Ryoncil (remestemcel-L-rknd) is a prescription medicine used to treat acute graft-versus-host disease (aGVHD), a condition that can occur after certain blood cell transplants when donor cells attack the recipient’s healthy tissues. This can affect the skin, gut, liver, or lungs. Ryoncil contains human mesenchymal stromal cells (MSCs), which help regulate the immune system and reduce inflammation, slowing the immune response to prevent further damage.