Hematopoiesis is improved when MDS marrow is exposed to a WT BMME. (A) Schematic of competitive repopulation assays in which NHD13 donor BM was transplanted with WT competitor BM into NHD13 recipients (blue diamonds) and WT recipients (gray squares). (B-F) Donor BM was from a 20-week-old NHD13 mouse transplanted into either lethally irradiated 23-week-old NHD13 mice (n = 3) or lethally irradiated WT littermates (n = 4). Comparison of engraftment of NHD13 marrow (B) in WT recipients vs NHD13 recipients (2-way ANOVA: P < .0001). At 16 weeks following transplant, whole BM of recipients was analyzed to determine contribution of NHD13 donor marrow to the total LSK pool (C) in WT and NHD13 recipients. Serial hematologic parameters hemoglobin (Hgb) (D), WBC count (E), and platelet count (Plt) (F) were measured in recipient mice every 4 weeks from time of transplant. (G-K) Donor BM was from a 15-week-old NHD13 mouse transplanted into either lethally irradiated 15-week-old NHD13 mice (n = 3) or WT littermates (n = 5). Comparison of engraftment of NHD13 marrow (G) in WT recipients vs NHD13 recipients (2-way ANOVA: P > .05). At 16 weeks following transplant, whole BM of recipients was analyzed to determine contribution of NHD13 donor marrow to the total LSK pool (H) in WT and NHD13 recipients. Serial hematologic parameters Hgb (I), WBC count (J), and Plt (K) were measured in recipient mice every 4 weeks from time of transplant. (L) Frequency of myeloid vs lymphoid cells within CD45.1⁺ WT competitor-derived cells in peripheral blood of all WT and NHD13 recipients at 16 weeks posttransplant. For hematologic data, upper and lower borders of gray boxes represent the interquartile range of Hgb, WBC, or Plt values for nontransplanted WT mice (from Figure 1).