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The canine spontaneous cancer model is increasingly utilized to evaluate new combined cancer immunotherapy approaches. While the major leukocyte subsets and phenotypes are closely related in dogs and humans, the functionality of T cells and antigen presenting cells in the two species has not been previously compared in detail. Such information would be important in interpreting immune response data and evaluating the potential toxicities of new cancer immunotherapies in dogs. To address this question, we used in vitro assays to compare the transcriptomic, cytokine, and proliferative responses of activated canine and human T cells, and also compared responses in activated macrophages. Transcriptomic analysis following T cell activation revealed shared expression of 515 significantly upregulated genes and 360 significantly downregulated immune genes. Pathway analysis identified 33 immune pathways shared between canine and human activated T cells, along with 34 immune pathways that were unique to each species. Activated human T cells exhibited a marked Th1 bias, whereas canine T cells were transcriptionally less active overall. Despite similar proliferative responses to activation, canine T cells produced significantly less IFN-γ than human T cells. Moreover, canine macrophages were significantly more responsive to activation by IFN-γ than human macrophages, as reflected by co-stimulatory molecule expression and TNF-α production. Thus, these studies revealed overall broad similarity in responses to immune activation between dogs and humans, but also uncovered important key quantitative and qualitative differences, particularly with respect to T cell responses, that should be considered in designing and evaluating cancer immunotherapy studies in dogs.

Mesenchymal stem cells (MSC) have been shown to improve wound healing and suppress inflammatory immune responses. Newer research also indicates that MSC exhibit antimicrobial activity, although the mechanisms underlying this activity have not been fully elucidated. Therefore, we conducted in vitro and in vivo studies to examine the ability of resting and activated MSC to kill bacteria, including multidrug resistant strains. We investigated direct bacterial killing mechanisms and the interaction of MSC with host innate immune responses to infection. In addition, the activity of MSC against chronic bacterial infections was investigated in a mouse biofilm infection model. We found that MSC exhibited high levels of spontaneous direct bactericidal activity in vitro. Moreover, soluble factors secreted by MSC inhibited Staphylococcus aureus biofilm formation in vitro and disrupted the growth of established biofilms. Secreted factors from MSC also elicited synergistic killing of drug‐resistant bacteria when combined with several major classes of antibiotics. Other studies demonstrated interactions of activated MSC with host innate immune responses, including triggering of neutrophil extracellular trap formation and increased phagocytosis of bacteria. Finally, activated MSC administered systemically to mice with established S. aureus biofilm infections significantly reduced bacterial numbers at the wound site and improved wound healing when combined with antibiotic therapy. These results indicate that MSC generate multiple direct and indirect, immunologically mediated antimicrobial activities that combine to help eliminate chronic bacterial infections when the cells are administered therapeutically. Human bone marrow MSC secrete factors that interact synergistically with antibiotics to media direct bacterial killing. Activation of MSC enhances indirect mechanisms of bacterial killing in a mouse biofilm infection model, and facilitates increased anti bacterial activity of neutrophils.

Traumatic brain injury (TBI) is an increasingly frequent and poorly understood condition lacking effective therapeutic strategies. Inflammation and oxidative stress (OS) are critical components of injury, and targeted interventions to reduce their contribution to injury should improve neurobehavioral recovery and outcomes. Recent evidence reveals potential protective, yet short-lived, effects of the endocannabinoids (ECs), 2-arachidonoyl glycerol (2-AG) and N-arachidonoyl-ethanolamine (AEA), on neuroinflammatory and OS processes after TBI. The aim of this study was to determine whether EC degradation inhibition after TBI would improve neurobehavioral recovery by reducing inflammatory and oxidative damage. Adult male Sprague-Dawley rats underwent a 5-mm left lateral craniotomy, and TBI was induced by lateral fluid percussion. TBI produced apnea (17±5 sec) and a delayed righting reflex (479±21 sec). Thirty minutes post-TBI, rats were randomized to receive intraperitoneal injections of vehicle (alcohol, emulphor, and saline; 1:1:18) or a selective inhibitor of 2-AG (JZL184, 16 mg/kg) or AEA (URB597, 0.3 mg/kg) degradation. At 24 h post-TBI, animals showed significant neurological and -behavioral impairment as well as disruption of blood–brain barrier (BBB) integrity. Improved neurological and -behavioral function was observed in JZL184-treated animals. BBB integrity was protected in both JZL184- and URB597-treated animals. No significant differences in ipsilateral cortex messenger RNA expression of interleukin (IL)-1β, IL-6, chemokine (C-C motif) ligand 2, tumor necrosis factor alpha, cyclooxygenase 2 (COX2), or nicotinamide adenine dinucleotide phosphate oxidase (NOX2) and protein expression of COX2 or NOX2 were observed across experimental groups. Astrocyte and microglia activation was significantly increased post-TBI, and treatment with JZL184 or URB597 blocked activation of both cell types. These findings suggest that EC degradation inhibition post-TBI exerts neuroprotective effects. Whether repeated dosing would achieve greater protection remains to be examined.

Mesenchymal stromal cells (MSCs) have been evaluated as a local therapeutic option to treat osteoarthritis (OA) with conflicting clinical results. Our previous studies have evaluated immune licensing of MSC through activation of Toll-like receptor and cytosolic cGAS-STING pathways, with demonstrated improvement in functional and structural outcomes in a rodent model of OA. The objective of this study was to investigate impact of MSC activation on their interaction with relevant joint target cells to better understand the mechanisms by which pre-activation improves MSC activity for treatment of osteoarthritis. Equine bone-marrow-derived MSCs (passage 2-3) from 3 healthy donors were stimulated with a TLR3-pathway agonist (polyinosinic:polycytidylic acid) or STING pathway agonist (2'3'-cGAMP) (10 μg/mL, 2 h, 2 × 10 cells/mL in suspension). Cells were plated (100,000 cells/well, 24-well plates) and conditioned media (CM) collected at 24 h. Equine monocyte-derived macrophages, synovial cells, and chondrocytes were stimulated with IL-1ß/TNF-α (20 ng/mL, 2 h), washed and treated 24 h with MSC-CM, TLR-MSC-CM or STING-MSC-CM, washed and cultured 24 h. CM was examined for cytokine secretion by multiplex immunoassay and ELISA (25 cytokines). Bulk RNA sequencing was performed on MSC and joint cell lines via an Illumina based platform. TLR-MSC-CM decreased IL-1β (p = 0.02), IL-6 (p = 0.02) secretion by synoviocytes and IL-18 secretion by activated chondrocytes (p = 0.002). STING-MSC-CM decreased IL-6, IL-8 secretion (p = 0.08) by synoviocytes, decreased IL-8 (p = 0.05) by activated chondrocytes, increased G-CSF (p = 0.01), IL-4 (p = 0.01) and decreased IL-5 (p = 0.01) by activated macrophages. Transcriptomic analyses indicated differential gene expression in each cell line following CM treatment varied by cell line. STING-MSC-CM vs TLR-MSC-CM induced 38 significantly altered DEGs in synoviocytes, 20 in chondrocytes, and 47 in macrophages. These findings indicate that joint cells respond differently to factors secreted by TLR or STING pathway activated MSC. The pathways altered were different for each target cell type and no clear pattern of responses was apparent. These results indicate that modeling of target cell responses to \"licensed\" MSC can provide new information on the MSC and target cell interactions, though ultimately the functional impacts of activated MSC need to be evaluated using models.

Objectives/Goals: Osteoarthritis (OA) is a multifactorial disease where sustained gut inflammation is a continued source of inflammatory mediators driving degenerative processes in joints. The goal was to use spontaneous equine model to compare fecal and leukocyte microbiome and correlation to transcriptome in OA. Methods/Study Population: Seventy-six horses (31 OA, 45 controls) were enrolled by population-based sampling. Feces and peripheral blood mononuclear cells (PBMC) were collected. Horses were determined to have OA by clinical and radiographic evidence. Horses were excluded if they received medications or joint injections within two months. Fecal and circulating leukocyte bacterial microbial 16s-seq was performed. Bulk RNAseq of PBMC was performed by the Illumina platform. Gene expression data were mapped to the equine genome, and differential expression analysis was performed with DESeq2. Qiime2 was used for microbial analysis. Enrichment analysis was performed with a cluster profiler. Correlation analyses were performed between the datasets. Results/Anticipated Results: Beta and alpha microbial diversity differed in feces and PBMC of OA vs. healthy horses. Horses with OA had an increased Firmicutes to Bacteroidetes ratio compared with controls. The fecal microbiome of OA horses had significantly higher amounts of Firmicutes Oribacterium (q Discussion/Significance of Impact: These data suggest that altered microbiome and PBMC gene expression are associated with naturally occurring OA in the translational equine model. While Oribacterium has been detected in humans with rheumatoid arthritis, its role in OA warrants further proteomic and metabolomic profiling.

Intra-articular administration of mesenchymal stromal cells (MSC) has demonstrated anti-inflammatory and chondroprotective activity in both preclinical models and in randomized clinical trials in patients with osteoarthritis (OA). Nonetheless, precedent from MSC studies in non-OA models suggests that the overall anti-inflammatory effectiveness of MSC can be improved by prior immune activation through cytokines or innate immune pathways. Therefore, in the current study, we determined whether activation of MSC by two different innate immune pathways (Toll-like receptor 3 (TLR3) pathway or Stimulator of Interferon Genes (STING) pathway could improve their effectiveness for intra-articular treatment of OA, using a murine destabilization of the medial meniscus (DMM) model. Outcome parameters included voluntary gait activity, joint histology and RNA transcriptomic analyses of synovial tissues. We found that activation of MSC via either innate immune pathway improved functional voluntary movement outcomes compared to treatment with non-activated MSC. Moreover, cartilage integrity, including cartilage preservation, was significantly improved in mice receiving activated MSC, with greater benefits observed in animals treated with STING pathway-activated MSC compared to animals treated with non-activated MSC alone. Transcriptomic analysis of joint tissues revealed that treatment with activated MSC upregulated pathways associated with tissue remodeling, angiogenesis, and wound healing compared to tissues from animals treated with non-activated MSC. These findings indicate therefore that innate immune activation of MSC prior to intra-articular delivery for treatment of OA can significantly improve functional gait activity and chondroprotective effects compared to non-activated MSC and suggest that this strategy could be evaluated clinically.

Chronic rhinitis (CR) is a frustrating clinical syndrome in dogs and our understanding of the disease pathogenesis in is limited. Increasingly, host–microbe interactions are considered key drives of clinical disease in sites of persistent mucosal inflammation such as the nasal and oral cavities. Therefore, we applied next generation sequencing tools to interrogate abnormalities present in the nose of dogs with CR and compared immune and microbiome profiles to those of healthy dogs. Host nasal cell transcriptomes were evaluated by RNA sequencing, while microbial communities were assessed by 16S rRNA sequencing. Correlation analysis was then used to identify significant interactions between nasal cell transcriptomes and the nasal microbiome and how these interactions were altered in animals with CR. Notably, we observed significant downregulation of multiple genes associated with ciliary function in dogs with CR, suggesting a previously undetected role for ciliary dysfunction in this syndrome. We also found significant upregulation of immune genes related to the TNF-α and interferon pathways. The nasal microbiome was also significantly altered in CR dogs, with overrepresentation of several potential pathobionts. Interactome analysis revealed significant correlations between bacteria in the genus Porphyromonas and the upregulated host inflammatory responses in dogs with CR, as well as defective ciliary function which was correlated with Streptococcus abundance. These findings provide new insights into host–microbe interactions in a canine model of CR and indicate the presence of potentially causal relationships between nasal pathobionts and the development of nasal inflammation and ciliary dysfunction.

Multiple biological therapies for orthopedic injuries are marketed to veterinarians, despite a lack of rigorous comparative biological activity data to guide informed decisions in selecting a most effective compound. Therefore, the goal of this study was to use relevant bioassay systems to directly compare the anti-inflammatory and immunomodulatory activity of three commonly used orthobiological therapies (OTs): mesenchymal stromal cells (MSC), autologous conditioned serum (ACS), and platelet rich plasma (PRP). Equine monocyte-derived macrophages were used as the readout system to compare therapies, including cytokine production and transcriptomic responses. Macrophages were stimulated with IL-1ß and treated 24 h with OTs, washed and cultured an additional 24 h to generate supernatants. Secreted cytokines were measured by multiplex immunoassay and ELISA. To assess global transcriptomic responses to treatments, RNA was extracted from macrophages and subjected to full RNA sequencing, using an Illumina-based platform. Data analysis included comparison of differentially expressed genes and pathway analysis in treated vs. untreated macrophages. All treatments reduced production of IL-1ß by macrophages. Secretion of IL-10 was highest in MSC-CM treated macrophages, while PRP lysate and ACS resulted in greater downregulation of IL-6 and IP-10. Transcriptomic analysis revealed that ACS triggered multiple inflammatory response pathways in macrophages based on GSEA, while MSC generated significant downregulation of inflammatory pathways, and PRP lysate induced a mixed immune response profile. Key downregulated genes in MSC-treated cultures included type 1 and type 2 interferon response, TNF-α and IL-6. PRP lysate cultures demonstrated downregulation of inflammation-related genes IL-1RA, SLAMF9, ENSECAG00000022247 but concurrent upregulation of TNF-α, IL-2 signaling, and Myc targets. ACS induced upregulation of inflammatory IL-2 signaling, TNFα and KRAS signaling and hypoxia, but downregulation of MTOR signaling and type 1 interferon signaling. These findings, representing the first comprehensive look at immune response pathways for popular equine OTs, reveal distinct differences between therapies. These studies address a critical gap in our understanding of the relative immunomodulatory properties of regenerative therapies commonly used in equine practice to treat musculoskeletal disease and will serve as a platform from which further comparisons may build.

The use of large animal spontaneous models of solid cancers, such as dogs with osteosarcoma (OS), can help develop new cancer immunotherapy approaches, including chimeric antigen receptor (CAR) T cells. The goal of the present study was to generate canine CAR T cells targeting the B7-H3 (CD276) co-stimulatory molecule overexpressed by several solid cancers, including OS in both humans and dogs, and to assess their ability to recognize B7-H3 expressed by canine OS cell lines or by canine tumors in xenograft models. A second objective was to determine whether a novel dual CAR that expressed a chemokine receptor together with the B7-H3 CAR improved the activity of the canine CAR T cells. Therefore, in the studies reported here we examined B7-H3 expression by canine OS tumors, evaluated target engagement by canine B7-H3 CAR T cells in vitro, and compared the relative effectiveness of B7-H3 CAR T cells versus B7-H3-CXCR2 dual CAR T cells in canine xenograft models. We found that most canine OS tumors expressed B7-H3; whereas, levels were undetectable on normal dog tissues. Both B7-H3 CAR T cells demonstrated activation and OS-specific target killing in vitro, but there was significantly greater cytokine production by B7-H3-CXCR2 CAR T cells. In canine OS xenograft models, little anti-tumor activity was generated by B7-H3 CAR T cells; whereas, B7-H3-CXCR2 CAR T cells significantly inhibited tumor growth, inducing complete tumor elimination in most treated mice. These findings indicated therefore that addition of a chemokine receptor could significantly improve the anti-tumor activity of canine B7-H3 CAR T cells, and that evaluation of this new dual CAR construct in dogs with primary or metastatic OS is warranted since such studies could provide a critical and realistic validation of the chemokine receptor concept.