Humanized mice are an experimentally tractable model for studying human haematopoiesis and immune responses in vivo. Humanized mice models can be made by transplanting immune-deficient mice with haematopoietic stem cells (HSCs) from sources such as umbilical cord blood or adult mobilized PBMCs. Following transplantation, human HSCs home to the bone marrow and underpin the development of a human immune system within engrafted mice. While traditional humanized mouse models have been highly informative, they have significant limitations, including donor variability and availability (from cord blood), and difficulties in introducing genetically modifications. These limitations restrict the use of humanized mouse models and present an unavoidable roadblock to experimental reproducibility. Crucially, mechanistic molecular studies are not possible with currently available sources of HSCs, which effectively preclude the possibility of nuanced genetic manipulation.
We recently developed a protocol for differentiating induced pluripotent stem cells (iPSCs) into long-term engrafting hematopoietic stem cells (iHSCs). Here, we document the capacity of laboratory made iHSCs to generate functionally diverse immune lineages following transplantation into neonatal NBSGW mice. Engraftment was quantified using HLA-I in conjunction with CD45 and CD235a, enabling clear discrimination of human hematopoietic cells. By 20 weeks post-transplant, mice displayed stable multilineage human haematopoiesis, including robust B- and T-lymphoid, myeloid, and erythroid populations in bone marrow, spleen, and peripheral blood. Comparative analysis demonstrated that the distribution and frequencies of myeloid, lymphoid and erythroid lineages closely paralleled that observed in mice reconstituted with human cord blood HSCs. iHSC humanized mice produced IgM and IgG at levels comparable to those observed in cord blood–humanized mice and generated mature T cell subsets capable of proliferation, indicating that iHSC derived B and T cell compartments are functionally competent. With this renewable system, it is possible to create an infinite supply of human HSCs for the production of humanized mice.