Canine and Equine Mesenchymal Stem Cells Grown in Serum Free Media Have Altered Immunophenotype

The systemic cellular immune response against allogeneic mesenchymal stem cells is influenced by inflammation, differentiation and MHC compatibility: in vivo study in the horse

The effectiveness and safety of allogeneic mesenchymal stem/stromal cells (MSCs) can be affected by patient's immune recognition. Thus, MSC immunogenicity and their immunomodulatory properties are crucial aspects for therapy. Immune responses after allogeneic MSC administration have been reported in different species, including equine. Interactions of allogenic MSCs with the recipient's immune system can be influenced by factors like matching or mismatching for the major histocompatibility complex (MHC) between donor-recipient, and by the levels of MHC expression in MSCs. The latter can vary upon MSC inflammatory exposure or differentiation, such as chondrogenic induction, making both priming and differentiation interesting therapeutic strategies. This study investigated the systemic in vivo immune cellular response against allogeneic equine MSCs in these situations. Either MSCs in basal conditions (MSC-naïve), pro-inflammatory primed (MSC-primed) or chondrogenically differentiated (MSC-chondro) were repeatedly administered subcutaneously into autologous, MHC-matched or MHC-mismatched allogeneic equine recipients. At different time-points after each administration, lymphocytes were obtained from recipient horses and exposed in vitro to the same type of MSCs to assess the proliferative response of different T cell subsets (cytotoxic, helper, regulatory), B cells, and interferon gamma (IFNγ) secretion. Higher proliferative response of helper and cytotoxic T lymphocytes and IFNγ secretion was observed in response to all types of MHC-mismatched MSCs over MHC-matched ones. MSC-primed produced the highest immune response, followed by MSC-naïve, and MSC-chondro. However, MSC-primed activated Treg and had a mild effect on B cells, and the response after their second administration was similar to the first one. On the other hand, both MSC-chondro and MSC-naïve barely induced Treg response but promoted B lymphocyte activation, and proportionally induced a higher cell response after the second administration. In conclusion, both the type of MSC conditioning and the MHC compatibility influenced systemic immune recognition of equine MSCs after single and repeated administrations, but the response was different. Selecting MHC-matched donors would be particularly recommended for MSC-primed and repeated MSC-naïve administrations. While MHC-mismatching in MSC-chondro would be less critical, B cell response should not be ignored. Comprehensively investigating the in vivo immune response against equine allogeneic MSCs is crucial for advancing veterinary cell therapies.

Therapeutic Potential in Wound Healing of Allogeneic Use of Equine Umbilical Cord Mesenchymal Stem Cells

Wound healing after skin injury is a complex process, particularly in equines where leg wounds are prevalent and their repair is complicated due to the anatomical characteristics. Conventional treatments are not effective enough. The umbilical cord offers an unlimited source of adult mesenchymal stem cells (ucMSCs) from Wharton's jelly tissue. The present study aims to demonstrate the safety and therapeutic potential of the allogeneic use of equine ucMSCs (e-ucMSCs) in the healing of severe equine leg wounds. The methods employed were the isolation, culture and expansion of e-ucMSCs. Flow cytometry and a PCR assay were used for cell characterization. This study included an immunomodulation assay, a murine pre-clinical trial and the first phase of an equine clinical trial. Our results showed that e-ucMSCs express a functional HLA-G homolog, EQMHCB2. In the immunomodulation assay, the e-ucMSCs inhibited the proliferation of activated equine peripheral blood mononuclear cells (e-PBMCs). In the murine pre-clinical trial, e-ucMSCs reduced healing time by 50%. In the equine clinical trial, the injection of e-ucMSCs into severe leg lesions improved the closure time and quality of the tissues involved, regenerating them without fibrous tissue scar formation. In conclusion, the results of this study suggest that e-ucMSCs can be used allogeneically for wound healing by creating a tolerogenic environment.

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.

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.

Outlook of Adipose-Derived Stem Cells: Challenges to Their Clinical Application in Horses

Adipose tissue is recognized as the major endocrine organ, potentially acting as a source of mesenchymal stem cells for various applications in regenerative medicine. Athletic horses are often exposed to traumatic injuries, resulting in severe financial losses. The development of adipose-derived stem cells' regenerative potential depends on many factors. The extraction of stem cells from subcutaneous adipose tissue is non-invasive, non-traumatic, cheaper, and safer than other sources. Since there is a lack of unique standards for identification, the isolated cells and applied differentiation protocols are often not species-specific; therefore, the cells cannot reveal their multipotent properties, so their stemness features remain questionable. The current review discusses some aspects of the specificity of equine adipose stem cells concerning their features, immunophenotyping, secretome profile, differentiation abilities, culturing conditions, and consequent possibilities for clinical application in concrete disorders. The presented new approaches elucidate the possibility of the transition from cell-based to cell-free therapy with regenerative purposes in horses as an alternative treatment to cellular therapy. In conclusion, their clinical benefits should not be underestimated due to the higher yield and the physiological properties of adipose-derived stem cells that facilitate the healing and tissue regeneration process and the ability to amplify the effects of traditional treatments. More profound studies are necessary to apply these innovative approaches when treating traumatic disorders in racing horses.

Advanced cell-based products generated via automated and manual manufacturing platforms under the quality by design principle: Are they equivalent or different?

Mesenchymal stem/stromal cells (MSCs) are multipotent stem cells that can be isolated from bone marrow, adipose tissue, the umbilical cord, dental pulp, etc. These cells have unique properties that give them excellent therapeutic potential, including immunoregulation, immunomodulation, and tissue regeneration functions. MSC-based products are considered advanced therapy medicinal products (ATMPs) under European regulations (1394/2007); thus, they must be manufactured under good manufacturing practices and via effective manufacturing methods. The former can be achieved via a proper laboratory design and compliance with manufacturing protocols, whereas the latter requires an approach that ensures that the quality of the products is consistent regardless of the manufacturing procedure. To meet these daunting requirements, this study proposes an exchangeable approach that combines optimized and equivalent manufacturing processes under the Quality by Design (QbD) principle, allowing investigators to convert from small laboratory-scale to large-scale manufacturing of MSC-based products for clinical applications without altering the quality and quantity of the cell-based products.

Equine osteoarthritis: Strategies to enhance mesenchymal stromal cell-based acellular therapies

Osteoarthritis (OA) is a degenerative disease that eventually leads to the complete degradation of articular cartilage. Articular cartilage has limited intrinsic capacity for self-repair and, to date, there is no curative treatment for OA. Humans and horses have a similar articular cartilage and OA etiology. Thus, in the context of a One Health approach, progress in the treatment of equine OA can help improve horse health and can also constitute preclinical studies for human medicine. Furthermore, equine OA affects horse welfare and leads to significant financial losses in the equine industry. In the last few years, the immunomodulatory and cartilage regenerative potentials of mesenchymal stromal cells (MSCs) have been demonstrated, but have also raised several concerns. However, most of MSC therapeutic properties are contained in their secretome, particularly in their extracellular vesicles (EVs), a promising avenue for acellular therapy. From tissue origin to in vitro culture methods, various aspects must be taken into consideration to optimize MSC secretome potential for OA treatment. Immunomodulatory and regenerative properties of MSCs can also be enhanced by recreating a pro-inflammatory environment to mimic an in vivo pathological setting, but more unusual methods also deserve to be investigated. Altogether, these strategies hold substantial potential for the development of MSC secretome-based therapies suitable for OA management. The aim of this mini review is to survey the most recent advances on MSC secretome research with regard to equine OA.

The immunomodulation-immunogenicity balance of equine Mesenchymal Stem Cells (MSCs) is differentially affected by the immune cell response depending on inflammatory licensing and major histocompatibility complex (MHC) compatibility

The immunomodulatory properties of equine mesenchymal stem cells (MSCs) are important for their therapeutic potential and for their facilitating role in their escape from immune recognition, which may also be influenced by donor-recipient major histocompatibility complex (MHC) matching/mismatching and MHC expression level. Factors such as inflammation can modify the balance between regulatory and immunogenic profiles of equine MSCs, but little is known about how the exposure to the immune system can affect these properties in equine MSCs. In this study, we analyzed the gene expression and secretion of molecules related to the immunomodulation and immunogenicity of equine MSCs, either non-manipulated (MSC-naive) or stimulated by pro-inflammatory cytokines (MSC-primed), before and after their exposure to autologous or allogeneic MHC-matched/-mismatched lymphocytes, either activated or resting. Cytokine priming induced the immunomodulatory profile of MSCs at the baseline (MSCs cultured alone), and the exposure to activated lymphocytes further increased the expression of interleukin 6 (IL6), cyclooxygenase 2, and inducible nitric oxide synthase, and IL6 secretion. Activated lymphocytes were also able to upregulate the regulatory profile of MSC-naive to levels comparable to cytokine priming. On the contrary, resting lymphocytes did not upregulate the immunomodulatory profile of equine MSCs, but interestingly, MSC-primed exposed to MHC-mismatched lymphocytes showed the highest expression and secretion of these mediators, which may be potentially linked to the activation of lymphocytes upon recognition of foreign MHC molecules. Cytokine priming alone did not upregulate the immunogenic genes, but MSC-primed exposed to activated or resting lymphocytes increased their MHC-I and MHC-II expression, regardless of the MHC-compatibility. The upregulation of immunogenic markers including CD40 in the MHC-mismatched co-culture might have activated lymphocytes, which, at the same time, could have promoted the immune regulatory profile aforementioned. In conclusion, activated lymphocytes are able to induce the equine MSC regulatory profile, and their effects seem to be additive to the priming action. Importantly, our results suggest that the lymphocyte response against MHC-mismatched MSC-primed would promote further activation of their immunomodulatory ability, which eventually might help them evade this reaction. Further studies are needed to clarify how these findings might have clinical implications in vivo, which will help developing safer and more effective therapies.

Comparing the immunomodulatory properties of equine BM-MSCs culture expanded in autologous platelet lysate, pooled platelet lysate, equine serum and fetal bovine serum supplemented culture media

Joint injury often leads to cartilage damage and posttraumatic inflammation, which drives continued extracellular matrix degradation culminating in osteoarthritis. Mesenchymal stem cells (MSCs) have been proposed as a biotherapeutic to modulate inflammation within the joint. However, concerns have been raised regarding the immunogenicity of MSCs cultured in traditional fetal bovine serum (FBS) containing media, and the potential of xenogenic antigens to activate the immune system causing rejection and destruction of the MSCs. Xenogen-free alternatives to FBS have been proposed to decrease MSC immunogenicity, including platelet lysate (PL) and equine serum. The objective of this study was to compare the immunomodulatory properties of BM-MSCs culture-expanded in media supplemented with autologous PL (APL), pooled PL (PPL), equine serum (ES) or FBS. We hypothesized that BM-MSCs culture expanded in media with xenogen-free supplements would exhibit superior immunomodulatory properties to those cultured in FBS containing media. Bone marrow-derived MSCs (BM-MSCs) were isolated from six horses and culture expanded in each media type. Blood was collected from each horse to isolate platelet lysate. The immunomodulatory function of the BM-MSCs was assessed via a T cell proliferation assay and through multiplex immunoassay quantification of cytokines, including IL-1β, IL-6, IL-8, IL-10, and TNFα, following preconditioning of BM-MSCs with IL-1β. The concentration of platelet-derived growth factor BB (PDGF-BB), IL-10, and transforming growth factor-β (TGF-β) in each media was measured via immunoassay. BM-MSCs cultured in ES resulted in significant suppression of T cell proliferation (p = 0.02). Cell culture supernatant from preconditioned BM-MSCs cultured in ES had significantly higher levels of IL-6. PDGF-BB was significantly higher in APL media compared to FBS media (p = 0.016), while IL-10 was significantly higher in PPL media than ES and FBS (p = 0.04). TGF-β was highest in APL media, with a significant difference in comparison to ES media (p = 0.03). In conclusion, expansion of equine BM-MSCs in ES may enhance their immunomodulatory abilities, while PL containing media may have some inherent therapeutic potential associated with higher concentrations of growth factors. Further studies are needed to elucidate which xenogen-free supplement optimizes BM-MSC performance.

Manufacturing Mesenchymal Stromal Cells for the Treatment of Osteoarthritis in Canine Patients: Challenges and Recommendations

The recent interest in advanced biologic therapies in veterinary medicine has opened up opportunities for new treatment modalities with considerable clinical potential. Studies with mesenchymal stromal cells (MSCs) from animal species have focused on in vitro characterization (mostly following protocols developed for human application), experimental testing in controlled studies and clinical use in veterinary patients. The ability of MSCs to interact with the inflammatory environment through immunomodulatory and paracrine mechanisms makes them a good candidate for treatment of inflammatory musculoskeletal conditions in canine species. Analysis of existing data shows promising results in the treatment of canine hip dysplasia, osteoarthritis and rupture of the cranial cruciate ligament in both sport and companion animals. Despite the absence of clear regulatory frameworks for veterinary advanced therapy medicinal products, there has been an increase in the number of commercial cell-based products that are available for clinical applications, and currently the commercial use of veterinary MSC products has outpaced basic research on characterization of the cell product. In the absence of quality standards for MSCs for use in canine patients, their safety, clinical efficacy and production standards are uncertain, leading to a risk of poor product consistency. To deliver high-quality MSC products for veterinary use in the future, there are critical issues that need to be addressed. By translating standards and strategies applied in human MSC manufacturing to products for veterinary use, in a collaborative effort between stem cell scientists and veterinary researchers and surgeons, we hope to facilitate the development of quality standards. We point out critical issues that need to be addressed, including a much higher level of attention to cell characterization, manufacturing standards and release criteria. We provide a set of recommendations that will contribute to the standardization of cell manufacturing methods and better quality assurance.

A Review of Fetal Bovine Serum in the Culture of Mesenchymal Stromal Cells and Potential Alternatives for Veterinary Medicine

Fetal bovine serum (FBS) remains widely used as a supplement in cell culture media used in the isolation and expansion of mesenchymal stromal cells (MSC) despite longstanding practical, clinical, and ethical concerns over its use. As a result, research on alternative culture media supplement solutions that conserve crucial MSC characteristics has become increasingly relevant. Species-specific supplements and serum-free media such as platelet lysate or chemically defined media have been assessed for their effect in MSC cultures regarding proliferation, differentiation, and immunomodulatory capacity. While none of the alternatives offer a complete solution in replacing traditional FBS supplemented media for culturing MSCs for all species, short-term or transitional use of FBS-free media can perform equally well and could address some of the concerns over the use of FBS.

Equine Mesenchymal Stem Cells Influence the Proliferative Response of Lymphocytes: Effect of Inflammation, Differentiation and MHC-Compatibility

Simple Summary

Mesenchymal stem cells are investigated for therapy because of their ability to regulate the immune response to an injury. Cell therapy is increasingly important in veterinary patients such as horses, which are also valuable as a model. Therefore, what is learned in these animals can benefit both them and people. However, the patient’s immune system could recognize and destroy mesenchymal stem cells, impairing effectiveness and potentially leading to adverse effects. In this study, we analysed how equine mesenchymal stem cells interact with immune cells in different scenarios. We tested the effect of inflammation and differentiation of these cells, and how they acted depending on donor–patient compatibility. As we expected, inflammation activated the regulatory ability of equine mesenchymal stem cells, but also increased the risk of immune recognition. We anticipated that, after differentiation, these cells would lose their regulatory ability and would be more easily targeted by the immune system. However, they maintained similar features after differentiating into cartilage cells. The balance between the ability of mesenchymal stem cells to stimulate and to regulate an immune response is of the utmost importance to develop safe and effective cell therapies for animals and people.

Abstract

Immunomodulation and immunogenicity are pivotal aspects for the therapeutic use of mesenchymal stem cells (MSCs). Since the horse is highly valuable as both a patient and translational model, further knowledge on equine MSC immune properties is required. This study analysed how inflammation, chondrogenic differentiation and compatibility for the major histocompatibility complex (MHC) influence the MSC immunomodulatory–immunogenicity balance. Equine MSCs in basal conditions, pro-inflammatory primed (MSC-primed) or chondrogenically differentiated (MSC-chondro) were co-cultured with either autologous or allogeneic MHC-matched/mismatched lymphocytes in immune-suppressive assays (immunomodulation) and in modified one-way mixed leukocyte reactions (immunogenicity). After co-culture, frequency and proliferation of T cell subsets and B cells were assessed by flow cytometry and interferon-ɣ (IFNɣ) secretion by ELISA. MSC-primed showed higher regulatory potential by decreasing proliferation of cytotoxic and helper T cells and B cells. However, MHC-mismatched MSC-primed can also activate lymphocytes (proliferative response and IFNɣ secretion), likely due to increased MHC-expression. MSC-chondro maintained their regulatory ability and did not increase their immunogenicity, but showed less capacity than MSC-primed to induce regulatory T cells and further stimulated B cells. Subsequent in vivo studies are needed to elucidate the complex interactions between MSCs and the recipient immune system, which is critical to develop safe and effective therapies.

The secretion profile of mesenchymal stem cells and potential applications in treating human diseases

Mesenchymal stromal/stem cells (MSCs) possess multi-lineage differentiation and self-renewal potentials. MSCs-based therapies have been widely utilized for the treatment of diverse inflammatory diseases, due to the potent immunoregulatory functions of MSCs. An increasing body of evidence indicates that MSCs exert their therapeutic effects largely through their paracrine actions. Growth factors, cytokines, chemokines, extracellular matrix components, and metabolic products were all found to be functional molecules of MSCs in various therapeutic paradigms. These secretory factors contribute to immune modulation, tissue remodeling, and cellular homeostasis during regeneration. In this review, we summarize and discuss recent advances in our understanding of the secretory behavior of MSCs and the intracellular communication that accounts for their potential in treating human diseases.

Impact of Three Different Serum Sources on Functional Properties of Equine Mesenchymal Stromal Cells

Culture and expansion of equine mesenchymal stromal cells (MSCs) are routinely performed using fetal bovine serum (FBS) as a source of growth factors, nutrients, and extracellular matrix proteins. However, the desire to minimize introduction of xenogeneic bovine proteins or pathogens and to standardize cellular products intended for clinical application has driven evaluation of alternatives to FBS. Replacement of FBS in culture for several days before administration has been proposed to reduce antigenicity and potentially prolong survival after injection. However, the functional consequences of MSC culture in different serum types have not been fully evaluated. The objective of this study was to compare the immunomodulatory and antibacterial properties of MSCs cultured in three serum sources: FBS or autologous or allogeneic equine serum. We hypothesized that continuous culture in FBS would generate MSCs with improved functionality compared to equine serum and that there would not be important differences between MSCs cultured in autologous vs. allogeneic equine serum. To address these questions, MSCs from three healthy donor horses were expanded in medium with FBS and then switched to culture in FBS or autologous or allogeneic equine serum for 72 h. The impact of this 72-h culture period in different sera on cell viability, cell doubling time, cell morphology, bactericidal capability, chondrogenic differentiation, and production of cytokines and antimicrobial peptides was assessed. Altering serum source did not affect cell viability or morphology. However, cells cultured in FBS had shorter cell doubling times and secreted more interleukin 4 (IL-4), IL-5, IL-17, RANTES, granulocyte–macrophage colony-stimulating factor, fibroblast growth factor 2, eotaxin, and antimicrobial peptide cathelicidin/LL-37 than cells cultured in either source of equine serum. Cells cultured in FBS also exhibited greater spontaneous bactericidal activity. Notably, significant differences in any of these parameters were not observed when autologous vs. allogeneic equine serum was used for cell culture. Chondrogenic differentiation was not different between different serum sources. These results indicate that MSC culture in FBS will generate more functional cells based on a number of parameters and that the theoretical risks of FBS use in MSC culture should be weighed against the loss of MSC function likely to be incurred from culture in equine serum.

Extracellular Vesicles Derived From Canine Mesenchymal Stromal Cells in Serum Free Culture Medium Have Anti-inflammatory Effect on Microglial Cells

Mesenchymal stem/stromal cells (MSCs) have been used as cell sources for treating dogs with naturally-occurring diseases. Extracellular vesicles (EVs) derived from MSCs are now recognized as pivotal to modulating the immune response and supporting tissue repair. Manufacture of MSC-EVs for clinical application mandates removal of the xeno-proteins, including fetal bovine serum. The objective of this study was to examine whether canine MSCs survived and secreted EVs in serum-free medium (SFM) conditions and to assess the immunomodulatory effect of EVs in vitro. Canine MSCs were found to survive and secrete EVs under SFM conditions. The surface markers of MSCs in the SFM were similar to MSCs in complete culture medium. Canine MSC-EVs had a diameter of ~300 nm and were positive for EV markers. MSC-derived EVs from the serum-free condition reduced the levels of IL-1β by BV-2 cells in response to LPS stimulation. These results warrant further studies of the use of SFM for producing EVs derived from canine MSCs.

Translational Animal Models Provide Insight Into Mesenchymal Stromal Cell (MSC) Secretome Therapy

The therapeutic potential of the mesenchymal stromal cell (MSC) secretome, consisting of all molecules secreted by MSCs, is intensively studied. MSCs can be readily isolated, expanded, and manipulated in culture, and few people argue with the ethics of their collection. Despite promising pre-clinical studies, most MSC secretome-based therapies have not been implemented in human medicine, in part because the complexity of bioactive factors secreted by MSCs is not completely understood. In addition, the MSC secretome is variable, influenced by individual donor, tissue source of origin, culture conditions, and passage. An increased understanding of the factors that make up the secretome and the ability to manipulate MSCs to consistently secrete factors of biologic importance will improve MSC therapy. To aid in this goal, we can draw from the wealth of information available on secreted factors from MSC isolated from veterinary species. These translational animal models will inspire efforts to move human MSC secretome therapy from bench to bedside.

Comparison of Canine and Feline Adipose-Derived Mesenchymal Stem Cells/Medicinal Signaling Cells With Regard to Cell Surface Marker Expression, Viability, Proliferation, and Differentiation Potential

Remarkable immunomodulatory abilities of mesenchymal stem cells, also called multipotent mesenchymal stromal cells or medicinal signaling cells (MSCs), have entailed significant advances in veterinary regenerative medicine in recent years. Despite positive outcomes from MSC therapies in various diseases in dogs and cats, differences in MSC characteristics between small animal veterinary patients are not well-known. We performed a comparative study of cells' surface marker expression, viability, proliferation, and differentiation capacity of adipose-derived MSCs (ADMSCs) from dogs and domestic cats. The same growth media and methods were used to isolate, characterize, and culture canine and feline ADMSCs. Adipose tissue was collected from 11 dogs and 8 cats of both sexes. The expression of surface markers CD44, CD90, and CD34 was detected by flow cytometry. Viability at passage 3 was measured with the hemocytometer and compared to the viability measured by flow cytometry after 1 day of handling. The proliferation potential of MSCs was measured by calculating cell doubling and cell doubling time from second to eighth passage. Differentiation potential was determined at early and late passages by inducing cells toward adipogenic, osteogenic, and chondrogenic differentiation using commercial media. Our study shows that the percentage of CD44⁺CD90⁺ and CD34^−/− cells is higher in cells from dogs than in cells from cats. The viability of cells measured by two different methods at passage 3 differed between the species, and finally, canine ADMSCs possess greater proliferation and differentiation potential in comparison to the feline ADMSCs.

In vitro preconditioning of equine adipose mesenchymal stem cells with prostaglandin E2, substance P and their combination changes the cellular protein secretomics and improves their immunomodulatory competence without compromising stemness

Mesenchymal stem cells (MSC) are modern tools in regenerative therapies of humans and animals owed to their immunomodulatory properties, which are activated in a pro-inflammatory environment. Different preconditioning strategies had been devised to enhance the immunomodulatory properties of MSC. In this research, we evaluated the immunological attributes of equine adipose MSC (eAMSC) before and after preconditioning in vitro with prostaglandin E₂ (PGE₂), substance P (SP), their combination and IFNγ. PGE₂/SP was the best combination to keep or enhance the mesodermal lineage differentiation of eAMSC. Alongside with this, preconditioning of eMSC with PGE₂ and SP did not affect expression of stemness MSC surface phenotype: CD90⁺, CD44⁺, MHC class I⁺, MHC class II^- and CD45^-, assessed by cytometry. Both naïve and preconditioned eAMSC expressed genes related with immune properties, such as MHC-I, PTGES, IL6, IL1A, TNFα and IL8 assessed by qPCR. Only TNFα was under expressed in treated cells, while the other markers were either overexpressed or not changed. In no cases MHC-II expression was detected. The antiproliferative effect of preconditioned eAMSC exposed to activated peripheral blood mononuclear cells (PBMC) showed that SP treatment significantly inhibited proliferation of LPS stimulated PBMC. When eAMSC were stimulated with Poly I:C, all the treatments significantly inhibited proliferation of stimulated PBMC (p < 0.05). Direct contact (coculture) between the preconditioned eAMSC and PBMC, induced a shift of significantly more (CD4/CD25/FOXP3)⁺ T-regulatory PBMC than naïve eAMSC. In the experiments of this research, we investigated the secreted proteomic profile of naïve and preconditioned eAMSC, 42 up-regulated and 40 down-regulated proteins were found in the proteomic assay. Our proteomic data revealed profound changes in the secretory pattern of MSC exposed to different treatments, compared to naïve eAMSC as well as among treatments. In overall, compared to naïve cells, the protein profile of preconditioned cells resembled the mesenchymal-epithelial transition (MET). Here we showed that the combined use of PGE₂ and SP provoked in overall the highest expression of anti-inflammatory markers as well as lead to an increased acquisition of a T-regulatory phenotype in preconditioned eAMSC without affecting their "stemness".

Placenta-derived multipotent mesenchymal stromal cells: a promising potential cell-based therapy for canine inflammatory brain disease

Background

Canine inflammatory brain disease (IBD) is a severe inflammatory disorder characterized by infiltration of activated immune cell subsets into the brain and spinal cord. Multipotent mesenchymal stromal cells (MSCs) are a promising therapy for IBD, based on their potent pro-angiogenic, neuroprotective, and immunomodulatory properties. The aims of this study were to compare the immunomodulatory attributes of canine adipose-derived MSCs (ASCs) and placenta-derived MSCs (PMSCs) in vitro. These data will serve as potency information to help inform the optimal MSC cell source to treat naturally occurring canine IBD.

Methods

Indoleamine 2,3 dioxygenase (IDO) activity and prostaglandin E₂ (PGE₂) concentration at baseline and after stimulation with interferon gamma (IFNγ) and/or tumor necrosis factor alpha (TNFα) were measured from canine ASC and PMSC cultures. Leukocyte suppression assays (LSAs) were performed to compare the ability of ASCs and PMSCs to inhibit activated peripheral blood mononuclear cell (PBMC) proliferation. IDO activity and PGE₂; interleukin (IL)-2, IL-6, and IL-8; TNFα; and vascular endothelial growth factor (VEGF) concentrations were also measured from co-culture supernatants. Cell cycle analysis was performed to determine how ASCs and PMSCs altered lymphocyte proliferation.

Results

Activated canine MSCs from both tissue sources secreted high concentrations of IDO and PGE₂, after direct stimulation with IFNγ and TNFα, or indirect stimulation by activated PBMCs. Both ASCs and PMSCs inhibited activated PBMC proliferation in LSA assays; however, PMSCs inhibited PBMC proliferation significantly more than ASCs. Blocking PGE₂ and IDO in LSA assays determined that PGE₂ is important only for ASC inhibition of PBMC proliferation. Activated ASCs increased IL-6 and VEGF secretion and decreased TNFα secretion, while activated PMSCs increased IL-6, IL-8, and VEGF secretion. ASCs inhibited lymphocyte proliferation via cell cycle arrest in the G0/G1 and PMSCs inhibited lymphocyte proliferation via induction of lymphocyte apoptosis.

Conclusion

Our results demonstrate that ASCs and PMSCs have substantial in vitro potential as a cell-based therapy for IBD; however, PMSCs more potently inhibited lymphocyte proliferation by inducing apoptosis of activated lymphocytes. These data suggest that the mechanism by which ASCs and PMSCs downregulate PBMC proliferation differs. Additional studies may elucidate additional mechanisms by which canine MSCs modulate neuroinflammatory responses.

A Protocol for the Isolation, Culture, and Cryopreservation of Umbilical Cord-Derived Canine Mesenchymal Stromal Cells: Role of Cell Attachment in Long-Term Maintenance

Mesenchymal stromal cells (MSCs) hold great promise in the field of regenerative medicine due to their ability to create a variable localized anti-inflammatory effect in injuries such as Crohn's disease and osteoarthritis or by incorporation in tissue engineered constructs. Currently, the MSC literature uses rodents for preclinical disease models. There is growing interest in using naturally occurring disease in large animals for modeling human disease. By review of the canine MSCs literature, it appears that canine MSCs can be difficult to maintain in culture for extended passages and this greatly varies between tissue sources, compared with human and rodent MSCs, and limited lifespan is an obstacle for preclinical investigation and therapeutic use. Research using canine MSCs has been focused on cells derived from bone marrow or adipose tissue, and the differences in manufacturing MSCs between laboratories are problematic due to lack of standardization. To address these issues, here, a stepwise process was used to optimize canine MSCs isolation, expansion, and cryopreservation utilizing canine umbilical cord-derived MSCs. The culture protocol utilizes coating of tissue culture surfaces that increases cellular adherence, increases colony-forming units-fibroblast efficiency, and decreases population doubling times. Canine MSCs isolated with our protocol could be maintained longer than published canine MSCs methods before senescing. Our improved cryopreservation protocols produce on average >90% viable MSCs at thaw. These methods enable master-bank and working-bank scenarios for allogeneic MSC testing in naturally occurring disease in dogs.

The Potential of Mesenchymal Stem Cells to Treat Systemic Inflammation in Horses

One hallmark of mesenchymal stem cells (MSCs) is the ability to differentiate into multiple tissue types which assists in tissue regeneration. Another hallmark of MSCs is their potent anti-inflammatory and immunomodulatory properties and the potential to treat inflammatory, immune-mediated, and ischemic conditions. In equine practice, MSCs have shown efficacy in the treatment of musculoskeletal disorders such as tendinopathy, meniscal tears and cartilage injury. However, there are many equine disease processes and conditions that may benefit from the immunomodulatory properties of MSCs. Examples include conditions associated with overwhelming acute inflammatory response such as systemic inflammatory response syndrome to chronic diseases characterized by a prolonged low level of inflammation such as equine asthma and recurrent uveitis. For the acute inflammatory response processes, there is often high morbidity and mortality with no effective immunomodulatory treatment to prevent the overwhelming synthesis of proinflammatory mediators. For chronic inflammatory disease processes, frequently long-term corticosteroid treatment is the therapeutic mainstay, with serious potential complications. Thus, there is an unmet need for alternative anti-inflammatory treatments for both acute and chronic illnesses in horses. While MSCs show promise for such conditions, much research is needed before a clinically safe and effective treatment will be available. Optimal MSC tissue source, patient vs. donor source (autologous vs. allogeneic) and cell growth conditions need to be determined for each problem. For immediate use, allogeneic MSC treatments is preferable, but immune tolerance and adequate safety require further study. MSC collection and cryopreservation from horses before they are injured or ill, whether from umbilical cord tissue, bone marrow or adipose might become more widespread. Once these fundamental approaches to treating specific diseases with MSCs are determined, the route of administration, dose and timing of administration also need to be studied. To provide a framework for development of MSC immunomodulatory treatments, this article reviews the current understanding of equine MSC anti-inflammatory and immunomodulatory properties and proposes how MSC therapy may be further developed to treat acute onset systemic inflammatory processes and chronic inflammatory diseases.

Influence of Donor's Age on Immunomodulatory Properties of Canine Adipose Tissue-Derived Mesenchymal Stem Cells

Osteoarthritis challenges traditional therapies and remains a leading cause of lameness in older dogs. Regenerative medicine offers new strategies, typically involving the injection of autologous adipose-derived mesenchymal stem cells (MSCs). Conversely, allogenic MSCs are appealing candidates to palliate patient morbidity and cell preparation time. Regardless of the source of cells, identifying critical donor characteristics, such as age, is essential to obtain the most competent MSCs. The objectives of this study were to determine the influence of donor's age on proliferation, gene expression, and immunomodulatory properties of MSCs in dogs. Canine adipose tissue-derived MSCs (cAD-MSCs) were isolated from the falciform-ligament adipose tissues of nine pairs of gender-matched young (<2 years) or old (>7 years) client-owned dogs undergoing abdominal surgery. Growth kinetics, transcriptome before and after stimulation by tumor necrosis factor alpha and interferon gamma, MSC-induced lymphocyte suppression assay, and secretion of prostaglandin E2 (PGE₂) and indoleamine 2,3-dioxygenase (IDO) were compared between cells obtained from young or old dogs. The doubling times at passages 2 and 3 were shorter when MSCs were isolated from young (34.8 ± 1.8 h and 46.3 ± 2.3 h) rather than old dogs (56.5 ± 8.0 h and 123.8 ± 46.7 h, P < 0.05). The MSC transcriptomes from both populations were similar without stimulation, while stimulation resulted in a 3-fold greater expression of osteogenic gene, fibroblast growth factor 10, in cells from old dogs. cAD-MSCs from young dogs suppressed proliferation of activated T cells more strongly (P < 0.05), although secretion of PGE₂ and IDO did not differ between groups. In conclusion, donors' age affected proliferation, immunomodulatory properties of cAD-MSCs, and increased expression of osteogenic gene under proinflammatory conditions in our population of dogs. Collectively, our results provide evidence to support further evaluation of allogenic MSC therapies derived from young donors as alternatives to autologous MSC therapy in older dogs.

A serum-free medium formulation efficiently supports isolation and propagation of canine adipose-derived mesenchymal stem/stromal cells

Medium containing Fetal Bovine Serum (FBS) provides a supportive environment for isolation and expansion of mesenchymal stromal/stem cells (MSCs); however, the inherent variability of FBS may contribute to inconsistencies in cell growth and yield between batches of stem cell products. For this reason, we set out to develop a serum-free medium capable of supporting the in vitro expansion of MSCs. First a naïve serum-free medium was formulated by Sato's approach. Once it was established that the naïve serum-free medium supported the expansion of canine adipose-derived MSCs (Ad-MSCs), the serum-free medium was optimized by addition of growth factors. Combinations of growth factors were chosen and compared by their effect on cell proliferation and colony formation. Growth characteristics of canine adipose-derived MSCs cultured in the serum-free medium were comparable to those cultured in standard FBS containing medium. In addition, cell surface marker expression and differentiation potential of serum-free and FBS-based cultures were also comparable. However, a commercial serum-free medium developed for human MSC culture did not support growth of canine Ad-MSCs. In summary, canine Ad-MSCs isolated and cultured in serum-free medium retained the basic characteristics of MSCs cultured in FBS containing medium.

Mesenchymal stem cell basic research and applications in dog medicine

The stem cells, owing to their special characteristics like self-renewal, multiplication, homing, immunomodulation, anti-inflammatory, and dedifferentiation are considered to carry an "all-in-one-solution" for diverse clinical problems. However, the limited understanding of cellular physiology currently limits their definitive therapeutic use. Among various stem cell types, currently mesenchymal stem cells are extensively studied for dog clinical applications owing to their readily available sources, easy harvesting, and ability to differentiate both into mesodermal, as well as extramesodermal tissues. The isolated, culture expanded, and characterized cells have been applied both at preclinical as well as clinical settings in dogs with variable but mostly positive results. The results, though positive, are currently inconclusive and demands further intensive research on the properties and their dependence on the applications. Further, numerous clinical conditions of dog resemble to that of human counterparts and thus, if proved rewarding in the former may act as basis of therapy for the latter. The current review throws some light on dog mesenchymal stem cell properties and their potential therapeutic applications.

Extracellular Vesicles from Wharton's Jelly Mesenchymal Stem Cells Suppress CD4 Expressing T Cells Through Transforming Growth Factor Beta and Adenosine Signaling in a Canine Model

Mesenchymal stem cells (MSCs) are widely investigated as potential therapeutic agents due to their potent immunomodulatory capacity. Although specific mechanisms by which MSC acts on immune cells are emerging, many questions remain, including the potential of extracellular vesicles (EVs) to mediate biological activities. Canine MSCs are of interest for both veterinary and comparative models of disease and have been shown to suppress CD4^pos T cell proliferation. The aim of this study was to determine whether EV isolated from canine Wharton's jelly-derived MSC (WJ-MSC EV) suppresses CD4^pos T cell proliferation using biochemical mechanisms previously ascribed to soluble mediators [transforming growth factor beta (TGF-β) and adenosine]. WJ-MSC EV exhibited mode of 125 nm diameter, low buoyant density (1.1 g/mL), and expression of EV proteins Alix and TSG101. Functionally, EVs inhibited CD4^pos T cell proliferation in a dose-dependent manner, which was absent in EV-depleted samples and EVs from non-MSC fibroblasts. EV suppression of CD4^pos T cell proliferation was inhibited by a TGF-βRI antagonist, neutralizing antibodies to TGF-β, or A2A adenosine receptor blockade. TGF-β was present on EVs as latent complexes most likely tethered to EV membrane by betaglycan. These data demonstrate that canine WJ-MSC EV utilizes TGF-β and adenosine signaling to suppress proliferation of CD4^pos T cell and will enable further investigation into mechanisms of immune cell modulation, as well as refinement of WJ-MSC and their EVs for therapeutic application.

Equine Mesenchymal Stem Cells: Properties, Sources, Characterization, and Potential Therapeutic Applications

Properties like sustained multiplication and self-renewal, and homing and multilineage differentiation to undertake repair of the damaged tissues make stem cells the lifeline for any living system. Therefore, stem cell therapy is regarded to carry immense therapeutic potential. Though the dearth of understanding about the basic biological properties and pathways involved in therapeutic benefits currently limit the application of stem cells in humans as well as animals, there are innumerable reports that suggest clinical benefits of stem cell therapy in equine. Among various stem cell sources, currently adult mesenchymal stem cells (MSCs) are preferred for therapeutic application in horse owing to their easy availability, capacity to modulate inflammation, and promote healing. Also the cells carry very limited teratogenic risk compared to the pluripotent stem cells. Mesenchymal stem cells were earlier considered mainly for musculoskeletal tissues, but now may also be utilized in other diverse clinical problems in horse, and the results may be extrapolated even for human medicine. The current review highlights biological properties, sources, mechanisms, and potential therapeutic applications of stem cells in equine practice.

Practical considerations for clinical use of mesenchymal stem cells: From the laboratory to the horse

Since the clinical use of mesenchymal stem cells (MSCs) for treating musculoskeletal injuries is gaining popularity, practitioners should be aware of the factors that may affect MSCs from tissue harvesting for MSC isolation to cell delivery into the injury site. This review provides equine practitioners with up-to-date, practical knowledge for the treatment of equine patients using MSCs. A brief overview of laboratory procedures affecting MSCs is provided, but the main focus is on shipping conditions, routes of administration, injection methods, and which commonly used products can be combined with MSCs and which products should be avoided as they have deleterious effects on cells. There are still several knowledge gaps regarding MSC-based therapies in horses. Therefore, it is important to properly manage the factors which are currently known to affect MSCs, to further strengthen the evidence basis of this treatment.

Cell-Based Therapies for Joint Disease in Veterinary Medicine: What We Have Learned and What We Need to Know

Biological cell-based therapies for the treatment of joint disease in veterinary patients include autologous-conditioned serum, platelet-rich plasma, and expanded or non-expanded mesenchymal stem cell products. This narrative review outlines the processing and known mechanism of action of these therapies and reviews current preclinical and clinical efficacy in joint disease in the context of the processing type and study design. The significance of variation for biological activity and consequently regulatory approval is also discussed. There is significant variation in study outcomes for canine and equine cell-based products derived from whole blood or stem cell sources such as adipose and bone marrow. Variation can be attributed to altering bio-composition due to factors including preparation technique and source. In addition, study design factors like selection of cases with early vs. late stage osteoarthritis (OA), or with intra-articular soft tissue injury, influence outcome variation. In this under-regulated field, variation raises concerns for product safety, consistency, and efficacy. Cell-based therapies used for OA meet the Food and Drug Administration’s (FDA’s) definition of a drug; however, researchers must consider their approach to veterinary cell-based research to meet future regulatory demands. This review explains the USA’s FDA guidelines as an example pathway for cell-based therapies to demonstrate safety, effectiveness, and manufacturing consistency. An understanding of the variation in production consistency, effectiveness, and regulatory concerns is essential for practitioners and researchers to determine what products are indicated for the treatment of joint disease and tactics to improve the quality of future research.

Platelet lysate as a novel serum-free media supplement for the culture of equine bone marrow-derived mesenchymal stem cells

Background

Mesenchymal stem cells (MSCs) produced for clinical purposes rely on culture media containing fetal bovine serum (FBS) which is xenogeneic and has the potential to significantly alter the MSC phenotype, rendering these cells immunogenic. As a result of bovine-derived exogenous proteins expressed on the cell surface, MSCs may be recognized by the host immune system as non-self and be rejected. Platelet lysate (PL) may obviate some of these concerns and shows promising results in human medicine as a possible alternative to FBS. Our goal was to evaluate the use of equine platelet lysate (ePL) pooled from donor horses in place of FBS to culture equine MSCs. We hypothesized that ePL, produced following apheresis, will function as the sole media supplement to accelerate the expansion of equine bone marrow-derived MSCs without altering their phenotype and their immunomodulatory capacity.

Methods

Platelet concentrate was obtained via plateletpheresis and ePL were produced via freeze-thaw and centrifugation cycles. Population doublings (PD) and doubling time (DT) of bone marrow-derived MSCs (n = 3) cultured with FBS or ePL media were calculated. Cell viability, immunophenotypic analysis, and trilineage differentiation capacity of MSCs were assessed accordingly. To assess the ability of MSCs to modulate inflammatory responses, E. coli lipopolysaccharide (LPS)-stimulated monocytes were cocultured with MSCs cultured in the two different media formulations, and cell culture supernatants were assayed for the production of tumor necrosis factor (TNF)-α.

Results

Our results showed that MSCs cultured in ePL media exhibited similar proliferation rates (PD and DT) compared with those cultured in FBS at individual time points. MSCs cultured in ePL showed a statistically significant increased viability following a single washing step, expressed similar levels of MSC markers compared to FBS, and were able to differentiate towards the three lineages. Finally, MSCs cultured in ePL efficiently suppressed the release of TNF-α when exposed to LPS-stimulated monocytes similar to those cultured in FBS.

Conclusion

ePL has the potential to be used for the expansion of MSCs before clinical application, avoiding the concerns associated with the use of FBS.

Serum-free human MSC medium supports consistency in human but not in equine adipose-derived multipotent mesenchymal stromal cell culture

For clinical applications of multipotent mesenchymal stromal cells (MSCs), serum-free culture is preferable to standardize cell products and prevent contamination with pathogens. In contrast to human MSCs, knowledge on serum-free culture of large animal MSCs is limited, despite its relevance for preclinical studies and development of veterinary cellular therapeutics. This study aimed to evaluate the suitability of a commercially available serum-free human MSC medium for culturing equine adipose-derived MSCs in comparison with human adipose MSCs. Enzyme-free isolation by explant technique and expansion of equine and human cells in the serum-free medium were feasible. However, serum-free culture altered the morphology and complicated handling of equine MSCs, with cell aggregation and spontaneous detachment of multilayers, compared to culture in standard medium supplemented with fetal bovine serum. Furthermore, proliferation and the surface immunophenotype of equine cells were more variable compared to the controls and appeared to depend on the lot of the serum-free medium. Particularly the expression of CD90 was different between experimental groups (P < 0.05), with lower percentages of CD90⁺ cells found in equine MSC samples cultured in serum-free medium (5.21-83.40%) compared to standard medium (86.20-99.50%). Additionally, small subpopulations expressing MSC exclusion markers such as CD14 (0.28-11.60%), CD34 (0.00-9.87%), CD45 (0.35-10.50%), or MHCII (0.00-3.67%) were found in equine samples after serum-free culture. In contrast, human samples displayed a more consistent morphology and a consistent CD29⁺ (98.60-99.90%), CD73⁺ (94.60-98.40%), CD90⁺ (99.60-99.90%), and CD105⁺ (97.40-99.80%) immunophenotype after culture in serum-free medium. The obtained data demonstrate that the serum-free medium was suitable for human MSC culture but did not lead to entirely satisfactory results in equine MSCs. This underlines that requirements regarding serum-free culture conditions are species-specific, indicating a need for serum-free media to be optimized for MSCs from relevant animal species. © 2017 International Society for Advancement of Cytometry.

Effects of a defined xeno-free medium on the growth and neurotrophic and angiogenic properties of human adult stem cells

BACKGROUND

The growth properties and neurotrophic and angiogenic effects of human mesenchymal stromal cells (MSCs) cultured in a defined xeno-free, serum-free medium (MesenCult-XF) were investigated.

METHODS

Human MSCs from adipose tissue (ASCs) and bone marrow (BMSCs) were cultured in Minimum Essential Medium-alpha (α-MEM) containing fetal calf serum or in MesenCult-XF. Proliferation was measured over 10 passages and the colony-forming unit (CFU) assay and expression of cluster of differentiation (CD) surface markers were determined. Neurite outgrowth and angiogenic activity of the MSCs were determined.

RESULTS

At early passage, both ASCs and BMSCs showed better proliferation in MesenCult-XF compared with standard α-MEM-containing serum. However, CFUs were significantly lower in MesenCult-XF. ASCs cultured in MesenCult-XF continued to expand at faster rates than cells grown in serum. BMSCs showed morphological changes at late passage in MesenCult-XF and stained positive for senescence β-galactosidase activity. Expression levels of CD73 and CD90 were similar in both cell types under the various culture conditions but CD105 was significantly reduced at passage 10 in MesenCult-XF. In vitro stimulation of the cells enhanced the expression of brain-derived neurotrophic factor (BDNF), vascular endothelial growth factor (VEGF-A) and angiopoietin-1. Stimulated ASCs grown in MesenCult-XF evoked the longest neurite outgrowth in a neuron co-culture model. Stimulated BMSCs grown in MesenCult-XF produced the most extensive network of capillary-like tube structures in an in vitro angiogenesis assay.

CONCLUSIONS

ASCs and BMSCs exhibit high levels of neurotrophic and angiogenic activity when grown in the defined serum-free medium indicating their suitability for treatment of various neurological conditions. However, long-term expansion in MesenCult-XF might be restricted to ASCs.

Human and feline adipose-derived mesenchymal stem cells have comparable phenotype, immunomodulatory functions, and transcriptome

Background

Adipose-derived mesenchymal stem cells (ASCs) are a promising cell therapy to treat inflammatory and immune-mediated diseases. Development of appropriate pre-clinical animal models is critical to determine safety and attain early efficacy data for the most promising therapeutic candidates. Naturally occurring diseases in cats already serve as valuable models to inform human clinical trials in oncologic, cardiovascular, and genetic diseases. The objective of this study was to complete a comprehensive side-by-side comparison of human and feline ASCs, with an emphasis on their immunomodulatory capacity and transcriptome.

Methods

Human and feline ASCs were evaluated for phenotype, immunomodulatory profile, and transcriptome. Additionally, transwells were used to determine the role of cell-cell contact in ASC-mediated inhibition of lymphocyte proliferation in both humans and cats.

Results

Similar to human ASCs, feline ASCs were highly proliferative at low passages and fit the minimal criteria of multipotent stem cells including a compatible surface protein phenotype, osteogenic capacity, and normal karyotype. Like ASCs from all species, feline ASCs inhibited mitogen-activated lymphocyte proliferation in vitro, with or without direct ASC-lymphocyte contact. Feline ASCs mimic human ASCs in their mediator secretion pattern, including prostaglandin E2, indoleamine 2,3 dioxygenase, transforming growth factor beta, and interleukin-6, all augmented by interferon gamma secretion by lymphocytes. The transcriptome of three unactivated feline ASC lines were highly similar. Functional analysis of the most highly expressed genes highlighted processes including: 1) the regulation of apoptosis; 2) cell adhesion; 3) response to oxidative stress; and 4) regulation of cell differentiation. Finally, feline ASCs had a similar gene expression profile to noninduced human ASCs.

Conclusions

Findings suggest that feline ASCs modulate lymphocyte proliferation using soluble mediators that mirror the human ASC secretion pattern. Uninduced feline ASCs have similar gene expression profiles to uninduced human ASCs, as revealed by transcriptome analysis. These data will help inform clinical trials using cats with naturally occurring diseases as surrogate models for human clinical trials in the regenerative medicine arena.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0528-z) contains supplementary material, which is available to authorized users.

Mechanisms of Immune Suppression Utilized by Canine Adipose and Bone Marrow-Derived Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) from rodents and humans have been shown to suppress T cells by distinct primary pathways, with nitric oxide (NO)-dependent pathways dominating in rodents and indoleamine 2,3-deoxygenase (IDO)-dependent pathways dominating in humans. However, the immune suppressive pathways utilized by canine MSC have not been thoroughly studied, nor have bone marrow-derived MSC (BM-MSC) and adipose-derived MSC (Ad-MSC) been directly compared for their immune modulatory potency or pathway utilization. Therefore, canine BM-MSC and Ad-MSC were generated in vitro and their potency in suppressing T cell proliferation and cytokine production was compared, and differential gene expression. Mechanisms of T cells suppression were also investigated for both MSC types. We found that BM-MSC and Ad-MSC were roughly equivalent in terms of their ability to suppress T cell activation. However, the two MSC types used both shared and distinct biochemical pathways to suppress T cell activation. Ad-MSC utilized TGF-β signaling pathways and adenosine signaling to suppress T cell activation, whereas BM-MSC used cyclooxygenase, TGF-β and adenosine signaling pathways to suppress T cell activation. These results indicate that canine MSC are distinct from human and rodent MSC terms of their immune suppressive pathways, relying primarily on cyclooxygenase and TGF-β pathways for T cell suppression, rather than on NO or IDO-mediated pathways.

External factors influencing mesenchymal stem cell fate in vitro

Mesenchymal stem cells (MSCs) have extensive potentials, which make them attractive candidates for the developmental biology, drug discovery and regenerative medicine. However, the use of MSCs is limited by their scarceness in tissues and in culture conditions. They also exhibit various degrees of potency which subsequently influencing their applications. Nowadays, questions remain about how self-renewal and differentiation of MSCs can be controlled in vitro and in vivo, how they will behave and migrate to the right place and how they modulate the immune system. Therefore, identification of factors and culture conditions to affect the fate and function of MSCs may be effective to enhance their applications in clinical situations. Studies have indicated that the fate of MSCs in culture is influenced by various external factors, including the specific cell source, donor age, plating density, passage number and plastic surface quality. Some other factors such as cell culture media and their supplementary factors, O₂ concentration, mechano-/electro-stimuli and three-dimensional scaffolds are also shown to be influential. This review addresses the current state of MSC research for describing and discussing the findings about external factors that influence the fate and function of MSCs. Additionally, the new discoveries and suggestions regarding their molecular mechanisms will be explained.

A new clinical-scale serum-free xeno-free medium efficient in ex vivo amplification of mesenchymal stromal cells does not support mesenchymal stem cells

BACKGROUND

We evaluated a new serum-free, xeno-free medium (Xuri, GE HealthCare) in ex vivo cultures for amplification of mesenchymal stromal cells (MStroC) in comparison with classical culture supplemented with fetal calf serum and basic fibroblast growth factor.

STUDY DESIGN AND METHODS

MStroC and mesenchymal stem cell (MSC) proliferative capacities were studied in bulk cultures and single-cell cultures with assay of secondary replating capacity of individual clones. Flow-cytometric phenotype analysis and proliferative history analysis were also performed.

RESULTS

In cultures initiated with previously amplified and cryopreserved MStroC from human marrow, Xuri medium enabled a total cell expansion fold comparable to one obtained in control fetal calf serum (FCS)-supplemented culture. However, both the number and the proliferative capacity of colony-forming unit-fibroblast were greatly reduced in Xuri medium cultures. This is even more evident in single-cell cultures, where, in rare positive wells, only several cells were found in Xuri cultures, compared to abundant cell content in FCS and α-minimal essential medium cultures. Replating these single-cell clones in secondary cultures (FCS in both cases) revealed a total exhaustion of MSC proliferative capacity after Xuri primary culture.

CONCLUSION

Since in both conditions after a 7-day bulk culture, similar immunophenotype and proliferative history were found when the standard MSC immunophenotype panel was employed, the loss of proliferative capacity in Xuri medium shows that it cannot maintain functional MSC population. This is a drastic example showing that the real MSC activity can be completely unrelated to the immunophenotype considered as MSC phenotype.

Canine mesenchymal stem cells are neurotrophic and angiogenic: An in vitro assessment of their paracrine activity

Mesenchymal stem cells (MSCs) have been used in cell replacement therapies for connective tissue damage, but also can stimulate wound healing through paracrine activity. In order to further understand the potential use of MSCs to treat dogs with neurological disorders, this study examined the paracrine action of adipose-derived canine MSCs on neuronal and endothelial cell models. The culture-expanded MSCs exhibited a MSC phenotype according to plastic adherence, cell morphology, CD profiling and differentiation potential along mesenchymal lineages. Treating the SH-SY5Y neuronal cell line with serum-free MSC culture-conditioned medium (MSC CM) significantly increased SH-SY5Y cell proliferation (P <0.01), neurite outgrowth (P = 0.0055) and immunopositivity for the neuronal marker βIII-tubulin (P = 0.0002). Treatment of the EA.hy926 endothelial cell line with MSC CM significantly increased the rate of wound closure in endothelial cell scratch wound assays (P = 0.0409), which was associated with significantly increased endothelial cell proliferation (P <0.05) and migration (P = 0.0001). Furthermore, canine MSC CM induced endothelial tubule formation in EA.hy926 cells in a soluble basement membrane matrix. Hence, this study has demonstrated that adipose-derived canine MSC CM stimulated neuronal and endothelial cells probably through the paracrine activity of MSC-secreted factors. This supports the use of canine MSC transplants or their secreted products in the clinical treatment of dogs with neurological disorders and provides some insight into possible mechanisms of action.

Allogeneic Mesenchymal Stem Cell Treatment Induces Specific Alloantibodies in Horses

Background. It is unknown whether horses that receive allogeneic mesenchymal stem cells (MSCs) injections develop specific humoral immune response. Our goal was to develop and validate a flow cytometric MSC crossmatch procedure and to determine if horses that received allogeneic MSCs in a clinical setting developed measurable antibodies following MSC administration. Methods. Serum was collected from a total of 19 horses enrolled in 3 different research projects. Horses in the 3 studies all received unmatched allogeneic MSCs. Bone marrow (BM) or adipose tissue derived MSCs (ad-MSCs) were administered via intravenous, intra-arterial, intratendon, or intraocular routes. Anti-MSCs and anti-bovine serum albumin antibodies were detected via flow cytometry and ELISA, respectively. Results. Overall, anti-MSC antibodies were detected in 37% of the horses. The majority of horses (89%) were positive for anti-bovine serum albumin (BSA) antibodies prior to and after MSC injection. Finally, there was no correlation between the amount of anti-BSA antibody and the development of anti-MSC antibodies. Conclusion. Anti allo-MSC antibody development was common; however, the significance of these antibodies is unknown. There was no correlation between either the presence or absence of antibodies and the percent antibody binding to MSCs and any adverse reaction to a MSC injection.

Th17 Pathway As a Target for Multipotent Stromal Cell Therapy in Dogs: Implications for Translational Research

Detrimental Th17 driven inflammatory and autoimmune disease such as Crohn's disease, graft versus host disease and multiple sclerosis remain a significant cause of morbidity and mortality worldwide. Multipotent stromal/stem cell (MSC) inhibit Th17 polarization and activation in vitro and in rodent models. As such, MSC based therapeutic approaches are being investigated as novel therapeutic approaches to treat Th17 driven diseases in humans. The significance of naturally occurring diseases in dogs is increasingly recognized as a realistic platform to conduct pre-clinical testing of novel therapeutics. Full characterization of Th17 cells in dogs has not been completed. We have developed and validated a flow-cytometric method to detect Th17 cells in canine blood. We further demonstrate that Th17 and other IL17 producing cells are present in tissues of dogs with naturally occurring chronic inflammatory diseases. Finally, we have determined the kinetics of a canine specific Th17 polarization in vitro and demonstrate that canine MSC inhibit Th17 polarization in vitro, in a PGE2 independent mechanism. Our findings provide fundamental research tools and suggest that naturally occurring diseases in dogs, such as inflammatory bowel disease, may be harnessed to translate novel MSC based therapeutic strategies that target the Th17 pathway.