Properties of the EpCAM-specific heterodimeric B7-1 construct. (A) SDS-PAGE under non-reducing (lanes I and II) and reducing conditions (lanes III and IV). Lanes I and IV, molecular weight markers. Lanes II and III, purified heterodimeric B7-1 construct. (B) Flow cytometric analysis of the heterodimeric B7-1 construct on untransfected CHO cells (negative control) and CHO cells transfected with a full length cDNA encoding the human EpCAM antigen. (C) ELISA on immobilized recombinant CD28. The OD₄₀₅ values shown correspond to different concentrations of purified heterodimeric B7-1 construct (in µg/ml). Immobilized recombinant EGF receptor (EGFR) incubated with 2.5 µg/ml heterodimeric B7-1 construct served as a negative control. (D) ELISA on immobilized CTLA-4-IgG fusion protein. The OD₄₀₅ values shown correspond to different concentrations of purified heterodimeric B7-1 construct (in µg/ml). Immobilized CD4-IgG fusion protein incubated with 100 µg/ml heterodimeric B7-1 construct served as a negative control.