Development of immunodeficient mice for xenograft studies. Discovery of nude and SCID mice, in which T cells or T/B cells are deficient, contributed to the early-phase development of xenograft models. NOD/SCID mice, which harbor defects in T, B, and macrophage activity, supported higher levels of human engraftment and promoted the further development of xenomodels. Currently, mice with almost no murine immunity, such as NOG and NSG mice, are widely in xenograft studies. Variations of these strains including the BLT model and human cytokine mice are becoming available to provide optimal xenomodels for specific studies.