Figure 5

Soluble EpCAM in ascites inhibits ADCC of tumor cells. Effects of sEpCAM/EpEX on catumaxomab-dependent cell mediated cytotoxicity (A) Colorectal carcinoma cells HRT-18 and human diploid fibroblasts (HDFs) were analyzed by Western Blot for the expression of EpCAM. (B) Flow cytometry analysis of EpCAM expression on HRT-18 cells and HDFs. (C) HRT-18 cells were incubated with or without 1 ng/mL catumaxomab (cat.) together with a 10-fold excess of human PBMNCs (lymphocytes and monocytes). PBMNCs with catumaxomab were efficiently killing cells, but did not attack HRT18 cells in the presence of 5 ng/mL recombinant EpEX (upper panel). Experiments were repeated with catumaxomab and sEpCAM positive (A ^pos, 5 ng/mL) and negative (A ^neg <200 pg/mL) ascites pools (lower panel). ADCC was inhibited in ascites samples with high sEpCAM levels. (D) Viable tumor cells are displayed as EpCAM⁺/Annexin⁻ cells after staining and analysis by flow cytometry. EpEX and ascites with high concentrations of sEpCAM inhibited catumaxomab-dependent cell mediated cytotoxicity (Mean ± SEM).