A STREPTOCOCCAL PREPARATION (OK-432) ENHANCES MONOCLONAL-ANTIBODY NCC-ST-421 CYTOTOXICITY AGAINST HUMAN COLON-CANCER

The murine IgG3 monoclonal antibody NCC-ST-421 (ST-421), raised agains t human gastric cancer; shows strong reactivity with the Le(a)/Le(a) ( al-fucosylated extended type 1 chain) antigen expressed on gastrointes tinal (GI) cancer cells. ST-421 is capable of mediating both antibody- dependent cellular cytotoxicity (ADCC) by human peripheral blood lymph ocytes (PBL), and complement dependent cytotoxicity (CDC). We investig ated combination immunotherapy with OK-435 a streptococcal preparation , and ST-421 in vitro and in vivo. ADCC against Cole 205 (a human colo n cancer cell line) was enhanced 2 to 3 fold after preincubation of PB L with OK-432 in vitro. These effect's were strongest when PBL were pr eincubated with OK-432 at a concentration of 0.5 ng/ml for 24 hours. I n vivo, a human colon cancer xenograft model exhibited significant gro wth suppression after combined treatment with ST-421 and OK-432. Such combination immunotherapy may therefore be clinically useful in GI can cer.