There is no such thing as a free lunch." This adage aptly summarizes the risks associated with allogeneic hematopoietic cell transplantation (HCT). These perils are well described in the medical literature and are quoted to patients considering allogeneic HCT for long-term disease control at centers across the world. Patients that proceed must accept the risks of transplant, particularly graft-versus-host disease (GVHD), which is among the most challenging for clinicians to manage. GVHD is associated with a diminished quality of life, increased healthcare resource utilization, and shortened survival [1]. Several studies have uniformly demonstrated that acute and chronic GVHD fuel transplant-related mortality and negatively impact survival regardless of graft source or conditioning regimen [2-6]. Although our understanding of the pathobiology of GVHD continues to deepen, many knowledge gaps persist, and the optimal management strategy remains an area of active clinical and translational investigation. Enhancing our understanding and optimizing the management of these patients represent an unmet need in the care of patients with hematologic malignancies. The increasing number of allogeneic HCTs performed annually further broadens the scope of this disease. The Center for International Blood and Marrow Transplant Research registry data indicates that the number of allogeneic HCTs has steadily increased over the last 3 decades. A variety of factors, such as advances in supportive care, reduced-intensity conditioning regimens that permit older patients to be transplanted, and the acceptance of alternative stem cell donors are fueling this increase [7]. As a result, allogeneic HCT is performed in a larger and more diverse patient population than ever before. This is underpinned by a