Stem cells in burn wound healing: A systematic review of the literature

Exploring the therapeutic potential of different sources of mesenchymal stem cells: a novel approach to combat burn wound infections

The most prevalent and harmful injuries are burns, which are still a major global health problem. Burn injuries can cause issues because they boost the inflammatory and metabolic response, which can cause organ malfunction and systemic failure. On the other hand, a burn wound infection creates an environment that is conducive to the growth of bacteria and might put the patient at risk for sepsis. In addition, scarring is unavoidable, and this results in patients having functional and cosmetic issues. Wound healing is an amazing phenomenon with a complex mechanism that deals with different types of cells and biomolecules. Cell therapy using stem cells is one of the most challenging treatment methods that accelerates the healing of burn wounds. Since 2000, the use of mesenchymal stem cells (MSCs) in regenerative medicine and wound healing has increased. They can be extracted from various tissues, such as bone marrow, fat, the umbilical cord, and the amniotic membrane. According to studies, stem cell therapy for burn wounds increases angiogenesis, has anti-inflammatory properties, slows the progression of fibrosis, and has an excellent ability to differentiate and regenerate damaged tissue. Figuring out the main preclinical and clinical problems that stop people from using MSCs and then suggesting the right ways to improve therapy could help show the benefits of MSCs and move stem cell-based therapy forward. This review's objective was to assess mesenchymal stem cell therapy's contribution to the promotion of burn wound healing.

The Brazilian-Portuguese version of the Upper Extremity Functional Index (UEFI): Translation, cross-cultural adaptation and measurement properties for Brazilian adults after a burn injury

OBJECTIVES

To translate, cross-culturally adapt, validate, verify the reliability and estimate the minimal detectable change (MDC) of the UEFI to Brazilian Portuguese (UEFI-Br) for burns.

METHODS

The study was carried out with 131 Brazilian burn cases at two time points, at discharge and at the first outpatient follow-up (15-21 days after discharge) in a Burn Treatment Center. The adaptation process of the UEFI was based on international recommendations. The Burn Specific Health Scale-Brief-Br (BSHS-B-Br) was also applied in order to analyze construct validity of the UEFI-Br and distribution-based methods were used to estimate its MDC.

RESULTS

Intra- and inter-rater reliability were good with ICC of 0.986 (CI 95 %: 0.98-0.99) and 0.969 (CI 95 %: 0.955-0.979), respectively, at discharge and 0.997 (CI 95 %: 0.996-0.998) and 0.987 (CI 95 %: 0.981-0.991), respectively, at the first outpatient follow-up appointment. We found good internal consistency with Cronbach's α values of 0.987 and 0.996, respectively, at the two times. The SEM was 4.42 and 2.31 at the first and second time points, respectively. The UEFI-Br scores demonstrated strong correlation with the Burn Specific Health Scale-Brief-Br (BSHS-B-Br) function domain scores (r = 0.87-0.90). No significant correlation was found between UEFI-Br scores and participants' characteristics. The MDC of the UEFI-Br lies between 11 and 13 points.

CONCLUSION

The Brazilian version of the UEFI-Br, a useful tool to assess upper limb function and disability, is a valid and reliable tool for use with Brazilian burn survivors. The MDC for the instrument was determined to be 11-13 points.

Exploring the wound-healing and antimicrobial potential of Dittrichia viscosa L lipidic extract: Chemical composition and in vivo evaluation

Dittrichia viscosa belongs to the Dittrichia genus, it grows abundantly in the east and northeast of Morocco, and traditionally its fresh leaves are crushed and given for topical application after burns, wounds, and infections. In this study, we examine the wound-healing activity of Dittrichia viscosa lipidic extract in vivo, assess its anti-microbial effect, and explore the specific compounds that contribute to these effects. To assess the effectiveness of wound healing, a burn-induced wound model was employed in Wistar rats, and the levels of hydroxyproline as well as histopathological changes in the skin tissues were evaluated. Furthermore, the antimicrobial potential against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Candida glabrata, and Malassezia furfur was investigated using the agar disc diffusion method. Gas Chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography (HPLC) techniques were employed to analyze the composition of fatty acids, phytosterols, and tocopherols. Topical application of Dittrichia viscosa lipidic fraction ointment exhibited significant improvements in wound contraction, achieving an impressive rate of 82% within 21 days. Additionally, the lipidic extract of Dittrichia viscosa displayed notable efficacy against various microbial strains, including Candida albicans (25.07 ± 0.2), Candida glabrata (24 ± 0.6), and Malassezia furfur (22 ± 0.7). The primary fatty acids identified in the sample were linolenic acid (58.95% ± 0), oleic acid (16.75% ±0.04), and linoleic acid (11.97% ± 0.1). Notably, the sample contained significant amounts of γ-Tocopherols (732.08 ± 21mg/kg), while the sterol fraction primarily consisted of 7-Campesterol (1937 ± 0 mg/kg), 7-β-Sitosterol (1621 ± 0 mg/kg), and Stigmasterol (1439 ± 26 mg/kg). By its richness in active compound content, Dittrichia viscosa effectively accelerates wound healing while safeguarding against microbial infections.

Use of autologous adipose tissue in acute burn wound management: A systematic review

Fat transfer is increasingly used as part of our reconstructive armamentarium to address the challenges encountered in burn wounds and reconstructive surgery. The present systematic review aimed to evaluate the effectiveness of autologous fat transfer for acute burn wound management. A systematic review of the US National Library of Medicine, Cochrane Library, Web of Science, and Embase was conducted on October 15, 2022 (registration number CDR42022369726). A database watch was performed until submission of the manuscript. The review focused on wound healing. All studies reporting fat transfer in adult patients (at least 5 patients reported) with deep 2nd degree burn wounds were included. The database search yielded a total of 720 records and 367 patients were included from 3 studies. A statistically significant improvement in scar texture, scar appearance, and time to healing was reported in one study in the fat transfer group versus control (P<0.001). Similarly, scores for scar color, scar thickness, scar stiffness, and scar regularity increased significantly. The small number of included studies and their heterogeneity did not allow a meta-regression to be performed. This systematic review emphasizes the limited evidence currently available regarding the use of autologous fat transfer to improve burn wound healing in adult patients, even though it seems promising. Future search should focus on randomized controlled trials with a larger number of participants.

Effect of mesenchymal stromal cells-derived extracellular vesicles as a treatment to heal diabetic wounds: A meta-analysis

A meta-analysis study to assess the influence of mesenchymal stromal cells-derived extracellular vesicles (MSC-EVs) as a treatment to heal the diabetic wound (DW). A comprehensive literature examination till February 2023 was implemented and 2975 linked studies were appraised. The picked studies contained 381 animals with diabetes mellitus in the picked studies' baseline, 217 of them were using MSC-EVs, and 173 were using control. Odds ratio in addition to 95% confidence intervals (CIs) were used to calculate the consequence of MSC-EVs as a therapy to heal DWs by the dichotomous and continuous styles and a fixed or random model. MSCs-EVs had a significantly higher rate of wound closure of DWs (Mean deviation [MD], 22.20; 95% CI, 19.16-25.24, P < .001), lower width of the scar (MD, -2.57; 95% CI, -3.35 to -1.79, P < .001), higher collagen deposition (MD, 30.82; 95% CI, 20.77-40.86, P < .001), and a higher rate of re-epithelialisation (MD, 34.36; 95% CI, 20.13-48.58, P < .001) compared with the control. MSCs-EVs had a significantly higher rate of wound closure of DWs, lower width of the scar, higher collagen deposition, and higher rate of re- epithelialisation compared with the control. Although precautions should be taken when commerce with the consequences because all of the picked studies for this meta-analysis was with low sample sizes.

Zwitterionic Polysaccharide-Based Hydrogel Dressing as a Stem Cell Carrier to Accelerate Burn Wound Healing

Stem cell therapy integrated with hydrogels has shown promising potential in wound healing. However, the existing hydrogels usually cannot reach the desired therapeutic efficacy for burn wounds due to the inadaptability to wound shape and weak anti-infection ability. Moreover, it is difficult to improve the environment for the survival and function of stem cells under complicated wound microenvironments. In this study, an injectable and self-healing hydrogel (DSC), comprising sulfobetaine-derived dextran and carboxymethyl chitosan, is fabricated through a Schiff-base reaction. Meanwhile, the DSC hydrogel shows high nonfouling properties, including resistance to bacteria and nonspecific proteins; moreover, the prepared hydrogel can provide a biomimetic microenvironment for cell proliferation whilst maintaining the stemness of adipose-derived stem cells (ADSCs) regardless of complex microenvironments. In burnt murine animal models, the ADSCs-laden hydrogel can significantly accelerate wound healing rate and scarless skin tissue regeneration through multiple pathways. Specifically, the ADSCs-laden DSC hydrogel can avoid immune system recognition and activation and thus reduce the inflammatory response. Moreover, the ADSCs-laden DSC hydrogel can promote collagen deposition, angiogenesis, and enhance macrophage M2 polarization in the wound area. In summary, sulfobetaine-derived polysaccharide hydrogel can serve as a versatile platform for stem cell delivery to promote burn wound healing.

Wound contraction rate in excised and unexcised burn wounds with laser photobiomodulation: Systematic review and meta-analysis of preclinical studies

INTRODUCTION

Laser photobiomodulation (laser PBM) is an effective means of accelerating burn wound contraction, however it is still unclear whether laser PBM produces greater benefit when applied directly to excised and unexcised burn wounds . The aim of this systematic review of preclinical studies was to determine the effectiveness of laser PBM in the wound contraction rate in excised and unexcised burn wounds.

MATERIALS AND METHODS

A systematic search was conducted in the EMBASE, MEDLINE and LILACS databases. Preclinical studies were included that analysed the effectiveness of laser PBM in burn wound contraction, and assessed wound closure. The SYRCLE risk of bias tool was used. Random effects models were used to estimate the pooled effect.

RESULTS

Thirteen studies were included in the qualitative analysis and six in the quantitative analysis. Two weeks after the lesion, laser PBM favoured the wound contraction percentage, increasing the closure rate in excised burn wounds (SMD= 1.34, CI 95% 0.41 to 2.27, 0.41-2.27, I²=0%, =0%, low certainty of evidence. In unexcised burns, it was uncertain whether laser PBM increased or diminished the wound contraction rate (SMD=1.22(SMD=1.22 CI 95% -0.05 to 2.49, I²=68%; =68%; very low certainty of evidence).

CONCLUSIONS

In the animal model, laser PBM is effective in increasing the wound contraction rate in excised burns. However, due to the low certainty of the evidence, uncertainty remains about the true magnitude of the effect of laser on wound contraction in animals; our results should therefore be interpreted with caution.

Mesenchymal Stem Cells in Burn Wound Management

Mesenchymal stem cells have a known regenerative potential and are used in many indications. They secrete many growth factors, including for fibroblasts (FGF), endothelium (VEGF), as well as 14 anti-inflammatory cytokines, and they stimulate tissue regeneration, promoting the secretion of proteins and glycosaminoglycans of extracellular matrices, such as collagen I, II, III, and V, elastin, and also metalloproteinases. They secrete exosomes that contain proteins, nucleic acids, lipids, and enzymes. In addition, they show the activity of inactivating free radicals. The aim of this study was an attempt to collect the existing literature on the use of stem cells in the treatment of a burn wound. There were 81 studies included in the analysis. The studies differed in terms of the design, burn wound model, source of stem cells, and methods of cellular therapy application. No major side effects were reported, and cellular therapy reduced the healing time of the burn wound. Few case reports on human models did not report any serious adverse events. However, due to the heterogeneity of the evidence, cellular therapy in burn wound treatment remains an experimental method.

An Evaluation of the Treatment of Full-Thickness Wounds Using Adipose Micro-Fragments within a Liquid Dermal Scaffold

In full-thickness wounds, inflammation, lack of matrix deposition, and paucity of progenitor cells delay healing. As commercially available solid (sheet) scaffolds are unable to conform to wounds of varying shapes and sizes, we previously generated a nutritious, injectable, liquid skin substitute that can conform to wound topography. In combination with adipose micro-fragments as a viable source of progenitor cells, a composite, in situ forming skin substitute was tested for the treatment of silicon ring splinted full-thickness wounds in rats. The in vitro survivability and migratory capacity of adipocytes derived from rat micro-fragmented fat cultured in our scaffold was examined with a Live/Dead assay, showing viability and migration after 7 and 14 days. In vivo, the efficacy of our scaffold alone (LDS) or with adipose micro-fragments (LDS+A) was compared to a standard dressing protocol (NT). LDS and LDS+A showed ameliorated wound healing, including complete epithelialization and less immune cell infiltration, compared to the NT control. Our findings demonstrate that a 3D liquid skin scaffold is a rich environment for adipocyte viability and migration, and that the addition of adipose micro-fragments to this scaffold can be used as a rich source of cells for treating full-thickness wounds.

Human adipose-derived mesenchymal stem cells-derived exosomes encapsulated in pluronic F127 hydrogel promote wound healing and regeneration

Background

Large area skin trauma has always been a great challenge for both patients and clinicians. Exosomes originating from human adipose-derived mesenchymal stem cells (hADSCs) have been a novel promising cell-free treatment in cutaneous damage repair. Nevertheless, the low retention rate of exosomes post-transplantation in vivo remains a significant challenge in clinical applications. Herein, we purposed to explore the potential clinical application roles of hADSCs-Exos encapsulated in functional PF-127 hydrogel in wound healing.

Methods

hADSCs-Exos were isolated from human hADSCs by ultracentrifugation. An injectable, biocompatible, and thermo-sensitive hydrogel Pluronic F-127 hydrogel was employed to encapsulate allogeneic hADSCs-Exos, and this complex was topically applied to a full-thickness cutaneous wound in mice. On different days post-transplantation, the mice were sacrificed, and the skin tissue was excised for histological and immunohistochemical analysis.

Results

Compared with hADSCs-Exos or PF-127 only, PF-127/hADSCs-Exos complexes enhanced skin wound healing, promoted re-epithelialization, increased expression of Ki67, α-SMA, and CD31, facilitated collagen synthesis (Collagen I, Collagen III), up-regulated expression of skin barrier proteins (KRT1, AQP3), and reduced inflammation (IL-6, TNF-α, CD68, CD206). By using PF-127/hADSCs-Exos complexes, hADSCs-Exos can be administrated at lower doses frequency while maintaining the same therapeutic effects.

Conclusion

Administration of hADSCs-Exos in PF-127 improves the efficiency of exosome delivery, maintains the bioactivity of hADSCs-Exos, and optimizes the performance of hADSCs-Exos. Thus, this biomaterial-based exosome will be a promising treatment approach for the cutaneous rejuvenation of skin wounds.

Exploring the Immunomodulatory Aspect of Mesenchymal Stem Cells for Treatment of Severe Coronavirus Disease 19

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is an enveloped, positive sense, single stranded RNA (+ssRNA) virus, belonging to the genus Betacoronavirus and family Coronaviridae. It is primarily transmitted from infected persons to healthy ones through inhalation of virus-laden respiratory droplets. After an average incubation period of 2–14 days, the majority of infected individuals remain asymptomatic and/or mildly symptomatic, whereas the remaining individuals manifest a myriad of clinical symptoms, including fever, sore throat, dry cough, fatigue, chest pain, and breathlessness. SARS-CoV-2 exploits the angiotensin converting enzyme 2 (ACE-2) receptor for cellular invasion, and lungs are amongst the most adversely affected organs in the body. Thereupon, immune responses are elicited, which may devolve into a cytokine storm characterized by enhanced secretion of multitude of inflammatory cytokines/chemokines and growth factors, such as interleukin (IL)-2, IL-6, IL-7, IL-8, IL-9, tumor necrosis factor alpha (TNF-α), granulocyte colony-stimulating factor (GCSF), basic fibroblast growth factor 2 (bFGF2), monocyte chemotactic protein-1 (MCP1), interferon-inducible protein 10 (IP10), macrophage inflammatory protein 1A (MIP1A), platelet-derived growth factor subunit B (PDGFB), and vascular endothelial factor (VEGF)-A. The systemic persistence of inflammatory molecules causes widespread histological injury, leading to functional deterioration of the infected organ(s). Although multiple treatment modalities with varying effectiveness are being employed, nevertheless, there is no curative COVID-19 therapy available to date. In this regard, one plausible supportive therapeutic modality may involve administration of mesenchymal stem cells (MSCs) and/or MSC-derived bioactive factors-based secretome to critically ill COVID-19 patients with the intention of accomplishing better clinical outcome owing to their empirically established beneficial effects. MSCs are well established adult stem cells (ASCs) with respect to their immunomodulatory, anti-inflammatory, anti-oxidative, anti-apoptotic, pro-angiogenic, and pro-regenerative properties. The immunomodulatory capabilities of MSCs are not constitutive but rather are highly dependent on a holistic niche. Following intravenous infusion, MSCs are known to undergo considerable histological trapping in the lungs and, therefore, become well positioned to directly engage with lung infiltrating immune cells, and thereby mitigate excessive inflammation and reverse/regenerate damaged alveolar epithelial cells and associated tissue post SARS-CoV-2 infection. Considering the myriad of abovementioned biologically beneficial properties and emerging translational insights, MSCs may be used as potential supportive therapy to counteract cytokine storms and reduce disease severity, thereby facilitating speedy recovery and health restoration.

Recent advances in nanotherapeutics for the treatment of burn wounds

Moderate or severe burns are potentially devastating injuries that can even cause death, and many of them occur every year. Infection prevention, anti-inflammation, pain management and administration of growth factors play key roles in the treatment of burn wounds. Novel therapeutic strategies under development, such as nanotherapeutics, are promising prospects for burn wound treatment. Nanotherapeutics, including metallic and polymeric nanoformulations, have been extensively developed to manage various types of burns. Both human and animal studies have demonstrated that nanotherapeutics are biocompatible and effective in this application. Herein, we provide comprehensive knowledge of and an update on the progress of various nanoformulations for the treatment of burn wounds.

Acute Skin Wounds Treated with Mesenchymal Stem Cells and Biopolymer Compositions Alone and in Combination: Evaluation of Agent Efficacy and Analysis of Healing Mechanisms

We studied the efficacy of using mesenchymal stem cells (MSC) and a polymeric compound (based on chitosan and cellulose with integrated cerium dioxide nanoparticles (PCCD)) in wound healing, and to compare the effects with various invasive and external drugs used for the same purpose. Two wounds were made on the backs of each of 112 Wistar rats, removing the skin. Eight groups were studied: Control_0—intact wounds; Control_ss—0.9% NaCl injections; MSC injections; Control_msc—intact wounds on the opposite side of the body from the MSC group; external application of the PCCD; external application of a combination of the drugs PCCD + MSC; DCh –ointment Dioxomethyltetrahydropyrimidine + Chloramphenicol; and DHCB—injections of a deproteinized hemoderivative of calf blood. After 14 days, we evaluated the state and size of the wounds, studied the level of microcirculation, performed a histological study, and identified and counted the different types of cells. The most effective remedy was combination PCCD + MSC. The treatments in the PCCD and MSC groups were more effective than in the DHCB and DCh groups. Invasive drugs and DCh slowed the regeneration process. DHCB did not affect the rate of healing for acute wounds without ischemia during the first week. The proven efficacy of developed polymeric compounds demonstrates the feasibility of further studies in clinical practice.

Stem Cell Therapy for Burns: Story so Far

Burn injuries affect approximately 11 million people annually, with fatalities amounting up to 180,000. Burn injuries constitute a global health issue associated with high morbidity and mortality. Recent years have seen advancements in regenerative medicine for burn wound healing encompassing stem cells and stem cell-derived products such as exosomes and conditioned media with promising results compared to current treatment approaches. Sources of stem cells used for treatment vary ranging from hair follicle stem cells, embryonic stem cells, umbilical cord stem cells, to mesenchymal stem cells, such as adipose-derived mesenchymal stem cells, bone marrow-derived mesenchymal stem cells, and even stem cells harvested from discarded burn tissue. Stem cells utilize various pathways for wound healing, such as PI3/AKT pathway, WNT-β catenin pathway, TGF-β pathway, Notch and Hedgehog signaling pathway. Due to the paracrine signaling mechanism of stem cells, exosomes and conditioned media derived from stem cells have also been utilized in burn wound therapy. As exosomes and conditioned media are cell-free therapy and contain various biomolecules that facilitate wound healing, they are gaining popularity as an alternative treatment strategy with significant improvement in outcomes. The treatment is provided either as direct injections or embedded in a natural/artificial scaffold. This paper reviews in detail the different sources of stem cells, stem cell-derived products, their efficacy in burn wound repair, associated signaling pathways and modes of delivery for wound healing.

Local and Remote Effects of Mesenchymal Stem Cell Administration on Skin Wound Regeneration

Wound healing is an important medical problem. We evaluated the efficacy of locally administered mesenchymal stem cells (MSCs) isolated from human umbilical cords on the dynamics of skin wound healing. The study was conducted on the backs of Wistar rats, where two square wounds were created by removing all layers of the skin. Four groups were studied in two series of experiments: (1) a Control_NaCl group (the wounds were injected with 0.9% NaCl solution) and a Control_0 group (intact wounds on the opposite side of the same rat's back); (2) an MSC group (injected MSCs, local effect) and a Control_sc group (intact wounds on the opposite side of the back, remote MSC effect). The area and temperature of the wounds and the microcirculation of the wound edges were measured. Histological and morphometric studies were performed on days 3 and 7 after the wounds were created. The results showed that the injection trauma (Control_NaCl) slowed the regeneration process. In both MSC groups (unlike in either control group), we observed no increase in the area of the wounds; in addition, we observed inhibition of the inflammatory process and improved wound regeneration on days 1-3 in the remote group and days 1-5 in the local (injected) group. The MSC and Control_sc groups demonstrated improved microcirculation and suppression of leukocyte infiltration on day 3. On day 7, all the studied parameters of the wounds of the Control_0 group were the same as those of the wounds that received cell therapy, although in contrast to the results of the Control_ NaCl group, fibroblast proliferation was greater in the MSC and Control_sc groups. The dynamics of the size of the wounds were comparable for both local and remote application of MSCs. Thus, even a one-time application of MSCs was effective during the first 3-5 days after injury due to anti-inflammatory processes, which improved the regeneration process. Remote application of MSC, as opposed to direct injection, is advisable, especially in the case of multiple wounds, since the results were indistinguishable between the groups and injection trauma was shown to slow healing.

Umbilical Cord Mesenchymal Stem Cells for Inflammatory Regulation After Excision and Grafting of Severe Burn Wounds in Rats

Severe burns predispose to shock and necessitate escharectomy and skin grafting. Previous studies show that mesenchymal stem cells are effective for burn wound healing and immune regulation. In this study, we combined escharectomy and skin grafting after burn injury with stem cell application, so as to examine the immune regulation of stem cells and the effect on the transplanted skin graft. SD rats were randomly divided into normal group, sham group, normal + hUCMSCs group, and normal + SB203580 group. Normal saline, hUCMSCs, and SB203580 were injected into the tail vein of each group, and serum inflammatory factors were detected by ELISA. The expression of p38 MAPK/NF-κB pathway proteins in rat liver was detected by western blot. Skin activity was detected by Trypan blue staining and western blot. Skin graft inflammatory infiltration was detected by histological analysis. We found that hUCMSCs could regulate the phosphorylation levels of P38MAPK and NF-B P65 proteins in the liver to reduce the inflammatory response. These effects could continue to reduce the production of inflammatory factors HMGB-1, IL-6, and TNF-α, and increase the anti-inflammatory factor IL-10. The infiltration of inflammatory cells in skin graft was significantly reduced in the normal + hUCMSCs group, and the macrophages in the hUCMSCs group polarized to the anti-inflammatory M2 direction in 3 days. However, the changes of skin graft activity and necroptosis markers protein RIP3 were not observed. The present study demonstrates the immunomodulatory effects of hUCMSCs on the systemic and skin graft microenvironment after excision.

Mesenchymal stem cell-based therapy for burn wound healing

Burns, with their high incidence and mortality rates, have a devastating effect on patients. There are still huge challenges in the management of burns. Mesenchymal stem cells (MSCs), which have multidirectional differentiation potential, have aroused interest in exploring the capacity for treating different intractable diseases due to their strong proliferation, tissue repair, immune tolerance and paracrine abilities, among other features. Currently, several animal studies have shown that MSCs play various roles and have beneficial effects in promoting wound healing, inhibiting burn inflammation and preventing the formation of pathological scars during burn healing process. The substances MSCs secrete can act on peripheral cells and promote burn repair. According to preclinical research, MSC-based treatments can effectively improve burn wound healing and reduce pain. However, due to the small number of patients and the lack of controls, treatment plans and evaluation criteria vary widely, thus limiting the value of these clinical studies. Therefore, to better evaluate the safety and effectiveness of MSC-based burn treatments, standardization of the application scheme and evaluation criteria of MSC therapy in burn treatment is required in the future. In addition, the combination of MSC pretreatment and dressing materials are also conducive to improving the therapeutic effect of MSCs on burns. In this article, we review current animal research and clinical trials based on the use of stem cell therapy for treating burns and discuss the main challenges and coping strategies facing future clinical applications.

MSC-Derived Extracellular Vesicles to Heal Diabetic Wounds: a Systematic Review and Meta-Analysis of Preclinical Animal Studies

Introduction

Extracellular vesicles from mesenchymal stromal cells (MSC-EVs) have shown promise in wound healing. Their use in diabetic wounds specifically, however, remains pre-clinical and their efficacy remains uncertain less clear. A systematic review of preclinical studies is needed to determine the efficacy of MSC-EVs in the treatment of diabetic wounds to accelerate the clinical translation of this cell-based therapy.

Methods

PubMed and Embase were searched (to June 23, 2020). All English-language, full-text, controlled interventional studies comparing MSC-EVs to placebo or a “no treatment” arm in animal models of diabetic wounds were included. Study outcomes, including wound closure (primary outcome), scar width, blood vessel number and density, and re-epithelialisation were pooled using a random effects meta-analysis. Risk of bias (ROB) was assessed using the SYRCLE tool for pre-clinical animal studies.

Results

A total of 313 unique records were identified from our search, with 10 full text articles satisfying inclusion criteria (n = 136 animals). The administration of MSC-EVs improved closure of diabetic wounds compared to controls with a large observed effect (Standardized Mean Difference (SMD) 5.48, 95% Confidence Interval (CI) 3.55–8.13). Healing was further enhanced using MSC-EVs enriched in non-coding RNAs or microRNAs compared to controls (SMD 9.89, 95%CI 7.32–12.46). Other outcomes, such as blood vessel density and number, scar width, and re-epithelialisation were improved with the administration of MSC-EVs, with a large effect. ROB across studies was unclear.

Conclusion

MSC-EVs, particularly following enrichment for specific RNAs, are a promising treatment for diabetic wounds in pre-clinical studies and translation to the clinical domain appears warranted.

Registration

PROSPERO #CRD42020199327 [248].

Graphical abstract

Mesenchymal Stromal Cells in Viral Infections: Implications for COVID-19

Mesenchymal stromal cells (MSCs) constitute a heterogeneous population of stromal cells with immunomodulatory and regenerative properties that support their therapeutic use. MSCs isolated from many tissue sources replicate vigorously in vitro and maintain their main biological properties allowing their widespread clinical application. To date, most MSC-based preclinical and clinical trials targeted immune-mediated and inflammatory diseases. Nevertheless, MSCs have antiviral properties and have been used in the treatment of various viral infections in the last years. Here, we revised in detail the biological properties of MSCs and their preclinical and clinical applications in viral diseases, including the disease caused by the severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection (COVID-19). Notably, rapidly increasing numbers of MSC-based therapies for COVID-19 have recently been reported. MSCs are theoretically capable of reducing inflammation and promote lung regeneration in severe COVID-19 patients. We critically discuss the rationale, advantages and disadvantages of MSC-based therapies for viral infections and also specifically for COVID-19 and point out some directions in this field. Finally, we argue that MSC-based therapy may be a promising therapeutic strategy for severe COVID-19 and other emergent respiratory tract viral infections, beyond the viral infection diseases in which MSCs have already been clinically applied.

Graphical Abstract

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Liquid Dermal Scaffold With Adipose-Derived Stem Cells Improve Tissue Quality in a Murine Model of Impaired Wound Healing

Wound repair and regeneration is a multidisciplinary field of research with considerable potential value to the management of deep and large burn injuries. These injuries lack an appropriate tissue scaffold and pro-healing cells making them difficult to heal. An alternative to the often limited autologous skin is a therapy that would restore the essential matrix and cellular components for rapid healing. In this study, they use a novel liquid dermal scaffold capable of gelation in vivo to show that it is biocompatible with adipose-derived stem cells. Using a validated method of wound splinting in a delayed-healing murine model, we show that wounds treated with the scaffold and stem cells had a significant reduction in wound size and had accelerated healing compared with control. The wounds treated with stem cells had increased capillary formation, collagen content, epidermal thickness, and essential growth factor expression in the healed tissue compared with control and liquid scaffold alone. This liquid dermal scaffold combined with cells is a feasible treatment strategy for complex or large burn wounds that are otherwise lacking the appropriate cellular matrix necessary for healing.