SCREENING OF ANTI-MUC1 ANTIBODIES FOR REACTIVITY WITH NATIVE (ASCITES) AND RECOMBINANT (BACULOVIRUS) MUC1 AND FOR BLOCKING MUC1 SPECIFIC CYTOTOXIC T-LYMPHOCYTES

We report the results of a panel of 56 monoclonal antibodies submitted to the ISOBM TD-4 Workshop for the study of the epithelial MUC1 mucin . We used three forms of the MUC1 as antigen. One form of mucin was th e native, highly glycosylated MUC1 isolated from the ascites of breast or pancreatic cancer patients. Two other forms of the mucin were reco mbinantly expressed in a baculovirus expression system as either fully glycosylated, or underglycosylated. Based on the results of Western b lot analysis we were able to group the antibodies into 7 clusters depe nding on their recognition of the MUC1 forms tested. We then selected several antibodies, representatives of each cluster, to test for the a bility to block MUC1-specific cytotoxic T-lymphocyte (CTL) function. W e found that antibodies ISOBM-163 and ISOBM-147 blocked cytotoxicity o f MUC1-specific CTL against two tumor targets in a concentration-depen dent manner.