Flow cytometric analysis of CD45 isoform expression. (A) Unseparated CD8+ T cells. (B) Purified naive CD8+ T cells (no additional MHC II depletion). These were subsequently stimulated with EpCAM-transfected CHO cells armed either with (C) 250 ng/ml bscAb EpCAM x CD3 alone, thus providing only a TCR-like primary signal, or with (D) 250 ng/ml bscAb EpCAM x CD3 and 500 ng/ml heterodimeric B7-1 construct additionally providing a costimulatory or second signal. C1 and D1 show the results after 4 days and C2 and D2 after 6 days of stimulation respectively.