Human EPO increases hRBC levels in peripheral blood of HMOX-1^–/– HIS mice. HMOX-1^–/– MSRG47 mice were intrahepatically engrafted with hHSCs. At 12 weeks after engraftment, mice were bled retro-orbitally to examine the level of hRBCs in peripheral blood before being injected intraperitoneally with 100 units of hEPO. At 1 week after injection, hRBCs were reassessed from the retro-orbital bleed. (A) Percentage of hRBCs in peripheral blood of HMOX-1^–/– MSRG47 mice before and after hEPO treatment. (B) Total number of hRBCs per microliter of peripheral blood before and after hEPO treatment. (C) Total number of RBCs per microliter of peripheral blood before and after hEPO treatment. Two independent experiments were performed. Data represent the mean ± SEM with individual mice shown. Statistical analysis was evaluated by paired Student t test.