Using low and high avidity OVA-specific transgenic T cells, bilateral implantation of tumors bearing either low- or high-affinity epitopes, and immunization with either antigen, Martinez-Usatorre et al. evaluated the role of TCR avidity in immune response and tumor control, reflecting neoantigens (high presumed avidity) and tumor-associated antigens (TAAs; low presumed avidity). Low-avidity T cells retained significant functionality in vivo and appeared less exhausted, but expanded poorly upon stimulation. Enhanced stimulation via vaccine and addition of anti-PD-1 demonstrated the in vivo tumor control potential of TAA-specific T cells.
Antitumor T cell responses involve CD8(+) T cells with high affinity for mutated self-antigen and low affinity for nonmutated tumor-associated Ag. Because of the highly individual nature of nonsynonymous somatic mutations in tumors, however, immunotherapy relies often on an effective engagement of low-affinity T cells. In this study, we studied the role of T cell affinity during peripheral priming with single-peptide vaccines and during the effector phase in the tumor. To that end, we compared the antitumor responses after OVA257-264 (N4) peptide vaccination of CD8(+) T cells carrying TCRs with high (OT-1) and low (OT-3) avidity for the N4 peptide in B16.N4 tumor-bearing C57BL/6 mice. Additionally, we assessed the response of OT-1 cells to either high-affinity (B16.N4) or low-affinity (B16.T4) Ag-expressing tumors after high-affinity (N4) or low-affinity (T4) peptide vaccination. We noticed that although low-affinity tumor-specific T cells expand less than high-affinity T cells, they express lower levels of inhibitory receptors and produce more cytokines. Interestingly, tumor-infiltrating CD8(+) T cells show similar in vivo re-expansion capacity to their counterparts in secondary lymphoid organs when transferred to tumor-free hosts, suggesting that T cells in tumors may be rekindled upon relief of tumor immunosuppression. Moreover, our results show that alphaPD-1 treatment enhances tumor control of high- and low-affinity ligand-expressing tumors, suggesting that combination of high-affinity peripheral priming by altered peptide ligands and checkpoint blockade may enable tumor control upon low-affinity Ag recognition in the tumor.