MTOR and chronic graft versus host disease: First-line treatment of chronic GVHD remains corticosteroids [21], with second-line options including targeting activation with calcineurin inhibitors, anti-proliferative reagents including mycophenolate mofetil, mammalian target of rapamycin (mTOR) inhibitors, adenosine analogues including pentostatin, proteasome inhibitors, tyrosine kinase inhibitors including ibrutinib or extra-corporal photopheresis [22,26].