Non-Fc receptor-binding humanized anti-CD3 antibodies induce apoptosis of activated human T cells

Human trials in organ allografts have demonstrated that murine anti-CD3 mAb s are immunosuppressive. By mimicking Ag, anti-CD3 can produce T cell activ ation, anergy, or death, Activation of resting T cells in vivo results in d ose-limiting cytokine release and is caused by Ab-mediated cross-linking of T cells and Fc gamma receptor (FcR)-bearing cells, With the goal of minimi zing cytokine-induced toxicity, anti-CD3 have been engineered to lower Fc b inding avidity, Preclinical murine studies have indicated that non-FcR-bind ing anti-CD3 can induce apoptosis of Ag-activated T cells. Since induction: of T cell apoptosis may be an important mechanism of immunosuppression by anti-CD3, we tested whether Fc mutations affect the ability of anti-human C D3 to induce apoptosis of activated T cells, We compared wild-type murine a nti-CD3, M291, and OKT3 and their humanized, PcR- and non-FcR-binding struc tural variants in quantitative assays of T cell apoptosis, Non-FcR-binding variants produced more sustainable phosphorylation of extracellular signal- regulated kinase-2, greater release of IFN-gamma, and more effectively caus ed activation-dependent T cell apoptosis, Non-FcR-binding variants dissocia ted more quickly from the T cell surface and caused less internalization of the TCR, which then remained available in greater abundance on the cell su rface for signaling. Cross-linking of non-FcR-binding variants by antiglobu lin enhanced TCR internalization and minimized induction of T cell apoptosi s, We conclude that non-FcR-binding, humanized anti-CD3 have improved abili ty to induce apoptosis of activated T cells, presumably by allowing durable expression of the TCR and sustained signaling.