SOLUBLE CD4 AND CD4 IMMUNOGLOBULIN-SELECTED HIV-1 VARIANTS - A PHENOTYPIC CHARACTERIZATION

The selection of HIV-1 resistance to neutralization by both monovalent and bivalent forms of soluble CD4 was demonstrated under various cond itions. Phenotypic traits of the neutralization-resistant variants wer e systematically explored in order to gain insight into which aspects of the interactions with CD4 are most expendable to HIV-1 replication. The size of the nonneutralized fraction after treatment of preparatio ns of the HIV-1 isolate IIIB and a molecular clone derived from it (HX 10), with either monovalent soluble CD4 (sCD4) or bivalent CD4-Ig, was determined. These fractions were greater for the polyclonal IIIB than for the viral clone, and greater after treatment with sCD4 than with CD4-Ig. The virus in the nonneutralized fractions exhibited 2- to 20-f old lower sensitivity to the neutralizing agents than did unselected v irus. In addition, clonal HIV-1 (HX10) was cultured in the presence of sCD4 or CD4-Ig for 12 weeks, so as to allow for accumulation of mutat ions that would confer stronger resistance to the selecting agent. Var iants were obtained with up to 100-fold increased resistance to sCD4 o r CD4-Ig. Detergent-solubilized gp120 from sCD4- and CD4-Ig-selected v irus showed decreases in affinity for sCD4 and CD4-Ig. The monoclonal antibodies 6H10, to the gp120-binding site in domain 1 of CD4, and 5A8 , to domain 2 of CD4, inhibited the induction by the viral escape vari ants of syncytium formation of C8166 cells. In general, the concentrat ion of antibody 6H10 that inhibited the escape variants was lower than the concentration that inhibited the wild type, whereas there was no significant difference for the domain 2 antibody 5A8. We interpret thi s as a weaker attachment of the escape variants than of the wild-type virus to cellular CD4, but as an intact dependence of the variants on CD4 interactions for gaining entry into cells.