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

Companion animals in veterinary medicine develop multiple naturally occurring diseases analogous to human conditions. We previously reported a comprehensive review on the feasibility, safety, and biologic activity of using novel stem cell therapies to treat a variety of inflammatory conditions in dogs and cats (2008-2015) [1]. The purpose of this review is to provide an updated summary of current studies in companion animal disease models that have evaluated stem cell therapeutics that are relevant to human disease. Here we have reviewed the literature from 2015 to 2023 for publications on stem cell therapies that have been evaluated in companion animals, including dogs, cats, and horses. The review excluded case reports or studies performed in experimentally induced models of disease, studies involving cancer, or studies in purpose-bred laboratory species such as rodents. We identified 45 manuscripts meeting these criteria, an increase from 19 that were described in the previous review [1]. The majority of studies were performed in dogs (n=28), with additional studies in horses (n=9) and cats (n=8). Disease models included those related to musculoskeletal disease (osteoarthritis, tendon/ligament injury), neurologic disease (canine cognitive dysfunction, intervertebral disc disease, spinal cord injury) gingival/dental disease (gingivostomatitis), dermatologic disease (atopic dermatitis), chronic multi-drug resistant infections, ophthalmic disease (keratoconjunctivitis sicca, eosinophilic keratitis, immune mediated keratitis), cardiopulmonary disease (asthma, degenerative valve disease, dilated cardiomyopathy), gastrointestinal disease (inflammatory bowel disease, chronic enteropathy) and renal disease (chronic kidney disease). The majority of studies reported beneficial responses to stem cell treatment, with the exception of those related to more chronic processes such as spinal cord injury and chronic kidney disease. However, it should also be noted that 22 studies were open-label, baseline-controlled trials and only 12 studies were randomized and controlled, making overall study interpretation difficult. As noted in the previous review, improved regulatory oversight and consistency in manufacturing of stem cell therapies is needed. Enhanced understanding of the temporal course of disease processes using advanced -omics approaches may further inform mechanisms of action and help define appropriate timing of interventions. Future directions of stem cell-based therapies could include use of stem-cell derived extracellular vesicles, or cell conditioning approaches to direct cells to specific pathways that are tailored to individual disease processes and stages of illness.

Antimicrobial Properties of Equine Stromal Cells and Platelets and Future Directions.

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

Intravenous injection of adipose-derived mesenchymal stromal cells benefits gait and inflammation in a spontaneous osteoarthritis model.

Osteoarthritis (OA) is a leading cause of morbidity among aging populations, yet symptom and/or disease-modification remains elusive. Adipose-derived mesenchymal stromal cells (adMSCs) have demonstrated immunomodulatory and anti-inflammatory properties that may alleviate clinical signs and interrupt disease onset and progression. Indeed, multiple manuscripts have evaluated intra-articular administration of adMSCs as a therapeutic; however, comparatively few evaluations of systemic delivery methods have been published. Therefore, the aim of this study was to evaluate the short-term impact of intravenous (IV) delivery of allogeneic adMSCs in an established model of spontaneous OA, the Hartley guinea pig. Animals with moderate OA received once weekly injections of 2 × 106 adMSCs or vehicle control for 4 weeks in peripheral veins; harvest occurred 2 weeks after the final injection. Systemic administration of adMSCs resulted in no adverse effects and was efficacious in reducing clinical signs of OA (as assessed by computer-aided gait analysis) compared to control injected animals. Further, there were significant decreases in key inflammatory mediators (including monocyte chemoattractant protein-1, tumor necrosis factor, and prostaglandin E2 ) both systemically (liver, kidney, and serum) and locally in the knee (joint tissues and synovial fluid) in animals treated with IV adMSCs relative to controls (as per enzyme-linked immunosorbent assay and/or immunohistochemistry, dictated by tissue sample). Thus, systemic administration of adMSCs by IV injection significantly improved gait parameters and reduced both systemic and intra-articular inflammatory mediators in animals with OA. These findings demonstrate the potential utility of alternative delivery approaches for cellular therapy of OA, particularly for patients with multiple affected joints.

Losartan Blocks Osteosarcoma-Elicited Monocyte Recruitment, and Combined With the Kinase Inhibitor Toceranib, Exerts Significant Clinical Benefit in Canine Metastatic Osteosarcoma.

PURPOSE: There is increasing recognition that progress in immuno-oncology could be accelerated by evaluating immune-based therapies in dogs with spontaneous cancers. Osteosarcoma (OS) is one tumor for which limited clinical benefit has been observed with the use of immune checkpoint inhibitors. We previously reported the angiotensin receptor blocker losartan suppressed metastasis in preclinical mouse models through blockade of CCL2-CCR2 monocyte recruitment. Here we leverage dogs with spontaneous OS to determine losartan's safety and pharmacokinetics associated with monocyte pharmacodynamic endpoints, and assess its antitumor activity, in combination with the kinase inhibitor toceranib. PATIENTS AND METHODS: CCL2 expression, monocyte infiltration, and monocyte recruitment by human and canine OS tumors and cell lines were assessed by gene expression, ELISA, and transwell migration assays. Safety and efficacy of losartan-toceranib therapy were evaluated in 28 dogs with lung metastatic OS. Losartan PK and monocyte PD responses were assessed in three dose cohorts of dogs by chemotaxis, plasma CCL2, and multiplex cytokine assays, and RNA-seq of losartan-treated human peripheral blood mononuclear cells. RESULTS: Human and canine OS cells secrete CCL2 and elicit monocyte migration, which is inhibited by losartan. Losartan PK/PD studies in dogs revealed that a 10-fold-higher dose than typical antihypertensive dosing was required for blockade of monocyte migration. Treatment with high-dose losartan and toceranib was well-tolerated and induced a clinical benefit rate of 50% in dogs with lung metastases. CONCLUSIONS: Losartan inhibits the CCL2-CCR2 axis, and in combination with toceranib, exerts significant biological activity in dogs with metastatic osteosarcoma, supporting evaluation of this drug combination in patients with pediatric osteosarcoma. See related commentary by Weiss et al., p. 571.

Susceptibility of canine chondrocytes and synoviocytes to antibiotic cytotoxicity in vitro.

OBJECTIVE: To evaluate relative cytotoxicity of antibiotics to normal canine joint tissues in vitro. STUDY DESIGN: Experimental in vitro study. SAMPLE POPULATION: Chondrocytes and synoviocytes (three dogs); cartilage explants (three dogs); six dogs total. METHODS: Chondrocytes and synoviocytes from normal femoropatellar joints of three dogs were plated on 24-well plates (50 000 cells/cm2 , triplicate, 48 hours) and exposed to antibiotics (ampicillin sulbactam, vancomycin, cefazolin, ceftazidime, amikacin, enrofloxacin; 0.39-25 mg/mL, 24 hours). Viability was assessed by using trypan blue dye exclusion. Antibiotic concentrations at which 50% cell death occurred (half-maximal inhibitory concentration) were determined to rank antibiotics for relative cytotoxicity. Occurrence of caspase-3 expression after antibiotic exposure was assessed as an indication of apoptosis induction. Cartilage explants from three different dogs were minced and exposed to antibiotics (amikacin, ceftazidime, cefazolin, enrofloxacin; 5 mg/mL, 72 hours). Live/dead staining was performed, and fluorescence was visualized by using confocal microscopy. Percentage of live vs dead cells was quantitated. RESULTS: Viability of chondrocytes and synoviocytes decreased with increasing antibiotic concentrations. Half-maximal inhibitory concentrations were determined for synoviocytes (vancomycin 13.77, ampicillin sulbactam 3.07, amikacin 2.26, ceftazidime 1.62, cefazolin 1.48, enrofloxacin 1.25 mg/mL) and chondrocytes (vancomycin 8.65, ampicillin sulbactam 8.63, ceftazidime 3.16, amikacin 2.74, cefazolin 1.67, enrofloxacin 0.78 mg/mL). Caspase-3 expression was upregulated, providing evidence that apoptotic pathways were active in cell death. CONCLUSION: Half-maximal inhibitory concentration data provided evidence of lower toxicity of vancomycin and ampicillin sulbactam to joint tissues in vitro. CLINICAL SIGNIFICANCE: These results provide evidence to justify future in vitro work with osteoarthritic joint tissues and in vivo clinical trials to evaluate safety and efficacy of intra-articular antibiotics to treat dogs with septic arthritis.

Clinical evaluation of hyperimmune plasma for treatment of dogs with naturally occurring parvoviral enteritis.

OBJECTIVE: To evaluate the clinical efficacy of a single infusion of hyperimmune plasma (HIP) in dogs with canine parvovirus (CPV). DESIGN: Prospective, randomized, placebo-controlled clinical trial. SETTING: University teaching hospital. ANIMALS: Client-owned dogs with naturally occurring CPV. INTERVENTIONS: Dogs presenting for CPV treatment (n = 31) underwent cardiovascular resuscitation and were randomized to receive a single dose of either HIP (10 mL/kg IV) or placebo (0.9% sodium chloride [10 mL/kg IV]) during the first 6 hours of hospitalization. All dogs were treated with a standardized treatment protocol (IV fluid therapy [120 mL/kg/d isotonic crystalloids], cefoxitin [30 mg/kg IV q 8 h], maropitant [1 mg/kg IV q 24 h], and buprenorphine [0.01-0.02 mg/kg IV q 8 h]) until hospital discharge. MEASUREMENTS AND MAIN RESULTS: Dogs treated with HIP (n = 16) demonstrated a lower shock index at 24 hours (median = 0.77, range: 0.5-1.5) than those treated with placebo (n = 15, median = 1.34, range: 0.5-1.7; P = 0.02). Plasma lactate concentration was lower at 24 hours in HIP-treated dogs (median = 1.3 mmol/L, range: 0.9-3.4 mmol/L) than in placebo-treated dogs (median = 2.1 mmol/L, range: 1.1-3.4 mmol/L; P = 0.01). There was no difference in duration of hospitalization when comparing HIP-treated dogs (median = 3.2 days, range: 0.83-10 days) to placebo-treated dogs (median = 2.83 days, range: 1-8.38 days; P = 0.35). Survival was 16 of 16 (100%) for the HIP group and 14 of 15 (93.3%) for the placebo group (P = 0.32). CONCLUSIONS: HIP at 10 mL/kg IV administered to dogs with CPV within the first 6 hours of hospitalization improves markers of shock during the initial 24 hours of hospitalization. No effects were observed on duration of hospitalization or mortality; however, this study was underpowered to evaluate these effects. HIP was well tolerated in this population of critically ill dogs.

Pretreatment aerobic bacterial swab cultures to predict infection in acute open traumatic wounds: A prospective clinical study of 64 dogs.

OBJECTIVE: To determine the value of initial aerobic bacterial cultures of acute open traumatic wounds to predict bacterial species in wounds that become infected. STUDY DESIGN: Prospective clinical trial. ANIMALS: Sixty-four dogs with naturally occurring acute cutaneous traumatic wounds (2017-2018). METHODS: Initial swabs were taken from each wound prior to and after lavage and debridement for quantitative and qualitative aerobic bacterial culture. Cultures were repeated on wounds that displayed any clinical sign of infection within 14 days of presentation. RESULTS: Fewer bacteria were cultured from postlavage than from prelavage swabs in 43 of 50 (86%) acute wounds. All primary clinicians prescribed ß-lactam antibiotics to the dogs at initial presentation. All bacteria cultured from postlavage/debridement cultures at initial presentation were susceptible to the prophylactic antimicrobial prescribed. Postoperative infection was subsequently diagnosed in 14 of 64 (22%) dogs; 13 of these dogs had positive culture results. No correlation was detected between the results of initial wound cultures and the subsequent development of wound infection. Bacterial species present in the initial wound swab did not correlate with those subsequently cultured from infected tissues. CONCLUSION: Results of pretreatment wound cultures from open traumatic wounds in dogs were not predictive of bacterial species subsequently recovered from infected wounds. The bacterial burden present in pretreatment wounds was not predictive of whether wounds would ultimately become infected after surgical management. CLINICAL SIGNIFICANCE: Routine bacterial culturing of acute wounds is not likely to help predict subsequent wound infection, nor is it likely to accurately guide early selection of antimicrobials to treat wounds that become infected.

Mesenchymal stem cells for treatment of musculoskeletal disease in horses: Relative merits of allogeneic versus autologous stem cells.

Mesenchymal stem cells (MSCs) are widely used for treatment of musculoskeletal diseases in horses, but there is ongoing debate regarding the relative safety and efficacy of allogeneic MSCs, compared with autologous equine MSCs. This review summarises the currently available published data regarding the therapeutic use of autologous and allogeneic MSCs in horses. Arguments that have been advanced against the use of allogeneic MSCs include higher risk of immunological reactions and shorter cell survival times following injection. Arguments favouring the use of allogeneic MSCs include the ability to bank cells and reduce the time to treatment, to collect MSCs from younger donor animals and the ability to manipulate banked cells prior to administration. In vitro studies and a limited set of experimental in vivo studies have indicated that adverse immunological reactions may occur when allogeneic MSCs are administered to horses. However, newer studies lack evidence of inflammatory reactions or adverse clinical responses when allogeneic MSCs are administered and compared with autologous MSCs. Thus, while the relative merits of allogeneic vs autologous MSCs for treatment of musculoskeletal injuries in horses have not been fully established, accumulating evidence from studies in horses suggests that allogeneic MSCs maybe a safe alternative to autologous MSCs. Large, properly designed, randomised trials in addition to careful immunological evaluation of short-term and long-term, local and systemic immune responses are needed to more fully resolve the issue.

Single and repeated intra-articular injections in the tarsocrural joint with allogeneic and autologous equine bone marrow-derived mesenchymal stem cells are safe, but did not reduce acute inflammation in an experimental interleukin-1ß model of synovitis.

BACKGROUND: Allogeneic and autologous bone marrow-derived mesenchymal stem cells (BMDMSCs) have been administered in equine joints for their anti-inflammatory effects. However, allogeneic BMDMSC offer multiple clinical and practical advantages. Therefore, it is important to determine the relative effectiveness of allogeneic vs autologous BMDMSCs. OBJECTIVES: The objective of the study was to compare the inflamed joint response to autologous vs allogeneic BMDMSCs injections, and to determine if either treatment generated an anti-inflammatory effect. STUDY DESIGN: Randomised controlled study. METHOD: Bone marrow was harvested from eight horses. Autologous BMDMSCs and pooled allogeneic BMDMSCs were culture expanded, cryopreserved and thawed immediately prior to administration. Ten million autologous BMDMSCs were administered with 75 ng rIL-1ß into one tarsocrural joint and the contralateral tarsocrural joint received allogeneic BMDMSC plus 75 ng rIL-1ß. Repeat injections were performed with the same treatment administered into the same joint. Four additional horses received 75 ng rIL-1ß alone in a single tarsocrural joint. Clinical parameters (lameness, joint circumference and joint effusion) and synovial fluid parameters, including nucleated cell count (NCC), differential cell count, total protein (TP), prostaglandin E2 (PGE2 ) and C-reactive protein (CRP), were measured at baseline, 6, 12, 24, 72, 168 and 336 hours post-injection. RESULTS: No difference was detected between autologous and allogeneic treatment groups with respect to subjective lameness, joint effusion, joint circumference, NCC, TP, differential cell count, CRP or PGE2 . Neither autologous nor allogeneic treatments resulted in an improvement in clinical or cytological parameters over that elicited by rIL-1ß alone. MAIN LIMITATIONS: A single dose of rIL-1ß was evaluated and resulted in a severe synovitis which may have been too severe to observe a BMDMSC-mediated effect. CONCLUSIONS: This study revealed that allogeneic and autologous BMDMSCs resulted in an equivalent clinical and cytological response. Allogeneic and autologous BMDMSCs were equally ineffective in reducing the inflammatory response from acute rIL-1ß-induced joint inflammation in horses.

The Angiotensin Receptor Blocker Losartan Suppresses Growth of Pulmonary Metastases via AT1R-Independent Inhibition of CCR2 Signaling and Monocyte Recruitment.

Inflammatory monocytes have been shown to play key roles in cancer metastasis through promotion of tumor cell extravasation, growth, and angiogenesis. Monocyte recruitment to metastases is mediated primarily via the CCL2-CCR2 chemotactic axis. Thus, disruption of this axis represents an attractive therapeutic target for the treatment of metastatic disease. Losartan, a type I angiotensin II receptor (AT1R) antagonist, has been previously shown to have immunomodulatory actions involving monocyte and macrophage activity. However, the exact mechanisms accounting for these effects have not been fully elucidated. Therefore, we investigated the effects of losartan and its primary metabolite on CCL2-mediated monocyte recruitment and CCR2 receptor function using mouse tumor models and in vitro human monocyte cultures. We show, in this study, that losartan and its metabolite potently inhibit monocyte recruitment through the noncompetitive inhibition of CCL2-induced ERK1/2 activation, independent of AT1R activity. Studies in experimental metastasis models demonstrated that losartan treatment significantly reduced the metastatic burden in mice, an effect associated with a significant decrease in CD11b+/Ly6C+-recruited monocytes in the lungs. Collectively, these results indicate that losartan can exert antimetastatic activity by inhibiting CCR2 signaling and suppressing monocyte recruitment and therefore suggest that losartan (and potentially other AT1R blocker drugs) could be repurposed for use in cancer immunotherapy.

Programmed Cell Death Ligand 1 (PD-L1) Signaling Regulates Macrophage Proliferation and Activation.

Tumor-associated macrophages (TAMs) express programmed cell death ligand 1 (PD-L1) and contribute to the immune-suppressive tumor microenvironment. Although the role of the PD-L1 and PD-1 interaction to regulate T-cell suppression is established, less is known about PD-L1 signaling in macrophages and how these signals may affect the function of TAMs. We used in vitro and in vivo models to investigate PD-L1 signaling in macrophages and the effects of PD-L1 antibody treatment on TAM responses. Treatment of mouse and human macrophages with PD-L1 antibodies increased spontaneous macrophage proliferation, survival, and activation (costimulatory molecule expression, cytokine production). Similar changes were observed in macrophages incubated with soluble CD80 and soluble PD-1, and in PD-L1-/- macrophages. Macrophage treatment with PD-L1 antibodies upregulated mTOR pathway activity, and RNAseq analysis revealed upregulation of multiple macrophage inflammatory pathways. In vivo, treatment with PD-L1 antibody resulted in increased tumor infiltration with activated macrophages. In tumor-bearing RAG-/- mice, upregulated costimulatory molecule expression by TAMs and reduced tumor growth were observed. Combined PD-1/ PD-L1 antibody treatment of animals with established B16 melanomas cured half of the treated mice, whereas treatment with single antibodies had little therapeutic effect. These findings indicate that PD-L1 delivers a constitutive negative signal to macrophages, resulting in an immune-suppressive cell phenotype. Treatment with PD-L1 antibodies reverses this phenotype and triggers macrophage-mediated antitumor activity, suggesting a distinct effect of PD-L1, but not PD-1, antibody treatment. Cancer Immunol Res; 6(10); 1260-73. ©2018 AACR.

Immunization against full-length protein and peptides from the Lutzomyia longipalpis sand fly salivary component maxadilan protects against Leishmania major infection in a murine model.

Leishmaniasis is an arthropod vectored disease causing considerable human morbidity and mortality. Vaccination remains the most realistic and practical means to interrupt the growing number and diversity of sand fly vectors and reservoirs of Leishmania. Since transmission of Leishmania is achieved exclusively by sand fly vectors via immune-modulating salivary substances, conventional vaccination requiring an unmodified host immune response for success are potentially destined to fail unless immunomodulatory factors are somehow neutralized. Using cationic liposome DNA complexes (CLDC) as an adjuvant system along with Lu. longipalpis sand fly salivary component maxadilan (MAX) as antigen (Ag), we show that mice are protected from the MAX-induced exacerbation of infection with Leishmania major (Lm). The CLDC adjuvant and alum were comparable in terms of lesion induration and decreased parasite burden, however the alum adjuvant imposed more inflammation at the injection site. BALB/c, C3H and C57BL/6 mice vaccinated with MAX-CLDC containing either the full-length MAX or peptides spanning the N- and C-terminal regions of MAX are protected against footpad challenges with Lm co-injected with MAX. When compared to unvaccinated controls, all strains of mice immunized with CLDC containing either peptides encompassing the first 20 N-terminal AA or those spanning the last 15 AA of the C-terminal domain of MAX demonstrated decreased parasite burden after 9 or 18 weeks post challenge with Lm + MAX. MAX-CLDC immunized mice showed increased IFNγ-secreting and decreased IL-4-secreting CD4+ cells in footpad-draining lymph nodes. Antisera from C-terminal peptide (P11) MAX-CLDC-vaccinated animals was capable of recognizing FL-MAX and its C-terminal domain and also blocked MAX-mediated reprogramming of bone marrow-derived dendritic cells (BM-DC) in vitro. This peptide vaccine targeting sand fly MAX, improves host immunity against MAX-mediated immunomodulation.

Autologous and Allogeneic Equine Mesenchymal Stem Cells Exhibit Equivalent Immunomodulatory Properties In Vitro.

The use of allogeneic bone marrow-derived mesenchymal stem cells (BMDMSCs) may provide an effective alternative to autologous BMDMSCs for treatment of equine musculoskeletal injuries. However, concerns have been raised regarding the potential safety and effectiveness of allogeneic BMDMSCs. We conducted studies to assess the immunological properties of equine allogeneic BMDMSCs compared with those of autologous BMDMSCs. For assessment of inherent immunogenicity, the relative ability of allogeneic and autologous BMDMSCs to stimulate spontaneous proliferation of equine lymphocytes was compared. The immunosuppressive activity of the two cell types was evaluated by adding autologous or allogeneic BMDMSCs to activated lymphocytes and assessing suppression of lymphocyte proliferation and IFNγ production. Fifty-six allogeneic and 12 autologous combinations were evaluated. Studies were also done to elucidate mechanisms by which equine mesenchymal stem cells (MSCs) suppress lymphocyte function. Potential mechanisms evaluated included production of prostaglandin E2 (PGE2), nitric oxide, transforming growth factor-beta, and indoleamine 2,3-dioxygenase. We found that autologous and allogeneic BMDMSCs both induced mild but equivalent levels of spontaneous lymphocyte activation in vitro. In in vitro assays assessing the ability of BMDMSCs to suppress activated lymphocytes, both allogeneic and autologous BMDMSCs suppressed T cell proliferation and IFNγ production to an equal degree. The primary mechanism of equine BMDMSC suppression of T cells was mediated by PGE2. We concluded that allogeneic and autologous BMDMSCs are equivalent in terms of their immunomodulatory properties, and stimulated peripheral blood mononuclear cells appear to trigger the immunosuppressive properties of MSCs. Therefore, both cell types appear to have equal potency in modulating inflammatory processes related to acute or chronic musculoskeletal injuries in the horse.

Suppression of Canine Dendritic Cell Activation/Maturation and Inflammatory Cytokine Release by Mesenchymal Stem Cells Occurs Through Multiple Distinct Biochemical Pathways.

Mesenchymal stem cells (MSC) represent a readily accessible source of cells with potent immune modulatory activity. MSC can suppress ongoing inflammatory responses by suppressing T cell function, while fewer studies have examined the impact of MSC on dendritic cell (DC) function. The dog spontaneous disease model represents an important animal model with which to evaluate the safety and effectiveness of cellular therapy with MSC. This study evaluated the effects of canine MSC on the activation and maturation of canine monocyte-derived DC, as well as mechanisms underlying these effects. Adipose-derived canine MSC were cocultured with canine DC, and the MSC effects on DC maturation and activation were assessed by flow cytometry, cytokine ELISA, and confocal microscopy. We found that canine MSC significantly suppressed lipopolysaccharide (LPS)-stimulated upregulation of DC activation markers such as major histocompatibility class II (MHCII), CD86, and CD40. Furthermore, pretreatment of MSC with interferon gamma (IFNγ) augmented this suppressive activity. IFNγ-activated MSC also significantly reduced LPS-elicited DC secretion of tumor necrosis factor alpha without reducing secretion of interleukin-10. The suppressive effect of IFNγ-treated MSC on LPS-induced DC activation was mediated by soluble factors secreted by both MSC and DC. Pathways of DC functional suppression included programmed death ligand-1 expression and secretion of nitrous oxide, prostaglandin E2, and adenosine by activated MSC. Coculture of DC with IFNγ-treated MSC maintained DC in an immature state and prolonged DC antigen uptake during LPS maturation stimulus. Taken together, canine MSC are capable of potently suppressing DC function in a potentially inflammatory microenvironment through several separate immunological pathways and confirm the potential for immune therapy with MSC in canine immune-mediated disease models.

Concise Review: Stem Cell Trials Using Companion Animal Disease Models.

Studies to evaluate the therapeutic potential of stem cells in humans would benefit from more realistic animal models. In veterinary medicine, companion animals naturally develop many diseases that resemble human conditions, therefore, representing a novel source of preclinical models. To understand how companion animal disease models are being studied for this purpose, we reviewed the literature between 2008 and 2015 for reports on stem cell therapies in dogs and cats, excluding laboratory animals, induced disease models, cancer, and case reports. Disease models included osteoarthritis, intervertebral disc degeneration, dilated cardiomyopathy, inflammatory bowel diseases, Crohn's fistulas, meningoencephalomyelitis (multiple sclerosis-like), keratoconjunctivitis sicca (Sjogren's syndrome-like), atopic dermatitis, and chronic (end-stage) kidney disease. Stem cells evaluated in these studies included mesenchymal stem-stromal cells (MSC, 17/19 trials), olfactory ensheathing cells (OEC, 1 trial), or neural lineage cells derived from bone marrow MSC (1 trial), and 16/19 studies were performed in dogs. The MSC studies (13/17) used adipose tissue-derived MSC from either allogeneic (8/13) or autologous (5/13) sources. The majority of studies were open label, uncontrolled studies. Endpoints and protocols were feasible, and the stem cell therapies were reportedly safe and elicited beneficial patient responses in all but two of the trials. In conclusion, companion animals with naturally occurring diseases analogous to human conditions can be recruited into clinical trials and provide realistic insight into feasibility, safety, and biologic activity of novel stem cell therapies. However, improvements in the rigor of manufacturing, study design, and regulatory compliance will be needed to better utilize these models. Stem Cells 2016;34:1709-1729.

Intravenous adipose-derived mesenchymal stem cell therapy for the treatment of feline asthma: a pilot study.

OBJECTIVES: The aim of this study was to evaluate the feasibility and efficacy of serially administered adipose-derived mesenchymal stem cells (MSCs) in an experimental feline asthma model. METHODS: Allergic asthma was acutely induced with Bermuda grass allergen in six purpose-bred cats. Five intravenous infusions of allogeneic MSCs (n = 4; MSC-treated) or saline (n = 2; placebo-treated) were administered over the first 130 days after asthma induction. Infusions contained 2 × 106, 4 × 106, 4.7 × 106, 1 × 107 and 1 × 107 cryopreserved MSCs/cat. For thoracic imaging additional cats were enrolled as control groups: four untreated, experimentally asthmatic cats (combined with placebo-treated cats), and six healthy, non-asthmatic cats. Outcome measures included airway eosinophilia, pulmonary mechanics, thoracic computed tomography and several immunologic assays. RESULTS: Cats were assessed for 9 months after treatment. At early points, airway eosinophil percentage was not affected by MSC administration (post-treatment average of days 12, 26, 47, 108 and 133 in MSC-treated cats was 41 ± 15% and in placebo-treated cats it was 34 ± 16%). By month 9, eosinophil percentages in all MSC-treated cats decreased to normal reference intervals (MSC-treated 6%; placebo-treated 20%; normal <17%). Diminished airway hyper-responsiveness was noted in all MSC-treated compared with placebo-treated cats at day 133 (dose of methacholine to double baseline airway resistance: MSC-treated median 22.9 mg/ml [range 6.4-64.0]; individual placebo-treated cats 1.1 and 5.0 mg/ml). Lung attenuation (mean ± SEM MSC-treated -865 ± 12 Hounsfield units [HU]; untreated asthmatics -820 ± 11 HU; P = 0.004) and bronchial wall thickening scores (median [interquartile range] MSC-treated 0 [0-1.5]; untreated asthmatic 11.6 [7.3-27.3]; P = 0.010) were significantly reduced in MSC-treated vs untreated asthmatic cats, consistent with decreased airway remodeling at month 9. No clear immunologic mechanisms by which MSCs act were determined. CONCLUSIONS AND RELEVANCE: MSCs may have a delayed effect in reducing airway inflammation, airway hyper-responsiveness and remodeling in experimentally induced asthmatic cats. Results warrant additional investigation of MSC therapy for asthma in cats.

Comparison of cancer stem cell antigen expression by tumor cell lines and by tumor biopsies from dogs with melanoma and osteosarcoma.

Cancer stem cells (CSCs) represent a small subpopulation of tumor cells that play a critical role in initiating and sustaining tumor growth. However, we currently have an incomplete understanding of the expression patterns of CSC antigens in tumors of dogs, nor do we understand how expression of these antigens vary between tumor cell lines and tumor biopsy specimens. Therefore, we used flow cytometry and commonly reported CSC surface and intracellular markers to evaluate the phenotype and overall frequency of CSC subpopulations in tumor cell lines and primary tumor biopsy samples from dogs with melanoma and osteosarcoma. We found that cells expressing common CSC antigens were rare in tumor cell lines, with the exception of tumor cells expressing CD44 and CD90. In contrast, tumor cells expressing conventional CSC antigens such as CD133, CD34, CD44, CD24 and Oct3/4 were much more common in tumor biopsy samples. Notably, the frequency and types of putative CSC subpopulations were very similar in biopsy samples from dogs with either melanoma or osteosarcoma. Our results suggest that the tumor microenvironment significantly influences CSC subpopulations within tumors and that tumor cell lines may not accurately reflect the actual frequency or types of CSC subpopulations present in tumor tissues in vivo.

Blocking phosphatidylcholine utilization in Pseudomonas aeruginosa, via mutagenesis of fatty acid, glycerol and choline degradation pathways, confirms the importance of this nutrient source in vivo.

Pseudomonas aeruginosa can grow to very high-cell-density (HCD) during infection of the cystic fibrosis (CF) lung. Phosphatidylcholine (PC), the major component of lung surfactant, has been hypothesized to support HCD growth of P. aeruginosa in vivo. The phosphorylcholine headgroup, a glycerol molecule, and two long-chain fatty acids (FAs) are released by enzymatic cleavage of PC by bacterial phospholipase C and lipases. Three different bacterial pathways, the choline, glycerol, and fatty acid degradation pathways, are then involved in the degradation of these PC components. Here, we identified five potential FA degradation (Fad) related fadBA-operons (fadBA1-5, each encoding 3-hydroxyacyl-CoA dehydrogenase and acyl-CoA thiolase). Through mutagenesis and growth analyses, we showed that three (fadBA145) of the five fadBA-operons are dominant in medium-chain and long-chain Fad. The triple fadBA145 mutant also showed reduced ability to degrade PC in vitro. We have previously shown that by partially blocking Fad, via mutagenesis of fadBA5 and fadDs, we could significantly reduce the ability of P. aeruginosa to replicate on FA and PC in vitro, as well as in the mouse lung. However, no studies have assessed the ability of mutants, defective in choline and/or glycerol degradation in conjunction with Fad, to grow on PC or in vivo. Hence, we constructed additional mutants (ΔfadBA145ΔglpD, ΔfadBA145ΔbetAB, and ΔfadBA145ΔbetABΔglpD) significantly defective in the ability to degrade FA, choline, and glycerol and, therefore, PC. The analysis of these mutants in the BALB/c mouse lung infection model showed significant inability to utilize PC in vitro, resulted in decreased replication fitness and competitiveness in vivo compared to the complement strain, although there was little to no variation in typical virulence factor production (e.g., hemolysin, lipase, and protease levels). This further supports the hypothesis that lung surfactant PC serves as an important nutrient for P. aeruginosa during CF lung infection.

Safety and efficacy of intravenous infusion of allogeneic cryopreserved mesenchymal stem cells for treatment of chronic kidney disease in cats: results of three sequential pilot studies.

INTRODUCTION: Administration of mesenchymal stem cells (MSCs) has been shown to improve renal function in rodent models of chronic kidney disease (CKD), in part by reducing intrarenal inflammation and suppressing fibrosis. CKD in cats is characterized by tubulointerstitial inflammation and fibrosis, and thus treatment with MSCs might improve renal function and urinary markers of inflammation in this disease. Therefore, a series of pilot studies was conducted to assess the safety and efficacy of intravenous administration of allogeneic adipose-derived MSCs (aMSCs) in cats with naturally occurring CKD. METHODS: Cats enrolled in these studies received an intravenous infusion of allogeneic aMSCs every 2 weeks collected from healthy, young, specific pathogen-free cats. Cats in pilot study 1 (six cats) received 2 × 106 cryopreserved aMSCs per infusion, cats in pilot study 2 (five cats) received 4 × 106 cryopreserved aMSCs per infusion, and cats in pilot study 3 (five cats) received 4 × 106 aMSCs cultured from cryopreserved adipose. Serum biochemistry, complete blood count, urinalysis, urine protein, glomerular filtration rate, and urinary cytokine concentrations were monitored during the treatment period. Changes in clinical parameters were compared statistically by means of repeated measures analysis of variance (ANOVA) followed by Bonferroni's correction. RESULTS: Cats in pilot study 1 had few adverse effects from the aMSC infusions and there was a statistically significant decrease in serum creatinine concentrations during the study period, however the degree of decrease seems unlikely to be clinically relevant. Adverse effects of the aMSC infusion in cats in pilot study 2 included vomiting (2/5 cats) during infusion and increased respiratory rate and effort (4/5 cats). Cats in pilot study 3 did not experience any adverse side effects. Serum creatinine concentrations and glomerular filtration rates did not change significantly in cats in pilot studies 2 and 3. CONCLUSIONS: Administration of cryopreserved aMSCs was associated with significant adverse effects and no discernible clinically relevant improvement in renal functional parameters. Administration of aMSCs cultured from cryopreserved adipose was not associated with adverse effects, but was also not associated with improvement in renal functional parameters.

Urinary cytokine levels in apparently healthy cats and cats with chronic kidney disease.

Chronic kidney disease (CKD) is a common cause of illness and death in cats. The hallmark of CKD in cats is chronic tubulointerstitial nephritis, and inflammation contributes to the progression of renal fibrosis. However, at present, it is difficult to assess directly the degree of intra-renal inflammation without renal biopsy. Measurement of inflammatory cytokine levels in urine may provide a non-invasive means of assessing intra-renal inflammation. Urine cytokine levels (urine cytokine/urine creatinine ratio) were measured in 18 healthy cats and 26 cats with CKD. When urine cytokine levels in healthy and CKD cats were compared, we found significantly higher levels of IL-8 and transforming growth factor-ß1 (TGF-ß1) in urine of CKD cats, along with significantly lower vascular endothelial growth factor (VEGF) levels. A significant positive correlation between serum creatinine and TGF-ß1 levels was found in CKD cats. Urinary cytokine measurement may, potentially, be a useful means of assessing intra-renal inflammation, fibrosis and vascular health in cats with CKD.