Immunodeficient mice play a critical role in preclinical research, particularly in oncology and immunology. With compromised immune systems, these models support the engraftment of human cancer cell lines (CDX), patient-derived tumors (PDX), and human immune components such as PBMCs or CD34⁺ HSCs. This makes them indispensable for studying tumor biology, evaluating immunotherapies, and developing humanized mouse models.