IL-2 receptor

Class

Engineered cytokine (PEGylated, non-alpha-biased IL-2 agonist fusion protein; SAR444245)

Pathway

IL-2/JAK-STAT5 signaling, selectively expanding CD8+ effector T and NK cells while sparing CD4+ regulatory T cells

Notes

original target text: IL-2 receptor (non-alpha-biased -- engineered to avoid IL-2Ralpha/CD25 engagement, activating IL-2Rbeta/gamma on effector CD8+ T cells and NK cells)

The interleukin-2 (IL-2) receptor is a three-part cell-surface complex — a high-affinity alpha subunit (CD25) and two subunits, beta and gamma, that trigger intracellular signaling. Natural IL-2 is a cytokine, a small signaling protein, that drives proliferation of immune cells through the JAK-STAT5 pathway. Ordinarily, IL-2 binds CD25 with high affinity, which strongly favors regulatory T cells (Tregs), a subset that dampens immune responses, because they express abundant CD25. This limits IL-2's usefulness as an immune-stimulating therapy, since expanding Tregs can blunt anti-tumor immunity. Engineered IL-2 variants that avoid CD25 and instead engage only the beta/gamma subunits redirect activity toward CD8+ effector T cells and natural killer (NK) cells, both central to killing tumor cells and infected cells, while largely sparing Tregs. This selectivity is the biological rationale for developing non-alpha-biased IL-2 agonists: it aims to convert a broadly immunostimulatory cytokine into one that favors cytotoxic immune expansion. Such mechanisms are relevant across oncology, where sustained cytotoxic lymphocyte activity is desired, and inform strategies for combination immunotherapy more broadly.