CMV- and FLU-Directed CD8+ T Cells Mediate Public Cross-Reactive Responses Against Different Allo-HLA Molecules.: Abstract# B769

Study purpose Virus-specific CD8+ memory T cells have the intrinsic capability to not only recognize self-HLA presenting a viral peptide, but also allo-HLA. This dual recognition is explained by TCR cross-reactivity, widely known as heterologous immunity. For clinical purposes, it would be relevant to know whether dominant heterologous immune responses are present in multiple individuals, in order to predict alloresponses in a transplantation setting. This knowledge could be useful in clinical decision making with regard to immunosuppressive regimens. So far, only few dominant or “public” alloresponses have been documented. Our aim is therefore to identify new public alloresponses. Methods Seventy-five healthy individuals were stained with a range of different virus-specific tetramers (CMV, EBV, FLU). PBMCs of tetramer-positive individuals were labeled with CFSE and stimulated against a panel of HLA-typed PBMCs in a mixed-lymphocyte reaction in vitro. This panel was designed to cover the most common HLA-I antigens in the Western population (>5%). Proliferation of virus-specific CD8+ T cells was determined by flow cytometry. CD8+ T cells from different individuals, specific for the same tetramer and showing a similar reactive pattern against the panel were cell-sorted into clones and cell lines. The cross-reactive HLA alloantigen was further confirmed based on cytokine production (IFNg ELISA) and cytotoxicity (51Chromium-release assay). Results Two public cross-reactivities of virus-specific CD8+ T cells were identified. CD8+ T cells specific for the CMV peptide IPSINVHHY presented by HLA-B35 cross-react with HLA-B51/B58, whereas CD8+ T cells recognizing the FLU-derived peptide GILGFVFTL presented by HLA-A2 cross-react with HLA-B38. These responses were detected in respectively 46% (6/13) and 41% (7/17) of healthy individuals containing these virus-specific cells. Proliferation, IFNg production and cytotoxicity supported these findings. Conclusion We have identified two novel public heterologous immune responses mediated by virus-specific CD8+ T cells in a significant proportion of individuals. Currently, we are investigating whether the HLA-background of the responders plays a determinative role in the onset of cross-reactivity.