPOT analyzer (AID ELISPOT Classic Reader; Autoimmune Diagnostika GmbH, Strassberg, Germany). The average spot-forming units (SFU) per antigen will be calculated. A response will be considered positive when the average SFU in wells with a given peptide was at least twice that of the average SFU in the no-peptide control wells.

Inclusion Criteria: Histological documented diagnosis of prostate cancer 18 years of age or older Signed informed consent form approved by the University of Arkansas for Medical Sciences (UAMS) Institutional Review Board (IRB) Exclusion Criteria: Subjects must have no other current malignancies. Subjects with prior history at any time of any basal or squamous skin cancer are eligible, provided they are disease-free at the time of registration. Subjects with other malignancies are eligible if they have been continuously disease free for ≥ 5 years prior to the time of registration