*Purpose: Epstein-Barr virus (EBV) infects more than 90% of adults worldwide and is associated with several malignancies, including post-transplant lymphoproliferative disorder (PTLD). PTLD is a potentially fatal complication of organ transplantation characterized by an aberrant proliferation of lymphoid cells in the setting of immunosuppression. Several lines of evidence suggest that innate immune responses including Natural Killer (NK) cells are critical in host immunity to EBV. Recently, a specific NK cell subset has been demonstrated to recognize and respond to autologous B cells latently infected with EBV. This NK subset expresses NKG2A/CD94, an inhibitory receptor that recognizes HLA-E. Since EBV-infected cells induced NK cell activation despite the expression of HLA-E, we hypothesize that EBV encoded peptides alter the recognition and response of NKG2A+ NK cells towards latently infected EBV+ cells.

*Methods: Using in silico analysis (NetMHCpan 4.0), a peptide library derived from EBV latent cycle proteins LMP1 and 2 was generated. The LMP1 C-terminal domain (192-386aa) was amplified and sequenced from DNA isolated from whole blood of 79 pediatric transplant recipients. Peptide stabilization assays were performed to test the ability of individual peptides to be presented by HLA-E and CD107a was used as a readout for NK cell activity.

*Results: Computational analysis generated 26 peptides, from LMP1 and 2 that could potentially bind to HLA-E, and binding was confirmed for ten peptides. A nine amino sequence that corresponds to one peptide (GGDPHLPTL) was found in 82% of patient samples. Sequence variations were detected in the remaining 18% of patients. We assessed whether these sequence variations have an effect on HLA-E stabilization and NKG2A+ NK cell function. Two sequence variations (4% of patients) demonstrated comparable stabilization of HLA-E as the original peptide, while three other sequence variations, which were detected in 14% of patient samples, did not stabilize HLA-E. Further, NKG2A+ NK cells killed EBV-infected cells in the presence of only the HLA-E binding peptides.

*Conclusions: Some pediatric transplant recipients have variations in the sequence of the critical EBV protein, LMP1 that may impair NK and T cell mediated killing of EBV-infected cells and increase the risk of PTLD.

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