TWiV 164: Six steps forward, four steps back

xmrvHosts: Vincent RacanielloRich Condit, and Alan Dove

Vincent, Alan, and Rich review ten compelling virology stories of 2011.

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Ten virology stories of 2011:

  1. XMRV, CFS, and prostate cancer (TWiV 119, 123, 136, 150)
  2. Influenza H5N1, ferrets, and the NSABB (TWiV 159)
  3. The Panic Virus (TWiV 117)
  4. Polio eradication (TWiV 127, 149)
  5. Viral oncotherapy (TWiV 124, 131, 142, 156)
  6. Hepatitis C virus (TWiV 130, 137, 141)
  7. Zinc finger nuclease and HIV therapy (TWiV 144)
  8. Bacteria help viruses (TWiV 154)
  9. Human papillomaviruses (TWiV 126)
  10. Combating dengue with Wolbachia (TWiV 115, 147)

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Brain Picking’s 11 best science books of 2011

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Authors retract paper on detection of murine leukemia virus-releated sequences in CFS patients

x or pA paper that reported finding retroviral sequences in blood from patients with chronic fatigue syndrome (CFS) has been retracted by the authors. Just four days ago the 2009 Science report of Lombardi and colleagues was editorially retracted. As 2011 comes to an end, so does the hypothesis that retroviruses are etiologic agents of CFS.

Readers of virology blog know that in 2009 Lombardi et al. published a Science report indicating they had detected the new retrovirus XMRV – first detected a few years earlier in prostate tumors – in the blood of a high proportion of patients with chronic fatigue syndrome. Many other laboratories attempted to reproduce this finding, but none were successful.

The next year Alter and colleagues reported finding retroviral sequences in the blood of a substantial number of CFS patients. No viruses were isolated in the Alter study; viral sequences were obtained by polymerase chain reaction (PCR). The viral sequences were not XMRV, but were closely related to endogenous retroviruses of mice called polytropic murine leukemia viruses. (Polytropic means the viruses can infect many species, including mice; xenotropic means that the viruses, though originating in mice, only infect non-mouse species).

The Lo-Alter finding was viewed by many (including myself) as supporting the findings of Lombardi et al., but upon closer inspection it became apparent that they only clouded the situation. The viral sequences reported in the Alter study were not XMRV, and it was not clear why CFS would be caused by such a diverse range of viruses. A second report in 2011 reported MLV-like sequences in a CFS cohort but many other studies failed to find any kind of retrovirus in the blood of CFS patients.

Earlier this year it became clear that XMRV is a laboratory-generated recombinant murine retrovirus: it arose during the passage of a prostate tumor in nude mice in the early 1990s. This finding made it highly unlikely that the virus could be associated with human disease. Lombardi and colleagues then retracted part of the 2009 Science paper that reported viral nucleic acid sequence; they noted that their samples were contaminated with XMRV plasmids. What remained of the paper were serological and virus culture experiments that were not specific for XMRV. Last week the remainder of this paper was editorially retracted by Science.

That left the Lo-Alter findings. The first warning came from the observation made by several laboratories that reagents used to carry out PCR are often contaminated with mouse DNA (an example is Singh’s study). The presence of this adventitious DNA can lead to detection of MLV-like sequences that resemble those found in the Lo-Alter study. The implication was clear: the Lo-Alter findings were wrong, a result of contamination of PCR reagents with mouse DNA.

More doubt came from a report of the Blood XMRV Scientific Working Group, which was assembled to determine if XMRV constituted a threat to the blood supply. In this study, sets of coded samples previously shown to be XMRV positive, as well as samples from healthy controls, were blinded and provided to 9 laboratories for analysis by PCR, virus culture, and serology. Two laboratories reported evidence of XMRV in the coded samples. Only the Whittemore-Peterson Institute identified positive specimens by PCR: two from negative controls, and one from a CFS patient. The Lo laboratory did not detect any positives by PCR, using the same nested assay that they had previously reported in their PNAS paper. The samples tested included 5 specimens that were positive in the Lo-Alter study.

The retraction of the Lo-Alter PNAS paper curiously begins with the assertion that the authors could not detect contaminating mouse DNA in their samples – which was most certainly present and lead to their detection of MLV-like sequences.

Although our published findings were reproducible in our laboratory and while there has been no evidence of contamination using sensitive mouse mitochondrial DNA or IAP assays or in testing coded panels…

This failure remains puzzling and unexplained; but as they report in the next paragraph, they appear to have run out of material to distribute to other laboratories for ‘independent confirmation’.

The authors provide three additional reasons why they are retracting this paper. They note that no one has been able to reproduce their findings, including the Blood XMRV Scientific Working Group. They have not been able to find (along with collaborators) anti-XMRV antibody, XMRV virions, or viral integration sites in patient samples. Finally, they mention their finding from the PNAS paper that a second set of samples taken 15 years later from the same CFS patients also were positive for MLV-like viruses. Phylogenetic analyses revealed that these sequences were clearly not descendants of the original strains. The sequence data used to make this conclusion were available for the PNAS publication, so it is not clear why this evolutionary incompatibility was not noted previously.

The authors conclude:

…in consideration of the aggregate data from our own laboratory and that of others, it is our current view that the association of murine gamma retroviruses with CFS has not withstood the test of time or of independent verification and that this association is now tenuous. Therefore, we retract the conclusions in our article.

The retraction of the Lombardi et al and Lo-Alter papers erases the published evidence suggesting involvement of a retrovirus with CFS. While it is theoretically possible that CFS has a viral origin, at the moment there are no data in support of a specific viral etiology. Some have suggested that gammaretroviruses related to XMRV might be involved in CFS. But I don’t see how a lab contaminant can point you in the direction of a bona fide etiologic agent. Contaminants cloud our vision, they do not improve it.

In light of these developments, the ongoing Lipkin study (sponsored by the National Institute of Allergy and Infectious Diseases, involving analysis of a coded panel of samples from 150 well-characterized and geographically diverse CFS patients and controls) seems less compelling. Many laboratories have failed to find any retrovirus in CFS patients, and the two papers central to this hypothesis have been retracted. Will results from one laboratory clear the matter up further? Whatever the Lipkin study finds, it will have to be validated by others – because we trust science, not scientists.

Update: The retraction has been published at PNAS.

Science retracts paper on detection of XMRV in CFS patients

Bruce Alberts, Editor-in-Chief of Science magazine, writes that the journal is retracting the 2009 paper describing the detection of the retrovirus XMRV in patients with chronic fatigue syndrome:

Science is fully retracting the Report “Detection of an infectious retrovirus, XMRV, in blood cells of patients with chronic fatigue syndrome”.

He writes that the decision was reached because multiple laboratories have failed to reliably detect XMRV or related viruses in CFS patients. He also cites evidence of ‘poor quality control in a number of specific experiments in the report’, and that Figure 1, table S1, and figure S2 have been retracted by the authors. Finally, he notes the omission of information from the legend of figure 2C, specifically that the authors failed to indicate that the peripheral blood mononuclear cells had been treated with azacytidine, phytohemagglutinin, and IL-2. He concludes:

Given all of these issues, Science has lost confidence in the Report and the validity of its conclusions. We note that the majority of the authors have agreed in principle to retract the Report but they have been unable to agree on the wording of their statement. It is Science’s opinion that a retraction signed by all the authors is unlikely to be forthcoming. We are therefore editorially retracting the Report. We regret the time and resources that the scientific community has devoted to unsuccessful attempts to replicate these results.

TWiV 158: Wolverines go viral

poliovirus + CD155Hosts: Vincent RacanielloRich Condit, Alice Telesnitsky, and Kathy Spindler

Vincent and Rich visit the Microbiology and Immunology Department at the University of Michigan Medical School, and speak with Alice and Kathy about their work on HIV genome dimerization, and packaging and pathogenesis of mouse adenovirus.

Model of poliovirus bound to CD155 made by Stefan Taube.

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TWiV 157: Better innate than never

dendritic cellHosts: Vincent RacanielloRich Condit, Alan Dove, Dickson Despommier, Jeremy Luban, and Gabriel Victora

A large TWiV panel remembers Ralph Steinman, and considers a new innate sensor of retroviral capsids.

Photograph of a dendritic cell (green) interacting with T cells (cyan) near a blood vessel by Gabriel Victora.

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Dickson – Eats, Shoots & Leaves by Lynne Truss
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DavidCarl Sagan’s Pale Blue Dot (YouTube)

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TWiV 154: Symbiotic safecrackers

mmtvHosts: Vincent Racaniello, Alan Dove, and Rich Condit

Vincent, Alan, and Rich are very enthusiastic about two studies that show how gut bacteria help viral invaders.

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Trust science, not scientists

XMRVWhether or not the retrovirus XMRV is a human pathogen has been debated since the virus was first described in 2006. The answer is now clear: the results of Blood XMRV Scientific Research Group, along with a partial retraction of the 2009 Science paper describing identification of the retrovirus in patients with chronic fatigue syndrome (CFS) show that detection of XMRV in patient samples is a result of contamination.

The Blood XMRV group obtained new blood samples from 15 individuals previously shown to be positive for XMRV (Lombardi et al., 2009) or MLV (Lo et al., 2010) ; 14 of these were from CFS patients. Fifteen blood samples were also obtained from healthy donors. The samples were coded and sent to 9 laboratories for analysis. These laboratories (Abbott Molecular, Abbott Diagnostics, CDC, FDA/Lo, FDA/Hewlett, Gen-Probe, NCI/DRP, and WPI) conducted validated assays for viral nucleic acid, viral replication, or viral antibodies. Positive control samples were also included that were ‘spiked’ with XMRV, in the form of cell culture fluids from the cell line 22Rv1. Each laboratory was at liberty to choose which assays to carry out.

Two laboratories reported evidence of XMRV in the coded samples.  Only WPI identified positive specimens by PCR: two from negative controls, and one from a CFS patient. The FDA/Lo laboratory did not detect any positives by PCR, using the same nested assay that they had previously reported in their published study. The samples tested included 5 specimens that were positive in the Lo et al. study.

Lombardi and colleagues have previously concluded that viral culture is the most sensitive method for detecting XMRV; however the FDA/Hewlett laboratory failed to culture virus from CFS samples. This laboratory did culture virus from positive control specimens, demonstrating the sensitivity of their methods. The FDA/Ruscetti laboratory recovered virus from 3/15 CFS samples but also from 6/15 negative control specimens. WPI did not carry out viral culture assays due to contamination of their cell lines with mycoplasma.

Four laboratories tested the samples for the presence of antibodies that react with XMRV proteins. Only WPI and NCI/Ruscetti detected reactive antibodies, both in CFS specimens and negative controls. There was no statistically significant difference in the rates of positivity between the positive and negative controls, nor in the identity of the positive samples between the two laboratories.

These results demonstrate that XMRV or antibodies to the virus are not present in clinical specimens. Detection of XMRV nucleic acid by WPI is likely a consequence of contamination. The positive serology reported by WPI and NCI/Ruscetti laboratories remained unexplained, but are most likely the result of the presence of cross-reactive epitopes. The authors of the study conclude that ‘routine blood screening for XMRV/P-MLV is not warranted at this time’.

One of the authors on Lombardi et al., Robert Silverman, decided to reexamine some of the DNA preparations from CFS patients that were originally used to detect XMRV DNA by PCR. He found that all the positive specimens from CFS patients were contaminated with XMRV plasmid DNA. Therefore the authors of the original study have retracted Figure 1 (single-round PCR detection of XMRV in CFS PBMC DNA); table S1, XMRV sequences, and figure S2, phylogenetic analysis of XMRV sequences.

A puzzling aspect of Silverman’s results is that XMRV plasmid DNA was detected only in samples from CFS patients, not healthy controls. This pattern would not be expected if the specimens were properly blinded, that is, coded so that the investigators did not know which were controls and which were from CFS patients. The authors offer no explanation of these findings.

The paper reporting contamination of samples with XMRV is entitled ‘Partial Retraction‘. It’s not clear to me why the entire paper has not been retracted. After removing the PCR and nucleic acid sequencing results, there is no evidence indicating the presence of XMRV in the patient samples. The remaining experiments show detection of a retrovirus by cell culture experiments, and the presence of viral proteins or antibodies to the virus in clinical specimens. None of these findings prove that what is being studied is XMRV. The title of the original paper ‘Detection of an infectious retrovirus’, XMRV, in blood cells of patients with chronic fatigue syndrome‘, is unsupported.

In an accompanying article on the XMRV story entitled ‘False Positive‘, Judy Mikovits of WPI notes that “Anyone who says this is a lab contaminant has drawn the wrong conclusion and has done a disservice to the public”. She goes on to imply that a gammaretrovirus is likely involved in CFS. On the contrary, pursuing the CFS-gammaretrovirus hypothesis is a disservice to those with CFS, and detracts from efforts to solve the disease. There are no data to support such an association, and to suggest that a lab contaminant, XMRV, has pointed the way to a bona fide etiologic agent seems implausible.

XMRV does not cause CFS. The virus arose in mice between 1993-96, and its detection in patient samples is clearly a result of contamination. Reaching these conclusions has required a long and often contentious journey that has highlighted the best and worst aspects of scientific research. There are many lessons to be learned from XMRV, but an important one is that science progresses not from the work of a single investigator, but from the collective efforts of many laboratories. XMRV reminds us to trust science, not scientists.

TWiV 143: Live at ASV in Minneapolis

asv minneapolisHosts: Vincent Racaniello, Rich Condit, Julie Overbaugh, and Stacey Schultz-Cherry

Vincent, Rich, Julie and Stacey recorded TWiV at the 30th Annual Meeting of the American Society for Virology in Minneapolis, where they discussed the role of neutralizing antibodies in protection against HIV-1 infection, and astroviruses, agents of gastroenteritis.

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TWiV 136: Exit XMRV

nude mouseHosts: Vincent Racaniello, Alan Dove, Rich Condit, and Stephen Goff

Retrovirologist Stephen Goff joins Vincent, Rich, and Alan for a discussion of recent papers on the retrovirus XMRV and its association with chronic fatigue syndrome and prostate cancer.

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XMRV is a recombinant virus from mice

recombinant xmrvThe novel human retrovirus XMRV has been associated with prostate cancer and chronic fatigue syndrome. The nucleotide sequence of XMRV isolated from humans indicates that the virus is nearly identical with XMRV produced from a human prostate tumor cell line called 22Rv1. This cell line was derived by passage of human prostate tumor tissue in nude mice. Sequence analyses reveal that the genomes of these mouse strains contain two different proviral DNAs related to XMRV. These viral genomes recombined to produce XMRV that has been isolated from humans.

XMRV was originally isolated from a human prostate cancer in 2006, and subsequently associated with ME/CFS. The human cell line 22Rv1, which was established from a human prostate tumor (CWR22), produces infectious XMRV. An important question is whether XMRV was present in the original prostate tumor, or was obtained by passage through nude mice. To answer this question, DNA from various passages of the prostate tumor in nude mice (called xenografts), and the mouse strains used to passage the tumor, were analyzed for the presence of XMRV proviral DNA.

Early-passage xenografts did not contain XMRV, but mouse cells found in them did contain two related proviruses called PreXMRV-1 and PreXMRV-2. The 3’-3211 nucleotides of PreXMRV-1, and both LTRs, are identical to XMRV save for two nucleotide differences. The genomic 5’-half of XMRV and PreXMRV-1 differs by 9-10%. PreXMRV-1 is defective for replication due to mutations in genes encoding the gag and pol proteins. PreXMRV-2 does not contain obvious mutations that would prevent the production of infectious viruses. The gag-pro-pol and a part of the env region of this viral genome is identical to that of XMRV save for two base differences; the LTRs and the remainder of the genome differ by 6-12% from XMRV.

Comparison of the sequences of PreXMRV-1 and PreXMRV-2 indicates that recombination between the two viral genomes led to the formation of XMRV. When the sequences of PreXMRV-1 and −2 are used to construct the recombinant XMRV, the resulting virus differs by only 4 nucleotides from the consensus XMRV sequence derived from all human isolates reported to date.

The nude mice used for passage of the original prostate tumor were likely the NU/NU and Hsd strains. Neither mouse strain contains XMRV proviral DNA, but both contain PreXMRV-1 and PreXMRV-2 proviral DNA.

These data demonstrate that XMRV was not present in the original CWR22 prostate tumor, but arose by recombination of PreXMRV-1 and PreXMRV-2 between 1993-1996. When the original prostate tumor was implanted into nude mice, some of the mice harbored both pre-XMRV-1 and −2 endogenous proviruses, which recombined to form XMRV. The authors believe that XMRV originating from the CRWR22 xenografts, the22Rv1 cell line, or other related cell lines has contaminated all human samples positive for the virus. In addition, they suggest that PCR assays for XMRV may actually detect PreXMRV-1 and −2 or other endogenous viral DNA from contaminating mouse DNA.

Another possibility to explain the origin of XMRV is that it arose in mice and can infect humans. If this is true, then XMRV would have to be present in the nude mice used to passage the CWR22 human prostate tumor. No evidence for an XMRV provirus was found in 12 different nude mouse strains, including two used to passage the CWR22 tumor. Furthermore, a screen of 89 inbred and wild mice failed to reveal the presence of proviral XMRV DNA. Hence the authors conclude:

…that XMRV arose from a recombination event between two endogenous MLVs that took place around 1993-1996 in a nude mouse carrying the CWR22 PC xenograft, and that all of the XMRV isolates reported to date are descended from this one event.

It is possible that XMRV produced during passage of CWR22 in nude mice subsequently infected humans. Because XMRV arose between 1993-1996, this scenario could not explain cases of prostate cancer and chronic fatigue syndrome that arose prior to that date.

How can these findings be reconciled with the published evidence that sera of ME/CFS patients from the 1980s contain antibodies to XMRV? Those antibodies were not shown to be directed specifically against XMRV, and therefore cannot be used to prove that XMRV circulated in humans prior to 1993-96. Furthermore, in the absence of clear isolation of an infectious virus, antibody tests alone have proven highly unreliable for identification of new viruses.

Where do these findings leave the hypothesis that XMRV is the etiologic agent of prostate cancer and ME/CFS? All published sequences of human XMRV isolates are clearly derived by recombination of PreXMRV-1 and −2. The finding of human XMRV isolates that are not derived from PreXMRV-1 and −2 would leave a role for XMRV in human disease. As of this writing, no such XMRV isolates have been reported in the scientific literature.

Update: A second paper has also been published in Science Express today entitled “No evidence of murine-like gammaretroviruses in CFS patients previously identified as XMRV-infected”. Editors of the journal Science have asked the authors to retract their 2009 paper linking XMRV infection with chronic fatigue syndrome. The authors have refused.

T. Paprotka, K. A. Delviks-Frankenberry, O. Cingoz, A. Martinez, H.-J. Kung, C.G. Tepper, W-S Hu, M. J. Fivash, J.M. Coffin, & V.K. Pathak (2011). Recombinant origin of the retrovirus XMRV. Science Express