Mesenchymal Stromal Cells as Potential Antimicrobial for Veterinary Use-A Comprehensive Review

The mesenchymal stromal cell secretome promotes tissue regeneration and increases macrophage infiltration in acute and methicillin-resistant Staphylococcus aureus-infected skin wounds in vivo

BACKGROUND AIMS

The prevalence of chronic wounds continues to be a burden in human medicine. Methicillin-resistant Staphylococcus aureus (MRSA) is commonly isolated from infected wounds. MRSA infections primarily delay healing by impairing local immune cell functions. This study aimed to investigate the potential of mesenchymal stromal cell (MSC)-secreted bioactive factors, defined as the secretome, to improve innate immune responses in vivo. MSCs were isolated from the bone marrow of horses, which serve as valuable translational models for wound healing. The MSC secretome, collected as conditioned medium (CM), was evaluated in vivo using mouse models of acute and MRSA-infected skin wounds.

METHODS

Punch biopsies were used to create two full-thickness skin wounds on the back of each mouse. Acute wounds were treated daily with control medium or bone marrow-derived MSC (BM-MSC) CM. The antibiotic mupirocin was administered as a positive control for the MRSA-infected wound experiments. Wounds were photographed daily, and wound images were measured to determine the rate of closure. Trichrome staining was carried out to examine wound tissue histologically, and immunofluorescence antibody binding was used to assess immune cell infiltration. Wounds in the MRSA-infected model were swabbed for quantification of bacterial load.

RESULTS

Acute wounds treated with BM-MSC CM showed accelerated wound closure compared with controls, as illustrated by enhanced granulation tissue formation and resolution, increased vasculature and regeneration of hair follicles. This treatment also led to increased neutrophil and macrophage infiltration. Chronic MRSA-infected wounds treated with BM-MSC CM showed reduced bacterial load accompanied by better resolution of granulation tissue formation and increased infiltration of pro-healing M2 macrophages compared with control-treated infected wounds.

CONCLUSIONS

Collectively, our findings indicate that BM-MSC CM exerts pro-healing, immunomodulatory and anti-bacterial effects on wound healing in vivo, validating further exploration of the MSC secretome as a novel treatment option to improve healing of both acute and chronic wounds, especially those infected with antibiotic-resistant bacteria.

Anti-inflammatory and immunomodulatory effects of mesenchymal stem cell therapy on parasitic drug resistance

INTRODUCTION

The emergence of antiparasitic drug resistance poses a concerning threat to animals and humans. Mesenchymal Stem Cells (MSCs) have been widely used to treat infections in humans, pets, and livestock. Although this is an emerging field of study, the current review outlines possible mechanisms and examines potential synergism in combination therapies and the possible harmful effects of such an approach.

AREAS COVERED

The present study delved into the latest pre-clinical research on utilizing MSCs to treat parasitic infections. As per investigations, the introduction of MSCs to patients grappling with parasitic diseases like schistosomiasis, malaria, cystic echinococcosis, toxoplasmosis, leishmaniasis, and trypanosomiasis has shown a reduction in parasite prevalence. This intervention also alters the levels of both pro- and anti-inflammatory cytokines. Furthermore, the combined administration of MSCs and antiparasitic drugs has demonstrated enhanced efficacy in combating parasites and modulating the immune response.

EXPERT OPINION

Mesenchymal stem cells are a potential solution for addressing parasitic drug resistance. This is mainly because of their remarkable immunomodulatory abilities, which can potentially help combat parasites' resistance to drugs.

Cytokine production by bovine adipose tissue stromal vascular fraction cells upon Neospora caninum stimulation

In bovines few studies addressed the contribution of adipose tissue to the host immune response to infection. Here we evaluated the in vitro response of bovine adipose tissue stromal vascular fraction (SVF) cells to the protozoan parasite Neospora caninum, using live and freeze-killed tachyzoites. Live N. caninum induced the production of IL-6, IL-1β and IL-10 by SVF cells isolated from subcutaneous adipose tissue (SAT), while in mesenteric adipose tissue (MAT) SVF cell cultures only IL-1β and IL-10 production was increased, showing slight distinct responses between adipose tissue depots. Whereas a clear IL-8 increase was detected in peripheral blood leucocytes (PBL) culture supernatants in response to live N. caninum, no such increase was observed in SAT or MAT SVF cell cultures. Nevertheless, in response to LPS, increased IL-8 levels were detected in all cell cultures. IL-10 levels were always increased in response to stimulation (live, freeze-killed N. caninum and LPS). Overall, our results show that bovine adipose tissue SVF cells produce cytokines in response to N. caninum and can therefore be putative contributors to the host immune response against this parasite.

Use of Biologics and Stem Cells for Wound Healing in the Horse

Treatment of skin wounds is a high priority in veterinary medicine because healthy uncompromised skin is essential for the well-being of horses. Stem cells and other biologic therapies offer benefits by reducing the need for surgical procedures and conventional antibiotics. Evidence from in vitro studies and small in vivo trials supports the use of equine stem cells and biologics for the treatment of acute and chronic cutaneous wounds. Larger clinical trials are warranted to better evaluate the regenerative and immunological responses to these treatments. Additionally, delivery methods and treatment schedules should be optimized to improve efficacy of these novel therapies.

Antimicrobial Properties of Equine Stromal Cells and Platelets and Future Directions

Increasing antimicrobial resistance in veterinary practice has driven the investigation of novel therapeutic strategies including regenerative and biologic therapies to treat bacterial infection. Integration of biological approaches such as platelet lysate and mesenchymal stromal cell (MSC) therapy may represent adjunctive treatment strategies for bacterial infections that minimize systemic side effects and local tissue toxicity associated with traditional antibiotics and that are not subject to antibiotic resistance. In this review, we will discuss mechanisms by which biological therapies exert antimicrobial effects, as well as potential applications and challenges in clinical implementation in equine practice.

Overview of Equine Stem Cells: Sources, Practices, and Potential Safety Concerns

Over the past 2 decades, equine veterinarians are turning increasingly to stem cell therapies to repair damaged tissues or to promote healing through modulation of the immune system. Research is ongoing into optimizing practices associated with stem cell product transport, dosage, and administration. Culture-expanded equine mesenchymal stem cell therapies seem safe, even when used allogeneically, but various safety concerns should be considered. Stem cells and cellular reprogramming tools hold great promise for future equine therapies.

Mesenchymal stem cells: A promising antimicrobial therapy in veterinary medicine

Growing antimicrobial resistance (AMR) is a threat to human and animal populations citing the limited available options. Alternative antimicrobial options or functional enhancement of currently available antimicrobials remains only options. One of the potential options seems stem cells especially the mesenchymal stem cells (MSCs) that show antimicrobial properties. These cells additionally have pro-healing effects that may plausibly improve healing outcomes. MSCs antimicrobial actions are mediated either through direct cell-cell contact or their secretome that enhances innate immune mediated antimicrobial activities. These cells synergistically enhance efficacy of currently available antimicrobials especially against the biofilms. Reciprocal action from antimicrobials on the MSCs functionality remains poorly understood. Currently, the main limitation with MSCs based therapy is their limited efficacy. This demands further understanding and can be enhanced through biotechnological interventions. One of the interventional options is the 'priming' to enhance MSCs resistance and specific expression potential. The available literature shows potential antimicrobial actions of MSCs both ex vivo as well as in vivo. The studies on veterinary species are very promising although limited by number and extensiveness in details for their utility as standard therapeutic agents. The current review aims to discuss the role of animals in AMR and the potential antimicrobial actions of MSCs in veterinary medicine. The review also discusses the limitations in their utilization as standard therapeutics.

Characterization of canine adipose- and endometrium-derived Mesenchymal Stem/Stromal Cells and response to lipopolysaccharide

Mesenchymal stem/stromal cells (MSCs) are used for regenerative therapy in companion animals. Their potential was initially attributed to multipotency, but subsequent studies in rodents, humans and veterinary species evidenced that MSCs produce factors that are key mediators of immune, anti-infective and angiogenic responses, which are essential in tissue repair. MSCs preparations have been classically obtained from bone marrow and adipose tissue (AT) in live animals, what requires the use of surgical procedures. In contrast, the uterus, which is naturally exposed to external insult and infection, can be accessed nonsurgically to obtain samples, or tissues can be taken after neutering. In this study, we explored the endometrium (EM) as an alternative source of MSCs, which we compared with AT obtained from canine paired samples. Canine AT- and EM-MSCs, formed CFUs when seeded at low density, underwent tri-lineage differentiation into adipocytes, osteocytes and chondrocytes, and expressed the CD markers CD73, CD90 and CD105, at equivalent levels. The immune genes IL8, CCL2 and CCL5 were equally expressed at basal levels by both cell types. However, in the presence of the inflammatory stimulus lipopolysaccharide (LPS), expression of IL8 was higher in EM- than in AT-MSCs (p < 0.04) while the other genes were equally elevated in both cell types (p < 0.03). This contrasted with the results for CD markers, where the expression was unaltered by exposing the MSCs to LPS. Overall, the results indicate that canine EM-MSCs could serve as an alternative cell source to AT-MSCs in therapeutic applications.

Immune Activated Cellular Therapy for Drug Resistant Infections: Rationale, Mechanisms, and Implications for Veterinary Medicine

Simple Summary

Mesenchymal stromal/stem cells have intrinsic antimicrobial properties, thus making them attractive as an alternative treatment strategy in chronic, drug-resistant bacterial infections. Recent evidence has suggested that these antimicrobial effects can be significantly enhanced by immune activation just prior to injection. This review examines the potential role for cellular therapies in treatment of drug resistant infections in veterinary medicine, drawing on insights across species and discussing the therapeutic potential of this approach overall in today’s veterinary patients.

Abstract

Antimicrobial resistance and biofilm formation both present challenges to treatment of bacterial infections with conventional antibiotic therapy and serve as the impetus for development of improved therapeutic approaches. Mesenchymal stromal cell (MSC) therapy exerts an antimicrobial effect as demonstrated in multiple acute bacterial infection models. This effect can be enhanced by pre-conditioning the MSC with Toll or Nod-like receptor stimulation, termed activated cellular therapy (ACT). The purpose of this review is to summarize the current literature on mechanisms of antimicrobial activity of MSC with emphasis on enhanced effects through receptor agonism, and data supporting use of ACT in treatment of bacterial infections in veterinary species including dogs, cats, and horses with implications for further treatment applications. This review will advance the field’s understanding of the use of activated antimicrobial cellular therapy to treat infection, including mechanisms of action and potential therapeutic applications.

The non-protein fraction of embryonic stem cell secretome has antibacterial effects against antibiotic-resistant strains of bacteria

In recent years, the search for new antibacterial agents has been shown to be extremely important, as the burgeoning problem of antibiotic resistance and the toxicity of many antimicrobial compounds has forced scientists to turn their attention to alternatives. Searching stem cell secretomes, including the non-protein part, for new antimicrobials is a promising area of current research. We investigated the effect of the non-protein part of an embryonic stem cell secretome on various bacterial strains, including antibiotic-resistant ones. The non-protein fraction of the stem cell secretome was obtained by preparative high-performance liquid chromatography. Bactericidal activity was tested against eight museum strains and 206 clinical strains of bacteria by comparing the secretomes effects on growth of bacterial cultures. The museum strains showed some dose-dependent effects at concentrations of 25-100 g/ml. Against the clinical strains of Gram-negative microorganisms of different species, some bactericidal activity was shown at a concentration of 100 g/ml, but sensitivity of bacteria to the secretome fraction varied, with growth stimulation being detected in some strains. Application of higher concentrations of 100-1000 g/ml showed no dose-dependent effect. The clinical strains of E. coli and P. aeruginosa were shown to have reduced bactericidal activity after one day of incubation. Thus, this study has shown that the non-protein fraction of the embryonic stem cell secretome has bactericidal effects against some strains. However, more detailed studies are needed to identify the mechanism of action and to determine the most effective dose and frequency of administration.

Mesenchymal stromal cells isolated from chicken peripheral blood secrete bioactive factors with antimicrobial and regenerative properties

Mesenchymal stromal cells (MSCs) are adult multipotent progenitor cells that have been isolated from various tissue sources of many species, primarily mammals. Generally, these cells proliferate extensively in culture and have been shown to secrete bioactive factors that contribute to healing processes by regulating inflammation, modulating immune responses, inhibiting bacterial growth, and promoting tissue regeneration. The present study reports on the isolation and characterization of MSCs from the peripheral blood (PB) of chickens. Chicken PBMSCs were characterized based on their trilineage differentiation potential and gene and protein expression of MSC-specific cell surface markers. To determine functionality, conditioned medium (CM), which contains all bioactive factors secreted by MSCs, was collected from chicken PBMSCs, and used in in vitro antimicrobial, migration, and angiogenesis assays. Chicken PBMSC CM was found to (i) inhibit the growth of planktonic Staphylococcus aureus (S. aureus), and even more significantly the methicillin-resistant S. aureus (MRSA), (ii) decrease adhesion and promote migration of fibroblasts, and (iii) support endothelial cell tube formation. Collectively, these data indicate that chicken PBMSCs secrete bioactive factors with antimicrobial and regenerative properties, and as such, provide a novel source of cell-based therapies for the poultry industry.

Mesenchymal Stem Cell-Derived Antimicrobial Peptides as Potential Anti-Neoplastic Agents: New Insight into Anticancer Mechanisms of Stem Cells and Exosomes

Mesenchymal stem cells (MSCs), as adult multipotent cells, possess considerable regenerative and anti-neoplastic effects, from inducing apoptosis in the cancer cells to reducing multidrug resistance that bring them up as an appropriate alternative for cancer treatment. These cells can alter the behavior of cancer cells, the condition of the tumor microenvironment, and the activity of immune cells that result in tumor regression. It has been observed that during inflammatory conditions, a well-known feature of the tumor microenvironment, the MSCs produce and release some molecules called “antimicrobial peptides (AMPs)” with demonstrated anti-neoplastic effects. These peptides have remarkable targeted anticancer effects by attaching to the negatively charged membrane of neoplastic cells, disrupting the membrane, and interfering with intracellular pathways. Therefore, AMPs could be considered as a part of the wide-ranging anti-neoplastic effects of MSCs. This review focuses on the possible anti-neoplastic effects of MSCs-derived AMPs and their mechanisms. It also discusses preconditioning approaches and using exosomes to enhance AMP production and delivery from MSCs to cancer cells. Besides, the clinical administration of MSCs-derived AMPs, along with their challenges in clinical practice, were debated.

Clinical applications of adipose-derived stromal vascular fraction in veterinary practice

Adipose tissue-derived stromal vascular fraction (AdSVF) comprises a heterogeneous cell population, including the multipotent mesenchymal stem cells, hematopoietic stem cells, immune cells, endothelial cells, fibroblasts, and pericytes. As such, multipotent adipose tissue-derived mesenchymal stem cells (AdMSCs), are one of the important components of AdSVF. Commonly used techniques to harvest AdSVF involve enzymatic or non-enzymatic methods. The enzymatic method is considered to be the gold standard technique due to its higher yield. The cellular components of AdSVF can be resuspended in normal saline, platelet-rich plasma, or phosphate-buffered saline to produce a ready-to-use solution. Freshly isolated AdSVF has exhibited promising osteogenic and vasculogenic capacity. AdSVF has already been proven to possess therapeutic potential for osteoarthritis management. It is also an attractive therapeutic option for enhancing wound healing. In addition, the combined use of AdSVF and platelet-rich plasma has an additive stimulatory effect in accelerating wound healing and can be considered an alternative to AdMSC treatment. It is also widely used for managing various orthopaedic conditions in clinical settings and has the potential for regenerating bone, cartilage, and tendons. Autologous AdSVF cells are used along with bone substitutes and other biological factors as an alternative to conventional bone grafting techniques owing to their promising osteogenic and vasculogenic capacity. It can also be used for treating osteonecrosis, meniscus tear, chondromalacia, and tendon injuries in veterinary practice. It has several advantages over in vitro expanded AdMSC, including precluding the need for culturing, reduced risk of cell contamination, and cost-effectiveness, making it ideal for clinical use.

Activated Mesenchymal Stromal Cell Therapy for Treatment of Multi-Drug Resistant Bacterial Infections in Dogs

New and creative approaches are required to treat chronic infections caused by increasingly drug-resistant strains of bacteria. One strategy is the use of cellular therapy employing mesenchymal stromal cells (MSC) to kill bacteria directly and to also activate effective host immunity to infection. We demonstrated previously that activated MSC delivered systemically could be used effectively together with antibiotic therapy to clear chronic biofilm infections in rodent models. Therefore, we sought in the current studies to gain new insights into the antimicrobial properties of activated canine MSC and to evaluate their effectiveness as a novel cellular therapy for treatment of naturally-occurring drug resistant infections in dogs. These studies revealed that canine MSC produce and secrete antimicrobial peptides that synergize with most classes of common antibiotics to trigger rapid bactericidal activity. In addition, activated canine MSC migrated more efficiently to inflammatory stimuli, and secreted factors associated with wound healing and fibroblast proliferation and recruitment of activated neutrophils. Macrophages incubated with conditioned medium from activated MSC developed significantly enhanced bactericidal activity. Clinical studies in dogs with chronic multidrug resistant infections treated by repeated i.v. delivery of activated, allogeneic MSC demonstrated significant clinical benefit, including infection clearance and healing of infected tissues. Taken together, the results of these studies provide new insights into antimicrobial activity of canine MSC, and their potential clinical utility for management of chronic, drug-resistant infections.

Application of exosomes for the alleviation of COVID-19-related pathologies

The pandemic of COVID‐19 caused worldwide concern. Due to the lack of appropriate medications and the inefficiency of commercially available vaccines, lots of efforts are being made to develop de novo therapeutic modalities. Besides this, the possibility of several genetic mutations in the viral genome has led to the generation of resistant strains such as Omicron against neutralizing antibodies and vaccines, leading to worsening public health status. Exosomes (Exo), nanosized vesicles, possess several therapeutic properties that participate in intercellular communication. The discovery and application of Exo in regenerative medicine have paved the way for the alleviation of several pathologies. These nanosized particles act as natural bioshuttles and transfer several biomolecules and anti‐inflammatory cytokines. To date, several approaches are available for the administration of Exo into the targeted site inside the body, although the establishment of standard administration routes remains unclear. As severe acute respiratory syndrome coronavirus 2 primarily affects the respiratory system, we here tried to highlight the transplantation of Exo in the alleviation of COVID‐19 pathologies.

Exosomes (Exo) are nanosized vesicles that are released from each cell type and can transfer therapeutic molecules to the injured sites. It has been shown that Exo therapy circumvents difficulties that are associated with whole cell‐based therapies. Due to recent advances in the field of Exo‐based therapies, the current review article highlighted recent data and the applicability of Exo during viral diseases such as COVID‐19. The mechanism action and superiority of Exo were also debated in detail.

Potential of Mesenchymal Stem Cell-Derived Exosomes as a Novel Treatment for Female Infertility Caused by Bacterial Infections

Neisseria gonorrhoeae and Chlamydia trachomatis are the most common causes of bacterial sexually transmitted diseases (STDs) with complications in women, including pelvic inflammatory disease (PID), ectopic pregnancy, and infertility. The main concern with these infections is that 70% of infected women are asymptomatic and these infections ascend to the upper female reproductive tract (FRT). Primary infection in epithelial cells creates a cascade of events that leads to secretion of pro-inflammatory cytokines that stimulate innate immunity. Production of various cytokines is damaging to mucosal barriers, and tissue destruction leads to ciliated epithelial destruction that is associated with tubal scarring and ultimately provides the conditions for infertility. Mesenchymal stem cells (MSCs) are known as tissue specific stem cells with limited self-renewal capacity and the ability to repair damaged tissues in a variety of pathological conditions due to their multipotential differentiation capacity. Moreover, MSCs secrete exosomes that contain bioactive factors such as proteins, lipids, chemokines, enzymes, cytokines, and immunomodulatory factors which have therapeutic properties to enhance recovery activity and modulate immune responses. Experimental studies have shown that local and systemic treatment of MSC-derived exosomes (MSC-Exos) suppresses the destructive immune response due to the delivery of immunomodulatory proteins. Interestingly, some recent data have indicated that MSC-Exos display strong antimicrobial effects, by the secretion of antimicrobial peptides and proteins (AMPs), and increase bacterial clearance by enhancing the phagocytic activity of host immune cells. Considering MSC-Exos can secrete different bioactive factors that can modulate the immune system and prevent infection, exosome therapy is considered as a new therapeutic method in the treatment of inflammatory and microbial diseases. Here we intend to review the possible application of MSC-Exos in female reproductive system bacterial diseases.

Microfluidic Tools for Enhanced Characterization of Therapeutic Stem Cells and Prediction of Their Potential Antimicrobial Secretome

Antibiotic resistance is creating enormous attention on the development of new antibiotic-free therapy strategies for bacterial diseases. Mesenchymal stromal stem cells (MSCs) are the most promising candidates in current clinical trials and included in several cell-therapy protocols. Together with the well-known immunomodulatory and regenerative potential of the MSC secretome, these cells have shown direct and indirect anti-bacterial effects. However, the low reproducibility and standardization of MSCs from different sources are the current limitations prior to the purification of cell-free secreted antimicrobial peptides and exosomes. In order to improve MSC characterization, novel label-free functional tests, evaluating the biophysical properties of the cells, will be advantageous for their cell profiling, population sorting, and quality control. We discuss the potential of emerging microfluidic technologies providing new insights into density, shape, and size of live cells, starting from heterogeneous or 3D cultured samples. The prospective application of these technologies to studying MSC populations may contribute to developing new biopharmaceutical strategies with a view to naturally overcoming bacterial defense mechanisms.

Clinical applications of mesenchymal stromal cell-based therapies for pulmonary diseases: An Update and Concise Review

Lung disorders are a leading cause of morbidity and death worldwide. For many disease conditions, no effective and curative treatment options are available. Mesenchymal stromal cell (MSC)-based therapy is one of the cutting-edge topics in medical research today. It offers a novel and promising therapeutic option for various acute and chronic lung diseases due to its potent and broad-ranging immunomodulatory activities, bacterial clearance, tissue regeneration, and proangiogenic and antifibrotic properties, which rely on both cell-to-cell contact and paracrine mechanisms. This review covers the sources and therapeutic potential of MSCs. In particular, a total of 110 MSC-based clinical applications, either completed clinical trials with safety and early efficacy results reported or ongoing worldwide clinical trials of pulmonary diseases, are systematically summarized following preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines, including acute/viral pulmonary disease, community-acquired pneumonia (CAP), chronic obstructive pulmonary disease (COPD), bronchopulmonary dysplasia (BPD), interstitial lung diseases (ILD), chronic pulmonary fibrosis, bronchiolitis obliterans syndrome (BOS) and lung cancer. The results of recent clinical studies suggest that MSCs are a promising therapeutic approach for the treatment of lung diseases. Nevertheless, large-scale clinical trials and evaluation of long-term effects are necessary in further studies.