Detection of Minority Variants and Mixed Infections in Mycobacterium tuberculosis by Direct Whole-Genome Sequencing on Noncultured Specimens Using a Specific-DNA Capture Strategy

We present a new strategy to identify mixed infections and minority variants in Mycobacterium tuberculosis by whole-genome sequencing. The objective of the strategy is the direct detection in patient sputum; in this way, minority populations of resistant strains can be identified at the time of diagnosis, facilitating identification of the most appropriate treatment for the patient from the first moment.

SARS-CoV-2 Evolution among Oncological Population: In-Depth Virological Analysis of a Clinical Cohort

Background: Oncological patients have a higher risk of prolonged SARS-CoV-2 shedding, which, in turn, can lead to evolutionary mutations and emergence of novel viral variants. The aim of this study was to analyze biological samples of a cohort of oncological patients by deep sequencing to detect any significant viral mutations. Methods: High-throughput sequencing was performed on selected samples from a SARS-CoV-2-positive oncological patient cohort. Analysis of variants and minority variants was performed using a validated bioinformatics pipeline. Results: Among 54 oncological patients, we analyzed 12 samples of 6 patients, either serial nasopharyngeal swab samples or samples from the upper and lower respiratory tracts, by high-throughput sequencing. We identified amino acid changes D614G and P4715L as well as mutations at nucleotide positions 241 and 3037 in all samples. There were no other significant mutations, but we observed intra-host evolution in some minority variants, mainly in the ORF1ab gene. There was no significant mutation identified in the spike region and no minority variants common to several hosts. Conclusions: There was no major and rapid evolution of viral strains in this oncological patient cohort, but there was minority variant evolution, reflecting a dynamic pattern of quasi-species replication.

Tiled-ClickSeq for targeted sequencing of complete coronavirus genomes with simultaneous capture of RNA recombination and minority variants

High-throughput genomics of SARS-CoV-2 is essential to characterize virus evolution and to identify adaptations that affect pathogenicity or transmission. While single-nucleotide variations (SNVs) are commonly considered as driving virus adaption, RNA recombination events that delete or insert nucleic acid sequences are also critical. Whole genome targeting sequencing of SARS-CoV-2 is typically achieved using pairs of primers to generate cDNA amplicons suitable for next-generation sequencing (NGS). However, paired-primer approaches impose constraints on where primers can be designed, how many amplicons are synthesized and requires multiple PCR reactions with non-overlapping primer pools. This imparts sensitivity to underlying SNVs and fails to resolve RNA recombination junctions that are not flanked by primer pairs. To address these limitations, we have designed an approach called ‘Tiled-ClickSeq’, which uses hundreds of tiled-primers spaced evenly along the virus genome in a single reverse-transcription reaction. The other end of the cDNA amplicon is generated by azido-nucleotides that stochastically terminate cDNA synthesis, removing the need for a paired-primer. A sequencing adaptor containing a Unique Molecular Identifier (UMI) is appended to the cDNA fragment using click-chemistry and a PCR reaction generates a final NGS library. Tiled-ClickSeq provides complete genome coverage, including the 5’UTR, at high depth and specificity to the virus on both Illumina and Nanopore NGS platforms. Here, we analyze multiple SARS-CoV-2 isolates and clinical samples to simultaneously characterize minority variants, sub-genomic mRNAs (sgmRNAs), structural variants (SVs) and D-RNAs. Tiled-ClickSeq therefore provides a convenient and robust platform for SARS-CoV-2 genomics that captures the full range of RNA species in a single, simple assay.

A new sensitive and robust next-generation sequencing platform for HIV-1 drug resistance mutations testing

Next-generation sequencing (NGS) is a trending new platform which allows cheap, quantitative, high-throughput, parallel sequencing for minority variants with frequencies less than 20% of the HIV-1 quasi-species. In clinical setting, these advantages are crucial for choosing antiretroviral drugs with low genetic barriers and will potentially benefit treatment outcomes. In this investigation, we implemented the Boxin HIV-1 NGS platform for genotyping the drug-resistance-associated variants in PR/RT regions. Plasmids with known mutations were used to analyze the accuracy, reproducibility, and reliability of the Boxin NGS assay. Variant frequencies reported by Boxin NGS and the theoretical value were highly concordant. The Bland-Altman plot and the coefficient of variation (7%) suggested that the method has excellent reproducibility and reliability. Sanger sequencing confirmed the existence of these known variants with frequencies equal or above 20%. 78 blood samples were obtained from AIDS patients and underwent PR/RT region genotyping by Sanger sequencing and Boxin NGS. 33 additional drug resistance mutations were identified by Boxin NGS, 23/33 mutations were minority variants with frequencies below 20%. 15 blood samples obtained from AIDS patients underwent PR/RT region genotyping by Sanger sequencing, Boxin NGS, and Vela NGS. The Bland-Altman plot suggested that the variant frequencies detected by Boxin and Vela were highly concordant. Moreover, Boxin NGS assay detected five more minority variants with frequencies ranged from 1% to 20%. In a series of samples collected from 2016 to 2017, Boxin NGS reported a M184V mutation with a frequency of 4.92%, 3 months earlier than this mutation was firstly detected by Vela NGS and Sanger sequencing. In conclusion, Boxin NGS had good accuracy, reproducibility, and reliability. Boxin NGS was highly concordant with Sanger sequencing and Vela NGS. In terms of genotyping HIV-1 variants in PR/RT regions, Boxin NGS was more cost-efficient and appeared to have increased sensitivity without compromising sequence accuracy.

Diversity and selection of SARS-CoV-2 minority variants in the early New York City outbreak

High error rates of viral RNA-dependent RNA polymerases lead to diverse intra-host viral populations during infection. Errors made during replication that are not strongly deleterious to the virus can lead to the generation of minority variants. Here we analyzed minority variants within the SARS-CoV-2 data in 12 samples from the early outbreak in New York City, using replicate sequencing for reliable identification. While most minority variants were unique to a single sample, we found several instances of shared variants. We provide evidence that some higher-frequency minority variants may be transmitted between patients or across short transmission chains, while other lower-frequency, more widely shared variants arise independently. Further, our data indicate that even with a small transmission bottleneck, the heterogeneity of intra-host viral populations is enhanced by minority variants present in transmission samples. Our data suggest that analysis of shared minority variants could help identify regions of the SARS-CoV-2 genome that are under increased selective pressure, as well as inform transmission chains and give insight into variant strain emergence.

Reverse transcriptase and protease inhibitors mutational viral load in HIV infected pregnant women with transmitted drug resistance in Argentina

Objective. Argentina has reported high levels of transmitted drug resistance (TDR), in HIV-infected pregnant women by population sequencing. We aimed to describe, in patients with TDR, the percentage of quasispecies harboring resistance mutations (RAMs) and mutational load (ML). Patients and Methods. Retrospective study in a cohort of 40 naïve HIV-infected pregnant women, whose pretreatment samples had been genotyped by TRUGENE (period 2008-2014). Samples were re-sequenced with Ultra-deep Sequencing and ML was calculated considering baseline HIV-1 RNA load multiplied by the frequency of quasispecies harboring RAMs. Results. TDR for NNRTIs, NRTIs and PIs was 17.5% (n=7 patients), 10% (n=4), 12.5% (n=5) respectively. Predominant NNRTI RAMs were K103N (n=4; 10%) and G190A/E/S (n=3; 7.5%). For NNRTIs, 78% of RAMs were present in >93.5% of viral population and ML was >1000 copies/mL (c/mL) for 89%, with a median (IQR) of 8330 c/ml (7738-29796). The following NRTI RAMs were described (per patient: % of quasispecies, ML): T215I (99.7%, 11014 c/ml); D67G (1.28%, 502 c/mL); M41L (79.8%, 88578 c/mL) and M184I (1.02%, 173 c/mL). Most frequent PI-RAMs were I85V, M46I, I50V and L90M (n=2, 5% each). For PIs, quasispecies with RAMs were <2.3% of viral population and ML was <350 c/mL for 77.8% of them. Conclusion. NNRTI-RAMs are predominant within the viral population, usually exceeding the threshold of 1000 c/mL, indicating potential higher risk of perinatal transmission. Conversely, PI mutations appear mostly as minority variants, with potential lower risk of transmission. Among NRTI, quasispecies harboring RAMs and ML values were variable.

Resistance-associated substitutions and response to treatment in a chronic hepatitis C virus infected-patient: an unusual virological response case report

Background Direct-Acting agents (DAAs) target and inhibit essential viral replication proteins. They have revolutionized the treatment of Hepatitis C virus (HCV) infection reaching high levels of sustained virologic response. However, the detection of basal resistance-associated substitutions (RASs) to DAAs in naïve patients could be important in predicting the treatment outcome in some patients exhibiting failures to DAA-based therapies. Therefore, the aim of this work was to evaluate the presence of RASs as minority variants within intra-host viral populations, and assess their relationship to response to therapy on a multiple times relapser patient infected chronically with HCV. Case presentation A male HCV infected-patient with a genotype 1a strain was evaluated. He had previously not responded to dual therapy (pegylated interferon-α plus ribavirin) and was going to start a direct-acting agent-based therapy (DAAs). He showed no significant liver fibrosis (F0). Viral RNA was extracted from serum samples taken prior and after therapy with DAAs (sofosbubir/ledipasvir/ribavirin). NS5A and NS5B genomic regions were PCR-amplified and the amplicons were sequenced using Sanger and next-generation sequencing (NGS) approaches. RASs were searched in in-silico translated sequences for all DAAs available and their frequencies were determined for those detected by NGS technology. Sanger sequencing did not reveal the presence of RASs in the consensus sequence neither before nor after the DAA treatment. However, several RASs were found at low frequencies, both before as well as after DAA treatment. RASs found as minority variants (particularly substitutions in position 93 within NS5A region) seem to have increased their frequency after DAA pressure. Nevertheless, these RASs did not become dominant and the patient still relapsed, despite perfect adherence to treatment and having no other complications beyond the infection (no significant fibrosis, no drug abuse). Conclusions This report shows that some patients might relapse after a DAA-based therapy even when RASs (pre- and post-treatment) are detected in very low frequencies (< 1%) within intra-host viral populations. Increased awareness of this association may improve detection and guide towards a personalized HCV treatment, directly improving the outcome in hard-to-treat patients.

Tiled-ClickSeq for targeted sequencing of complete coronavirus genomes with simultaneous capture of RNA recombination and minority variants

High-throughput genomics of SARS-CoV-2 is essential to characterize virus evolution and to identify adaptations that affect pathogenicity or transmission. While single-nucleotide variations (SNVs) are commonly considered as driving virus adaption, RNA recombination events that delete or insert nucleic acid sequences are also critical. Whole genome targeting sequencing of SARS-CoV-2 is typically achieved using pairs of primers to generate cDNA amplicons suitable for Next-Generation Sequencing (NGS). However, paired-primer approaches impose constraints on where primers can be designed, how many amplicons are synthesized and requires multiple PCR reactions with non-overlapping primer pools. This imparts sensitivity to underlying SNVs and fails to resolve RNA recombination junctions that are not flanked by primer pairs. To address these limitations, we have designed an approach called ‘Tiled-ClickSeq’. Tiled-ClickSeq uses hundreds of tiled-primers spaced evenly along the virus genome in a single reverse-transcription reaction. The other end of the cDNA amplicon is generated by azido-nucleotides that stochastically terminate cDNA synthesis, obviating the need for a paired-primer. A sequencing adaptor containing a Unique Molecular Identifier (UMI) is appended using click-chemistry and a PCR reaction using Illumina adaptors generates a final NGS library. Tiled-ClickSeq provides complete genome coverage, including the 5’UTR, at high depth and specificity to virus on both Illumina and Nanopore NGS platforms. Here, we analyze multiple SARS-CoV-2 isolates and simultaneously characterize minority variants, sub-genomic mRNAs (sgmRNAs), structural variants (SVs) and D-RNAs. Tiled-ClickSeq therefore provides a convenient and robust platform for SARS-CoV-2 genomics that captures the full range of RNA species in a single, simple assay.

Compartmentalized Replication of SARS-Cov-2 in Upper vs. Lower Respiratory Tract Assessed by Whole Genome Quasispecies Analysis

We report whole-genome and intra-host variability of SARS-Cov-2 assessed by next generation sequencing (NGS) in upper (URT) and lower respiratory tract (LRT) from COVID-19 patients. The aim was to identify possible tissue-specific patterns and signatures of variant selection for each respiratory compartment. Six patients, admitted to the Intensive Care Unit, were included in the study. Thirteen URT and LRT were analyzed by NGS amplicon-based approach on Ion Torrent Platform. Bioinformatic analysis was performed using both realized in-house and supplied by ThermoFisher programs. Phylogenesis showed clade V clustering of the first patients diagnosed in Italy, and clade G for later strains. The presence of quasispecies was observed, with variants uniformly distributed along the genome and frequency of minority variants spanning from 1% to ~30%. For each patient, the patterns of variants in URT and LRT were profoundly different, indicating compartmentalized virus replication. No clear variant signature and no significant difference in nucleotide diversity between LRT and URT were observed. SARS-CoV-2 presents genetic heterogeneity and quasispecies compartmentalization in URT and LRT. Intra-patient diversity was low. The pattern of minority variants was highly heterogeneous and no specific district signature could be identified, nevertheless, analysis of samples, longitudinally collected in patients, supported quasispecies evolution.