DE-NOVO REVERSE TRANSCRIPTION OF HTLV-1 FOLLOWING CELL-TO-CELL TRANSMISSION OF INFECTION

Analogous to transmission of human T-cell leukemia virus type 1 (HTLV- 1) in vivo, an in vitro cell-to-cell infection model was established b y coculturing MT-2 cells as virus donors and HUT78 cells as recipients . At a donor:recipient ratio of 1:2, cell fusion occurred and a new ro und of HTLV-1 genome replication was initiated in the cocultured cells . Newly synthesized unintegrated viral DNA was detected by Southern bl ot within 4-8 h and then increased between 8 and 48 h following cell m ixing. The most dominant species of unintegrated viral DNA was 3.7 kb in size which hybridized to a full-length HTLV-1 DNA probe but not to a Kpnl viral DNA fragment that is absent from a defective proviral gen ome that has been previously identified in MT-2 cells. Northern blot a nalysis showed large amounts of viral RNA in the virus donor cells and in the cocultured cells, with a 3.4-kb species being the most abundan t. This 3.4-kb RNA gave a pattern identical to that of the 3.7-kb unin tegrated viral DNA in hybridization studies using the two probes. It s eems likely that the unspliced RNA transcript from the defective provi ral genome in MT-2 cells was effectively reverse transcribed upon init iation of cell-to-cell viral transmission to susceptible HUT78 cells. Despite active de novo reverse transcription, however, viral RNA level s remained unchanged following cell-to-cell transmission of HTLV-1 inf ection and no viral antigen production could be attributed to the newl y initiated round of viral genome replication. As an abortive infectio n model this simple cell-to-cell infection system warrants more detail ed study as it has the potential to provide reliable information regar ding the early events in HTLV-I transmission and infection. (C) 1998 A cademic Press.