Next we determined whether we could obtain stable cell lines from STAT5bER pos memory B cells isolated from clonal density cultures. For this we isolated CD27 pos memory B cells from the peripheral blood of two different donors, cultured these cells with CD40L-L cells plus IL-21 for 36 hrs, transduced them with STAT5bER-IRES-GFP and subsequently cultured these cells with CD40L-L cells, IL-2, IL-4 and tamoxifen. After seven days GFP pos B cells were plated out at a density of 1000, 100, 10 and 1 cell per well using high speed cell sorting and cultured with CD40L-L cells, IL-2, IL-4 and tamoxifen. Within two weeks multiple poly-and monoclonal STAT5bER memory B cell clones expanded. The frequency of outgrowth was 84%, 42%, 8% and 4% for the 1000, 100, 10 and 1 cell per well cultures respectively. These data show that stable STAT5bER pos memory B cell clones can be obtained from clonal cultures.