NSGTM mice (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ, Stock# 005557) have revolutionized human disease modeling by providing a platform with which to create new and valuable models to study human hematopoiesis, cancer, infectious and many other diseases. With their severely immunodeficient phenotype, NSGTM mice support higher levels of engraftment with many kinds of human cells and tissues than traditional immunocompromised host strains. While NSGTM mice are still the first choice for studies that require immunodeficient mice, efforts continue to create NSGTM strains with additional genetic modifications that will enhance further their suitability for certain uses. In a February 2015 article published in Stem Cell Reports (McIntosh et al.), a team led by Dr. James Thompson of the Morgridge Institute for Research in Madison, WI describe and validate a novel NSGTM variant line, called NBSGW (NOD.Cg-KitW-41J Tyr+ Prkdcscid Il2rgtm1Wjl/ThomJ (Stock# 026622), that does not require preconditioning irradiation to support engraftment of human hematapoietic stem cells. This strain should benefit researchers who require a severely immunodeficient host, but do not have access to, or who choose not to use, a radiation source.
To generate an NSGTM-derivative strain that does not require myeloablative irradiation, the Thompson team bred NSGTM with C57BL/6J-KitW-41J/J (000119) mice. The Kit gene encodes c-Kit, a membrane receptor in the type III tyrosine kinase growth factor receptor family that is expressed in hematopoietic cells, as well as in melanocytes and in some neural and germ cells. c-Kit activation is required for normal hematopoiesis; therefore, an inactivating mutation such as KitW-41J prevents development of these cell types. Mice with Kit mutations promote engraftment of donor cells, including human hematopoietic stem cells (hHSCs) without myeloablative irradiation. The resulting NBSGW strain (026622; the “B” in the strain’s name represents the C57BL/6J origins of the Tyr+ and KitW-41J alleles) confers all of the immunodeficiency of the NSGTM strain with genetic myeloablation conferred by the KitW-41J allele.
Twelve weeks after engraftment of hCD34+ hHSCs, NBSGW and irradiated NSGTM showed similar numbers of hCD45+ cells in peripheral blood, bone marrow, and spleen, indicating comparable engraftment efficiency. Bone marrow from engrafted NBSGW also contained cells from multiple human hematopoietic lineages and supported serial transplantation into a second NBSGW recipient, indicating persistence of reconstituting hHSCs. Additionally, human hCD45+ cells were more numerous in NBSGW spleens than in NSGTM spleens 12 weeks after engraftment (94% to 55% respectively), and the engrafted NBSGW spleens showed more CD11b+ myeloid cells and CD1a+ dendritic cells compared to NSGTM in immunohistochemically stained sections.
Although immunocompetency of the various reconstituted human immune cells were not evaluated in this study, the researchers demonstrated that comparable, if not improved, hCD45+ cell engraftment can be achieved in non-irradiated NBSGW as in irradiated NSGTM following hCD34+ hHSC injection. This new model may facilitate research by investigators that require a humanized mouse model who do not have access to, or chose not to use, myeloablative irradiation.