Critical role of enhanced CD4 affinity in laboratory adaptation of human immunodeficiency virus type 1

Strains of human immunodeficiency virus type 1 (HIV-1) that use the corecep tor CXCR4 (X4 strains) become laboratory adapted (LA) when selected for abi lity to replicate in leukemic T cell lines such as H9, Compared with patien t X4 viruses, the gp120-gp41 complexes of LA viruses have a constellation o f common properties including enhanced affinities for CD4, greater sensitiv ities to inactivations by diverse antibodies and by soluble CD4, increased shedding of gp120, and improved abilities to infect HeLa-CD4 cell clones th at contain only trace quantities of CD4, These common characteristics, whic h may result from a concerted structural rearrangement of the gp120-gp41 co mplexes, have made it difficult to identify a specific feature that is crit ical for laboratory adaptation, To test the hypothesis that replication of patient X4 HIV-1 is limited by the low CD4 concentration in H9 cells (7.0 x 10(3) CD4/cell), we constructed H9 derivatives that express at least 10 ti mes more of this receptor, Interestingly, most patient X4 isolates readily grew in these derivative cells, and the resulting virus preparations retain ed the characteristics of primary viruses throughout multiple passages, In contrast, selection of the same viruses in the parental H9 cells resulted i n outgrowth of LA derivatives, We conclude that a weak interaction of patie nt X4 HIV-1 isolates with CD4 is the primary factor that limits their repli cation in leukemic T cell lines.