Garetosmab, a fully human monoclonal antibody (generated using VelocImmune technology)18,19, binds activin A and blocks its ability to activate FOP-mutant ACVR1. Garetosmab blocked the emergence of new HO lesions and stopped the growth or induced regression of pre-existing lesions in a genetically humanized murine FOP model14,15. Here, ACVR1 is linked to fibrodysplasia ossificans progressiva.