Generation of CD68+ macrophage-depleted NOG mice for <i>in vivo</i> engraftment of human red blood cells

Humanized mice are invaluable models for investigating human cell engraftment in vivo post-transplantation. Mice engrafted with human red blood cells (hRBCs) are useful for examining the physiological roles of hRBCs in vivo, including studies on blood disorders, immune responses, and transfusion-related research. These models hold promise for malaria infection studies and vaccine development. However, engrafted hRBCs in vivo in immunodeficient mice presents challenges that must be addressed to establish effective in vivo models. In this study, we explored the rejection mechanisms of hRBCs in immunodeficient NOD/Shi-scid-IL2rγnull (NOG) mice and developed a novel model for long-term RBC engraftment. We observed rapid depletion of fluorescent-labeled hRBCs in the liver, but not in other organs, of NOG mice, with Gr-1midCD68+ mouse macrophages play a significant role in the elimination of hRBCs in the liver. To counteract this, we created thymidine kinase (TK) transgenic (Tg) mice under the human CD68 promoter (NOG-pCD68-TK Tg), which, upon administration of valganciclovir (VGCV), led to the successful depletion of macrophages. Consequently, hRBCs showed significantly prolonged engraftment in NOG-pCD68-TK Tg mice compared to non-Tg mice following macrophage depletion, maintaining engraftment for up to 14 days post-transplantation. This study elucidates the erythrophagocytosis mechanisms of hRBCs in mice and establishes NOG-pCD68-TK Tg mice as a valuable model for the long-term engraftment of hRBCs, potentially advancing in vivo hRBC research.