H^−/−/T^tg/wt mice show a premature accumulation of CD19⁺CD5⁺ cells. (A) Mice were grouped according to the presence of at least 30% CD19⁺CD5⁺ cells in PB (leukemic mice) compared with less than 30% (nonleukemic mice). Nonleukemic H^wt/wt/T^tg/wt mice (7-13 month old; n = 8), age-matched leukemic H^−/−/T^tg/wt (n = 6), and leukemic H^wt/wt/T^tg/wt (13-18 month old; n = 5) mice were analyzed by flow cytometry. The mean value ± SD of the relative contribution of CD19⁺CD5⁺ cells to the whole B-cell pool in the bone marrow (BM), spleen (SP), peritoneal cavity (PE), and peripheral blood (PB) is shown in the graph. Statistical significance was analyzed by T test. *P ≤ .05; **P ≤ .01; ***P < .001. (B) Flow cytometric plot from a representative leukemic H^−/−/T^tg mouse (9 months old) show CD19⁺CD5⁺ cells in the spleen. The cells were first gated on physical parameters and then on side scatter (SSC) and CD19. Percentage of leukemic CD19⁺CD5⁺ cells is indicated. Flow cytometric plots from a representative leukemic H^−/−/T^tg animal (9 months old) showing (C) Igκ and (D) IgM expression on CD19⁺CD5⁺ cells from the spleen (B). (E) Kaplan-Meier survival curves of H^−/−/T^tg/wt (n = 18) and H^wt/wt/T^tg/wt (n = 17) mice are shown. Mice were included in the analysis after spontaneous death or when killed because of frank leukemia development (presence of ≥ 30% CD19⁺CD5⁺ expansion at least in the PB, monoclonal IGH gene rearrangements, tissue infiltration). Statistical analysis between groups was performed with the log-rank test (H^−/−/T^tg/wt vs H^wt/wt/T^tg/wt, P < .001).