Minority Drug-resistant Variants Research Articles

Genomic markers of drug resistance in Mycobacterium tuberculosis populations with minority variants.

Minority variants of Mycobacterium tuberculosis harboring mutations conferring resistance can become dominant populations during tuberculosis (TB) treatment, leading to treatment failure. Our understanding of drug-resistant within-host subpopulations and the frequency of resistance-conferring mutations in minority variants remains limited. M. tuberculosis sequences recovered from liquid cultures of culture-confirmed TB cases notified between January 2017 and December 2021 in New South Wales, Australia were examined. Potential drug resistance-conferring minority variants were identified using LoFreq, and mixed populations of different M. tuberculosis strains (≥100 SNPs apart) were examined using QuantTB. A total of 1831 routinely sequenced M. tuberculosis strains were included in the analysis. Drug resistance-conferring minority variants were detected in 3.5% (65/1831) of sequenced cultures; 84.6% (55/65) had majority strains that were drug susceptible and 15.4% (10/65) had majority strains that were drug resistant. Minority variants with high-confidence drug resistance-conferring mutations were 1.5 times more common when the majority strains were drug resistant. Mixed M. tuberculosis strain populations were documented in 10.0% (183/1831) of specimens. Minority variants with high-confidence drug resistance-conferring mutations were more frequently detected in mixed M. tuberculosis strain populations (2.7%, 5/183) than in single strain populations (0.6%, 10/1648; P = 0.01). Drug-resistant minority variants require monitoring in settings that implement routine M. tuberculosis sequencing. The frequency with which drug-resistant minority variants are detected is likely influenced by pre-culture requirement. Culture-independent sequencing methods should provide a more accurate reflection of drug-resistant subpopulations.

Evaluation of minor drug-resistant viral variants in patients experiencing virological failure (VF) on a first-line regimen in Fujian Province by high-throughput sequencing

It is largely unknown how frequently minor HIV drug-resistant variants at levels under limit of detection of conventional genotyping are present in patients experiencing virological failure (VF). Further, the clinical implications of minor drug-resistant variants at time of virologic failure are unknown. Fifteen patients experiencing VF on a first-line regimen were evaluated by high-throughput sequencing and compared with the conventional Sanger genotype drug resistance detection method. NRTI drug resistant mutations (DRMs) were detected in a high proportion of subjects, with the most common being M184V and TAMs. Minor resistant mutations accounted for 19.27% of the total drug-resistant mutations in patients with VF. A mean of 1.7 additional mutations per subject were detected by high-throughput sequencing, the difference was statistically significant, and those additional low-abundance drug-resistant mutations increased the genotypic resistance scores in 10 of 11 subjects (90.9%). Among persons experiencing VF, minor variants possessing major PI (protease inhibitor) DRMs were present in a minority of cases, which was also the case in ARV-naive subjects, and suggests PIs may be effective in subjects experiencing VF on subsequent second-line PI-based antiretroviral regimen. The high-throughput sequencing results of mutations between ART failure subjects and treatment naïve subjects were also compared. Three novel mutations were then screened with higher frequencies in the ART failure subjects. It is important to guide the replacement of treatment programs and screening for new drug-resistant mutation sites, and the use of high-throughput sequencing methods can more comprehensively study the characteristics of drug-resistant viral variants of patients experiencing VF on a first-line regimen.

Fact and Fiction about 1%: Next Generation Sequencing and the Detection of Minor Drug Resistant Variants in HIV-1 Populations with and without Unique Molecular Identifiers.

Next generation sequencing (NGS) platforms have the ability to generate almost limitless numbers of sequence reads starting with a PCR product. This gives the illusion that it is possible to analyze minor variants in a viral population. However, including a PCR step obscures the sampling depth of the viral population, the key parameter needed to understand the utility of the data set for finding minor variants. Also, these high throughput sequencing platforms are error prone at the level where minor variants are of interest, confounding the interpretation of detected minor variants. A simple strategy has been applied in multiple applications of NGS to solve these problems. Prior to PCR, individual molecules are “tagged” with a unique molecular identifier (UMI) that can be used to establish the actual sample size of viral genomes sequenced after PCR and sequencing. In addition, since PCR generates many copies of each sequence tagged to a specific UMI, a template consensus sequence (TCS) can be created from the many reads of each template, removing virtually all of the method error. From this perspective we examine our own use of a UMI, called Primer ID, in the detection of minor drug resistant variants in HIV-1 populations.

A single variant sequencing method for sensitive and quantitative detection of HIV-1 minority variants

HIV drug resistance is a major threat to achieving long-term viral suppression in HIV-positive individuals. Drug resistant HIV variants, including minority variants, can compromise response to antiretroviral therapy. Many studies have investigated the clinical relevance of drug resistant minority variants, but the level at which minority variants become clinically relevant remains unclear. A combination of Primer-ID and deep sequencing is a promising approach that may quantify minority variants more accurately compared to standard deep sequencing. However, most studies that used the Primer-ID method have analyzed clinical samples directly. Thus, its sensitivity and quantitative accuracy have not been adequately validated using known controls. Here, we constructed defined proportions of artificial RNA and virus quasispecies and measured their relative proportions using the Primer-ID based, quantitative single-variant sequencing (qSVS) assay. Our results showed that minority variants present at 1% of quasispecies were detected reproducibly with minimal variations between technical replicates. In addition, the measured frequencies were comparable to the expected frequencies. These data validate the accuracy and reproducibility of the qSVS assay in quantifying authentic HIV minority variants, and support the use of this approach to examine the impacts of minority HIV variants on virologic response and clinical outcome.

Shall I trust the report? Variable performance of Sanger sequencing revealed by deep sequencing on HIV drug resistance mutation detection

BackgroundThe clinical utilisation of deep sequencing in HIV treatment has been hindered due to its unknown correlation with standard Sanger genotyping and the undetermined value of minority drug resistance mutation (DRM) detection. ObjectivesTo compare deep sequencing performance to standard Sanger genotyping with clinical samples, in an effort to delineate the correlation between the results from the two methods and to find the optimal deep sequencing threshold for clinical utilisation. MethodsWe conducted a retrospective study using stored plasma collected from August 2014 to March 2018 for HIV genotyping with the commercial Sanger genotyping kit. Samples with available Sanger genotyping reports were further deep sequenced. Drug resistance was interpreted according to the Stanford HIV drug resistance database algorithm. ResultsAt 15–25% minority detection thresholds, 9–15% cases had underestimated DRMs by Sanger sequencing. The concordance between the Sanger and deep sequencing reports was 68–82% in protease-reverse transcriptase region and 88–97% in integrase region at 5–25% thresholds. The undetected drug resistant minority variants by Sanger sequencing contributed to the lower negative predictive value of Sanger genotyping in cases harbouring DRMs. ConclusionsUse of deep sequencing improved detection of antiretroviral resistance mutations especially in cases with virological failure or previous treatment interruption. Deep sequencing with 10–15% detection thresholds may be considered a suitable substitute for Sanger sequencing on antiretroviral DRM detection.

Minority and majority pretreatment HIV-1 drug resistance associated with failure of first-line nonnucleoside reverse-transcriptase inhibitor antiretroviral therapy in Kenyan women.

Among women initiating first-line nonnucleoside reverse-transcriptase inhibitor (NNRTI)-based-ART with and without a history of single-dose nevirapine (sdNVP) with or without zidovudine with or without lamivudine (ZDV with and without 3TC) for prevention of mother-to-child HIV transmission (PMTCT), we hypothesized that pre-ART HIV-drug resistance would be associated with virologic failure DESIGN/METHODS:: In a prospectively enrolled study, three genotypic drug-resistance assays [oligonucleotide-ligation-assay (OLA), consensus sequencing, and next-generation sequencing by Illumina] were retrospectively performed to detect pre-ART drug resistance. Minority or majority drug-resistant variants identified in pre-ART RNA and/or DNA, a history of antiretrovirals for PMTCT, and other risk factors were assessed for association with virologic failure. Failure occurred in 38/169 (22.5%) women, and was associated with pre-ART drug resistance detected by any assay (OLA of plasma or PBMC, consensus sequencing of PBMC and/or plasma, and next-generation sequencing of PBMC at frequencies of at least 10% and as minority variants; all P < 0.0001). Failure was also associated with PMTCT using sdNVP and ZDV with or without 3TC, but not sdNVP only; however, the longer time-interval between PMTCT and ART initiation observed for sdNVP-only women showed no interaction with failure. Viral loads and OLA of PBMC in longitudinal specimens demonstrated rapid failure and emergence of drug resistance, particularly among sdNVP and ZDV with or without 3TC-experienced women with pre-ART drug-resistant minority variants by next-generation sequencing but without drug resistance by OLA or consensus sequencing. Pre-ART drug resistance was detected similarly by OLA of PBMC or plasma and by consensus sequencing, and was associated with virologic failure soon after initiation of first-line NVP-based ART. A history of sdNVP and ZDV with or without 3TC for PMTCT or minority variants detected by next-generation sequencing identified additional women with failure. These findings emphasize the value of assessing individual antiretroviral history, particularly nonsuppressive antiretrovirals with at least two drug classes, and testing for pre-ART drug resistance, including minority variants.

Detection of pretreatment minority HIV-1 reverse transcriptase inhibitor-resistant variants by ultra-deep sequencing has a limited impact on virological outcomes.

Ultra-deep sequencing (UDS) is a powerful tool for exploring the impact on virological outcome of minority variants with low frequencies, some even <1% of the virus population. Here, we compared HIV-1 minority variants at baseline, through plasma RNA and PBMC DNA analyses, and the dominant variants at the virological failure (VF) point, to evaluate the impact of minority drug-resistant variants (MDRVs) on virological outcomes. Single-molecule real-time sequencing (SMRTS) was performed on baseline RNA and DNA. The Stanford HIV-1 drug resistance database was used for the identification and evaluation of drug resistance-associated mutations (DRAMs). We classified 50 patients into virological success (VS) and VF groups. We found that the rates of reverse transcriptase inhibitor (RTI) DRAMs determined by SMRTS did not differ significantly within or between groups, whether based on RNA or DNA analyses. There was no significant difference in the level of resistance to specific drugs between groups, in either DNA or RNA analyses, except for the DNA-based analysis of lamivudine, for which there was a trend towards a higher prevalence of intermediate/high-level resistance in the VF group. The RNA MDRVs corresponded to DNA MDRVs, except for M100I and Y188H. Sequencing from DNA appeared to be more sensitive than from RNA to detect MDRVs. Detection of pretreatment minority HIV-1 RTI-resistant variants by UDS showed that MDRVs at baseline were not significantly associated with virological outcome. However, HIV-1 DNA sequencing by UDS was useful for detecting pretreatment drug resistance mutations in patients, potentially affecting virological responses, suggesting a potential clinical relevance for ultra-deep DNA sequencing.

Determining the Origins of Human Immunodeficiency Virus Type 1 Drug-resistant Minority Variants in People Who Are Recently Infected Using Phylogenetic Reconstruction.

BackgroundDrug-resistant minority variants (DRMinVs) detected in patients who recently acquired human immunodeficiency virus type 1 (HIV-1) can be transmitted, generated de novo through virus replication, or technical errors. The first form is likely to persist and result in treatment failure, while the latter two could be stochastic and transient.MethodsUltradeep sequencing of plasma samples from 835 individuals with recent HIV-1 infection in the United Kingdom was performed to detect DRMinVs at a mutation frequency between 2% and 20%. Sequence alignments including >110 000 HIV-1 partial pol consensus sequences from the UK HIV Drug Resistance Database (UK-HDRD), linked to epidemiological and clinical data from the HIV and AIDS Reporting System, were used for transmission cluster analysis. Transmission clusters were identified using Cluster Picker with a clade support of >90% and maximum genetic distances of 4.5% or 1.5%, the latter to limit detection to likely direct transmission events.ResultsDrug-resistant majority variants (DRMajVs) were detected in 66 (7.9%) and DRMinVs in 84 (10.1%) of the recently infected individuals. High levels of clustering to sequences in UK-HDRD were observed for both DRMajV (n = 48; 72.7%) and DRMinV (n = 63; 75.0%) sequences. Of these, 43 (65.2%) with DRMajVs were in a transmission cluster with sequences that harbored the same DR mutation compared to only 3 (3.6%) sequences with DRMinVs (P < .00001, Fisher exact test). Evidence of likely direct transmission of DRMajVs was observed for 25/66 (37.9%), whereas none were observed for the DRMinVs (P < .00001).ConclusionsUsing a densely sampled HIV-infected population, we show no evidence of DRMinV transmission among recently infected individuals.

Assessment of Transmitted HIV-1 Drug Resistance Mutations Using Ultra- Deep Pyrosequencing in a Turkish Cohort.

Antiretroviral treatment (ART) reduces morbidity and mortality caused by human immunodeficiency virus (HIV) infection; however, the emergence of drug-resistant strains poses an important obstacle to treatment success. Using conventional sequencing methods to determine antiretroviral resistance, mutations present in ≥20% of quasispecies can be identified, but drug-resistant minority variants can lead to virologic failure. We aimed to assess transmitted drug resistance mutations (TDRMs) within minority variants using ultra-deep pyrosequencing (UDPS). Treatment-naive adult patients were included in this observational study. Surveillance TDRMs were classified as ≥20% or at minority variant level (≥2% - <20%). Genotypic sensitivity score calculated by using all pre-treatment drug resistance mutations (PDRMs) was also evaluated. Thirty-six patients were analyzed. Any TDRM at ≥20% level was detected in 8.3% of the patients (n=3). This prevalence increased to 30.6% (n=11) with the inclusion of minority variants. All non-nucleoside reverse transcriptase inhibitor and protease inhibitor-related TDRMs were within minority variants. The genotypic sensitivity score of rilpivirine-based regimens was considerably diminished when minority variants were included in the PDRM analysis. UDPS was used for the first time to assess TDRM in a Turkish HIV cohort and uncovered several mutations hidden within minority variants. UDPS may be preferred to detect PDRMs for avoiding virologic failure with rilpivirine-based ART regimens.

Clinically relevant thresholds for ultrasensitive HIV drug resistance testing: a multi-country nested case-control study

Implementation of ultrasensitive HIV drug resistance tests for routine clinical use is hampered by uncertainty about the clinical relevance of drug-resistant minority variants. We assessed different detection thresholds for pretreatment drug resistance to predict an increased risk of virological failure. We did a case-control study nested within a prospective multicountry cohort. Our study included patients from 12 clinical sites in Kenya, Nigeria, South Africa, Uganda, and Zambia. We defined cases as patients with virological failure (ie, those who had either viral load ≥400 copies per mL at 12 months or had switched to second-line antiretroviral therapy [ART] as a result of virological failure before 12 months) and controls as those with viral suppression (viral load <400 copies per mL at 12 months) on first-line non-nucleoside reverse transcriptase inhibitor-based antiretroviral therapy. We assessed pretreatment drug resistance with Illumina MiSeq next-generation sequencing, using the International Antiviral Society (IAS)-USA mutation list or the Stanford HIV Drug Resistance Database (HIVDB) genotypic sensitivity score. We calculated diagnostic accuracy measures and assessed the odds of virological failure using conditional logistic regression for 1%, 5%, and 10% pretreatment drug resistance detection thresholds, compared with the conventional 20% or more used in Sanger-based sequencing. Paired viral load results before ART and at month 12 of follow-up were available from 1896 participants. We identified 178 patients with virological failure and selected 338 matched controls. We excluded 117 patients from pretreatment drug resistance analysis; therefore, 152 cases of virological failure and 247 controls were included in the final analysis. With the IAS-USA mutation list, at a detection threshold of 20% or more in patients with pretreatment drug resistance, the adjusted odds ratio (OR) for virological failure was 9·2 (95% CI 4·2-20·1) compared with those without pretreatment drug resistance. Lowering the threshold resulted in adjusted ORs of virological failure of 6·8 (95% CI 3·3-13·9) at the 10% threshold, 7·6 (3·4-17·1) at the 5% threshold, and 4·5 (2·0-10·2) at the 1% threshold. Lowering the detection threshold from 20% improved the sensitivity (ie, ability to identify cases) from 12% (n=18) to 13% (n=19) at detection threshold 10%, to 15% (n=23) at detection threshold 5%, and to 17% (n=26) at detection threshold 1%, but caused a slight reduction in specificity (ie, ability to identify controls) from 98% (n=241) to 96% (n=238) at the 10% threshold, 96% (n=236) at the 5% threshold, and a larger reduction to 92% (n=227) at the 1% threshold. Diagnostic ORs were 5·4 (95% CI 2·1-13·9) at the 20% threshold, 3·8 (1·7-8·6) at the 10% threshold, 3·8 (1·8-8·1) at the 5% threshold, and 2·3 (1·2-4·2) at the 1% threshold. Use of the Stanford HIVDB genotypic sensitivity scores yielded similar ORs for virological failure, sensitivities, specificities, and diagnostic ORs. Ultrasensitive resistance testing for pretreatment drug resistance improved identification of people at risk of virological failure; however, this came with a reduction in our ability to identify people with viral suppression, especially at very low thresholds. Further modelling is needed to estimate the optimal trade-off for the 5% and 20% thresholds, balancing improved case finding against unnecessary regimen switching. The Netherlands Ministry of Foreign Affairs, IrsiCaixa, and European Union.

Transmission of HIV-1 drug resistance mutations within partner-pairs: A cross-sectional study of a primary HIV infection cohort.

BackgroundTransmission of human immunodeficiency virus type 1 (HIV-1) drug resistance mutations, particularly that of minority drug-resistant variants, remains poorly understood. Population-based studies suggest that drug-resistant HIV-1 is less transmissible than drug-susceptible viruses. We compared HIV-1 drug-resistant genotypes among partner-pairs in order to assess the likelihood of transmission of drug resistance mutations and investigate the role of minority variants in HIV transmission.Methods and findingsFrom 1992–2010, 340 persons with primary HIV-1 infection and their partners were enrolled into observational research studies at the University of Washington Primary Infection Clinic (UWPIC). Out of 50 partner-pairs enrolled, 36 (72%) transmission relationships were confirmed by phylogenetic distance analysis of HIV-1 envelope (env) sequences, and 31 partner-pairs enrolled after 1995 met criteria for this study. Drug resistance mutations in the region of the HIV-1 polymerase gene (pol) that encodes protease and reverse transcriptase were assessed by 454-pyrosequencing. In 25 partner-pairs where the transmission direction could be determined, 12 (48%) transmitters had 1–4 drug resistance mutations (23 total) detected in their HIV-1 populations at a median frequency of 6.0% (IQR 1.5%–98.7%, range 1.0%–99.6%). Of 10 major mutations detected in five transmitters at a frequency >95%, 100% (95% CI 69.2%–100%) were detected in recipients. All of these transmitters were antiretroviral (ARV)-naïve at the time of specimen collection. Fourteen mutations (eight major mutations and six accessory mutations) were detected in nine transmitters at low frequencies (1.0%–11.8%); four of these transmitters had previously received ARV therapy. Two (14% [95% CI 1.8%–42.8%]) G73S accessory mutations were detected in both transmitter and recipient. This number is not significantly different from the number expected based on the observed frequencies of drug-resistant viruses in transmitting partners. Limitations of this study include the small sample size and uncertainties in determining the timing of virus transmission and mutation history.ConclusionsDrug-resistant majority variants appeared to be commonly transmitted by ARV-naïve participants in our analysis and may contribute significantly to transmitted drug resistance on a population level. When present at low frequency, no major mutation was observed to be shared between partner-pairs; identification of accessory mutations shared within a pair could be due to transmission, laboratory artifact, or apolipoprotein B mRNA-editing enzyme, catalytic polypeptides (APOBECs), and warrants further study.

Characterization of HIV-1 Near Full-Length Proviral Genome Quasispecies from Patients with Undetectable Viral Load Undergoing First-Line HAART Therapy.

Increased access to highly active antiretroviral therapy (HAART) by human immunodeficiency virus postive (HIV+) individuals has become a reality worldwide. In Brazil, HAART currently reaches over half of HIV-infected subjects. In the context of a remarkable HIV-1 genetic variability, highly related variants, called quasispecies, are generated. HIV quasispecies generated during infection can influence virus persistence and pathogenicity, representing a challenge to treatment. However, the clinical relevance of minority quasispecies is still uncertain. In this study, we have determined the archived proviral sequences, viral subtype and drug resistance mutations from a cohort of HIV+ patients with undetectable viral load undergoing HAART as first-line therapy using next-generation sequencing for near full-length virus genome (NFLG) assembly. HIV-1 consensus sequences representing NFLG were obtained for eleven patients, while for another twelve varying genome coverage rates were obtained. Phylogenetic analysis showed the predominance of subtype B (83%; 19/23). Considering the minority variants, 18 patients carried archived virus harboring at least one mutation conferring antiretroviral resistance; for six patients, the mutations correlated with the current ARVs used. These data highlight the importance of monitoring HIV minority drug resistant variants and their clinical impact, to guide future regimen switches and improve HIV treatment success.

The Role of HIV-1 Drug-Resistant Minority Variants in Treatment Failure.

Human immunodeficiency virus type 1 (HIV-1) drug resistance genotyping is recommended to help in the selection of antiretroviral therapy and to prevent virologic failure. There are several ultrasensitive assays able to detect HIV-1 drug-resistance minority variants (DRMVs) not detectable by standard population sequencing-based HIV genotyping assays. Presence of these DRMVs has been shown to be clinically relevant, but its impact does not appear to be uniform across drug classes. In this review, we summarize key evidence for the clinical impact of DRMVs across drug classes for both antiretroviral treatment-naive and antiretroviral treatment-experienced patients, and highlight areas where more supporting evidence is needed.

Prevalence of Drug-Resistant Minority Variants in Untreated HIV-1-Infected Individuals With and Those Without Transmitted Drug Resistance Detected by Sanger Sequencing.

Minority variant human immunodeficiency virus type 1 (HIV-1) nonnucleoside reverse transcriptase inhibitor (NNRTI) resistance mutations are associated with an increased risk of virological failure during treatment with NNRTI-containing regimens. To determine whether individuals to whom variants with isolated NNRTI-associated drug resistance were transmitted are at increased risk of virological failure during treatment with a non-NNRTI-containing regimen, we identified minority variant resistance mutations in 33 individuals with isolated NNRTI-associated transmitted drug resistance and 49 matched controls. We found similar proportions of overall and nucleoside reverse transcriptase inhibitor-associated minority variant resistance mutations in both groups, suggesting that isolated NNRTI-associated transmitted drug resistance may not be a risk factor for virological failure during treatment with a non-NNRTI-containing regimen.

Ultra-Deep Sequencing Analysis on HIV Drug-Resistance-Associated Mutations Among HIV-Infected Individuals: First Report from the Philippines.

A sharp increase in the number of people living with HIV has been documented in the Philippines. In response, the government has instituted antiretroviral therapy (ART) nationwide through HIV treatment hubs. However, no data presently exist on the status of ART drug-resistance-associated mutations (DRMs). In this study, we aim at analyzing DRM profiles in the Philippines and at providing comprehensive data on DRMs to guide treatment decisions and prevent viral failures. We conducted a cross-sectional study in 119 volunteers who tested positive for HIV from more than 8,000 participants screened for HIV across the nation through the 2013 Integrated HIV Behavioral and Serologic Surveillance (IHBSS) program. Amplicons were generated from plasma RNA by using primers designed to analyze diverse HIV-1 isolates targeting the reverse transcriptase region and sequenced on a 454 ultra-deep sequencing (UDS) platform to assess DRMs. DRMs were defined by using the Stanford HIV drug resistance database, and we found only 2 from 110 evaluable individuals with major HIV variants (>20% prevalence) that were highly resistant to the non-nucleoside reverse transcriptase inhibitor (NNRTI: efavirenz and nevirapine). However, a larger fraction of individuals harbored minority drug-resistant HIV variants (0.5%-20% prevalence) and they were highly resistant to NNRTI nevirapine (89/110), rilpivirine (5/110), and efavirenz (49/110). This study is the first report on the presence of HIV drug resistance in the Philippines and demonstrates the utility of UDS in assisting the detection of HIV minor variants. Monitoring for ART-DRMs will assist in improving HIV management strategies in curtailing the evolving epidemic in the Philippines.

Genomic Analysis of the Evolution of Fluoroquinolone Resistance in Mycobacterium tuberculosis Prior to Tuberculosis Diagnosis.

Fluoroquinolones (FQs) are effective second-line drugs for treating antibiotic-resistant tuberculosis (TB) and are being considered for use as first-line agents. Because FQs are used to treat a range of infections, in a setting of undiagnosed TB, there is potential to select for drug-resistant Mycobacterium tuberculosis mutants during FQ-based treatment of other infections, including pneumonia. Here we present a detailed characterization of ofloxacin-resistant M. tuberculosis samples isolated directly from patients in Taiwan, which demonstrates that selection for FQ resistance can occur within patients who have not received FQs for the treatment of TB. Several of these samples showed no mutations in gyrA or gyrB based on PCR-based molecular assays, but genome-wide next-generation sequencing (NGS) revealed minority populations of gyrA and/or gyrB mutants. In other samples with PCR-detectable gyrA mutations, NGS revealed subpopulations containing alternative resistance-associated genotypes. Isolation of individual clones from these apparently heterogeneous samples confirmed the presence of the minority drug-resistant variants suggested by the NGS data. Further NGS of these purified clones established evolutionary links between FQ-sensitive and -resistant clones derived from the same patient, suggesting de novo emergence of FQ-resistant TB. Importantly, most of these samples were isolated from patients without a history of FQ treatment for TB. Thus, selective pressure applied by FQ monotherapy in the setting of undiagnosed TB infection appears to be able to drive the full or partial emergence of FQ-resistant M. tuberculosis, which has the potential to confound diagnostic tests for antibiotic susceptibility and limit the effectiveness of FQs in TB treatment.

Low-Frequency Drug Resistance in HIV-Infected Ugandans on Antiretroviral Treatment Is Associated with Regimen Failure.

Most patients failing antiretroviral treatment in Uganda continue to fail their treatment regimen even if a dominant drug-resistant HIV-1 genotype is not detected. In a recent retrospective study, we observed that approximately 30% of HIV-infected individuals in the Joint Clinical Research Centre (Kampala, Uganda) experienced virologic failure with a susceptible HIV-1 genotype based on standard Sanger sequencing. Selection of minority drug-resistant HIV-1 variants (not detectable by Sanger sequencing) under antiretroviral therapy pressure can lead to a shift in the viral quasispecies distribution, becoming dominant members of the virus population and eventually causing treatment failure. Here, we used a novel HIV-1 genotyping assay based on deep sequencing (DeepGen) to quantify low-level drug-resistant HIV-1 variants in 33 patients failing a first-line antiretroviral treatment regimen in the absence of drug-resistant mutations, as screened by standard population-based Sanger sequencing. Using this sensitive assay, we observed that 64% (21/33) of these individuals had low-frequency (or minority) drug-resistant variants in the intrapatient HIV-1 population, which correlated with treatment failure. Moreover, the presence of these minority HIV-1 variants was associated with higher intrapatient HIV-1 diversity, suggesting a dynamic selection or fading of drug-resistant HIV-1 variants from the viral quasispecies in the presence or absence of drug pressure, respectively. This study identified low-frequency HIV drug resistance mutations by deep sequencing in Ugandan patients failing antiretroviral treatment but lacking dominant drug resistance mutations as determined by Sanger sequencing methods. We showed that these low-abundance drug-resistant viruses could have significant consequences for clinical outcomes, especially if treatment is not modified based on a susceptible HIV-1 genotype by Sanger sequencing. Therefore, we propose to make clinical decisions using more sensitive methods to detect minority HIV-1 variants.

Antiviral resistance testing.

Current genotypic resistance tests fail to amplify drug-resistant minority variants when they are present below 20% of the total virus population. Next-generation sequencing (NGS) addresses this issue and is being introduced into diagnostic laboratories. This review gives an overview of the resistance tests currently used and explores the opportunities and challenges that NGS genotypic resistance tests will bring. The technical challenges of NGS, such as PCR and sequence-related errors, are being addressed and various assays are currently undergoing technical validation for clinical use. Although not conclusive, the data seem to suggest that NGS will be valuable for low genetic barrier drugs and certain types of tests such as the HIV-1 tropism test. Clinical validation of the reporting and interpretation of minority variant results are essential when laboratories start reporting these results. The first wave of NGS technology is being rolled out in diagnostic laboratories. Antiviral test benefits include increased sensitivity and eventually cheaper antiviral resistance tests. There is a risk that low percentage minority variants may be over interpreted. This could result in antiviral drugs, which may have been effective, being possibly denied to patients if proper clinical validation studies are not performed.

Dynamics of hepatitis B virus quasispecies heterogeneity in association with nucleos(t)ide analogue treatment determined by MALDI-TOF MS

Minor drug-resistant variants may preexist in every subject infected with hepatitis B virus (HBV). However, understanding the dynamic of genotypic evolution within the HBV population requires accurately following allele frequencies through time. We used MALDI-TOF MS (matrix-assisted laser desorption-ionization time-of-flight mass spectrometry) for localization and quantitative allele frequency detection to investigate preexisting HBV quasispecies and the genotypic evolution of drug-resistant variants during nucleos(t)ide analogue therapy. We found a significant difference between the genotypic evolution of drug-resistant variants depending on response to treatment.

Low-frequency drug-resistant HIV-1 and risk of virological failure to first-line NNRTI-based ART: a multicohort European case-control study using centralized ultrasensitive 454 pyrosequencing.

ObjectivesIt is still debated if pre-existing minority drug-resistant HIV-1 variants (MVs) affect the virological outcomes of first-line NNRTI-containing ART.MethodsThis Europe-wide case–control study included ART-naive subjects infected with drug-susceptible HIV-1 as revealed by population sequencing, who achieved virological suppression on first-line ART including one NNRTI. Cases experienced virological failure and controls were subjects from the same cohort whose viraemia remained suppressed at a matched time since initiation of ART. Blinded, centralized 454 pyrosequencing with parallel bioinformatic analysis in two laboratories was used to identify MVs in the 1%–25% frequency range. ORs of virological failure according to MV detection were estimated by logistic regression.ResultsTwo hundred and sixty samples (76 cases and 184 controls), mostly subtype B (73.5%), were used for the analysis. Identical MVs were detected in the two laboratories. 31.6% of cases and 16.8% of controls harboured pre-existing MVs. Detection of at least one MV versus no MVs was associated with an increased risk of virological failure (OR = 2.75, 95% CI = 1.35–5.60, P = 0.005); similar associations were observed for at least one MV versus no NRTI MVs (OR = 2.27, 95% CI = 0.76–6.77, P = 0.140) and at least one MV versus no NNRTI MVs (OR = 2.41, 95% CI = 1.12–5.18, P = 0.024). A dose–effect relationship between virological failure and mutational load was found.ConclusionsPre-existing MVs more than double the risk of virological failure to first-line NNRTI-based ART.