Bootcongres

Background Virus-specific CD8+ memory T cells often recognize not only self-HLA presenting a viral peptide, but also allo-HLA molecules. This dual recognition can be explained by TCR cross-reactivity, and is widely known as heterologous immunity. For clinical purposes, it would be relevant to know if dominant heterologous immune responses are present in multiple individuals, in order to predict alloresponses in a transplantation setting. This knowledge could potentially be useful in clinical decision making, such as the choice of immunosuppressive regimens. So far, only few dominant or “public” alloresponses have been documented.  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 irradiated 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%). Upon eight days of culture, 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 (IFNγ 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 and/or HLA-B58, and CD8+ T cells recognizing the FLU-derived peptide GILGFVFTL in the context of 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, IFNγ production and cytotoxicity supported these findings.

Conclusion We have identified two additional public heterologous immune responses mediated by virus-specific CD8+ T cells. CMV-specific CD8+ T cells directed against self-HLA-B35+IPSINVHHY peptide show cross-reactivity with allo-HLA-B51/B58, whereas FLU-specific CD8+ T cells directed against self-HLA-A2+GILGFVFTL peptide show cross-reactivity with allo-HLA-B38 in a proportion of individuals. Currently, we are investigating whether the HLA-background of the responders plays a determinative role in the onset of cross-reactivity.