Definition

A polyethylene glycol (PEG)-conjugated mutein form of the cytokine interleukin-2 (IL-2), with potential and specific activity on enhancing proliferation, survival and anti-tumor activity of engineered orthoIL-2Rb-expressing CAR T cells. Upon subcutaneous administration, pegylated orthogonal (ortho) IL-2 STK-009 specifically targets and binds to mutated orthoIL-2Rbeta (hoRbeta; hoRb) that is specifically expressed on certain engineered CAR T cells. This induces selective proliferation, survival, and cytotoxic function of orthoIL-2Rbeta-expressing CAR T cells, which enhances tumor cell killing and decreases tumor cell proliferation. Pegylation of IL-2 protects the cytokine from degradation. STK-009 does not bind to the wild type (WT) IL-2b receptor and does not activate IL-2-mediated signaling in bystander T and NK cells, thereby limiting systemic toxicity.