Cancer testis antigen PASD1 expression and immunogenicity in human colorectal cancer and polyps

Colorectal cancer (CRC) is a malignant tumor arising from a human inner colon lining that may spread to other organs such as the liver and lungs. Per ARNT Sim domain containing 1 (PASD1) is a cancer-testis antigen expressed in cancers including CRC but not in normal tissues except for normal testes. This study aims to study PASD1 protein as a potential target for CRC immunotherapy. A total of 90 CRC and polyps tissue samples were investigated for PASD1 RNA and protein expression using a real-time polymerase chain reaction and immunohistochemical staining, respectively. Matched patients' peripheral blood mononuclear cells were pulsed with PASD1 peptides and measured for immunogenicity, cell cytotoxicity, and cytokine assays. The clinical data were collected and analyzed accordingly. Our results show that PASD1_v2 mRNA expression was highly expressed in CRC (46.0%) and polyps samples (33.3%). Both PASD1-1 and PASD1-2 proteins were expressed in 31.7% of CRC and 29.4% of polyps samples. Protein expression was weak to moderate positive in the cytoplasm and/or nucleus of the tissues. Immune responses towards CD4-specific PASD1 peptides were detected in 21.7% of CRC and 23.5% of polyps patients. The most immunogenic peptide was PASD1 (1) in CRC while PASD1 (3) in polyps. Cytotoxicity effects were detected up to 57.20% observed in CRC samples while IL-17A and IL-6 cytokines were highly expressed. The demographic data suggest that Chinese female patients more than 60 years old, diagnosed with late-stage rectosigmoid tumors may benefit from the PASD1 peptide immunotherapy approach. This is the first report describing CD4-positive T-helper response to the PASD1 positive CRC patients and its cytotoxicity.