Resolving the full spectrum of human genome variation using Linked-Reads.

Large-scale population analyses coupled with advances in technology have demonstrated that the human genome is more diverse than originally thought. To date, this diversity has largely been uncovered using short-read whole-genome sequencing. However, these short-read approaches fail to give a complete picture of a genome. They struggle to identify structural events, cannot access repetitive regions, and fail to resolve the human genome into haplotypes. Here, we describe an approach that retains long range information while maintaining the advantages of short reads. Starting from ∼1 ng of high molecular weight DNA, we produce barcoded short-read libraries. Novel informatic approaches allow for the barcoded short reads to be associated with their original long molecules producing a novel data type known as "Linked-Reads". This approach allows for simultaneous detection of small and large variants from a single library. In this manuscript, we show the advantages of Linked-Reads over standard short-read approaches for reference-based analysis. Linked-Reads allow mapping to 38 Mb of sequence not accessible to short reads, adding sequence in 423 difficult-to-sequence genes including disease-relevant genes STRC, SMN1, and SMN2 Both Linked-Read whole-genome and whole-exome sequencing identify complex structural variations, including balanced events and single exon deletions and duplications. Further, Linked-Reads extend the region of high-confidence calls by 68.9 Mb. The data presented here show that Linked-Reads provide a scalable approach for comprehensive genome analysis that is not possible using short reads alone.

Primer ID ultra-deep sequencing reveals dynamics of drug resistance-associated variants in breakthrough hepatitis C viruses: relevance to treatment outcome and resistance screening.

BACKGROUND: Use of direct-acting antiviral drugs (DAAs) that target HCV may be hampered by the rapid selection of viral strains that harbour drug resistance-associated variants (RAVs). These RAVs are often associated with a fitness cost and tend to occur on low-frequency strains within treatment-naive subjects. To address the clinical relevance of low frequency RAVs in the setting of DAAs, this study utilized a Primer ID ultra-deep sequencing approach to mitigate PCR errors and bias to accurately quantify viral sequences in subjects that failed DAA treatment. METHODS: Subjects were enrolled in the follow-up study P05063, and had previous treatment with boceprevir and all had detectable RAVs at virological failure (VF) based on Sanger-based population sequencing. Twelve subjects had three time points available: baseline, VF and follow-up (median 830.5 days). Viral RNA was amplified using unique primer identifiers (Primer IDs) and sequenced using 454 ultra-deep sequencing. RESULTS: The sequencing strategy used in this study improved the detection of clinically relevant low frequency strains bearing RAVs compared to population sequencing and showed that these strains can persist for up to 2 years post-treatment failure. Strains carrying multiple RAVs were common in breakthrough viruses. Putative compensatory mutations were identified. CONCLUSIONS: The Primer ID ultra-deep sequencing approach identifies RAVs that can reduce drug sensitivity at levels below the detection threshold for population sequencing. The approach also removes PCR errors and biases, suggesting this sequencing strategy should become the standard approach by which to perform temporal quasispecies studies and resistance screening. ClinicalTrials.gov NCT00689390.

Hepatitis C Virus (HCV) NS3 sequence diversity and antiviral resistance-associated variant frequency in HCV/HIV coinfection.

HIV coinfection accelerates disease progression in chronic hepatitis C and reduces sustained antiviral responses (SVR) to interferon-based therapy. New direct-acting antivirals (DAAs) promise higher SVR rates, but the selection of preexisting resistance-associated variants (RAVs) may lead to virologic breakthrough or relapse. Thus, pretreatment frequencies of RAVs are likely determinants of treatment outcome but typically are below levels at which the viral sequence can be accurately resolved. Moreover, it is not known how HIV coinfection influences RAV frequency. We adopted an accurate high-throughput sequencing strategy to compare nucleotide diversity in HCV NS3 protease-coding sequences in 20 monoinfected and 20 coinfected subjects with well-controlled HIV infection. Differences in mean pairwise nucleotide diversity (π), Tajima's D statistic, and Shannon entropy index suggested that the genetic diversity of HCV is reduced in coinfection. Among coinfected subjects, diversity correlated positively with increases in CD4(+) T cells on antiretroviral therapy, suggesting T cell responses are important determinants of diversity. At a median sequencing depth of 0.084%, preexisting RAVs were readily identified. Q80K, which negatively impacts clinical responses to simeprevir, was encoded by more than 99% of viral RNAs in 17 of the 40 subjects. RAVs other than Q80K were identified in 39 of 40 subjects, mostly at frequencies near 0.1%. RAV frequency did not differ significantly between monoinfected and coinfected subjects. We conclude that HCV genetic diversity is reduced in patients with well-controlled HIV infection, likely reflecting impaired T cell immunity. However, RAV frequency is not increased and should not adversely influence the outcome of DAA therapy.

Genetic background for development of resistance mutations within the HCV NS3 protease-helicase in direct acting antiviral naive patients.

BACKGROUND: Subtype-specific response to ketoamide NS3 protease inhibitors is observed in patients with genotype 1 HCV infection. Whether the genetic diversity in the molecular target site of ketoamide compounds prior to treatment plays a role for resistance development and lower treatment response in subtype 1a is poorly understood. METHODS: Using a public database, we retrieved worldwide NS3-sequence information of 581 dominant HCV variants from patients chronically infected with genotype 1 that were naive to direct-acting antivirals. We applied measures from phylogeny to study the pretreatment genetic diversity and complexity in NS3 full-length as well as the protease-helicase interface for subtype 1a and 1b, respectively. RESULTS: We found polymorphic sites more frequently in variants of subtype 1b than subtype 1a. Moreover, a significantly higher number of synonymous and non-synonymous substitutions were found in subtype 1b (P<0.001). Transitions were more frequent than transversions, most notably in subtype 1a, whereas the higher average number of nucleotide differences per site was found in subtype 1b. A comparison of NS3 full-length versus domain interface residues for both subtypes revealed a significant difference only for synonymous substitutions (P<0.001). CONCLUSIONS: Our study suggests that the nature of a mismatch nucleotide exchange in NS3 may constitute an important viral genetic factor for response to ketoamide protease inhibitors. Our analysis further suggests that the subtype-specific pace of resistance development seen in clinical trials is not primarily related to differences in genetic diversity in the direct acting antiviral naive population, but rather appears to correlate with the natural frequency of transition mutations characteristic of each subtype.

HIV-1 transmission during early antiretroviral therapy: evaluation of two HIV-1 transmission events in the HPTN 052 prevention study.

In the HPTN 052 study, transmission between HIV-discordant couples was reduced by 96% when the HIV-infected partner received suppressive antiretroviral therapy (ART). We examined two transmission events where the newly infected partner was diagnosed after the HIV-infected partner (index) initiated therapy. We evaluated the sequence complexity of the viral populations and antibody reactivity in the newly infected partner to estimate the dates of transmission to the newly infected partners. In both cases, transmission most likely occurred significantly before HIV-1 diagnosis of the newly infected partner, and either just before the initiation of therapy or before viral replication was adequately suppressed by therapy of the index. This study further strengthens the conclusion about the efficacy of blocking transmission by treating the infected partner of discordant couples. However, this study does not rule out the potential for HIV-1 transmission to occur shortly after initiation of ART, and this should be recognized when antiretroviral therapy is used for HIV-1 prevention.

Central nervous system compartmentalization of HIV-1 subtype C variants early and late in infection in young children.

HIV-1 subtype B replication in the CNS can occur in CD4+ T cells or macrophages/microglia in adults. However, little is known about CNS infection in children or the ability of subtype C HIV-1 to evolve macrophage-tropic variants. In this study, we examined HIV-1 variants in ART-naïve children aged three years or younger to determine viral genotypes and phenotypes associated with HIV-1 subtype C pediatric CNS infection. We examined HIV-1 subtype C populations in blood and CSF of 43 Malawian children with neurodevelopmental delay or acute neurological symptoms. Using single genome amplification (SGA) and phylogenetic analysis of the full-length env gene, we defined four states: equilibrated virus in blood and CSF (n = 20, 47%), intermediate compartmentalization (n = 11, 25%), and two distinct types of compartmentalized CSF virus (n = 12, 28%). Older age and a higher CSF/blood viral load ratio were associated with compartmentalization, consistent with independent replication in the CNS. Cell tropism was assessed using pseudotyped reporter viruses to enter a cell line on which CD4 and CCR5 receptor expression can be differentially induced. In a subset of compartmentalized cases (n = 2, 17%), the CNS virus was able to infect cells with low CD4 surface expression, a hallmark of macrophage-tropic viruses, and intermediate compartmentalization early was associated with an intermediate CD4 entry phenotype. Transmission of multiple variants was observed for 5 children; in several cases, one variant was sequestered within the CNS, consistent with early stochastic colonization of the CNS by virus. Thus we hypothesize two pathways to compartmentalization: early stochastic sequestration in the CNS of one of multiple variants transmitted from mother to child, and emergence of compartmentalized variants later in infection, on average at age 13.5 months, and becoming fully apparent in the CSF by age 18 months. Overall, compartmentalized viral replication in the CNS occurred in half of children by year three.

Accurate sampling and deep sequencing of the HIV-1 protease gene using a Primer ID.

Viruses can create complex genetic populations within a host, and deep sequencing technologies allow extensive sampling of these populations. Limitations of these technologies, however, potentially bias this sampling, particularly when a PCR step precedes the sequencing protocol. Typically, an unknown number of templates are used in initiating the PCR amplification, and this can lead to unrecognized sequence resampling creating apparent homogeneity; also, PCR-mediated recombination can disrupt linkage, and differential amplification can skew allele frequency. Finally, misincorporation of nucleotides during PCR and errors during the sequencing protocol can inflate diversity. We have solved these problems by including a random sequence tag in the initial primer such that each template receives a unique Primer ID. After sequencing, repeated identification of a Primer ID reveals sequence resampling. These resampled sequences are then used to create an accurate consensus sequence for each template, correcting for recombination, allelic skewing, and misincorporation/sequencing errors. The resulting population of consensus sequences directly represents the initial sampled templates. We applied this approach to the HIV-1 protease (pro) gene to view the distribution of sequence variation of a complex viral population within a host. We identified major and minor polymorphisms at coding and noncoding positions. In addition, we observed dynamic genetic changes within the population during intermittent drug exposure, including the emergence of multiple resistant alleles. These results provide an unprecedented view of a complex viral population in the absence of PCR resampling.

HIV-1 Populations in Semen Arise through Multiple Mechanisms.

HIV-1 is present in anatomical compartments and bodily fluids. Most transmissions occur through sexual acts, making virus in semen the proximal source in male donors. We find three distinct relationships in comparing viral RNA populations between blood and semen in men with chronic HIV-1 infection, and we propose that the viral populations in semen arise by multiple mechanisms including: direct import of virus, oligoclonal amplification within the seminal tract, or compartmentalization. In addition, we find significant enrichment of six out of nineteen cytokines and chemokines in semen of both HIV-infected and uninfected men, and another seven further enriched in infected individuals. The enrichment of cytokines involved in innate immunity in the seminal tract, complemented with chemokines in infected men, creates an environment conducive to T cell activation and viral replication. These studies define different relationships between virus in blood and semen that can significantly alter the composition of the viral population at the source that is most proximal to the transmitted virus.

Cross-sectional characterization of HIV-1 env compartmentalization in cerebrospinal fluid over the full disease course.

OBJECTIVES: To characterize HIV-1 env compartmentalization between cerebrospinal fluid (CSF) and peripheral blood plasma over all stages of the HIV-1 disease course, and to determine the relationship between the extent of CSF HIV-1 env compartmentalization and clinical neurologic disease status. DESIGN: Paired blood plasma and CSF specimens were collected from 66 HIV-infected patients cross-sectionally representing all major clinical stages relating to HIV-associated neurologic disease, including primary infection, asymptomatic chronic infection, chronic infection with minor global impairment, and immune deficiency with HIV-associated dementia. METHODS: Heteroduplex tracking assays and bulk sequence analysis targeting the V1/V2, C2-V3, and V4/V5 regions of env were performed to characterize the genetic makeup of complex HIV-1 populations in the cross-sectional blood plasma and CSF specimens. The levels of blood plasma/CSF env compartmentalization were quantified and compared across the different clinical stages of HIV-1 neurologic disease. RESULTS: Blood plasma/CSF env compartmentalization levels varied considerably by disease stage and were generally consistent across all three regions of env characterized. Little or no compartmentalization was observed in non-impaired individuals with primary HIV-1 infection. Compartmentalization levels were elevated in chronically infected patients, but were not significantly different between mildly impaired and non-impaired patients. Patients with HIV-associated dementia showed significantly greater blood plasma/CSF env compartmentalization relative to other groups. CONCLUSION: : Increased CSF compartmentalization of the HIV-1 env gene, which may reflect independent HIV-1 replication and evolution within the central nervous system, is specifically associated with HIV-associated dementia and not the less severe forms of HIV-1 neurologic disease.

Enfuvirtide resistance mutations: impact on human immunodeficiency virus envelope function, entry inhibitor sensitivity, and virus neutralization.

Enfuvirtide (ENF/T-20/Fuzeon), the first human immunodeficiency virus (HIV) entry inhibitor to be licensed, targets a structural intermediate of the entry process. ENF binds the HR1 domain in gp41 after Env has bound CD4, preventing conformational changes needed for membrane fusion. Mutations in HR1 that confer ENF resistance can arise following ENF therapy. ENF resistance mutations were introduced into an R5- and X4-tropic Env to examine their impact on fusion, infection, and sensitivity to different classes of entry inhibitors and neutralizing antibodies. HR1 mutations could reduce infection and fusion efficiency and also delay fusion kinetics, likely accounting for their negative impact on viral fitness. HR1 mutations had minimal effect on virus sensitivity to other classes of entry inhibitors, including those targeting CD4 binding (BMS-806 and a CD4-specific monoclonal antibody [MAb]), coreceptor binding (CXCR4 inhibitor AMD3100 and CCR5 inhibitor TAK-779), or fusion (T-1249), indicating that ENF-resistant viruses can remain sensitive to other entry inhibitors in vivo. Some HR1 mutations conferred increased sensitivity to a subset of neutralizing MAbs that likely target fusion intermediates or with epitopes preferentially exposed following receptor interactions (17b, 48D, 2F5, 4E10, and IgGb12), as well as sera from some HIV-positive individuals. Mechanistically, enhanced neutralization correlated with reduced fusion kinetics, indicating that, in addition to steric constraints, kinetics may also limit virus neutralization by some antibodies. Therefore, escape from ENF comes at a cost to viral fitness and may confer enhanced sensitivity to humoral immunity due to prolonged exposure of epitopes that are not readily accessible in the native Env trimer. Resistance to other entry inhibitors was not observed.