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Frequent recognition of BCRF1, a late lytic cycle protein of Epstein‐Barr virus, in the HLA‐B*2705 context: evidence for a TAP‐independent processing

Using a transient COS transfection assay, allowing a rapid estimation of the dominant CD8+ T cell responses against a large number of HLA/viral protein combinations within polyclonal cell lines, we searched for HLA‐B*2705‐restricted CD8 T cell responses to Epstein‐Barr virus (EBV) within T cell samples enriched for EBV‐reactive cells. Among the 18 EBV proteins tested, only 2, the latent protein EBNA3A and the late lytic protein BCRF1 (viral IL‐10), appeared dominant in the B27 context, as they triggered significant TNF and cytolytic responses in some donors. We provide evidence that the B27/BCRF1 epitope (RRLVVTLQC) is located in the signal sequence and that it can be presented in a TAP‐independent manner. Using B27/BCRF1 monomeric complexes coated on immunomagnetic beads, we sorted out BCRF1‐specific CD8 T cells from 8 of 15 HLA‐B27+ donors. This is, to our knowledge, the first demonstration of a recognition of BCRF1, suggesting that some immune control against EBV exists even during the late stage of the lytic cycle. This result also strengthens the unusual ability of HLA‐B*2705 to present peptide in a TAP‐independent manner.