Abstract 5384: Frequency of gene allelic variants of the PAP prostate tumor antigen and association with immune response following antigen-specific genetic vaccination

Abstract

Abstract Prostatic acid phosphatase (PAP) and prostate-specific antigen (PSA) are target antigens in genetic vaccines (viral and DNA plasmid vaccines) being evaluated as treatments for prostate cancer. Amino acid allelic variants and different splicing variants of each protein have been identified as part of the human genome sequencing project. We hypothesized that allelic variants in the coding sequence of one of these target proteins in a vaccine recipient, different from the amino acid sequence of the gene encoded by the vaccine, could account for some immune responses observed following genetic vaccination. Such a finding would be essentially analogous to xenoantigen vaccination approaches using highly homologous antigens. In this report, we used direct Sanger sequencing to identify allelic variations in the genes encoding PAP and PSA from 33 patients with prostate cancer who had been previously immunized with a DNA vaccine encoding PAP. The goal of this study was to identify the frequency of variants encoding amino acid changes for two common tumor antigens, and to specifically determine if PAP-specific amino acid variants were more frequent in patients with evidence of immunological response following genetic vaccination and whether these responses localized to regions of allelic variance. Three synonymous coding mutations within the coding sequence of PAP were observed, one of which was observed in 10/33 patients (30.3%), another in 15/33 patients (45.5%), and another in 17/33 patients (51.5%). These variants appear to be linked, as 9 patients possessed all three. No non-synonymous coding mutations were identified. Thus, while a small and somewhat homogeneous patient population, these findings suggest that PAP amino acid variants may be uncommon and immune responses observed are indeed reactive to the host PAP amino acid sequence, not to antigen amino acid variants. Studies are currently underway to alternatively determine whether immune responses were elicited to peptides spanning four known splice variants of PAP. In contrast, we observed four synonymous coding mutations as well as three non-synonymous coding mutations among the five exons of the non-target antigen PSA. Synonymous or non-synonymous mutations were detected in 11/33 individuals (33.3 %). However, while more variations were observed, each occurred in a smaller frequency of patients and did not appear to be linked. The more heterogeneous sequence of PSA may warrant further investigation to determine whether immune responses elicited by genetic vaccines encoding PSA are reactive to host or vaccine-encoded epitopes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5384. doi:1538-7445.AM2012-5384