Severely immunodeficient mice engrafted with human hematopoietic stem cells (HSCs) are widely used in immuno-oncology studies to evaluate cancer therapies. GemPharmatech has developed the NCG-XM model, which expresses human granulocyte-macrophage colony-stimulating factor 2 (GM-CSF), interleukin-3 (IL-3), and stem cell factor (SCF), along with a W41/W41 inactivation mutation in the Kit gene. The goal of this model is to support multilineage human immune cell differentiation without the need for irradiation. The HSC-NCG-XM model enables better reconstitution of human T cells, B cells, NK cells, and myeloid cells (such as granulocytes, monocytes, neutrophils, macrophages, and dendritic cells) without requiring murine myeloablation prior to HSC engraftment, typically achieved through sublethal radiation or chemoablation. Furthermore, HSC-NCG-XM mice can survive for over 22 weeks post-engraftment, making them ideal for long-term immuno-oncology studies.