Computational analysis of cas proteins unlocks new potential in HIV-1 targeted gene therapy.

Introduction: The human immunodeficiency virus type 1 (HIV-1) pandemic has been slowed with the advent of anti-retroviral therapy (ART). However, ART is not a cure and as such has pushed the disease into a chronic infection. One potential cure strategy that has shown promise is the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas gene editing system. It has recently been shown to successfully edit and/or excise the integrated provirus from infected cells and inhibit HIV-1 in vitro, ex vivo, and in vivo. These studies have primarily been conducted with SpCas9 or SaCas9. However, additional Cas proteins are discovered regularly and modifications to these known proteins are being engineered. The alternative Cas molecules have different requirements for protospacer adjacent motifs (PAMs) which impact the possible targetable regions of HIV-1. Other modifications to the Cas protein or gRNA handle impact the tolerance for mismatches between gRNA and the target. While reducing off-target risk, this impacts the ability to fully account for HIV-1 genetic variability. Methods: This manuscript strives to examine these parameter choices using a computational approach for surveying the suitability of a Cas editor for HIV-1 gene editing. The Nominate, Diversify, Narrow, Filter (NDNF) pipeline measures the safety, broadness, and effectiveness of a pool of potential gRNAs for any PAM. This technique was used to evaluate 46 different potential Cas editors for their HIV therapeutic potential. Results: Our examination revealed that broader PAMs that improve the targeting potential of editors like SaCas9 and LbCas12a have larger pools of useful gRNAs, while broader PAMs reduced the pool of useful SpCas9 gRNAs yet increased the breadth of targetable locations. Investigation of the mismatch tolerance of Cas editors indicates a 2-missmatch tolerance is an ideal balance between on-target sensitivity and off-target specificity. Of all of the Cas editors examined, SpCas-NG and SPRY-Cas9 had the highest number of overall safe, broad, and effective gRNAs against HIV. Discussion: Currently, larger proteins and wider PAMs lead to better targeting capacity. This implies that research should either be targeted towards delivering longer payloads or towards increasing the breadth of currently available small Cas editors. With the discovery and adoption of additional Cas editors, it is important for researchers in the HIV-1 gene editing field to explore the wider world of Cas editors.

Gene and Base Editing as a Therapeutic Option for Cystic Fibrosis-Learning from Other Diseases.

Cystic fibrosis (CF) is a monogenic autosomal recessive disorder caused by mutations in the CFTR gene. There are at least 346 disease-causing variants in the CFTR gene, but effective small-molecule therapies exist for only ~10% of them. One option to treat all mutations is CFTR cDNA-based therapy, but clinical trials to date have only been able to stabilise rather than improve lung function disease in patients. While cDNA-based therapy is already a clinical reality for a number of diseases, some animal studies have clearly established that precision genome editing can be significantly more effective than cDNA addition. These observations have led to a number of gene-editing clinical trials for a small number of such genetic disorders. To date, gene-editing strategies to correct CFTR mutations have been conducted exclusively in cell models, with no in vivo gene-editing studies yet described. Here, we highlight some of the key breakthroughs in in vivo and ex vivo gene and base editing in animal models for other diseases and discuss what might be learned from these studies in the development of editing strategies that may be applied to cystic fibrosis as a potential therapeutic approach. There are many hurdles that need to be overcome, including the in vivo delivery of editing machinery or successful engraftment of ex vivo-edited cells, as well as minimising potential off-target effects. However, a successful proof-of-concept study for gene or base editing in one or more of the available CF animal models could pave the way towards a long-term therapeutic strategy for this disease.

Rapid and Simple Screening of CRISPR Guide RNAs (gRNAs) in Cultured Cells Using Adeno-Associated Viral (AAV) Vectors.

Genome editing reagents including the recently introduced CRISPR/Cas9 system have become established and widely used molecular tools to answer fundamental biological questions and to target and treat genetic diseases. The CRISPR system, originally derived from bacteria and archaea, can be delivered into cells using different techniques, comprising (1) transfection of mRNA or plasmid DNA, (2) electroporation of plasmid DNA or the Cas9 protein in a complex with a g(uide)RNA, or (3) use of nonviral or viral vectors. Among the latter, Adeno-associated viruses (AAVs) are particularly attractive owing to many favorable traits: (1) their apathogenicity and episomal persistence, (2) the ease of virus production and purification, (3) the safe handling under lowest biosafety level 1 conditions, and (4) the availability of numerous natural serotypes and synthetic capsid variants with distinct cell specificities. Here, we describe a fast and simple protocol for small-scale packaging of CRISPR/Cas9 components into AAV vectors. To showcase its potential, we employ this method for screening of gRNAs targeting the murine miR-122 locus in Hepa1-6 cells (using AAV serotype 6, AAV6) or the 5'LTR of the human immunodeficiency virus (HIV) in HeLaP4-NLtr cells (using a synthetic AAV9 variant). We furthermore provide a detailed protocol for large-scale production of purified AAV/CRISPR vector stocks that permit higher cleavage efficiencies in vitro and are suitable for direct in vivo applications.

Design and Assembly of CRISPR/Cas9 Lentiviral and rAAV Vectors for Targeted Genome Editing.

Clustered regularly interspaced short palindromic repeat (CRISPR/Cas) system has emerged as an extremely useful tool for biological research and as a potential technology for gene therapy approaches. CRISPR/Cas mediated genome editing can be used to easily and efficiently modify endogenous genes in a large variety of cells and organisms. Furthermore, a modified version of the Cas9 nuclease has been developed that can be used for regulation of endogenous gene expression and labeling of genomic loci, among other applications. This chapter provides an introduction to the basis of the technology and a detail protocol for the most classic application: gene inactivation by CRISPR/Cas9 nuclease system from Streptococcus pyogenes. This workflow can be easily adapted for other CRISPR systems and applications.

Current progress in CRISPR-based diagnostic platforms.

The CRISPR-Cas system is a key technology for genome editing and regulation in a wide range of organisms and cell types. Recently, CRISPR-Cas-based diagnostic platform has shown idealistic properties for pathogen detection. Integrating the CRISPR-Cas platform along with lateral flow system allows rapid, sensitive, specific, cheap, and reliable diagnostic. It has the potential to be in frontline for not only pathogen detection during the epidemic outbreak, but also cancer, and genetic diseases.

Applying Human ADAR1p110 and ADAR1p150 for Site-Directed RNA Editing-G/C Substitution Stabilizes GuideRNAs against Editing.

Site-directed RNA editing is an approach to reprogram genetic information at the RNA level. We recently introduced a novel guideRNA that allows for the recruitment of human ADAR2 to manipulate genetic information. Here, we show that the current guideRNA design is already able to recruit another human deaminase, ADAR1, in both isoforms, p110 and p150. However, further optimization seems necessary as the current design is less efficient for ADAR1 isoforms. Furthermore, we describe hotspots at which the guideRNA itself is edited and show a way to circumvent this auto-editing without losing editing efficiency at the target. Both findings are important for the advancement of site-directed RNA editing as a tool in basic biology or as a platform for therapeutic editing.