Enhanced antitumor activity of a combination treatment with a mouse human chimeric anti-MK-1 antibody and lymphokine-activated killer cells in vitro and in a severe combined immunodeficient mouse xenograft model

Mouse monoclonal antibody FU-MK-1, raised against a human gastric adenocarc inoma, recognizes a glycoprotein antigen (termed MK-1 antigen) present on m ost carcinomas and seems to be valuable in immunodiagnosis and immunotherap y of various cancers. In a recent study, we constructed a mouse/human chime ric antibody, designated Ch FU-MK-1, by fusing the FU-MK-1 V-H and V kappa genes to the human C gamma 1 and C kappa genes, respectively. In the presen t study, we tested combination immunotherapy of Ch FU-MK-1 with human lymph okine-activated killer (LAK) cells In vitro and in mice with severe combine d immunodeficiency (SCID) bearing human MK-1-expressing tumors. In in vitro experiments, Ch FU-MK-1 effectively mediated antibody-dependent cell-media ted cytotoxicity (ADCC) against MK-1-expressing MKN-74 cells, which was com pletely blocked by an anti-FcR antibody. Since the apoptotic pathway as wel l as the necrotic pathway have been shown to be utilized in various cytotox ic effector mechanisms, we investigated the role of apoptosis in ADCC media ted by LAK cells and Ch FU-MK-1 against MKN-74 cells. The implication of th e apoptosis during ADCC was demonstrated by means of both a terminal-deoxyn ucleotidyltransferase-mediated dUTP- biotin nick-end-labeling assay and a p ropidium iodide staining method. In vivo antitumor activity of combination treatment with LAK cells and Ch FU-MK-1 was estimated using SCID mice inocu lated s.c. with MKN-74 cells. The i.v. administration of LAK cells and i.p. administration of Ch FU-MK-1 and interleukin-2 (IL-2) produced a marked gr owth inhibition of MKN-74 tumors in SCID mice. When the actual tumor weight s were measured 16 days after initiation of treatment, more than 70% reduct ion was observed in the group receiving LAK cells plus Ch FU-MK-1 plus IL-2 as compared to the control untreated group. Together these results suggest that Ch FU-MK-1 may serve as a potentially useful immunotherapeutic reagen t for human MK-1-expressing tumors.