Characterization of T cell-expressed chimeric receptors with antibody-type specificity for the CD4 binding site of HIV-1 gp120.

Chimeric T cell receptors (cTCR) with an antibody specificity have been proposed in several models as a combination of antibody and cellular immunotherapy without MHC restriction. Such a tool could be of a limited use in HIV infection because of the great variability of the virus. The human single-chain antibody (ScFv-b12) derives from the b12 antibody directed to the CD4 binding site of gp120, a potent neutralizer of different HIV-1 strains, including a large panel of primary isolates. A single-chain fragment variable (ScFv) bearing the VH Pro-->Glu mutation that improves b12 affinity 54-fold, called ScFv-b12E, was also constructed. The ScFv were linked to the signal-transducing y chain of the Fc(gamma)RIII, with or without spacer region, and expressed in the murine MD45 T cell line. The different cTCR formats behave similarly in terms of ScFv surface expression, but differ according to their activation threshold. T cell transfectants can be stimulated with immobilized gp120 derived from all HIV strains tested. BHK cells infected with Semliki forest virus (SFV) carrying an HIV-1 envelope gene (SFV-env) derived from either HIV-1 laboratory strains (LAI, MN12, HXB2) or field isolates (BX08, CHAR or 133) were used as targets for the transfectants. All gp120-expressing cells induced cTCR-specific activation. The latter result is contrasting with the lack of specific recognition of SFV-CHAR- or 133-infected cells by the native b12 antibody, as measured by cytofluorometric analysis. Finally, HeLa cells (which constitutively express the coreceptor CXCR4) are able to bind HIV-1 gp160 when transfected with the chimeric receptor ScFv-b12-gamma, but, importantly, do not become infected by the virus. Our results therefore suggest that cTCR with b12 specificity can confer to T cells broad anti-HIV reactivity without making them susceptible to HIV infection.