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.