The effect of mesenchymal stem cells improves the healing of burn wounds: a phase 1 dose-escalation clinical trial

Abstract

Background: Stem cell therapy holds promise to improve healing and stimulate tissue regeneration after burn injury. Preclinical evidence has supported this; however, clinical studies are lacking. We examined the application of bone marrow-derived mesenchymal stem cells (BM-MSC) to deep second-degree burn injuries using a two-dose escalation protocol.

Methods: Ten individuals aged 18 years or older with deep second-degree burn wounds were enrolled. The first five patients were administered 2.5 × 10³ BM-MSC/cm² to their wounds. After safety of the initial dose level was assessed, a second group of five patients was treated with a higher concentration of 5 × 10³ allogeneic BM-MSC/cm². Safety was assessed clinically and by evaluating cytokine levels in mixed recipient lymphocyte/donor BM-MSC reactions (INFγ, IL-10 and TNFα). At each visit, we performed wound measurements and assessed wounds using a Patient and Observer Scar Assessment Scale (POSAS).

Results: All patients responded well to treatment, with 100% closure of wounds and minimal clinical evidence of fibrosis. No adverse reactions or evidence of rejection were observed for both dose levels. Patients receiving the first dose concentration had a wound closure rate of 3.64 cm²/day. Patients receiving the second dose concentration demonstrated a wound closure rate of 10.47 cm²/day. The difference in healing rates between the two groups was not found to be statistically significant (P = 0.17).

Conclusion: BM-MSC appear beneficial in optimising wound healing in patients with deep second-degree burn wounds. Adverse outcomes were not observed when administering multiple doses of allogeneic BM-MSC.

Lay summary: Thermal injuries are a significant source of morbidity and mortality, constituting 5%-20% of all injuries and 4% of all deaths. Despite overall improvements in the management of acutely burned patients, morbidities associated with deeper burn injuries remain commonplace. Burn patients are too often left with significant tissue loss, scarring and contractions leading to physical loss of function and long-lasting psychological and emotional impacts.In previous studies, we have demonstrated the safety and efficacy of administering bone marrow-derived mesenchymal stem cells (BM-MSC) to chronic wounds with substantial improvement in healing and evidence of tissue regeneration. In this report, we have examined the application of BM-MSC to deep second-degree burn injuries in patients.The aim of the present phase I/II clinical trial was to examine the safety and efficacy of administering allogeneic BM-MSC to deep second-degree burns. We utilised two different dose levels at concentrations 2.5 × 10³ and 5 × 10³ cells/cm². Patients with deep second-degree burn wounds up to 20% of the total body surface area were eligible for treatment. Allogeneic BM-MSC were applied to burn wounds topically or by injection under transparent film dressing <7 days after injury. Patients were followed for at least six months after treatment.Using two dose levels allowed us to gain preliminary information as to whether different amounts of BM-MSC administered to burn wounds will result in significant differences in safety/ clinical response. Once the safety and dose-response analysis were completed, we evaluated the efficacy of allogeneic stem cell therapy in the treatment of deep second-degree burn wounds.In this study, we examined the role of allogeneic BM-MSC treatment in patients with deep second-degree burn injuries, in a dose-dependent manner. No significant related adverse events were reported. Safety was evaluated both clinically and by laboratory-based methods. Efficacy was assessed clinically through evidence of re-pigmentation, hair follicle restoration and regenerative change. While these findings are encouraging, more studies will be needed to better establish the benefit of BM-MSC in the treatment of burn injuries.

Keywords: Second-degree burn; bone marrow–derived mesenchymal stem cells; burn scar; cell therapy; thermal injury; wound healing.

Figure 1.

Case 6 was a 47-year-old African American man who accidentally submerged his arm in hot oil attempting to catch a falling fry basket. (a) Wound before treatment. (b) Transparent film dressing applied to patient’s arm and BM-MSC were injected between the wound and transparent dressing. (c) Ten days after first treatment. (d) Seven days after second treatment (17 days after first treatment). (e) One year after treatment and showing limited to no fibrosis with pinch test.

Figure 5.

Screenshot of the E-Z graph® wound assessment system. Left: Empty E-Z Graph used to measure the wound. Right: Tracing graph of the wound healing area. We calculate this traced area using digital analytical software.

Figure 4.

Case 9 was a 24-year-old white Hispanic man who sustained a flame burn while pouring an accelerant into a fire. The designated treatment area on the left arm was 29 cm². (a) Before treatment and (b) one year after treatment. The dotted line outlines the treated area of the original wound. More hair development was noted at the site of BM-MSC treatment. The BM-MSC treatment may have created an optimal environment that supplemented hair growth.

Figure 2.

Case 6 wrist where the bandage prevented the treatment from reaching shows areas of no pigmentation. (a) The team placing the wrap around the wrist. (b) Ten days after first BM-MSC treatment. There is prominent stimulation of (follicular) re-pigmentation in the area treated. The area less accessible to BM-MSC due to the Coban pressure dressing is not well re-pigmentated. (c) One year after burn injury. Most of the burn injury has re-pigmentated. There is however persistent leukoderma in the area less accessible to BM-MSC due to the Coban pressure dressing.

Figure 3.

Case 5 was a 63-year-old African American man who sustained a flame burn while working on his car engine, which caught fire. (a) Day 0 of treatment with circle around a treated area that represented the deepest region of burn injury. (b) Eleven days after first BM-MSC treatment. There are prominent follicular buds in the deep portion of the treated wound. (c) A total of 34 days after two BM-MSC treatments. There is hair growth in the deeper burned area of the treated wound. This was not seen elsewhere. Perhaps BM-MSC and their paracrine effects of had greater access to the deeper dermis in this area of injury.

Figure 6.

After administration of BM-MSC to a burn patient, the remainder of the unused material was examined for the presence of extracelllular vesicles (EVs) in the sample. The unused material was handled under identical conditions to those used before administration. (a) After removal of cells, the vehicle was found to contain more than 1011 EVs/mL. (b, c) The isolated material also demonstrated particle morphology, size and distribution consistent with EVs as well as expressing characteristic EV markers.