T-cell retargeting using bispecific monoclonal antibodies in a rat colon carcinoma model. I. Significant bispecific lysis of syngeneic colon carcinoma CC531 is critically dependent on prolonged preactivation of effector T-lymphocytes by immobilized anti-T-cell receptor antibody.

In order to develop a rat model that reflects human weakly or nonimmunogenic tumor-host relationships and allows investigation of T-cell retargeting with bispecific monoclonal antibodies in vivo, we prepared several mixed hybridomas. One fusion partner was the anti-rat-T-cell receptor (TCR)-framework hybridoma R73 and the others were hybridomas producing antibodies against CC531, a Wag rat colon carcinoma. Stimulation of Wag rat spleen cells with immobilized R73 mAb and rIL-2 yielded predominantly CD8 positive effector T-lymphocytes, which lysed control P815 target cells efficiently in R73-mediated reverse antibody-dependent cellular cytotoxicity (ADCC). The capacity of these effectors to cause significant hybrid antibody-mediated lysis of CC531 emerged several days later, was critically dependent on prolonged stimulation with immobilized R73, and was associated with increased N-alfa-benzyloxycarbonyl-L-lysine thiobenzyl esterase content.