Restrictions upon Epstein-Barr virus infection of the leukemic cell are demonstrated in patients with hairy cell leukemia.

We tested the hypothesis that Epstein-Barr virus (EBV) might actually infect leukemic hairy cells in vivo by examining those cells for the EBV-receptor, EBV nuclear antigen (EBNA) and membrane antigen (MA), for spontaneous transformation and rescue of infectious virus and for presence of EBV genome. EBV-receptors were found on subpopulations of leukemic cells from each of 7 patients with hairy cell leukemia (HCL) tested. MA was present on low numbers (1-5 per cent) of fresh leukemic cells of 7 patients and in some instances occurred with a greater frequency after 3 to 5 days in culture, with or without 12-O-tetradecanoylphorbol-13-acetate. In 11 fresh leukemic cell preparations from 8 HCL patients, no EBNA was demonstrated. However, 2 samples after 4 days in culture expressed low frequencies of EBNA-positive cells. Spontaneous, EBV-positive cell lines were established with a high transformation efficiency from 3 HCL blood samples but not from 8 other specimens. Infectious EBV could be rescued from some hairy leukemic cell preparations by co-cultivation with cord blood lymphocytes. These results demonstrated that leukemic cell populations harbored infectious EBV, that the leukemic cells expressed virus receptors and suggested that a small subpopulation of leukemic cells might become infected in vivo at least transiently and possibly transformed in vitro by EBV. To test for the extent of occult in vivo infection of leukemic cells with EBV, Southern type hybridization studies were performed with a probe for EBV genome (Bam HI W). At a sensitivity level of 0.1 genome per cell, EBV genome was not detected in the leukemic cell populations of 7 patients. We conclude that host defence mechanisms protecting these individuals from EBV also prevent infections of the leukemic cell and/or most hairy leukemic cells are not suitable targets for both infection and transformation.