Critical limb ischemia -an advanced stage of lower extremity arterial disease with presence of rest pain and/or ischemic ulcers -remains an important cause of major amputations and disability in developed societies. Novel treatment strategies are urgently needed to prevent (or delay) amputations in particular for patients in whom effective revascularization is no longer feasible for anatomic and/or technical reasons (no-option critical limb ischemia -N-O CLI). Cellular therapies have been gaining the growing attention of researchers and clinicians in the last two decades. Several cell types have been used in pre-clinical and clinical studies, and a number of mechanisms have been proposed to contribute to vascular reparation and regeneration in N-O CLI. Although early trials suggested clinical improvement with use of cell-based therapies in N-O CLI, meta-analyses that included randomized controlled trials have not provided definitive conclusions. Fundamental limitations have involved poorly defined cell lines/populations, limited numbers of study participants and limited follow-up periods, and enrolling patients "too sick to benefit" (such as those in Rutherford class 6). Recent advances include standardized "unlimited" sources of therapeutic cells and better understanding of mechanisms that may contribute to vascular reparation and regeneration. Furthermore, based on recent pre-clinical and clinical studies, cell-free preparations (such as microvesicle-based) are being increasingly developed along with advanced therapy medical products consisting of engineered cells and pro-angiogenic factors.

Introduction: Despite progress in pharmacologic and revascularization therapies, no-option critical limb ischemia poses a major clinical and societal problem. Prior cell-based strategies involved mainly autologous (limited) cell sources.Aim: To evaluate the safety and feasibility of a novel ischemic tissue reparation/regeneration strategy using Wharton's jelly mesenchymal stem/stromal cells (WJMSCs) as an "unlimited" cell source in N-O CLI (first-in-man study, FIM).Material and methods: Enrollment criteria included Rutherford-4 to Rutherford-6 in absence of anatomic/technical feasibility for revascularization and adequate inflow via the common femoral artery with patency of at least one below-the-knee artery. 30 × 10 6 WJMSCs were administered intra-arterially and intra-muscularly (50%/50%) over 3-6-week intervals (3-6 administrations). Safety, feasibility and potential signals of efficacy were assessed at 12 and 48 months.Results: Five patients (age 61-71, 60% male, Rutherford-6 20%, Rutherford-5 60%, Rutherford-4 20%) were enrolled. WJMSCs were administered per protocol in absence of administration technique-related adverse events. Hyperemia, lasting 12-24 h, occurred in 4/5 subjects. Transient edema and pain (reactive to paracetamol) occurred in 3 (60%) patients. Amputation-free survival was 80% after 12 and 48 months. In those who avoided amputation, ischemic ulcerations healed and Rutherford stage improved. 4/5 patients were free of resting pain after 3-6 doses.Conclusions: This FIM study demonstrated the safety and feasibility of WJMSCs use in patients with N-O CLI and suggested treatment efficacy with ≥ 3 doses. Our findings provide a basis for a randomized, double-blind clinical trial to assess the efficacy of WJMSC-based therapeutic strategy in N-O CLI patients.