Evaluation of costimulatory molecules in dogs with B cell high grade lymphoma

Immune checkpoint regulation is critically involved in canine cutaneous histiocytoma regression

Introduction

Canine cutaneous histiocytoma (CCH) is a benign tumor frequently occurring in young dogs which is derived from Langerhans cells (LC). Distinguishing features of this tumor are its spontaneous regression following a rapid tumor growth. Impaired control of immune checkpoints during tumor development and progression is a widespread phenomenon which may result in an absent or ineffective immune response. The interaction between the inflammatory response and the expression of immune checkpoint molecules is only partially described in this tumor type. The aim of this study was to identify immune checkpoint molecules and molecules from the interferon-mediated immune response that are involved in the regression of CCH.

Methods

Forty-eight CCH derived from dogs ≤ 4 years of age were assigned to one of four groups according to the severity and distribution of lymphocyte infiltration. Using immunohistochemistry and whole-slide image scans of consecutive sections the expression of programmed death protein ligand 1 (PD-L1), CD80, CD86, Survivin, forkhead box protein 3, Ki-67, cleaved caspase-3, CD3, and mx1 were investigated. RNA in-situ hybridization was performed for transcripts of mx1 and interferon-γ.

Results

Neoplastic cells showed an expression of PD-L1, CD80, CD86, and Survivin. The density of CD80 expressing cells was negatively correlated with regression while the density of cleaved caspase-3 positive cells increased with regression. Mx1 transcripts and protein were predominantly localized in neoplastic cells while interferon-γ transcripts were most frequently detected in T-cells.

Conclusion

The expression of the immune checkpoint molecules CD86 and PD-L1 and particularly the reduced expression of CD80 in groups 3 and 4 indicate an influence of the investigated immune checkpoints on tumor regression. In parallel an activation of the apoptotic cascade during regression is suggested. Finally, the detection of mx1 within the neoplasm pinpoints to a yet undisclosed role of anti-cellular signaling in tumor immunity.

Checkpoint Inhibitors in Dogs: Are We There Yet?

Immune checkpoint inhibitors (ICI) have revolutionised cancer treatment in people. Immune checkpoints are important regulators of the body's reaction to immunological stimuli. The most studied immune checkpoint molecules are programmed death (PD-1) with its ligand (PD-L1) and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) with its ligands CD80 (B7-1) and CD86 (B7-2). Certain tumours can evade immunosurveillance by activating these immunological checkpoint targets. These proteins are often upregulated in cancer cells and tumour-infiltrating lymphocytes, allowing cancer cells to evade immune surveillance and promote tumour growth. By blocking inhibitory checkpoints, ICI can help restore the immune system to effectively fight cancer. Several studies have investigated the expression of these and other immune checkpoints in human cancers and have shown their potential as therapeutic targets. In recent years, there has been growing interest in studying the expression of immune checkpoints in dogs with cancer, and a few small clinical trials with ICI have already been performed on these species. Emerging studies in veterinary oncology are centred around developing and validating canine-targeted antibodies. Among ICIs, anti-PD-1 and anti-PD-L1 treatments stand out as the most promising, mirroring the success in human medicine over the past decade. Nevertheless, the efficacy of caninized antibodies remains suboptimal, especially for canine oral melanoma. To enhance the utilisation of ICIs, the identification of predictive biomarkers for treatment response and the thorough screening of individual tumours are crucial. Such endeavours hold promise for advancing personalised medicine within veterinary practice, thereby improving treatment outcomes. This article aims to review the current research literature about the expression of immune checkpoints in canine cancer and the current results of ICI treatment in dogs.

Comparative characterization of two monoclonal antibodies targeting canine PD-1

Monoclonal antibodies targeting immune checkpoints have revolutionized oncology. Yet, the effectiveness of these treatments varies significantly among patients, and they are associated with unexpected adverse events, including hyperprogression. The murine research model used in drug development fails to recapitulate both the functional human immune system and the population heterogeneity. Hence, a novel model is urgently needed to study the consequences of immune checkpoint blockade. Dogs appear to be uniquely suited for this role. Approximately 1 in 4 companion dogs dies from cancer, yet no antibodies are commercially available for use in veterinary oncology. Here we characterize two novel antibodies that bind canine PD-1 with sub-nanomolar affinity as measured by SPR. Both antibodies block the clinically crucial PD-1/PD-L1 interaction in a competitive ELISA assay. Additionally, the antibodies were tested with a broad range of assays including Western Blot, ELISA, flow cytometry, immunofluorescence and immunohistochemistry. The antibodies appear to bind two distinct epitopes as predicted by molecular modeling and peptide phage display. Our study provides new tools for canine oncology research and a potential veterinary therapeutic.

Clinical Implications of Immune Checkpoints and the RANK/RANK-L Signaling Pathway in High-Grade Canine Mast Cell Tumors

Mast cell tumors (MCTs) are the most common malignant cutaneous tumors in dogs, and they present extremely variable biological behavior. The interaction between RANK, RANK-L, and immune checkpoints is frequently detected in the tumor microenvironment, and, together, they participate in every stage of cancer development. Thus, the aim of this study was to characterize the molecular profiles of PD-L1, CTLA-4, RANK/RANK-L signaling pathway, and IFN-γ in primary tumors and lymph node metastases. Formalin-fixed, paraffin-embedded slides of MCTs and metastatic lymph nodes of ten dogs were submitted to immunohistochemical investigations. The results demonstrated that the tumor microenvironment of the high-grade mast cell tumors showed moderate or intense immunolabeling of all proteins, and the lymph node metastases also showed moderate or intense immunolabeling of checkpoint proteins. In addition, MCTs larger than 3 cm were associated with intensified PD-L1 (p = 0.03) in metastatic lymph nodes and RANK-L (p = 0.049) immunoreactivity in the tumor. Furthermore, dogs with a survival time of less than 6 months showed higher PD-L1 immunoreactivity (p = 0.042). In conclusion, high-grade MCT is associated with an immunosuppressive microenvironment that exhibits elevated RANK/RANK-L signaling and enhanced immune checkpoint immunoreactivity, potentially facilitating intratumorally immune escape. These biomarkers show promise as clinical indicators of disease progression and might response to immunotherapy in dogs with high-grade MCTs, thus emphasizing their importance for guiding treatment decisions and improving outcomes.

Exploring the association of intratumoral immune cell infiltrates with histopathologic grade in canine mast cell tumors

Cutaneous canine mast cell tumors (ccMCTs) vary in their biological behavior, treatment, and prognosis, based on their grade. Immune cell infiltration has been associated with prognosis and response to treatments in some human cancers, and immune-targeting therapeutics are increasingly being explored in veterinary oncology. However, currently little is known about the tumor microenvironment (TME) in ccMCTs. Therefore, the objective of this study was to determine the prevalence of T lymphocytes, T regulatory lymphocytes, PD-1+ cells and macrophages in low- and high-grade ccMCTs. Thirty low-grade and 20 high-grade formalin-fixed paraffin-embedded ccMCT samples were included. Immunohistochemistry (IHC) was performed to detect CD3, FOXP3, Iba1, and PD-1 on sequential sections. Three 400x fields with the highest numbers of CD3+ cells were identified for each tumor. The percentage of CD3+, FOXP3+, and Iba1+ cells, and the number of PD-1+ cells, was quantified in each of these three "hot-spot" fields using ImageJ software. Iba1 expression was significantly greater in high-grade compared to low-grade ccMCTs (mean = 12.5% vs. 9.6%, p = 0.043). PD-1 expression was low overall, but a significantly higher number of PD-1-expressing cells was observed in high-grade ccMCTs (median 1 vs. 0, p = 0.001). No significant difference was noted in CD3 and FOXP3 expression between ccMCT grades. Macrophages and PD-1+ cells were more frequent in high-grade, compared to low-grade ccMCTs. Further studies are needed to define the role of macrophages and rare PD-1+ cells in high-grade ccMCTs.

Development of a fully canine anti-canine CTLA4 monoclonal antibody for comparative translational research in dogs with spontaneous tumors

The immune checkpoint inhibitor (ICI) ipilimumab has revolutionized the treatment of patients with different cancer histologies, including melanoma, renal cell carcinoma, and non-small cell lung carcinoma. However, only a subset of patients shows dramatic clinical responses to treatment. Despite intense biomarker discovery efforts linked to clinical trials using CTLA4 checkpoint blockade, no single prognostic correlate has emerged as a valid predictor of outcome. Client-owned, immune competent, pet dogs develop spontaneous tumors that exhibit similar features to human cancers, including shared chromosome aberrations, molecular subtypes, immune signatures, tumor heterogeneity, metastatic behavior, and response to chemotherapy. As such, they represent a valuable parallel patient population in which to investigate novel predictive biomarkers and rational therapeutic ICI combinations. However, the lack of validated, non-immunogenic, canine ICIs for preclinical use hinders this comparative approach. To address this, fully canine single-chain variable fragments (scFvs) that bind canine CTLA4 were isolated from a comprehensive canine scFv phage display library. A lead candidate for clinical development was selected based on its subnanomolar binding affinity to canine CTLA4 and its ability to prevent CTLA4 binding to CD80/CD86 and promote T cell proliferation and effector function. In vivo mouse studies revealed pharmacokinetics similar to isotype control IgG with no evidence of short-term adverse effects. This work paves the way for in vivo analysis of the first fully canine, anti-canine CTLA4 antibody to promote anti-tumor immunity in dogs with immune-responsive cancers and provide an important comparative tool to investigate correlative biomarkers of response and mechanisms of resistance to CTLA4 checkpoint inhibition.

Evaluation of lymphocyte-specific programmed cell death protein 1 receptor expression and cytokines in blood and urine in canine urothelial carcinoma patients

Urothelial carcinoma (UC) is the most common urinary tumour in dogs. Despite a range of treatment options, prognosis remains poor in dogs. In people, breakthroughs with checkpoint inhibitors have established new standards of care for muscle-invasive bladder cancer patients and elevated levels of programmed cell death protein 1 (PD-1) suggest immune checkpoint blockade may be a novel target for therapy. The goal of this study was to determine if canine UC patients express elevated levels of lymphocyte-specific PD-1 and/or urinary cytokine biomarkers compared to healthy dogs. Paired blood and urine were evaluated in 10 canine UC patients, five cystitis patients and 10 control dogs for lymphocyte-specific PD-1 expression via flow cytometry and relative cytokine expression. In UC patients, PD-1 expression was significantly elevated on CD8⁺ lymphocytes in urine samples. UC patients had a higher CD4:CD8 ratio in their urine compared to healthy dogs, however, there was no significant variation in the CD8:Treg ratio between any group. Cystitis patients had significantly elevated levels of CD4⁺ T cells, CD8⁺ T cells and Tregs in their blood samples compared to UC patients and healthy dogs. Cytokine analysis demonstrated significant elevations in urinary cytokines (granulocyte-macrophage colony-stimulating factor, interferon-gamma [IFN-γ], interleukin (IL)-2, IL-6 IL-7, IL-8 and IL-15, IP-10, KC-like, IL-18, monocyte chemoattractant protein-1 and tumour necrosis factor-alpha). Several of these cytokines have been previously correlated with both lymphocyte-specific PD-1 expression (IFN-γ, IL-2, IL-7 and IL-15) in muscle-invasive urothelial carcinoma in humans. Our results provide evidence of urinary lymphocyte PD-1 expression and future studies could elucidate whether veterinary UC patients will respond favourably to anti-PD-1 immune checkpoint inhibitor therapy.

Immunotherapeutic Strategies for Canine Lymphoma: Changing the Odds Against Non-Hodgkin Lymphoma

The new era of immune-oncology has brought complexities and challenges that emphasize the need to identify new strategies and models to develop successful and cost-effective therapies. The inclusion of a canine model in the drug development of cancer immunotherapies is being widely recognized as a valid solution to overcome several hurdles associated with conventional preclinical models. Driven by the success of immunotherapies in the treatment of human non-Hodgkin lymphoma (NHL) and by the remarkable similarities of canine NHL to its human counterpart, canine NHL has been one of the main focus of comparative research. Under the present review, we summarize a general overview of the challenges and prospects of today's cancer immunotherapies and the role that comparative medicine might play in solving the limitations brought by this rapidly expanding field. The state of art of both human and canine NHL and the rationale behind the use of the canine model to bridge the translational gap between murine preclinical studies and human clinical trials are addressed. Finally, a review of currently available immunotherapies for canine NHL is described, highlighting the potential of these therapeutic options.

PD-1, PD-L1, and PD-L2 Gene Expression and Tumor Infiltrating Lymphocytes in Canine Melanoma

Melanoma in humans and dogs is considered highly immunogenic; however, the function of tumor-infiltrating lymphocytes (TILs) is often suppressed in the tumor microenvironment. In humans, current immunotherapies target checkpoint molecules (such as PD-L1, expressed by tumor cells), inhibiting their suppressive effect over TILs. The role of PD-L2, an alternative PD-1 ligand also overexpressed in malignant tumors and in patients with anti-PD-L1 resistance, remains poorly understood. In the current study, we evaluated the expression of checkpoint molecule mRNAs in canine melanoma and TILs. Analysis of checkpoint molecule gene expression was performed by RT-qPCR (real-time quantitative polymerase chain reaction) using total RNA isolated from formalin-fixed and paraffin-embedded melanomas (n = 22) and melanocytomas (n = 9) from the Virginia Tech Animal Laboratory Services archives. Analysis of checkpoint molecule expression revealed significantly higher levels of PDCD1 (PD-1) and CD274 (PD-L1) mRNAs and an upward trend in PDCD1LG2 (PD-L2) mRNA in melanomas relative to melanocytomas. Immunohistochemistry revealed markedly increased numbers of CD3⁺ T cells in the highest PD-1-expressing subgroup of melanomas compared to the lowest PD-1 expressors, whereas densities of IBA1⁺ cells (macrophages) were similar in both groups. CD79a⁺ cell numbers were low for both groups. As in human melanoma, overexpression of the PD-1/PD-L1/PD-L2 axis is a common feature of canine melanoma. High expression of PD-1 and PD-L1 correlates with increased numbers of CD3⁺ cells. Additionally, the high level of IBA1⁺ cells in melanomas with low PD-1 expression and low CD3⁺ cells levels suggest that the expression of checkpoint molecules is modulated by interactions between T cells and cancer cells rather than histiocytes.

Cross-Reactivity and Functionality of Approved Human Immune Checkpoint Blockers in Dogs

BACKGROUND

Rodent cancer models have limitations in predicting efficacy, tolerability and accompanying biomarkers of ICIs in humans. Companion dogs suffering from neoplastic diseases have gained attention as a highly relevant translational disease model. Despite successful reports of PD-1/PD-L1 blockade in dogs, no compounds are available for veterinary medicine.

METHODS

Here, we assessed suitability of seven FDA-approved human ICIs to target CTLA-4 or PD-1/PD-L1 in dogs. Cross-reactivity and blocking potential was assessed using ELISA and flow cytometry. Functional responses were assessed on peripheral blood mononuclear cells (PBMCs) derived from healthy donors (n = 12) and cancer patient dogs (n = 27) as cytokine production after stimulation. Immune composition and target expression of healthy donors and cancer patients was assessed via flow cytometry.

RESULTS

Four candidates showed cross-reactivity and two blocked the interaction of canine PD-1 and PD-L1. Of those, only atezolizumab significantly increased cytokine production of healthy and patient derived PBMCs in vitro. Especially lymphoma patient PBMCs responded with increased cytokine production. In other types of cancer, response to atezolizumab appeared to correlate with a lower frequency of CD8 T cells.

CONCLUSIONS

Cross-functionality of atezolizumab encourages reverse translational efforts using (combination) immunotherapies in companion dog tumor patients to benefit both veterinary and human medicine.

FoxP3, CTLA-4, and IDO in Canine Melanocytic Tumors

Despite promising immunotherapy strategies in human melanoma, there are few studies on the immune environment of canine melanocytic tumors. In humans, the activation of immunosuppressive cell subpopulations, such as regulatory T cells (Tregs) that express forkhead box protein P3 (FoxP3), the engagement of immunosuppressive surface receptors like cytotoxic T lymphocyte antigen (CTLA-4), and the secretion of molecules inhibiting lymphocyte activation, such as indoleamine-pyrrole 2,3-dioxygenase (IDO), are recognized as immunoescape mechanisms that allow tumor growth and progression. The aim of our study was to investigate the expression of these immunosuppression markers in canine melanocytic tumors and to postulate their possible role in melanoma biology and progression. Fifty-five formalin-fixed, paraffin-embedded canine melanocytic tumors (25 oral melanomas; 20 cutaneous melanomas; 10 cutaneous melanocytomas) were selected to investigate the expression of FoxP3, CTLA-4, and IDO by immunohistochemistry and RT-qPCR (real-time quantitative polymerase chain reaction). All of the tested markers showed high gene and protein expression in oral melanomas and were differently expressed in cutaneous melanomas when compared to their benign counterpart. IDO expression was associated with an increased hazard of death both in univariable and multivariable analyses (P < .05). FoxP3 protein expression >6.9 cells/HPF (high-power field) was an independent predictor of death (P < .05). CTLA-4 gene and protein expressions were associated with a worse prognosis, but only in the univariable analysis (P < .05). FoxP3, CTLA-4, and IDO likely play a role in canine melanoma immunoescape. Their expression, if supported by future studies, could represent a prognostic tool in canine melanoma and pave the way to future immunotherapeutic approaches in dogs.

Naturally-Occurring Invasive Urothelial Carcinoma in Dogs, a Unique Model to Drive Advances in Managing Muscle Invasive Bladder Cancer in Humans

There is a great need to improve the outlook for people facing urinary bladder cancer, especially for patients with invasive urothelial carcinoma (InvUC) which is lethal in 50% of cases. Improved outcomes for patients with InvUC could come from advances on several fronts including emerging immunotherapies, targeted therapies, and new drug combinations; selection of patients most likely to respond to a given treatment based on molecular subtypes, immune signatures, and other characteristics; and prevention, early detection, and early intervention. Progress on all of these fronts will require clinically relevant animal models for translational research. The animal model(s) should possess key features that drive success or failure of cancer drugs in humans including tumor heterogeneity, genetic-epigenetic crosstalk, immune cell responsiveness, invasive and metastatic behavior, and molecular subtypes (e.g., luminal, basal). Experimental animal models, while essential in bladder cancer research, do not possess these collective features to accurately predict outcomes in humans. These key features, however, are present in naturally-occurring InvUC in pet dogs. Canine InvUC closely mimics muscle-invasive bladder cancer in humans in cellular and molecular features, molecular subtypes, immune response patterns, biological behavior (sites and frequency of metastasis), and response to therapy. Thus, dogs can offer a highly relevant animal model to complement other models in research for new therapies for bladder cancer. Clinical treatment trials in pet dogs with InvUC are considered a win-win-win scenario; the individual dog benefits from effective treatment, the results are expected to help other dogs, and the findings are expected to translate to better treatment outcomes in humans. In addition, the high breed-associated risk for InvUC in dogs (e.g., 20-fold increased risk in Scottish Terriers) offers an unparalleled opportunity to test new strategies in primary prevention, early detection, and early intervention. This review will provide an overview of canine InvUC, summarize the similarities (and differences) between canine and human InvUC, and provide evidence for the expanding value of this canine model in bladder cancer research.

Canine Melanomas as Models for Human Melanomas: Clinical, Histological, and Genetic Comparison

Despite recent genetic advances and numerous ongoing therapeutic trials, malignant melanoma remains fatal, and prognostic factors as well as more efficient treatments are needed. The development of such research strongly depends on the availability of appropriate models recapitulating all the features of human melanoma. The concept of comparative oncology, with the use of spontaneous canine models has recently acquired a unique value as a translational model. Canine malignant melanomas are naturally occurring cancers presenting striking homologies with human melanomas. As for many other cancers, dogs present surprising breed predispositions and higher frequency of certain subtypes per breed. Oral melanomas, which are much more frequent and highly severe in dogs and cutaneous melanomas with severe digital forms or uveal subtypes are subtypes presenting relevant homologies with their human counterparts, thus constituting close models for these human melanoma subtypes. This review addresses how canine and human melanoma subtypes compare based on their epidemiological, clinical, histological, and genetic characteristics, and how comparative oncology approaches can provide insights into rare and poorly characterized melanoma subtypes in humans that are frequent and breed-specific in dogs. We propose canine malignant melanomas as models for rare non-UV-induced human melanomas, especially mucosal melanomas. Naturally affected dogs offer the opportunity to decipher the genetics at both germline and somatic levels and to explore therapeutic options, with the dog entering preclinical trials as human patients, benefiting both dogs and humans.

Prognostic role of non-neoplastic lymphocytes in lymph node aspirates from dogs with diffuse large B-cell lymphoma treated with chemo-immunotherapy

Dogs with Diffuse Large B-Cell Lymphoma (DLBCL) benefit from the addition of active immunotherapy to traditional chemotherapy. We hypothesized that immune cells within neoplastic lymph nodes (LNs) may play a role in the tumor pathobiology and treatment response. The present study describes the composition and prognostic role of non-neoplastic lymphocytes in LNs of 59 dogs with treatment-naive DLBCL receiving chemo-immunotherapy. The percentage of small non-neoplastic cells and of CD5+, CD21+, CD4+ and CD8+ small cells was recorded via flow cytometry. CD4+/CD8+ and CD5+/large CD21+ cell ratios were calculated. The likelihood of progression significantly diminished with increasing percentage of small cells, CD5+ and CD8+ small cells, and CD5+/large CD21+ cell ratio, with decreasing CD4+/CD8+ ratio and in non-anemic dogs. Active immunotherapy is more effective in dogs with higher percentage of non-neoplastic lymphocytes at diagnosis. We lay the ground for future studies assessing the role of the immune system in the pathobiology of canine DLBCL.