Peripheral human red blood cell development in human immune system (HIS) mouse model with heme oxygenase-1 (HMOX-1) deficiency
A challenge for human immune system (HIS) mouse models has been the lack of  human red blood cells (hRBCs) survival after engraftment of these immune-deficient mice with human CD34+ hematopoietic stem cells (HSCs). Even though human white blood cells can develop in the peripheral blood of these human HSC-engrafted mice, and human erythroid progenitors are found in the murine bone marrow (BM), the hRBCs are quickly phagocytosed by murine macrophages upon egress from the BM. The challenge is further exacerbated by the pathology in BM development that occurs upon complete genetic ablation of murine myeloid cells, rendering such an approach impractical. Heme oxygenase-1 (HMOX-1) deficient mice have reduced macrophages due to toxic build-up of intracellular heme upon engulfment of red blood cells, but do not have an overall loss of myeloid cells. We took advantage of this observation and generated a HMOX-1-/- on a humanized M-CSF/SIRPa/CD47 Rag2-/- IL-2Ryc-/- background. These mice have reduced murine macrophages but comparable level of murine myeloid cells to HMOX-1+/+ control mice in the same background. Injected hRBCs survive longer in HMOX-1-/- mice than in HMOX-1+/+ controls. Since hRBC are present in the peripheral blood of engrafted HMOX-1-/- mice, these mice have the potential to be used for hematological disease modeling, and to test therapeutic treatments for hRBC diseases in vivo. Overall design: Spleen and bone marrow will be harvested from 3 different cohorts of engrafted HMOX-1 KO mice (HSC donor-matched; 3 mice per cohort). Single cell suspension will be prepared and mCD45+ cells and hCD45+ cells sorted from each tissue. Samples from each tissue and species will be hashed and used for single cell analysis of leukocyte subsets.