Differential inhibition of human immunodeficiency virus type 1 fusion, gp120 binding, and CC-chemokine activity by monoclonal antibodies to CCR5

The CC-chemokine receptor CCR5 mediates fusion and entry of the most common ly transmitted human immunodeficiency virus type 1 (HIV-1) strains. We have isolated six new anti-CCR5 murine monoclonal antibodies (MAbs), designated PA8, PA9, PA10, PA11, PA12, and PA14. A panel of CCR5 alanine point mutant s was used to map the epitopes of these MAbs and the previously described M Ab 2D7 to specific amino acid residues in the N terminus and/or second extr acellular loop regions of CCR5. This structural information was correlated with the MAbs' abilities to inhibit (i) HIV-1 entry, (ii) HIV-1 envelope gl ycoprotein-mediated membrane fusion, (iii) gp120 binding to CCR5, and (iv) CC-chemokine activity. Surprisingly, there was no correlation between the a bility of a MAb to inhibit HIV-1 fusion-entry and its ability to inhibit ei ther the binding of a gp120-soluble CD4 complex to CCR5 or CC-chemokine act ivity. MAbs PA9 to PA12, whose epitopes include residues in the CCR5 N term inus, strongly inhibited gp120 binding but only moderately inhibited HIV-1 fusion and entry and had no effect on RANTES-induced calcium mobilization. MAbs PA14 and 2D7, the most potent inhibitors of HIV-1 entry and fusion, we re less effective at inhibiting gp120 binding and were variably potent at i nhibiting RANTES-induced signaling. With respect to inhibiting HIV-1 entry and fusion, PA12 but not PA14 was potently synergistic when used in combina tion with 2D7, RANTES, and CD4-immunoglobulin G2, which inhibits HIV-1 atta chment. The data support a model wherein HIV-1 entry occurs in three stages : receptor (CD4) binding, coreceptor (CCR5) binding, and coreceptor-mediate d membrane fusion. The antibodies described will be useful for further diss ecting these events.