Relating TCR-peptide-MHC affinity to immunogenicity for the design of tumor vaccines

Abstract

One approach to enhancing the T cell response to tumors is vaccination with mimotopes, mimics of tumor epitopes. While mimotopes can stimulate proliferation of T cells that recognize tumor-associated antigens (TAAs), this expansion does not always correlate with control of tumor growth. We hypothesized that vaccination with mimotopes of optimal affinity in this interaction will improve antitumor immunity. Using a combinatorial peptide library and a cytotoxic T lymphocyte clone that recognizes a TAA, we identified a panel of mimotopes that, when complexed with MHC, bound the TAA-specific TCR with a range of affinities. As expected, in vitro assays showed that the affinity of the TCR-peptide-MHC (TCR-pMHC) interaction correlated with activity of the T cell clone. However, only vaccination with mimotopes in the intermediate-affinity range elicited functional T cells and provided protection against tumor growth in vivo. Vaccination with mimotopes with the highest-affinity TCR-pMHC interactions elicited TAA-specific T cells to the tumor, but did not control tumor growth at any of the peptide concentrations tested. Further analysis of these T cells showed functional defects in response to the TAA. Thus, stimulation of an antitumor response by mimotopes may be optimal with peptides that increase but do not maximize the affinity of the TCR-pMHC interaction.

Age-dependent tolerance to an endogenous tumor-associated antigen

“…Gp70-sufficient and -deficient mice were injected with live CT26 cells and the injection site was monitored for tumor growth. Most of the gp70-sufficient mice developed tumors within 2 weeks, consistent with previous reports and our experience with this tumor [30,32]. However, only half of the gp70-deficient mice developed detectable tumors, confirming previous data [18] that the dominant T cell response is to the gp70 antigen and processing of the gp70 antigen in the tumor does not differ in gp70-sufficient or -deficient mice.…”

“…Mice were sacrificed when the tumor reached 1 cm in any direction. Peptide vaccinations were performed as described [32]. Briefly, mice were injected with 1x10 5 CT26 cells as above.…”

“…Briefly, mice were injected with 1x10 5 CT26 cells as above. Four and 6 days later, mice were injected with the indicated peptides and LANAC adjuvant [containing liposomes, CpG plasmid DNA, and 10 μg peptide as described [32,33]]. 14 days after tumor injection, when the tumors were still less than 1 cm in all directions, the tumors were removed and the infiltrating T cells were analyzed.…”

“…Tumor-infiltrating lymphocytes were stained ex vivo. Antigen-specific T cells were identified using a live-gate, a dump-gate [included directly conjugated CD4 (GK1.5, ATCC), B220 (RA3.6B2, eBioscience), and MHC class II (M5/114.15.2, eBioscience) antibodies], H-2L d tetramers [32] and a CD8 antibody (53-6.7, eBioscience) as described [32]. CD3+ cells were stained with 2.C.11 antibody (eBiosciences).…”

“…Previous work showed that, despite the detection of T cell responses specific for the CT26 tumor, T cells cannot prevent tumor growth in normal BALB/c recipient mice [32]. Data from other investigators demonstrated that proteins from MuLV are expressed in BALB/c mice [35].…”