A similarity in peptide cross-reactivity between alloantigen- and nominal antigen-induced CD8+ T cell responses in vitro

Raising tumor-specific allorestricted T cells in vitro for adoptive transfusion is expected to circumvent host tumor tolerance. However, it has been assumed that alloreactive T cell clones activated in vitro ranges from peptide-specific with high avidity to peptide-degenerate with low avidity. In this study, we examined the peptide specificity and cross-reactivity of T cell responses in vitro to an allogeneic epitope and a nominal epitope with a modified co-culture of lymphocytes and autologous monocytes. After binding to the monocyte via the interaction of its Fc part and the cell surface IgG Fc receptor type I (FcγRI), a fusion protein consisting of the extracellular domains of HLA-A2 molecule and the Fc region of IgG1 (the dimer) introduced a single epitope into the co-culture. The dimer-coated monocytes stimulated the proliferation of autologous CD8⁺ T cells after co-culturing. The CD8⁺ T cell responses were self-HLA-restricted for HLA-A2-positive (HLA-A2+ve) samples and allo-HLA-restricted for HLA-A2-negative (HLA-A2-ve) samples, since the co-cultural bulks stained with HLA-A2 tetramers, human interferon-gamma (IFN-γ) production in response to T cell receptor (TCR) ligands, and cytotoxicity against a panel of target cells exhibited peptide-specific properties. Two HLA-A2-restricted peptides with sequence homology were included, allowing the comparison of cross-reactivity between allo-antigen- and nominal antigen-induced CD8⁺ T cell responses. Interestingly, the allo- and self-HLA-restricted CD8⁺ T cell responses were similar in the peptide cross-reactivity, although the allorestricted T cell response seemed, overall, more intensive and had higher binding affinity to specific tetramer. Our findings indicated the alloreactive T cells raised by the co-culture in vitro were as peptide specific and cross-reactive as the self-HLA-restricted ones.