Interleukin-15 Receptor α Chain Knockout NOD-SCID mice have reduced numbers of NK cells, develop thymic lymphomas and fail to engraft human hematopoietic cells

NOD-SCID IL2rγcnull (NSG) mice are widely used to model human immune cell development because they are more permissive for human hematopoietic cell engraftment and reconstitution than NOD-SCID mice. While increased human reconstitution in the blood of NSG mice has been attributed to the absence of mouse NK cells, deletion of the common gamma chain (γc) limits development of lymphoid tissue inducer cells and precludes development of normal secondary lymphoid structures. The disorganized lymphoid tissue leads to compromised human T cell-B cell interactions and results in variable human immune cell function in human immune system (HIS) NSG compared to NOD-SCID mice. We attempted to remove mouse NK cells from NOD-SCID mice while retaining other γc-dependent cytokine responses by targeted disruption of the mouse genomic IL15RA locus with CRISPR/Cas9. IL15Rα is required for the development, function and survival of NK cells. NOD-SCID IL15Rα-/- mice showed reductions in NK cells and NK cell function. However, NOD-SCID IL15Rα-/- mice demonstrated accelerated thymic lymphomagenesis and showed earlier mortality compared to NOD-SCID mice. This result suggests that mouse NK cells are important to delay lymphoma development in NOD-SCID mice. We transplanted thymectomized NOD-SCID ILl5Rα-/- mice with human fetal liver CD34+ cells and thymus to determine if these mice supported engraftment and development of a transplanted HIS. Surprisingly, we found that peripheral human engraftment was inferior (mean 0.05% of lymphocytes) to that in both NOD-SCID (mean, 10.5% of lymphocytes) and NSG (mean, 54% of lymphocytes) mice. These results indicate that NOD-SCID IL15Rα-/- mice are not permissive for human CD34+ cell engraftment. ### Competing Interest Statement The authors have declared no competing interest.