HEMATOPOIESIS AND STEM CELLS Development of human CD4 FoxP3 regulatory T cells in human stem cell factor–, granulocyte-macrophage colony-stimulating factor–, and interleukin-3–expressing NOD-SCID IL2R null humanized mice

Human hematolymphoid mice have become valuable tools for the study of human hematopoiesis and uniquely human pathogens in vivo. Recent improvements in xenorecipient strains allow for longterm reconstitution with a human immune system. However, certain hematopoietic lineages, for example, the myeloid lineage, are underrepresented, possibly because of the limited cross-reactivity of murine and human cytokines. Therefore, we created a nonobese diabetic/severe combined immunodeficiency/interleukin2 receptor–null (NOD-SCID IL2R null) mouse strain that expressed human stem cell factor, granulocyte-macrophage colonystimulating factor, and interleukin-3, termed NSG-SGM3. Transplantation of CD34 human hematopoietic stem cells into NSG-SGM3 mice led to robust human hematopoietic reconstitution in blood, spleen, bone marrow, and liver. Human myeloid cell frequencies, specifically, myeloid dendritic cells, were elevated in the bone marrow of humanized NSG-SGM3 mice compared with nontransgenic NSG recipients. Most significant, however, was the increase in the CD4 FoxP3 regulatory T-cell population in all compartments analyzed. These CD4 FoxP3 regulatory T cells were functional, as evidenced by their ability to suppress T-cell proliferation. In conclusion, humanized NSGSGM3 mice might serve as a useful model to study human regulatory T-cell development in vivo, but this unexpected lineage skewing also highlights the importance of adequate spatiotemporal expression of human cytokines for future xenorecipient strain development. (Blood. 2011;117(11): 3076-3086)