JAK1 and graft versus host disease: Although ruxolitinib, a selective Janus kinase (JAK)1/2 inhibitor demonstrated significantly higher response rates in randomized trials compared to the best available therapy, and thus, is of benefit in both acute as well as chronic GvHD, there is an urgent medical need to improve results, such as durability of responses, response in eye, liver and lung manifestations and reduction of infectious complications.