POSSIBLE INVOLVEMENT OF CELL-FUSION AND VIRAL RECOMBINATION IN GENERATION OF HUMAN-IMMUNODEFICIENCY-VIRUS VARIANTS THAT DISPLAY DUAL RESISTANCE TO AZT AND 3TC

We have attempted to relate genetic recombination involving human immu nodeficiency virus type 1 (HIV-1) to multiple drug resistance by using PEG to fuse subclones of U937 cells that carried HIV-1 recombinants r esistant to either 3'-azido-3'-deoxythymidine (AZT) or the (-) enantio mer of 2',3'-dideoxy-3'-thiacytidine (3TC). The parental viruses emplo yed contained well-defined mutations in the pol gene. Fused cells were cocultured with the MT4 lymphocyte cell line for virus amplification to yield progeny that, in some cases, possessed different patterns of drug resistance from parental viruses. Mutational analyses were perfor med by PCR to substantiate these observations, which were also confirm ed by direct sequencing of single strands of DNA segments, obtained fr om plaque-purified viruses. These studies indicate that viral recombin ation had occurred, and establish a theoretical basis on which to conc lude that the acquisition of multiple drug resistance on the part of H IV-1 may be related to its ability to promote cell fusion.