EFFICIENCY OF T-CELL TRIGGERING BY ANTI-CD3 MONOCLONAL-ANTIBODIES (MAB) WITH POTENTIAL USEFULNESS IN BISPECIFIC MAB GENERATION

T cell triggering can be achieved by monoclonal antibodies (mAbs) spec ific for the CD3/TcR complex. In the presence of appropriate costimula tion and/or progression factors, such triggering permits the generatio n of effector cells for immunotherapy protocols involving the redirect ion of T cell lysis against tumor cells by mAbs bispecific for anti-CD 3/anti-tumor cells (bs-mAbs). Focusing our analysis on the clinically relevant bs-mAb OC/TR, we found that bs-mAbs generated with the same a nti tumor specificity, but two other anti-CD3 mAbs, TR66 and OKT3, hav e the same and a significantly lower lyric potential, respectively, co mpared with that of OC/TR. To evaluate the relevance of the anti-CD3 c omponent, we examined several anti-CD3 mAbs with respect to binding pa rameters and the ability to trigger T lymphocytes. Competitive binding assays suggested that all anti-CD3 mAbs recognized the same or overla pping epitopes, although mAbs BMA030 and OC/TR bound with lower avidit y than did alpha CD3 (the bivalent anti-CD3 mAb produced by the hybrid hybridoma OC/TR), TR66 and OKT3, as determined by measurement of the affinity constants. In all lymphocyte populations examined, which incl uded resting peripheral blood mononuclear cells (PBMC), activated PBMC and T cell clones, OKT3, BMA033 and OC/TR failed to mobilize Ca2+ wit hout cross-linking, whereas alpha CD3, in both murine and murine-human chimeric versions, TR66 and BMA030, did not require cross-linking. Th e ability to induce CD3 modulation was associated in part with the ind uction of Ca2+ fluxes. Despite the differences in the behavior of thes e mAbs in triggering the events that precede proliferation, all of the m ultimately led to expression of the IL-2 receptor and to proliferati on in T cells in the presence of accessory cells. Our data suggest tha t anti-CD3 mAbs that bind more rapidly (strong Ca2+ mobilizers) and mo re tightly under physiological conditions are good candidates for reta rgeting T cells in the bs-mAb clinical application.