New NSG-variant model does not require irradiation for engraftment of HSCs

Recipient xenotransplantation hosts

NSG^TM mice (NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/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, NSG^TM mice support higher levels of engraftment with many kinds of human cells and tissues than traditional immunocompromised host strains. While NSG^TM mice are still the first choice for studies that require immunodeficient mice, efforts continue to create NSG^TM 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 NSG^TM variant line, called NBSGW (NOD.Cg-Kit^W-41J Tyr+ Prkdc^scid Il2rg^tm1Wjl/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. 

Development and validation of the NBSGW strain

To generate an NSG^TM-derivative strain that does not require myeloablative irradiation, the Thompson team bred NSG^TM with C57BL/6J-Kit^W-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 Kit^W-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 Kit^W-41J alleles) confers all of the immunodeficiency of the NSG^TM strain with genetic myeloablation conferred by the Kit^W-41J allele.

Twelve weeks after engraftment of hCD34⁺ hHSCs, NBSGW and irradiated NSG^TM 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 NSG^TM 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 NSG^TM 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 NSG^TM 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.