FACS analyses of tumor cells stained with MORAb-009. (A) Parental A431 cells, as well as cells expressing mesothelin (A431-K5), were reacted with FITC-labeled anti-human IgG antibody, with or without MORAb-009. Positive staining was observed only in the presence of MORAb-009 in A431-K5 cells, demonstrating specificity of the immune staining and lack of reactivity of MORAb-009 with other unrelated membrane proteins. (B) Tumor cells were reacted with FITC-labeled anti-human IgG antibody alone to determine background staining (not shown) and to create gate P2 to capture fluorescent signal above background. MORAb-009 was able to bind mesothelin expressed by ovarian (OVCAR-3), mesothelioma (NCI-H226), and pancreatic (Panc 3.014) cancer cells.