Sirolimus restores HSPCs following irradiation. A, B6 mice were irradiated at 5 Gy, followed by 10 daily i.p. injection of 2 mg/kg sirolimus (SIR, N = 10) in 2 weeks or untreated (TBI, N = 10). B, Complete blood counts (WBCs, RBCs, and platelets) and total BM cell recovery following irradiation with or without sirolimus treatment. C, Proportions and total numbers of HSPCs, defined by c-Kit⁺Sca-1⁺Lin⁻ (KSL), KSLCD150⁺ (KSLS) and KSLCD150⁺CD48⁻ (KSLSS) markers. D, Frequencies of CFU-G, CFU-M, CFU-GM and total CFC following BM cell culture in vitro in methylcellulose media for 10 days. E, Expression of genes related to hematopoiesis in BM Lin⁻CD150⁺ cells following irradiation with or without sirolimus treatment. Each column in the heatmap represents a pooled sample from the same group. Red color represents high expression, blue low expression. Genes with more than twofold change compared with TBI controls are shown. ** P < .01; ***P < .001; ****P < .0001. BM, bone marrow; CFU, colony-forming unit; CFC, colony-forming cells; HSPCs, hematopoietic stem and progenitor cells; i.p., intraperitoneal; TBI, total body irradiation