Cellular tropism of human T-cell leukemia virus type II is enlarged to B lymphocytes in patients with high proviral load.

To establish the in vivo cellular tropism of human T-cell leukemia virus type II (HTLV-II) in peripheral blood, subpopulations of mononuclear cells isolated from patients with a history of drug abuse and with high proviral load were analyzed by polymerase chain reaction for the presence of the proviral sequences. After purification of cellular subsets by immunomagnetic fractionation of blood cells of an infected patient, HTLV-II DNA was detected in CD4+ and CD8+ T-cells as well as in CD19+ B-cells. A positive PCR signal was obtained for purified B-cells also at limiting dilutions. This observation was confirmed by purifying the B-cell fraction by a two-step immunomagnetic procedure from the peripheral blood of another patient with very high HTLV-II copy number and quantifying the B-cell proviral load by means of competitive PCR. A proviral copy number of 90/100 B-cells was found, demonstrating that the great majority of these cells were infected by HTLV-II in this subject. The results indicate that HTLV-II has a broad host range in some infected individuals, showing an enlargement of cellular tropism to B lymphocytes and suggesting that this expression is associated with an increase in proviral load.