Identification and prevalence of CD8+ T‐cell responses directed against Epstein‐Barr virus‐encoded latent membrane protein 1 and latent membrane protein 2

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Abstract
Epstein‐Barr virus (EBV) is associated with several human malignancies that each show different viral gene expression profiles. In malignancies such as Hodgkin's disease and nasopharyngeal carcinoma only Epstein‐Barr nuclear antigen 1 (EBNA1) and varying levels of latent membrane proteins 1 and 2 (LMP1 and ‐2) are expressed. Since endogenously expressed EBNA1 is protected from CTL recognition, LMP1 and LMP2 are the most likely target antigens for anti‐tumor immunotherapy. Therefore, we sought to identify in a systematic way CD8+ T‐cell responses directed against eptitopes derived from LMP1 and LMP2. Using IFNγ‐ELISPOT assays of interferon‐γ release, peripheral blood mononuclear cells (PBMC) of healthy donors were screened with peptide panels (15 mer overlapping by 10) spanning the LMP1 and LMP2 sequences of the prototype EBV strain B95.8. When positive responses were found, CD4+ or CD8+ T cells were depleted from donor PBMC to determine the origin of the responder population. We detected CD8+ T‐cell responses to LMP1 in 9/50(18%) donors and to LMP2 in 15/28 (54%) donors. In addition to the already described epitopes, 3 new LMP1‐ and 5 new LMP2‐derived CD8+ epitopes were identified. In most donors LMP1‐ and LMP2‐specific CD8+ precursor frequencies were low compared with precursors against immunodominant EBV epitopes from latent (EBNA3A, ‐3B and ‐3C) and lytic cycle antigens. These results demonstrate that CD8+ memory T cell responses to LMP1 and especially to LMP2 do exist in Caucasians, albeit at low levels and could potentially be exploited for therapeutic use.

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