CD3 directed bispecific antibodies induce increased lymphocyte-endothelialcell interactions in vitro

Bispecific antibody (BsMAb) BIS-1 has been developed to redirect the cytoly tic activity of cytotoxic T lymphocytes (CTL) to epithelial glycoprotein-2 (EGP-2) expressing tumour cells; intravenous administration of BIS-1 F(ab') (2) to carcinoma patients in a phase I/II clinical trial, caused immunomodu lation as demonstrated by a rapid lymphopenia prior to a rise in plasma tum our necrosis factor-or and interferon-gamma levels. Yet, no lymphocyte accu mulation in the tumour tissue and no anti-tumour effect could be observed. These data suggest a BsMAb-induced lymphocyte adhesion to blood vessel wall s and/or generalized-redistribution of the lymphocytes into tissues. In thi s study, we describe the effects pf BIS-1 F(ab')(2) binding to peripheral b lood mononuclear cells (PBMC) on their capacity to interact with resting en dothelial cells in vitro. Resting and pre-activated PBMC exhibited a signif icant increase in adhesive interaction with endothelial cells when preincub ated with BIS-1 F(ab')(2) followed by an increase in transendothelial migra tion (tem). Binding of BIS-1 F(ab')(2) to PBMC affected the expression of a number of adhesion molecules-involved in lymphocyte adhesion/migration. Fu rthermore, PBMC preincubated with BIS-1 F(ab')(2) induced the expression of endothelial cell adhesion molecules E-selectin, VCAM-1 and ICAM-1 during a dhesion/tem. These phenomena were related to the CD3 recognizing antibody f ragment of the BsMAb and dependent on lymphocyte-endothelial cell contact. Possibly, in patients, the BIS-1 F(ab')(2) infusion induced lymphopenia is a result of generalized activation of endothelial cells, leading to the for mation of a temporary sink for lymphocytes. This process may distract the l ymphocytes from homing to the tumour cells, and hence prevent the occurrenc e of BIS-1 F(ab')(2) - CTL-mediated tumour cell lysis; (C) 2000 cancer Rese arch Campaign.