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 th e dominant CD8(+) T cell responses against a large number of HLA/viral prot ein combinations within polyclonal cell lines, we searched for HLA-B*2705-r estricted CD8 T cell responses to Epstein-Barr virus (EBV) within T cell sa mples enriched for EBV-reactive cells. Among the 18 EBV proteins tested, on ly 2, the latent protein EBNA3A and the late lytic protein BCRF1 (viral IL- 10), appeared dominant in the B27 context, as they triggered significant TN F 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 complex es 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 demon stration of a recognition of BCRF1, suggesting that some immune control aga inst 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.