Pabinafusp is a humanized, bispecific antibody-enzyme fusion protein designed to treat neuronopathic mucopolysaccharidosis type II (Hunter syndrome). It consists of a monoclonal antibody against the human transferrin receptor (TfR) fused to iduronate-2-sulfatase (IDS), the enzyme deficient in Hunter syndrome. The anti-TfR antibody acts as a molecular Trojan horse, facilitating receptor-mediated transcytosis across the blood-brain barrier (BBB) to deliver the functional IDS enzyme into the central nervous system (CNS). This enables enzyme replacement in both the periphery and the brain, addressing the severe neurocognitive decline characteristic of the neuronopathic form of the disease.