In vivo circulating B-cell depletion with antihuman CD20 mAbs. Transgenic hCD20 mice on C57Bl/6 (A) or BALB/c (B) backgrounds received 250 μg of anti-hCD20 mAb or an isotype-matched control (WR17) intravenously on day 0. The numbers of circulating B cells were then assessed by CD19 and B220 staining of peripheral blood and flow cytometry. The results are expressed as percentage of B cells observed at time 0, n ≥ 4 from at least 2 to 4 independent experiments.