Definition

A pegylated, engineered variant form of the human cytokine interleukin 2 (IL-2; IL2), with selective binding affinity for IL-2 receptor subunit alpha (IL-2Ralpha; CD25) and beta (IL-2Rbeta; CD122), with potential immunoregulatory and antineoplastic activities. Upon administration, pegylated CD25/CD122-selective IL-2 mutein STK-012 targets and binds to CD25 and CD122 on antigen-activated effector T cells and activates CD25/CD122-mediated signaling. This activates cytotoxic T lymphocytes (CTLs), enhances T-cell-mediated tumor cell killing and decreases tumor cell proliferation. STK-012 does not activate peripheral natural killer (NK) and naive T cells, thereby circumventing the exacerbation of vascular leak syndrome (VLS) and other NK cell-mediated adverse effects associated with recombinant IL-2. CD25 and CD122 are highly expressed in antigen-activated and tumor-specific T cells.