Viral diversity is an obligate consideration in CRISPR/Cas9 designs for targeting the HIV reservoir.
ABSTRACT: RNA-guided CRISPR/Cas9 systems can be designed to mutate or excise the integrated HIV genome from latently infected cells and have therefore been proposed as a curative approach for HIV. However, most studies to date have focused on molecular clones with ideal target site recognition and do not account for target site variability observed within and between patients. For clinical success and broad applicability, guide RNA (gRNA) selection must account for circulating strain diversity and incorporate the within-host diversity of HIV.We identified a set of gRNAs targeting HIV LTR, gag, and pol using publicly available sequences for these genes and ranked gRNAs according to global conservation across HIV-1 group M and within subtypes A-C. By considering paired and triplet combinations of gRNAs, we found triplet sets of target sites such that at least one of the gRNAs in the set was present in over 98% of all globally available sequences. We then selected 59 gRNAs from our list of highly conserved LTR target sites and evaluated in vitro activity using a loss-of-function LTR-GFP fusion reporter. We achieved efficient GFP knockdown with multiple gRNAs and found clustering of highly active gRNA target sites near the middle of the LTR. Using published deep-sequence data from HIV-infected patients, we found that globally conserved sites also had greater within-host target conservation. Lastly, we developed a mathematical model based on varying distributions of within-host HIV sequence diversity and enzyme efficacy. We used the model to estimate the number of doses required to deplete the latent reservoir and achieve functional cure thresholds. Our modeling results highlight the importance of within-host target site conservation. While increased doses may overcome low target cleavage efficiency, inadequate targeting of rare strains is predicted to lead to rebound upon cART cessation even with many doses.Target site selection must account for global and within host viral genetic diversity. Globally conserved target sites are good starting points for design, but multiplexing is essential for depleting quasispecies and preventing viral load rebound upon therapy cessation.
Project description:There is an urgent need for the development of HIV-1 genome eradication strategies that lead to a permanent cure for HIV-1/AIDS. We previously reported that four guide RNAs (gRNAs) targeting HIV-1 long terminal repeats (LTR) effectively eradicated the entire HIV-1 genome. In this study, we sought to identify the best gRNAs targeting HIV-1 LTR and viral structural region and optimize gRNA pairing that can efficiently eradicate the HIV-1 genome.Highly specific gRNAs were designed using bioinformatics tools, and their capacity of guiding CRISPR-associated system 9 to cleave HIV-1 proviral DNA was evaluated using high-throughput HIV-1 luciferase reporter assay and rapid Direct-PCR genotyping.The target seed sequences for each gRNA were cloned into lentiviral vectors. HEK293T cells were cotransfected with a pEcoHIV-NL4-3-firefly-luciferase reporter vector (1?:?20) over lentiviral vectors carrying CRISPR-associated system 9 and single gRNA or various combinations of gRNAs. The EcoHIV DNA cleaving efficiency was evaluated by Direct-PCR genotyping, and the EcoHIV transcription/replication activity was examined by a luciferase reporter assay.Most of the designed gRNAs are effective to eliminate the predicted HIV-1 genome sequence between the selected two target sites. This is evidenced by the presence of PCR genotypic deletion/insertion and the decrease of luciferase reporter activity. In particular, a combination of viral structural gRNAs with LTR gRNAs provided a higher efficiency of genome eradication and an easier approach for PCR genotyping.Our screening strategy can specifically and effectively identify gRNAs targeting HIV-1 LTR and structural region to excise proviral HIV-1 from the host genome.
Project description:Chronic human immunodeficiency virus type 1 (HIV-1) disease is characterized by the retention of provirus within latently infected cells. Anti-HIV-1 CRISPR-Cas9 gene editing is an attractive strategy to excise or inactivate the HIV-1 genome. Recent strategies have focused on designing gRNAs that target the long terminal repeat (LTR) because 5' and 3' LTR symmetry can facilitate proviral excision. However, the promiscuity of CRISPR-Cas9 gene editing system necessitates the investigation of potential off-target effects. Here, potential gRNAs designed from HIV-1 phylogenetic subtypes using the CRISPRseek tool were investigated. Across the LTR, it was found that certain regions show higher human homology than others. When using recommended cutoffs, 96.40% of gRNAs were predicted to have no high probability off-target effects. Given this observation, while high-probability off-target effects are a potential danger, they can be avoided with proper gRNA design.
Project description:The CRISPR/Cas9 system has been proposed as a cure strategy for HIV. However, few published guide RNAs (gRNAs) are predicted to cleave the majority of HIV-1 viral quasispecies (vQS) observed within and among patients. We report the design of a novel pipeline to identify gRNAs that target HIV across a large number of infected individuals. Next generation sequencing (NGS) of LTRs from 269 HIV-1-infected samples in the Drexel CARES Cohort was used to select gRNAs with predicted broad-spectrum activity. In silico, D-LTR-P4-227913 (package of the top 4 gRNAs) accounted for all detectable genetic variation within the vQS of the 269 samples and the Los Alamos National Laboratory HIV database. In silico secondary structure analyses from NGS indicated extensive TAR stem-loop malformations predicted to inactivate proviral transcription, which was confirmed by reduced viral gene expression in TZM-bl or P4R5 cells. Similarly, a high sensitivity in vitro CRISPR/Cas9 cleavage assay showed that the top-ranked gRNA was the most effective at cleaving patient-derived HIV-1 LTRs from five patients. Furthermore, the D-LTR-P4-227913 was predicted to cleave a median of 96.1% of patient-derived sequences from other HIV subtypes. These results demonstrate that the gRNAs possess broad-spectrum cutting activity and could contribute to an HIV cure.
Project description:Viral latency of human immunodeficiency virus type 1 (HIV-1) has become a major hurdle to a cure in the highly effective antiretroviral therapy (ART) era. The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system has successfully been demonstrated to excise or inactivate integrated HIV-1 provirus from infected cells by targeting the long terminal repeat (LTR) region. However, the guide RNAs (gRNAs) have classically avoided transcription factor binding sites (TFBSs) that are readily observed and known to be important in human promoters. Although conventionally thought unfavorable due to potential impact on human promoters, our computational pipeline identified gRNA sequences that were predicted to inactivate HIV-1 transcription by targeting the nuclear factor ?B (NF-?B) binding sites (gNFKB0, gNFKB1) with a high safety profile (lack of predicted or observed human edits) and broad-spectrum activity (predicted coverage of known viral sequences). Genome-wide, unbiased identification of double strand breaks (DSBs) enabled by sequencing (GUIDE-seq) showed that the gRNAs targeting NF-?B binding sites had no detectable CRISPR-induced off-target edits in HeLa cells. 5' LTR-driven HIV-1 transcription was significantly reduced in three HIV-1 reporter cell lines. These results demonstrate a working model to specifically target well-known TFBSs in the HIV-1 LTR that are readily observed in human promoters to reduce HIV-1 transcription with a high-level safety profile and broad-spectrum activity.
Project description:The clustered regularly interspaced short palindromic repeats (CRISPR)-associated Cas9 system has been used to excise the HIV-1 proviral genome from latently infected cells, potentially offering a cure for HIV-infected patients. Recent studies have shown that most published HIV-1 guide RNAs (gRNAs) do not account for the diverse viral quasispecies within or among patients, which continue to diversify with time even in long-term antiretroviral therapy (ART)-suppressed patients. Given this observation, proviral genomes were deep sequenced from 23 HIV-1-infected patients in the Drexel Medicine CNS AIDS Research and Eradication Study cohort at two different visits. Based on the spectrum of integrated proviral DNA polymorphisms observed, three gRNA design strategies were explored: based on the patient's own HIV-1 sequences (personalized), based on consensus sequences from a large sample of patients [broad-spectrum (BS)], or a combination of both approaches. Using a bioinformatic algorithm, the personalized gRNA design was predicted to cut 46 of 48 patient samples at 90% efficiency, whereas the top 4 BS gRNAs (BS4) were predicted to excise provirus from 44 of 48 patient samples with 90% efficiency. Using a mixed design with the top three BS gRNAs plus one personalized gRNA (BS3?+?PS1) resulted in predicted excision of provirus from 45 of 48 patient samples with 90% efficiency. In summary, these studies used an algorithmic design strategy to identify potential BS gRNAs to target a spectrum of HIV-1 long teriminal repeat (LTR) quasispecies for use with a small HIV-1-infected population. This approach should advance CRISPR/Cas9 excision technology taking into account the extensive molecular heterogeneity of HIV-1 that persists in situ after prolonged ART.
Project description:Clustered regularly interspaced short palindromic repeats (CRISPR) CRISPR-associated protein 9 (Cas9), including specific guide RNAs (gRNAs), can excise integrated human immunodeficiency virus type 1 (HIV-1) provirus from host chromosomes. To date, anti-HIV-1 gRNAs have been designed to account for off-target activity, however, they seldom account for genetic variation in the HIV-1 genome within and between patients, which will be crucial for therapeutic application of this technology. This analysis tests the ability of published anti-HIV-1 gRNAs to cleave publicly available patient-derived HIV-1 sequences to inform gRNA design and provides basic computational tools to researchers in the field.
Project description:The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 system is widely explored for sequence-specific attack on HIV-1 proviral DNA. We recently identified dual-guide RNA (dual-gRNA) combinations that can block HIV-1 replication permanently in infected cell cultures and prevent viral escape. Although the gRNAs were designed to target highly conserved viral sequences, their efficacy may be challenged by high genetic variation in the HIV-1 genome. We therefore evaluated the breadth of these dual-gRNA combinations against distinct HIV-1 isolates, including several subtypes. Replication of nearly all virus isolates could be prevented by at least one gRNA combination, which caused inactivation of the proviral genomes and the gradual loss of replication-competent virus over time. The dual-gRNA efficacy was not affected by most single nucleotide (nt) mismatches between gRNA and the viral target. However, 1-nt mismatches at the Cas9 cleavage site and two mismatches anywhere in the viral target sequence significantly reduced the inhibitory effect. Accordingly, sequence analysis of viruses upon breakthrough replication revealed the acquisition of escape mutations in perfectly matching and most 1-nt mismatching targets, but not in targets with a mismatch at the Cas9 cleavage site or with two mismatches. These results demonstrate that combinatorial CRISPR-Cas9 treatment can cure T cells infected by distinct HIV-1 isolates, but even minor sequence variation in conserved viral target sites can affect the efficacy of this strategy. Successful cure attempts against isolates with divergent target sequences may therefore require adaptation of the gRNAs.
Project description:During retroviral RNA encapsidation, two full-length genomic (g) RNAs are selectively incorporated into assembling virions. Packaging involves a cis-acting packaging element (?) within the 5' untranslated region of unspliced HIV-1 RNA genome. However, the mechanism(s) that selects and limits gRNAs for packaging remains uncertain. Using a dual complementation system involving bipartite HIV-1 gRNA, we observed that gRNA packaging is additionally dependent on a cis-acting RNA element, the genomic RNA packaging enhancer (GRPE), found within the gag p1-p6 domain and overlapping the Gag-Pol ribosomal frameshift signal. Deleting or disrupting the two conserved GRPE stem loops diminished gRNA packaging and infectivity >50-fold, while deleting gag sequences between ? and GRPE had no effect. Downregulating the translation termination factor eRF1 produces defective virus particles containing 20 times more gRNA. Thus, only the HIV-1 RNAs employed for Gag-Pol translation may be specifically selected for encapsidation, possibly explaining the limitation of two gRNAs per virion.
Project description:The CRISPR/Cas9 system provides a novel and promising tool for editing the HIV-1 proviral genome. We designed RNA-guided CRISPR/Cas9 targeting the HIV-1 regulatory genes tat and rev with guide RNAs (gRNA) selected from each gene based on CRISPR specificity and sequence conservation across six major HIV-1 subtypes. Each gRNA was cloned into lentiCRISPRv2 before co-transfection to create a lentiviral vector and transduction into target cells. CRISPR/Cas9 transduction into 293?T and HeLa cells stably expressing Tat and Rev proteins successfully abolished the expression of each protein relative to that in non-transduced and gRNA-absent vector-transduced cells. Tat functional assays showed significantly reduced HIV-1 promoter-driven luciferase expression after tat-CRISPR transduction, while Rev functional assays revealed abolished gp120 expression after rev-CRISPR transduction. The target gene was mutated at the Cas9 cleavage site with high frequency and various indel mutations. Conversely, no mutations were detected at off-target sites and Cas9 expression had no effect on cell viability. CRISPR/Cas9 was further tested in persistently and latently HIV-1-infected T-cell lines, in which p24 levels were significantly suppressed even after cytokine reactivation, and multiplexing all six gRNAs further increased efficiency. Thus, the CRISPR/Cas9 system targeting HIV-1 regulatory genes may serve as a favorable means to achieve functional cures.
Project description:BACKGROUND:CRISPR/Cas9 gene editing has become a revolutionary technique for crop improvement as it can facilitate fast and efficient genetic changes without the retention of transgene components in the final plant line. Lack of robust bioinformatics tools to facilitate the design of highly specific functional guide RNAs (gRNAs) and prediction of off-target sites in wheat is currently an obstacle to effective application of CRISPR technology to wheat improvement. DESCRIPTION:We have developed a web-based bioinformatics tool to design specific gRNAs for genome editing and transcriptional regulation of gene expression in wheat. A collaborative study between the Broad Institute and Microsoft Research used large-scale empirical evidence to devise algorithms (Doech et al., 2016, Nature Biotechnology 34, 184-191) for predicting the on-target activity and off-target potential of CRISPR/SpCas9 (Streptococcus pyogenes Cas9). We applied these prediction models to determine on-target specificity and potential off-target activity for individual gRNAs targeting specific loci in the wheat genome. The genome-wide gRNA mappings and the corresponding Doench scores predictive of the on-target and off-target activities were used to create a gRNA database which was used as a data source for the web application termed WheatCRISPR. CONCLUSION:The WheatCRISPR tool allows researchers to browse all possible gRNAs targeting a gene or sequence of interest and select effective gRNAs based on their predicted high on-target and low off-target activity scores, as well as other characteristics such as position within the targeted gene. It is publicly available at https://crispr.bioinfo.nrc.ca/WheatCrispr/ .