Eftansomatropin alfa (TJ101) is a potential highly differentiated long-acting recombinant human growth hormone being developed as a more convenient and effective therapy for growth hormone deficiency (GHD). Like endogenous growth hormone, eftansomatropin alfa stimulates the production of insulin-like growth factor 1 (IGF-1) in the liver, which has growth-stimulating effects on a variety of tissues, including osteoblast and chondrocyte activities that stimulate bone growth. IGF-1 is a reliable pharmacodynamic marker and the key mediator of growth-promoting activity of eftansomatropin alfa. Eftansomatropin alfa is based on Genexine’s patented hyFc® technology. The hyFc part consists of a portion of human immunoglobulin D (“IgD”) and G4 (“IgG4”). The former contains a flexible hinge, and the latter is responsible for half-life extension through neonatal Fc receptor (“FcRn”)-mediated recycling.