[The enhancement of cytolytic activity in lymphokine activated killer cells using bispecific F(ab')2].

In this study, we show that bispecific hetero-F(ab')2 enhances cytolytic activity in human lymphokine activated killer (LAK) cells derived from peripheral blood mononuclear cells against human small cell lung cancer (SCLC) cell lines. We used two types of bispecific F(ab')2 (anti-CD3-LU246mAb, anti-CD16-LU246mAb) which play different roles in the enhancement of cytolytic activity in LAK cells against the human SCLC cell lines N231, H69 and Lu135. Anti-CD3 Fab' or anti-CD16 Fab' were coupled with LU246 Fab' that recognized the antigen on human SCLC cells for reproducing bispecific F(ab')2. Anti-CD16 (3G8) Fab' conjugated with LU246 Fab' targeted NK-LAK cells to SCLC cells to mediate cytolysis, but NK-LAK cells induced by LGL-enriched fraction did not display enhanced cytotoxicity even when bispecific antibody was used in 51Cr release assay. Anti-CD3 (OKT3) Fab' conjugated with LU246 Fab' cross-linked T-LAK cells to SCLC cells activated T-LAK cells through the CD3 complex, and enhanced the cytolytic activity of T-LAK cells against SCLC lines. Although OKT3-LU246 F(ab')2 was not so potent in enhancing cytolytic activity in 51Cr release assay, it played a greater role in enhancing the inhibitory effect on tumor growth than 3G8-LU246 F(ab')2 in human tumor clonogenic assay and in vivo tumor neutralization assay. In addition, the enhancement of target cell lysis by bispecific antibodies was generally more potent than antibody dependent cellular cytotoxicity (ADCC) using LU246 monoclonal antibody.