Rationale and design of the SAIL trial for intramuscular injection of allogeneic mesenchymal stromal cells in no-option critical limb ischemia

Critical limb ischemia (CLI) represents the most severe form of peripheral artery disease and has an immense impact on quality of life, morbidity, and mortality. A considerable proportion of CLI patients are ineligible for revascularization, leaving amputation as the only option. Mesenchymal stromal cells (MSCs), because of their vasculoregenerative and immunomodulatory characteristics, have emerged as a potential new treatment. The primary objective of this trial is to investigate whether intramuscular administration of allogeneic bone marrow (BM)-derived MSCs is safe and potentially effective. The SAIL (allogeneic mesenchymal Stromal cells for Angiogenesis and neovascularization in no-option Ischemic Limbs) trial is a double-blind, placebo-controlled randomized clinical trial to investigate the effect of allogeneic BM-MSCs in patients with CLI who are not eligible for conventional revascularization. A total of 66 patients will be included and randomized (1:1) to undergo 30 intramuscular injections with either BM-MSCs (5 × 106 MSCs per injection) or placebo in the ischemic lower extremity. Primary outcome, that is, therapy success, a composite outcome consisting of mortality, limb status, clinical status, and changes in pain score, will be assessed at 6 months. All study-related procedures will take place in the University Medical Center Utrecht in The Netherlands. If our results indicate that intramuscular allogeneic BM-MSC therapy for CLI is safe and potentially effective, this will have important consequences for treatment of patients with CLI. A large multicenter clinical trial with longer follow-up focusing on hard end points should then be initiated to confirm these findings.