Clinical evidence of a relationship between severe chronic active Epstein-Barr virus (EBV) infection and clonal expansion of EBV-infected T or NK cells has been accumulated. In order to clarify pathogenesis of EBV-infected cell proliferation in patients with severe chronic active EBV infection, cytotoxic T lymphocyte (CTL) responses of two patients against B-lymphoblastoid cell lines (B-LCL) and EBV-infected NK cells were examined in comparison with those of HLA-identical healthy siblings. Unexpectedly, patients' CTL activities induced by mixed culture with autologous B-LCLs were markedly reduced, although uncontrolled EBV-related B-cell proliferations have never been experienced. In contrast, limiting dilution analysis demonstrated that B-LCL-specific CTL precursor (CTLp) frequencies of patients were comparable to those of their healthy sisters. The existence of normal levels of B-LCL-specific T cell responses was confirmed by flow-cytometric analysis of IFN-gamma-producing T cells after stimulation with B-LCLs. Infected NK-cell-specific CTLp frequencies of the patients were at undetectable levels despite their expression of latent membrane protein (LMP) 1, suggesting mechanisms to escape immunologic surveillance. In the patients' HLA-identical healthy sisters, infected NK-cell-specific CTLps were detected, and infected NK-cell-specific CTL clones could be established. From these findings, two treatment options for severe chronic active EBV infection are offered for consideration: adoptive transfer of in vitro-cultured CTL, and bone marrow transplantation from HLA-identical donors.
Copyright 2001 Wiley-Liss, Inc.