XL050

XL050 is a preclinical-stage therapeutic candidate developed by XL-protein for the prevention of organ transplant rejection. It is a PASylated Fab fragment (Fab-PAS) designed to target and block the CD40 ligand (CD40L), also known as CD154. The drug utilizes XL-protein's proprietary PASylation technology, which involves the genetic fusion of the antibody fragment with a conformationally disordered polypeptide sequence consisting of Proline, Alanine, and Serine (PAS). This modification increases the hydrodynamic volume of the molecule, significantly extending its plasma half-life compared to unmodified Fab fragments. By antagonizing CD40L, XL050 inhibits the CD40-CD40L costimulatory pathway, which is essential for T-cell activation and the subsequent immune response that leads to graft rejection.