Induction of porcine granulocyte-mediated tumor cytotoxicity by two distinct monoclonal antibodies against lytic trigger molecules (PNK-E/G7)

PNK-E and G7 mAb bind to distinct porcine granulocyte function-associated molecules and induce granulocyte-mediated cytotoxicity against tumor targets. PNK-E mAb binds to a 205-kDa molecule that reduces to a dispersed band of 50 kDa on SDS-PAGE analysis. Previous work demonstrates that G7 mAb immunoprecipitates a molecule that appears as a heterodispersed 40-kDa band under both reducing and nonreducing conditions on SDS-PAGE analysis. Whole but not F(ab′)₂ PNK-E and G7 mAb induce dose-dependent porcine granulocyte-mediated lysis of FcR⁺ but not FcR^- targets, suggesting a redirected cytotoxicity mechanism of granulocyte-mediated killing. Fresh porcine granulocytes also mediate significant levels of antibody-dependent cellular cytotoxicity (ADCC) against nucleated (SB) target cells. Neither whole nor F(ab′)₂ PNK-E mAb affects granulocyte-mediated ADCC against SB target cells. However, both whole and F(ab′)₂ G7 mAb inhibit granulocyte-mediated ADCC against SB targets by approximately 50%. Bound F(ab′)₂ G7 mAb inhibits PNK-E mAb-induced granulocyte-mediated cytotoxicity against K562 targets, but bound F(ab′)₂ PNK-E mAb does not inhibit G7 mAb-induced granulocyte-mediated cytotoxicity, suggesting a physical association between the PNK-E and G7 molecules on the surface of porcine granulocytes. PNK-E and G7 hybridoma cells are readily lysed by granulocyte effectors, further supporting that the PNK-E and G7 molecules are cytolytic trigger molecules on granulocytes. These data demonstrate that PNK-E and G7 mAb bind to distinct granulocyte lytic trigger molecules and induce potent granulocyte-mediated cytotoxicity against nucleated tumor targets through a mechanism of redirected cytotoxicity.