CLONAL EXPANSION OF HUMAN T-CELL LEUKEMIA-VIRUS TYPE-II IN PATIENTS WITH HIGH PROVIRAL LOAD

In previous studies we demonstrated that individuals infected by human T-cell leukemia virus type II (HTLV-II) presented a high degree of va riation in proviral load and that the cellular tropism of this virus w as expanded in some patients to B-lymphocytes. To understand whether t he observed high proviral load could be associated with the clonal exp ansion of the infected cells, we have studied the mode of integration of HTLV-II in six infected individuals with proviral load higher than 1% of total peripheral blood mononuclear cells (PBMCs). An inverse pol ymerase chain reaction (PCR) analysis, which allowed the amplification of the region flanking the 5' end of the provirus, was developed for HTLV-II. A single band, corresponding to a monoclonal expansion, was f ound in four of six patients analyzed, while in the other two patients an oligoclonal type of integration was observed. The results for inve rse PCR analysis were confirmed by sequencing the PCR products and sho wing that the 5' LTR flanking sequences of proviral DNA obtained from the different subjects presented no homology, thus suggesting that no specific site or sequence is required for the integration process of H TLV-II. The results indicate that the HTLV-II high proviral load obser ved in PBMCs from infected patients is associated with a clonal expans ion of HTLV-II-infected cells. This study also suggests that the very high genetic stability of HTLV-II could be explained by viral amplific ation via clonal expansion rather than by reverse transcription. (C) 1 996 Academic Press, Inc.