Finally, to examine the potential of Rm0443 as a therapeutic antibody for FOP patients in a relevant animal model, we established a mouse model of FOP [mAlk2(R206H) FlEx KI], in which mouse Alk2(R206H) was knocked-in to the endogenous Alk2 locus and its expression was induced by Cre-dependent recombination (Supplementary Fig. 6a). Here, ACVR1 is linked to fibrodysplasia ossificans progressiva.