Secreted responses of umbilical cord mesenchymal cells to full thickness swine burns are refined by the zone of injury

Abstract

Background & Aim Primary treatment of battlefield burns is often inadequate due to delayed field evacuation or limited care in mass casualty incidents. Untreated burns expand in depth and surface area and elicit a hyper-immune response until the damaged tissue is removed. Third degree (full-thickness) burns penetrate the dermis and comprise 3 concentric zones of injury. The central zone of coagulation is irrevocably damaged while the surrounding zone of stasis is at risk. Tissue in the outermost zone of hyperemia can be saved despite an acute inflammatory response and increased perfusion. Mesenchymal stromal cells (MSCs) reportedly improve outcomes as post-surgical burn treatments. We assessed in vitro whether MSCs may also benefit burn sequelae if applied prior to surgical intervention. Methods, Results & Conclusion Nine anaesthetized swine received 3rddegree burns on the inner flank by a heated brass bar. After 30 minutes, the burn was excised ∼1 cm outside the zone of hyperemia. Control (unburned) samples were also excised. The burn center (zones of coagulation and stasis) and margin (zone of hyperemia) were isolated by dissection. Human umbilical cord MSCs (UC-MSCs), were co-incubated with 0.4 +/- 0.005g of tissue using a 6-well Transwell system for 24, 48 or 72 hours (h) in xeno-free media. Secreted proteins were assessed by multiplex ELISA of 115 analytes. Within 24h of exposure to any burn tissue, UC-MSCs increased output of inflammation mediators including fractalkine, GCP-2, GRO-β, I-309, IL-19, MCP-3, MIP3-α, MMP-2 and TSLP. IL-2Ra and MIG were specifically elevated in response to the necrotic center tissue, followed by β-NGF and IL-3 at 48h and SCF and SCGF-β at 72h. Intriguingly, the burn margin stimulated production of wound healing molecules in addition to inflammation mediators. G-CSF, HGF, IL-1β, IL-1RA, LIF and TECK increased significantly at 24 hours, followed by IL-20, IL-35, MDC, sCD163 and sTNF-R1 at 72h. Thus, UC-MSCs exhibit refined soluble responses that may improve outcomes for severe burn patients that initially receive sub-optimal treatment and delayed definitive care. The observed zone-specific responses suggest that the molecular mechanisms of MSC treatments may differ if the cells are applied before or after surgical debridement and depending on their localization within the wound. UC-MSCs delivered to unsalvageable tissue can produce a response focused on managing inflammation, while UC-MSCs delivered to the viable peripheral zone additionally promote wound healing.