Background: Graft-versus-host disease (GvHD) is the main life-threatening complication of allogeneic hematopoietic stem cell transplantation (HSCT). Thirty to 80% of GvHD patients do not respond to first-line treatment and a second-line treatment is not universally established. Based on their immunomodulatory properties, mesenchymal stromal cells (MSC) have been proposed for the prevention and the treatment of GvHD in patients undergoing HSCT. Unfortunately, previous studies reported conflicting results regarding the prophylactic and therapeutic effects of MSC for GvHD. Consequently, we carried out a meta-analysis to clarify whether MSC administration can improve the dismal outcome of these patients. Methods:We carried out a systematic review and selected studies (2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019) reporting data about the administration of allogeneic MSC for the prevention (n = 654 patients) or treatment of acute (n = 943 patients) or chronic (n = 76 patients) GvHD after HSCT. Our primary outcome was overall survival at the last follow-up. The secondary outcomes were the response and development of GvHD. Subgroup analyses included age, MSC dose, first infusion day after HSCT, number of organs and organ-specific involvement, acute GvHD grade (I-IV), and chronic GvHD grade (limited or extensive).Results: Patients infused with MSC for GvHD prophylaxis showed a 17% increased overall survival (95% CI, 1.02-1.33) and a reduced incidence of acute GvHD grade IV (RR = 0.22; 95% CI, 0.06-0.81) and chronic GvHD (RR = 0.64; 95% CI, 0.47-0.88) compared with controls. Overall survival of acute GvHD patients (0.50; 95% CI, 0.41-0.59) was positively correlated with MSC dose (P = 0.0214). The overall response was achieved in 67% (95% CI, 0.61-0.74) and was complete in 39% (95% CI, 0.31-0.48) of acute patients. Organ-specific response was higher for the skin. Twentytwo percent (95% CI, 0.16-0.29) of acute patients infused with MSC developed chronic GvHD. Sixty-four percent (95% CI, 0.47-0.80) of chronic patients infused with MSC survived; the overall response was 66% (95% CI, 0.55-0.76) and was complete in 23% (95% CI 0.12-0.34) of patients. Conclusions:Our meta-analysis indicates that allogeneic MSC could be instrumental for the prophylaxis and treatment of GvHD. Future trials should investigate the effect of the administration of MSC as an adjuvant therapy for the treatment of patients with GvHD from the onset of the disease.

Graft versus host disease (GVHD) is a severe complication after allogenic hematopoietic cell transplantation (HSCT). Several clinical trials have reported the use of mesenchymal stromal cells (MSCs) for the treatment of GVHD. In March 2008, the Andalusian Health Care System launched a compassionate use program to treat steroid-resistant GVHD with MSC. Clinical-grade MSC were obtained under GMP conditions. MSC therapy was administered intravenously in four separate doses of 1 × 106 cells/kg. Sixty-two patients, 45 males (7 children) and 17 females (2 children), received the treatment. Patients had a median age of 39 years (range: 7–66) at the time of the allogenic HSCT. The overall response was achieved in 58.7% of patients with acute (a)GVHD. Two years’ survival for aGVHD responders was 51.85%. The overall response for patients with chronic (c)GVHD was 65.50% and the 2-year survival rate for responders was 70%. Age at the time of HSCT was the only predictor found to be inversely correlated with survival in aGVHD. Regarding safety, four adverse events were reported, all recovered without sequelae. Thus, analysis of this compassionate use experience shows MSC to be an effective and safe therapeutic option for treating refractory GVHD, resulting in a significant proportion of patients responding to the therapy.