Elevated tumor-associated antigen expression suppresses variant peptide vaccine responses

摘要

Variant peptide vaccines are used clinically to expand T cells that cross-react with tumor-associated antigens (TAA). To investigate the effects of elevated endogenous TAA expression on variant peptide-induced responses, we used the GP70 TAA model. Although young BALB/c mice display T cell tolerance to the TAA GP70423–431 (AH1), expression of GP70 and suppression of AH1-specific responses increases with age. We hypothesized that as TAA expression increases, the AH1-crossreactivity of variant peptide-elicited T cell responses diminishes. Controlling for immunosenescence, we showed that elevated GP70 expression suppressed AH1-crossreactive responses elicited by two AH1 peptide variants. A variant that elicited almost exclusively AH1-crossreactive T cells in young mice elicited few or no T cells in aging mice with antibody-detectable GP70 expression. In contrast, a variant that elicited a less AH1-crossreactive T cell response in young mice successfully expanded AH1-crossreactive T cells in all aging mice tested. However, these T cells bound the AH1/MHC complex with a relatively short half-life and responded poorly to ex vivo stimulation with the AH1 peptide. Variant peptide vaccine responses were also suppressed when AH1 peptide is administered tolerogenically to young mice prior to vaccination. Analyses of variant-specific precursor T cells from naïve mice with antibody-detectable GP70 expression determined that these T cells expressed PD-1 and had downregulated IL-7Rα expression, suggesting they were anergic or undergoing deletion. Although variant peptide vaccines were less effective as TAA expression increases, data presented here also suggest that complementary immunotherapies may induce the expansion of T cells with functional TAA recognition.