Effect of Human Blood Mononuclear Cell Populations in Antibody Dependent Cellular Cytotoxicity (ADCC) Using Two Murine (CO 17-1A and Br55-2) and One Chimeric (17-1A) Monoclonal Antibodies Against a Human Colorectal Carcinoma Cell Line (SW948)

Peripheral blood mononuclear cells (PBMC) from healthy individuals were studied for their lytic capability in ADCC using SW948 (a human colorectal carcinoma cell line) as target cells. Three monoclonal antibodies (MAbs) were used: two mouse MAbs (IgG_2A) against the antigenic structures CO 17-1A and BR55-2 respectively and one chimeric MAb 17-1A (IgG₁) (mouse-human). Three kinds of effector cells were prepared. PBMC were purified on a Ficoll-Isopaque gradient (FIP cells) (a mixture of lymphocytes and monocytes). To obtain pure monocytes (>90%), PBMC were centrifuged on a Nycodenz gradient (Nycodenz cells). Highly purified lymphocytes (>98%) were obtained by treatment of FIP cells with iron powder and removal of phagocytic cells (PBL cells). Monocytes had the highest lytic capability. FIP cells were less effective than monocytes. PBL cells had the poorest killing activity. In reconstitution experiments addition of increasing amount of monocytes to PBL resulted in an augmented cytotoxicity. The numbers of Leu-M3⁺ cells, Leu-M5⁺ cells (monocytes) and CD16⁺ cells correlated positively to cytotoxicity. Higher concentration of MAb 17-1A was required to reach the same level of cytotoxicity using FIP cells as effector cells as compared to monocytes. MAb BR55-2 induced the same cytotoxic activity as MAb 17-1A. Combination of these two MAbs did not increase the lytic capability. Chimeric MAb 17-1A mediated ADCC in a dose-dependent fashion. The chimeric MAb was consistently more effective than the mouse MAb.