Jeremy A. Garson

The MIQE Guidelines: Minimum Information for Publication of Quantitative Real-Time PCR Experiments

BACKGROUND Currently, a lack of consensus exists on how best to perform and interpret quantitative real-time PCR (qPCR) experiments. The problem is exacerbated by a lack of sufficient experimental detail in many publications, which impedes a readers ability to evaluate critically the quality of the results presented or to repeat the experiments. CONTENT The Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines target the reliability of results to help ensure the integrity of the scientific literature, promote consistency between laboratories, and increase experimental transparency. MIQE is a set of guidelines that describe the minimum information necessary for evaluating qPCR experiments. Included is a checklist to accompany the initial submission of a manuscript to the publisher. By providing all relevant experimental conditions and assay characteristics, reviewers can assess the validity of the protocols used. Full disclosure of all reagents, sequences, and analysis methods is necessary to enable other investigators to reproduce results. MIQE details should be published either in abbreviated form or as an online supplement. SUMMARY Following these guidelines will encourage better experimental practice, allowing more reliable and unequivocal interpretation of qPCR results.

The Digital MIQE Guidelines: Minimum Information for Publication of Quantitative Digital PCR Experiments

There is growing interest in digital PCR (dPCR) because technological progress makes it a practical and increasingly affordable technology. dPCR allows the precise quantification of nucleic acids, facilitating the measurement of small percentage differences and quantification of rare variants. dPCR may also be more reproducible and less susceptible to inhibition than quantitative real-time PCR (qPCR). Consequently, dPCR has the potential to have a substantial impact on research as well as diagnostic applications. However, as with qPCR, the ability to perform robust meaningful experiments requires careful design and adequate controls. To assist independent evaluation of experimental data, comprehensive disclosure of all relevant experimental details is required. To facilitate this process we present the Minimum Information for Publication of Quantitative Digital PCR Experiments guidelines. This report addresses known requirements for dPCR that have already been identified during this early stage of its development and commercial implementation. Adoption of these guidelines by the scientific community will help to standardize experimental protocols, maximize efficient utilization of resources, and enhance the impact of this promising new technology.

A pilot study of combination therapy with ribavirin plus interferon alfa for interferon alfa-resistant chronic hepatitis C

BACKGROUND/AIMS In chronic hepatitis C, interferon alfa (IFN-alpha) therapy fails to achieve a sustained response in approximately 75% of patients. Similarly, ribavirin induces only a transient response. The aim of this study was to evaluate whether ribavirin and IFN-alpha in combination could be effective in IFN-alpha-resistant chronic hepatitis C. METHODS Twenty patients with chronic hepatitis C resistant to a previous course of IFN-alpha were randomly assigned to receive either ribavirin combined with IFN-alpha or IFN-alpha alone for 6 months. RESULTS Serum alanine aminotransferase levels decreased significantly during therapy in both treatment groups, but after therapy, the levels remained significantly decreased only in the combination therapy group. Nine months after treatment, sustained normalization of aminotransferase levels, associated with sustained loss of serum hepatitis C virus RNA, was observed in 40% of the patients in the combination therapy group but in none of the patients treated with IFN-alpha alone (P < 0.05). The sustained response was accompanied by reduced hepatic necroinflammatory activity on biopsy. CONCLUSIONS These findings suggest that ribavirin plus IFN-alpha combination therapy is able to induce a sustained biochemical and virological response in a significant proportion of patients with IFN-alpha-resistant chronic hepatitis C.

Disease-associated XMRV sequences are consistent with laboratory contamination

BackgroundXenotropic murine leukaemia viruses (MLV-X) are endogenous gammaretroviruses that infect cells from many species, including humans. Xenotropic murine leukaemia virus-related virus (XMRV) is a retrovirus that has been the subject of intense debate since its detection in samples from humans with prostate cancer (PC) and chronic fatigue syndrome (CFS). Controversy has arisen from the failure of some studies to detect XMRV in PC or CFS patients and from inconsistent detection of XMRV in healthy controls.ResultsHere we demonstrate that Taqman PCR primers previously described as XMRV-specific can amplify common murine endogenous viral sequences from mouse suggesting that mouse DNA can contaminate patient samples and confound specific XMRV detection. To consider the provenance of XMRV we sequenced XMRV from the cell line 22Rv1, which is infected with an MLV-X that is indistinguishable from patient derived XMRV. Bayesian phylogenies clearly show that XMRV sequences reportedly derived from unlinked patients form a monophyletic clade with interspersed 22Rv1 clones (posterior probability >0.99). The cell line-derived sequences are ancestral to the patient-derived sequences (posterior probability >0.99). Furthermore, pol sequences apparently amplified from PC patient material (VP29 and VP184) are recombinants of XMRV and Moloney MLV (MoMLV) a virus with an envelope that lacks tropism for human cells. Considering the diversity of XMRV we show that the mean pairwise genetic distance among env and pol 22Rv1-derived sequences exceeds that of patient-associated sequences (Wilcoxon rank sum test: p = 0.005 and p < 0.001 for pol and env, respectively). Thus XMRV sequences acquire diversity in a cell line but not in patient samples. These observations are difficult to reconcile with the hypothesis that published XMRV sequences are related by a process of infectious transmission.ConclusionsWe provide several independent lines of evidence that XMRV detected by sensitive PCR methods in patient samples is the likely result of PCR contamination with mouse DNA and that the described clones of XMRV arose from the tumour cell line 22Rv1, which was probably infected with XMRV during xenografting in mice. We propose that XMRV might not be a genuine human pathogen.

The need for transparency and good practices in the qPCR literature

Two surveys of over 1,700 publications whose authors use quantitative real-time PCR (qPCR) reveal a lack of transparent and comprehensive reporting of essential technical information. Reporting standards are significantly improved in publications that cite the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines, although such publications are still vastly outnumbered by those that do not.

Differential susceptibility of PCR reactions to inhibitors: an important and unrecognised phenomenon

BackgroundPCR inhibition by nucleic acid extracts is a well known yet poorly described phenomenon. Inhibition assessment generally depends on the assumption that inhibitors affect all PCR reactions to the same extent; i.e. that the reaction of interest and the control reaction are equally susceptible to inhibition. To test this assumption we performed inhibition assessment on DNA extracts from human urine samples, fresh urine and EDTA using different PCR reactions.ResultsWhen copurified inhibitors were assessed using two different PCR reactions one reaction appeared to be inhibited whilst the other was not. Further experiments using various concentrations of unextracted urine to inhibit six different PCR reactions revealed that susceptibility to inhibition was highly variable between reactions. Similar results were obtained using EDTA as the PCR inhibitor. We could find no obvious explanation why one reaction should be more susceptible to inhibition than another, although a possible association with amplicon GC content was noted.ConclusionThese findings have serious implications for all PCR-based gene expression studies, including the relatively new PCR array method, and for both qualitative and quantitative PCR-based molecular diagnostic assays, suggesting that careful consideration should be given to inhibition compatibility when conducting PCR analyses. We have demonstrated unequivocally that it is not safe to assume that different PCR reactions are equally susceptible to inhibition by substances co-purified in nucleic acid extracts.

Diagnosis of Neuroinvasive Astrovirus Infection in an Immunocompromised Adult With Encephalitis by Unbiased Next-Generation Sequencing

Metagenomic next-generation sequencing (NGS) was used to diagnose an unusual and fatal case of progressive encephalitis in an immunocompromised adult presenting at disease onset as bilateral hearing loss. The sequencing and confirmatory studies revealed neuroinvasive infection of the brain by an astrovirus belonging to a recently discovered VA/HMO clade.

Combination therapy with interferon alpha and ribavirin for chronic hepatitis C virus infection in thalassaemic patients.

Hepatitis C virus (HCV) infection is common in multi‐transfused thalassaemic patients, and, in combination with transfusional iron overload, can result in progressive liver disease. Therapy with interferon‐alpha causes a sustained loss of HCV in only 15–25% of patients, and there is as yet no established effective therapy for those who fail to respond. We have conducted a pilot study of combination anti‐viral therapy for patients who failed to respond, or relapsed after an initial response to single‐agent interferon‐alpha. Patients were treated for 6 months with interferon‐alpha 2b, given subcutaneously three mega units thrice weekly, together with ribavirin, orally 1 g daily. 11 patients were enrolled, their median age was 24.9 years. 8/10 evaluable patients had cirrhosis on biopsy, five were infected with HCV type 1 and all but one had initial HCV RNA titres > 106 genomes/ml. Five patients (45.5%) had a sustained virological response with loss of serum HCV RNA for > 6 months after finishing therapy. There was no clear association between response to therapy and age, histology, HCV genotype, or HCV RNA titre. Transfusion requirements were significantly increased during the treatment phase, probably due to ribavirin‐induced haemolysis, and this necessitated intensification of iron chelation therapy. Serum ferritin levels decreased significantly in those who responded. These results suggest that combination therapy is potent in clearing HCV infection, and may provide effective second‐line therapy for thalassaemic patients who have failed to respond to interferon‐alpha monotherapy.

Detection of SARS Coronavirus in Plasma by Real-Time RT-PCR

To the Editor: The identification and sequencing of a novel coronavirus1 associated with the recently described severe acute respiratory syndrome (SARS)2 have permitted the development of antibody-...

Comparative Study of Sensitivity, Linearity, and Resistance to Inhibition of Digital and Nondigital Polymerase Chain Reaction and Loop Mediated Isothermal Amplification Assays for Quantification of Human Cytomegalovirus

Performing nucleic acid amplification techniques (NAATs) in digital format using limiting dilution provides potential advantages that have recently been demonstrated with digital polymerase chain reaction (dPCR). Key benefits that have been claimed are the ability to quantify nucleic acids without the need of an external calibrator and a greater resistance to inhibitors than real-time quantitative PCR (qPCR). In this study, we evaluated the performance of four NAATs, qPCR, dPCR, real-time quantitative loop mediated isothermal amplification (qLAMP), and digital LAMP (dLAMP), for the detection and quantification of human cytomegalovirus (hCMV). We used various DNA templates and inhibitors to compare the performance of these methods using a conventional real-time thermocycler platform (Bio-Rad CFX96) and a chip based digital platform (Fluidigm Biomark 12.765 Digital Array). dPCR performed well and demonstrated greater resistance to inhibitors than the other methods although this resistance did not apply equally to all inhibitors tested. dLAMP was found to be less sensitive than dPCR, but its quantitative performance was better than qLAMP, the latter being unable to quantify below 1000 copies. dLAMP was also more resistant to inhibitors than qLAMP. Unlike qPCR, both digital methods were able to quantify viral genomes without requiring a calibrator; however, neither can currently compete with the large reaction volumes, and thus the greater absolute sensitivity, of qPCR. With the introduction of digital instrumentation that will enable larger reaction volumes, digital amplification methods such as those evaluated in this study could potentially offer a robust alternative to qPCR for nucleic acid quantification.