Generation of Novel Human Red Blood Cell-Bearing Humanized Mouse Models Based on C3-Deficient NOG Mice

Understanding erythroid physiology and pathology in humanized mice: A closer look

Erythropoiesis, the process of red blood cell (RBC) development from haematopoietic stem cells, is crucial in haematology research due to its intricate regulation and implications in various pathologies such as anaemia and haemoglobinopathies. Humanized mice, created by introducing human cells or tissues into immunodeficient mice, offer a promising avenue in vivo approach. However, challenges persist in fully replicating human erythropoiesis in these models, particularly in generating mature human RBCs capable of sustained circulation. This review discusses the differences between human and mouse erythropoiesis, recent progress made using refined humanized mouse models for studying human erythropoiesis and erythropoietic disorders, the challenges that impede a faithful mimicking of human phenotypes in these mice and recommendations for future research improvements. Despite progress being made, enhancing the translational potential of humanized mouse models for human erythropoiesis research remains a priority.

Peripheral human red blood cell development in human immune system mouse model with heme oxygenase-1 deficiency

ABSTRACT

A challenge for human immune system (HIS) mouse models has been the lack of human red blood cell (hRBC) survival after engraftment of these immune-deficient mice with human CD34+ hematopoietic stem cells (HSCs). This limits the use of HIS models for preclinical testing of targets directed at hRBC-related diseases. Although human white blood cells can develop in the peripheral blood of mice engrafted with human HSCs, peripheral hRBCs are quickly phagocytosed by murine macrophages upon egress from the bone marrow. Genetic ablation of murine myeloid cells results in severe pathology in resulting mice, rendering such an approach to increase hRBC survival in HIS mice impractical. Heme oxygenase-1 (HMOX-1)-deficient mice have reduced macrophages due to toxic buildup of intracellular heme upon engulfment of RBCs, but do not have an overall loss of myeloid cells. We took advantage of this observation and generated HMOX-1-/- mice on a humanized M-CSF/SIRPα/CD47 Rag2-/- IL-2Rγ-/- background. These mice have reduced murine macrophages but comparable levels 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. Additionally, upon human HSC engraftment, hRBCs can be observed in the peripheral blood of HMOX-1-/- humanized M-CSF/SIRPα/CD47 Rag2-/- IL-2Rγ-/- mice, and hRBC levels can be increased by treatment with human erythropoietin. Given that hRBC are present in the peripheral blood of engrafted HMOX-1-/- mice, these mice have the potential to be used for hematologic disease modeling, and for testing therapeutic treatments for hRBC diseases in vivo.

A Monocytic Barrier to the Humanization of Immunodeficient Mice

Mice with severe immunodeficiencies have become very important tools for studying foreign cells in an in vivo environment. Xenotransplants can be used to model cells from many species, although most often, mice are humanized through the transplantation of human cells or tissues to meet the needs of medical research. The development of immunodeficient mice is reviewed leading up to the current state-of-the-art strains, such as the NOD-scid-gamma (NSG) mouse. NSG mice are excellent hosts for human hematopoietic stem cell transplants or immune reconstitution through transfusion of human peripheral blood mononuclear cells. However, barriers to full hematopoietic engraftment still remain; notably, the survival of human cells in the circulation is brief, which limits overall hematological and immune reconstitution. Reports have indicated a critical role for monocytic cells - monocytes, macrophages, and dendritic cells - in the clearance of xenogeneic cells from circulation. Various aspects of the NOD genetic background that affect monocytic cell growth, maturation, and function that are favorable to human cell transplantation are discussed. Important receptors, such as SIRPα, that form a part of the innate immune system and enable the recognition and phagocytosis of foreign cells by monocytic cells are reviewed. The development of humanized mouse models has taken decades of work in creating more immunodeficient mice, genetic modification of these mice to express human genes, and refinement of transplant techniques to optimize engraftment. Future advances may focus on the monocytic cells of the host to find ways for further engraftment and survival of xenogeneic cells.

Interplay between Liposomes and IgM: Principles, Challenges, and Opportunities

Liposomes have received tremendous attention as a class of versatile pharmaceutical vehicles of great potential over the past several decades. However, the application of liposomes encounters major challenges due to the knowledge gaps in their in vivo delivery process. Immunoglobulin M (IgM) displays both pervasiveness and complexity in regulating the biological functions as well as eliciting adverse effects of liposomes. Understanding, mitigating, and exploiting the duality of IgM are prerequisites for achieving various biomedical applications of liposomes. In this review, the intricate relationship between liposomes and their biological environments has been summarized, with an emphasis on the regulatory effects of IgM on in vivo performance of liposomes. Corresponding solutions have also been discussed to evade IgM-mediated opsonization for safe and efficient drug delivery.

Humanized mice for investigating sustained Plasmodium vivax blood-stage infections and transmission

Plasmodium vivax is the most widespread human malaria parasite. Due to the presence of extravascular reservoirs and relapsing infections from dormant liver stages, P. vivax is particularly difficult to control and eliminate. Experimental research is hampered by the inability to maintain P. vivax cultures in vitro, due to its tropism for immature red blood cells (RBCs). Here, we describe a new humanized mice model that can support efficient human erythropoiesis and maintain long-lasting multiplication of inoculated cryopreserved P. vivax parasites and their sexual differentiation, including in bone marrow. Mature gametocytes were transmitted to Anopheles mosquitoes, which led to the formation of salivary gland sporozoites. Importantly, blood-stage P. vivax parasites were maintained after the secondary transfer of fresh or frozen infected bone marrow cells to naïve chimeras. This model provides a unique tool for investigating, in vivo, the biology of intraerythrocytic P. vivax.