BISPECIFIC ANTIBODY-MEDIATED LYSIS OF PLACENTAL AND GERM-CELL ALKALINE-PHOSPHATASE TARGETED SOLID TUMORS IN IMMUNOCOMPETENT MICE

Recently, an immunocompetent in vivo mouse model was developed based o n germ cell alkaline phosphatase (GCAP) transgenic (FVB/N x C3H) mice in which both placental alkaline phosphatase (PLAP)(+) and GCAP(+) sol id MO(4) tumors develop. A bispecific anti-PLAP/GCAP anti-mouse CD3 an tibody (Ab) 7E8 x 7D6, previously shown to induce efficient dose-depen dent T-cell proliferation and PLAP(+) tumor cell lysis in the presence of recombinant IL-2 and the anti-mouse CD3 Ab 7D6, was used in this r eport in in vivo lysis experiments targeting GCAP(+) tumors grown in G CAP(+) transgenic mice. Mice received injections i.v. twice a week wit h PBS (group 1) or with 10 mu g of the bispecific Ab 7E8 x 7D6, either alone (group 2) or combined with 1 mu g of the anti-CD3 Ab 7D6 (group 3), starting 7 days after the tumor inoculation. A fourth group recei ved a local treatment with mouse splenocytes precoated with 10 mu g 7E 8 x 7D6 and 1 mu g 7D6. In between Ab injections, groups 2, 3, and 4 r eceived 10(4) units recombinant IL-2 (i.v.) every day. Two weeks of tr eatment with the bispecific Ab either alone or combined with 7D6 resul ted in a significant decrease of GCAP(+) tumor cells in groups 2 and 3 (4 +/- 3% and 10 +/- 11% GCAP(+) cells/tumor) as compared to the nont reated tumors (95 +/- 5% GCAP(+) cells), although tumor volumes were n ot significantly different (12 +/- 15 cm(3) and 14 +/- 11 cm(3) versus 16 +/- 7 cm(3)). Apparently, the elimination of GCAP(+) cells from th e tumor seemed to favor conditions enabling the outgrowth of the few G CAP(-) cells originally present in the tumor inoculate. In contrast, t umor volumes in group 4 (local treatment) were significantly smaller ( P < 0.03; 5 +/- 10 cm(3), 8 +/- 11% GCAP(+) cells) as compared to the nontreated group, probably due to the presence of higher amounts of Ab and infiltrated activated T cells (567 +/- 322 CD5(+) cells/mm(2)) ca pable of secreting cytostatic cytokines like tumor necrosis factor alp ha and INF-gamma as compared to groups 2 and 3 (266 +/- 135 and 198 +/ - 86 CD5(+) cells/mm(2), respectively). In summary, this study clearly demonstrated that bispecific antibodies specifically concentrate cyto toxic T cells into a solid tumor in vivo, with subsequent elimination of the targeted tumor cell.