From Brehm et al: No mature T cells, B cells, NK cells; radiosensitive. From Jackson Labs: These mice are most often referred to using their branded name NSG and are extremely immunodeficient. The mice carry two mutations on the NOD/ShiLtJ genetic background; severe combined immune deficiency (scid) and a complete null allele of the IL2 receptor common gamma chain (IL2rgnull). The scid mutation is in the DNA repair complex protein Prkdc and renders the mice B and T cell deficient. The IL2rgnull mutation prevents cytokine signaling through multiple receptors, leading to a deficiency in functional NK cells. The severe immunodeficiency allows the mice to be humanized by engraftment of human CD34+ hematopoietic stem cells (HSC), peripheral blood mononuclear cells (PBMC), patient derived xenografts (PDX), or adult stem cells and tissues. The immunodeficient NSG mice enable research in human immune function, infectious disease, diabetes, oncology, and stem cell biology.