Background and aim Mesenchymal stromal cells (MSCs) are pluripotent cells that have immunosuppressive effects both in vitro and in experimental colitis. Promising results of MSC therapy have been obtained in patients with severe graft versus host disease of the gut. Our objective was to determine the safety and feasibility of autologous bone marrow derived MSC therapy in patients with refractory Crohn's disease.

Patients and intervention 10 adult patients with refractory Crohn's disease (eight females and two males) underwent bone marrow aspiration under local anaesthesia. Bone marrow MSCs were isolated and expanded ex vivo. MSCs were tested for phenotype and functionality in vitro. 9 patients received two doses of 1–2×10⁶ cells/kg body weight, intravenously, 7 days apart. During follow-up, possible side effects and changes in patients' Crohn's disease activity index (CDAI) scores were monitored. Colonoscopies were performed at weeks 0 and 6, and mucosal inflammation was assessed by using the Crohn's disease endoscopic index of severity.

Results MSCs isolated from patients with Crohn's disease showed similar morphology, phenotype and growth potential compared to MSCs from healthy donors. Importantly, immunomodulatory capacity was intact, as Crohn's disease MSCs significantly reduced peripheral blood mononuclear cell proliferation in vitro. MSC infusion was without side effects, besides a mild allergic reaction probably due to the cryopreservant DMSO in one patient. Baseline median CDAI was 326 (224–378). Three patients showed clinical response (CDAI decrease ≥70 from baseline) 6 weeks post-treatment; conversely three patients required surgery due to disease worsening.

Conclusions Administration of autologous bone marrow derived MSCs appears safe and feasible in the treatment of refractory Crohn's disease. No serious adverse events were detected during bone marrow harvesting and administration.