Depletion of B-ALL–associated cells after timed MCMV infections. (A) Neonatal and adult BALB/c mice injected with 1 to 2 × 10³ Eμ-ret leukemic cells were euthanized at 10 dpi to assess leukemic cell burden in spleens of phosphate-buffered saline (PBS)-injected (control [Ctrl]) or virus-infected (CMV) recipients (Mann-Whitney; n = 14 Ctrl and 16 CMV neonates; n = 14 Ctrl and 11 CMV adults; pooled results for 3 different leukemias). (B) Neonatal and adult BALB/c mice injected with 0.5 to 1 × 10³ Eμ-ret leukemic cells were infected 5 to 6 days later with PBS (Ctrl) or virus (CMV) and then monitored for leukemia-free survival of recipients (log-rank [Mantel-Cox] test; n = 6-10 mice in each group; pooled results from 2 independent experiments). (C) Neonatal and adult C57BL/6 mice injected with 0.5 to 1 × 10³ E2A-PBX1 leukemic cells were euthanized 10 days after subsequent infection to assess leukemia burden in spleens of PBS- or CMV-infected recipients (Mann-Whitney; n = 18 Ctrl and 15 CMV-infected neonates; n = 12 Ctrl and 11 infected adults; pooled results from 4 independent experiments). (D) Splenic PLC burden in Eμ-ret mice 10 days after injection with PBS or CMV at the indicated age (Mann-Whitney test; number of mice in Ctrl/infected groups: week 1 [wk1] = 21/21, wk2 = 11/6, wk3 = 8/5, and wk4 = 12/11). (E) Spleen (n = 11 Ctrl; n = 10 CMV) and BM (n = 12 Ctrl; n = 6 CMV) B-cell Fr cell numbers in neonatal Eμ-ret mice 10 days after injection with PBS or CMV at 5 to 7 days of age (Mann-Whitney test). (F) Leukemia-free survival of neonatal Eμ-ret mice after PBS (Ctrl) or virus (CMV) injection at 5 to 7 days of age (log-rank [Mantel-Cox] test; n = 23 Ctrl; n = 17 CMV; ∗P = .0166). All data presented as mean ± standard error of the mean (SEM). ns, not significant; ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. Ctrl, control.