Cutting Edge: Targeted Ligation of CTLA-4 In Vivo by Membrane-Bound Anti-CTLA-4 Antibody Prevents Rejection of Allogeneic Cells

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Abstract
Natural engagement of CTLA-4 on host B7 limits T cell activation. We hypothesized that therapeutic cross-linking of CTLA-4 in vivo may further inhibit T cell function and prevent allograft rejection. However, none of the currently available CTLA-4-binding reagents have ligating properties when injected in vivo. The observation that surface-immobilized anti-CTLA-4 mAb inhibits T cell activation in vitro prompted us to develop a membrane-bound single-chain anti-CTLA-4 Ab (7M). To model whether tissue expression of 7M could suppress allograft rejection, we examined the ability of H-2Ld-specific TCR-transgenic T cells to reject 7M-expressing allogeneic tumor cells injected s.c. Expression of 7M significantly inhibited allogeneic rejection in mice that received CTLA-4+/+ but not CTLA-4−/− T cells. Furthermore, CTLA-4+/+ T cells that had encountered 7M-expressing tumors in vivo acquired defects in cytokine production and cytotoxicity. Thus, deliberate ligation of CTLA-4 in vivo potently inhibits allogeneic T cell responses.