Bispecific antibody-mediated lysis of primary cultures of ovarian carcinoma cells using multiple target antigens

We have shown previously that a bispecific antibody (BsAb) directed against both germ-cell alkaline phosphatase (GCAP) and the CD3 complex on mouse T cells could effectively eliminate GCAP-positive tumor cells in vivo using a n immunocompetent mouse model. However, some GCAP-negative tumor cells were still able to grow, suggesting that BsAb therapy, when used in a clinical setting, could benefit from targeting several tumor markers to prevent outg rowth of tumor cells lacking a targeted marker. To test this hypothesis, we developed an in vitro model based on primary human ovarian carcinoma (OC) cultures and BsAbs directed against human T cells and several tumor markers [placental alkaline phosphatase (PLAP), GCAP, folate binding protein (FBP) and CA19.9], OC cells, isolated from primary tumors, were co-cultured with human peripheral blood mononuclear cells in the presence or absence of var ious concentrations of BsAbs against PLAP/GCAP, FBP and CA19.9 administered separately or in combination. Results derived from 18 primary OC samples s howed that the combination treatment was better than or equally effective a s the best single BsAB treatment in 60% of cases. Sometimes targeting FBP, PLAP/GCAP or CA19.9 alone was superior to targeting all simultaneously. Com bining each BsAb with a low dose of IL-2 was always beneficial. These resul ts indicate that before using a specific BsAb in the clinic, it is importan t to determine the optimal BsAb for each patient using this in vitro assay on cells from the removed tumor mass. (C) 1999 Wiley-Liss, Inc.