TIMP-deficient BM cells have reduced B-lymphopoiesis potential. (A) Schematic of experimental pipeline for competitive BM transplant. (B) Percentage of QT3^+/− donor’s B cells (of total B cells) or myeloid cells (of total myeloid cells) in tail vein blood of recipient mice, 4 weeks after either young WT (n = 9), young QT3^+/− (n = 10), old WT (n = 8), or old QT3^+/− (n = 16) donor BM transplant. Statistics by 1-way ANOVA; data represent mean plus or minus SEM; **P < .01, ***P < .001, and ****P < .0001 by the Bonferroni multiple comparisons test. (C) Percentage of experimental donor (CD45.2⁺) B cells (top) or myeloid cells (bottom) in recipient tail blood at 20 weeks posttransplant, having received either young WT (n = 8), young QT3^+/− (n = 8), old WT (n = 3), or old QT3^+/− (n = 5) BM. For both statistics by 1-way ANOVA; data represent mean plus or minus SEM; *P < .05, **P < .01, and ***P < .001 by the Bonferroni multiple comparisons test. (D) Schematic outline of methylcellulose colony-forming assay, using either pre-B or granulocyte/macrophage (GM) supporting media. (E) The number of pre-B-cell and GM colonies that developed in 6 days per 1 × 10⁵ BM cells from 4-week-old mice (WT, n = 10; QT3^+/−, n = 10; QT, n = 3). Statistics by 1-way ANOVA; individual data points are shown as well as the mean plus or minus SEM; ***P < .001 by the Bonferroni multiple comparisons test.