Detection of a gammaretrovirus, XMRV, in the human population: open questions and implications for xenotransplantation

Identification of multiple potential viral diseases in a large urban center using wastewater surveillance

Viruses are linked to a multitude of human illnesses and can disseminate widely in urbanized environments causing global adverse impacts on communities and healthcare infrastructures. Wastewater-based epidemiology was employed using metagenomics and quantitative polymerase chain reaction (qPCR) assays to identify enteric and non-enteric viruses collected from a large urban area for potential public health monitoring and outbreak analysis. Untreated wastewater samples were collected from November 2017 to February 2018 (n = 54) to evaluate the diversity of human viral pathogens in collected samples. Viruses were classified into virus types based on primary transmission routes and reviewed against viral associated diseases reported in the catchment area. Metagenomics detected the presence of viral pathogens that cause clinically significant diseases reported within the study area during the sampling year. Detected viruses belong to the Adenoviridae, Astroviridae, Caliciviridae, Coronaviridae, Flaviviridae, Hepeviridae, Herpesviridae, Matonaviridae, Papillomaviridae, Parvoviridae, Picornaviridae, Poxviridae, Retroviridae, and Togaviridae families. Furthermore, concentrations of adenovirus, norovirus GII, sapovirus, hepatitis A virus, human herpesvirus 6, and human herpesvirus 8 were measured in wastewater samples and compared to metagenomic findings to confirm detected viral genus. Hepatitis A virus obtained the greatest average viral load (1.86 × 10⁷ genome copies/L) in wastewater samples compared to other viruses quantified using qPCR with a 100% detection rate in metagenomic samples. Average concentration of sapovirus (1.36 × 10⁶ genome copies/L) was significantly greater than norovirus GII (2.94 × 10⁴ genome copies/L) indicating a higher burden within the study area. Findings obtained from this study aid in evaluating the utility of wastewater-based epidemiology for identification and routine monitoring of various viruses in large communities. This methodology has the potential to improve public health responses to large scale outbreaks and viral pandemics.

Role of Exosomes in Human Retroviral Mediated Disorders

Retroviruses comprise an ancient and varied group of viruses with the unique ability to integrate DNA from an RNA transcript into the genome, a subset of which are able to integrate in humans. The timing of these integrations during human history has dictated whether these viruses have remained exogenous and given rise to various human diseases or have become inseparable from the host genome (endogenous retroviruses). Given the ability of retroviruses to integrate into the host and subsequently co-opt host cellular process for viral propagation, retroviruses have been shown to be closely associated with several cellular processes including exosome formation. Exosomes are 30-150 nm unilamellar extracellular vesicles that originate from intraluminal vesicles (ILVs) that form in the endosomal compartment. Exosomes have been shown to be important in intercellular communication and immune cell function. Almost every cell type studied has been shown to produce these types of vesicles, with the cell type dictating the contents, which include proteins, mRNA, and miRNAs. Importantly, recent evidence has shown that infection by viruses, including retroviruses, alter the contents and subsequent function of produced exosomes. In this review, we will discuss the important retroviruses associated with human health and disease. Furthermore, we will delve into the impact of exosome formation and manipulation by integrated retroviruses on human health, survival, and human retroviral disease pathogenesis.

Interactions of host proteins with the murine leukemia virus integrase

Retroviral infections cause a variety of cancers in animals and a number of diverse diseases in humans such as leukemia and acquired immune deficiency syndrome. Productive and efficient proviral integration is critical for retroviral function and is the key step in establishing a stable and productive infection, as well as the mechanism by which host genes are activated in leukemogenesis. Host factors are widely anticipated to be involved in all stages of the retroviral life cycle, and the identification of integrase interacting factors has the potential to increase our understanding of mechanisms by which the incoming virus might appropriate cellular proteins to target and capture host DNA sequences. Identification of MoMLV integrase interacting host factors may be key to designing efficient and benign retroviral-based gene therapy vectors; key to understanding the basic mechanism of integration; and key in designing efficient integrase inhibitors. In this review, we discuss current progress in the field of MoMLV integrase interacting proteins and possible roles for these proteins in integration.

Infection barriers to successful xenotransplantation focusing on porcine endogenous retroviruses

Xenotransplantation may be a solution to overcome the shortage of organs for the treatment of patients with organ failure, but it may be associated with the transmission of porcine microorganisms and the development of xenozoonoses. Whereas most microorganisms may be eliminated by pathogen-free breeding of the donor animals, porcine endogenous retroviruses (PERVs) cannot be eliminated, since these are integrated into the genomes of all pigs. Human-tropic PERV-A and -B are present in all pigs and are able to infect human cells. Infection of ecotropic PERV-C is limited to pig cells. PERVs may adapt to host cells by varying the number of LTR-binding transcription factor binding sites. Like all retroviruses, they may induce tumors and/or immunodeficiencies. To date, all experimental, preclinical, and clinical xenotransplantations using pig cells, tissues, and organs have not shown transmission of PERV. Highly sensitive and specific methods have been developed to analyze the PERV status of donor pigs and to monitor recipients for PERV infection. Strategies have been developed to prevent PERV transmission, including selection of PERV-C-negative, low-producer pigs, generation of an effective vaccine, selection of effective antiretrovirals, and generation of animals transgenic for a PERV-specific short hairpin RNA inhibiting PERV expression by RNA interference.

Phylogeny-directed search for murine leukemia virus-like retroviruses in vertebrate genomes and in patients suffering from myalgic encephalomyelitis/chronic fatigue syndrome and prostate cancer

Gammaretrovirus-like sequences occur in most vertebrate genomes. Murine Leukemia Virus (MLV) like retroviruses (MLLVs) are a subset, which may be pathogenic and spread cross-species. Retroviruses highly similar to MLLVs (xenotropic murine retrovirus related virus (XMRV) and Human Mouse retrovirus-like RetroViruses (HMRVs)) reported from patients suffering from prostate cancer (PC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) raise the possibility that also humans have been infected. Structurally intact, potentially infectious MLLVs occur in the genomes of some mammals, especially mouse. Mouse MLLVs contain three major groups. One, MERV G3, contained MLVs and XMRV/HMRV. Its presence in mouse DNA, and the abundance of xenotropic MLVs in biologicals, is a source of false positivity. Theoretically, XMRV/HMRV could be one of several MLLV transspecies infections. MLLV pathobiology and diversity indicate optimal strategies for investigating XMRV/HMRV in humans and raise ethical concerns. The alternatives that XMRV/HMRV may give a hard-to-detect “stealth” infection, or that XMRV/HMRV never reached humans, have to be considered.

Absence of xenotropic murine leukemia virus-related virus in blood donors in China

BACKGROUND

Xenotropic murine leukemia virus-related virus (XMRV) is a novel human gammaretrovirus that was first identified in patients with prostate cancer in 2006. Subsequent studies have shown that XMRV is also detected in patients with chronic fatigue syndrome (CFS) and even in some healthy controls and blood donors. However, some conflicting findings have been reported by different laboratories or in different regions. The association of XMRV with human diseases and the prevalence of XMRV in different populations needs to be further determined.

STUDY DESIGN AND METHODS

XMRV was screened in 391 blood samples from healthy blood donors in China. Nested reverse transcription-polymerase chain reaction (PCR) was used to amplify gag and env genes of XMRV from total RNA of peripheral blood mononuclear cells (PBMNCs) and plasma, respectively. Quantitative PCR was performed to detect XMRV env gene in genomic DNA of PBMNCs. To enhance the detection sensitivity, plasma was added into LNCaP cells to amplify XMRV in the plasma samples.

RESULTS

No XMRV was found in the 391 blood donors in China or in the LNCaP cells inoculated with plasma from the blood donors.

CONCLUSION

Both PCR and virus isolation in highly permissive LNCaP cells failed to detect XMRV in 391 Chinese blood donors, indicating that XMRV infection might not be present in blood donors in China.

Development of sensitive methods for detection of porcine endogenous retrovirus-C (PERV-C) in the genome of pigs

Porcine endogenous retroviruses (PERV) represent a risk for xenotransplantation using pig cells, tissues or organs. PERV-A and PERV-B are present in the genome of all pigs and both infect human cells in vitro. PERV-C infects only pig cells and it is integrated in the genome of most, but not all pigs. Recombinants between PERV-A and PERV-C were described that infect human cells and replicate at high titres. To avoid such recombinations, PERV-C positive animals should not be used for breeding animals suited for xenotransplantation. In order to detect PERV-C positive pigs, different methods were developed such as specific PCRs using different primers, a highly sensitive nested PCR and a real-time PCR allowing measurement of proviral copy numbers. The real-time PCR was found to be useful to discriminate between contamination and actual provirus copies. The PCRs were optimized and their sensitivity was determined. Screening can be started with PCR1, if the result is negative, PCR2 to PCR5 or the nested PCR should be used, if the result is positive, the real-time PCR should be used to exclude contaminations. All methods were used to evaluate the prevalence of PERV-C and to identify PERV-C free animals. Due to the risk of contamination with cells from other animals testing should be performed with blood cells, not with ear biopsies.

Evidence and controversies on the role of XMRV in prostate cancer and chronic fatigue syndrome

The recent discovery of xenotropic murine leukaemia virus-related virus (XMRV) in prostate cancer tissues and in the blood of individuals suffering from chronic fatigue syndrome has attracted considerable interest. However, the relevance and significance of XMRV to human disease remain unclear, since the association has not been confirmed in other studies. XMRV is the first gammaretrovirus to be found in humans. XMRV and murine leukaemia viruses share similar structures and genomic organisation. Human restriction factors such as APOBEC3 or tetherin inhibit XMRV replication. Although XMRV induces low rates of transformation in cell culture, it might be able to induce cancer by low-frequency insertional activation of oncogenes or through the generation of highly active transforming viruses. A preference for regulatory regions of transcriptional active genes has been observed after a genomic-wide analysis of XMRV integration sites. Genes related to carcinogenesis and androgen signalling have been identified in the vicinity of integration sites. The XMRV genome contains a glucocorticoid responsive element, and androgens could modulate viral replication in the prostate. Evidence supporting the involvement of XMRV in chronic fatigue syndrome is still very weak, and needs further confirmation and validation. Currently approved anti-retroviral drugs such as zidovudine, tenofovir and raltegravir are efficient inhibitors of XMRV replication in vitro. These drugs might be useful to treat XMRV infection in humans. The identification of XMRV has potentially serious health implications for the implementation of novel techniques including gene therapy or xenotransplantation, while raising concerns on the need for screening donated blood to prevent transmission through transfusion.