Antibody-dependent cell-mediated cytotoxicity can be induced by MUC1 peptide vaccination of breast cancer patients

Human polymorphic epithelial mucin (PEM, MUCI) is a high molecular weight transmembrane glycoprotein expressed on the apical cell surface of glandular epithelium and is over-expressed and hypo-glycosylated in adenocarcinomas. The extracellular part of the molecule consists mainly of a variable number of 20 amino acid repeats that contain cryptic epitopes exposed in malignancy. The objective of our study was to determine whether humanized MUCI MAbs and Abs induced by vaccination of breast cancer patients with MUCI peptides can effect an antibody-dependent cell-mediated cytotoxicity (ADCC), An in vitro assay has been set up in which the breast tumor cell line ZR-75-I is used as target and PBMC of healthy donors as effector cells. Different target and effector cells, as well as various MUCI MAbs were tested to optimize the efficacy of the in vitro assay. The humanized MAb HuHMFG-I, which recognizes the PDTR sequence in the MUCI tandem repeat, induced a strong cell-mediated cytotoxicity. Nine MUCI-expressing tumor cell lines, including 3 bone marrow-derived cell lines, as well as 2 MUCI -transfected cell lines were susceptible to different extent to MUCI Ah-dependent killing, Large variations in the killing capacity of PBMC from healthy donors were found. The NK cells were the essential effector cells for the MUCI Ab-dependent killing. Plasma samples with induced high levels of MUCI Ab were obtained from breast cancer patients repeatedly immunized with a KLH-conjugated 33-mer or 106-mer MUCI tandem repeat. Pre- and post-vaccinated plasma samples of these patients were compared in the ADCC assay and it could be clearly demonstrated that the induced MUCI Abs can effect tumor cell killing. MUCI Ab-dependent cell-mediated tumor cell killing may occur in vivo and the ADCC assay can be applied to monitor MUCI vaccination trials. (C) 2001 Wiley-Liss, Inc.