Safety and efficacy of the mesenchymal stem cell in feline eosinophilic keratitis treatment

Mesenchymal stem cell therapy in veterinary ophthalmology: clinical evidence and prospects

Mesenchymal stem cell (MSC) therapy presents a promising strategy for treating various ocular conditions in veterinary medicine. This review explores the therapeutic potential of MSCs in managing corneal ulcers, immune-mediated keratitis, chronic superficial keratitis, keratoconjunctivitis sicca, retinal degeneration, and ocular burns in feline, equine, and canine patients. Studies have demonstrated the immunomodulatory and regenerative properties of MSCs, highlighting their ability to mitigate inflammation and promote tissue regeneration. Experimental studies have shown the potential of MSC therapy in reducing corneal opacity and vascularization, indicating significant therapeutic advantages. Delivery methods play a crucial role in optimizing the therapeutic efficacy of MSCs in ocular diseases. Various delivery methods, such as intravitreal injection, subconjunctival injection, topical administration, and scaffold-mediated delivery, are being explored to optimize MSC delivery to the target ocular tissues. Clinical trials have shown significant improvements in clinical signs following MSC therapy, underscoring its efficacy in treating ocular diseases. Additionally, tissue engineering approaches incorporating MSCs, growth factors, and scaffolds offer innovative strategies for corneal regeneration and tissue repair. Despite challenges such as standardization of protocols and long-term safety assessment, ongoing research endeavours seek to unlock the full therapeutic potential of MSC therapy in ocular diseases. Future prospects in MSC therapy involve exploring scaffold and hydrogel-based approaches and cell-free therapies leveraging the bioactive molecules released by MSCs. Continued research and development efforts are essential to unlock the full therapeutic potential of MSCs and realize their transformative impact on ocular diseases in veterinary patients.

Morphologic, Proliferative, and Cytogenetic Changes during In Vitro Propagation of Cat Adipose Tissue-Derived Mesenchymal Stromal/Stem Cells

Stem cell therapy in cat patients needs a high quantity of mesenchymal stromal/stem cells (MSCs) requiring in vitro propagation under culture conditions which may potentially impact cellular characteristics and genetic stability. This study aimed to assess the in vitro characteristics and cytogenetic stability of cat adipose tissue-derived MSCs (cAT-MSCs). For this purpose, morphological features, clonogenic potential, and proliferative capacity of cAT-MSCs were assessed at passages 2 (P2), P4, and P6. Multipotency and immunophenotype were evaluated. Cytogenetic analyses were conducted up to P6. The cAT-MSCs exhibited a spindle-shaped morphology in early passages. The doubling time increased from 2.5 days at P2 to 9.4 at P4 and 10.5 at P6, accompanied by the observation of nuclear abnormalities such as cluster formation, karyorrhexis, karyolysis, and a decline in the mitotic index at P4. Cells demonstrated multipotency capacity and were CD45-, CD90+, and CD44+. Metaphase analysis at P2 and P4 revealed some indications of structural instability such as gaps, breaks, deletions, duplications, and early chromatid segregation, but these alterations did not show an increase across passages. In conclusion, cAT-MSCs decreased their proliferative capacity after P4, accompanied by morphological alterations and signs of structural instability.

Evaluation of stem-cell therapies in companion animal disease models: a concise review (2015-2023)

Companion animals in veterinary medicine develop multiple naturally occurring diseases analogous to human conditions. We previously reported a comprehensive review on the feasibility, safety, and biologic activity of using novel stem cell therapies to treat a variety of inflammatory conditions in dogs and cats (2008-2015) [Hoffman AM, Dow SW. Concise review: stem cell trials using companion animal disease models. Stem Cells. 2016;34(7):1709-1729. https://doi.org/10.1002/stem.2377]. The purpose of this review is to provide an updated summary of current studies in companion animal disease models that have evaluated stem cell therapeutics that are relevant to human disease. Here we have reviewed the literature from 2015 to 2023 for publications on stem cell therapies that have been evaluated in companion animals, including dogs, cats, and horses. The review excluded case reports or studies performed in experimentally induced models of disease, studies involving cancer, or studies in purpose-bred laboratory species such as rodents. We identified 45 manuscripts meeting these criteria, an increase from 19 that were described in the previous review [Hoffman AM, Dow SW. Concise review: stem cell trials using companion animal disease models. Stem Cells. 2016;34(7):1709-1729. https://doi.org/10.1002/stem.2377]. The majority of studies were performed in dogs (n = 28), with additional studies in horses (n = 9) and cats (n = 8). Disease models included those related to musculoskeletal disease (osteoarthritis and tendon/ligament injury), neurologic disease (canine cognitive dysfunction, intervertebral disc disease, spinal cord injury) gingival/dental disease (gingivostomatitis), dermatologic disease (atopic dermatitis), chronic multi-drug resistant infections, ophthalmic disease (keratoconjunctivitis sicca, eosinophilic keratitis, immune-mediated keratitis), cardiopulmonary disease (asthma, degenerative valve disease, dilated cardiomyopathy), gastrointestinal disease (inflammatory bowel disease, chronic enteropathy), and renal disease (chronic kidney disease). The majority of studies reported beneficial responses to stem cell treatment, with the exception of those related to more chronic processes such as spinal cord injury and chronic kidney disease. However, it should also be noted that 22 studies were open-label, baseline-controlled trials and only 12 studies were randomized and controlled, making overall study interpretation difficult. As noted in the previous review, improved regulatory oversight and consistency in manufacturing of stem cell therapies are needed. Enhanced understanding of the temporal course of disease processes using advanced-omics approaches may further inform mechanisms of action and help define appropriate timing of interventions. Future directions of stem-cell-based therapies could include use of stem-cell-derived extracellular vesicles, or cell conditioning approaches to direct cells to specific pathways that are tailored to individual disease processes and stages of illness.

The Omentum-A Forgotten Structure in Veterinary Surgery in Small Animals' Surgery

The greater and lesser omentum are derived from embryonic mesogastrium. The expansive greater omentum in dogs covers intestinal coils, while in cats, it is smaller. Comprising distinct portions, the greater omentum is rich in lymphatics and blood vessels. Conversely, the lesser omentum spans the liver, stomach, and duodenum. Studies on canine omentum reveal unique immune cell composition and regenerative potential attributed to adipose tissue-derived stromal cells (ADSCs). These cells hold promise in regenerative medicine, showing enhanced abilities compared with ADSCs from other sources. The omentum is critical in tissue repair and pathology, making it invaluable in veterinary surgery across various medical fields. The aim of this article was to research current knowledge about the applications of the omentum in veterinary surgery and the possibilities of using this structure in the future.

Current Advances in Mesenchymal Stem Cell Therapies Applied to Wounds and Skin, Eye, and Neuromuscular Diseases in Companion Animals

Mesenchymal stem cells (MSCs) are considered a very promising alternative tool in cell therapies and regenerative medicine due to their ease of obtaining from various tissues and their ability to differentiate into different cell types. This manuscript provides a review of current knowledge on the use of MSC-based therapies as an alternative for certain common pathologies in dogs and cats where conventional treatments are ineffective. The aim of this review is to assist clinical veterinarians in making decisions about the suitability of each protocol from a clinical perspective, rather than focusing solely on research. MSC-based therapies have shown promising results in certain pathologies, such as spinal cord injuries, wounds, and skin and eye diseases. However, the effectiveness of these cell therapies can be influenced by a wide array of factors, leading to varying outcomes. Future research will focus on designing protocols and methodologies that allow more precise and effective MSC treatments for each case.

Influence of the Anatomical Site on Adipose Tissue-Derived Stromal Cells' Biological Profile and Osteogenic Potential in Companion Animals

Adipose tissue-derived stromal cells (ADSCs) have generated considerable interest in the field of veterinary medicine, particularly for their potential in therapeutic strategies focused on bone regeneration. These cells possess unique biological characteristics, including their regenerative capacity and their ability to produce bioactive molecules. However, it is crucial to recognize that the characteristics of ADSCs can vary depending on the animal species and the site from which they are derived, such as the subcutaneous and visceral regions (SCAT and VAT, respectively). Thus, the present work aimed to comprehensively review the different traits of ADSCs isolated from diverse anatomical sites in companion animals, i.e., dogs, cats, and horses, in terms of immunophenotype, morphology, proliferation, and osteogenic differentiation potential. The findings indicate that the immunophenotype, proliferation, and osteogenic potential of ADSCs differ according to tissue origin and species. Generally, the proliferation rate is higher in VAT-derived ADSCs in dogs and horses, whereas in cats, the proliferation rate appears to be similar in both cells isolated from SCAT and VAT regions. In terms of osteogenic differentiation potential, VAT-derived ADSCs demonstrate the highest capability in cats, whereas SCAT-derived ADSCs exhibit superior potential in horses. Interestingly, in dogs, VAT-derived cells appear to have greater potential than those isolated from SCAT. Within the VAT, ADSCs derived from the falciform ligament and omentum show increased osteogenic potential, compared to cells isolated from other anatomical locations. Consequently, considering these disparities, optimizing isolation protocols becomes pivotal, tailoring them to the specific target species and therapeutic aims, and judiciously selecting the anatomical site for ADSC isolation. This approach holds promise to enhance the efficacy of ADSCs-based bone regenerative therapies.

Low-dose xenogeneic mesenchymal stem cells target canine osteoarthritis through systemic immunomodulation and homing

BACKGROUND

As current therapies for canine osteoarthritis (OA) provide mainly symptomatic improvement and fail to address the complex pathology of the disease, mesenchymal stem cells (MSCs) offer a promising biological approach to address both aspects of OA through their immunomodulatory properties.

METHODS

This study aimed to investigate the safety and efficacy of xenogeneic MSCs in dogs with OA at different dose levels after intravenous injection. OA was surgically induced in the right stifle joint. Thirty-two male and female dogs were divided into three treatment groups and a control group. Regular general physical examinations; lameness, joint, radiographic, and animal caretaker assessments; pressure plate analyses; and blood analyses were performed over 42 days. At study end, joint tissues were evaluated regarding gross pathology, histopathology, and immunohistochemistry. In a follow-up study, the biodistribution of intravenously injected 99mTc-labeled equine peripheral blood-derived MSCs was evaluated over 24h in three dogs after the cruciate ligament section.

RESULTS

The dose determination study showed the systemic administration of ePB-MSCs in a canine OA model resulted in an analgesic, anti-inflammatory, and joint tissue protective effect associated with improved clinical signs and improved cartilage structure, as well as a good safety profile. Furthermore, a clear dose effect was found with 0.3 × 106 ePB-MSCs as the most effective dose. In addition, this treatment was demonstrated to home specifically towards the injury zone in a biodistribution study.

CONCLUSION

This model-based study is the first to confirm the efficacy and safety of systemically administered xenogeneic MSCs in dogs with OA. The systemic administration of a low dose of xenogeneic MSCs could offer a widely accessible, safe, and efficacious treatment to address the complex pathology of canine OA and potentially slow down the disease progression by its joint tissue protective effect.

Eosinophilic Keratoconjunctivitis in Cats

Eosinophilic keratitis is a disease of the feline ocular surface. It is characterized by conjunctivitis, white to pink raised plaques on the corneal and conjunctival surfaces, corneal vascularization, and variable ocular pain. Cytology is the diagnostic test of choice. Identification of eosinophils in a corneal cytology sample usually confirms the diagnosis, although lymphocytes, mast cells, and neutrophils are often present concurrently. Immunosuppressives are the mainstay of therapy, topically or systemically. The role of feline herpesvirus-1 in the pathogenesis of eosinophilic keratoconjunctivitis (EK) remains unclear. Eosinophilic conjunctivitis is a less common manifestation of EK and presents as severe conjunctivitis without corneal involvement.

The Pivotal Role of Stem Cells in Veterinary Regenerative Medicine and Tissue Engineering

The introduction of new regenerative therapeutic modalities in the veterinary practice has recently picked up a lot of interest. Stem cells are undifferentiated cells with a high capacity to self-renew and develop into tissue cells with specific roles. Hence, they are an effective therapeutic option to ameliorate the ability of the body to repair and engineer damaged tissues. Currently, based on their facile isolation and culture procedures and the absence of ethical concerns with their use, mesenchymal stem cells (MSCs) are the most promising stem cell type for therapeutic applications. They are becoming more and more well-known in veterinary medicine because of their exceptional immunomodulatory capabilities. However, their implementation on the clinical scale is still challenging. These limitations to their use in diverse affections in different animals drive the advancement of these therapies. In the present article, we discuss the ability of MSCs as a potent therapeutic modality for the engineering of different animals' tissues including the heart, skin, digestive system (mouth, teeth, gastrointestinal tract, and liver), musculoskeletal system (tendons, ligaments, joints, muscles, and nerves), kidneys, respiratory system, and eyes based on the existing knowledge. Moreover, we highlighted the promises of the implementation of MSCs in clinical use in veterinary practice.

Secretory Profile of Adipose-Tissue-Derived Mesenchymal Stem Cells from Cats with Calicivirus-Positive Severe Chronic Gingivostomatitis

The feline calicivirus (FCV) causes infections in cats all over the world and seems to be related to a broad variety of clinical presentations, such as feline chronic gingivostomatitis (FCGS), a severe oral pathology in cats. Although its etiopathogeny is largely unknown, FCV infection is likely to be a main predisposing factor for developing this pathology. During recent years, new strategies for treating FCGS have been proposed, based on the use of mesenchymal stem cells (MSC) and their regenerative and immunomodulatory properties. The main mechanism of action of MSC seems to be paracrine, due to the secretion of many biomolecules with different biological functions (secretome). Currently, several pathologies in humans have been shown to be related to functional alterations of the patient’s MSCs. However, the possible roles that altered MSCs might have in different diseases, including virus-mediated diseases, remain unknown. We have recently demonstrated that the exosomes produced by the adipose-tissue-derived MSCs (fAd-MSCs) from cats suffering from FCV-positive severe and refractory FCGS showed altered protein contents. Based on these findings, the goal of this work was to analyze the proteomic profile of the secretome produced by feline adipose-tissue-derived MSCs (fAd-MSCs) from FCV-positive patients with FCGS, in order to identify differences between them and to increase our knowledge of the etiopathogenesis of this disease. We used high-resolution mass spectrometry and functional enrichment analysis with Gene Ontology to compare the secretomes produced by the fAd-MSCs of healthy and calicivirus-positive FCGS cats. We found that the fAd-MSCs from cats with FCGS had an increased expression of pro-inflammatory cytokines and an altered proteomic profile compared to the secretome produced by cells from healthy cats. These findings help us gain insight on the roles of MSCs and their possible relation to FCGS, and may be useful for selecting specific biomarkers and for identifying new therapeutic targets.

Suicide gene therapy by canine mesenchymal stem cell transduced with thymidine kinase in a u-87 glioblastoma murine model: Secretory profile and antitumor activity

The role played by certain domestic species such as dogs as a translational model in comparative oncology shows great interest to develop new therapeutic strategies in brain tumors. Gliomas are a therapeutic challenge that represents the most common form of malignant primary brain tumors in humans and the second most common form in dogs. Gene-directed enzyme/prodrug therapy using adipose mesenchymal stem cells (Ad-MSCs) expressing the herpes simplex virus thymidine kinase (TK) has proven to be a promising alternative in glioblastoma therapy, through its capacity to migrate and home to the tumor and delivering local cytotoxicity avoiding other systemic administration. In this study, we demonstrate the possibility for canine Ad-MSCs (cAd-MSCs) to be genetically engineered efficiently with a lentiviral vector to express TK (TK-cAd-MSCs) and in combination with ganciclovir (GCV) prodrug demonstrated its potential antitumor efficacy in vitro and in vivo in a mice model with the human glioblastoma cell line U87. TK-cAd-MSCs maintained cell proliferation, karyotype stability, and MSCs phenotype. Genetic modification significantly affects its secretory profile, both the analyzed soluble factors and exosomes. TK-cAd-MSCs showed a high secretory profile of some active antitumor immune response cytokines and a threefold increase in the amount of secreted exosomes, with changes in their protein cargo. We also found that the prodrug protein is not released directly into the culture medium by TK-cAd-MSCs. We believe that our work provides new perspectives for glioblastoma gene therapy in dogs and a better understanding of this therapy in view of its possible implantation in humans.

Subconjunctival use of allogeneic mesenchymal stem cells to treat chronic superficial keratitis in German shepherd dogs: Pilot study

Background

Chronic superficial keratitis (CSK) is an ocular condition in dogs characterized by corneal opacification leading to visual function impairment. Control of this chronic condition requires the use of topical immunomodulators or corticosteroids daily. Regenerative medicine has shown promising results in several fields of medicine.

Aim

The aim of this study was to evaluate the clinical effect of allogeneic mesenchymal stem cells (MSCs) of adipose tissue applied via subconjunctival in dogs with CSK.

Methods

A series of cases of eight dogs diagnosed with CSK were divided into two groups, four dogs each; the conventional treatment group received prednisolone 1% as topical eye drops and the experimental group (EG) received allogeneic MSCs transplantation. The dogs had not previously been treated for CSK. Systemic and ophthalmologic examinations were performed to exclude other abnormalities. An administered amount of MSC (1 × 10⁶ cells each time) was injected via subconjunctival in the peri-limbal region at 0 and 30 days. The animals were followed for 110 days for clinical evaluation, and, at the same time, the images of the corneal abnormalities were obtained and analyzed in the ImageJ software. The statistical analysis was performed in the GrandPrism 7.0 software.

Results

Initial and final images revealed that areas with neovascularization, inflammatory infiltrate, and opacity regressed in most eyes in both groups (7/8 eyes in each group) at the end of the 110 days, p = 0.0391 and p = 0.0078 respectively, but this response was minor in the EG comparing to conventional group (CG) (p = 0.026). No local or systemic side effects were observed.

Conclusions

Despite the small melioration, MSCs treatment suggests clinical improvement in patients with CSK after 110 days without any local or systemic side effects. However, the improvement achieved was significantly less than the observed within CG. Further studies still are needed to evaluate the use and benefits of stem cells as an adjunct treatment for CSK.

Feline Eosinophilic Keratitis—A Review

Eosinophilic keratitis is a disease occurring in cats, horses and rabbits. Its clinical signs include blepharo-spasm, discharge, chemosis, conjunctival hyperaemia and the presence of corneal ulceration. The typical signs of the disease are white to pink plaques on the cornea accompanied with keratitis. The diagnosis of the disease has to be confirmed with cytology examination and the presence of eosinophils and mast cells in the specimen. Local application of corticosteroids and cyclosporine has good therapeutic effect and has been recommended in all affected species. In samples collected from cats, the presence of feline herpes virus DNA has been reported. Eosinophilic keratitis might be caused by an aberrant immune response or reaction to unknown allergic stimuli. The primary cause of the disease is currently unknown.

Feline adipose-derived mesenchymal stem cells induce effector phenotype and enhance cytolytic function of CD8+ T cells

BACKGROUND

Feline adipose-derived mesenchymal stem cells (ASCs) engage with a variety of immune cells and have been used in several clinical trials for the treatment of inflammatory and immune-dysregulated diseases in cats, but the impact they exert on the functional characteristics on T cells, particularly CD8+ T cells, remains to be elucidated.

METHODS

Modified mixed leukocyte reaction was performed between feline ASCs and PBMCs. Changes of cell cycle stages, phenotype and cellular senescence were determined through flow cytometry and gene expression analysis. Cytotoxicity assay was performed to evaluate CD8+ T cell effector function.

RESULTS

Feline ASCs induce cell cycle arrest on CD8+ T cells in a contact-dependent manner, downregulate CD8 surface expression, and shift their phenotype toward terminally differentiated effector cells (CD57+, CD45R+, CD62L-). CD8 T cells interacted with feline ASCs also upregulated granzyme B, IL-2 and KLRG-1 expression and have enhanced cytotoxic potential, evident by the increased percentage of lysis on target cells.

CONCLUSIONS

Our findings suggest that feline ASCs (1) alter CD8+ T cells toward terminally differentiated, proinflammatory effector phenotype with limited proliferative capacity, and (2) enhance their cytotoxic potential through granzyme B upregulation. These cytotoxic CD8+ T cells could aid in disease cure in cases caused by an underlying, unresolved viral infection.

Altered Proteomic Profile of Adipose Tissue-Derived Mesenchymal Stem Cell Exosomes from Cats with Severe Chronic Gingivostomatitis

Simple Summary

Feline chronic gingivostomatitis (FCGS) is a common pathology in cats, related to an aberrant immune response. The cause of FCGS remains elusive, despite extensive investigations. A multitude of conditions and infectious agents have been related, without proof of causation, as follows: virus, bacteria, environmental stress, hypersensitivity, etc. In recent years, therapies based on feline adipose-derived mesenchymal stem cells (fAd-MSC) have become an interesting alternative for the treatment of different complex pathologies in cats. Mesenchymal stem cells secrete a wide variety of therapeutic elements, such as bioactive molecules and extracellular vesicles, such as exosomes. It is essential to characterize these elements, to better understand their mechanisms of action. In this study, we show, for the first time, that the proteomic profile of fAd-MSC-derived exosomes, from calicivirus-positive patients with severe FCGS, is altered. Using bioinformatic tools, we have demonstrated the existence of different proteins in the exosomes from diseased patients, responsible for an altered biological effect. In addition, the exosomes do not only experience changes in their cargo, but are also produced in larger quantities. This study might contribute to the better prediction of the clinical outcomes of mesenchymal stem cell treatments in veterinary patients with immune-mediated diseases, such as FCGS.

Abstract

Feline chronic gingivostomatitis (FCGS) is a pathology with a complicated therapeutic approach and with a prevalence between 0.7 and 12%. Although the etiology of the disease is diverse, feline calicivirus infection is known to be a predisposing factor. To date, the available treatment helps in controlling the disease, but cannot always provide a cure, which leads to a high percentage of refractory animals. Mesenchymal stem cells (MSCs) play a pivotal role in the homeostasis and reparation of different tissues and have the ability to modulate the immune system responses. This ability is, in part, due to the capacity of exosomes to play a part in intercellular cell communication. However, the precise role of MSC-derived exosomes and their alterations in immunocompromised pathologies remains unknown, especially in veterinary patients. The goal of this work was to analyze the proteomic profile of feline adipose tissue-derived MSCs (fAd-MSCs) from calicivirus-positive FCGS patients, and to detect possible modifications of the exosomal cargo, to gain better knowledge of the disease’s etiopathogenesis. Using high-resolution mass spectrometry and functional enrichment analysis with Gene Ontology, exosomes isolated from the fAd-MSCs of five healthy cats and five calicivirus-positive FCGS patients, were pooled and compared. The results showed that the fAd-MSCs from cats suffering from FCGS not only had a higher exosome production, but also their exosomes showed significant alterations in their proteomic profile. Eight proteins were exclusively found in the exosomes from the FCGS group, and five proteins could only be found in the exosomes from the healthy cats. When comparing the exosomal cargo between the two groups, significant upregulation of 17 and downregulation of 13 proteins were detected in the FCGS group compared to the control group. These findings shed light on new perspectives on the roles of MSCs and their relation to this disease, which may help in identifying new therapeutic targets and selecting specific biomarkers.

Correlations between clinical signs and corneal cytology in feline eosinophilic keratoconjunctivitis

Objective

To assess correlations between clinical and cytological features of feline eosinophilic keratoconjunctivitis at the time of cytological diagnosis.

Animals Studied

Fifteen client‐owned, domestic breed cats (18 eyes) examined between 2007 and 2019.

Procedures

An electronic search and medical record review of cats diagnosed with feline eosinophilic keratitis or keratoconjunctivitis (FEK) based on clinical examination findings and eosinophils detected on corneal cytology were conducted. Clinical severity was graded using a modified version of a previously validated semiquantitative preclinical ocular toxicology scoring (SPOTS) system. Clinical grades were assigned following review of clinical images and medical record descriptions, and cytological grades were assigned following review of archived corneal cytology slides. Correlations were analyzed for significance using Spearman's rank correlation coefficient.

Results

Higher total corneal scores correlated with higher total conjunctival scores, but not with total fluorescein scores. Small lymphocyte scores correlated negatively with scores for collagen degeneration or mineralization. Globule leukocytes, a unique cell type not previously described in ocular cytology, were identified in 4 of 18 cytological samples. Higher globule leukocyte scores were correlated with higher scores for mast cells or plasma cells. Specimens with lower eosinophil scores had higher globule leukocyte scores.

Conclusions

Large variability was detected in the cytological characteristics and clinical features of FEK‐affected cats. This is the first report of globule leukocytes being identified in ocular cytology from any species. The role of globule leukocytes in the etiopathogenesis and progression of FEK remains unknown and warrants further investigation.

Proteomic Analysis of the Secretome and Exosomes of Feline Adipose-Derived Mesenchymal Stem Cells

Simple Summary

The enormous advances in stem cell research have generated high expectations in the development of new therapies to repair or regenerate damaged tissues. For this reason, laboratory studies of stem cells enable scientists to learn about cells’ essential properties. Specifically, in recent years, therapies based on mesenchymal stem cells have become an interesting alternative for the treatment of different complex pathologies in veterinary medicine. Mesenchymal stem cells secrete a wide variety of therapeutic elements such as bioactive molecules and extracellular vesicles (e.g., exosomes). Thus, it is essential to characterize them before future use as biotechnological products. Therefore, the objective of this study was to determine and compare their protein profile to understand better the mechanisms of action of these components and facilitate their possible use in future therapies. The data demonstrate the existence of different proteins responsible for the biological effects of cells. In addition, these approaches and techniques can contribute to the better prediction of clinical outcomes of mesenchymal stem cell treatment.

Abstract

Mesenchymal stem cells (MSCs) have been shown to have therapeutic efficacy in different complex pathologies in feline species. This effect is attributed to the secretion of a wide variety of bioactive molecules and extracellular vesicles, such as exosomes, with significant paracrine activity, encompassed under the concept of the secretome. However, at present, the exosomes from feline MSCs have not yet been studied in detail. The objective of this study is to analyze and compare the protein profiles of the secretome as a whole and its exosomal fraction from feline adipose-derived MSCs (fAd-MSCs). For this, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and Protein–Protein Interaction Networks Functional Enrichment Analysis (STRING) were utilized. A total of 239 proteins were identified in the secretome, and 228 proteins specific to exosomes were identified, with a total of 133 common proteins. The proteins identified in the secretome were located in the extracellular regions and in the cytoplasm, while the exosomal proteins were located mainly in the membrane, cytoplasm and cytosol. Regarding function, in the secretome, proteins involved in different metabolic pathways, in pathways related to the immune system and the endocrine system and in the processing of proteins in the endoplasmic reticulum predominated. In contrast, proteins specific to exosomes were predominantly associated with endocytosis, cell junctions, platelet activation and other cell signaling pathways. The possible future use of the secretome, or some of its components, such as exosomes, would provide a non-cell-based therapeutic strategy for the treatment of different diseases that would avoid the drawbacks of cell therapy.

Characterization of the secretory profile and exosomes of limbal stem cells in the canine species

Limbal stem cells (LSCs) are a quiescent cell population responsible for the renewal of the corneal epithelium. Their deficiency is responsible for the conjunctivization of the cornea that is seen in different ocular pathologies, both in humans and in the canine species. The canine species represents an interesting preclinical animal model in ocular surface pathologies. However, the role of LSCs in physiological and pathological conditions in canine species is not well understood. Our objective was to characterize for the first time the soluble factors and the proteomic profile of the secretome and exosomes of canine LSCs (cLSCs). In addition, given the important role that fibroblasts play in the repair of the ocular surface, we evaluated the influence of the secretome and exosomes of cLSCs on their proliferation in vitro. Our results demonstrated a secretory profile of cLSCs with high concentrations of MCP-1, IL-8, VEGF-A, and IL-10, as well as significant production of exosomes. Regarding the proteomic profile, 646 total proteins in the secretome and 356 in exosomes were involved in different biological processes. Functionally, the cLSC secretome showed an inhibitory effect on the proliferation of fibroblasts in vitro, which the exosomes did not. These results open the door to new studies on the possible use of the cLSC secretome or some of its components to treat certain pathologies of the ocular surface in canine species.

Is Stem Cell Commerce in Small Animal Therapies Scientifically and Morally Justified?

The lack of clear regulations for the use of veterinary stem cells has triggered the commercialization of unproven experimental therapies for companion animal diseases. Adult stem cells have complex biological characteristics that are directly related to the therapeutic application, but several questions remain to be answered. In order to regulate the use of these cells, well-conducted, controlled scientific studies that generate high-quality data should be performed, in order to assess the efficacy and safety of the intended treatment. This paper discusses the scientific challenges of mesenchymal stem cell therapy in veterinary regenerative medicine, and reviews published trials of adipose-tissue-derived stem cells in companion animal diseases that spontaneously occur.

Stem Cell Therapy and Cats: What Do We Know at This Time

Regenerative medicine is a complex field of research, with much hope placed on the ability to use regenerative therapies such as stem cells to provide new treatment options for many frustrating disease processes in human and veterinary medicine. Significant research is still needed and ongoing from basic mechanistic studies to advanced bioengineering applications to practical cell delivery methods. Small studies of mesenchymal stem cell therapy shows significant promise in inflammatory feline diseases. Continued research will hopefully help determine the potential of mesenchymal stem cell therapy in feline medicine and lead to development of safe and effective products for clinical use.

Safety and immunomodulatory properties of equine peripheral blood-derived mesenchymal stem cells in healthy cats

OBJECTIVE

Due to the immunomodulatory properties of mesenchymal stem cells (MSCs) through stimulation of endogenous immune cells by paracrine signals and cell contact, they have been proposed as alternative treatment option for many inflammatory and immune-mediated diseases in veterinary medicine. However, the long-term cultivation possibilities of feline MSCs are currently compromised due to a restricted proliferation capacity. Therefore, the xenogeneic use of equine peripheral blood-derived MSCs (ePB-MSCs) would present an interesting alternative thanks to their superior cultivation properties. To the authors' knowledge, there are currently no safety reports concerning the xenogeneic use of ePB-MSCs in cats. Therefore, the overall goal of this preliminary study was to investigate if ePB-MSCs can safely be administered in healthy cats and by extension evaluating their immunogenic and immunomodulatory properties.

METHODS

Ten healthy cats were intravenously (i.v.) injected with 3 × 10⁵ ePB-MSCs at three time points (T₀, T₁, T₂). All cats were daily inspected by the caretaker and underwent a physical examination with hematological and biochemical analysis at day 0 (T₀), week 2 (T₁), week 4 (T₂) and week 6 (T₃) by a veterinarian. Furthermore, a modified mixed lymphocyte reaction (MLR) was performed at T₀ and T₃ for each cat in order to evaluate immunogenic and immunomodulatory properties of the ePB-MSCs RESULTS: No adverse clinical effects could be detected following repeated i.v. administration of ePB-MSCs in all cats. Significant lower protein (T₁: P-value = 0.002; T₂: P-value > 0.001; T₃: P-value = 0.004) and albumin levels (T₁: P-value = 0.003; T₂: P-value = 0.001) were seen after repeated administration of ePB-MSCs, compared to T₀. However, all biochemical and hematological parameters stayed within clinical acceptance level. In addition, the repeated injections did not induce a cellular immune response before and after repeated ePB-MSCs administration. Furthermore, convincing immunomodulatory properties of ePB-MSCs on feline peripheral blood mononuclear cells were confirmed in the MLR-assay CONCLUSION: This preliminary study demonstrates that ePB-MSCs can safely be administered in healthy cats and provide a promising alternative for the treatment of various inflammatory diseases in cats.

Stem Cells in Veterinary Medicine-Current State and Treatment Options

Regenerative medicine is a branch of medicine that develops methods to grow, repair, or replace damaged or diseased cells, organs or tissues. It has gained significant momentum in recent years. Stem cells are undifferentiated cells with the capability to self—renew and differentiate into tissue cells with specialized functions. Stem cell therapies are therefore used to overcome the body's inability to regenerate damaged tissues and metabolic processes after acute or chronic insult. The concept of stem cell therapy was first introduced in 1991 by Caplan, who proposed that massive differentiation of cells into the desired tissue could be achieved by isolation, cultivation, and expansion of stem cells in in vitro conditions. Among different stem cell types, mesenchymal stem cells (MSC) currently seem to be the most suitable for therapeutic purposes, based on their simple isolation and culturing techniques, and lack of ethical issues regarding their usage. Because of their remarkable immunomodulatory abilities, MSCs are increasingly gaining recognition in veterinary medicine. Developments are primarily driven by the limitations of current treatment options for various medical problems in different animal species. MSCs represent a possible therapeutic option for many animal diseases, such as orthopedic, orodental and digestive tract diseases, liver, renal, cardiac, respiratory, neuromuscular, dermal, olfactory, and reproductive system diseases. Although we are progressively gaining an understanding of MSC behavior and their mechanisms of action, some of the issues considering their use for therapy are yet to be resolved. The aim of this review is first to summarize the current knowledge and stress out major issues in stem cell based therapies in veterinary medicine and, secondly, to present results of clinical usage of stem cells in veterinary patients.

Potential therapeutic application of mesenchymal stem cells in ophthalmology

At present a wide variety of methods have been proposed to treat eye disorders, drug therapies are most commonly used. It should be noted that effective treatment modalities especially for degeneration of the retina and optic nerve are lacking. In the last few years stem cell transplantation has been proposed as an alternative method. The opportunities that stem cells provide within clinical use are almost unlimited. These cells are presently applied to treat various traumatic and degenerative disorders due to their unique biologic properties. Stem cells have high proliferative capabilities and are a self-maintained population of cells capable of differentiating into different cell types. Thus, they are represent a very primary stage of a cell lineage. Their ability to differentiate into different pathways provides animals with great plasticity in the renewal of somatic cells in postnatal ontogenesis. Pre-clinical and clinical ophthalmology studies where mesenchymal stem cells are applied and various methods of their administration are discussed herein. In addition the safety and efficacy of using bone marrow- and adipose tissue-derived mesenchymal stem cells have been discussed.

Effect of allogeneic mesenchymal stem cells (MSCs) on corneal wound healing in dogs

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Allogeneic MSCs are safety to be transplanted by subconjunctival route.

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Allogeneic MSCs therapy seems to be efficient in improving corneal healing in dogs.

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Allogeneic MSCs therapy applied to depth corneal ulcers promoted healing in 14 days.

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The paracrine effect of MSCs must provide a rapid corneal wound healing.

Comparative analysis and characterization of soluble factors and exosomes from cultured adipose tissue and bone marrow mesenchymal stem cells in canine species

The two main sources of mesenchymal stem cell (MSCs) in the canine species are bone marrow (cBM-MSCs) and adipose tissue (cAd-MSCs). The secretion of multitude bioactive molecules, included under the concept of secretome and found in the cultured medium, play a predominant role in the mechanism of action of these cells on tissue regeneration. Although certain features of its characterization are well documented, their secretory profiles remain unknown. We described and compared, for the first time, the secretory profile and exosomes characterization in standard monolayer culture of MSCs from both sources of the same donor as well as its immunomodulatory potential. We found that despite the similarity in surface immunophenotyping and trilineage differentiation, there are several differences in terms of proliferation rate and secretory profile. cAd-MSCs have advantages in proliferative capacity, whereas cBM-MSCs showed a significantly higher secretory production of some soluble factors (IL-10, IL-2, IL-6, IL-8, IL-12p40, IFN-γ, VEGF-A, NGF-β, TGF-β, NO and PGE2) and exosomes under the same standard culture conditions. Proteomics analysis confirm that cBM-MSCs exosomes have a greater number of characterized proteins involved in metabolic processes and in the regulation of biological processes compared to cAd-MSCs. On the other hand, secretome from both sources demonstrate similar immunomodulatory capacity when tested in mitogen stimulated lymphocyte reaction, but not in their exosomes at the dose used. Considering that the use of secretome open as a new therapeutic strategy for different diseases, without the need to implant cells, those biological differences should be considered, when choosing the MSCs source, for either cellular implantation or direct use of secretome for a specific clinical application.