Infection of female primary lower genital tract epithelial cells after natural pseudotyping of HIV-1: possible implications for sexual transmission of HIV-1

The global AIDS pandemic continues to expand and in some regions of the world, such as southern Africa, the prevalence of HIV-1 infection exceeds 20%. The devastating spread of the virus in young women in these countries appears disproportional to overall risk of infection. Regions with high prevalence of HIV-1 are often also highly endemic for other pathogenic viruses including HSV, CMV and HTLV. We propose that acquisition by HIV-1 of the envelope glycoproteins of other viruses, in a process we call “natural pseudotyping,” expands the cellular tropism of HIV-1, enabling it to infect female genital epithelial cells directly and thereby dramatically increasing risk of infection during sexual intercourse. In this proof-of-concept study, we demonstrate that when HIV-1 co-infects T cells along with the gammaretrovirus xenotropic murine leukemia virus-related virus (XMRV), progeny HIV-1 particles are produced capable of infecting primary vaginal, ectocervical and endocervical epithelial cells. These cell types are normally resistant to HIV-1 infection. Infection of primary genital cells was neutralized by antisera against the XMRV glycoprotein, confirming that infection was mediated by the XMRV glycoprotein acquired through pseudotyping of HIV. Inhibition by AZT showed that active replication of HIV-1 occurred in these cells and ruled out non-specific endocytic uptake of the virus. These results demonstrate that natural pseudotyping can expand the tropism of HIV-1 to include genital epithelial cells and have potential implications for sexual transmission of the virus.

The use of preliminary scientific evidence in public health: a case study of XMRV

Kumanan Wilson and colleagues explain how the rapid response to XMRV as a novel pathogen has highlighted some challenges pertaining to policy-making and editorial responsibilities. The impact on policy and the propagation of the initial scientific information may not cease if the evidence is disproven and retracted from the peer-reviewed literature, which creates a challenge for regulators and scientific journals. Please see later in the article for the Editors' Summary.

Utilization of replication-competent XMRV reporter-viruses reveals severe viral restriction in primary human cells

The gammaretrovirus termed xenotropic murine leukemia virus-related virus (XMRV) was described to be isolated from prostate cancer tissue biopsies and from blood of patients suffering from chronic fatigue syndrome. However, many studies failed to detect XMRV and to verify these disease associations. Data suggesting the contamination of specimens in particular by PCR-based methods and recent reports demonstrating XMRV generation via recombination of two murine leukemia virus precursors raised serious doubts about XMRV being a genuine human pathogen. To elucidate cell tropism of XMRV, we generated replication competent XMRV reporter viruses encoding a green fluorescent protein or a secretable luciferase as tools to analyze virus infection of human cell lines or primary human cells. Transfection of proviral DNAs into LNCaP prostate cancer cells resulted in readily detectably reporter gene expression and production of progeny virus. Inoculation of known XMRV susceptible target cells revealed that these virions were infectious and expressed the reporter gene, allowing for a fast and highly sensitive quantification of XMRV infection. Both reporter viruses were capable of establishing a spreading infection in LNCaP and Raji B cells and could be easily passaged. However, after inoculation of primary human blood cells such as CD4 T cells, macrophages or dendritic cells, infection rates were very low, and a spreading infection was never established. In line with these results we found that supernatants derived from these XMRV infected primary cell types did not contain infectious virus. Thus, although XMRV efficiently replicated in some human cell lines, all tested primary cells were largely refractory to XMRV infection and did not support viral spread. Our results provide further evidence that XMRV is not a human pathogen.

XMRV induces cell migration, cytokine expression and tumor angiogenesis: are 22Rv1 cells a suitable prostate cancer model?

22Rv1 is a common prostate cancer cell line used in xenograft mouse experiments as well as in vitro cell culture assays to study aspects of prostate cancer tumorigenesis. Recently, this cell line was shown to harbor multiple copies of a gammaretrovirus, called XMRV, integrated in its genome. While the original prostate cancer xenograft CWR22 is free of any retrovirus, subsequently generated cell lines 22Rv1 and CWR-R1, carry this virus and additionally shed infectious gammaretroviral particles in their supernatant. Although XMRV most likely was generated by recombination events in cell culture this virus has been demonstrated to infect human cells in vitro and 22Rv1 as well as CWR-R1 cells are now considered biosafety 2 reagents. Here, we demonstrate that 22Rv1 cells with reduced retroviral transcription show reduced tumor angiogenesis and increased necrosis of the primary tumor derived from xenografted cells in scid mice when compared to the parental cell line. The presence of XMRV transcripts significantly increases secretion of osteopontin (OPN), CXCL14, IL13 and TIMP2 in 22Rv1 cells. Furthermore, these data are supported by in vitro cell invasion and differentiation assays. Collectively, our data suggest that the presence of XMRV transcripts at least partially contributes to 22Rv1 characteristics observed in vitro and in vivo with regard to migration, invasion and tumor angiogenesis. We propose that data received with 22Rv1 cells or equivalent cells carrying xenotropic gammaretroviruses should be carefully controlled including other prostate cancer cell lines tested for viral sequences.

Moloney murine leukemia virus glyco-gag facilitates xenotropic murine leukemia virus-related virus replication through human APOBEC3-independent mechanisms

BACKGROUND

One of the unique features of gammaretroviruses is that they contain an additional extended form of Gag, glyco-gag, which initiates in the leader sequence. MuLV glyco-gag, gPr80Gag, promotes retrovirus replication and disease progression. Although virtually all infectious MuLVs encode glyco-gag, XMRV (xenotropic murine leukemia virus-related virus) lacks the classical gPr80Gag sequence. We examined XMRV to determine if its leader sequence contains glyco-gag activity, whether the presence of conventional gPr80Gag affects replication of XMRV, and we describe the evolution of glyco-gag-deficient MuLVs in Mus.

RESULTS

We introduced several mutations disrupting two putative but noncanonical glyco-gag proteins in the leader sequence region in XMRV and found that those mutations did not affect virus release nor susceptibility to the antiviral activity of hA3G (human APOBEC3G). A chimeric XMRV encoding the Moloney MuLV (M-MuLV) leader sequence (MXMRV) demonstrated that M-MuLV glyco-gag facilitated MXMRV release and increased infectivity. Infectivity assays with several cell lines showed that glyco-gag increases XMRV infectivity in all cell lines tested, but the level of this increase varies in different cell lines. Because MuLV glyco-gag counteracts mouse APOBEC3, we investigated whether M-MuLV glyco-gag enhances XMRV infection by counteracting human APOBEC3. Comparison of hAPOBEC3 isoforms expressed in different cell lines indicated that hA3B was the most likely candidate for a restrictive hA3. However over-expression of hA3B showed no enhanced restriction of infection by XMRV compared to MXMRV. Endogenous MuLVs in the sequenced mouse genome were screened for canonical glyco-gag, which was identified in two clades of xenotropic MuLVs (X-MuLVs) and ecotropic MuLVs, but not in other X-MuLVs or in any polytropic MuLVs.

CONCLUSIONS

M-MuLV glyco-gag facilitates XMRV replication, and the leader sequence region in XMRV does not encode proteins equivalent to M-MuLV glyco-gag. The fact that the ability of glyco-gag to enhance XMRV infection varies in different cell lines suggests a glyco-gag sensitive restrictive factor that further reduces XMRV infectivity. The M-MuLV glyco-gag enhancement for XMRV replication is through a hAPOBEC3 independent mechanism. The absence of glyco-gag in MuLVs carried by western European mice suggests that loss of this sequence is a relatively recent event with limited subspecies distribution.

XMRV accelerates cellular proliferation, transformational activity, and invasiveness of prostate cancer cells by downregulating p27(Kip1)

BACKGROUND

Xenotropic murine leukemia virus-related retrovirus (XMRV) is a recently discovered gammaretrovirus that was originally detected in prostate tumors. However, a causal relationship between XMRV and prostate cancer remains controversial due to conflicting reports on its etiologic occurrence. Even though gammaretroviruses are known to induce cancer in animals, a mechanism for XMRV-induced carcinogenesis remains unknown. Several mechanisms including insertional mutagenesis, proinflammatory effects, oncogenic viral proteins, immune suppression, and altered epithelial/stromal interactions have been proposed for a role of XMRV in prostate cancer. However, biochemical data supporting any of these mechanisms are lacking. Therefore, our aim was to evaluate a potential role of XMRV in prostate carcinogenesis.

METHODS

Growth kinetics of prostate cancer cells are conducted by MTT assay. In vitro transformation and invasion was carried out by soft agar colony formation, and Matrigel cell invasion assay, respectively. p27(Kip1) expression was determined by Western blot and MMP activation was evaluated by gelatin-zymography. Up-regulation of miR221 and miR222 expression was examined by real-time PCR.

RESULTS

We demonstrate that XMRV infection can accelerate cellular proliferation, enhance transformation, and increase invasiveness of slow growing prostate cancer cells. The molecular basis of these viral induced activities is mediated by the downregulation of cyclin/cyclin dependent kinase inhibitor p27(Kip1) . Downstream analyses illustrated that XMRV infection upregulates miR221 and miR222 expression that target p27(Kip1) mRNA.

CONCLUSIONS

We propose that downregulation of p27(Kip1) by XMRV infection facilitates transition of G1 to S, thereby accelerates growth of prostate cancer cells. Our findings implicate that if XMRV is present in humans, then under appropriate cellular microenvironment it may serve as a cofactor to promote cancer progression in the prostate.

No detection of XMRV in blood samples and tissue sections from prostate cancer patients in Northern Europe

BACKGROUND

We recently published the rare detection of xenotropic murine leukemia virus-related virus (XMRV) (1/105) in prostate cancer (PCA) tissue of patients in Northern Europe by PCR. The controversial discussion about the virus being detected in PCA tissue, blood samples from patients suffering from chronic fatigue syndrome (CFS), as well as from a significant number of healthy controls prompted us to deepen our studies about detection of XMRV infection applying different detection methods (PCR, cocultivation and immunohistochemistry [IHC]).

METHODOLOGY/PRINCIPAL FINDINGS

Peripheral blood mononuclear cells (PBMCs) from 92 PCA and 7 healthy controls were isolated, PHA activated and cocultivated with LNCaP cells for up to 8 weeks. Supernatant of these cells was applied to a reporter cell line, DERSE-iGFP. Furthermore, the PBMCs and cocultivated LNCaP cells were tested for the presence of XMRV by PCR as well as Western Blot analysis. While all PCR amplifications and Western Blot analyses were negative for signs of XMRV infection, DERSE-iGFP cells displayed isolated GFP positive cells in three cases. In all three cases XMRV presence could not be confirmed by PCR technology. In addition, we performed XMRV specific IHC on PCA tissue sections. Whole tissue sections (n = 20), as well as tissue microarrays (TMA) including 50 benign prostate hyperplasia (BPH), 50 low grade and 50 high grade PCA sections and TMAs including breast cancer, colon cancer and normal tissues were stained with two XMRV specific antisera. XMRV protein expression was not detected in any cancer sections included. One BPH tissue displayed XMRV specific protein expression in random isolated basal cells.

CONCLUSION

We were unable to conclusively detect XMRV in the blood from PCA patients or from healthy controls and there is no conclusive evidence of XMRV protein expression in PCA, breast cancer and colon cancer tissue sections tested by IHC staining.

Xenotropic murine leukaemia virus-related virus (XMRV) does not cause chronic fatigue

The xenotropic murine leukaemia virus-related virus (XMRV), a gammaretrovirus, was discovered in prostate cancer tumours by Virochip technology in 2006. It was subsequently detected in chronic fatigue patients in 2009. The association between XMRV and chronic fatigue has proved to be controversial. No study has confirmed these findings and many have refuted them. Here, we present the evidence for our contention that XMRV is not a human pathogen.

Biology and pathophysiology of the new human retrovirus XMRV and its association with human disease

Xenotropic murine leukemia virus-related virus (XMRV) is a new human retrovirus originally identified in prostate cancer patients with a deficiency in the antiviral enzyme RNase L. XMRV has been detected with varying frequencies in cases of prostate cancer and chronic fatigue syndrome (CFS), as well as in a small proportion of healthy individuals. An etiologic link between XMRV infection and human disease, however, has yet to be established. Here, we summarize existing knowledge regarding the characteristics of XMRV replication, association of XMRV with prostate cancer and CFS, and potential mechanisms of XMRV pathophysiology. We also highlight several areas, such as the establishment of standardized assays and the development of animal models, as future directions to advance our current understanding of XMRV and its relevance to human disease.

Xenotropic murine leukemia virus-related virus-associated chronic fatigue syndrome reveals a distinct inflammatory signature

BACKGROUND

The recent identification of xenotropic murine leukemia virus-related virus (XMRV) in the blood of patients with chronic fatigue syndrome (CFS) establishes that a retrovirus may play a role in the pathology in this disease. Knowledge of the immune response might lead to a better understanding of the role XMRV plays in this syndrome. Our objective was to investigate the cytokine and chemokine response in XMRV-associated CFS.

MATERIALS AND METHODS

Using Luminex multi-analyte profiling technology, we measured cytokine and chemokine values in the plasma of XMRV-infected CFS patients and compared these data to those of healthy controls. Analysis was performed using the Gene Expression Pattern Analysis Suite and the Random Forest tree classification algorithm.

RESULTS

This study identifies a signature of 10 cytokines and chemokines which correctly identifies XMRV/CFS patients with 93% specificity and 96% sensitivity.

CONCLUSION

These data show, for the first time, an immunological pattern associated with XMRV/CFS.

XMRV as a human pathogen?

Xenotropic murine leukemia virus-related virus (XMRV) has been proposed to be associated with prostate cancer and chronic fatigue syndrome (CFS). This proposition has been controversial because many investigators have failed to replicate the reported associations. Here, we explore whether XMRV is an authentic human pathogen in the light of recent findings that indicate otherwise.

Investigation into the presence of and serological response to XMRV in CFS patients

The novel human gammaretrovirus xenotropic murine leukemia virus-related virus (XMRV), originally described in prostate cancer, has also been implicated in chronic fatigue syndrome (CFS). When later reports failed to confirm the link to CFS, they were often criticised for not using the conditions described in the original study. Here, we revisit our patient cohort to investigate the XMRV status in those patients by means of the original PCR protocol which linked the virus to CFS. In addition, sera from our CFS patients were assayed for the presence of xenotropic virus envelope protein, as well as a serological response to it. The results further strengthen our contention that there is no evidence for an association of XMRV with CFS, at least in the UK.

Lack of infection with XMRV or other MLV-related viruses in blood, post-mortem brains and paternal gametes of autistic individuals

Background

Autistic spectrum disorder (ASD) is characterized by impaired language, communication and social skills, as well as by repetitive and stereotypic patterns of behavior. Many autistic subjects display a dysregulation of the immune system which is compatible with an unresolved viral infection with prenatal onset, potentially due to vertical viral transmission. Recently, the xenotropic murine leukemia virus-related virus (XMRV) has been implicated in chronic fatigue syndrome (CFS) and in prostate cancer by several, though not all studies.

Methodology/Principal Findings

We assessed whether XMRV or other murine leukemia virus (MLV)-related viruses are involved in autistic disorder. Using nested PCR targeted to gag genomic sequences, we screened DNA samples from: (i) peripheral blood of 102 ASD patients and 97 controls, (ii) post-mortem brain samples of 20 ASD patients and 17 sex- and age-matched controls, (iii) semen samples of 11 fathers of ASD children, 25 infertile individuals and 7 fertile controls. No XMRV gag DNA sequences were detected, whereas peripheral blood samples of 3/97 (3.1%) controls were positive for MLV.

Conclusions|Significance

No MLV-related virus was detected in blood, brain, and semen samples of ASD patients or fathers. Hence infection with XMRV or other MLV-related viruses is unlikely to contribute to autism pathogenesis.

Human APOBEC3 proteins can inhibit xenotropic murine leukemia virus-related virus infectivity

Xenotropic murine leukemia virus-related virus (XMRV) is a novel retrovirus, related to murine leukemia virus (MLV), that has been implicated in human disease. If XMRV is indeed able to replicate in humans, then one might predict that XMRV would have developed resistance to human innate antiviral resistance factors such as APOBEC3G (hA3G). In fact, we observed that XMRV and MLV are both highly sensitive to inhibition by hA3G and equally resistant to inhibition by murine APOBEC3. While several human prostate cancer cell lines were found to lack hA3G, stable expression of physiological levels of hA3G rendered these cells refractory to XMRV replication. Few human tissues fail to express hA3G, and we therefore hypothesize that XMRV replicates in one or more hA3G-negative reservoir tissues and/or that human XMRV infections are likely to be rare and potentially of zoonotic origin.