LYSIS OF HUMAN TUMOR-CELL LINES BY CANINE COMPLEMENT PLUS MONOCLONAL ANTIGANGLIOSIDE ANTIBODIES OR NATURAL CANINE XENOANTIBODIES

Because certain antiganglioside monoclonal antibodies can facilitate a ntibody-dependent cellular cytotoxicity against GD2(+) ganglioside-bea ring human and canine tumor cells, we wished to determine if clinicall y relevant antiganglioside monoclonal. antibodies (Mabs) could also fi x canine complement to lyse tumor cells in vitro. Using flow cytometry , human tumor cell Lines (M21 melanoma and OHS osteosarcoma) were show n to highly express ganglioside GD2 and, to a lesser degree, GD3. In C r-51 release assays, M21 cells were lysed with canine serum, as a sour ce of complement, plus either Mab 14.G2a or its mouse-human chimera, c h 14.18, specific for GD2. Heating canine serum abrogated its lytic ac tivity and addition of rabbit complement reconstituted M21 lysis. Simi lar results were obtained with M21 cells when Mab R24 (against GD3) an d canine serum were used. OHS cells were also lysed with canine serum plus Mab 14.G2a and lytic activity was abolished by heating canine ser um but reconstituted with rabbit complement. Alone, canine serum or Ma bs were not lytic to M21 or OHS cells. Conversely, human neuroblastoma (LAN-5) and K562 erythroleukemia cells were lysed by canine serum alo ne which was shown by flow cytometry to contain naturally occurring ca nine IgM: antibodies that bound LAN-5 and K562 cells. The lytic activi ty of canine serum for LAN-5 or K562 cells was abolished by heating an d restored by addition of either human or rabbit complement. Thus, hum an tumor cell lines can be lysed with antiganglioside Mabs through fix ation and activation of canine complement-dependent lytic pathways. Ca nine xenoantibodies also mediate complement-dependent cytotoxicity of some human tumor cell lines, Together, these results are significant b ecause they demonstrate an antitumor effect of the canine immune syste m which is of potential importance for cancer immunotherapy in a promi sing animal model. (C) 1996 Academic Press,Inc.