A Murine Monoclonal Antibody that Recognizes an Extracellular Domain of the Human c‐erbB‐2 Protooncogene Product

A marine IgM monoclonal antibody, designated SV2–61, was generated against human c‐erbB‐2 gene‐transfected NIH‐3T3 (SV11) cells. SV2–61 defined a 185‐kDa molecule present on the surface of SV11 cells, another line of c‐erbB‐2 gene‐transfected NIH‐3T3 (A4–15) cells, and MKN‐7 human gastric cancer cell line carrying an amplified human c‐erbB‐2 gene. The SV2–61‐defined antigen was found to show protein kinase activity in vitro. The SV2–61 was reactive with human c‐erbB‐2 gene‐transfected NIH‐3T3 cell lines but not with transfectants carrying c‐erbB‐2 gene mutants which lack a coding region for the extracellular domain. It was reactive with a portion of human epithelial cell lines hut not with native NIH‐3T3, TGF‐a‐coding gene‐, activated c‐rafgene‐ or Ha‐ras gene‐transfected NIH‐3T3 cells, or non‐epithelial human cells. These results indicate that the SV2–61 is an antibody which recognizes an extracellular domain of the c‐erbB‐2 gene product, 185‐kDa protein.