Clinical update on the use of mesenchymal stem cells in equine orthopaedics

Safety assessment of equine allogeneic tenogenic primed mesenchymal stem cells in horses with naturally occurring tendon and ligament injuries

Background

Mesenchymal stem cells provide a valuable treatment option in orthopedic injuries in horses.

Objectives

The aim of this study was to evaluate the hematological, biochemical, immunological and immunomodulatory parameters following intralesional treatment with tenogenic primed equine allogeneic peripheral blood-derived mesenchymal stem cells (tpMSCs) in client-owned horses with naturally occurring superficial digital flexor tendon (SDFT) and suspensory ligament (SL) injuries.

Methods

The immunogenicity and immunomodulatory capacities of tpMSCs were assessed in a modified mixed lymphocyte reaction, including peripheral blood mononuclear cells (PBMCs) of 14 horses with SDFT and SL injuries after treatment with tpMSCs. In a second study, 18 horses with SDFT and SL injuries received either an intralesional injection with tpMSCs (n = 9) or no treatment (n = 9).

Results

The tpMSCs did not provoke a cellular immune response (p < 0.001) and were able to immunomodulate stimulated T lymphocytes (p < 0.001) in vitro. Therapeutic use of tpMSCs did not result in relevant hematologic or biochemical abnormalities.

Main limitations

Both studies had a small sample size. No statistical analyses were performed in the second study. Fibrinogen was only analyzed in a single horse prior to treatment.

Conclusion

Co-incubation of tpMSCs and PBMCs of horses that have been previously exposed to tpMSCs did not elicit a cellular immune response and tpMSCs were able to immunomodulate stimulated T lymphocytes. Intralesional treatment with tpMSCs did not provoke abnormal changes in hematological and biochemical parameters.

Addition of synthetic polymer in the freezing solution of mesenchymal stem cells from equine adipose tissue as a future perspective for reducing of DMSO concentration

The regenerative therapies with stem cells (SC) has been increased by the cryopreservation, permitting cell storage for extended periods. However, the permeating cryoprotectant agents (CPAs) such as dimethylsulfoxide (DMSO) can cause severe adverse effects. Therefore, this study evaluated equine mesenchymal stem cells derived from adipose tissue (eAT-MSCs) in fresh (Control) or after slow freezing (SF) in different freezing solutions (FS). The FS comprise DMSO and non-permeating CPAs [Trehalose (T) and the SuperCool X-1000 (X)] in association or not, totalizing seven different FS: (DMSO; T; X; DMSO+T; DMSO+X; T+X, and DMSO+T+X). Before and after cryopreservation were evaluated, viability, colony forming unit (CFU), and cellular differentiation capacity. After freezing-thawing, the viability of the eAT-MSCs reduced (P< 0.05) in all treatments compared to the control. However, the viability of frozen eAT-MSCs in DMSO (80.3 ± 0.6) was superior (P<0.05) to the other FS. Regarding CFU, no difference (P>0.05) was observed between fresh and frozen cells. After freezing-thawing, the eAT-MSCs showed osteogenic, chondrogenic, and adipogenic lineages differentiation potential. Nonetheless, despite the significative reduction in the osteogenic differentiation capacity between fresh and frozen cells, no differences (P > 0.05) were observed among FS. Furthermore, the number of chondrogenic differentiation cells frozen in DMSO+X solution reduced (P<0.05) comparing to the control, without differ (P>0.05) to the other FS. The adipogenic differentiation did not differ (P>0.05) among treatments. In conclusion, although these findings confirm the success of DMSO to cryopreserve eAT-MSCs, the Super Cool X-1000 could be a promise to reduce the DMSO concentration in a FS.

Regenerative Medicine Applied to Musculoskeletal Diseases in Equines: A Systematic Review

Musculoskeletal injuries in horses have a great economic impact, predominantly affecting tendons, ligaments, and cartilage, which have limited natural regeneration. Cell therapy, which uses mesenchymal stem cells due to their tissue differentiation properties and anti-inflammatory and immunoregulatory effects, aims to restore damaged tissue. In this manuscript, we performed a systematic review using the Parsifal tool, searching the PubMed and Web of Science databases for articles on regenerative medicine for equine musculoskeletal injuries. Our review covers 17 experimental clinical studies categorized by the therapeutic approach used: platelet-rich plasma, conditioned autologous serum, mesenchymal stem cells, and secretome. These therapies reduce healing time, promote regeneration of fibrocartilaginous tissue, improve cellular organization, and improve joint functionality and sustainability. In conclusion, regenerative therapies using platelet-rich plasma, conditioned autologous serum, equine mesenchymal stem cells, and the emerging field of the secretome represent a promising and highly effective approach for the treatment of joint pathologies in horses, implying a valuable advance in equine healthcare.

Treatment of racehorse superficial digital flexor tendonitis: A comparison of stem cell treatments to controlled exercise rehabilitation in 213 cases

BACKGROUND

Overstrain of the superficial digital flexor tendon (SDFT) is a common Thoroughbred racehorse limb injury requiring treatment.

OBJECTIVES

To determine whether treatment of SDFT lesions in flat Thoroughbred racehorses with autologous bone marrow-derived mesenchymal stem cells (BM-MSCs) or allogenic adipose-derived mesenchymal stem cells (A-MSCs) is associated with improved likelihood of returning to racing, when compared to racehorses managed with a controlled exercise rehabilitation program (CERP) alone.

STUDY DESIGN

Retrospective cohort study combining clinical treatment records with race records.

METHODS

A total of 213 Thoroughbred racehorses were identified. All were prescribed the same 12-month CERP and 66 also received intralesional BM-MSC and 17 A-MSC treatment. Follow-up was a minimum of 2 years after return to full race training. Multivariable logistic regression models were used to investigate associations between the treatments and the likelihood of returning to racing and completing five or more (C5+) races post-injury.

RESULTS

Compared to CERP alone, BM-MSC treatment was associated with increased odds of returning to racing (OR 3.19; 95% CI 1.55-6.81) and C5+ races post-injury (OR 2.64; 95% CI 1.32-5.33). Older age and increasing lesion length were associated with a reduced likelihood of returning to racing. Male sex and increased number of pre-injury starts were associated with increased odds of returning to racing. There was no observed increased likelihood of return to racing or C5+ races associated with treatment with A-MSCs compared to CERP alone.

MAIN LIMITATIONS

Due to the retrospective nature of the study it was not possible to ascertain how strictly the CERP was followed. Due to the novelty of the method, the A-MSC treatment group included a limited number of horses.

CONCLUSIONS

In the study population, intralesional BM-MSC treatment was significantly associated with an increased likelihood of returning to racing and C5+ races post-injury compared to CERP alone. Intralesional A-MSC showed no significant association between treatment and the two investigated outcomes.

Contrast administration via ultrasound-guided injection of the cranial tibial artery results in contrast enhancement of the soft tissues of the metatarsus in horses undergoing CT

Delivery of mesenchymal stem cells (MSC) via intravascular techniques to treat diffuse and/or inaccessible soft tissue injuries has grown in popularity. The purpose of the current prospective, analytical pilot study was to utilize CT to validate this novel technique and provide additional evidence to support its use for injectate delivery to specific soft tissue structures. Of particular interest was the proximal suspensory ligament, which presents a challenging injection target. Six adult horses without lameness underwent CT of the distal hindlimbs. Scans were obtained prior to ultrasound-guided catheterization of the cranial tibial artery, in addition to early and delayed scans acquired following intra-arterial contrast administration. Region of interest analysis of the superficial and deep digital flexor tendons and suspensory ligament was used to assess contrast enhancement within these structures. Linear mixed models were used to determine statistical significance. Significant (P < 0.05) mean contrast enhancement was seen in all postinjection time points in all soft tissue structures of interest. This indicates that ultrasound-guided injection of the cranial tibial artery results in perfusion of injectate throughout the distal hind limb, including the major soft tissue structures of the metatarsus. This provides further support for this technique as a method of MSC delivery to multifocal or inaccessible injury of these structures, including the proximal suspensory ligament.

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.

Donor age effects on in vitro chondrogenic and osteogenic differentiation performance of equine bone marrow- and adipose tissue-derived mesenchymal stromal cells

BACKGROUND

Bone marrow (BM)- and adipose tissue (AT)-derived mesenchymal stromal cells (MSCs) have shown potential as cell-based therapies for cartilage and bone injuries and are used increasingly in human and veterinary practice to facilitate the treatment of orthopedic conditions. However, human and rodent studies have documented a sharp decline in chondrogenic and osteogenic differentiation potential with increasing donor age, which may be problematic for the important demographic of older orthopedic patients. The aim of this study was to identify the effect of donor age on the chondrogenic and osteogenic differentiation performance of equine BM- and AT-MSCs in vitro. BM- and AT-MSCs and dermal fibroblasts (biological negative control) were harvested from horses in five different age groups (n = 4, N = 60); newborn (0 days), yearling (15-17 months), adult (5-8 years), middle-aged (12-18 years), and geriatric (≥ 22 years). Chondrogenic differentiation performance was assessed quantitatively by measuring pellet size, matrix proteoglycan levels, and gene expression of articular cartilage biomarkers. Osteogenic differentiation performance was assessed quantitatively by measuring alkaline phosphatase activity, calcium deposition, and gene expression of bone biomarkers.

RESULTS

Chondrogenic and osteogenic differentiation performance of equine BM- and AT-MSCs declined with increasing donor age. BM-MSCs had a higher chondrogenic differentiation performance. AT-MSCs showed minimal chondrogenic differentiation performance in all age groups. For osteogenesis, alkaline phosphatase activity was also higher in BM-MSCs, but BM-MSCs calcium deposition was affected by donor age earlier than AT-MSCs. Chondrogenic and osteogenic differentiation performance of BM-MSCs exhibited a decline as early as between the newborn and yearling samples. Steady state levels of mRNA encoding growth factors, chondrogenic, and osteogenic biomarkers were lower with increasing donor age in both MSC types.

CONCLUSIONS

The data showed that chondrogenic and osteogenic differentiation performance of equine BM-MSCs declined already in yearlings, and that AT-MSCs showed minimal chondrogenic potential, but were affected later by donor age with regards to osteogenesis (calcium deposition). The results highlight the importance of donor age considerations and MSC selection for cell-based treatment of orthopedic injuries and will help inform clinicians on when to implement or potentially cryopreserve cells. Moreover, the study provides molecular targets affected by donor age.

The Role of Mesenchymal Stem Cells (MSCs) in Veterinary Medicine and Their Use in Musculoskeletal Disorders

Regenerative medicine is a dynamically developing field of human and veterinary medicine. The animal model was most commonly used for mesenchymal stem cells (MSCs) treatment in experimental and preclinical studies with a satisfactory therapeutic effect. Year by year, the need for alternative treatments in veterinary medicine is increasing, and other applications for promising MSCs and their biological derivatives are constantly being sought. There is also an increase in demand for other methods of treating disease states, of which the classical treatment methods did not bring the desired results. Cell therapy can be a realistic option for treating human and animal diseases in the near future and therefore additional research is needed to optimize cell origins, numbers, or application methods in order to standardize the treatment process and assess its effects. The aim of the following work was to summarize available knowledge about stem cells in veterinary medicine and their possible application in the treatment of chosen musculoskeletal disorders in dogs and horses.

Chondrogenic potential of mesenchymal stem cells from horses using a magnetic 3D cell culture system

BACKGROUND

Mesenchymal stem cells (MSCs) represent a promising therapy for the treatment of equine joint diseases, studied due to their possible immunomodulatory characteristics and regenerative capacity. However, the source of most suitable MSCs for producing cartilage for regenerative processes in conjunction with biomaterials for an enhanced function is yet to be established.

AIM

To compare the chondrogenicity of MSCs derived from synovial fluid, bone marrow, and adipose tissue of horses, using the aggrecan synthesis.

METHODS

MSCs from ten horses were cultured, phenotypic characterization was done with antibodies CD90, CD44 and CD34 and were differentiated into chondrocytes. The 3D cell culture system in which biocompatible nanoparticles consisting of gold, iron oxide, and poly-L-lysine were added to the cells, and they were forced by magnets to form one microspheroid. The microspheroids were exposed to a commercial culture medium for 4 d, 7 d, 14 d, and 21 d. Proteoglycan extraction was performed, and aggrecan was quantified by enzyme-linked immunosorbent assay. Keratan sulfate and aggrecan in the microspheroids were identified and localized by immunofluorescence.

RESULTS

All cultured cells showed fibroblast-like appearance, the ability to adhere to the plastic surface, and were positive for CD44 and CD90, thus confirming the characteristics and morphology of MSCs. The soluble protein concentrations were higher in the microspheroids derived from adipose tissue. The aggrecan concentration and the ratio of aggrecan to soluble proteins were higher in microspheroids derived from synovial fluid than in those derived from bone marrow, thereby showing chondrogenic superiority. Microspheroids from all sources expressed aggrecan and keratan sulfate when observed using confocal immunofluorescence microscopy. All sources of MSCs can synthesize aggrecan, however, MSCs from synovial fluid and adipose tissue have demonstrated better biocompatibility in a 3D environment, thus suggesting chondrogenic superiority.

CONCLUSION

All sources of MSCs produce hyaline cartilage; however, the use of synovial liquid or adipose tissue should be recommended when it is intended for use with biomaterials or scaffolds.

Interactions Between Allogeneic Mesenchymal Stromal Cells and the Recipient Immune System: A Comparative Review With Relevance to Equine Outcomes

Despite significant immunosuppressive activity, allogeneic mesenchymal stromal cells (MSCs) carry an inherent risk of immune rejection when transferred into a recipient. In naïve recipients, this immune response is initially driven by the innate immune system, an immediate reaction to the foreign cells, and later, the adaptive immune system, a delayed response that causes cell death due to recognition of specific alloantigens by host cells and antibodies. This review describes the actions of MSCs to both suppress and activate the different arms of the immune system. We then review the survival and effectiveness of the currently used allogeneic MSC treatments.

Cellular Proliferation of Equine Bone Marrow- and Adipose Tissue-Derived Mesenchymal Stem Cells Decline With Increasing Donor Age

Background: Bone marrow (BM)- and adipose tissue (AT)-derived mesenchymal stem cells (MSCs) are used increasingly for autologous cell therapy in equine practice to treat musculoskeletal and other injuries. Current recommendations often call for 10–100 million MSCs per treatment, necessitating the expansion of primary cells in culture prior to therapeutic use. Of concern, human and rodent studies have shown a decline of both MSC recovery from sampled tissue and in vitro proliferative capacity with increasing donor age. This may be problematic for applications of autologous cell-based therapies in the important equine demographic of older patients.

Objectives: To investigate the effect of donor age on the cellular proliferation of equine BM- and AT-MSCs.

Study Design:In vitro study.

Methods: BM- and AT-MSCs and dermal fibroblasts (biological control) were harvested from horses in five different age groups (n = 4, N = 60); newborn (0 days), yearling (15–17 months), adult (5–8 years), middle-aged (12–18 years), and geriatric (≥22 years). Proliferation of the cells was tested using an EdU incorporation assay and steady state mRNA levels measured for targeted proliferation, aging, and senescence biomarkers.

Results: The cellular proliferation of equine BM- and AT-MSCs declined significantly in the geriatric cohort relative to the younger age groups. Proliferation levels in the two MSC types were equally affected by donor age. Analysis of steady state mRNA levels showed an up-regulation in tumor suppressors, apoptotic genes, and multiple growth factors in MSCs from old horses, and a down-regulation of some pro-cycling genes with a few differences between cell types.

Main Limitations: Potential age-dependent differences in cell function parameters relevant to cell-therapy application were not investigated.

Conclusions: The cellular proliferation of equine BM- and AT-MSCs declined at advanced donor ages. High levels of in vitro proliferation were observed in both MSC types from horses in the age groups below 18 years of age.

Triiodothyronine Has No Enhancement Effect on the Osteogenic or Chondrogenic Differentiation of Equine Adipose Tissue Stem Cells

The effects of two concentrations of triiodothyronine (T3; 0.01 and 1,000 nM) on the osteogenic and chondrogenic differentiation abilities of equine adipose-derived mesenchymal stem cells (AD-MSCs) were evaluated. The osteogenic study evaluated the effect of T3 using alkaline phosphatase activity (ALP) assay; cell viability and density; and formation of mineralized nodules at Days 7, 14, and 21 in culture. The chondrogenic study tested the effect of T3 through ALP assay, mitochondrial metabolism, cell density, and periodic acid-Schiff-positive (PAS+) matrix percentage at Days 7 and 14. In both experiments, analysis of variance was used to compare averages through the Student-Newman-Keuls test. In the osteogenic study, no differences in any variable were detected between groups at Day 7. At Day 14, 0.01 nM T3 reduced cell density and the number of mineralized nodules despite the increase in ALP activity and mitochondrial metabolism (P < .05). ALP activity increased at 1,000 nM T3 concentration (P < .05). At Day 21, 0.01 nM T3 treatment increased ALP activity compared with control treatment (P < .05). At 1,000 nM concentration, T3 reduced mitochondrial metabolism and cell density (P < .05). In the chondrogenic study, the two T3 concentrations increased cell density compared with control treatment at Day 7. At Day 14, higher T3 concentration reduced mitochondrial metabolism, ALP activity, cell density, and PAS+ chondrogenic matrix percentage compared with control treatment (P < .05). Thus, T3 addition to equine AD-MSC cultures has no enhancement effect on osteogenic or chondrogenic differentiation and may, in fact, negatively affect cell density and matrix synthesis depending on hormone concentration and culture time.

Equine adipose mesenchymal stem cells (eq-ASCs) appear to have higher potential for migration and musculoskeletal differentiation

Equine adipose-derived mesenchymal stem cells (eq-ASCs) possess excellent regeneration potential especially for treatment of musculoskeletal disorders. Besides their common characteristics, MSCs harvested from different species reveal some species-specific and donor-dependent behaviors. Hence, the molecular analysis of MSCs may shed more light on their future clinical application of these cells. This study aimed to investigate some behavioral aspects of eq-ASCs in vitro which may influence the efficacy of stem cell therapy. For this purpose, MSCs of a donor horse were isolated, characterized and expanded under normal culture conditions. During continuous culture condition, eq-ASCs were started to formed aggregated structures that was accompanied with the up-regulation of migratory related genes including transforming growth factor beta 1 (TGFB1) and its receptor 3 (TGFBR3), and snail family transcriptional repressor 1 (SNAI1), E-cadherin (CDH1) and β-catenin (CTNNB1). Moreover, the expression of a musculoskeletal progenitor marker, scleraxis bHLH transcription factor (SCX), was also increased after 3 days. In order to clarify the impact of TGFB signaling pathway on cultured cells, gain- and loss-of-function treatment by TGFB3 and SB431542 (TGFB inhibitor) were performed, respectively. We found that TGFB3 treatment exaggerated the aggregate formation effects, in some extend via induction of cytoskeletal actin rearrangement, while inhibition of TGFB signaling pathway by SB431542 reversed this phenomenon. Overall, our findings support the fact that eq-ASCs have an inherent capacity for migration, which was enhanced by TGFB3 treatment and, this ability may play crucial role in cell motility and wound healing of transplanted cells.

Synovium extra cellular matrices seeded with transduced mesenchymal stem cells stimulate chondrocyte maturation in vitro and cartilage healing in clinically-induced rat-knee lesions in vivo

Osteoarthritis (OA) is a progressive disease associated with cartilage injury and its inherently limited repair capability. Synovium-based cellular constructs (sConstructs) are proposed as possible treatments. Equine sConstructs were produced from decellularized synovium-based extracellular matrix scaffolds (sECM) seeded with synovium-derived mesenchymal stem cells (sMSC), and engineered to express green fluorescent protein (GFP), or bone morphogenetic protein-2 (BMP-2). Survival, distribution, and chondrogenic potential of the sConstructs in vitro and in vivo were assessed. sConstructs in co-culture with chondrocytes increased chondrocyte proliferation, viability, and Col II production, greatest in BMP-2-sConstructs. Chondrocyte presence increased the production of hyaluronic acid (HA), proteoglycan (PG), and BMP-2 by the sConstructs in a positive feedback loop. sECM alone, or GFP- or BMP-2-sConstructs were implanted in synovium adjacent to clinically created full-thickness rat-knee cartilage lesions. At 5 weeks, the lesion area and implants were resected. Gross anatomy, adjacent articulate cartilage growth and subchondral bone repair were scored; and peripheral, central and cartilage lesion measurements taken. For all scores and measurements, sConstruct implants were significantly greater than controls, greatest with the BMP-2-sConstructs. Immunohistochemistry demonstrated migration of endogenous cells into the sECM, with greater cellularity in the constructs with intense positive GFP staining confirming engraftment of implanted sMSC and continued gene expression. In summary, exposing cartilage to sConstructs was chondrogenic in vitro and in vivo, and resulted in substantially increased growth in vivo. This effect was mediated, in part, by soluble ECM and cell factors and upregulation of anabolic growth proteins, such as BMP-2. This work is "proof of concept" that sConstructs surgically implanted adjacent to cartilage damage can significantly improve cartilage and subchondral bone repair, and potentially prevent the progression of OA.

Effects of enzyme and cryoprotectant concentrations on yield of equine adipose-derived multipotent stromal cells

OBJECTIVE To evaluate effects of various concentrations of collagenase and dimethyl sulfoxide (DMSO) on yield of equine adipose-derived multipotent stromal cells (ASCs) before and after cryopreservation. SAMPLE Supragluteal subcutaneous adipose tissue from 7 Thoroughbreds. PROCEDURES Tissues were incubated with digests containing 0.1%, 0.05%, or 0.025% type I collagenase. Part of each resulting stromal vascular fraction was cryopreserved in 80% fetal bovine serum (FBS), 10% DMSO, and 10% Dulbecco modified Eagle medium F-12 and in 95% FBS and 5% DMSO. Half of each fresh and cryopreserved heterogeneous cell population was not immunophenotyped (unsorted) or was immunophenotyped for CD44⁺, CD105⁺, and major histocompatability complex class II (MHCII; CD44⁺-CD105⁺-MHCII⁺ cells and CD44⁺-CD105⁺-MHCII^- cells). Cell proliferation (cell viability assay), plasticity (CFU frequency), and lineage-specific target gene and oncogene expression (reverse transcriptase PCR assays) were determined in passage 1 cells before and after culture in induction media. RESULTS Digestion with 0.1% collagenase yielded the highest number of nucleated cells. Cell surface marker expression and proliferation rate were not affected by collagenase concentration. Cryopreservation reduced cell expansion rate and CD44⁺-CD105⁺-MHCII^- CFUs; it also reduced osteogenic plasticity of unsorted cells. However, effects appeared to be unrelated to DMSO concentrations. There were also variable effects on primordial gene expression among cell isolates. CONCLUSIONS AND CLINICAL RELEVANCE Results supported the use of 0.1% collagenase in an adipose tissue digest and 5% DMSO in cryopreservation medium for isolation and cryopreservation, respectively, of equine ASCs. These results may be used as guidelines for standardization of isolation and cryopreservation procedures for equine ASCs.

Ultrasound-guided injection of the cranial tibial artery for stem cell administration in horses

BACKGROUND

A technique for intra-arterial injection of mesenchymal stem cells (MSC) has been established for front limbs with the use of the median artery. This approach has been proposed for treatment of soft tissue injuries of the equine distal limb. A technique has not been validated yet for hindlimb injection.

OBJECTIVES

To assess the feasibility of injection of the cranial tibial artery in horses, and to evaluate the distribution and persistence of MSC after injection.

STUDY DESIGN

In vivo experiment.

METHODS

In a first phase, the cranial tibial arteries of both hindlimbs of three research horses were catheterised with ultrasound guidance under general anaesthesia and injected with iodinated contrast. In the second phase, iodinated contrast was injected in three standing sedated horses with ultrasound guidance. In the final phase, ^99m Technetium-HMPAO labelled allogenic bone marrow derived equine MSC were injected under standing sedation with the same technique in three other horses. Scintigraphy was used to assess MSC distribution and persistence for 24 h. Ultrasound was performed 24 h after injection to assess vessel impairment.

RESULTS

Arterial injection was achieved in all 18 limbs without any significant complications. Mild partial periarterial injection was observed in four limbs. Scintigraphic images demonstrated diffuse MSC distribution from the tarsal area to the foot. Persistence decreased over time but signal was still present at 24 h.

MAIN LIMITATIONS

Limited retention of the radiolabel in the MSC.

CONCLUSIONS

Ultrasound-guided injection of the cranial tibial artery can be performed both under general anaesthesia and standing sedation in horses. This technique could be used for MSC treatment of equine proximal suspensory desmopathy or other injuries in the distal hindlimb.

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.

Retrospective analysis of local injection site adverse reactions associated with 230 allogenic administrations of bone marrow-derived mesenchymal stem cells in 164 horses

BACKGROUND

Bone marrow-derived mesenchymal stem cells (BM-MSCs) are frequently used in the treatment of musculoskeletal injuries. Fully characterised cells that are readily available for use is optimum. Allogenic BM-MSCs can satisfy the need for rapid treatment, however, their safety has been questioned.

OBJECTIVES

Objectives were to characterise BM-MSCs from an adult donor horse, in vitro, and to identify and describe adverse reactions that occurred following their injection into other horses. We hypothesised that BM-MSCs capable of proliferation, differentiation and lacking MHC II from one donor could be implanted into another individual without significant adverse reactions and the frequency of adverse reactions in clinical cases would be similar to that previously reported for autologous BM-MSCs.

STUDY DESIGN

Retrospective clinical study.

METHODS

BM-MSCs were proliferated and characterised from one donor and cryopreserved for clinical use. Medical records for horses injected with allogenic BM-MSCs from this donor at a single hospital were used. After routine lameness exam, lesions were identified using diagnostic ultrasound or MRI. Post injection reaction was defined as increased pain, swelling, or heat at or near injection site, or increased lameness. Treatments required for each reaction were noted.

RESULTS

BM-MSCs proliferated and underwent differentiation. Cells were found to be negative for MHC-II (<2%) and were viable after cryopreservation and shipping. Ten of 230 (4.35%) injections were noted to be associated with an adverse reaction. Adverse reactions occurred in synovial structures (n = 3) and in soft tissues (n = 7).

MAIN LIMITATIONS

This investigation could underestimate the number and severity of reactions. Mild reactions, such as synovitis, may have been missed. Also, anti-inflammatory drugs could overshadow mild reactions, making them less likely to be detected.

CONCLUSIONS

Fully characterised allogenic BM-MSCs originating from a single donor horse can be administered to horses with soft tissue injuries with a low rate of adverse reaction. The Summary is available in Portuguese - see Supporting Information.

Recent advances in conservative and surgical treatment options of common equine foot problems

Foot problems are very common causes of lameness in horses. With the recent diagnostic advances to evaluate and treat foot pathology as well as to monitor response to therapy, it is now possible to more accurately evaluate the effectiveness of many of these treatments. This review details some of the recent advances of the most common conservative and surgical treatment options for foot problems in horses, including an overview of evidence on the efficacy to support the use of these treatment options and on factors that may affect prognosis.

Molecular Characteristics of the Equine Periodontal Ligament

The equine periodontal ligament (PDL) is a fibrous connective tissue that covers the intra-alveolar parts of the tooth and anchors it to the alveolar bone-it, therefore, provides a similar function to a tendinous structure. While several studies have considered the formation and structure of tendons, there is insufficient information particularly on the molecular composition of the PDL. Especially for the equine PDL, there is limited knowledge concerning the expression of genes commonly regarded as typical for tendon tissue. In this study, the gene expression of, e.g., collagen type 1 alpha 1 (COL1), collagen type 3 alpha 1 (COL3), scleraxis (SCX), and fibrocartilage markers was examined in the functional mature equine PDL compared with immature and mature equine tendon tissue. PDL samples were obtained from incisor, premolar, and molar teeth from seven adult horses. Additionally, tendon samples were collected from four adult horses and five foals at different sampling locations. Analyses of gene expression were performed using real-time quantitative polymerase chain reaction (qRT-PCR). Significantly higher expression levels of COL1 and 3 were found in the mature equine PDL in comparison with mature tendon, indicating higher rates of collagen production and turnover in the mature equine PDL. The expression levels of SCX, a specific marker for tenogenic-differentiated cells, were on a similar level in functional mature PDL and in mature tendon tissue. Evidence of chondrogenic metaplasia, often found in tendon entheses or in pressurized regions of tendons, was not found in the mature equine PDL. The obtained results justify further experiments focused on the possible use of equine PDL cells for cell-based regenerative therapies.

Equine mesenchymal stem cells derived from endometrial or adipose tissue share significant biological properties, but have distinctive pattern of surface markers and migration

Adult stromal mesenchymal stem cells (MSCs) have been postulated as responsible for cell renewal in highly and continuously regenerative tissues such as the endometrium. MSCs have been identified in the endometrium of many species including humans, rodents, pets and some farm animals, but not in horses. The objective of this work was to isolate such cells from the endometrium of mares and to compare their main biological attributes with horse adipose-derived MSCs. Here we successfully isolated and characterized endometrial MSCs (eMSCs) from mares. Said cells showed fibroblast-like morphology, grew on plastic, had doubling population times of 46.4 ± 3.38 h, underwent tri-lineage (osteo, chondro and adipogenic) differentiation after appropriate inductions, migrated toward the attraction of fetal calf serum and displayed a pattern of surface markers commonly accepted for horse MSCs. All these are properties of MSCs. Some of these attributes were shared with equine adipose-derived MSCs, but the migration pattern of eMSC at 12 and 24 h after stimulation was reduced in comparison with adipose MSCs. Also, expression of CD44, CD90 and MHCI surface markers were dramatically down-regulated in eMSCs. In conclusion, equine-derived endometrial MSC share biological attributes with adipose MSC of this species, but displayed a different surface marker phenotype and an impaired migration ability. Conceivably, this phenotype is distinctive for MSC of this origin.

Reconstruction of cranial cruciate ligament in rabbits using polyester implants saturated with PRP, antlerogenic stem cells MIC-1 and their homogenate

AIM OF THE STUDY

The attempt to limit the negative effects of polyester implants on the articular cavity by using preparations containing growth factors.

MATERIALS AND METHODS

Polyester implants used for the reconstruction of a rabbit's cranial cruciate ligament (CCL) were saturated with autogenic platelet-rich plasma (PRP), antlerogenic stem cells MIC-1 and their homogenate prior to the surgery. Six months after CCL reconstruction, morphological, and biochemical blood tests were carried out, including proteinogram and acute phase proteins. The knee joints were also examined macro- and microscopically.

RESULTS

The results, compared to the control group, showed a favorable effect of the PRP and homogenate of antlerogenic cells on limiting the inflammation caused by the presence of polyester implant in the knee joint. The addition of growth factors caused covering the implant faster with the recipient's connective tissue, thus contributing to reducing the inflammatory reaction of the articular capsule to the presence of polyester. At the same time, no enhanced local or general reaction of the rabbit organism was observed to the presence of xenogenic antlerogenic stem cells MIC-1 homogenate which, like the PRP, may provide an easily available source of growth factors, increasingly often used in regenerative medicine.

CONCLUSIONS

Applying antlerogenic stem cells, their homogenate or PRP increases the volume of connective tissue that surrounds and intertwines polyester CCL implant, separating it from synovial cavity environment.

Equine Mesenchymal Stromal Cells Retain a Pericyte-Like Phenotype

Mesenchymal stem/stromal cells (MSCs) have been used in human and equine regenerative medicine, and interest in exploiting their potential has increased dramatically over the years. Despite significant effort to characterize equine MSCs, the actual origin of these cells and how much of their native phenotype is maintained in culture have not been determined. In this study, we investigated the relationship between MSCs, derived from adipose tissue (AT) and bone marrow (BM), and pericytes in the horse. Both pericyte (CD146, NG2, and αSMA) and MSC (CD29, CD90, and CD73) markers were detected in equine AT and colocalized around blood vessels. Importantly, as assessed by flow cytometry, both pericyte (CD146, NG2, and αSMA) and MSC (CD29, CD44, CD90, and CD105) markers were present in a majority (≥90%) of cells in cultures of AT-MSCs and BM-MSCs; however, levels of pericyte markers were variable within each of those populations. Moreover, the expression of pericyte markers was maintained for at least eight passages in both AT-MSCs and BM-MSCs. Hematopoietic (CD45) and endothelial (CD144) markers were also detected at low levels in MSCs by quantitative polymerase chain reaction (qPCR). Finally, in coculture experiments, AT-MSCs closely associated with networks produced by endothelial cells, resembling the natural perivascular location of pericytes in vivo. Our results indicate that equine MSCs originate from perivascular cells and moreover maintain a pericyte-like phenotype in culture. Therefore, we suggest that, in addition to classical MSC markers, pericyte markers such as CD146 could be used when assessing and characterizing equine MSCs.

Effect of single intralesional treatment of surgically induced equine superficial digital flexor tendon core lesions with adipose-derived mesenchymal stromal cells: a controlled experimental trial

Background

Adipose tissue is a promising source of mesenchymal stromal cells (MSCs) for the treatment of tendon disease. The goal of this study was to assess the effect of a single intralesional implantation of adipose tissue-derived mesenchymal stromal cells (AT-MSCs) on artificial lesions in equine superficial digital flexor tendons (SDFTs).

Methods

During this randomized, controlled, blinded experimental study, either autologous cultured AT-MSCs suspended in autologous inactivated serum (AT-MSC-serum) or autologous inactivated serum (serum) were injected intralesionally 2 weeks after surgical creation of centrally located SDFT lesions in both forelimbs of nine horses. Healing was assessed clinically and with ultrasound (standard B-mode and ultrasound tissue characterization) at regular intervals over 24 weeks. After euthanasia of the horses the SDFTs were examined histologically, biochemically and by means of biomechanical testing.

Results

AT-MSC implantation did not substantially influence clinical and ultrasonographic parameters. Histology, biochemical and biomechanical characteristics of the repair tissue did not differ significantly between treatment modalities after 24 weeks. Compared with macroscopically normal tendon tissue, the content of the mature collagen crosslink hydroxylysylpyridinoline did not differ after AT-MSC-serum treatment (p = 0.074) while it was significantly lower (p = 0.027) in lesions treated with serum alone. Stress at failure (p = 0.048) and the modulus of elasticity (p = 0.001) were significantly lower after AT-MSC-serum treatment than in normal tendon tissue.

Conclusions

The effect of a single intralesional injection of cultured AT-MSCs suspended in autologous inactivated serum was not superior to treatment of surgically created SDFT lesions with autologous inactivated serum alone in a surgical model of tendinopathy over an observation period of 22 weeks. AT-MSC treatment might have a positive influence on collagen crosslinking of remodelling scar tissue. Controlled long-term studies including naturally occurring tendinopathies are necessary to verify the effects of AT-MSCs on tendon disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0564-8) contains supplementary material, which is available to authorized users.

From skeletal muscle to stem cells: an innovative and minimally-invasive process for multiple species

Bone marrow and adipose tissue represent the two most commonly exploited sources of adult mesenchymal stem cells for musculoskeletal applications. Unfortunately the sampling of bone marrow and fat tissue is invasive and does not always lead to a sufficient number of cells. The present study describes a novel sampling method based on microbiopsy of skeletal muscle in man, pigs, dogs and horses. The process includes explant of the sample, Percoll density gradient for isolation and subsequent culture of the cells. We further characterized the cells and identified their clonogenic and immunomodulatory capacities, their immune-phenotyping behavior and their capability to differentiate into chondroblasts, osteoblasts and adipocytes. In conclusion, this report describes a novel and easy-to-use technique of skeletal muscle-derived mesenchymal stem cell harvest, culture, characterization. This technique is transposable to a multitude of different animal species.

Effect of needle diameter on the viability of equine bone marrow derived mesenchymal stem cells

OBJECTIVES

Mesenchymal stem cells (MSCs) are frequently delivered via needle injection for treatment of musculoskeletal injuries. The purpose of this study was to evaluate the effect of needle diameter on the viability of MSCs.

METHODS

Equine bone marrow-derived MSCs from 5 horses were suspended in PBS, and held at room temperature for 7 hours to mimic shipping conditions. Two replicate samples for each needle size (20, 22, 23, or 25-gauge [ga]) were aspirated into a 3 mL syringe and re-injected into the holding vial 3 times, to reproduce the resuspension of cells prior to injection in clinical cases. Cells were stained with fluorescein diacetate and propidium iodide to measure viability. Flow cytometry (FC) was performed to compare cell debris and intact cells between groups.

RESULTS

MSC viability was higher when cells were passed through a 20-ga rather than a 25-ga needle. Cell suspensions passed through a 20-ga needle contained a larger percentage of intact cells, compared to 25-ga samples. The percentage of debris present in cell suspensions tended to increase with decreasing needle diameter. Neither horse nor passage had a significant effect on viability.

CONCLUSIONS

Cell damage is more likely when MSCs are passed through 25-ga rather than 20-ga needles.

CLINICAL RELEVANCE

Use of needles larger than 25-ga is recommended to maintain the viability of MSCs injected in horses.

Donor-Matched Comparison of Chondrogenic Potential of Equine Bone Marrow- and Synovial Fluid-Derived Mesenchymal Stem Cells: Implications for Cartilage Tissue Regeneration

Mesenchymal stem cells (MSCs) have been demonstrated to be useful for cartilage tissue regeneration. Bone marrow (BM) and synovial fluid (SF) are promising sources for MSCs to be used in cartilage regeneration. In order to improve the clinical outcomes, it is recommended that prior to clinical use, the cellular properties and, specifically, their chondrogenic potential must be investigated. The purpose of this study is to compare and better understand the in vitro chondrogenic potential of equine bone marrow-derived mesenchymal stem cells (BMMSCs) and synovial fluid-derived mesenchymal stem cells (SFMSCs) populated from the same equine donor. BM- and SF-derived MSCs cultures were generated from five equine donors, and the MSCs were evaluated in vitro for their morphology, proliferation, trilineage differentiation, and immunophenotyping. Differences in their chondrogenic potentials were further evaluated quantitatively using glycosaminoglycan (GAG) content and via immunofluorescence of chondrogenic differentiation protein markers, SRY-type HMG box9, Aggrecan, and collagen II. The BMMSCs and SFMSCs were similar in cellular morphology, viability, and immunophenotype, but, varied in their chondrogenic potential, and expression of the key chondrogenic proteins. The SFMSCs exhibited a significant increase in GAG content compared to the BMMSCs (P < 0.0001) in three donors, suggesting increased levels of chondrogenesis. The expression of the key chondrogenic proteins correlated positively with the GAG content, suggesting that the differentiation process is dependent on the expression of the target proteins in these three donors. Our findings suggest that even though SFMSCs were hypothesized to be more chondrogenic relative to BMMSCs, there was considerable donor-to-donor variation in the primary cultures of MSCs which can significantly affect their downstream application.

Isolation, proliferation and characterization of endometrial canine stem cells

In the last decade, progenitor cells isolated from dissociated endometrial tissue have been the subject of many studies in several animal species. Recently, endometrial cells showing characteristics of mesenchymal stem cells (MSC) have been demonstrated in human, pig and cow uterine tissue samples. The aim of this study was the isolation and characterization of stromal cells from the endometrium of healthy bitches, a tissue that after elective surgery is routinely discarded. Multipotent stromal cells could be isolated from all bitches enrolled in the study (n = 7). The multipotency of cells was demonstrated by their capacity to differentiate into adipocytic, osteocytic and chondrocytic lineages. Clonogenicity and cell proliferation ability were also tested. Furthermore, gene expression analysis by RT-PCR was used to compare the expression of a set of genes (CD44, CD29, CD34, CD45, CD90, CD13, CD133, CD73, CD31 CD105, Oct4) with adipose tissue-derived MSC. Stromal cells isolated from uterine endometrium showed similar morphology, ability of subculture and plasticity, and also expressed a panel of genes comparable with adipose tissue-derived MSC. These data suggest that endometrial stromal cells fulfil the basic criteria proposed by the "Mesenchymal and Tissue Stem Cell Committee of the International Society for Cellular Therapy" for the identification of mesenchymal stem cells. Although endometrial mesenchymal stem cells (EnMSC) showed a lower replicative ability in comparison with adipose tissue-derived MSC, they could be considered a cell therapeutic agent alternative to adipose tissue or bone marrow-derived MSC in dog.

Modulation of mesenchymal stem cell genotype and phenotype by extracellular matrix proteins

AIM

To investigate the effect of extracellular matrix (ECM) proteins on characteristics of mesenchymal stem cells (MSCs) and tendon-derived cells (TDCs).

MATERIALS AND METHODS

MSCs and TDCs, cultured in a monolayer (2D) or hydrogels (3D), with or without ECM protein supplementation, and on a non-viable native tendon (NNT) matrix were assayed for adhesion, proliferation, gene expression, and integrin expression.

RESULTS

MSCs exhibited a fibroblastic, spindle-shaped morphology on 2D matrices except in the presence of fibronectin. In 3D matrices, MSCs displayed a rounded phenotype except when cultured on NNTs where cells aligned along the collagen fibrils but, unlike TDCs, did not form inter-cellular cytoplasmic processes. MSC proliferation was significantly (p < 0.01) increased by collagen type I in 2D culture and fibronectin in 3D culture. TDC proliferation was unaffected by substrata. MSCs and TDCs differentially expressed α2 integrin. Adhesion to substrata was reduced by RGD-blocking peptide and β1 integrin antibody. The presence of collagen I or fibronectin upregulated MSC expression of collagen type I and collagen type III, COMP, decorin, osteopontin, and fibronectin.

CONCLUSIONS

The morphology, gene expression, and adhesion of both MSCs and TDCs are sensitive to the presence of specific ECM components. Interaction with the ECM is, therefore, likely to affect the mechanism of action of MSCs in vitro and may contribute to phenotypic modulation in vivo.

Advances in the Use of Stem Cells in Veterinary Medicine: From Basic Research to Clinical Practice

Today, several veterinary diseases may be treated with the administration of stem cells. This is possible because these cells present a high therapeutic potential and may be injected as autologous or allogenic, freshly isolated, or previously cultured. The literature supports that the process is safe and brings considerable benefits to animal health. Knowledge about how adult stem cells modulate the molecular signals to activate cell homing has also been increasingly determined, evidencing the mechanisms which enable cells to repair and regenerate injured tissues. Preclinical studies were designed for many animal models and they have contributed to the translation to the human clinic. This review shows the most commonly used stem cell types, with emphasis on mesenchymal stem cells and their mechanistic potential to repair, as well as the experimental protocols, studied diseases, and species with the highest amount of studies and applications. The relationship between stem cell protocols utilized on clinics, molecular mechanisms, and the physiological responses may offer subsidies to new studies and therefore improve the therapeutic outcome for both humans and animals.

Effects of pro-inflammatory cytokines on chondrogenesis of equine mesenchymal stromal cells derived from bone marrow or synovial fluid

Mesenchymal stromal cells (MSCs) have the capacity to differentiate into cells of mesenchymal lineage, such as chondrocytes, and have potential for use in regeneration of equine articular cartilage. MSCs instilled intra-articularly would be exposed to the inflamed environment associated with equine osteoarthritis (OA), which may compromise their function and ability to heal a cartilaginous defect. The aim of this study was to assess the ability of equine adult MSCs to differentiate into chondrocytes when stimulated with pro-inflammatory cytokines. MSCs derived from equine bone marrow (BM) and from synovial fluid (SF) were cultured in chondrogenic induction medium containing transforming growth factor (TGF)-β1. BM-derived MSCs (BMMSCs) and SF-derived MSCs (SFMSCs) were stimulated with 100 ng/mL interferon (IFN)-γ and 10 ng/mL tumor necrosis factor (TNF)-α. Chondrogenic differentiation was measured quantitatively with the glycosaminoglycan (GAG) assay and qualitatively by immunofluorescence (IF) for SOX-9, TGF-β1, aggrecan and collagen II. The viability of equine MSCs was maintained in the presence of IFN-γ and TNF-α, but production of GAGs from both types of MSCs was decreased in stimulated medium. Exposure of BMMSCs to pro-inflammatory cytokines reduced the levels of SOX-9, TGF-β1, aggrecan and collagen II, whereas exposure of SFMSCs to these cytokines reduced the levels of aggrecan only. These data suggest that pro-inflammatory cytokines do not affect proliferation of MSCs, but could inhibit chondrogenesis of MSCs.

Arthroscopic removal of discrete palmar carpal osteochondral fragments in horses: 25 cases (1999-2013)

OBJECTIVE

To characterize discrete palmar carpal osteochondral fragmentation in horses and to document the effect of osteoarthritis and surgical removal of these fragments on functional outcome.

DESIGN

Retrospective case series.

ANIMALS

25 horses.

PROCEDURES

Medical records and radiographic views were reviewed to identify horses that had radiographic evidence of palmar carpal fragmentation, which was subsequently treated by arthroscopic removal. Information collected included cause of fracture, initial and long-term clinical and radiographic findings, and functional outcome.

RESULTS

Palmar carpal fragmentation of 30 carpal bones was identified in 25 unilaterally affected horses. A known traumatic event was reported to cause the fragmentation in 17 of the 25 (68%) horses. Of the 25 horses, 17 (68%) had fragmentation involving the antebrachiocarpal joint, 7 (28%) had fragmentation involving the middle carpal joint, and 1 (4%) had fragmentation involving the carpometacarpal joint. The proximal aspect of the radial carpal bone was the most commonly affected site (12/30 fragments), followed by the accessory carpal bone (6/30). Of the 25 horses, 19 (76%) were not lame (sound) after surgery and returned to their intended use, 4 (16%) were considered pasture sound, and 2 were euthanized (because of severe postoperative osteoarthritis or long bone fracture during recovery from anesthesia). Eight of the 14 horses with preoperative evidence of osteoarthritis returned to function after surgery. Twelve of 17 horses with antebrachiocarpal joint fragments and 6 of 7 horses with middle carpal joint fragments returned to their previous use.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that the prognosis for horses after arthroscopic removal of palmar carpal osteochondral fragments is good. Early intervention, before the development of osteoarthritis, is recommended.

Tissues from equine cadaver ligaments up to 72 hours of post-mortem: a promising reservoir of stem cells

Background

Mesenchymal stem cells (MSCs) harvested from cadaveric tissues represent a promising approach for regenerative medicine. To date, no study has investigated whether viable MSCs could survive in cadaveric tissues from tendon or ligament up to 72 hours of post-mortem. The purpose of the present work was to find out if viable MSCs could survive in cadaveric tissues from adult equine ligaments up to 72 hours of post-mortem, and to assess their ability (i) to remain in an undifferentiated state and (ii) to divide and proliferate in the absence of any specific stimulus.

Methods

MSCs were isolated from equine cadaver (EC) suspensory ligaments within 48–72 hours of post-mortem. They were evaluated for viability, proliferation, capacity for tri-lineage differentiation, expression of cell surface markers (CD90, CD105, CD73, CD45), pluripotent transcription factor (OCT-4), stage-specific embryonic antigen-1 (SSEA-1), neuron-specific class III beta-tubulin (TUJ-1), and glial fibrillary acidic protein (GFAP). As well, they were characterized by transmission electron microscope (TEM).

Results

EC-MSCs were successfully isolated and maintained for 20 passages with high cell viability and proliferation. Phase contrast microscopy revealed that cells with fibroblast-like appearance were predominant in the culture. Differentiation assays proved that EC-MSCs are able to differentiate towards mesodermal lineages (osteogenic, adipogenic, chondrogenic). Flow cytometry analysis demonstrated that EC-MSCs expressed CD90, CD105, and CD73, while being negative for the leukocyte common antigen CD45. Immunofluorescence analysis showed a high percentage of positive cells for OCT-4 and SSEA-1. Surprisingly, in absence of any stimuli, some adherent cells closely resembling neuronal and glial morphology were also observed. Interestingly, our results revealed that approximately 15 % of the cell populations were TUJ-1 positive, whereas GFAP expression was detected in only a few cells. Furthermore, TEM analysis confirmed the stemness of EC-MSCs and identified some cells with a typical neuronal morphology.

Conclusions

Our findings raise the prospect that the tissues harvested from equine ligaments up to 72 hours of post-mortem represent an available reservoir of specific stem cells. EC-MSCs could be a promising alternative source for tissue engineering and stem cell therapy in equine medicine.

Characterization of mesenchymal stem cells derived from the equine synovial fluid and membrane

Background

Isolation of mesenchymal stem cells (MSCs) in equines, has been reported for different tissues including bone marrow, adipose, umbilical cord, peripheral blood, and yolk sac. In regard to the MSCs derived from synovial fluid (SF) or membrane (SM), there is data available for humans, dogs, pigs, goats and horses. Especially in equines, these cells have being considered promising candidates for articular regeneration. Herein, we established and characterized MSCs obtained from equine SF and SM. Samples were obtained during arthroscopy and cultured using MEM (Minimum Essential Medium). MSCs were characterized by morphology and expression of specific markers for stem cells, pluripotency, inflammation, and cell cycle.

Results

The medium MEM was more effective (97 % ± 2) to maintain both cultures. The cultures were composed by adherent cells with fibroblast-like shape, which had a growth pattern represented by a sigmoidal curve. After the expansion, the cells were analyzed by flow cytometry for stem cells, inflammatory, and cell cycle markers, and both lineages showed significant expression of CD45, Oct3/4, Nanog, CD105, CD90, CD34, CD117, CD133, TRA-1-81, VEGF, and LY6a. In contrast, there were differences in the cell cycle phases between the lineages, which was not observed in relation to the mitochondrial electrical potential.

Conclusion

Given the large impact that joint pathology has on the athletic performance horses, our results suggested that the SF and SM are promising sources of stem cells with satisfactory characteristics of growth and gene expression that can be used in equine regenerative medicine.

Safety and efficacy of allogeneic adipose tissue-derived mesenchymal stem cells for treatment of dogs with inflammatory bowel disease: Clinical and laboratory outcomes

Mesenchymal stem cells (MSCs) have shown immunomodulatory and anti-inflammatory effects in experimental colitis, and promising clinical results have been obtained in humans with Crohn's disease and ulcerative colitis. The aim of this study was to determine the safety and feasibility of adipose tissue-derived MSC (ASC) therapy in dogs with inflammatory bowel disease (IBD). Eleven dogs with confirmed IBD received one ASC intravascular (IV) infusion (2 × 10(6) cells/kg bodyweight). The outcome measures were clinical response based on percentage reduction of the validated Clinical Inflammatory Bowel Disease Activity Index (CIBDAI) and Canine Chronic Enteropathy Clinical Activity Index (CCECAI), as well as normalisation of C-reactive protein (CRP), albumin, folate and cobalamin serum concentrations at day 42 post-treatment. The Wilcoxon test was used to compare variables before and after treatment. No acute reaction to ASC infusion and no side effects were reported during follow-up in any dog. Six weeks post-treatment, the CIBDAI and CCECAI decreased significantly and albumin, cobalamin and folate concentrations increased substantially. Differences in CRP concentrations pre- and post-treatment were not significant (P = 0.050). Clinical remission (defined by a reduction of initial CIBDAI and CCECAI >75%) occurred in 9/11 dogs at day 42. The two remaining dogs showed a partial response with reduction percentages of 69.2% and 71.4%. In conclusion, a single IV infusion of allogeneic ASCs was well tolerated and appeared to produce clinical benefits in dogs with severe IBD.

Superparamagnetic iron oxide nanoparticles as a means to track mesenchymal stem cells in a large animal model of tendon injury

The goal of this study was to establish an SPIO-based cell-tracking method in an ovine model of tendonitis and to determine if this method may be useful for further study of cellular therapies in tendonitis in vivo. Functional assays were performed on labeled and unlabeled cells to ensure that no significant changes were induced by intracellular SPIOs. Following biosafety validation, tendon lesions were mechanically (n = 4) or chemically (n = 4) induced in four sheep and scanned ex vivo at 7 and 14 days to determine the presence and distribution of intralesional cells. Ovine MSCs labeled with 50 µg SPIOs/mL remained viable, proliferate, and undergo tri-lineage differentiation (p < 0.05). Labeled ovine MSCs remained detectable in vitro in concentrated cell numbers as low as 10 000 and in volumetric distributions as low as 100 000 cells/mL. Cells remained detectable by MRI at 7 days, as confirmed by correlative histology for dually labeled SPIO+/GFP+ cells. Histological evidence at 14 days suggested that SPIO particles remained embedded in tissue, providing MRI signal, although cells were no longer present. SPIO labeling has proven to be an effective method for cell tracking for a large animal model of tendon injury for up to 7 days post-injection. The data obtained in this study justify further investigation into the effects of MSC survival and migration on overall tendon healing and tissue regeneration.

Equine allogeneic bone marrow-derived mesenchymal stromal cells elicit antibody responses in vivo

Introduction

This study tested the hypothesis that Major Histocompatibility Complex (MHC) incompatible equine mesenchymal stromal cells (MSCs) would induce cytotoxic antibodies to donor MHC antigens in recipient horses after intradermal injection. No studies to date have explored recipient antibody responses to allogeneic donor MSC transplantation in the horse. This information is critical because the horse is a valuable species for assessing the safety and efficacy of MSC treatment prior to human clinical application.

Methods

Six MHC heterozygote horses were identified as non-ELA-A2 haplotype by microsatellite typing and used as allogeneic MHC-mismatched MSC recipients. MHC homozygote horses of known ELA-A2 haplotype were used as MSC and peripheral blood leukocyte (PBL) donors. One MHC homozygote horse of the ELA-A2 haplotype was the recipient of ELA-A2 donor MSCs as an MHC-matched control. Donor MSCs, which were previously isolated and immunophenotyped, were thawed and culture expanded to achieve between 30x10⁶ and 50x10⁶ cells for intradermal injection into the recipient’s neck. Recipient serum was collected and tested for the presence of anti-donor antibodies prior to MSC injection and every 7 days after MSC injection for the duration of the 8-week study using the standard two-stage lymphocyte microcytotoxicity dye-exclusion test. In addition to anti-ELA-A2 antibodies, recipient serum was examined for the presence of cross-reactive antibodies including anti-ELA-A3 and anti-RBC antibodies.

Results

All MHC-mismatched recipient horses produced anti-ELA-A2 antibodies following injection of ELA-A2 MSCs and developed a wheal at the injection site that persisted for the duration of the experiment. Anti-ELA-A2 antibody responses were varied both in terms of strength and timing. Four recipient horses had high-titered anti-ELA-A2 antibody responses resulting in greater than 80% donor PBL death in the microcytotoxicity assays and one of these horses also developed antibodies that cross-reacted when tested on lymphocyte targets from a horse with an unrelated MHC type.

Conclusions

Allogeneic MSCs are capable of eliciting antibody responses in vivo that can be strong and also cross-reactive with MHC types other than that of the donor. Such responses could limit the effectiveness of repeated allogeneic MSC use in a single horse, and could also result in untoward inflammatory responses in recipients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0053-x) contains supplementary material, which is available to authorized users.

The past, present and future in scaffold-based tendon treatments

Tendon injuries represent a significant clinical burden on healthcare systems worldwide. As the human population ages and the life expectancy increases, tendon injuries will become more prevalent, especially among young individuals with long life ahead of them. Advancements in engineering, chemistry and biology have made available an array of three-dimensional scaffold-based intervention strategies, natural or synthetic in origin. Further, functionalisation strategies, based on biophysical, biochemical and biological cues, offer control over cellular functions; localisation and sustained release of therapeutics/biologics; and the ability to positively interact with the host to promote repair and regeneration. Herein, we critically discuss current therapies and emerging technologies that aim to transform tendon treatments in the years to come.

Immune potential of allogeneic equine induced pluripotent stem cells

REASONS FOR PERFORMING STUDY

Induced pluripotent stem cells (iPSC) have brought immense hope to cellular therapy and regenerative medicine. However, the antigenicity of iPSC has not been well documented and remains a hurdle for clinical applications. Expression of major histocompatibility complex (MHC) molecules by human and murine iPSC is downregulated, making these cells potentially safe for transplantation. No such data are available for any large animal model.

OBJECTIVES

To measure expression of MHC molecules on equine iPSC (eiPSC) and describe their antigenicity using intradermal testing. The hypothesis was that allogeneic eiPSC weakly express MHC molecules and would not elicit a rejection response when injected intradermally.

STUDY DESIGN

Experimental study involving both in vitro and in vivo components.

METHODS

Two green fluorescent protein-expressing eiPSC lines were analysed by flow cytometry for MHC expression. One line was then transplanted intradermally, along with appropriate controls, into 2 unrelated experimental horses. Blood was collected pre- and 7 days post transplantation. The wheals formed at the sites of injection were measured at regular intervals beginning at 0.25 h until 4 weeks. Tissue samples of the injected sites were obtained at 2, 3, 7 and 30 days post transplantation and analysed by histopathology and immunofluorescence.

RESULTS

Both eiPSC lines weakly expressed MHC molecules. eiPSC were detectable up to 7 days following allogeneic transplantation and elicited no apparent systemic response. Injection of eiPSC caused small wheal formation at the skin surface. Skin sections revealed CD4(+) and CD8(+) mononuclear cells up to 30 days post transplantation.

CONCLUSIONS

These data suggest that while transplantation of allogeneic eiPSC elicits a moderate cellular response, it does not cause acute rejection. The feasibility of banking allogeneic iPSC for regenerative medicine applications should be explored.

State of the art: stem cells in equine regenerative medicine

According to Greek mythology, Prometheus' liver grew back nightly after it was removed each day by an eagle as punishment for giving mankind fire. Hence, contrary to popular belief, the concept of tissue and organ regeneration is not new. In the early 20th century, cell culture and ex vivo organ preservation studies by Alexis Carrel, some with famed aviator Charles Lindbergh, established a foundation for much of modern regenerative medicine. While early beliefs and discoveries foreshadowed significant accomplishments in regenerative medicine, advances in knowledge within numerous scientific disciplines, as well as nano- and micromolecular level imaging and detection technologies, have contributed to explosive advances over the last 20 years. Virtually limitless preparations, combinations and applications of the 3 major components of regenerative medicine, namely cells, biomaterials and bioactive molecules, have created a new paradigm of future therapeutic options for most species. It is increasingly clear, however, that despite significant parallels among and within species, there is no 'one-size-fits-all' regenerative therapy. Likewise, a panacea has yet to be discovered that completely reverses the consequences of time, trauma and disease. Nonetheless, there is no question that the promise and potential of regenerative medicine have forever altered medical practices. The horse is a relative newcomer to regenerative medicine applications, yet there is already a large body of work to incorporate novel regenerative therapies into standard care. This review focuses on the current state and potential future of stem cells in equine regenerative medicine.

Clinical follow-up of horses treated with allogeneic equine mesenchymal stem cells derived from umbilical cord blood for different tendon and ligament disorders

BACKGROUND

Mesenchymal stem cells (MSCs) offer promise as therapeutic aids in the repair of tendon and ligament disorders in sport horses. Equine allogeneic MSCs derived from umbilical cord blood (eUCB-MSCs) can be obtained in a minimally invasive fashion with successful propagation of MSCs.

OBJECTIVE

The objective of this study was to determine the applicability and therapeutic effect of eUCB-MSCs on tendinitis of the superficial digital flexor tendon, desmitis of the suspensory ligament, tendinitis of the deep digital flexor tendon, and desmitis of the inferior check ligament in clinical cases.

METHODS

A retrospective clinical study was performed. At two equine clinics, 52 warmblood horses were treated with cultured eUCB-MSCs between 2009 and 2012. About 2-10 × 10(6) cells per lesion were administered. When a lesion was treated twice, the total amount could run up to 20 × 10(6) cells. Pearson's chi-squared test was used to compare the effect of the injured structure on the success rate, as well as the effect of the age of the horse.

RESULTS

Based on repeated examinations, 40 horses (77%) returned to work on the same or a higher level based on information provided by the owner. Neither the injured structure nor the age of the horse had a statistically significant influence on the result.

CONCLUSION

Overall, the results of treatment of some tendon and ligament injuries with eUCB-MSCs in clinical cases are promising.

Use of mesenchymal stem cells or autologous conditioned serum to modulate the inflammatory response to spermatozoa in mares

Current treatments for Persistent mating-induced endometritis such as uterine lavage and oxytocin therapy focus on aiding the uterus in removal of inflammatory products, but these treatments do not modulate the inciting inflammatory response. Biological treatments, such as autologous conditioned serum (ACS) and mesenchymal stem cells (MSCs), have been used in human and veterinary medicine for immunomodulation for over 10 years. The objectives of this project were to evaluate the ability of ACS or MSCs to modulate the inflammatory response to spermatozoa after breeding. Two experiments were performed with six normal mares in each study to evaluate the effects of intrauterine administration of ACS, dexamethasone, or a placebo (experiment 1), or allogeneic MSCs or a placebo (experiment 2) on the inflammatory response to spermatozoa using clinical and biochemical endpoints. Treatment with ACS and MSCs significantly (P < 0.05) reduced the number of neutrophils in the uterine lumen 6 hours after the sperm challenge. An increase (P < 0.05) in the anti-inflammatory cytokine IL-1Ra was observed after treatment with MSCs before exposure to spermatozoa. There was no difference in IL-1Ra concentration in mares treated with ACS, dexamethasone, or a placebo. Mesenchymal stem cells and ACS were able to modulate the immune response to spermatozoa in normal mares. The effect may be due to an increase in IL-1Ra in MSCs-treated mares, but other bioactive molecules may be responsible for the decrease in neutrophils in ACS-treated mares. Autologous conditioned serum and bone-derived culture expanded MSCs were able to modulate the uterine inflammatory response to spermatozoa in normal mares. Treatment with allogeneic stem cells may be beneficial if a similar modulation in inflammatory cytokines occurs in mares affected by persistent mating-induced endometritis.

Equine bone marrow-derived mesenchymal stromal cells are heterogeneous in MHC class II expression and capable of inciting an immune response in vitro

Introduction

The horse is a valuable species to assess the effect of allogeneic mesenchymal stromal cells (MSCs) in regenerative treatments. No studies to date have examined recipient response to major histocompatibility complex (MHC)-mismatched equine MSCs. The purposes of this study were to immunophenotype MSCs from horses of known MHC haplotype and to compare the immunogenicity of MSCs with differing MHC class II expression.

Methods

MSCs and peripheral blood leukocytes (PBLs) were obtained from Thoroughbred horses (n = 10) of known MHC haplotype (ELA-A2, -A3, and -A9 homozygotes). MSCs were cultured through P8; cells from each passage (P2 to P8) were cryopreserved until used. Immunophenotyping of MHC class I and II, CD44, CD29, CD90, LFA-1, and CD45RB was performed by using flow cytometry. Tri-lineage differentiation assays were performed to confirm MSC multipotency. Recombinant equine IFN-γ was used to stimulate MHC class II negative MSCs in culture, after which expression of MHC class II was re-examined. To assess the ability of MHC class II negative or positive MSCs to stimulate an immune response, modified one-way mixed leukocyte reactions (MLRs) were performed by using MHC-matched and mismatched responder PBLs and stimulator PBLs or MSCs. Proliferation of gated CFSE-labeled CD3+ responder T cells was evaluated via CFSE attenuation by using flow cytometry and reported as the number of cells in the proliferating T-cell gate.

Results

MSCs varied widely in MHC class II expression despite being homogenous in terms of “stemness” marker expression and ability to undergo trilineage differentiation. Stimulation of MHC class II negative MSCs with IFN-γ resulted in markedly increased expression of MHC class II. MLR results revealed that MHC-mismatched MHC class II-positive MSCs caused significantly increased responder T-cell proliferation compared with MHC-mismatched MHC class II-negative and MHC-matched MSCs, and equivalent to that of the positive control of MHC-mismatched leukocytes.

Conclusions

The results of this study suggest that MSCs should be confirmed as MHC class II negative before allogeneic application. Additionally, it must be considered that even MHC class II-negative MSCs could upregulate MHC class II expression if implanted into an area of active inflammation, as demonstrated with in vitro stimulation with IFN-γ.

Clinical outcome after intra-articular administration of bone marrow derived mesenchymal stem cells in 33 horses with stifle injury

OBJECTIVE

To report outcome of horses with femorotibial lesions (meniscal, cartilage or ligamentous) treated with surgery and intra-articular administration of autologous bone marrow derived mesenchymal stem cells (BMSCs).

STUDY DESIGN

Prospective case series.

ANIMALS

Horses (n = 33).

METHODS

Inclusion criteria included horses that had lameness localized to the stifle by diagnostic anesthesia, exploratory stifle arthroscopy and subsequent intra-articular administration of autologous BMSCs. Case details and follow-up were gathered from medical records, owner, trainer or veterinarian. Outcome was defined as returned to previous level of work, returned to work, or failed to return to work.

RESULTS

Follow-up (mean, 24 months) was obtained; 43% of horses returned to previous level of work, 33% returned to work, and 24% failed to return to work. In horses with meniscal damage (n = 24) a higher percentage in the current study (75%) returned to some level of work compared to those in previous reports (60-63%) that were treated with arthroscopy alone, which resulted in a statistically significant difference between studies (P = .038). Joint flare post injection was reported in 3 horses (9.0%); however, no long-term effects were noted.

CONCLUSIONS

Intra-articular administration of BMSC postoperatively for stifle lesions appeared to be safe, with morbidity being similar to that of other biologic agents. Improvement in ability to return to work may be realized with BMSC treatment compared to surgery alone in horses with stifle injury.