Furthermore, pharmacologic JAK1/JAK2 blockade, either alone or in conjunction with other methods of GvHD prophylaxis may permit for those patients who lack a human leukocyte antigen (HLA)-matched sibling or matched unrelated donor (approximately 50% of patients) to proceed to transplant with limited GvHD and a well preserved GvL effect. Here, JAK1 is linked to graft versus host disease.