New Approaches to Multi-Parametric HIV-1 Genetics Using Multiple Displacement Amplification: Determining the What, How, and Where of the HIV-1 Reservoir

Development of potential HIV-1 curative interventions requires accurate characterization of the proviral reservoir, defined as host-integrated viral DNA genomes that drive rebound of viremia upon halting ART (antiretroviral therapy). Evaluation of such interventions necessitates methods capable of pinpointing the rare, genetically intact, replication-competent proviruses within a background of defective proviruses. This evaluation can be achieved by identifying the distinct integration sites of intact proviruses within host genomes and monitoring the dynamics of these proviruses and host cell lineages over longitudinal sampling. Until recently, molecular genetic approaches at the single proviral level have been generally limited to one of a few metrics, such as proviral genome sequence/intactness, host-proviral integration site, or replication competency. New approaches, taking advantage of MDA (multiple displacement amplification) for WGA (whole genome amplification), have enabled multiparametric proviral characterization at the single-genome level, including proviral genome sequence, host-proviral integration site, and phenotypic characterization of the host cell lineage, such as CD4 memory subset and antigen specificity. In this review, we will examine the workflow of MDA-augmented molecular genetic approaches to study the HIV-1 reservoir, highlighting technical advantages and flexibility. We focus on a collection of recent studies in which investigators have used these approaches to comprehensively characterize intact and defective proviruses from donors on ART, investigate mechanisms of elite control, and define cell lineage identity and antigen specificity of infected CD4+ T cell clones. The highlighted studies exemplify how these approaches and their future iterations will be key in defining the targets and evaluating the impacts of HIV curative interventions.

A target enrichment high throughput sequencing system for characterization of BLV whole genome sequence, integration sites, clonality and host SNP

Bovine leukemia virus (BLV) is an oncogenic retrovirus which induces malignant lymphoma termed enzootic bovine leukosis (EBL) after a long incubation period. Insertion sites of the BLV proviral genome as well as the associations between disease progression and polymorphisms of the virus and host genome are not fully understood. To characterize the biological coherence between virus and host, we developed a DNA-capture-seq approach, in which DNA probes were used to efficiently enrich target sequence reads from the next-generation sequencing (NGS) library. In addition, enriched reads can also be analyzed for detection of proviral integration sites and clonal expansion of infected cells since the reads include chimeric reads of the host and proviral genomes. To validate this DNA-capture-seq approach, a persistently BLV-infected fetal lamb kidney cell line (FLK-BLV), four EBL tumor samples and four non-EBL blood samples were analyzed to identify BLV integration sites. The results showed efficient enrichment of target sequence reads and oligoclonal integrations of the BLV proviral genome in the FLK-BLV cell line. Moreover, three out of four EBL tumor samples displayed multiple integration sites of the BLV proviral genome, while one sample displayed a single integration site. In this study, we found the evidence for the first time that the integrated provirus defective at the 5′ end was present in the persistent lymphocytosis cattle. The efficient and sensitive identification of BLV variability, integration sites and clonal expansion described in this study provide support for use of this innovative tool for understanding the detailed mechanisms of BLV infection during the course of disease progression.

CRISPR-Cas9 as a curative drug for chronic viral infection

The innovation of CRISPR-Cas9 has single-handedly revolutionized biotechnology by enabling efficient and specific cutting of DNA. CRISPR-Cas9 approaches are promising not only to targetthe human genome but also DNA of pathogenic viruses, which coincidentally is the canonical function in its bacterial origin. Since 2014, a myriad of studies has proven the efficacy of CRISPR-Cas9 treatment to cleave viral DNA intermediates in vitro. One of the most widely targeted is theproviral genome of human immunodeficiency virus type-1 (HIV-1). The disease burden of HIV-1 is massive—the infection is incurable and has remained a pandemic for over four decades. Integrated HIV-1 provirus inside the human genome causes viral persistence inside latent cellular reservoirs, eluding antiretroviral therapy (ART) and sterilizing cure. Specific targeting anddisruption of HIV-1 proviral genome is necessary to achieve viral clearance, which can be achieved with CRISPR-Cas9. Here, we review the features and up to date evidence of CRISPRCas9 to target the HIV-1 proviral genome and suppress viral replication. We will also discuss potential CRISPR/Cas9 delivery methods in vivo, combination with other gene editing modalities and other therapeutic approaches, to bring gene editing-based HIV-1 cure closer into clinical use.

A dynamic i-motif with a duplex stem-loop in the long terminal repeat promoter of the HIV-1 proviral genome modulates viral transcription

I-motifs are non-canonical nucleic acids structures characterized by intercalated H-bonds between hemi-protonated cytosines. Evidence on the involvement of i-motif structures in the regulation of cellular processes in human cells has been consistently growing in the recent years. However, i-motifs within non-human genomes have never been investigated. Here, we report the characterization of i-motifs within the long terminal repeat (LTR) promoter of the HIV-1 proviral genome. Biophysical and biochemical analysis revealed formation of a predominant i-motif with an unprecedented loop composition. One-dimensional nuclear magnetic resonance investigation demonstrated formation of three G-C H-bonds in the long loop, which likely improve the structure overall stability. Pull-down experiments combined with mass spectrometry and protein crosslinking analysis showed that the LTR i-motif is recognized by the cellular protein hnRNP K, which induced folding at physiological conditions. In addition, hnRNP K silencing resulted in an increased LTR promoter activity, confirming the ability of the protein to stabilize the i-motif-forming sequence, which in turn regulates the LTR-mediated HIV-1 transcription. These findings provide new insights into the complexity of the HIV-1 virus and lay the basis for innovative antiviral drug design, based on the possibility to selectively recognize and target the HIV-1 LTR i-motif.

First Complete Genome Sequence of a Simian Foamy Virus Isolate from a Cynomolgus Macaque

We report here the first complete proviral genome sequence (DDBJ/ENA/GenBank accession no. LC094267) of a simian foamy virus, SFVmfa/Cy5061, isolated from a cynomolgus macaque ( Macaca fascicularis ). This proviral genome consists of 12,965 nucleotides and has five open reading frames, gag , pol , env , tas , and bet , as with other foamy viruses.