Pabinafusp alfa (JR-141), developed by JCR Pharmaceuticals, consists of human iduronate-2-sulfatase (IDS), the enzyme in which patients with MPS-II are deficient (Hunter syndrome), fused to the C-terminus of the heavy chain of an anti-human transferrin receptor (hTfR) antibody. Here, TFRC is linked to mucopolysaccharidosis type 2.