Ex vivo expansion of canine cytotoxic large granular lymphocytes exhibiting characteristics of natural killer cells

Improved characterization and translation of NK cells for canine immunotherapy

The field of cancer immunology has seen a meteoric rise in interest and application due to the discovery of immunotherapies that target immune cells, often leading to dramatic anti-tumor effects. However, successful cellular immunotherapy for solid tumors remains a challenge, and the application of immunotherapy to dogs with naturally occurring cancers has emerged as a high yield large animal model to bridge the bench-to-bedside challenges of immunotherapies, including those based on natural killer (NK) cells. Here, we review recent developments in the characterization and understanding of canine NK cells, a critical springboard for future translational NK immunotherapy research. The characterization of canine NK cells is exceptionally pertinent given the ongoing challenges in defining them and contextualizing their similarities and differences compared to human and murine NK cells compounded by the limited availability of validated canine specific reagents. Additionally, we summarize the current landscape of the clinical and translational literature employing strategies to capitalize on endogenous and exogenous NK cell immunotherapy in canine cancer patients. The insights regarding efficacy and immune correlates from these trials provide a solid foundation to design and test novel combinational therapies to enhance NK cell activity with the added benefit of motivating comparative work to translate these findings to human cancers with extensive similarities to their canine counterparts. The compilation of knowledge from basic canine NK phenotype and function to applications in first-in-dog clinical trials will support the canine cancer model and enhance translational work to improve cancer outcomes for both dogs and humans.

Missing a "Missing Self" Mechanism: Modeling and Detection of Ly49 Expression in Canine NK Cells

NK cells are a key focus in immuno-oncology, based on their ability to eliminate malignant cells without prior sensitization. Dogs are valuable models for translational immunotherapy studies, especially for NK cells, where critical species differences exist between mice and humans. Given that the mechanism for recognition of "self" by canine NK cells is currently unknown, we sought to evaluate expression of Ly49 in canine NK cells using in silico and high-throughput techniques. We interrogated the identified polymorphism/mutation in canine Ly49 and assessed the potential impact on structure using computational modeling of three-dimensional protein structure and protein-protein docking of canine Ly49 with MHC class I (MHC-I). Bulk and single-cell RNA-sequencing analysis was performed to detect gene expression of Ly49/KLRA1 in resting and activated NK cells. Tertiary protein structure demonstrated significant structural similarity to the known murine system. Molecular docking of canine Ly49 with MHC-I was favorable, converging at a single low-energy conformation. RNA sequencing revealed expression of Ly49/KLRA1 in both resting and activated NK cells and demonstrated almost exclusive expression of the gene in the NK cluster at the single-cell level. Despite prior reports of a mutated, nonfunctional canine Ly49, our data support that the protein product is predicted to bind to MHC-I in a comparable conformation to the murine system and is expressed in canine NK cells with upregulation following activation. Taken together, these data suggest that Ly49 is capable of recognizing MHC-I and therefore regulating NK cell function in dogs.

Significant increase in MIC-A and MIC-B and soluble MIC-A and MIC-B in canine lymphomas

Non-Hodkin's lymphoma (NHL) is the most frequent hematologic malignancy in humans and dogs. NKG2D is one of the most critical receptors on NK cells, recognizing their natural ligands on malignant cells such as A and B major histocompatibility complex-related proteins (MIC-A and MIC-B). Soluble molecules (sMIC-A and sMIC-B) can interfere with immune synapsis between NK cells and tumor cells, impeding NK cytotoxicity. The main objectives of this study were to analyze, in dogs with diffuse large B cell lymphoma, NK cell lymphoma, and reactive lymphadenopathies, the role of NK cells, their activating receptors NKG2D and NKp46, and their ligands MIC-A and MIC-B, as well as soluble molecules sMIC-A and sMIC-B. Thirty-six dogs with a possible diagnosis of NHL and eight healthy dogs were studied. NHL was diagnosed in 28 (78 %) dogs; in the other 8 (22 %), reactive lymphadenopathies were present. Most of the lymphomas corresponded to B cell NHL (82 %). The most predominant subtype was diffuse large B cell lymphoma (21, 71.5 %), followed by five cases (18 %) that were Non-B Non-T lymphomas (presumably NK cell lymphomas) and other B cell lymphomas (3, 10.5%). There were no cases of T cell NHL. MIC-A was positive in 7 of 27 (26 %) cases of NHL, and MIC-B in 20 of 27 (74 %) NHL. In non-malignant lymphadenopathies, three (37.5 %) dogs were positive for MIC-A, and five (62.5 %) expressed MIC-B. Dogs with lymphoma had higher numbers of NK cells than eight healthy dogs. In 15 dogs (12 cases with NHL and three cases with reactive adenopathies) and eight controls, there were no differences in the number of NK cells expressing NKP46 and NKG2D. NHL dogs had higher values of sMIC-A and sMIC-B. B-cell and NK cell lymphomas correspond to 86 % and 14 % of all canine lymphomas. MIC-A, MIC-B, and sMIC-A and sMIC-B were increased in canine lymphomas.

Racing CARs to veterinary immuno-oncology

Chimeric antigen receptors (CARs) have demonstrated remarkable promise in human oncology over the past two decades, yet similar strategies in veterinary medicine are still in development. CARs are synthetically engineered proteins comprised of a specific antigen-binding single chain variable fragment (ScFv) fused to the signaling domain of a T cell receptor and co-receptors. Patient T cells engineered to express a CAR are directed to recognize and kill target cells, most commonly hematological malignancies. The U.S Food and Drug Administration (FDA) has approved multiple human CAR T therapies, but translation of these therapies into veterinary medicine faces many challenges. In this review, we discuss considerations for veterinary use including CAR design and cell carrier choice, and discuss the future promise of translating CAR therapy into veterinary oncology.

T Cell Immune Profiles of Blood and Tumor in Dogs Diagnosed With Malignant Melanoma

Investigation of canine T cell immunophenotypes in canine melanomas as prognostic biomarkers for disease progression or predictive biomarkers for targeted immunotherapeutics remains in preliminary stages. We aimed to examine T cell phenotypes and function in peripheral blood mononuclear cells (PBMC) and baseline tumor samples by flow cytometry, and to compare patient (n = 11–20) T cell phenotypes with healthy controls dogs (n = 10–20). CD3, CD4, CD8, CD25, FoxP3, Ki67, granzyme B, and interferon-γ (IFN-γ) were used to classify T cell subsets in resting and mitogen stimulated PBMCs. In a separate patient cohort (n = 11), T cells were classified using CD3, CD4, CD8, FoxP3, and granzyme B in paired PBMC and single cell suspensions of tumor samples. Analysis of flow cytometric data of individual T cell phenotypes in PBMC revealed specific T cell phenotypes including FoxP3+ and CD25+FoxP3- populations that distinguished patients from healthy controls. Frequencies of IFN-γ+ cells after ConA stimulation identified two different patient phenotypic responses, including a normal/exaggerated IFN-γ response and a lower response suggesting dysfunction. Principle component analysis of selected T cell immunophenotypes also distinguished patients and controls for T cell phenotype and revealed a clustering of patients based on metastasis detected at diagnosis. Findings supported the overall hypothesis that canine melanoma patients display a T cell immunophenotype profile that is unique from healthy pet dogs and will guide future studies designed with larger patient cohorts necessary to further characterize prognostic T cell immunophenotypes.

Comparative Immunogenomics of Canine Natural Killer Cells as Immunotherapy Target

Natural killer (NK) cells are key effectors of the innate immune system, but major differences between human and murine NK cells have impeded translation. Outbred dogs offer an important link for studies of NK biology and immunotherapy. We analyzed gene expression of putative NK populations from healthy dogs and dogs with naturally-occurring cancers examining differential gene expression across multiple conditions, including steady-state, in vitro activation with cytokines and co-culture, and in vivo activation with inhaled IL-15 in dogs receiving IL-15 immunotherapy. We also compared dog, mouse and human CD3-NKp46+ NK cells using a novel orthologous transcriptome. Distinct transcriptional profiles between NK populations exist between conditions and in vitro versus in vivo treatments. In cross-species analysis, canine NK cells were globally more similar to human NK cells than mice. These data define canine NK cell gene expression under multiple conditions and across species, filling an important gap in translational NK studies.

Immunotherapy for Dogs: Still Running Behind Humans

Despite all good intentions, dogs are still running behind humans in effective cancer immunotherapies. The more effective treatments in humans, like infusions of CAR-T and NK-cells are not broadly pursued for canines due to significant costs, the rather complicated logistics and the lack of targetable surface antigens. Monoclonal antibodies are challenging to develop considering the limited knowledge about canine target antigens and about their mode of action. Although immunogenic vaccines could be less costly, this approach is hampered by the fact that cancer by itself is immuno-suppressive and any preceding chemotherapy may suppress any clinically meaningful immune response. This review - rather than providing a comprehensive listing of all available immunotherapies for dogs, aims at pointing out the issues that are holding back this field but which hopefully can be addressed so that dogs can "catch up" with what is available to humans.

Comparative Expression Analysis of Innate Immune Markers and Phagocytic Activity in Peripheral Blood of Dogs with Mammary Tumors

Simple Summary

The presented study aimed to find out the differences between peripheral blood immune cell markers from healthy bitches and bitches with mammary tumors. Due to the fact that the role of canine innate immune cells in cancer remains poorly understood, the markers of innate cells were chosen for this research. Blood samples from female dogs with mammary tumors of epithelial and mesenchymal origin were investigated by flow cytometry. CD5 and CD11b markers of innate immune cells, phagocytic activity, and cellular killing were assessed. The number of CD11b lymphocytes was increased in tumors with epithelial origin. No significant differences were found between the percentages of phagocytic cells. However, the phagocytes of canine patients with tumors of epithelial origin showed increased phagocytosis compared to the control group. In oxidative burst test, a statistically significant difference between the number of reactive oxygen species (ROS) produced was demonstrated only between the group of bitches with epithelial tumors and the control group. These results may suggest that there are subpopulations of innate immune cells that may be involved in anti-tumor immune mechanisms and have a potential to be supportive diagnostic markers in canine mammary tumors.

Abstract

Canine innate immune system role in cancer prevention and progression remains poorly understood. It has been revealed that innate immune cells could play a dual role in cancer immunology promoting or inhibiting tumor development and growth. Current immunotherapies target mainly the adaptive anti-tumor response and that may be a reason why they remain ineffective in a majority of patients. It is important to acquire detailed knowledge about innate immune mechanisms to broaden the diagnostic and therapeutic options and employ innate immune cells in anti-cancer therapies. In the present study, 21 female dogs of different breeds and types of spontaneous mammary tumors were investigated. The study aimed to find simple and cheap markers that can be used for preliminary diagnosis, prior to the surgical resection of the tumor. The differences in innate immune cell quantity and function were investigated between female dogs with malignant mammary tumors of epithelial and mesenchymal origin. Flow cytometry was used to evaluate the percentages of CD5+ lymphocytes including CD5^low lymphocytes, CD11b integrin expression on leukocytes, phagocytosis, and oxidative burst. The number of CD11b lymphocytes was increased in tumors with epithelial origin compared to the control group. No significant differences were found between the percentages of phagocytic cells neither for granulocytes nor for monocytes. However, the phagocytes of canine patients with tumors of epithelial origin showed increased phagocytosis compared to the control group. The percentages of granulocytes that produced reactive oxygen species (ROS) in response to E.coli and PMA were not altered in patients with malignant tumors compared to control. A statistically significant difference between the number of ROS produced by the single granulocyte was demonstrated only between the group of bitches with epithelial tumors and the control group in case of E. coli stimulation. The obtained results suggest that some innate immune cells may be involved in anti-tumor immune mechanisms and have the potential to be supportive diagnostic markers in canine mammary tumors.

There and back again: Translating adoptive cell therapy to canine cancer and improving human treatment

Adoptive cell transfer (ACT) is a burgeoning therapeutic modality within human immuno-oncology. Novel approaches towards ACT are being developed in the pre-clinical setting faster than they can be evaluated in human clinical trials. Many of the therapeutic approaches used in human medicine have already been evaluated to some degree in canine patients. While this form of immunotherapy in veterinary medicine is still in its infancy, as these approaches develop, canine ACT will become a tool for both the veterinary oncologist and the translational researcher. This review details canine ACT trials to date, with attention given to the precedents provided by human oncology.

Quality of life-improving effect of autologous ex vivo expanded cytotoxic and opioid-producing lymphocytes for dogs with cancers

Activated lymphocyte therapy is one of the immunotherapies for cancer patients that is expected to prolong life without any adverse effects and maintain satisfactory quality of life (QOL). However, the objective assessment and maintenance of a standardized evaluation of QOL are not easy. We aimed to evaluate activated autologous lymphocyte therapy for cancer dogs using the characteristics of the cultured cells and QOL as perceived by owners. In in vitro experiments, peripheral blood mononuclear cells (PBMCs) collected from healthy dogs were stimulated using anti-CD3 antibody and recombinant interleukin-2 under a closed system. The number of CD4⁺ and CD8⁺ T lymphocytes in the cultured cells was higher than that of PBMCs (P < 0.05). Natural killer activity, proenkephalin (known as the precursor of endogenous opioids) and interferon-γ mRNA in activated lymphocytes were significantly higher than in PBMCs (P < 0.05). Met-enkephalin was detected in activated lymphocytes. QOL of 58 dogs afflicted with common types of cancers in humans increased after every administration of activated lymphocyte therapy (P < 0.05). Overall, these results indicated that activated lymphocyte therapy could have beneficial effects on QOL in dogs with cancers. This was objectively evaluated and this improvement was related to presence of opioid-producing lymphocytes.

Enhancement of natural killer cell activity by oral administration of a fermented soybean product in dogs

Background

Probiotics are known for their ability to enhance cellular immunity, including the activation of macrophages, natural killer (NK) cells, and cytotoxic T lymphocytes. Natto is a Japanese traditional probiotic food made by fermenting soybean with bacteria Bacillus subtilis var. natto. Components of natto include spores of B. subtilis natto, poly-γ-glutamic acid, and levan, which have demonstrated their immunoadjuvant and anti-allergic effects through various in vitro and in vivo studies. However, it remains unclear whether oral administration of natto can modulate the immune activity in animals.

Aim

This study aimed to investigate the effects of oral administration of natto on the immune system of dogs.

Methods

Eight dogs were randomly divided into two groups: a natto-treated group and an untreated group. The dogs in the natto-treated group were fed with 10 g/head/day of a freeze-dried natto product in addition to a usual amount of regular dry food for 14 days, whereas the dogs in the untreated group were fed with the regular dry food alone. To determine cellular immune activity, the cell surface antigen analysis of peripheral blood lymphocytes and cytotoxicity analysis of peripheral blood mononuclear cells were carried out before and after the natto administration period. Additionally, a relative expression of inflammatory cytokines in peripheral blood monocytes after the introduction of antigen-stimulation was also examined.

Results

At the end of the administration period, a proportion of NK cells (CD3- CD5- CD21- cells and CD3+ CD5dim CD8+ cells) in peripheral blood lymphocytes were found to be significantly increased, and the cytotoxic effect of the peripheral blood mononuclear cells on canine tumor cells were greatly enhanced in the natto-treated group, but not in the untreated group. The expression of TNF-α in peripheral blood mononuclear cells following an antigen-stimulation was increased considerably in the dogs after administration of natto.

Conclusion

We conclude that oral administration of natto activated the cytotoxic activity of peripheral NK cells in dogs, and a daily intake of natto might be helpful in augmenting cellular immune activity.

Adoptive Natural Killer Cell Immunotherapy for Canine Osteosarcoma

Osteosarcoma is the most common primary bone tumor in both humans and dogs. It is a highly metastatic cancer and therapy has not improved significantly since the inclusion of adjuvant chemotherapy into disease treatment strategies. Osteosarcoma is an immunogenic tumor, and thus development of immunotherapies for its treatment, especially treatment of microscopic pulmonary metastases might improve outcomes. NK cells are lymphocytes of the innate immune system and can recognize a variety of stressed cells, including cancer cells, in the absence of major histocompatibility complex (MHC)-restricted receptor ligand interactions. NK cells have a role in controlling tumor progression and metastasis and are important mediators of different therapeutic interventions. The core hypothesis of adoptive natural killer (NK) cell therapy is there exists a natural defect in innate immunity (a combination of cancer-induced reduction in NK cell numbers and immunosuppressive mechanisms resulting in suppressed function) that can be restored by adoptive transfer of NK cells. Here, we review the rationale for adoptive NK cell immunotherapy, NK cell biology, TGFβ and the immunosuppressive microenvironment in osteosarcoma, manufacturing of ex vivo expanded NK cells for the dog and provide perspective on the present and future clinical applications of adoptive NK cell immunotherapy in spontaneous osteosarcoma and other cancers in the dog.

Safety and immunological effects of recombinant canine IL-15 in dogs

Interleukin-15 (IL-15) is a pleiotropic cytokine that plays pivotal roles in innate and adaptive immunity. It is also a promising cytokine for treating cancer. Despite growing interest in its use as an immunotherapeutic, its safety and immunological effects in dogs have not been reported. In this study, healthy dogs were given recombinant canine IL-15 (rcIL-15) intravenously at a daily dose of 20 μg/kg for 8 days and monitored for 32 days to determine the safety and immunological effects of rcIL-15. The repeated administration of rcIL-15 was well tolerated, did not cause any serious side effects, and promoted the selective proliferation and activation of canine anti-cancer effector cells, including CD3⁺CD8⁺ cytotoxic T lymphocytes, CD3⁺CD5^dimCD21^-, and non-B/non-T NK cell populations, without stimulating T_reg lymphocytes. The rcIL-15 injections also stimulated the expression of molecules and transcription factors associated with the activation and effector functions of NK cells, including CD16, NKG2D, NKp30, NKp44, NKp46, perforin, granzyme B, Ly49, T-bet, and Eomes. These results suggest that rcIL-15 might be a valuable therapeutic adjuvant to improve immunity against cancer in dogs.

A newly established canine NK-type cell line and its cytotoxic properties

We established a canine natural killer (NK)-type cell line called CNK-89 derived from a dog with NK cell neoplasia. Immunophenotyping analysis showed positive staining for CD5, CD8, CD45, CD56, CD79a and NKp46, while negative for CD3, CD4, CD14, CD20, CD21, CD34, Thy1, IgG, IgM and MHCII. Polymerase chain reaction analysis revealed the presence of CD56, NKG2D, NKp30, NKp44, NKp46 and perforin, but the absence of CD16, Ly49 and granzyme B mRNA. Treating CNK-89 cells with IL-2 did not change the expression of activating receptors, TNFα and IFNγ secretion and cytotoxic activity, however, treatment with IL-12 alone or in combinations with IL-15, IL-18 and IL-21 caused an increase in granzyme B and CD16 mRNA, IFNγ secretion and cytotoxic properties of the CNK-89 cell line.

Safety analysis of ex vivo-expanded canine natural killer cells in a xenogeneic mouse model of graft-versus-host disease

Canine natural killer (NK) cells are large, granular lymphocytes that are neither B lymphocytes nor T lymphocytes. However, it has been reported that canine NK cells share some of the phenotypic characteristics of T lymphocytes, such as CD3 and CD5. Studies are needed to assess the safety of canine NK cells for immunotherapy, especially because the safety of using allogeneic NK cells as an immunotherapy for dogs has yet to be shown. In this study, the safety of cultured canine NK cells was assessed using a xenogeneic mouse model of graft-versus-host disease (GVHD). Mice were injected with either canine peripheral blood mononuclear cells (PBMCs) or cultured NK cells for 2 or 3 weeks. Data were then collected on changes in mice body weights, disease severity scores, and survival rates. Histopathological and immunohistochemical evaluations were also performed. All mice injected with canine PBMCs died within 45 days after injection. Severe clinical signs were caused by GVHD. The histopathological and immunohistochemical evaluations showed that mice injected with canine PBMCs had multiple lesions, including necrosis in their lungs, livers, kidneys, and stomachs, and the injected cells were present around the lesions. By contrast, no mice injected with cultured NK cells without removing the CD3⁺ TCR^- cells exhibited any clinical abnormalities. Moreover, they all survived the 90-day experimental period without exhibiting any histopathological changes. Accordingly, the results of this study suggest that canine NK cells do not cause significant side effects such as GVHD and allogeneic NK cells can safely be used for cancer immunotherapy in dogs.

CD94 Ex Vivo Cultures in a Bone Marrow Transplantation Setting

Background

Complementary, marrow donor-derived peripheral blood T-lymphocyte infusions enable consistent hematopoietic engraftment in lethally irradiated dog leukocyte antigen (DLA)-haploidentical littermate recipients, but at the cost of severe graft versus host disease (GVHD). Here, we explored whether CD94-selected and in vitro-expanded natural killer (NK) cells could be substituted for T-lymphocytes for enhancing marrow engraftment without causing severe GVHD.

Methods

Five dogs were conditioned with 700 cGy total body irradiation followed by infusion of DLA-haploidentical donor marrow and CD94-selected, in vitro-expanded NK cells. NK cells were infused at a median of 140 000 (range 78 000-317 000) cells/kg.

Results

Four dogs rejected their marrow grafts, whereas 1 dog fully engrafted and developed GVHD. We observed an increase in peripheral blood NK cells after infusion of CD94-selected, ex vivo-expanded NK in 2 dogs. Peripheral blood lymphocyte counts peaked at day 7 or 8 posttransplant in the 4 rejecting dogs, whereas in the fully engrafted dog, lymphocyte counts remained stable at suboptimal levels.

Conclusions

Our study indicates NK cells can be expanded in vitro and safely infused into DLA-haploidentical recipients. Within the range of CD94-selected and expanded cells infused we concluded that they failed to both uniformly promote engraftment and avert GVHD.

Blood and tissue biomarker analysis in dogs with osteosarcoma treated with palliative radiation and intra-tumoral autologous natural killer cell transfer

We have previously reported radiation-induced sensitization of canine osteosarcoma (OSA) to natural killer (NK) therapy, including results from a first-in-dog clinical trial. Here, we report correlative analyses of blood and tissue specimens for signals of immune activation in trial subjects. Among 10 dogs treated with palliative radiotherapy (RT) and intra-tumoral adoptive NK transfer, we performed ELISA on serum cytokines, flow cytometry for immune phenotype of PBMCs, and PCR on tumor tissue for immune-related gene expression. We then queried The Cancer Genome Atlas (TCGA) to evaluate the association of cytotoxic/immune-related gene expression with human sarcoma survival. Updated survival analysis revealed five 6-month survivors, including one dog who lived 17.9 months. Using feeder line co-culture for NK expansion, we observed maximal activation of dog NK cells on day 17-19 post isolation with near 100% expression of granzyme B and NKp46 and high cytotoxic function in the injected NK product. Among dogs on trial, we observed a trend for higher baseline serum IL-6 to predict worse lung metastasis-free and overall survival (P = 0.08). PCR analysis revealed low absolute gene expression of CD3, CD8, and NKG2D in untreated OSA. Among treated dogs, there was marked heterogeneity in the expression of immune-related genes pre- and post-treatment, but increases in CD3 and CD8 gene expression were higher among dogs that lived > 6 months compared to those who did not. Analysis of the TCGA confirmed significant differences in survival among human sarcoma patients with high and low expression of genes associated with greater immune activation and cytotoxicity (CD3e, CD8a, IFN-γ, perforin, and CD122/IL-2 receptor beta). Updated results from a first-in-dog clinical trial of palliative RT and autologous NK cell immunotherapy for OSA illustrate the translational relevance of companion dogs for novel cancer therapies. Similar to human studies, analyses of immune markers from canine serum, PBMCs, and tumor tissue are feasible and provide insight into potential biomarkers of response and resistance.

Characterization and Potential Applications of Dog Natural Killer Cells in Cancer Immunotherapy

Natural killer (NK) cells of the innate immune system are a key focus of research within the field of immuno-oncology based on their ability to recognize and eliminate malignant cells without prior sensitization or priming. However, barriers have arisen in the effective translation of NK cells to the clinic, in part because of critical species differences between mice and humans. Companion animals, especially dogs, are valuable species for overcoming many of these barriers, as dogs develop spontaneous tumors in the setting of an intact immune system, and the genetic and epigenetic factors that underlie oncogenesis appear to be similar between dogs and humans. Here, we summarize the current state of knowledge for dog NK cells, including cell surface marker phenotype, key NK genes and genetic regulation, similarities and differences of dog NK cells to other mammals, especially human and mouse, expression of canonical inhibitory and activating receptors, ex vivo expansion techniques, and current and future clinical applications. While dog NK cells are not as well described as those in humans and mice, the knowledge of the field is increasing and clinical applications in dogs can potentially advance the field of human NK biology and therapy. Better characterization is needed to truly understand the similarities and differences of dog NK cells with mouse and human. This will allow for the canine model to speed clinical translation of NK immunotherapy studies and overcome key barriers in the optimization of NK cancer immunotherapy, including trafficking, longevity, and maximal in vivo support.

Canine non-B, non-T NK lymphocytes have a potential antibody-dependent cellular cytotoxicity function against antibody-coated tumor cells

Background

The antibody-dependent cellular cytotoxicity (ADCC) is a cell-mediated immune defense mechanism in which effector immune cells actively lyse antibody-coated target cells. The ADCC of tumor cells is employed in the treatment of various cancers overexpressing unique antigens, and only natural killer (NK) cells are known to be major effectors of antibody mediated ADCC activity. Canine NK cells are still defined as non-B, non-T large granular lymphocytes because of the lack of information regarding the NK cell-restricted specific marker in dogs, and it has never been demonstrated that canine NK cells have ADCC ability against tumor cells. In the present study, we investigated whether canine non-B, non-T NK cells have ADCC ability against target antibody-coated tumor cells, using cetuximab and trastuzumab, the only human antibodies reported binding to canine cancer cells.

Results

Activated canine non-B, non-T NK cells (CD3⁻CD21⁻CD5⁻TCRαβ⁻TCRγδ⁻) for 13~17 days ex vivo showed ADCC ability against trastuzumab- or cetuximab-coated target tumor cells expressing various levels of human epidermal growth factor receptor 2 (HER-2) and epidermal growth factor receptor (EGFR). Trastuzumab and cetuximab induced significant ADCC responses of canine NK cells even in CMT-U334 and CF41.Mg cells expressing low levels of HER-2 and/or EGFR, as well as in SKBR3 and DU145 cells overexpressing HER-2 and/or EGFR. The trastuzumab-mediated ADCC activity of NK cells was significantly enhanced by treatment with rcIL-21.

Conclusions

The results of this study suggest that canine non-B, non-T NK lymphocytes have a potential ADCC function and that combinational strategies of monoclonal antibodies with either cytokines, which activate NK cells in vivo, or adoptive transfer of NK cells may be a feasible method for amplifying the efficacy of immunotherapy against malignant cancers even with very low expression of target molecules in dogs.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-2068-5) contains supplementary material, which is available to authorized users.

Development and characterization of a canine-specific anti-CD94 (KLRD-1) monoclonal antibody

Natural killer (NK) cells are non-T, non-B lymphocytes are part of the innate immune system and function without prior activation. The human NK cell surface determinant, CD94, plays a critical role in regulation of NK cell activity as a heterodimer with NKG2 subclasses. Canine NK cells are not as well defined as the human and murine equivalents, due in part to the paucity of reagents specific to cell surface markers. Canines possess NK/NKT cells that have similar morphological characteristics to those found in humans, yet little is known about their functional characteristics nor of cell surface expression of CD94. Here, we describe the development and function of a monoclonal antibody (mAb) to canine (ca) CD94. Freshly isolated canine CD94⁺ cells were CD3^+/-, CD8^+/-, CD4-, CD21-, CD5^low, NKp46⁺, and were cytotoxic against a canine target cell line. Anti-caCD94 mAb proved useful in enriching NK/NKT cells from PBMC for expansion on CTAC feeder cells in the presence of IL-2 and IL-15. The cultured cells were highly cytolytic with co-expression of NKp46 and reduced expression of CD3. Transmission electron microscopy revealed expanded CD94⁺ lymphocytes were morphologically large granular lymphocytes with large electron dense granules. Anti-caCD94 (mAb) can serve to enrich NK/NKT cells from dog peripheral blood for ex vivo expansion for HCT and is a potentially valuable reagent for studying NK/NKT regulation in the dog.

A case of hemophagocytic syndrome progressing into large granular lymphoma in a dog

A 12-year-old castrated male mixed breed dog was presented with anorexia, lethargy, intermittent vomiting, diarrhea, and weight loss. Clinicopathologic and imaging abnormalities included pancytopenia, icterus, and splenomegaly with multiple minute hypoechogenic nodules. Bone marrow (BM) smears revealed 2.5% hemophagocytic macrophages. In addition, an increased number of small to intermediate lymphocytes (16.3%) and plasma cells (3.2%) were recognized in the BM smears. More than 80% of the lymphocytes contained multiple small intracytoplasmic magenta granules. Histopathologic findings of the spleen revealed hemophagocytosis. Large granular lymphocytes (LGLs) were not found on the liver cytology or splenic histopathology at this time. PCR for antigen receptor rearrangement (PARR) analysis showed a clonal reaction in the T-cell receptor ɤ (TCRɤ) gene in the BM sample. The dog was diagnosed with hemophagocytic syndrome (HPS). The dog was maintained in good condition with immunosuppressive therapy. However, the dog developed hepatic LGL lymphoma 7 months later. At this time, PARR analysis showed a clonal TCRɤ gene rearrangement in the hepatic LGL lymphoma samples. The BM and liver sample clonal rearrangements showed 100% homology, indicating that the small to intermediate granular lymphocytes in the BM at the HPS stage had progressed to hepatic LGL lymphoma. To our knowledge, this is the first report of canine secondary HPS caused by the occurrence of a BM LGL lymphoma clone that progressed to hepatic LGL lymphoma.

Cellular Immunotherapy of Canine Cancer

Infusions with immune cells, such as lymphocytes or natural killer (NK) cells, represent one of several modalities of immunotherapy. In human patients with advanced B-cell leukemia or lymphoma, infusions with chimeric antigen receptor (CAR) T-lymphocytes have shown promising responses. However, the scientific and clinical development of cell-based therapies for dogs, who get cancer of similar types as humans, is lagging behind. One reason is that immune cells and their functionality in dogs are less well characterized, largely due a lack of canine-specific reagents to detect surface markers, and specific cytokines to isolate and expand their immune cells. This review summarizes the current status of canine cancer immunotherapies, with focus on autologous and allogeneic T-lymphocytes, as well as NK cells, and discusses potential initiatives that would allow therapies with canine immune cells to “catch up” with the advances in humans.

Antigen-Specific CD4+CD8+ Double-Positive T Cells Are Increased in the Blood and Spleen During Ehrlichia chaffeensis Infection in the Canine Host

Ehrlichia chaffeensis is an obligate intracellular bacterium belonging to the order, Rickettsiales and is a frequent cause of severe and fatal tick-borne infection in people in North America. The reservoir host for E. chaffeensis is the white-tailed deer, while humans and dogs are regarded as common incidental hosts. In dogs, we and others have shown that E. chaffeensis establishes a chronic infection that persists for several weeks to months, while promoting the development of Th1 and Th17 cellular responses and pathogen-specific humoral immunity. We demonstrate here that vaccination with a live, attenuated clone of E. chaffeensis bearing a targeted mutation in the Ech_0230 gene neither promotes the development of long-lived cellular or humoral immunity, nor confers protection against secondary wild-type E. chaffeensis challenge. In dogs, a population of mature CD4+CD8+ double-positive (DP) T cells exists in the periphery that shares similarities with the DP T cell populations that have been described in humans and swine. Little is known about the function of these cells, particularly in the context of infectious diseases. Here, we demonstrate that canine DP T cells expand significantly in response to E. chaffeensis infection. Using in vitro antigen recall assays, we further demonstrate that canine DP T cells undergo clonal expansion, produce IFNγ and IL-17, and upregulate expression of granzyme B and granulysin. Together, our results demonstrate that DP T cells accumulate in the host during E. chaffeensis infection, and suggest that alternative lymphocyte populations may participate in the immune response to tick-borne infections in the incidental host.

Comparison of Phenotypic and Functional Characteristics Between Canine Non-B, Non-T Natural Killer Lymphocytes and CD3+CD5dimCD21- Cytotoxic Large Granular Lymphocytes

Natural killer (NK) cells play a pivotal role in the immune response against infections and malignant transformation, and adopted transfer of NK cells is thought to be a promising therapeutic approach for cancer patients. Previous reports describing the phenotypic features of canine NK cells have produced inconsistent results. Canine NK cells are still defined as non-B and non-T (CD3⁻CD21⁻) large granular lymphocytes. However, a few reports have demonstrated that canine NK cells share the phenotypic characteristics of T lymphocytes, and that CD3⁺CD5^dimCD21⁻ lymphocytes are putative canine NK cells. Based on our previous reports, we hypothesized that phenotypic modulation could occur between these two populations during activation. In this study, we investigated the phenotypic and functional differences between CD3⁺CD5^dimCD21⁻ (cytotoxic large granular lymphocytes) and CD3⁻CD5⁻CD21⁻ NK lymphocytes before and after culture of peripheral blood mononuclear cells isolated from normal dogs. The results of this study show that CD3⁺CD5^dimCD21⁻ lymphocytes can be differentiated into non-B, non-T NK (CD3⁻CD5⁻CD21⁻TCRαβ⁻TCRγδ⁻GranzymeB⁺) lymphocytes through phenotypic modulation in response to cytokine stimulation. In vitro studies of purified CD3⁺CD5^dimCD21⁻ cells showed that CD3⁻CD5⁻CD21⁻ cells are derived from CD3⁺CD5^dimCD21⁻ cells through phenotypic modulation. CD3⁺CD5^dimCD21⁻ cells share more NK cell functional characteristics compared with CD3⁻CD5⁻CD21⁻ cells, including the expression of T-box transcription factors (Eomes, T-bet), the production of granzyme B and interferon-γ, and the expression of NK cell-related molecular receptors such as NKG2D and NKp30. In conclusion, the results of this study suggest that CD3⁺CD5^dimCD21⁻ and CD3⁻CD5⁻CD21⁻ cells both contain a subset of putative NK cells, and the difference between the two populations may be due to the degree of maturation.

Activating natural killer (NK) cytotoxicity of canine CD5-CD21- cells requires low surface CD5 density NK cells

Natural killer (NK) cells play a crucial role in regulating immune functions. Few studies have characterized canine NK cells. We previously demonstrated that canine peripheral blood lymphocytes (PBLs) with a low surface CD5 density (CD5lo) are considered a critical NK population. Natural killer cells in most mammals do not express T-cell markers, but canine CD5lo cells express surface molecules, such as CD3 T-cell receptors. These features make canines unique models for the study of comparative immunology in NK cells. In this study, we discovered that CD5lo and CD21 double-negative (CD5lo-ne/CD2^-) cells were originally low in NK cytotoxicity and their NK cytotoxicity was highly activated when co-cultured with CD5lo NK cells. The cytotoxicity was not activated when co-cultured with other cell types, such as high surface CD5 density (CD5hi) cells. The CD5lo-negative (CD5lo-ne) population comprises CD5^- and CD5hi cells. CD5-cells were low in NK cytotoxicity initially or after culturing with interleukin-2 (IL-2) without CD5lo cells; however, the addition of CD5lo cells in a similar medium markedly enhanced the NK activity. By contrast, CD5hi cells were always NK inactive, irrespective of them being cultured with CD5lo cells or not. We further verified that only the CD5^-CD21^- cells, which were separated from CD5^-CD21⁺ cells in the entire CD5^- population, showed activated NK activity through CD5lo cell induction. This study is the first to reveal that canine NK cells enhanced NK-inert cells to become NK-cytotoxic cells. Additionally, it is concluded that in beagles, except for CD5lo cells, CD5^-CD21^- cells show NK activity.

Radiotherapy enhances natural killer cell cytotoxicity and localization in pre-clinical canine sarcomas and first-in-dog clinical trial

BACKGROUND

We have previously shown that radiotherapy (RT) augments natural killer (NK) functions in pre-clinical models of human and mouse cancers, including sarcomas. Since dogs are an excellent outbred model for immunotherapy studies, we sought to assess RT plus local autologous NK transfer in canine sarcomas.

METHODS

Dog NK cells (CD5^dim, NKp46+) were isolated from PBMCs and expanded with irradiated K562-C9-mIL21 feeder cells and 100 IU/mL recombinant human IL-2. NK homing and cytotoxicity ± RT were evaluated using canine osteosarcoma tumor lines and dog patient-derived xenografts (PDX). In a first-in-dog clinical trial for spontaneous osteosarcoma, we evaluated RT and intra-tumoral autologous NK transfer.

RESULTS

After 14 days, mean NK expansion and yield were 19.0-fold (±8.6) and 258.9(±76.1) ×10⁶ cells, respectively. Post-RT, NK cytotoxicity increased in a dose-dependent fashion in vitro reaching ~ 80% at effector:target ratios of ≥10:1 (P < 0.001). In dog PDX models, allogeneic NK cells were cytotoxic in ex vivo killing assays and produced significant PDX tumor growth delay (P < 0.01) in vivo. After focal RT and intravenous NK transfer, we also observed significantly increased NK homing to tumors in vivo. Of 10 dogs with spontaneous osteosarcoma treated with focal RT and autologous NK transfer, 5 remain metastasis-free at the 6-month primary endpoint with resolution of suspicious pulmonary nodules in one patient. We also observed increased activation of circulating NK cells after treatment and persistence of labelled NK cells in vivo.

CONCLUSIONS

NK cell homing and cytotoxicity are increased following RT in canine models of sarcoma. Results from a first-in-dog clinical trial are promising, including possible abscopal effects.

Current update of adoptive immunotherapy using cytokine-induced killer cells to eliminate malignant gliomas

The therapeutic outcome for those with malignant glioma is poor, even though diverse therapeutic modalities have been developed. Immunotherapy has emerged as a therapeutic approach for malignant gliomas, making it possible to selectively treat tumors while sparing normal tissue. Here, we review clinical trials of adoptive immunotherapy approaches for malignant gliomas. We also describe a clinical trial that examined the efficacy and safety of autologous cytokine-induced killer (CIK) cells along with concomitant chemoradiotherapy for newly diagnosed glioblastoma. These CIK cells identify and kill autologous tumor cells. This review focuses on the use of adoptive immunotherapy for malignant gliomas and reviews the current literature on the concept of antitumor activity mediated by CIK cells.

Evaluation of blood T-lymphocyte subpopulations involved in host cellular immunity in dogs with mammary cancer

Cancer-bearing patients are often immunosuppressed. In dogs with mammary or other cancers, various alterations in blood cell populations involved in host cellular immunity have been reported; among these cell populations some T-lymphocyte subsets play an important role against cancer. The purpose of the present study was to investigate any alterations in circulating T-lymphocyte subpopulations involved in cellular immunity in bitches with mammary cancer, in comparison to age-matched healthy intact bitches. Twenty eight dogs with mammary cancer and 14 control dogs were included in this study. Twelve out of the 28 bitches had mammary cancer of clinical stage II and 16/28 of stage III. Histological examination revealed that 23/28 animals had carcinomas, 3/28 sarcomas and 2/28 carcinosarcomas. White blood cell, neutrophil and lymphocyte absolute numbers were measured by complete blood count. Furthermore, blood T-lymphocyte population (CD3⁺) and the subpopulations CD4⁺, CD8⁺ and CD5^low+ were assessed by flow cytometry. White blood cell and neutrophil but not lymphocyte absolute numbers were higher (P=0.003 and P=0.001, respectively) in cancer patients than controls. Flow cytometric analysis revealed that the relative percentage of T-lymphocytes (CD3⁺) and of CD4⁺, CD8⁺ subpopulations was lower (the CD4⁺/CD8⁺ ratio was higher), whereas the percentage of CD5^low+ T-cells was higher, in dogs with cancer compared to controls; however, a statistically significant difference was found only in the case of CD8⁺ T-cells (P=0.014), whereas in the case of the CD4⁺/CD8⁺ ratio the difference almost reached statistical significance (P=0.059). Based on these findings, it can be suggested that, although the absolute number of blood lymphocytes is unchanged, the relative percentages of T-lymphocyte subpopulations involved in host cell-mediated immunity are altered, but only cytotoxic CD8⁺ T-cells are significantly suppressed, in dogs with mammary cancer of clinical stage II or III compared to age-matched healthy controls.

Canine cancer immunotherapy studies: linking mouse and human

Despite recent major clinical breakthroughs in human cancer immunotherapy including the use of checkpoint inhibitors and engineered T cells, important challenges remain, including determining the sub-populations of patients who will respond and who will experience at times significant toxicities. Although advances in cancer immunotherapy depend on preclinical testing, the majority of in-vivo testing currently relies on genetically identical inbred mouse models which, while offering critical insights regarding efficacy and mechanism of action, also vastly underrepresent the heterogeneity and complex interplay of human immune cells and cancers. Additionally, laboratory mice uncommonly develop spontaneous tumors, are housed under specific-pathogen free conditions which markedly impacts immune development, and incompletely model key aspects of the tumor/immune microenvironment. The canine model represents a powerful tool in cancer immunotherapy research as an important link between murine models and human clinical studies. Dogs represent an attractive outbred combination of companion animals that experience spontaneous cancer development in the setting of an intact immune system. This allows for study of complex immune interactions during the course of treatment while also directly addressing long-term efficacy and toxicity of cancer immunotherapies. However, immune dissection requires access to robust and validated immune assays and reagents as well as appropriate numbers for statistical evaluation. Canine studies will need further optimization of these important mechanistic tools for this model to fulfill its promise as a model for immunotherapy. This review aims to discuss the canine model in the context of existing preclinical cancer immunotherapy models to evaluate both its advantages and limitations, as well as highlighting its growth as a powerful tool in the burgeoning field of both human and veterinary immunotherapy.

NCR1 Expression Identifies Canine Natural Killer Cell Subsets with Phenotypic Similarity to Human Natural Killer Cells

Canines spontaneously develop many cancers similar to humans - including osteosarcoma, leukemia, and lymphoma - offering the opportunity to study immune therapies in a genetically heterogeneous and immunocompetent environment. However, a lack of antibodies recognizing canine NK cell markers has resulted in suboptimal characterization and unknown purity of NK cell products, hindering the development of canine models of NK cell adoptive immunotherapy. To this end, we generated a novel antibody to canine NCR1 (NKp46), the putative species-wide marker of NK cells, enabling purification of NK cells for further characterization. We demonstrate that CD3^-/NKp46⁺ cells in healthy and osteosarcoma-bearing canines have phenotypic similarity to human CD3^-/NKp46⁺ NK cells, expressing mRNA for CD16 and the natural cytotoxicity receptors NKp30, NKp44, and NKp80. Functionally, we demonstrate with the calcein release assay that canine CD3^-/NKp46⁺ cells kill canine tumor cell lines without prior sensitization and secrete IFN-γ, TNF-α, IL-8, IL-10, and granulocyte-macrophage colony-stimulating factor as measured by Luminex. Similar to human NK cells, CD3^-/NKp46⁺ cells expand rapidly on feeder cells expressing 4-1BBL and membrane-bound IL-21 (median = 20,283-fold in 21 days). Furthermore, we identify a minor Null population (CD3^-/CD21^-/CD14^-/NKp46^-) with reduced cytotoxicity against osteosarcoma cells, but similar cytokine secretion as CD3^-/NKp46⁺ cells. Null cells in canines and humans have reduced expression of NKG2D, NKp44, and CD16 compared to NKp46⁺ NK cells and can be induced to express NKp46 with further expansion on feeder cells. In conclusion, we have identified and characterized canine NK cells, including an NKp46^- subset of canine and human NK cells, using a novel anti-canine NKp46 antibody, and report robust ex vivo expansion of canine NK cells sufficient for adoptive immunotherapy.

Expansion of NK Cells Using Genetically Engineered K562 Feeder Cells

Natural killer (NK) cells can be expanded upon activation by proliferative cytokines (such as IL-2 and IL-15). The NK cell expansion can be greatly enhanced by proteins from feeder cells such as tumor cell lines or PBMCs. Therefore, coculture systems of irradiated feeder cells and NK cells in media containing IL-2 and IL-15 have been developed to generate large numbers of NK cells, although NK cell expansion protocol using anti-CD3 antibody (OKT-3) without feeder cells has also been developed. Commonly used feeder cell lines are RPMI8866, Epstein-Barr lymphoblastoid cell line (EBV-LCL), and K562. Stimulation with NK-sensitive K562 cells is known to augment NK cell proliferation to IL-2, IL-15, and IL-21 in combination.Recently, remarkable NK cell-expansion rates are achieved when genetically engineered (GE) feeder cells are used. Dr. Dario Campana's group found that membrane-bound IL-15 and 4-1BBL, coexpressed by K562 cells, acted synergistically to augment K562-specific NK stimulatory capacity, resulting in vigorous expansion of peripheral blood CD56(+) CD3(-) NK cells without concomitant growth of T lymphocytes. Here, we describe an in vitro expansion method of human NK cells among PBMCs by coculturing with GE_K562 cells.

Gamma delta T-cell large granular lymphocyte lymphoma in a dog

A 2-year and 6-month-old female neutered Labrador Retriever with Horner syndrome, megaesophagus, and a mediastinal mass was referred to the Queen Mother Hospital for Animals of the Royal Veterinary College. A large granular lymphocyte (LGL) lymphoma was diagnosed on cytology; flow cytometric analysis revealed a γδ T-cell phenotype (CD3+, CD5+, CD45+, TCRγδ+, CD4-, CD8-, CD34-, CD21-). Chemotherapy was started with a combination of lomustine, vincristine, procarbazine, and prednisolone, followed by bleyomicin. Euthanasia was elected by the owners, due to progressive deterioration and lack of quality of life, 28 days after diagnosis. This is the first cytologic and immunophenotypic characterization of a canine γδ T-cell lymphoma with LGL morphology and probably of mediastinal origin. The role of chemotherapy in delaying the disease progression remains unknown.

Composition of lymphocyte subpopulations in normal canine lymph nodes

BACKGROUND

Flow cytometric immunophenotyping of lymph node aspirates has become a standard practice of canine lymphoma diagnostic workup. Ultimately, the combination of flow cytometry data, histopathology, and clinical signs allows consensus classification, and improves prognostic accuracy and therapeutic approaches.

OBJECTIVES

Although there is a growing body of information regarding lymphocyte population subsets in various types of lymphoma, only few studies provide information regarding the composition of the normal canine lymph node. The aim of this prospective study was to establish exploratory reference data for lymphocyte subpopulations in normal canine lymph nodes using an extended panel of antibodies.

METHODS

Popliteal lymph nodes excised from normal dogs were analyzed by cytology, multi-color flow cytometry using 11 different canine-specific and anti-human cross-reactive monoclonal antibodies, and polymerase chain reaction for antigen receptor rearrangement (PARR).

RESULTS

Subpopulations from lymph nodes of 26 dogs were classified according to the following positive antibody reactions: CD11a(+) 92.2 ± 12.3%, CD3(+) 55.0 ± 14.1%, CD3-12(+) 57.3 ± 14%, CD5(+) 52.3 ± 12.7%, CD21(+) 33.9 ± 11.8%, CD79αcγ(+) 46.9 ± 14.8%, CD56(+) 4.9 ± 5.9%, and CD14(+) 5.5 ± 6.8%. There were 58.7 ± 9% CD4(+) and 21.3 ± 7.8% CD8(+) cells inside the gate of CD3(+) cells. Cytology revealed a mixed population of mostly lymphoid cells in all samples. The absence of a monoclonal or oligoclonal neoplastic population was confirmed by PARR.

CONCLUSION

This study establishes for the first time flow cytometry data of lymphocyte populations in a larger group of normal canine lymph nodes, including populations positive for some new antibodies against CD3-12, CD5, CD11a, CD56, and CD79αcy.