FELINE LEUKEMIA-VIRUS VARIANTS IN EXPERIMENTALLY-INDUCED THYMIC LYMPHOSARCOMAS

This study was initiated to evaluate the in vivo infectivity and patho genicity of a group of recombinant feline leukemia viruses (rFeLVs) pr eviously generated by in vitro forced recombination between a FeLV sub group A virus (FeLV-A) and an endogenous FeLV (enFeLV) envelope (env) element (Sheets et al, 1992, Virology 190, 849-855). To determine infe ctivity of rFelVs, neonatal cats were inoculated with rFelVs alone or in combination with feLV-A. The recombinant viruses were able to repli cate efficiently in vivo only when administered along with FeLV-A. Of six cc-infected cats, three developed thymic lymphosarcomas, one sever e aplastic anemia, and two cachexia and depression; all were viremic a nd seroconverted shortly after inoculation. While both virus types wer e detected in virtually all tissues examined from these tumor-bearing cats, there was a particularly noteworthy sequence reversion in the rF eLVs. It is known that exogenous FeLV isolates carry a conserved neutr alizing MGPNL epitope in the middle of the surface glycoprotein domain of the env gene. In contrast, the parental recombinant viruses used t o inoculate these cats harbored the enFeLV-derived MGPNP-sequence at t his position. However, all in vivo-propagated recombinants displayed t he MGPNL sequence, while the env-encoded backbone flanking the MGPNL s equence was that of the parental recombinant virus. These results sugg est that viruses with the MGPNL epitope have an in vivo proliferative advantage. The data also provide an explanation for the conservation o f this epitope in exogenous FeLVs despite the existence of variant for ms in enFeLV proviral elements with which they can recombine. (C) 1995 Academic Press, Inc.