NIV Congres

Background Alloreactive  CD8+ memory T cells are present in all individuals, regardless of prior interaction with allogeneic cells. This finding is explained by heterologous immunity: virus-specific T cells can recognize multiple antigens through cross-reactivity of their TCR. In line with this, virus-specific TCRs have been shown to recognize not only multiple viral peptides, but also allo-HLA molecules by cross-reactivity. In a recent study we could demonstrate that allo-HLA reactivity of virus-specific T cells is common, and several research groups have succeeded in identifying allo-HLA reactivity by virus-specific T cells. However, this research focusses primarily on identification of allo-HLA reactive CD8 T cells on a clonal level, whereas most individuals develop a polyclonal response upon a viral infection. As a consequence, the impact of a broad virus-specific immune response on the allorepertoire within an individual is currently unknown. The aim of the present study was therefore to determine the impact of virus-specific polyclonal immune responses on the overall alloimmune response within an individual.

Methods An inventory was made of the incidence and specificity of virus-specific allo-HLA reactive T cells within a large group of healthy individuals. Hereto we used a panel of tetramers, consisting of 8 CMV-, 13 EBV-, 7 HSV-, and 2 Influenza virus-specific tetramers. PBMCs of multiple tetramer-positive healthy donors were labeled with CFSE and stimulated with irradiated allogeneic cells in a mixed lymphocyte reaction in vitro. Upon 8 days of culture, the cells were again stained with the relevant tetramers. Proliferation of tetramer positive cells was measured by FACS analysis, as identified by the tetramer+CFSE^lowCD8+ subset.

Results Preliminary results show that in vitro stimulation of a responder with a single stimulator can induce several memory CD8 T cell responses with different specificities. Even with the restricted amount of tetramers, we could identify several different responding specificities upon stimulation with a single donor. The tested responder contained memory CD8 T cells specific for 8 different viral epitopes, and 5 of these specificities -originating from three different viruses- responded upon stimulation with a single stimulator.

Conclusion Our results show that polyclonal immune responses directed against a virus can induce several virus-specific memory CD8 T cell responses with alloreactive potential against a single donor.