A high affinity bivalent TfRMAb, targeting the human TfR1, was genetically fused to another lysosomal enzyme, iduronate 2-sulfatase (IDS), and this TfRMAb-IDS fusion protein, designated pabinafusp alpha, was tested in a phase 2/3 clinical trial in pediatric subjects with MPS Type II (MPSII), also called Hunter syndrome [3]. The gene discussed is IDS; the disease is mucopolysaccharidosis type 2.