XTX501

XTX501 is a novel, tumor-activated bispecific molecule that targets both programmed cell death protein 1 (PD-1) and interleukin-2 (IL-2). It is designed to selectively stimulate PD-1 positive, antigen-experienced T cells within the tumor microenvironment and enhance their function. The molecule incorporates a masking strategy to overcome IL-2 receptor-mediated clearance and reduce peripheral activity, thereby localizing its immunostimulatory effects to tumors. Mechanistically, XTX501 acts as an agonist of the interleukin 2 receptor beta-gamma (IL-2Rβγ) complex and as an inhibitor of PD-1. Developed by Xilio Therapeutics using their proprietary tumor activation platform, it aims to improve anti-tumor immune responses while minimizing systemic toxicity commonly associated with immunotherapies. As of mid-2025, XTX501 remains in preclinical development for cancer indications[1][3][4][5][6].