Canine CD8 T cells showing NK cytotoxic activity express mRNAs for NK cell-associated surface molecules

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.

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

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 CD5low 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.

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.

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.

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.

Lymphokine-activated killer cell transplantation after anti-cancer treatment in two aged cats

Immunotherapy improves both survival and remission rates after cancer surgery in humans, but its veterinary use has been limited. We determined the safety and feasibility of lymphokine-activated killer (LAK) cell transplantation in two aged cats that had undergone surgery for malignancy. Case 1 involved an 18-year-old male Japanese domestic cat. The cat exhibited appetite loss and poor physical activity after the surgical excision of oral squamous cell carcinoma followed by four sessions of radiotherapy, and the owner strongly requested immunotherapy for preventing further deterioration in the animal’s quality of life (QOL). We subsequently administered LAK cells three times during a 2-month period. Case 2 involved a 20-year-old female Japanese domestic cat who had undergone mammectomy after a diagnosis of breast adenocarcinoma. The owner strongly requested immunotherapy for QOL maintenance. We administered LAK cells four times over a period of 5 months. Autologous peripheral blood mononuclear cells (PBMCs) fractionated using density gradient centrifugation were cultured in the media containing a high concentration of interleukin-2 and supplemented with 2.5% fetal calf serum. The derived LAK cells were centrifuged, suspended in 10 ml of saline containing 1% of the subject’s own blood, and infused into the cephalic vein of the cats over 30 min. The composition ratios of CD3, CD4, CD8, and CD21 were evaluated by flow cytometry. Bacterial culture and endotoxin testing for a sample of LAK cells showed negative results in both the cases. The leukocyte and erythrocyte counts and the body temperature were assessed on days 7, 14, and 21 after the transfusion. No abnormal signs were observed in either case, which confirmed the safety of the procedure. QOL scores showed no significant changes after the treatment, and the body temperature remained steady throughout the treatment. The findings from these cases suggest that the transplantation of LAK cells derived from PBMCs may be safe and feasible for use in cats, regardless of their age.

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.

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.

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.

PD-1 expression by canine T cells and functional effects of PD-1 blockade

The co-inhibitory checkpoint molecule programmed death receptor 1 (PD-1) can trigger T cell functional exhaustion upon binding to its ligand PD-L1 expressed on tumour cells or macrophages. PD-1 blocking antibodies have generated remarkable results in human cancer patients, including inducing durable responses in a number of advanced cancers. Therefore, monoclonal antibodies specific for canine PD-1 were assessed for T cell binding and induction of functional activation. A total of 5-10% of CD4 T cells and 20-25% of CD8 T cells from healthy dogs expressed PD-1, and PD-1 expression was upregulated on T cells from dogs with cancer. Functionally, PD-1 antibodies significantly enhanced T-cell activation, as assessed by proliferation and interferon-gamma (IFN-γ) production. PD-1 antibodies also reversed T-cell suppression induced by canine soluble PD-L1 and by tumour cells and tumour explant fragments. These findings indicate that PD-1 antibodies have potential for use in cancer immunotherapy in dogs.

Isolation and characterization of canine natural killer cells

NK cells are non-T, non-B lymphocytes that kill target cells without previous activation. The immunophenotype and function of these cells in humans and mice are well defined, but canine NK cells remain incompletely characterized. Our objectives were to isolate and culture canine peripheral blood NK cells, and to define their immunophenotype and killing capability. PBMC were obtained from healthy dogs and T cells were depleted by immunomagnetic separation. The residual cells were cultured in media supplemented with IL-2, IL-15 or both, or with mouse embryonic liver (EL) feeder cells. Non-T, non-B lymphocytes survived and expanded in these cultures. IL-2 was necessary and sufficient for survival; the addition of IL-15 was necessary for expansion, but IL-15 alone did not support survival. Culture with EL cells and IL-2 also fostered survival and expansion. The non-T, non-B lymphocytes uniformly expressed CD45, MHC I, and showed significant cytotoxic activity against CTAC targets. Expression of MHC II, CD11/18 was restricted to subsets of these cells. The data show that cells meeting the criteria for NK cells in other species, i.e., non-T, non-B lymphocytes with cytotoxic activity, can be expanded from canine PBMC by T-cell depletion and culture with cytokines or feeder cells.

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

Canine NK cells still are not well-characterized due to the lack of information concerning specific NK cell markers and the fact that NK cells are not an abundant cell population. In this study, we selectively expanded the canine cytotoxic large granular lymphocytes (CLGLs) that exhibit morphologic, genetic, and functional characteristics of NK cells from normal donor PBMCs. The cultured CLGLs were characterized by a high proportion of CD5(dim) expressing cells, of which the majority of cells co-expressed CD3 and CD8, but did not express TCRαβ and TCRγδ. The phenotype of the majority of the CLGLs was CD5(dim)CD3(+)CD8(+) TCRαβ(-)TCRγδ(-)CD4(-)CD21(-)CD11c(+/-)CD11d(+/-)CD44(+). The expression of mRNAs for NK cell-associated receptors (NKG2D, NKp30, NKp44, Ly49, perforin, and granzyme B) were highly upregulated in cultured CLGLs. Specifically, NKp46 was remarkably upregulated in the cultured CLGLs compared to PBMCs. The mRNAs for the NKT-associated iTCRα gene in CLGLs was present at a basal level. The cytotoxic activity of the CLGLs against canine NK cell-sensitive CTAC cells was remarkably elevated in a dose-dependent manner, and the CLGLs produced large amounts of IFN-γ. The antitumor activity of CLGLs extended to different types of canine tumor cells (CF41.Mg and K9TCC-pu-AXC) without specific antigen recognition. These results are consistent with prior reports, and strongly suggest that the selectively expanded CLGLs represent a population of canine NK cells. The results of this study will contribute to future research on canine NK cells as well as NK cell-based immunotherapy.

Understanding of the immunological heterogeneity of canine mammary carcinomas to provide immunophenotypic features of circulating leukocytes as clinically relevant prognostic biomarkers

We have evaluated the phenotypic features of peripheral blood leukocytes as putative novel biomarkers with prognostic values to monitor canine mammary carcinomas. Female dogs were categorized into distinct groups, referred as mammary carcinoma in benign mixed tumor-MC-BMT and mammary carcinoma-MC. Our findings demonstrate that decreased percentage of B-cells along with increased frequency of NK-cells, CD8(+)T-cells, and CD8(+)CD5(Low+)T-cells beside higher T/B-cells and lower CD4(+)/CD8(+) ratio were the hallmarks of MC-BMT. Despite the lower expression of MHCI and MHCII, the lymphocytes from MC-BMT and MC displayed higher migration potential as suggested by enhanced frequency of CD18(+) events. Although increased levels of macrophage-like cells/(CD14(+)CD16(+)) and decreased levels of MHCII expression were a common phenotypic feature in mammary carcinoma, down-regulation of MHCI was selectively observed in MC. Decreased frequency of CD4(+) T-cells with increased levels of CD8(+) T-cells and lower CD4(+)/CD8(+) T-cell ratio were relevant biomarkers of MC-BTM(-). Although decreased expression of MHCI by monocytes was observed in MC-BTM regardless of the presence of lymph node metastasis, this phenotypic feature was restricted to MC free of metastasis. The CD4(+)/CD8(+) T-cells ratio lower than 1.8 was elected as a valid parameter with outstanding performance to predict survival in MC-BMT. On the other hand, the MHCI expression by monocytes higher than 10(2) MFI showed good value to estimate worse outcome in MC. These results should help to improve our understanding of the immunological heterogeneity of canine mammary carcinomas and provide tools for the determination of cut-off scores of clinically relevant immonophenotypic prognostic biomarkers.