Examples of such targeted therapies includes inhibition of the Janus kinase (JAK) [25,26,27], Bruton’s tyrosine kinase (BTK) [28,29,30], and Rho-associated coiled-coil-containing protein kinase 2 (ROCK2) [31] signaling pathways, each of which now have FDA-approved medications for management of steroid-refractory acute and/or chronic GvHD [32]. This evidence concerns the gene BTK and graft versus host disease.