Immunohistochemical study of the local inflammatory infiltrate in spontaneous canine transmissible venereal tumour at different stages of growth

Canine Transmissible Venereal Tumor: An Infectious Neoplasia in Dogs

Canine transmissible venereal tumor is the oldest cancer in dogs and is transplanted via viable cancer cells. This cancer has a specific host, easy transmission, noticeable gross lesions, a predictable growth pattern, an immunologic relative host response, unique molecular characteristics, and is responsive to chemotherapeutic treatment. These points make researchers and practitioners interested in this cancer. Genital cases are noticeable and therefore easier to diagnose and treat than extragenital cases. By contrasting the anatomical features of the two types of cases, we highlight the uniqueness of canine transmissible venereal tumors and discuss the diagnosis, treatment, and prevention of this ancient cancer.

Cancer-Immunity Cycle and Therapeutic Interventions- Opportunities for Including Pet Dogs With Cancer

The tumor-immune interplay represents a dynamic series of events executed by cellular and soluble participants that either promote or inhibit successful tumor formation and growth. Throughout a tumor’s development and progression, the host organism’s immune system reacts by generating anti-cancer defenses through various incremental and combinatorial mechanisms, and this reactive orchestration is termed the cancer-immunity cycle. Success or failure of the cancer-immunity cycle dictates the fate of both host and tumor as winner or loser. Insights into how the tumor and host immune system continuously adapt to each other throughout the lifecycle of the tumor is necessary to rationally develop new effective immunotherapies. Additionally, the evolving nature of the cancer-immunity cycle necessitates therapeutic agility, requiring real-time serial assessment of immunobiologic markers that permits tailoring of therapies to the everchanging tumor immune microenvironment. In order to accelerate advances in the field of immuno-oncology, this review summarizes the steps comprising the cancer-immunity cycle, and underscores key breakpoints in the cycle that either favor cancer regression or progression, as well as shaping of the tumor microenvironment and associated immune phenotypes. Furthermore, specific large animal models of spontaneous cancers that are deemed immunogenic will be reviewed and proposed as unique resources for validating investigational immunotherapeutic protocols that are informed by the cancer-immunity cycle. Collectively, this review will provide a progressive look into the dynamic interplay between tumor and host immune responses and raise awareness for how large animal models can be included for developing combinatorial and sequenced immunotherapies to maximizing favorable treatment outcomes.

Tumor Infiltrating Lymphocytes in Pet Rabbit Mammary Carcinomas: A Study with Relevance to Comparative Pathology

Simple Summary

The interaction between tumors and immune cells influences tumor fate, i.e., regression, growth, or even metastases. The evaluation of tumor infiltrating lymphocytes (TILs) in human breast cancer has prognostic value. Pet rabbits develop spontaneous mammary carcinomas and have an immune system that is comparable with that of humans, so that they have the potential to provide an animal model for human breast cancer. To further substantiate this similarity, this study examined TILs in 107 pet rabbit mammary carcinomas according to criteria established for human breast cancer. For TIL evaluation routinely stained microscopic sections were examined by light microscopy. Relevant histological and immunohistochemical tumor characteristics were obtained from a data base. Results showed that increased presence of stromal TILs was statistically associated with histological tumor features indicative of a less aggressive biological behavior, i.e., reduced tumor cell proliferation and a lower histological grade. The expression by tumor cells of calponin, a presumed tumor suppressor protein, was also associated with their reduced proliferation and a higher percentage of stromal TILs. Data suggest that higher percentages of stromal TILs may have the potential to serve as favorable prognostic indicator in rabbit mammary carcinomas and support the value of pet rabbits for comparative research.

Abstract

Tumor infiltrating lymphocytes (TILs) serve as prognostic biomarker in human breast cancer. Rabbits have the potential to act as animal model for human breast cancer, and close similarities exist between the rabbit and human immune system. The aim of this study is to characterize TILs in pet rabbit mammary carcinomas and to statistically correlate results with histological and immunohistochemical tumor characteristics. Microscopic evaluation of TILs was performed in hematoxylin and eosin stained sections of 107 rabbit mammary carcinomas according to international guidelines for human breast cancer. Data on histological features of malignancy, estrogen and progesterone receptor status and calponin expression were obtained from the data base. This study revealed a statistical association between stromal TILs in the central tumor (CT) and infiltrative margin. Higher maximal percentages of stromal TILs at the CT were statistically correlated with decreased mitotic count and lower tumor grade. An increased number of calponin positive tumor cells was statistically associated with a lower mitotic count and a higher percentage of stromal TILs. Results suggest that higher percentages of stromal TILs are useful biomarkers that may point toward a favorable prognosis in rabbit mammary carcinomas and support the concept of the use of rabbits for translational research.

Tumor venéreo transmissível canino com resistência quimioterápica e metástase esplênica - Relato de caso

O Tumor Venéreo Transmissível Canino (TVTC) é uma neoplasia de células redondas que tem a particularidade de se implantar em mucosas que tenham perdido a sua integridade. Nesse local o tumor prolifera e ocasionalmente origina metástase. Em geral, o tumor responde ao tratamento com sulfato de vincristina, porém a resistência quimioterápica associada ao fenótipo tumoral tem sido documentada. Objetivou-se relatar um caso de TVTC genital de fenótipo citológico misto com metástase esplênica e o insucesso da quimioterapia com sulfato de vincristina, em uma fêmea canina, da raça Australian Cattle Dog, de cinco anos de idade. Após diagnóstico citológico e histológico, o tumor primário foi ainda caracterizado em fase de progressão e mostrou baixa expressão de moléculas do complexo principal de histocompatibilidade MHC (4,4 ± 2% classe I e 11 ± 4,1% classe II). A cadela foi submetida à ovariohisterectomia e esplenectomia terapêutica e não apresentou recidiva do tumor após 12 meses de acompanhamento clínico.

Detection of progressive and regressive phase and LINE-1 retrotransposon in transfected dogs with transmissible venereal tumor during chemotherapy

Canine transmissible venereal tumor (CTVT) is a tumor that commonly occurs in genital and extragenital sites of both genders. Long interspersed nuclear elements (LINE-1) retrotransposon has a pivotal role in allogenic transfection among uncontrolled dog populations. This study aimed to perform pathomorphological, immunohistochemical, and in situ polymerase chain reaction (PCR) evaluation of CTVT (n = 18) in transfected dogs during chemotherapy. Immunohistochemically, tumor phases were investigated by using specific markers (CD3, CD4, CD8, CD79, and transforming growth factor beta [TGF-β]), and investigated an amplified specific sequence of TVT LINE-1 retrotransposon by in situ PCR. Polyhedral-shaped neoplastic cells that had large, round, hypo/hyperchromatic nuclei and eosinophilic cytoplasm were detected. All marker results were positive, especially in the early weeks of recovery. CD4 and TGF-β markers were conspicuously positive at the initial stage. In situ PCR LINE-1 sequence was initially positive in only four cases. It is believed that the CD and TGF-β markers provide phase identification at tumor initiation and during chemotherapy. It is thought that presence of T and B lymphocytes, which have roles in cellular and humoral immunity, is needed so that regression of the tumor is possible.

The newly-arisen Devil facial tumour disease 2 (DFT2) reveals a mechanism for the emergence of a contagious cancer

Devil Facial Tumour 2 (DFT2) is a recently discovered contagious cancer circulating in the Tasmanian devil (Sarcophilus harrisii), a species which already harbours a more widespread contagious cancer, Devil Facial Tumour 1 (DFT1). Here we show that in contrast to DFT1, DFT2 cells express major histocompatibility complex (MHC) class I molecules, demonstrating that loss of MHC is not necessary for the emergence of a contagious cancer. However, the most highly expressed MHC class I alleles in DFT2 cells are common among host devils or non-polymorphic, reducing immunogenicity in a population sharing these alleles. In parallel, MHC class I loss is emerging in vivo, thus DFT2 may be mimicking the evolutionary trajectory of DFT1. Based on these results we propose that contagious cancers may exploit partial histocompatibility between the tumour and host, but that loss of allogeneic antigens could facilitate widespread transmission of DFT2.

Molecular Signatures of Regression of the Canine Transmissible Venereal Tumor

The canine transmissible venereal tumor (CTVT) is a clonally transmissible cancer that regresses spontaneously or after treatment with vincristine, but we know little about the regression mechanisms. We performed global transcriptional, methylation, and functional pathway analyses on serial biopsies of vincristine-treated CTVTs and found that regression occurs in sequential steps; activation of the innate immune system and host epithelial tissue remodeling followed by immune infiltration of the tumor, arrest in the cell cycle, and repair of tissue damage. We identified CCL5 as a possible driver of CTVT regression. Changes in gene expression are associated with methylation changes at specific intragenic sites. Our results underscore the critical role of host innate immunity in triggering cancer regression.

Immunology of naturally transmissible tumours

Naturally transmissible tumours can emerge when a tumour cell gains the ability to pass as an infectious allograft between individuals. The ability of these tumours to colonize a new host and to cross histocompatibility barriers contradicts our understanding of the vertebrate immune response to allografts. Two naturally occurring contagious cancers are currently active in the animal kingdom, canine transmissible venereal tumour (CTVT), which spreads among dogs, and devil facial tumour disease (DFTD), among Tasmanian devils. CTVT are generally not fatal as a tumour-specific host immune response controls or clears the tumours after transmission and a period of growth. In contrast, the growth of DFTD tumours is not controlled by the Tasmanian devil's immune system and the disease causes close to 100% mortality, severely impacting the devil population. To avoid the immune response of the host both DFTD and CTVT use a variety of immune escape strategies that have similarities to many single organism tumours, including MHC loss and the expression of immunosuppressive cytokines. However, both tumours appear to have a complex interaction with the immune system of their respective host, which has evolved over the relatively long life of these tumours. The Tasmanian devil is struggling to survive with the burden of this disease and it is only with an understanding of how DFTD passes between individuals that a vaccine might be developed. Further, an understanding of how these tumours achieve natural transmissibility should provide insights into general mechanisms of immune escape that emerge during tumour evolution.

Targeting epigenetic mechanisms for clinical translation: enhancing the efficacy of tumor immunotherapies

The ability to evade host immune surveillance is critical for the survival of tumor cells and is correlated with poor clinical outcomes. Many tumor types have been found to downregulate expression of genes involved in antigen production, processing and presentation to evade immune detection. Recent findings suggest that the mechanisms underlying these immune evasion phenomena extend beyond alterations in DNA sequence to include epigenetic modifications of DNA and associated proteins, including hypermethylation of DNA and altered histone acetylation patterns. This review will summarize alterations in antigen presentation machinery identified in malignant cells, epigenetic mechanisms that can be employed in the downregulation of genes relevant for antigen presentation and translational strategies to target these processes to enhance the efficacy of antitumor immunotherapies.

A role for T-lymphocytes in human breast cancer and in canine mammary tumors

Chronic inflammation in the tumor microenvironment has a prominent role in carcinogenesis and benefits the proliferation and survival of malignant cells, promoting angiogenesis and metastasis. Mammary tumors are frequently infiltrated by a heterogeneous population of immune cells where T-lymphocytes have a great importance. Interestingly, similar inflammatory cell infiltrates, cytokine and chemokine expression in humans and canine mammary tumors were recently described. However, in both species, despite all the scientific evidences that appoint for a significant role of T-lymphocytes, a definitive conclusion concerning the effectiveness of T-cell dependent immune mechanisms has not been achieved yet. In the present review, we describe similarities between human breast cancer and canine mammary tumors regarding tumor T-lymphocyte infiltration, such as relationship of TILs and mammary tumors malignancy, association of ratio CD4+/ CD8+ T-cells with low survival rates, promotion of tumor progression by Th2 cells actions, and association of great amounts of Treg cells with poor prognostic factors. This apparent parallelism together with the fact that dogs develop spontaneous tumors in the context of a natural immune system highlight the dog as a possible useful biological model for studies in human breast cancer immunology.

Reversible epigenetic down-regulation of MHC molecules by devil facial tumour disease illustrates immune escape by a contagious cancer

Contagious cancers that pass between individuals as an infectious cell line are highly unusual pathogens. Devil facial tumor disease (DFTD) is one such contagious cancer that emerged 16 y ago and is driving the Tasmanian devil to extinction. As both a pathogen and an allograft, DFTD cells should be rejected by the host-immune response, yet DFTD causes 100% mortality among infected devils with no apparent rejection of tumor cells. Why DFTD cells are not rejected has been a question of considerable confusion. Here, we show that DFTD cells do not express cell surface MHC molecules in vitro or in vivo, due to down-regulation of genes essential to the antigen-processing pathway, such as β2-microglobulin and transporters associated with antigen processing. Loss of gene expression is not due to structural mutations, but to regulatory changes including epigenetic deacetylation of histones. Consequently, MHC class I molecules can be restored to the surface of DFTD cells in vitro by using recombinant devil IFN-γ, which is associated with up-regulation of the MHC class II transactivator, a key transcription factor with deacetylase activity. Further, expression of MHC class I molecules by DFTD cells can occur in vivo during lymphocyte infiltration. These results explain why T cells do not target DFTD cells. We propose that MHC-positive or epigenetically modified DFTD cells may provide a vaccine to DFTD. In addition, we suggest that down-regulation of MHC molecules using regulatory mechanisms allows evolvability of transmissible cancers and could affect the evolutionary trajectory of DFTD.

Vincristine modulates the expression of Ki67 and apoptosis in naturally occurring canine transmissible venereal tumor (TVT)

We investigated eight adult dogs that were brought to veterinary clinics with a history of transmissible venereal tumors (TVT). Our goal was to demonstrate the occurrence of apoptosis and the cessation of cell proliferation at every phase of scheduled chemotherapy for naturally occurring TVT. Tissue samples were collected immediately after weekly treatments with vincristine sulfate and processed for histological purposes. Sections 5 μm thick were stained by the TUNEL reaction for apoptosis and immunostained for Ki67 as a proliferation marker. We observed that after vincristine applications, tumor cell proliferation ceased and apoptosis increased. Ki67 HSCORE values were significantly lowered after the first and second treatments with the chemotherapeutic agent compared to controls, whereas TUNEL HSCORE values were significantly higher after two applications of vincristine compared to controls. Our results suggest that scheduled vincristine sulfate applications stabilize the induction of tumor regression by inducing apoptosis and preventing cell proliferation.

Transrectal ultrasound-integrated spectral optical tomography of hypoxic progression of a regressing tumor in a canine prostate

The objective of this study was to evaluate if transrectal optical tomography implemented at three wavelength bands for spectral detection could monitor changes of the hemoglobin oxygen saturation (StO2) in addition to those of the total hemoglobin concentration ([HbT]) in lesions of a canine prostate, including an induced tumor modeling canine prostate cancer. Near-infrared (NIR) optical tomography was integrated with ultrasound (US) for transrectal imaging. Multi-spectral detection at 705_nm, 785_nm and 808_nm rendered measurements of [HbT] and StO2. Canine transmissible venereal tumor (TVT) cells were injected into the right lobe of a dog's prostate gland, which had a pre-existing cyst in the left lobe. Longitudinal assessments of the prostate were performed weekly over a 63-day duration by NIR imaging concurrent with grey-scale and Doppler US. Ultrasonography revealed a bi-lobular tumor-mass regressing from day-49 to day-63. At day-49 this tumor-mass developed a hypoxic core that became larger and more intense by day-56 and expanded further by day-63. The tumor-mass presented a strong hyper-[HbT] feature on day-56 that was inconsistent with US-visualized blood flow. Histology confirmed two necrotic TVT foci within this tumor-mass. The cyst appeared to have a large anoxic-like interior that was greater in size than its ultrasonographically delineated lesion, and a weak lesional elevation of [HbT]. On day-56, the cyst presented a strong hyper-[HbT] feature consistent with US-resolved blood flow. Histology revealed acute and chronic hemorrhage in the periphery of the cyst. The NIR imaging features of two other TVT nodules and a metastatic lymph node were evaluated retrospectively. Transrectal US-integrated spectral optical tomography seems to enable longitudinal monitoring of intra-lesional oxygenation dynamics in addition to the hemoglobin content of lesions in the canine prostate.

Cell proliferation markers in the transplanted canine transmissible venereal tumor

Adult male mongrel dogs were subcutaneously transplanted with the canine transmissible venereal tumor (TVT) on the hypogastric region. Twelve specimens of tumors were collected, half during the proliferative phase and the other half during the regressive phase. Fragments of the tumor were fixed in 10% buffered formalin and routinely processed for light microscopy. Sections of 4µm were stained by Schorr or AgNOR or either immunostained for MIB1 (Ki67). Schorr stain, AgNOR and MIB1 showed an increased proliferative activity through mitotic index, nuclear argyrophilic protein stain and cycling tumoral cells in the growing tumors, respectively. All of the three cell proliferation markers were able to distinguish the TVT in both evolution phases. MIB1 monoclonal antibody was the best in the morphologic evaluation of growth and regression of TVT. This resulted in higher values than AgNORs counting and mitotic index. MIB1 immunostaining was the most effective parameter of the proliferative activity of TVT. However, a significant correlation has been detected only between mitosis counting and AgNORs.

Tasmanian devil facial tumor disease: insights into reduced tumor surveillance from an unusual malignancy

Tasmanian devil facial tumor disease (DFTD) is a highly aggressive cancer involving the facial tissues that currently presents a serious extinction risk for the Tasmanian devil population. Although the histogenesis is uncertain, an origin from a neural crest cell-lineage is considered likely. Epidemiological, cytogenetic and immunological data all support the premise that DFTD arose from a single tumor clone from an individual diseased animal, and is being transmitted between individual animals as a tumor "allograft" by biting during social interaction. The spread of this cancer throughout the species is believed to be facilitated by a reduced MHC diversity, possibly as a result of an evolutionary bottleneck. The pathogenesis of DFTD has some similarities with certain human cancers, including donor-recipient tumor transmission, which may complicate organ transplantation, and certain forms of malignancy at the maternal/fetal interface. The natural history and pathology of DFTD, and the data describing this highly unusual tumor biology are discussed.

Clonally transmissible cancers in dogs and Tasmanian devils

Tasmanian devil facial tumor disease (DFTD) and canine transmissible venereal tumor (CTVT) are the only known naturally occurring clonally transmissible cancers. These cancers are transmitted by the physical transfer of viable tumor cells that can be transplanted across histocompatibility barriers into unrelated hosts. Despite their common etiology, DFTD and CTVT have evolved independently and have unique life histories and host adaptations. DFTD is a recently emerged aggressive facial tumor that is threatening the Tasmanian devil with extinction. CTVT is a sexually transmitted tumor of dogs that has a worldwide distribution and that probably arose thousands of years ago. By contrasting the biology, molecular genetics and immunology of these two unusual cancers, I highlight the common and unique features of clonally transmissible cancers, and discuss the implications of clonally transmissible cancers for host-pathogen evolution.

Testing the theory of immune selection in cancers that break the rules of transplantation

Modification of cancer cells likely to reduce their immunogenicity, including loss or down-regulation of MHC molecules, is now well documented and has become the main support for the concept of immune surveillance. The evidence that these modifications, in fact, result from selection by the immune system is less clear, since the possibility that they may result from reorganized metabolism associated with proliferation or from cell de-differentiation remains. Here, we (a) survey old and new transplantation experiments that test the possibility of selection and (b) survey how transmissible tumours of dogs and Tasmanian devils provide naturally evolved tests of immune surveillance.

An immunohistochemical study of the inflammatory infiltrate associated with nasal carcinoma in dogs and cats

The aims of this study were to characterize the inflammatory infiltrate associated with nasal carcinoma in dogs and cats and to determine whether this differed between the two species or with different types of carcinoma. Sections from fixed tissue biopsy samples of intranasal carcinoma from 31 dogs and six cats were labelled immunohistochemically to detect expression of the T-lymphocyte marker CD3, class II molecules of the major histocompatibility complex (MHC II), the myelomonocytic antigen MAC387 and immunoglobulin (Ig) G, IgA and IgM within the cytoplasm of plasma cells. All canine carcinomas were heavily infiltrated by MAC387(+) neutrophils, with smaller numbers of MAC387(+) macrophages. T cells were particularly prominent in the infiltrate associated with transitional carcinoma, and in such tumours were frequently mixed with MHC II(+) cells having macrophage or dendritic cell morphology. IgG(+) and IgA(+) plasma cells were detected at the peripheral margins of all types of canine carcinoma. In contrast, feline intranasal carcinoma was invariably associated with a marked infiltration of CD3(+) T cells. The feline tumour infiltrates contained sparse neutrophils and macrophages and few IgG(+) and IgA(+) plasma cells. These findings suggest that qualitatively different immune responses are induced in response to specific types of canine intranasal carcinoma, and that the canine and feline immune response to these neoplasms is also distinct.

Apoptosis in the transplanted canine transmissible venereal tumor during growth and regression phases

Twelve male, mongrel, adult dogs were subcutaneously transplanted with cells originated from two canine transmissible venereal tumors (TVT). The aim was to demonstrate and to quantify the occurrence of apoptosis in the TVT regression. After six months of transplantation, a tumor sample was obtained from each dog, being six dogs with TVT in the growing phase and six in the regression phase as verified by daily measurements. Samples were processed for histological and ultrastructural purposes as well as for DNA extraction. Sections of 4µm were stained by HE, Shorr, methyl green pyronine, Van Gieson, TUNEL reaction and immunostained for P53. The Shorr stained sections went through morphometry that demonstrated an increase of the apoptotic cells per field in the regressive tumors. It was also confirmed by transmission electron microscopy, which showed cells with typical morphology of apoptosis and by the TUNEL reaction that detected in situ the 3'OH nick end labeling mainly in the regressive tumors. The regressive TVTs also showed an intensified immunostaining for P53 besides a more intense genomic DNA fragmentation detected by the agarose gel electrophoresis. In conclusion, apoptosis has an important role in the regression of the experimental TVT in a way that is P53-dependent.

The regression of a canine Langerhans cell tumour is associated with increased expression of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA

Canine cutaneous histiocytoma is a benign epidermal neoplasm of Langerhans cell origin, which usually displays spontaneous regression. Based on the degree of lymphocytic infiltration, 30 histiocytomas were classified into four groups representing different stages of tumour regression. To elucidate further the mechanisms of the antitumour immune response CD3+, CD21+, CD4+, CD8+ and myeloid/histiocyte antigen+ inflammatory cells were differentiated by immunohistochemistry and quantified. In addition, the number of apoptotic cells was detected using the TdT-mediated biotin-dUTP nick-end labelling (TUNEL) method. Furthermore, the expression of interleukin- (IL-2), IL-12(p40), tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), IL-10 and transforming growth factor-beta (TGF-beta) as well as inducible nitric oxid synthase (iNOS) mRNA was determined by reverse transcription-polymerase chain reaction (RT-PCR). Phenotyping of inflammatory cells revealed a significantly increased infiltration of all lymphocyte subsets and myeloid/histiocytic cells with the onset of tumour regression. The latter was significantly correlated to up-regulation of IL-2, TNF-alpha, IFN-gamma and iNOS mRNA expression. Expression of remaining cytokines and percentage of apoptotic cells showed no group-specific changes. The results indicate an initial infiltration of CD4+ T cells followed by increased expression of Th1 cytokines and recruitment of antitumour effector cells as the principal mechanism for tumour regression. Canine cutaneous histiocytoma is a unique example for an effective immune response in a naturally occurring neoplasm derived from epidermal Langerhans cells and might represent a valuable animal model to investigate tumour immunity.

Canine Transmissible Venereal Tumour: Asessment of Mast Cell Numbers as Indicators of the Growth Phase

Mast cells are immune cells that are involved mainly in type 1 hypersensitivity reactions, and they have been implicated in tumour angiogenesis. In this study we assessed the presence of mast cell numbers and microvessel density during the progression and regression stages of natural spontaneous canine transmissible venereal tumours (CTVT). Mast cells were demonstrated by histochemical staining with toluidine blue, alcian blue and safranin O. Microvessel counts were demonstrated by immunohistochemical labelling with an antibody against the endothelial cell marker factor VIII. Mitotic cells, apoptotic cells and tumour infiltrating lymphocytes were counted from haematoxylin-eosin-stained sections. Tumour fibrosis was evaluated on Masson's trichome-stained sections. The results showed that progressing tumours had significantly higher mast cell counts and microvessel counts at the invasive edges of the tumours than did regressing tumours. In both the progressing and regressing tumours, microvessel counts were significantly positively correlated with mast cell counts. Regressing tumours had significantly higher mast cell counts of the whole tumour than progressing tumours. The results also showed that progressing tumours had significantly higher mitotic rate than regressing tumours, and fibrosis and apoptosis were significantly higher in regressing tumours than progressing tumours. There were no significant differences between the biochemical and haematological values of dogs with progressing and regressing tumours. These results suggests that mast cells play a role in CTVT progression probably by promoting vascularization at the invasion front during the progression phase, and that mast cell count could be used as one of the histological factors to indicate growth stage of CTVT.

Pegylated liposomal doxorubicin as a chemotherapeutic agent for treatment of canine transmissible venereal tumor in murine models

The effectiveness of Doxil as a new chemotherapeutic agent against canine transmissible venereal tumor was evaluated, using NOD/ SCID and CD1-nu xenograft mouse models and the response between the two mouse strains was compared. Samples of xenografted venereal tumor were inoculated SC into 20 six week-old NOD/SCID mice and 20 six week-old CD1-nu mice. Seven weeks later, tumor-bearing mice were divided into treatment and control groups. Treatment group was injected with Doxil (6 mg/kg, IP, as a single injection). Control group was injected with buffered saline (0.75cc, IP). Tumor size was determined by caliper measurements and tumor response was assessed according to standard criteria. In both strains there was a significant decrease in tumor size in response to Doxil treatment (P<0.0001). In CD1-nu eight out of nine tumors (88%) responded to the treatment, and in 2 cases complete remission was observed. In NOD/SCID group response to the treatment was seen in eight out of ten tumors (80%) but none regressed fully. Response to the treatment was statistically equal in both strains even though the apoptotic rate, confirmed by TUNEL staining, was higher in NOD/SCID than in CD-1-nu (8.65% and 0.7%, respectively) and tumor infiltrating cells were different: eosinophils in NOD/SCID and CD45R-positive B lymphocytes, and plasma cells in CD-1-nu. In untreated CD1-nu mice, tumor progress was slower than in NOD/SCID. Our results indicate that Doxil is effective against CTVT in mouse xenograft models.

Expression of a tumor-associated antigen, RCAS1, in canine mammary tumors

Receptor-binding cancer antigen expressed on SiSo cells (RCAS1), one of novel cancer cell-surface antigens, is strongly expressed in invasive cancers. RCAS1 inhibits the in vitro growth of lymphocytes such as T cells and natural killer (NK) cells, and induces apoptotic cell death. We investigated the expression of RCAS1 in canine mammary tumor cell lines and tumor cells by immunohistochemistry, and also in situ deoxyribonucleic acid (DNA) fragmentation in tumor-infiltrating lymphocytes (TILs) by the terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labeling (TUNEL) method. All canine mammary tumor cell lines expressed RCAS1 at both the messenger ribonucleic acid (mRNA) and protein level. Immunohistochemically, RCAS1 was negative in 100% of normal mammary glands, but was expressed in 100% of malignant tumors examined. In most malignant mammary tumors, RCAS1 was localized in the cytoplasm with no polarity of expression. In benign mammary tumors, it was detected on the luminal surface of the tumor cell. RCAS1 expression or localization was significantly correlated with malignancy. In situ DNA fragmentation of CD3-positive TILs was observed in RCAS1-expressing tumors. RCAS1-expressing tumors, indicating a possible induction of apoptotic cell death in TILs through RCAS1 expression. These observations suggest that RCAS1 probably plays an important role in tumor progression and escape from immune surveillance in canine mammary tumors.

Canine transmissible venereal tumour: Cytogenetic origin, immunophenotype, and immunobiology. A review

Canine transmissible venereal tumour (CTVT) is the only known naturally occurring tumour that can be transplanted as an allograft across major histocompatibility (MHC) barriers within the same species, and even to other members of the canine family, such as foxes, coyotes and wolves. The progression of this tumour is unique in that, it follows a predictable growth pattern. In natural and experimental cases, the growth pattern includes progressive growth phase, static phase and regression phase, and this is followed by transplantation immunity in immunocompetent adults, while metastasis occurs in puppies and immunosuppressed dogs. Because of the uniqueness of CTVT transmission and progression, experimental investigations of various aspects of the biology of CTVT have been used to provide clues to the immunobiology of both animal and human tumours. This review examines the current state of knowledge of the aspects of the cytogenetic origin, immunophenotype, immunobiology and immunotherapy of CTVT.

Canine transmissible venereal tumor cell depletion of B lymphocytes: molecule(s) specifically toxic for B cells

Canine transmissible venereal tumor (CTVT) is an excellent model for investigating the interaction between host immunity and tumor growth. Although CTVT is an allograft, initially the host immune system is unable to destroy the tumor cells, and the tumor grows progressively for about 4-6 months (P phase). After a short stable phase, the tumor undergoes regression (R phase). In this study, CTVT inoculation significantly reduced the proportion of B lymphocytes among all peripheral blood lymphocytes (PBL), but the proportion of B lymphocytes returned to normal after complete removal of CTVT. Following CTVT inoculation, immunoglobulin concentrations decreased gradually, coincident with B lymphocyte decline. Furthermore, CTVT secreted a soluble, heat- and protease K-sensitive cytotoxic molecule(s) that destroyed peripheral blood B lymphocytes (PBBL) but spared other types of immune cells regardless of whether mitogens, such as IL-2 or Con A, were present. The decrease in the proportion and viability of PBBL was caused by a cytotoxic molecule(s) that induced apoptosis. The molecular weight of the CTVT-derived cytotoxic molecule(s) was 30-100kDa. Human, domestic cat, horse and mouse B cells were also sensitive to the substance.

Effect of tumor infiltrating lymphocytes on the expression of MHC molecules in canine transmissible venereal tumor cells

Canine transmissible venereal tumor (CTVT) can be allo-transplanted across major histocompatibility complex barriers. The expression of MHC molecules is usually low in the progression (P) stage and then greatly increases during tumor regression (R). We investigated the effects of tumor infiltrating lymphocytes (TIL) on the expression of MHC molecules of CTVT cells. Isolated, viable CTVT cells were inoculated at each of 12 sites (1 x 10(8) CTVT cells per site) on the back of six, mixed-breed dogs. Tumor masses were collected every 2-3 weeks and prepared for histopathologic, immunocytochemistry, flow cytometry and immunoblotting studies. The level of MHC expression on tumor cells from different stages of growth was measured. Initially, expression of MHC I and II molecules in P phase CTVT was low. Twelve weeks post-inoculation (PI), expression increased dramatically and it continued to increase during R phase. Tumor growth slowed after 12 weeks PI and tumors entered R phase around 17 weeks PI. We hypothesize that CTVT evades host immunosurveillance and grows progressively for 12 weeks, when it becomes vulnerable and subject to the host's anti-tumor immune responses. We further demonstrated that R phase, but not P phase, TIL were closely associated with the over-expression of MHC I and II molecules by CTVT cells. The number and proportion of TIL were higher in R phase tumors. Supernatants, from R phase co-cultures (CTVT+TIL) and TIL only, promoted MHC I and II expression on P phase CTVT cells. After culturing alone for 1 month, expression of MHC classes I and II molecules in R phase CTVT cells decreased to the level of P phase CTVT cells. However, the above-mentioned supernatants restored their expression of MHC I and II molecules. In contrast, supernatants from P phase TIL or CTVT cells increased expression slightly or had no effect. Therefore, TIL, not CTVT cells, produce the effective substance (s) to promote the expression of MHC molecules by the tumor cells. Heat treated supernatant was unable to promote the expression of MHC I and II molecules by CTVT cells. In conclusion, TIL isolated from R phase CTVT secreted a heat-sensitive, soluble substance(s) that triggered over-expression of MHC I and II after 12 weeks PI. This caused the tumor to enter R phase and helped stop CTVT growth. Our findings will facilitate the understanding and further investigation of the mechanisms that initiate host immune surveillance against tumors.

Lack of MHC expression and retention of ultrastructural characteristics by xenograft transmissible venereal tumor cells in SCID mice

Canine transmissible venereal tumor (CTVT) is primarily a tumor of adult dogs with a high incidence of spontaneous regression. We recently reported a xenograft model of CTVT (XTVT) in NOD/SCID mice. XTVT cells retain cytological and histological features of CTVT as well as characteristic rearranged LINE/c-MYC junction [Am. J. Vet. Res. 62 (2001) 907]. In this paper, we demonstrate that XTVT cells maintain ultrastructural characteristics of CTVT and do not express MHC classes I and II molecules.

Heat shock proteins in canine transmissible venereal tumor

SDS-PAGE, Western blot analysis and immunohistochemical staining were used to detect heat shock proteins (HSPs) 60, 70 and 90 in canine transmissible venereal tumor (CTVT). Tissues tested for HSPs included: (1) tissues from different growth phases of CTVT tumors artificially induced in dogs; (2) tissues from other canine tumors; (3) normal dog tissues. Our results indicate that HSP 60 was consistently higher in CTVT cells in regressing phase than those in progressing phase. However, no detectable antibody response specific to the tested HSPs was found in the sera from CTVT-laden dogs in different growth phases. Although levels of the HSPs were all detectable in CTVT cells, only 60 and 70 were higher in CTVT cells than in normal tissues. In addition, none of the HSPs were detected in cells from five other canine tumors. These data suggest that canine HSP 60 and 70 are potential markers for CTVT and HSP 60 is appear to be involved in CTVT regression.PCR was used to confirm the existence of CTVT cells using primers designed to cover the sequence between the 5' end of c-myc near the first exon and the 3' end outside the LINE gene. Only CTVT samples were positive for this sequence; samples from other tumors and normal tissues were negative. The sequenced PCR products indicated that CTVT from Taiwan and other countries exhibited over 98% sequence homology. This reconfirms that, worldwide, all CTVT cells are very similar.

Canine transmissible venereal tumour: a morphological and immunohistochemical study of 11 tumours in growth phase and during regression after chemotherapy

Eleven dogs with canine transmissible venereal tumour (CTVT) were given vincristine sulphate chemotherapy to induce tumour regression. Biopsy specimens were collected from tumours during the growth phase, before chemotherapy, and again from the same dogs during the regression induced by chemotherapy. Laboratory assessment included cytology, histology, the number of tumour cells in relation to the number of intratumoral leucocytes, proliferative and apoptotic fractions of tumour cells, intratumoral vessel density, and fibrosis. The results revealed that during regression, tumour cell proliferation ceased, apoptosis increased, leucocytes increased (with increased proportion of T lymphocytes), tumour parenchyma collapsed around intratumoral vessels, and fibrosis increased. These results, which were similar to findings in dogs with spontaneous regression of CTVT, suggest that tumour immunity plays a role in tumour regression after modest chemotherapy.

Immunohistochemical study of the inflammatory infiltrate associated with equine squamous cell carcinoma

The distribution of T (CD3), B (CD79) lymphocytes, immunoglobulin (IgG, IgM and IgA)-producing plasma cells, macrophages (lysozyme, Mac387) and MHC Class II antigen was analysed in the inflammatory infiltrate associated with 19 equine squamous cell carcinomas (SCCs) and six cases of precancerous lesions (actinic keratosis). The SCCs came from the penis (11 cases), conjunctiva (four), skin (two), nasal cavity (one) and oral cavity (one). Seven cases were well-differentiated and 12 moderately differentiated. Nine cases showed no invasion of peritumoral deep tissues (locally invasive), whereas the remaining 10 cases were highly invasive. An abundant inflammatory infiltrate was associated with the majority of the SCCs and with lesions of actinic keratosis. This infiltrate was composed mainly of CD3(+)T lymphocytes, CD79(+)B cells and numerous IgG(+)plasma cells; IgM- and IgA-producing plasma cells were scarce and variable, respectively. Macrophages were usually numerous. Macrophages, lymphocytes, intra-epithelial dendritic cells and fibroblasts expressed MHC Class II antigen. No significant correlation was found between the nature of the inflammatory infiltrate and the SCC histological grade or degree of invasion, suggesting that the local anti-tumour immune response failed to prevent tumour invasion or metastasis. MHC Class II was expressed by a variable number of neoplastic epithelial cells in four SCCs, all of which were only locally invasive. In addition, in areas where SCC cells expressed Class II antigen, numerous CD3(+)T lymphocytes were present and some of them were associated with degenerate tumour cells. These findings suggest that the expression of MHC Class II by neoplastic cells induces an improved local anti-tumour immune response.

Immunohistochemical study of the inflammatory infiltrate associated with feline cutaneous squamous cell carcinomas and precancerous lesions (actinic keratosis)

The distribution of T lymphocytes (CD3+), B lymphocytes (CD79+), immunoglobulin-containing plasma cells (IgG, IgM and IgA), macrophages (Mac387+) and MHC Class II antigen was analysed in the inflammatory infiltrate associated with cutaneous squamous cell carcinomas (SCC) from 23 cats. Peri-tumoural skin (12 cases) and precancerous lesions of actinic keratosis (nine cases) were also evaluated for the expression of MHC Class II. The results revealed that an abundant inflammatory infiltrate was associated with the majority of SCC. This infiltrate was composed mainly of CD3+ T lymphocytes, B cells (CD79+) and IgG-bearing plasma cells, and the intensity of infiltration increased with the degree of invasiveness of the tumour. The number of CD3+ T cells and CD79+ cells was significantly increased in well-differentiated SCC compared with moderately differentiated tumours, whereas the number of IgM+, IgA+ plasma cells and Mac387+ macrophages was low or moderate and did not change significantly with histologic grade or invasiveness. MHC Class II antigen was expressed by infiltrating lymphocytes and macrophages, and by fibroblasts. A variable number of neoplastic cells (10% to 80%) in 10 SCC, and keratinocytes of basal layers in seven of nine cases of actinic keratosis also expressed MHC Class II, whereas keratinocytes of normal skin were always negative for this antigen. These results suggest that CD3+ T lymphocytes, CD79+ B cells and IgG-bearing plasma cells may participate in down-regulation of tumour growth, since these cell types were particularly numerous in well-differentiated and mildly invasive SCC, as well as in actinic keratosis. The expression of MHC Class II by neoplastic cells could enhance this local anti-tumour immune response.