Structure of MA01G4G344 TPO agonist antibody. MA01G4G344 is a novel anti-Mpl agonist antibody that has an upper hinge region of human IgG3 and the other parts of human IgG4. The IgG3 upper hinge improved agonist activity of the whole IgG. The EC₅₀ value of MA01G4344 in the UT7/TPO proliferation assay was 0.01 to 0.1 nM, comparable to rhTPO. Illustration by Paulette Dennis.