In this study, we report the beneficial effects of a newly identified dermal cell subpopulation expressing the ATP-binding cassette subfamily B member 5 (ABCB5) for the therapy of nonhealing wounds. Local administration of dermal ABCB5⁺-derived mesenchymal stem cells (MSCs) attenuated macrophage-dominated inflammation and thereby accelerated healing of full-thickness excisional wounds in the iron-overload mouse model mimicking the nonhealing state of human venous leg ulcers. The observed beneficial effects were due to interleukin-1 receptor antagonist (IL-1RA) secreted by ABCB5⁺-derived MSCs, which dampened inflammation and shifted the prevalence of unrestrained proinflammatory M1 macrophages toward repair promoting anti-inflammatory M2 macrophages at the wound site. The beneficial anti-inflammatory effect of IL-1RA released from ABCB5⁺-derived MSCs on human wound macrophages was conserved in humanized NOD-scid IL2rγ^null mice. In conclusion, human dermal ABCB5⁺ cells represent a novel, easily accessible, and marker-enriched source of MSCs, which holds substantial promise to successfully treat chronic nonhealing wounds in humans. Stem Cells  2019;37:1057–1074

The ATP-binding cassette protein ATP-binding cassette subfamily B member 5 (ABCB5), a single molecular marker, can be used to isolate dermal cell subpopulation of the skin with multipotent mesenchymal stromal cell (MSC) characteristics from its endogenous niche. The ABCB5⁺ MSCs maintain most of their stemness and mesenchymal marker during large in vitro expansion cultures as well as the capacity for clonal self-renewal and, importantly, promote healing of nonhealing iron-overload wounds in a murine model, which may be exploited as a potential regenerative therapy for chronic venous leg ulcers in human patients.