Successful treatment of Epstein-Barr virus-associated natural killer cell large granular lymphocytic leukaemia using allogeneic peripheral blood stem cell transplantation

We report a case of natural killer cell large granular lymphocytic (NK-LGL) leukaemia successfully treated with allogeneic peripheral blood stem cell transplantation (allo-PBSCT). The peripheral blood (PB) revealed an abnormal expansion of LGL that were CD3^-, CD16^- and CD56⁺, and had natural killer activity. In situ EBER-1 hybridization of the PB mononuclear cells showed the presence of Epstein-Barr virus (EBV) in the LGL as well as in lymphocytes infiltrating the tonsils and colon. Southern blotting with an EBV-terminal repetitive sequence probe demonstrated clonal proliferation of EBV⁺ cells. The patient received allo-PBSCT from his HLA-matched sister with a conditioning regimen involving the use of cyclophosphamide and fractionated total body irradiation. The patient promptly recovered trilineage haematopoiesis without graft-versus-host disease, and has been in complete remission without therapy for 10 months since allo-PBSCT, suggesting that allo-PBSCT could eradicate the NK-LGL leukaemic cells.