IN-VITRO SELECTION OF HIV-1 RESISTANT TO AN ANTI-CD4 MONOCLONAL-ANTIBODY THAT INHIBITS VIRUS TRANSCRIPTION

Phase I studies using monoclonal antibodies (mAbs) that bind to the Ig -CDR3-like loop in domain 1 of CD4 (e.g., 13B8-2 mAb) have already bee n documented for HIV-1-infected patients. In vitro, such mAbs do not i nhibit virus to cell fusion but are able to inhibit virus envelope-med iated syncytia formation. Moreover, these mAbs inhibit Tar-induced act ivation of HIV-1 promoter and KIN-I transcription in infected CD4(+) c ells. Here, we report the selection of escaped mutant virus or viruses derived from HIV-1(Lai) capable of replicating in vitro in the presen ce of concentrations of 13B8-2 mAb, that usually inhibit HIV-1(Lai) pa rticle production. The escaped mutant virus or viruses, termed HIV-1(L ai13EM), kept the major enzymatic restriction sites found in HIV-1,, a nd remained sensitive to anti-CD4 mAb-, soluble CD4-, and recombinant gp120-mediated inhibition of syncytia formation. Possible genetic chan ges affecting the rat gene or the 5' long terminal repeat (LTR) were i nvestigated. Partial sequence analysis of HIV-(1Lai13EM) and a control HIV-1(Lai) grown for 85 days in CEM cells, demonstrated that the firs t tat exon of these two viruses encoded identical proteins. Although a point mutation G>A was frequently encountered (6 of 13 sequences) in the LTRs of HIV-1(Lai13EM) at position -188 within the negative regula tory element (NRE), this mutation did not confer the escape mutant phe notype. Our study indicates that the mutant phenotype probably require s genetic changes in a region or regions outside the LTRs.