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Abstract Background While rapid healing of diabetic foot ulcers (DFUs) is highly desirable to avoid infections, amputations and life-threatening complications, DFUs often respond poorly to standard treatment. GMP-manufactured skin-derived ABCB5+ mesenchymal stem cells (MSCs) might provide a new adjunctive DFU treatment, based on their remarkable skin wound homing and engraftment potential, their ability to adaptively respond to inflammatory signals, and their wound healing-promoting efficacy in mouse wound models and human chronic venous ulcers. Methods The angiogenic potential of ABCB5+ MSCs was characterized with respect to angiogenic factor expression at the mRNA and protein level, in vitro endothelial trans-differentiation and tube formation potential, and perfusion-restoring capacity in a mouse hindlimb ischemia model. Finally, the efficacy and safety of ABCB5+ MSCs for topical adjunctive treatment of chronic, standard therapy-refractory, neuropathic plantar DFUs were assessed in an open-label single-arm clinical trial. Results Hypoxic incubation of ABCB5+ MSCs led to posttranslational stabilization of the hypoxia-inducible transcription factor 1α (HIF-1α) and upregulation of HIF-1α mRNA levels. HIF-1α pathway activation was accompanied by upregulation of vascular endothelial growth factor (VEGF) transcription and increase in VEGF protein secretion. Upon culture in growth factor-supplemented medium, ABCB5+ MSCs expressed the endothelial-lineage marker CD31, and after seeding on gel matrix, ABCB5+ MSCs demonstrated formation of capillary-like structures comparable with human umbilical vein endothelial cells. Intramuscularly injected ABCB5+ MSCs to mice with surgically induced hindlimb ischemia accelerated perfusion recovery as measured by laser Doppler blood perfusion imaging and enhanced capillary proliferation and vascularization in the ischemic muscles. Adjunctive topical application of ABCB5+ MSCs onto therapy-refractory DFUs elicited median wound surface area reductions from baseline of 59% (full analysis set, n = 23), 64% (per-protocol set, n = 20) and 67% (subgroup of responders, n = 17) at week 12, while no treatment-related adverse events were observed. Conclusions The present observations identify GMP-manufactured ABCB5+ dermal MSCs as a potential, safe candidate for adjunctive therapy of otherwise incurable DFUs and justify the conduct of a larger, randomized controlled trial to validate the clinical efficacy. Trial registration: ClinicalTrials.gov, NCT03267784, Registered 30 August 2017, https://clinicaltrials.gov/ct2/show/NCT03267784

A significant number of chronic venous ulcers (CVUs) fail to heal despite guideline-conform standards of care. Skin-derived ABCB5+ mesenchymal stem cells can dampen the sustained IL-1β‒driven inflammation present in chronic wounds. On the basis of their wound healing‒facilitating effects in a mouse CVU model and an autologous first-in-human study, ABCB5+ mesenchymal stem cells have emerged as a potential candidate for cell-based advanced therapy of nonhealing CVUs. In this interventional, multicenter, single-arm, phase I/IIa clinical trial, subjects whose CVUs had emerged as standard therapy resistant received one or two topical applications of 1 × 106 allogeneic ABCB5+ mesenchymal stem cells per cm2 wound area, in addition to standard treatment. Of 83 treatment-emergent adverse events, only three were judged related to the cell product; they were mild or moderate and recovered without sequelae. Wound size markedly decreased from baseline to week 12, resulting in a median wound size reduction of 76% (full analysis set, n = 31), 78% (per-protocol set, n = 27), and 87% (subset of responders, n = 21). In conclusion, the study treatment was well-tolerated and safe. The treatment elicited a profound wound size reduction within 12 weeks, identifying ABCB5+ mesenchymal stem cells as a potential candidate for adjunctive therapy of otherwise incurable CVUs. These results justify the conduct of a larger, randomized, controlled trial to confirm clinical efficacy.