BL3750 tumor cell expansion depletes circulating CD20 mAb in vivo. Mice were given 106 BL3750 cells subcutaneously with CD20 (IgG2c, •, n = 6) or control (IgG2a, ○, n = 8) mAb (250 μg/mouse) given intravenously on day 0 after the mice had demonstrable leukemia. Blood cells were isolated before mAb treatment and on the indicated days after mAb treatment. (A) CD20 mAb binding to circulating tumor cells. Numbers indicate the relative frequencies of gated CD19+ lymphoblast cells with IgG2a/c mAb bound in vivo on days 1 and 7. Blood leukocytes were incubated with either control IgG2c or MB20-11 (IgG2c) CD20 mAb in vitro, washed, stained using fluorochrome-conjugated IgG2c-specific secondary antibody, and analyzed by flow cytometry. (B) Percentages of circulating B lymphoblasts with IgG2a/c mAb bound to their cell surface. Values indicate mean (± SEM) percentages of circulating CD19+ lymphoblast cells staining positive as shown in panel A. (C) Mean white blood cell (WBC) numbers (± SEM) in mice given CD20 or control mAb.
