Defective human T-lymphotrophic virus type I provirus in T-cell prolymphocytic leukaemia

T-cell prolymphocytic leukaemia (T-PLL) is a rare form of post-thymic T-cel l neoplasm, the aetiology of which remains unknown. We examined human T-lym photropic virus (HTLV) provirus in five HTLV-I/II seronegative patients wit h T-PLL. Southern blotting did not show monoclonal integration of the HTLV- I genome in any of the DNA samples. However two of the five DNA samples con tained an HTLV-I tax sequence. Other sets of oligonucleotide primers for HT LV-I gag, pol, env and LTR regions were all negative. HTLV-I tax gene expre ssion and p40(tax) antibody were not detected in samples from cases with HT LV-I tax sequence. Our findings suggest that there may be alternative mecha nisms involved in HTLV-associated leukaemogenesis, in which HTLV-I genome i nsertion triggers T-PLL but the deletion of various regions of the integrat ed provirus subsequently prevents active replication and the expression of the virus.