Human immunodeficiency virus type 1 IIIB selected for replication in vivo exhibits increased envelope glycoproteins in virions without alteration in coreceptor usage: Separation of in vivo replication from macrophage tropism

Analysis of viral replication and pathogenicity after in vivo selection of human immunodeficiency virus type I (HIV-1) attenuated in vitro will help t o define the functions involved in replication and pathogenesis in vivo. Us ing the SCID-hu Thy/Liv mouse and human fetal thymus organ culture as in vi vo models, we previously defined HIV-1 env determinants (HXB2/LW) which wer e reverted for replication in vivo (L. Su et al., Virology 227:46-52, 1997) . In this study, we examined the replication of four highly related HIV-1 c lones directly derived from Lai/IIIB or after selection in vivo to investig ate the envelope gp120 determinants associated with replication in macropha ges and in the thymus models in vivo. The LW/C clone derived from the IIIB- infected laboratory worker and HXB2/LW both efficiently infected monocyte-d erived macrophages (MDM) and the human thymus. Although the laboratory work er (LW) isolates showed altered tropism from IIIB, they still predominantly used CXCR4 as coreceptors for infecting peripheral blood mononuclear cells , macrophages, and the thymus. Interestingly, a single amino acid mutation in the V3 loop associated with resistance to neutralizing antibodies was al so essential for the replication activity of the LW virus in the thymus mod els but not for its activity in infecting MDM. The LW virions were equally sensitive to a CXCR4 antagonist. We further demonstrated that the LW HIV-1 isolate selected in vivo produced more infectious viral particles that cont ained higher levels of the Env protein gp120. Thus, selection of the labora tory-attenuated Lai/IIIB isolate in vivo leads to altered tropism but not c oreceptor usage of the virus. The acquired replication activity in vivo is correlated with an early A-to-T mutation in the V3 loop and increased virio n association of HIV-1 Env gp120, but it is genetically separable from the acquired replication activity in macrophages.