The interleukin-2 receptor alpha subunit, encoded by the IL2RA gene and also known as CD25, is a critical determinant of IL-2 signaling, a pathway fundamental to T cell biology. While CD25 alone exhibits low affinity for IL-2, its assembly with the IL-2 receptor beta and gamma chains forms the high-affinity receptor complex essential for robust cellular responses to this pleiotropic cytokine ^[1]. Expressed prominently on activated T lymphocytes, including effector and regulatory T cells, CD25 is pivotal for diverse processes such as T cell proliferation, differentiation, and the maintenance of immune tolerance, largely mediated through its indispensable role in regulatory T cell development and function ^[2]. Consequently, perturbations in IL2RA expression or genetic variants within the locus are strongly associated with susceptibility to a range of severe autoimmune disorders, including multiple sclerosis, type 1 diabetes, and rheumatoid arthritis, highlighting its central involvement in immune homeostasis breakdown ^[3]. Furthermore, aberrant CD25 expression has been observed in certain malignancies, suggesting roles beyond adaptive immunity ^[4]. The demonstrable impact of IL2RA on immune regulation and disease pathogenesis underscores its significance as a key molecule in immunology and a compelling target for therapeutic intervention.

The B6-hIL2RA mouse is a humanized model constructed by replacing the sequence of the mouse Il2ra endogenous extracellular domain in situ with the corresponding extracellular domain from the human IL2RA. The murine signal peptide and transmembrane-cytoplasmic region were preserved. The B6-hIL2RA mice can be used for the study of the pathogenesis of autoimmune diseases such as multiple sclerosis, type 1 diabetes, and rheumatoid arthritis, and certain malignancies, as well as for IL2RA-targeted drug development.