Endogenous mouse mammary tumor viruses (mtv): new roles for an old virus in cancer, infection, and immunity

The Host miR-17-92 Cluster Negatively Regulates Mouse Mammary Tumor Virus (MMTV) Replication Primarily Via Cluster Member miR-92a

The mouse mammary tumor virus (MMTV) is a well-known causative agent of breast cancer in mice. Previously, we have shown that MMTV dysregulates expression of the host miR-17-92 cluster in MMTV-infected mammary glands and MMTV-induced tumors. This cluster, better known as oncomiR-1, is frequently dysregulated in cancers, particularly breast cancer. In this study, our aim was to uncover a functional interaction between MMTV and the cluster. Our results reveal that MMTV expression led to dysregulation of the cluster in both mammary epithelial HC11 and HEK293T cells with the expression of miR-92a cluster member being affected the most. Conversely, overexpression of the whole or partial cluster significantly repressed MMTV expression. Notably, overexpression of cluster member miR-92a alone repressed MMTV expression to the same extent as overexpression of the complete/partial cluster. Inhibition of miR-92a led to nearly a complete restoration of MMTV expression, while deletion/substitution of the miR-92a seed sequence rescued MMTV expression. Dual luciferase assays identified MMTV genomic RNA as the potential target of miR-92a. These results show that the miR-17-92 cluster acts as part of the cell's well-known miRNA-based anti-viral response to thwart incoming MMTV infection. Thus, this study provides the first evidence highlighting the biological significance of host miRNAs in regulating MMTV replication and potentially influencing tumorigenesis.

The endogenous Mtv8 locus and the immunoglobulin repertoire

The vast diversity of mammalian adaptive antigen receptors allows for robust and efficient immune responses against a wide number of pathogens. The antigen receptor repertoire is built during the recombination of B and T cell receptor (BCR, TCR) loci and hypermutation of BCR loci. V(D)J recombination rearranges these antigen receptor loci, which are organized as an array of separate V, (D), and J gene segments. Transcription activation at the recombining locus leads to changes in the local three-dimensional architecture, which subsequently contributes to which gene segments are utilized for recombination. The endogenous retrovirus (ERV) mouse mammary tumor provirus 8 (Mtv8) resides on mouse chromosome 6 interposed within the large array of light chain kappa V gene segments. As ERVs contribute to changes in genomic architecture by driving high levels of transcription of neighboring genes, it was suggested that Mtv8 could influence the BCR repertoire. We generated Mtv8-deficient mice to determine if the ERV influences V(D)J recombination to test this possibility. We find that Mtv8 does not influence the BCR repertoire.

Endogenous feline leukemia virus long terminal repeat integration site diversity is highly variable in related and unrelated domestic cats

Endogenous retroviruses (ERV) are indicators of vertebrate evolutionary history and play important roles as homeostatic regulators. ERV long terminal repeat (LTR) elements may act as cis-activating promoters or trans-activating enhancer elements modifying gene transcription distant from LTR insertion sites. We previously documented that endogenous feline leukemia virus (FeLV)-LTR copy number variation in individual cats tracks inversely with susceptibility to virulent FeLV disease. To evaluate FeLV-LTR insertion characteristics, we assessed enFeLV-LTR integration site diversity in 20 cats from three genetically distinct populations using a baited linker-mediated PCR approach. We documented 765 individual integration sites unequally represented among individuals. Only three LTR integration sites were shared among all individuals, while 412 sites were unique to a single individual. When primary fibroblast cultures were challenged with exogenous FeLV, we found significantly increased expression of both exogenous and endogenous FeLV orthologs, supporting previous findings of potential exFeLV-enFeLV interactions; however, viral challenge did not elicit transcriptional changes in genes associated with the vast majority of integration sites. This study assesses FeLV-LTR integration sites in individual animals, providing unique transposome genotypes. Further, we document substantial individual variation in LTR integration site locations, even in a highly inbred population, and provide a framework for understanding potential endogenous retroviral element position influence on host gene transcription.

Deletion of Vβ3+CD4+ T cells by endogenous mouse mammary tumor virus 3 prevents type 1 diabetes induction by autoreactive CD8+ T cells

In both humans and NOD mice, type 1 diabetes (T1D) develops from the autoimmune destruction of pancreatic beta cells by T cells. Interactions between both helper CD4+ and cytotoxic CD8+ T cells are essential for T1D development in NOD mice. Previous work has indicated that pathogenic T cells arise from deleterious interactions between relatively common genes which regulate aspects of T cell activation/effector function (Ctla4, Tnfrsf9, Il2/Il21), peptide presentation (H2-A g7, B2m), and T cell receptor (TCR) signaling (Ptpn22). Here, we used a combination of subcongenic mapping and a CRISPR/Cas9 screen to identify the NOD-encoded mammary tumor virus (Mtv)3 provirus as a genetic element affecting CD4+/CD8+ T cell interactions through an additional mechanism, altering the TCR repertoire. Mtv3 encodes a superantigen (SAg) that deletes the majority of Vβ3+ thymocytes in NOD mice. Ablating Mtv3 and restoring Vβ3+ T cells has no effect on spontaneous T1D development in NOD mice. However, transferring Mtv3 to C57BL/6 (B6) mice congenic for the NOD H2 g7 MHC haplotype (B6.H2 g7) completely blocks their normal susceptibility to T1D mediated by transferred CD8+ T cells transgenically expressing AI4 or NY8.3 TCRs. The entire genetic effect is manifested by Vβ3+CD4+ T cells, which unless deleted by Mtv3, accumulate in insulitic lesions triggering in B6 background mice the pathogenic activation of diabetogenic CD8+ T cells. Our findings provide evidence that endogenous Mtv SAgs can influence autoimmune responses. Furthermore, since most common mouse strains have gaps in their TCR Vβ repertoire due to Mtvs, it raises questions about the role of Mtvs in other mouse models designed to reflect human immune disorders.

Milk Transmission of Mammalian Retroviruses

The transmission of viruses from one host to another typically occurs through horizontal or vertical pathways. The horizontal pathways include transmission amongst individuals, usually through bodily fluids or excretions, while vertical transmission transpires from mother to their offspring, either during pregnancy, childbirth, or breastfeeding. While there are more than 200 human pathogenic viruses to date, only a small number of them are known to be transmitted via breast milk, including cytomegalovirus (CMV), human immunodeficiency virus type 1 (HIV-1), and human T cell lymphotropic virus type 1 (HTLV-1), the latter two belonging to the family Retroviridae. Breast milk transmission is a common characteristic among mammalian retroviruses, but there is a lack of reports summarizing our knowledge regarding this route of transmission of mammalian retroviruses. Here, we provide an overview of the transmission of mammalian exogenous retroviruses with a focus on Orthoretrovirinae, and we highlight whether they have been described or suspected to be transmitted through breast milk, covering various species. We also elaborate on the production and composition of breast milk and discuss potential entry sites of exogenous mammalian retroviruses during oral transmission.

Tumor-targeted superantigens produce curative tumor immunity with induction of memory and demonstrated antigen spreading

BACKGROUND

Despite remarkable progress, the immunotherapies currently used in the clinic, such as immune checkpoint blockade (ICB) therapy, still have limited efficacy against many types of solid tumors. One major barrier to effective treatment is the lack of a durable long-term response. Tumor-targeted superantigen (TTS) therapy may overcome this barrier to enhance therapeutic efficacy. TTS proteins, such as the clinical-stage molecule naptumomab estafenatox (NAP), increase tumor recognition and killing by both coating tumor cells with bacterial-derived superantigens (SAgs) and selectively expanding T-cell lineages that can recognize them. The present study investigated the efficacy and mechanism of action of repeated TTS (C215Fab-SEA) treatments leading to a long-term antitumor immune response as monotherapy or in combination with PD-1/PD-L1 inhibitors in murine tumor models.

METHODS

We used syngeneic murine tumor models expressing the human EpCAM target (C215 antigen) to assess the efficacy and mechanism of action of repeated treatment with TTS C215Fab-SEA alone or with anti-PD-1/PD-L1 monoclonal antibodies. Tumor draining lymph nodes (TDLNs) and tumor tissues were processed and analyzed by immunophenotyping and immunohistochemistry. Isolated RNA from tumors was used to analyze gene expression and the TCR repertoire. Tumor rechallenge and T-cell transfer studies were conducted to test the long-term antitumor memory response.

RESULTS

TTS therapy inhibited tumor growth and achieved complete tumor rejection, leading to a T-cell-dependent long-term memory response against the tumor. The antitumor effect was derived from inflammatory responses converting the immunosuppressive TME into a proinflammatory state with an increase in T-cell infiltration, activation and high T-cell diversity. The combination of TTS with ICB therapy was significantly more effective than the monotherapies and resulted in higher tumor-free rates.

CONCLUSIONS

These new results indicate that TTSs not only can turn a "cold" tumor into a "hot" tumor but also can enable epitope spreading and memory response, which makes TTSs ideal candidates for combination with ICB agents and other anticancer agents.

The Viral Origin of Human Breast Cancer: From the Mouse Mammary Tumor Virus (MMTV) to the Human Betaretrovirus (HBRV)

A Human Betaretrovirus (HBRV) has been identified in humans, dating as far back as about 4500 years ago, with a high probability of it being acquired by our species around 10,000 years ago, following a species jump from mice to humans. HBRV is the human homolog of the MMTV (mouse mammary tumor virus), which is the etiological agent of murine mammary tumors. The hypothesis of a HMTV (human mammary tumor virus) was proposed about 50 years ago, and has acquired a solid scientific basis during the last 30 years, with the demonstration of a robust link with breast cancer and with PBC, primary biliary cholangitis. This article summarizes most of what is known about MMTV/HMTV/HBRV since the discovery of MMTV at the beginning of last century, to make evident both the quantity and the quality of the research supporting the existence of HBRV and its pathogenic role. Here, it is sufficient to mention that scientific evidence includes that viral sequences have been identified in breast-cancer samples in a worldwide distribution, that the complete proviral genome has been cloned from breast cancer and patients with PBC, and that saliva contains HBRV, as a possible route of inter-human infection. Controversies that have arisen concerning results obtained from human tissues, many of them outdated by new scientific evidence, are critically discussed and confuted.

Endogenous Feline Leukemia Virus (FeLV) siRNA Transcription May Interfere with Exogenous FeLV Infection

Endogenous retroviruses (ERVs) are increasingly recognized for biological impacts on host cell function and susceptibility to infectious agents, particularly in relation to interactions with exogenous retroviral progenitors (XRVs). ERVs can simultaneously promote and restrict XRV infections using mechanisms that are virus and host specific. The majority of endogenous-exogenous retroviral interactions have been evaluated in experimental mouse or chicken systems, which are limited in their ability to extend findings to naturally infected outbred animals. Feline leukemia virus (FeLV) has a relatively well-characterized endogenous retrovirus with a coexisting virulent exogenous counterpart and is endemic worldwide in domestic cats. We have previously documented an association between endogenous FeLV (enFeLV) long terminal repeat (LTR) copy number and abrogated exogenous FeLV in naturally infected cats and experimental infections in tissue culture. Analyses described here examine limited FeLV replication in experimentally infected peripheral blood mononuclear cells, which correlates with higher enFeLV transcripts in these cells compared to fibroblasts. We further examine NCBI Sequence Read Archive RNA transcripts to evaluate enFeLV transcripts and RNA interference (RNAi) precursors. We find that lymphoid-derived tissues, which are experimentally less permissive to exogenous FeLV infection, transcribe higher levels of enFeLV under basal conditions. Transcription of enFeLV-LTR segments is significantly greater than that of other enFeLV genes. We documented transcription of a 21-nucleotide (nt) microRNA (miRNA) just 3' to the enFeLV 5'-LTR in the feline miRNAome of all data sets evaluated (n = 27). Our findings point to important biological functions of enFeLV transcription linked to solo LTRs distributed within the domestic cat genome, with potential impacts on domestic cat exogenous FeLV susceptibility and pathogenesis. IMPORTANCE Endogenous retroviruses (ERVs) are increasingly implicated in host cellular processes and susceptibility to infectious agents, specifically regarding interactions with exogenous retroviral progenitors (XRVs). Exogenous feline leukemia virus (FeLV) and its endogenous counterpart (enFeLV) represent a well-characterized, naturally occurring XRV-ERV dyad. We have previously documented an abrogated FeLV infection in both naturally infected cats and experimental fibroblast infections that harbor higher enFeLV proviral loads. Using an in silico approach, we provide evidence of miRNA transcription that is produced in tissues that are most important for FeLV infection, replication, and transmission. Our findings point to important biological functions of enFeLV transcription linked to solo-LTRs distributed within the feline genome, with potential impacts on domestic cat exogenous FeLV susceptibility and pathogenesis. This body of work provides additional evidence of RNA interference (RNAi) as a mechanism of viral interference and is a demonstration of ERV exaptation by the host to defend against related XRVs.

Retroviral integrations contribute to elevated host cancer rates during germline invasion

Repeated retroviral infections of vertebrate germlines have made endogenous retroviruses ubiquitous features of mammalian genomes. However, millions of years of evolution obscure many of the immediate repercussions of retroviral endogenisation on host health. Here we examine retroviral endogenisation during its earliest stages in the koala (Phascolarctos cinereus), a species undergoing germline invasion by koala retrovirus (KoRV) and affected by high cancer prevalence. We characterise KoRV integration sites (IS) in tumour and healthy tissues from 10 koalas, detecting 1002 unique IS, with hotspots of integration occurring in the vicinity of known cancer genes. We find that tumours accumulate novel IS, with proximate genes over-represented for cancer associations. We detect dysregulation of genes containing IS and identify a highly-expressed transduced oncogene. Our data provide insights into the tremendous mutational load suffered by the host during active retroviral germline invasion, a process repeatedly experienced and overcome during the evolution of vertebrate lineages.

Endogenous Retroviruses Drive Resistance and Promotion of Exogenous Retroviral Homologs

Endogenous retroviruses (ERVs) serve as markers of ancient viral infections and provide invaluable insight into host and viral evolution. ERVs have been exapted to assist in performing basic biological functions, including placentation, immune modulation, and oncogenesis. A subset of ERVs share high nucleotide similarity to circulating horizontally transmitted exogenous retrovirus (XRV) progenitors. In these cases, ERV-XRV interactions have been documented and include (a) recombination to result in ERV-XRV chimeras, (b) ERV induction of immune self-tolerance to XRV antigens, (c) ERV antigen interference with XRV receptor binding, and (d) interactions resulting in both enhancement and restriction of XRV infections. Whereas the mechanisms governing recombination and immune self-tolerance have been partially determined, enhancement and restriction of XRV infection are virus specific and only partially understood. This review summarizes interactions between six unique ERV-XRV pairs, highlighting important ERV biological functions and potential evolutionary histories in vertebrate hosts.

Human endogenous retrovirus-K (HML-2): a comprehensive review

The human genome contains a large number of retroviral elements acquired over the process of evolution, some of which are specific to primates. However, as many of these are defective or silenced through epigenetic changes, they were historically considered "junk DNA" and their potential role in human physiology or pathological circumstances have been poorly studied. The most recently acquired, human endogenous retrovirus-K (HERV-K), has multiple copies in the human genome and some of them have complete open reading frames that are transcribed and translated, especially in early embryogenesis. Phylogenetically, HERV-K is considered a supergroup of viruses. One of the subtypes, termed HML-2, seems to be the most active and hence, it is the best studied. Aberrant expression of HML-2 in adult tissues has been associated with certain types of cancer and with neurodegenerative diseases. This review discusses the discovery of these viruses, their classification, structure, regulation and potential for replication, physiological roles, and their involvement in disease pathogenesis. Finally, it presents different therapeutic approaches being considered to target these viruses.

A cis-Acting Element Downstream of the Mouse Mammary Tumor Virus Major Splice Donor Critical for RNA Elongation and Stability

BACKGROUND

The mouse mammary tumor virus (MMTV) encodes a functional signal peptide, a cleavage product of envelope and Rem proteins. Signal peptide interacts with a 3' cis-acting RNA element, the Rem-responsive element (RmRE), to facilitate expression of both unspliced genomic (gRNA) and spliced mRNAs. An additional RmRE has been proposed at the 5' end of the genome, facilitating nuclear export of the unspliced gRNA, whereas the 3' RmRE could facilitate translation of all other mRNAs, including gRNA.

RESULTS

To address this hypothesis, a series of mutations were introduced into a 24-nt region found exclusively in the unspliced gRNA. Mutant clones using MMTV or human cytomegalovirus promoters were tested in both transient and stable transfections to determine their effect on gRNA nuclear export, stability, and translation. Nuclear export of the gRNA was affected only in a small mutant subset in stably transfected Jurkat T cells. Quantitative real-time RT-PCR of actinomycin D-treated cells expressing MMTV revealed that multiple mutants were severely compromised for RNA expression and stability. Both genomic and spliced nuclear RNAs were reduced, leading to abrogation of Gag and Env protein expressed from unspliced and spliced mRNAs, respectively. RT-PCRs with multiple primer pairs indicated failure to elongate genomic MMTV transcripts beyond ~500 nt compared to the wild type in a cell line-dependent manner.

CONCLUSIONS

MMTV contains a novel cis-acting element downstream of the major splice donor critical for facilitating MMTV gRNA elongation and stability. Presence of a mirror repeat within the element may represent important viral/host factor binding site(s) within MMTV gRNA.

Canine mammary tumors as a model for human disease

Animal models for examining human breast cancer (HBC) carcinogenesis have been extensively studied and proposed. With the recent advent of immunotherapy, significant attention has been focused on the dog as a model for human cancer. Dogs develop mammary tumors and other cancer types spontaneously with an intact immune system, which exhibit a number of clinical and molecular similarities to HBC. In addition to the spontaneous tumor presentation, the clinical similarities between human and canine mammary tumors (CMT) include the age at onset, hormonal etiology and course of the diseases. Furthermore, factors that affect the disease outcome, including tumor size, stage and lymph node invasion, are similar in HBC and CMT. Similarly, the molecular characteristics of steroid receptor, epidermal growth factor, proliferation marker, metalloproteinase and cyclooxygenase expression, and the mutation of the p53 tumor suppressor gene in CMT, mimic HBC. Furthermore, ductal carcinomas in situ in human and canine mammary glands are particularly similar in their pathological, molecular and visual characteristics. These CMT characteristics and their similarities to HBC indicate that the dog could be an excellent model for the study of human disease. These similarities are discussed in detail in the present review, and are compared with the in vitro and other in vivo animal models available.

Lessons Learned from Mouse Mammary Tumor Virus in Animal Models

Mouse mammary tumor virus (MMTV), which was discovered as a milk-transmitted, infectious, cancer-inducing agent in the 1930s, has been used as an animal model for the study of retroviral infection and transmission, antiviral immune responses, and breast cancer and lymphoma biology. The main target cells for MMTV infection in vivo are cells of the immune system and mammary epithelial cells. Although the host mounts an immune response to the virus, MMTV has evolved multiple means of evading this response. MMTV causes mammary tumors when the provirus integrates into the mammary epithelial and lymphoid cell genome during viral replication and thereby activates cellular oncogene expression. Thus, tumor induction is a by-product of the infection cycle. A number of important oncogenes have been discovered by carrying out MMTV integration site analysis, some of which may play a role in human breast cancer.

Microparticles and cancer thrombosis in animal models

Cancer-associated venous thromboembolism (VTE) constitutes the second cause of death after cancer. Many risk factors for cancer-associated VTE have been identified, among them soluble tissue factor and microparticles (MPs). Few data are available about the implication of MPs in cancer associated-VTE through animal model of cancer. The objective of the present review was to report the state of the current literature about MPs and cancer-associated VTE in animal model of cancer. Fourteen series have reported the role of MPs in cancer-associated VTE, through three main mouse models: ectopic or orthotopic tumor induction, experimental metastasis by intravenous injection of tumor cells into the lateral tail vein of the mouse. Pancreatic cancer is the most used animal model, due to its high rate of cancer-associated VTE. All the series reported that tumor cell-derived MPs can promote thrombus formation in TF-dependent manner. Some authors reported also the implication of phosphatidylserine and PSGL1 in the generation of thrombin. Moreover, MPs seem to be implicated in cancer progression through a coagulation-dependent mechanism secondary to thrombocytosis, or a mechanism implicating the regulation of the immune response. For these reasons, few authors have reported that antiplatelet and anticoagulant treatments may prevent tumor progression and the formation of metastases in addition of coagulopathy.

HERV-K(HML-2), a seemingly silent subtenant - but still waters run deep

A large proportion of the human genome consists of endogenous retroviruses, some of which are well preserved, showing transcriptional activity, and expressing retroviral proteins. The HERV-K(HML-2) family represents the most intact members of these elements, with some having open and intact reading frames for viral proteins and the ability to form virus-like particles. Although generally suppressed in most healthy tissues by a variety of epigenetic processes and antiviral mechanisms, there is evidence that some members of this family are (at least partly) still active - particularly in certain stem cells and various tumors. This raises the possibility of their involvement in tumor induction or in developmental processes. In recent years, many new insights into this fascinating field have been attained, and this review focuses on new discoveries about coevolutionary events and intracellular defense mechanisms against HERV-K(HML-2) activity. We also describe what might occur when these mechanisms fail or become modulated by viral proteins or other viruses and discuss the new vistas opened up by the reconstitution of ancestral viral proteins and even complete HML-2 viruses.

Polypyrimidine tract-binding protein binds to the 5' untranslated region of the mouse mammary tumor virus mRNA and stimulates cap-independent translation initiation

The 5' untranslated region (UTR) of the full-length mRNA of the mouse mammary tumor virus (MMTV) harbors an internal ribosomal entry site (IRES). In this study, we show that the polypyrimidine tract-binding protein (PTB), an RNA-binding protein with four RNA recognition motifs (RRMs), binds to the MMTV 5' UTR stimulating its IRES activity. There are three isoforms of PTB: PTB1, PTB2, and PTB4. Results show that PTB1 and PTB4, but not PTB2, stimulate MMTV-IRES activity. PTB1 promotes MMTV-IRES-mediated initiation more strongly than PTB4. When expressed in combination, PTB1 further enhanced PTB4 stimulation of the MMTV-IRES, while PTB2 fully abrogates PTB4-induced stimulation. PTB1-induced stimulation of MMTV-IRES was not altered in the presence of PTB4 or PTB2. Mutational analysis reveals that stimulation of MMTV-IRES activity is abrogated when PTB1 is mutated either in RRM1/RRM2 or RRM3/RRM4. In contrast, a PTB4 RRM1/RRM2 mutant has reduced effect over MMTV-IRES activity, while stimulation of the MMTV-IRES activity is still observed when the PTB4 RRM3/RMM4 mutant is used. Therefore, PTB1 and PTB4 differentially stimulate the IRES activity. In contrast, PTB2 acts as a negative modulator of PTB4-induced stimulation of MMTV-IRES. We conclude that PTB1 and PTB4 act as IRES trans-acting factors of the MMTV-IRES.

Prenatal Allogeneic Tolerance in Mice Remains Stable Despite Potent Viral Immune Activation

Transplanting stem cells before birth offers an unparalleled opportunity to initiate corrective treatment for numerous childhood diseases with minimal or no host conditioning. Although long-term engraftment has been demonstrated following in utero hematopoietic cellular transplantation during immune quiescence, it is unclear if prenatal tolerance becomes unstable with immune activation such as during a viral syndrome. Using a murine model of in utero hematopoietic cellular transplantation, the impact of an infection with lymphocytic choriomeningitis virus on prenatal allospecific tolerance was examined. The findings in this report illustrate that established mechanisms of donor-specific tolerance are strained during potent immune activation. Specifically, a transient reversal in the anergy of alloreactive lymphocytes is seen in parallel with the global immune response toward the virus. However, these changes return to baseline following resolution of the infection. Importantly, prenatal engraftment remains stable during and after immune activation. Collectively, these findings illustrate the robust nature of allospecific tolerance in prenatal mixed chimerism compared with models of postnatal chimerism and provides additional support for the prenatal approach to the treatment of congenital benign cellular disease.

IL-21-driven neoplasms in SJL mice mimic some key features of human angioimmunoblastic T-cell lymphoma

SJL/J mice exhibit a high incidence of mature B-cell lymphomas that require CD4(+) T cells for their development. We found that their spleens and lymph nodes contained increased numbers of germinal centers and T follicular helper (TFH) cells. Microarray analyses revealed high levels of transcripts encoding IL-21 associated with high levels of serum IL-21. We developed IL-21 receptor (IL21R)-deficient Swiss Jim Lambart (SJL) mice to determine the role of IL-21 in disease. These mice had reduced numbers of TFH cells, lower serum levels of IL-21, and few germinal center B cells, and they did not develop B-cell tumors, suggesting IL-21-dependent B-cell lymphomagenesis. We also noted a series of features common to SJL disease and human angioimmunoblastic T-cell lymphoma (AITL), a malignancy of TFH cells. Gene expression analyses of AITL showed that essentially all cases expressed elevated levels of transcripts for IL21, IL21R, and a series of genes associated with TFH cell development and function. These results identify a mouse model with features of AITL and suggest that patients with the disease might benefit from therapeutic interventions that interrupt IL-21 signaling.

The effect of life history on retroviral genome invasions

Endogenous retroviruses (ERV), or the remnants of past retroviral infections that are no longer active, are found in the genomes of most vertebrates, typically constituting approximately 10% of the genome. In some vertebrates, particularly in shorter-lived species like rodents, it is not unusual to find active endogenous retroviruses. In longer-lived species, including humans where substantial effort has been invested in searching for active ERVs, it is unusual to find them; to date none have been found in humans. Presumably the chance of detecting an active ERV infection is a function of the length of an ERV epidemic. Intuitively, given that ERVs or signatures of past ERV infections are passed from parents to offspring, we might expect to detect more active ERVs in species with longer generation times, as it should take more years for an infection to run its course in longer than in shorter lived species. This means the observation of more active ERV infections in shorter compared to longer-lived species is paradoxical. We explore this paradox using a modeling approach to investigate factors that influence ERV epidemic length. Our simple epidemiological model may explain why we find evidence of active ERV infections in shorter rather than longer-lived species.

Recent developments linking retroviruses to human breast cancer: infectious agent, enemy within or both?

Evidence is accumulating that one or more beta-retrovirus is associated with human breast cancer. Retroviruses can exist as an infectious (exogenous) virus or as a part of the genetic information of cells due to germline integration (endogenous). An exogenous virus with a genome that is highly homologous to mouse mammary tumour virus is gaining acceptance as possibly being associated with human breast cancer, and recently furnished evidence is discussed in this article, as is the evidence for involvement of an endogenous human beta-retrovirus, HERV-K. Modes of interaction are also reviewed and linkages to the APOBEC3 family are suggested.