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

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Abstract
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 γ chain of the FcγRIII, 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‐γ, 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.