The number of isolated cells from spleen and antigen-specific B cell clones that were generated with the BCL6/BCL-XL transduction approach is provided in the Table S2 . Since the frequency of antigen-specific B cell clones was unknown, we started with microcell cultures ranging from 0.6 to 640 cells per well. The wells containing antigen-specific B cells -as determined by HBsAgspecific or TT-specific ELISA -were subsequently cultured by limiting dilution to obtain monoclonal B cell lines. Overall, we generated 15 anti-HBsAg IgM + B cell clones from 3 HIS mice vaccinated with HBsAg, and 18 anti-TT IgM + B cell clones from 3 HIS mice vaccinated with TT ( Table S2 ). The estimated frequency of HBsAg-specific B cells (clones) in the HIS mice after vaccination was 1/350. The IgM secretion level of the B cell clones were in the range of 1 mg per 10 5 cells over 3 days in culture, which was in a similar range of secretion (0.6-5 mg/10 5 cells/3 days) to what was previously reported for B cell clones generated from human blood [9] .