Stromal insufficiency to support hematopoiesis. (A) CFU-F assays show comparable frequency of mesenchymal progenitor cells in ADA^+/+ or ADA^−/− total BM. (B) LTC-IC assays of ADA^+/+ or ADA^−/− feeder layers cocultured with ADA^+/+ or ADA^−/− lineage⁻ cells. ADA^+/+ or ADA^−/− LTC-IC grow significantly less when cocultured with ADA^−/− feeder layers (P = .012). (C) Proteome profile from supernatants of ADA^+/+ and ADA^−/− cocultures, performed in triplicate; average ± SD. **P = .001-.005. *P = .005-.05. (D) TaqMan gene expression analyses for IL-1ra. Spleen, liver, BM, and bone in vivo. Stromal cells as used for LTC-IC, mesenchymal progenitor cells as cultured for CFU-F assays, OBs in vitro; fold expression versus wild-type (represented by dashed line), normalized for HPRT endogenous control (average of 3 experiments ± SD. (E) The percentage of quiescent HSCs, as assessed by FACS staining for lineage⁻, Sca1⁺, cKit⁺, CD150⁺, CD48⁻ cells is significantly lower in ADA^−/− (n = 8) compared with ADA^+/+ mice (n = 8). ***P < .001. (F) Survival curves of ADA^+/+ and ADA^−/− mice transplanted with ADA^+/+ lineage⁻ cells after multiple 5-fluorouracil injections at days 7, 14, 21, and 28. P = .011.