Immunology of naturally transmissible tumours

Bridging clinic and wildlife care with AI-powered pan-species computational pathology

Cancers occur across species. Understanding what is consistent and varies across species can provide new insights into cancer initiation and evolution, with significant implications for animal welfare and wildlife conservation. We build a pan-species cancer digital pathology atlas (panspecies.ai) and conduct a pan-species study of computational comparative pathology using a supervised convolutional neural network algorithm trained on human samples. The artificial intelligence algorithm achieves high accuracy in measuring immune response through single-cell classification for two transmissible cancers (canine transmissible venereal tumour, 0.94; Tasmanian devil facial tumour disease, 0.88). In 18 other vertebrate species (mammalia = 11, reptilia = 4, aves = 2, and amphibia = 1), accuracy (range 0.57-0.94) is influenced by cell morphological similarity preserved across different taxonomic groups, tumour sites, and variations in the immune compartment. Furthermore, a spatial immune score based on artificial intelligence and spatial statistics is associated with prognosis in canine melanoma and prostate tumours. A metric, named morphospace overlap, is developed to guide veterinary pathologists towards rational deployment of this technology on new samples. This study provides the foundation and guidelines for transferring artificial intelligence technologies to veterinary pathology based on understanding of morphological conservation, which could vastly accelerate developments in veterinary medicine and comparative oncology.

Canine transmissible venereal tumor with spontaneous remission: case study with emphasis on clinical and cytopathological exams to monitor tumor evolution

Abstract The canine transmissible venereal tumor (TVTC) is a neoplasm transmitted mainly through copulation and with a high incidence in stray dogs in Brazil. In the process of tumor evolution of TVTC, the progression, stationary and regression phases are recognized. The host immunity is related to the disease’s biological behavior, however, spontaneous regression observation in cases of naturally occurring TVTC is uncommon. A canine patient was attended, after beeing rescued from the street, due to an ulcerated mass in the external genitália and tick infestation. Cytopathological examination, which diagnosed TVTC, and laboratory tests that showed mild anemia and severe thrombocytopenia were performed. In view of the impossibility of carrying out other exams, it was made the presumptive diagnosis of canine monocytic ehrlichiosis (CME), and treatment was instituted. During follow-up it was observed quick improvement in clinical signs and laboratory changes, as well as a reduction in tumor mass. A new cytopathological evaluation was carried out, and was verified increase in mature lymphocytes and plasmocytes in the midst of the tumor cells, finding compatible with the stationary phase of the disease. From that moment on, it was decided to perform only clinical and cytopathological follow-up. In the following evaluations, continuous clinical remission and cytopathological findings compatible with those described in the regression phase were observed, until its complete remission. It is considered that the improvement in the general health of the patient after the treatment of CME is related to the spontaneous regression of TVTC, and that simultaneous performance of serial clinical and cytopathological exams may be feasible and useful for monitoring the stages of evolution of TVTC.

Tumor venéreo transmissível canino com remissão espontânea: estudo de caso com ênfase aos exames clínico e citopatológico para monitoramento da evolução tumoral

Resumo O tumor venéreo transmissível canino (TVTC) é uma neoplasia transmitida principalmente através da cópula, com elevada incidência em cães errantes no Brasil. No processo de evolução tumoral do TVTC, são reconhecidas as fases de progressão, estacionária e de regressão. O estado imunológico do hospedeiro está relacionado ao comportamento biológico da doença, contudo, a observação de regressão espontânea em casos de TVTC de ocorrência natural é incomum. Foi atendida uma paciente canina, resgatada da rua, por apresentar massa ulcerada na genitália externa e infestação por carrapatos. Foram realizados exame citopatológico, que diagnosticou TVTC, e exames laboratoriais que evidenciaram anemia discreta e grave trombocitopenia. Com isso e diante da impossibilidade de realizar outros exames, foi também estabelecido o diagnóstico presuntivo de erlichiose monocítica canina (EMC) e instituído tratamento para a hemoparasitose. Durante o acompanhamento, foi observada rápida melhora dos sinais clínicos e das alterações laboratoriais, bem como a redução espontânea da massa tumoral. Em sequência, foi realizada nova avaliação citopatológica do TVTC e verificado o aumento quantitativo de linfócitos maduros e plasmócitos, em meio as células tumorais, achado compatível com a fase estacionária da doença. A partir desse momento, optou-se por realizar apenas acompanhamento clínico e avaliação citopatológica da neoplasia. Foram observados contínua remissão clínica e achados microscópicos compatíveis com a fase de regressão do tumor, até sua remissão completa. Pondera-se que a melhora na saúde geral da paciente após o tratamento da EMC esteja relacionada à regressão espontânea do TVTC, e que realização simultânea de exames clínico e citopatológico seriados pode ser viável e útil ao acompanhamento das fases de evolução do TVTC.

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.

Temporospatial distribution and country of origin of canine transmissible venereal tumours in the UK

OBJECTIVE

Transmissable venereal tumour (TVT) is a tumour transplanted by physical contact between dogs. Lesions typically affect the genitalia. TVT is not considered enzootic in the United Kingdom (UK), with cases seen in imported dogs. We sought to determine the patient characteristics, temporal and spatial distribution and country of origin of affected dogs in the UK.

METHODS

Electronic pathology records (EPRs) from four UK veterinary diagnostic laboratories collected between 2010 and 2019 were searched for the terms 'venereal' or 'TVT'. Reports were reviewed for statements confirming a TVT and descriptive statistics collated.

RESULTS

Of 182 EPRs matching the search terms, a diagnosis of TVT was confirmed in 71. Country of origin was noted in 36 cases (50.7%) with Romania being the most common (n = 29). Cases were reported in each UK constituent country, with the majority being in England (64, 90.1%). The incidence of TVT diagnosis increased over the last decade (z = 2.78, p = 0.005).

CONCLUSIONS/DISCUSSION

The incidence of TVT diagnosed in the UK is increasing. The majority of cases were known to have been imported. Autochthonous transmission cannot be excluded due to study design. Vets are encouraged to carefully examine the genitalia of dogs imported to the UK from countries with enzootic TVT.

PD-L1 immunohistochemistry for canine cancers and clinical benefit of anti-PD-L1 antibody in dogs with pulmonary metastatic oral malignant melanoma

Immunotherapy targeting programmed cell death 1 (PD-1) and PD-ligand 1 (PD-L1) represents promising treatments for human cancers. Our previous studies demonstrated PD-L1 overexpression in some canine cancers, and suggested the therapeutic potential of a canine chimeric anti-PD-L1 monoclonal antibody (c4G12). However, such evidence is scarce, limiting the clinical application in dogs. In the present report, canine PD-L1 expression was assessed in various cancer types, using a new anti-PD-L1 mAb, 6C11-3A11, and the safety and efficacy of c4G12 were explored in 29 dogs with pulmonary metastatic oral malignant melanoma (OMM). PD-L1 expression was detected in most canine malignant cancers including OMM, and survival was significantly longer in the c4G12 treatment group (median 143 days) when compared to a historical control group (n = 15, median 54 days). In dogs with measurable disease (n = 13), one dog (7.7%) experienced a complete response. Treatment-related adverse events of any grade were observed in 15 dogs (51.7%). Here we show that PD-L1 is a promising target for cancer immunotherapy in dogs, and dogs could be a useful large animal model for human cancer research.

The evolution of resistance and tolerance as cancer defences

Although there is a plethora of cancer associated-factors that can ultimately culminate in death (cachexia, organ impairment, metastases, opportunistic infections, etc.), the focal element of every terminal malignancy is the failure of our natural defences to control unlimited cell proliferation. The reasons why our defences apparently lack efficiency is a complex question, potentially indicating that, under Darwinian terms, solutions other than preventing cancer progression are also important contributors. In analogy with host-parasite systems, we propose to call this latter option ‘tolerance’ to cancer. Here, we argue that the ubiquity of oncogenic processes among metazoans is at least partially attributable to both the limitations of resistance mechanisms and to the evolution of tolerance to cancer. Deciphering the ecological contexts of alternative responses to the cancer burden is not a semantic question, but rather a focal point in understanding the evolutionary ecology of host-tumour relationships, the evolution of our defences, as well as why and when certain cancers are likely to be detrimental for survival.

Transmissible Cancers and Immune Downregulation in Tasmanian Devil (Sacrophilus harrisii) and Canine Populations

Known as devil facial tumor disease (DFTD) and canine transmissible venereal tumor (CTVT), transmissible cancer occurs in both Tasmanian devil and canine populations, respectively. Both malignancies show remarkable ability to be transmitted as allografts into subsequent hosts. How DFTD and CTVT avoid detection by immunocompetent hosts is of particular interest, given that these malignancies are rarely seen in other species in nature. Both of these transmissible cancers can downregulate the host immune system, enabling proliferation. DFTD is characterized by epigenetic modifications to the DNA promoter regions of β₂microglobulin, transporters associated with antigen processing 1 and 2, MHC I, and MHC II-crucial proteins required in the detection and surveillance of foreign material. Downregulation during DFTD may be achieved by altering the activity of histone deacetylases. DFTD has caused widespread destruction of devil populations, placing the species on the brink of extinction. CTVT demonstrates a proliferative phase, during which the tumor evades immune detection, allowing it to proliferate, and a regressive phase when hosts mount an effective immune response. Alteration of TGFβ signaling in CTVT likely impedes the antigen-processing capabilities of canine hosts in addition to hindering the ability of natural killer cells to detect immune system downregulation. Immunosuppressive cytokines such as CXCL7 may contribute to a favorable microenvironment that supports the proliferation of CTVT. When viewed from an evolutionary paradigm, both DFTD and CTVT may conform to a model of host-parasite coevolution. Furthermore, various genetic features, such as genetically active transposons in CTVT and chromosomal rearrangements in DFTD, play important roles in promoting the survival of these disease agents. Understanding the mode of transmission for these transmissible cancers may shed light on mechanisms for human malignancies and reveal opportunities for treatment in the future.

Somatic evolution and global expansion of an ancient transmissible cancer lineage

The canine transmissible venereal tumor (CTVT) is a cancer lineage that arose several millennia ago and survives by "metastasizing" between hosts through cell transfer. The somatic mutations in this cancer record its phylogeography and evolutionary history. We constructed a time-resolved phylogeny from 546 CTVT exomes and describe the lineage's worldwide expansion. Examining variation in mutational exposure, we identify a highly context-specific mutational process that operated early in the cancer's evolution but subsequently vanished, correlate ultraviolet-light mutagenesis with tumor latitude, and describe tumors with heritable hyperactivity of an endogenous mutational process. CTVT displays little evidence of ongoing positive selection, and negative selection is detectable only in essential genes. We illustrate how long-lived clonal organisms capture changing mutagenic environments, and reveal that neutral genetic drift is the dominant feature of long-term cancer evolution.

Evaluation of a Canine Transmissible Venereal Tumour Cell Line with Tumour Immunity Capacity but Without Tumorigenic Property

Introduction

Canine transmissible venereal tumour (CTVT) is a sexually transmitted tumour affecting dogs worldwide, imposing a financial burden on dog owners. A stable culture cell line in continuous passages for >18 months has only been achieved once. The present study investigated a stable CTVT cell line isolated from a bitch and its potential as a vaccine.

Material and Methods

A biopsy from a 2-year-old mongrel bitch with CTVT was obtained for histopathological confirmation and isolation of tumour cells. The isolated cells were cultured to passage 55 and characterised by flow cytometry, with karyotyping by GTG-banding and by PCR detection of myc S-2 and LINE AS1. The isolated CTVT cell line was also used as a preventive vaccine in a canine model.

Results

Histopathological analysis of the isolated tumour cells revealed typical CTVT characteristics. Constant proliferation and stable morphological characteristics were observed during culture. Phenotypic analysis determined the expression of HLA-DR⁺, CD5.1⁺, CD14⁺, CD45⁺, CD83⁺, CD163⁺, and Ly-6G-Ly-6C⁺. GTG-banding revealed a mean of 57 chromosomes in the karyotype with several complex chromosomal rearrangements. LINE-c-myc insertion in the isolated CTVT cell line at 550 bp was not detected. However, a 340-bp band was amplified. Isolated CTVT cell line inoculation at a concentration of 1×10⁸ did not induce tumour growth in bitches, nor did a challenge with primary CTVT cells.

Conclusion

The present study successfully identified and isolated a stable CTVT cell line that may be useful in CTVT prevention.

Factor Analysis for Bicluster Acquisition (FABIA) revealed vincristine-sensitive transcript pattern of canine transmissible venereal tumors

Chemotherapeutic treatment for Canine transmissible venereal tumor (CTVT) commonly relies on vincristine administration. Since the treatment outcomes can vary among CTVT cases, gaining insight into the tumor cell mechanisms influencing vincristine's potency should render veterinarians novel knowledge to enhance its therapeutic effect. This study aimed to attain such knowledge from a meta-analysis of CTVT mRNA sequencing (mRNA-seq) transcriptome data using Factor Analysis for Bicluster Acquisition (FABIA) biclustering. FABIA biclustering identified 459 genes consistently expressed among mRNA-seq transcription profiling of CTVT samples regressed by vincristine. These genes were also differentially expressed from those of progressive CTVT (FDR ≤ 0.001). Enrichment analysis illustrated the affiliation of these genes with "Antigen presentation" and "Lysosome" GO terms (FDR ≤ 0.05). Several genes in "Lysosome" term involved 5 cell mechanisms-antigen presentation, autophagy, cell-adhesion, lysosomal membrane permeabilization (LMP), and PI3K/mTOR signaling. This study integrated FABIA biclustering in CTVT transcriptome analysis to gain insight into cell mechanisms responsible for vincristine-sensitive characteristics of the tumor, in order to identify new molecular targets augmenting therapeutic effect of vincristine. Interestingly, the analysis indicated LMP targeting by lysosome destabilizing agent-siramesine as the promising vincristine's enhancer for future study. As far as we know, this is the first canine tumor transcriptomic meta-analysis applying FABIA biclustering for the betterment of future CTVT therapy. This study hereby provided an interesting manifestation to acquire such knowledge in other canine neoplasia.

Cancer in wildlife: patterns of emergence

Cancer is ubiquitous in wildlife, affecting animals from bivalves to pachyderms and cetaceans. Reports of increasing frequency demonstrate that neoplasia is associated with substantial mortality in wildlife species. Anthropogenic activities and global weather changes are shaping new geographical limitations for many species, and alterations in living niches are associated with visible examples of genetic bottlenecks, toxin exposures, oncogenic pathogens, stress and immunosuppression, which can all contribute to cancers in wild species. Nations that devote resources to monitoring the health of wildlife often do so for human-centric reasons, including for the prediction of the potential for zoonotic disease, shared contaminants, chemicals and medications, and for observing the effect of exposure from crowding and loss of habitat. Given the increasing human footprint on land and in the sea, wildlife conservation should also become a more important motivating factor. Greater attention to the patterns of the emergence of wildlife cancer is imperative because growing numbers of species are existing at the interface between humans and the environment, making wildlife sentinels for both animal and human health. Therefore, monitoring wildlife cancers could offer interesting and novel insights into potentially unique non-age-related mechanisms of carcinogenesis across species.

Intratumoral recombinant human interferon alpha-2a and vincristine combination therapy in canine transmissible venereal tumour

Canine transmissible venereal tumour (CTVT) is a naturally occurring contagious neoplasm of dogs located mainly on the external genitalia of both sexes. The course of vincristine chemotherapy, the most effective and practical therapy, is affected by the immune status of the host. The aim was to investigate recombinant human interferon alpha‐2a (rhIFNα‐2a) and vincristine for treatment of CTVT. A total of 21 female dogs were included. In group I (n = 9), vincristine (0.025 mg/kg, IV) was administered weekly. In group II (n = 6), dogs were injected intratumorally weekly with 1.5 million IU rhIFNα‐2a. In group III (n = 6), rhIFNα‐2a and vincristine were combined. No tumour regression was observed after three injections of rhIFNα‐2a in group II and weekly vincristine was administered. The number of tumour infiltrating lymphocytes (TILs), mitotic figures and apoptotic cells were counted in subsequent incisional tumour biopsies. The Kaplan–Meier Method was used to analyse survival using complete tumour regression as the outcome and Breslow Test was used for comparison of survival curves. Differences in TILs, cell proliferation and apoptosis between groups were assessed by analysis of covariance. Complete regression was observed in all animals included. Mean duration of vincristine treatment for complete regression was shorter in group II (3.50 weeks, 95% CI, 3.06–3.94, P < 0.05) and group III (3.17 weeks, 95% CI, 2.84–3.49, P < 0.01) compared to group I (5.11 weeks, 95% CI, 4.42–5.80). Vincristine and rhIFNα‐2a combination increased TILs in CTVT biopsies compared to vincristine treatment (P = 0.017) and vincristine treatment after rhIFNα‐2a (P = 0.049). Vincristine treatment after rhIFNα‐2a (Group II; P < 0.001) and rhIFNα‐2a and vincristine combination (Group III; P < 0.001) decreased apoptosis. The results indicate that intratumoral rhIFNα‐2a treatment alone is not effective in CTVT. However, combination of rhIFNα‐2a and vincristine shortens the duration of treatment compared to vincristine therapy.

The role of MHC genes in contagious cancer: the story of Tasmanian devils

The Tasmanian devil, a marsupial species endemic to the island of Tasmania, harbours two contagious cancers, Devil Facial Tumour 1 (DFT1) and Devil Facial Tumour 2 (DFT2). These cancers pass between individuals in the population via the direct transfer of tumour cells, resulting in the growth of large tumours around the face and neck of affected animals. While these cancers are rare, a contagious cancer also exists in dogs and five contagious cancers circulate in bivalves. The ability of tumour cells to emerge and transmit in mammals is surprising as these cells are an allograft and should be rejected due to incompatibility between Major Histocompatibility Complex (MHC) genes. As such, considerable research has focused on understanding how DFT1 cells evade the host immune system with particular reference to MHC molecules. This review evaluates the role that MHC class I expression and genotype plays in allowing DFT1 to circumvent histocompatibility barriers in Tasmanian devils. We also examine recent research that suggests that Tasmanian devils can mount an immune response to DFT1 and may form the basis of a protective vaccine against the tumour.

ERBB3: A potential serum biomarker for early detection and therapeutic target for devil facial tumour 1 (DFT1)

Devil Facial Tumour 1 (DFT1) is one of two transmissible neoplasms of Tasmanian devils (Sarcophilus harrisii) predominantly affecting their facial regions. DFT1's cellular origin is that of Schwann cell lineage where lesions are evident macroscopically late in the disease. Conversely, the pre-clinical timeframe from cellular transmission to appearance of DFT1 remains uncertain demonstrating the importance of an effective pre-clinical biomarker. We show that ERBB3, a marker expressed normally by the developing neural crest and Schwann cells, is immunohistohemically expressed by DFT1, therefore the potential of ERBB3 as a biomarker was explored. Under the hypothesis that serum ERBB3 levels may increase as DFT1 invades local and distant tissues our pilot study determined serum ERBB3 levels in normal Tasmanian devils and Tasmanian devils with DFT1. Compared to the baseline serum ERBB3 levels in unaffected Tasmanian devils, Tasmanian devils with DFT1 showed significant elevation of serum ERBB3 levels. Interestingly Tasmanian devils with cutaneous lymphoma (CL) also showed elevation of serum ERBB3 levels when compared to the baseline serum levels of Tasmanian devils without DFT1. Thus, elevated serum ERBB3 levels in otherwise healthy looking devils could predict possible DFT1 or CL in captive or wild devil populations and would have implications on the management, welfare and survival of Tasmanian devils. ERBB3 is also a therapeutic target and therefore the potential exists to consider modes of administration that may eradicate DFT1 from the wild.

Exchange of Genetic Sequences Between Viruses and Hosts

Although genetic transfer between viruses and vertebrate hosts occurs less frequently than gene flow between bacteriophages and prokaryotes, it is extensive and has affected the evolution of both parties. With retroviruses, the integration of proviral DNA into chromosomal DNA can result in the activation of adjacent host gene expression and in the transduction of host transcripts into retroviral genomes as oncogenes. Yet in contrast to lysogenic phage, there is little evidence that viral oncogenes persist in a chain of natural transmission or that retroviral transduction is a significant driver of the horizontal spread of host genes. Conversely, integration of proviruses into the host germ line has generated endogenous retroviral genomes (ERV) in all vertebrate genomes sequenced to date. Some of these genomes retain potential infectivity and upon reactivation may transmit to other host species. During mammalian evolution, sequences of retroviral origin have been repurposed to serve host functions, such as the viral envelope glycoproteins crucial to the development of the placenta. Beyond retroviruses, DNA viruses with complex genomes have acquired numerous genes of host origin which influence replication, pathogenesis and immune evasion, while host species have accumulated germline sequences of both DNA and RNA viruses. A codicil is added on lateral transmission of cancer cells between hosts and on migration of host mitochondria into cancer cells.

Development of novel associations between MHC alleles and susceptibility to parasitic infections in an isolated population of an endangered mammal

The role of pathogens in dynamics of endangered species is not fully understood, and the effect of infection often interacts with other processes affecting those species, such as fragmentation and isolation or loss of genetic variation. Small, isolated populations are prone to losing functional alleles due to demographic processes and genetic drift, which may diminish their ability to resist infection if immune genes are affected. Demographic processes may also alter the selective pressure exerted by a parasite, as they influence the rate of parasite transmission between individuals. In the present paper we studied changes in parasite infection levels and genetic variability in an isolated population of spotted suslik (Spermophillus suslicus). Over a three-year period (approx. three generations), when the population size remained relatively stable, we observed a considerable increase in parasite prevalence and infection intensity, followed by the development of novel associations between MHC DRB alleles and parasite burden. Contrary to expectations, the change in MHC allele frequency over time was not consistent with the effect of the allele - for instance, Spsu-DRB*07, associated with higher intensity of infection with a nematode Capillaria sp., increased in frequency from 11.8 to 20.2%. Yet, we found no signatures of selection in the studied loci. Our results show that an isolated, stable population may experience a sudden increase in parasitic infections, resulting in a development of novel associations between MHC alleles and parasite susceptibility/resistance, even though no signatures of selection can be found.

The evolutionary ecology of transmissible cancers

Transmissible tumours, while rare, present a fascinating opportunity to examine the evolutionary dynamics of cancer as both an infectious agent and an exotic, invasive species. Only three naturally-occurring transmissible cancers have been observed so far in the wild: Tasmanian devil facial tumour diseases, canine transmissible venereal tumour, and clam leukaemia. Here, we define four conditions that are necessary and sufficient for direct passage of cancer cells between either vertebrate or invertebrate hosts. Successful transmission requires environment and behaviours that facilitate transfer of tumour cells between hosts including: tumour tissue properties that promote shedding of large numbers of malignant cells, tumour cell plasticity that permits their survival during transmission and growth in a new host, and a 'permissible' host or host tissue. This rare confluence of multiple host- and tumour cell-traits both explains the rarity of tumour cell transmission and provides novel insights into the dynamics that both promote and constrain their growth.

Devil Facial Tumor Disease

Devil facial tumor disease (DFTD) is an emergent transmissible cancer exclusive to Tasmanian devils (Sarcophilus harrisii) and threatening the species with extinction in the wild. Research on DFTD began 10 years ago, when nothing was known about the tumor and little about the devils. The depth of knowledge gained since then is impressive, with research having addressed significant aspects of the disease and the devils' responses to it. These include the cause and pathogenesis of DFTD, the immune response of the devils and the immune evasion mechanisms of the tumor, the transmission patterns of DFTD, and the impacts of DFTD on the ecosystem. This review aims to collate this information and put it into the context of conservation strategies designed to mitigate the impacts of DFTD on the devil and the Tasmanian ecosystem.

Immunology of a Transmissible Cancer Spreading among Tasmanian Devils

Devil facial tumor disease (DFTD) is a transmissible cancer that has killed most of the Tasmanian devil (Sarcophilus harrissii) population. Since the first case appeared in the mid-1990s, it has spread relentlessly across the Tasmanian devil's geographic range. As Tasmanian devils only exist in Tasmania, Australia, DFTD has the potential to cause extinction of this species. The origin of DFTD was a Schwann cell from a female devil. The disease is transmitted when devils bite each other around the facial areas, a behavior synonymous with this species. Every devil that is 'infected' with DFTD dies from the cancer. Once the DFTD cells have been transmitted, they appear to develop into a cancer without inducing an immune response. The DFTD cancer cells avoid allogeneic recognition because they do not express MHC class I molecules on the cell surface. A reduced genetic diversity and the production of immunosuppressive cytokines may also contribute.

Cancer in the parasitic protozoans Trypanosoma brucei and Toxoplasma gondii

Cancer is a general name for more than 100 malignant diseases. It is postulated that all cancers start from a single abnormal cell that grows out of control. Untreated cancers can cause serious consequences and deaths. Great progress has been made in cancer research that has significantly improved our knowledge and understanding of the nature and mechanisms of the disease, but the origins of cancer are far from being well understood due to the limitations of suitable model systems and to the complexities of the disease. In view of the fact that cancers are found in various species of vertebrates and other metazoa, here, we suggest that cancer also occurs in parasitic protozoans such as Trypanosoma brucei, a blood parasite, and Toxoplasma gondii, an obligate intracellular pathogen. Without treatment, these protozoan cancers may cause severe disease and death in mammals, including humans. The simpler genomes of these single-cell organisms, in combination with their complex life cycles and fascinating life cycle differentiation processes, may help us to better understand the origins of cancers and, in particular, leukemias.

What's the host and what's the microbe? The Marjory Stephenson Prize Lecture 2015

The interchange between retroviruses and their hosts is an intimate one because retroviruses integrate proviral DNA into host chromosomal DNA as an obligate step in the replication cycle. This has resulted in the occasional transduction of host genes into retroviral genomes as oncogenes, and also led to the integration of viral genomes into the host germ line that gives rise to endogenous retroviruses. I shall reflect on the evolutionary consequences of these events for virus and host. Then, I shall discuss the emergence of non-viral infections of host origin, namely, how malignant cells can give rise to eukaryotic single cell 'parasites' that colonize new hosts and how these in turn have been colonized by host mitochondria.

Horizontal transmission of clonal cancer cells causes leukemia in soft-shell clams

Outbreaks of fatal leukemia-like cancers of marine bivalves throughout the world have led to massive population loss. The cause of the disease is unknown. We recently identified a retrotransposon, Steamer, that is highly expressed and amplified to high copy number in neoplastic cells of soft-shell clams (Mya arenaria). Through analysis of Steamer integration sites, mitochondrial DNA single-nucleotide polymorphisms (SNPs), and polymorphic microsatellite alleles, we show that the genotypes of neoplastic cells do not match those of the host animal. Instead, neoplastic cells from dispersed locations in New York, Maine, and Prince Edward Island (PEI), Canada, all have nearly identical genotypes that differ from those of the host. These results indicate that the cancer is spreading between animals in the marine environment as a clonal transmissible cell derived from a single original clam. Our findings suggest that horizontal transmission of cancer cells is more widespread in nature than previously supposed.

The clammy grip of parasitic tumors

An epidemic of leukemia among bivalve molluscs is spreading along the Atlantic coast of North America, with a serious population decline of soft-shelled clams. In this issue of Cell, Metzger et al. use forensic DNA markers to demonstrate that the leukemia cells have a clonal origin and appear to be transmitted through sea water.