Leukemia development in Eμ-TCL1/IgPtC transgenic mice. (A) The percentage and absolute number of B cells in the peripheral blood of Eμ-TCL1/IgPtC transgenic mice (n = 15) are shown in panels Ai and Aii, respectively. B cells that express only an endogenous HC (IgMa⁻) are indicated by empty circles, whereas B cells that express only the transgenic HC (IgMa⁺) or coexpress the transgenic and an endogenous HC are indicated by filled circles. Each circle represents the value for an individual mouse at the indicated time point; horizontal lines represent mean values. Two mice died of leukemia between 6 and 8 months and 3 between 8 and 9 months of age. (B) Flow cytometry analysis of surface IgMa and IgMb expression in representative leukemias. Analysis was performed on the lymphocyte gate. (C) Flow cytometry analysis of leukemic cells stained with PtC-liposomes and anti-CD19. B cells obtained from the spleen of a normal mouse were used as a negative control.