Cell-penetrating peptide-mediated delivery of TALEN proteins via bioconjugation for genome engineering

The Future of Gene Therapy: A Review of In Vivo and Ex Vivo Delivery Methods for Genome Editing-Based Therapies

The development of gene therapy based on genome editing has opened up new possibilities for the treatment of human genetic disorders. This field has developed rapidly over the past few decades, some genome editing-based therapies are already in phase 3 clinical trials. However, there are several challenges to be addressed before widespread adoption of gene editing therapy becomes possible. The main obstacles in the development of such therapy are safety and efficiency, so one of the biggest issues is the delivery of genetic constructs to patient cells. Approaches in genetic cargo delivery divide into ex vivo and in vivo, which are suitable for different cases. The ex vivo approach is mainly used to edit blood cells, improve cancer therapy, and treat infectious diseases. To edit cells in organs researches choose in vivo approach. For each approach, there is a fairly large set of methods, but, unfortunately, these methods are not universal in their effectiveness and safety. The focus of this article is to discuss the current status of in vivo and ex vivo delivery methods used in genome editing-based therapy. We will discuss the main methods employed in these approaches and their applications in current gene editing treatments under development.

Excision of HIV-1 Provirus in Human Primary Cells with Nanocapsuled TALEN Proteins

Despite the tremendous success of combination antiretroviral therapy (ART) to treat human immunodeficiency virus (HIV) infection, the durability and persistence of latent reservoirs of HIV-infected cells in HIV-infected patients remain obstacles to achieving HIV cure. While technically challenging, the most direct means to eradicate latent reservoirs is to destroy the HIV provirus, thus ensuring that HIV virions are not produced while preserving resident cells. Transcription activator-like effector nucleases (TALEN)─a genome editing method with high DNA targeting efficiency─have been investigated as a potential gene therapy by disrupting the HIV-1 coreceptor CCR5 genes in HIV target cells or HIV proviral DNA in infected cells. However, the transduction and editing efficiencies are low in primary cells and vary by cell type. Using a nanotechnology platform, which we term nanocapsules, the TALEN protein can be effectively delivered into primary cells and escape from endosome/lysosome sequestration. We report that TALEN nanocapsules can effectively mutagenize the HIV-1 proviral DNA integrated into two primary HIV-1 reservoir cells─T cells and macrophages, such that replication and/or reactivation from latency is aborted. We envision that this study provides a useful platform to deliver a wide range of DNA-modifying enzymes for effective HIV therapy.

AAV-based in vivo gene therapy for neurological disorders

Recent advancements in gene supplementation therapy are expanding the options for the treatment of neurological disorders. Among the available delivery vehicles, adeno-associated virus (AAV) is often the favoured vector. However, the results have been variable, with some trials dramatically altering the course of disease whereas others have shown negligible efficacy or even unforeseen toxicity. Unlike traditional drug development with small molecules, therapeutic profiles of AAV gene therapies are dependent on both the AAV capsid and the therapeutic transgene. In this rapidly evolving field, numerous clinical trials of gene supplementation for neurological disorders are ongoing. Knowledge is growing about factors that impact the translation of preclinical studies to humans, including the administration route, timing of treatment, immune responses and limitations of available model systems. The field is also developing potential solutions to mitigate adverse effects, including AAV capsid engineering and designs to regulate transgene expression. At the same time, preclinical research is addressing new frontiers of gene supplementation for neurological disorders, with a focus on mitochondrial and neurodevelopmental disorders. In this Review, we describe the current state of AAV-mediated neurological gene supplementation therapy, including critical factors for optimizing the safety and efficacy of treatments, as well as unmet needs in this field.

Gene Editing of the Follicle-Stimulating Hormone Gene to Sterilize Channel Catfish, Ictalurus punctatus, Using a Modified Transcription Activator-like Effector Nuclease Technology with Electroporation

Follicle-stimulating hormone (fsh) plays an important role in sexual maturation in catfish. Knocking out the fsh gene in the fish zygote should suppress the reproduction of channel catfish (Ictalurus punctatus). In this study, transcription activator-like effector nuclease (TALEN) plasmids targeting the fsh gene were electroporated into fertilized eggs with the standard double electroporation technique. Targeted fsh cleavage efficiency was 63.2% in P1fsh-knockout catfish. Ten of fifteen (66.7%) control pairs spawned, and their eggs had 32.3–74.3% average hatch rates in 2016 and 2017. Without hormone therapy, the spawning rates of P1 mutants ranged from 33.3 to 40.0%, with an average egg hatching rate of 0.75%. After confirmation of the low fertility of P1 mutants in 2016, human chorionic gonadotropin (HCG) hormone therapy improved the spawning rates by 80% for female mutants and 88.9% for male mutants, and the mean hatch rate was 35.0% for F1 embryos, similar to that of the controls (p > 0.05). Polymerase chain reaction (PCR) identification showed no potential TALEN plasmid integration into the P1 channel catfish genome. Neither the P1 nor the F1 mutant fish showed any noticeable changes in in body weight, survival rate, and hatching rate when the reproductive gene was knocked out. F1 families had a mean inheritance rate of 50.3%. The results brought us one step closer to allowing implementation of certain genetic techniques to aquaculture and fisheries management, while essentially eliminating the potential environment risk posed by transgenic, hybrid, and exotic fish as well as domestic fish.

Transgene-free genome editing and RNAi ectopic application in fruit trees: Potential and limitations

For the past fifteen years, significant research advances in sequencing technology have led to a substantial increase in fruit tree genomic resources and databases with a massive number of OMICS datasets (transcriptomic, proteomics, metabolomics), helping to find associations between gene(s) and performance traits. Meanwhile, new technology tools have emerged for gain- and loss-of-function studies, specifically in gene silencing and developing tractable plant models for genetic transformation. Additionally, innovative and adapted transformation protocols have optimized genetic engineering in most fruit trees. The recent explosion of new gene-editing tools allows for broadening opportunities for functional studies in fruit trees. Yet, the fruit tree research community has not fully embraced these new technologies to provide large-scale genome characterizations as in cereals and other staple food crops. Instead, recent research efforts in the fruit trees appear to focus on two primary translational tools: transgene-free gene editing via Ribonucleoprotein (RNP) delivery and the ectopic application of RNA-based products in the field for crop protection. The inherent nature of the propagation system and the long juvenile phase of most fruit trees are significant justifications for the first technology. The second approach might have the public favor regarding sustainability and an eco-friendlier environment for a crop production system that could potentially replace the use of chemicals. Regardless of their potential, both technologies still depend on the foundational knowledge of gene-to-trait relationships generated from basic genetic studies. Therefore, we will discuss the status of gene silencing and DNA-based gene editing techniques for functional studies in fruit trees followed by the potential and limitations of their translational tools (RNP delivery and RNA-based products) in the context of crop production.

Genome editing via non-viral delivery platforms: current progress in personalized cancer therapy

Cancer is a severe disease that substantially jeopardizes global health. Although considerable efforts have been made to discover effective anti-cancer therapeutics, the cancer incidence and mortality are still growing. The personalized anti-cancer therapies present themselves as a promising solution for the dilemma because they could precisely destroy or fix the cancer targets based on the comprehensive genomic analyses. In addition, genome editing is an ideal way to implement personalized anti-cancer therapy because it allows the direct modification of pro-tumor genes as well as the generation of personalized anti-tumor immune cells. Furthermore, non-viral delivery system could effectively transport genome editing tools (GETs) into the cell nucleus with an appreciable safety profile. In this manuscript, the important attributes and recent progress of GETs will be discussed. Besides, the laboratory and clinical investigations that seek for the possibility of combining non-viral delivery systems with GETs for the treatment of cancer will be assessed in the scope of personalized therapy.

Strategies for High-Efficiency Mutation Using the CRISPR/Cas System

Clustered regularly interspaced short palindromic repeats (CRISPR)-associated systems have revolutionized traditional gene-editing tools and are a significant tool for ameliorating gene defects. Characterized by high target specificity, extraordinary efficiency, and cost-effectiveness, CRISPR/Cas systems have displayed tremendous potential for genetic manipulation in almost any organism and cell type. Despite their numerous advantages, however, CRISPR/Cas systems have some inherent limitations, such as off-target effects, unsatisfactory efficiency of delivery, and unwanted adverse effects, thereby resulting in a desire to explore approaches to address these issues. Strategies for improving the efficiency of CRISPR/Cas-induced mutations, such as reducing off-target effects, improving the design and modification of sgRNA, optimizing the editing time and the temperature, choice of delivery system, and enrichment of sgRNA, are comprehensively described in this review. Additionally, several newly emerging approaches, including the use of Cas variants, anti-CRISPR proteins, and mutant enrichment, are discussed in detail. Furthermore, the authors provide a deep analysis of the current challenges in the utilization of CRISPR/Cas systems and the future applications of CRISPR/Cas systems in various scenarios. This review not only serves as a reference for improving the maturity of CRISPR/Cas systems but also supplies practical guidance for expanding the applicability of this technology.

Cell-Penetrating Botulinum Neurotoxin Type A With Improved Cellular Uptake and Therapeutic Index

Botulinum neurotoxin serotype A (BoNTA) is widely used for treating neuromuscular disorders. Despite of the various marketed products, BoNTA is known to have small therapeutic index ranging from 5 to 15. In the present study, we designed and characterized engineered BoNTA proteins with fusion of cell-penetrating peptides (CPPs). We have shown that CPPs, particularly a recently reported zinc finger protein could improve the cellular uptake and intramuscular therapeutic index of BoNTA. Our study has shed the light on developing next-generation neuromuscular modulators using CPP fusion.

Utilization of CRISPR-Mediated Tools for Studying Functional Genomics in Hematological Malignancies: An Overview on the Current Perspectives, Challenges, and Clinical Implications

Hematological malignancies (HM) are a group of neoplastic diseases that are usually heterogenous in nature due to the complex underlying genetic aberrations in which collaborating mutations enable cells to evade checkpoints that normally safeguard it against DNA damage and other disruptions of healthy cell growth. Research regarding chromosomal structural rearrangements and alterations, gene mutations, and functionality are currently being carried out to understand the genomics of these abnormalities. It is also becoming more evident that cross talk between the functional changes in transcription and proteins gives the characteristics of the disease although specific mutations may induce unique phenotypes. Functional genomics is vital in this aspect as it measures the complete genetic change in cancerous cells and seeks to integrate the dynamic changes in these networks to elucidate various cancer phenotypes. The advent of CRISPR technology has indeed provided a superfluity of benefits to mankind, as this versatile technology enables DNA editing in the genome. The CRISPR-Cas9 system is a precise genome editing tool, and it has revolutionized methodologies in the field of hematology. Currently, there are various CRISPR systems that are used to perform robust site-specific gene editing to study HM. Furthermore, experimental approaches that are based on CRISPR technology have created promising tools for developing effective hematological therapeutics. Therefore, this review will focus on diverse applications of CRISPR-based gene-editing tools in HM and its potential future trajectory. Collectively, this review will demonstrate the key roles of different CRISPR systems that are being used in HM, and the literature will be a representation of a critical step toward further understanding the biology of HM and the development of potential therapeutic approaches.

CRISPR/Cas9 Plasmid Delivery Through the CPP: PepFect14

Gene editing is increasing its popularity day by day especially as an essential tool for the research. It is based on two recombination mechanisms in mammalian cells: nonhomologous end-joining (NHEJ) and homology-directed repair (HDR). The first one can be used to silence a specific gene or a portion of it and the second one to insert new DNA, in presence of a donor template, in a targeted position in the genome. In order to exploit one of these two mechanisms, three major targeted nucleases have been developed: zinc-finger nucleases (ZFN), transcription activator-like effector nucleases (TALEN), and CRISPR-Cas (clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein). The last one seems to be the most promising tool among the others for gene editing. By using the properties and versatility of the Cell Penetrating Peptide (CPP) PepFect14, we developed a protocol to deliver a plasmid encoding for CRISPR-Cas9 and Green Fluorescent Protein (GFP) in BHM cell line expressing luciferase (Bomirsky Hamster Melanoma pLuc). Aiming to knocking down the luciferase gene in the cell line and to expressing GFP. Having two fast and easy read-outs of the plasmid's activity at the same time. Furthermore, by labeling the CRISPR plasmid with Cy5 it is possible to have a visual confirmation of the cellular uptake of the pDNA/CPP complex, via fluorescent microscopy, as described.

Proteins, Small Peptides and Other Signaling Molecules Identified as Inconspicuous but Possibly Important Players in Microspores Reprogramming Toward Embryogenesis

In this review, we describe and integrate the latest knowledge on the signaling role of proteins and peptides in the stress-induced microspore embryogenesis (ME) in some crop plants with agricultural importance (i.e., oilseed rape, tobacco, barley, wheat, rice, triticale, rye). Based on the results received from the most advanced omix analyses, we have selected some inconspicuous but possibly important players in microspores reprogramming toward embryogenic development. We provide an overview of the roles and downstream effect of stress-related proteins (e.g., β-1,3-glucanases, chitinases) and small signaling peptides, especially cysteine—(e.g., glutathione, γ-thionins, rapid alkalinization factor, lipid transfer, phytosulfokine) and glycine-rich peptides and other proteins (e.g., fasciclin-like arabinogalactan protein) on acclimation ability of microspores and the cell wall reconstruction in a context of ME induction and haploids/doubled haploids (DHs) production. Application of these molecules, stimulating the induction and proper development of embryo-like structures and green plant regeneration, brings significant improvement of the effectiveness of DHs procedures and could result in its wider incorporation on a commercial scale. Recent advances in the design and construction of synthetic peptides–mainly cysteine-rich peptides and their derivatives–have accelerated the development of new DNA-free genome-editing techniques. These new systems are evolving incredibly fast and soon will find application in many areas of plant science and breeding.

Targeted drug delivery strategies for precision medicines

Progress in the field of precision medicine has changed the landscape of cancer therapy. Precision medicine is propelled by technologies that enable molecular profiling, genomic analysis, and optimized drug design to tailor treatments for individual patients. Although precision medicines have resulted in some clinical successes, the use of many potential therapeutics has been hindered by pharmacological issues, including toxicities and drug resistance. Drug delivery materials and approaches have now advanced to a point where they can enable the modulation of a drug's pharmacological parameters without compromising the desired effect on molecular targets. Specifically, they can modulate a drug's pharmacokinetics, stability, absorption, and exposure to tumours and healthy tissues, and facilitate the administration of synergistic drug combinations. This Review highlights recent progress in precision therapeutics and drug delivery, and identifies opportunities for strategies to improve the therapeutic index of cancer drugs, and consequently, clinical outcomes.

Advances in peptide-mediated cytosolic delivery of proteins

The number of protein-based drugs is exponentially increasing. However, development of protein therapeutics against intracellular targets is hampered by the lack of efficient cytosolic delivery strategies. In recent years, the use of cell-penetrating peptides has been proposed as a strategy to promote protein internalization. In this article, we provide the reader with a succinct update on the strategies exploited to enable peptide-mediated cytosolic delivery of proteins. First, we analyse the various methods available for delivery. We then describe the most popular and the in vitro assays designed to assess the intracellular distribution of protein cargo.

Identification of efficient prokaryotic cell-penetrating peptides with applications in bacterial biotechnology

In bacterial biotechnology, instead of producing functional proteins from plasmids, it is often necessary to deliver functional proteins directly into live cells for genetic manipulation or physiological modification. We constructed a library of cell-penetrating peptides (CPPs) capable of delivering protein cargo into bacteria and developed an efficient delivery method for CPP-conjugated proteins. We screened the library for highly efficient CPPs with no significant cytotoxicity in Escherichia coli and developed a model for predicting the penetration efficiency of a query peptide, enabling the design of new and efficient CPPs. As a proof-of-concept, we used the CPPs for plasmid curing in E. coli and marker gene excision in Methylomonas sp. DH-1. In summary, we demonstrated the utility of CPPs in bacterial engineering. The use of CPPs would facilitate bacterial biotechnology such as genetic engineering, synthetic biology, metabolic engineering, and physiology studies.

Lee et al. construct a cell-penetrating peptides (CPP) library and identify CPPs that can penetrate bacterial cells with minimum or no impact on cell viability. For the identified top CPP candidates, their abilities to deliver macromolecules such as I-SceI and Cre recombinase proteins to bacteria are evaluated as proof-of-concept studies for potential applications.

Multivalent dextran hybrids for efficient cytosolic delivery of biomolecular cargoes

The development of novel biotherapeutics based on peptides and proteins is often limited to extracellular targets, because these molecules are not able to reach the cytosol. In recent years, several approaches were proposed to overcome this limitation. A plethora of cell-penetrating peptides (CPPs) was developed for cytoplasmic delivery of cell-impermeable cargo molecules. For many CPPs, multimerization or multicopy arrangement on a scaffold resulted in improved delivery but also higher cytotoxicity. Recently, we introduced dextran as multivalent, hydrophilic polysaccharide scaffold for multimerization of cell-targeting cargoes. Here, we investigated covalent conjugation of a CPP to dextran in multiple copies and assessed the ability of resulted molecular hybrid to enter the cytoplasm of mammalian cells without largely compromising cell viability. As a CPP, we used a novel, low-toxic cationic amphiphilic peptide L17E derived from M-lycotoxin. Here, we show that cell-penetrating properties of L17E are retained upon multivalent covalent linkage to dextran. Dextran-L17E efficiently mediated cytoplasmic translocation of an attached functional peptide and a peptide nucleic acid (PNA). Moreover, a synthetic route was established to mask the lysine side chains of L17E with a photolabile protecting group thus opening avenues for light-triggered activation of cellular uptake.

Aspects of Gene Therapy Products Using Current Genome-Editing Technology in Japan

The development of genome-editing technology could lead to breakthrough gene therapy. Genome editing has made it possible to easily knock out or modify a target gene, while current gene therapy using a virus vector or plasmid hampering modification with respect to gene replacement therapies. Clinical development using these genome-editing tools is progressing rapidly. However, it is also becoming clear that there is a possibility of unintended gene sequence modification or deletion, or the insertion of undesired genes, or the selection of cells with abnormalities in the cancer suppressor gene p53; these unwanted actions are not possible with current gene therapy. The Science Board of the Pharmaceuticals and Medical Devices Agency of Japan has compiled a report on the expected aspects of such genome-editing technology and the risks associated with it. This article summarizes the history of that discussion and compares the key concepts with information provided by other regulatory authorities.

Delivery Approaches for Therapeutic Genome Editing and Challenges

Impressive therapeutic advances have been possible through the advent of zinc-finger nucleases and transcription activator-like effector nucleases. However, discovery of the more efficient and highly tailorable clustered regularly interspaced short palindromic repeats (CRISPR) and associated proteins (Cas9) has provided unprecedented gene-editing capabilities for treatment of various inherited and acquired diseases. Despite recent clinical trials, a major barrier for therapeutic gene editing is the absence of safe and effective methods for local and systemic delivery of gene-editing reagents. In this review, we elaborate on the challenges and provide practical considerations for improving gene editing. Specifically, we highlight issues associated with delivery of gene-editing tools into clinically relevant cells.

Tumor microenvironment targeting with dual stimuli-responsive nanoparticles based on small heat shock proteins for antitumor drug delivery

Tumour microenvironment (TME)-targeting nanoparticles (NPs) were developed based on Methanococcus jannaschii small heat shock proteins (Mj-sHSPs). Transactivator of transcription (TAT) were modified on the surface of Mj-sHSPs (T-HSPs) to enhance their cellular internalization ability (CIA), and a pH/enzyme dual sensitive PEG/N-(2-aminoethyl)piperidine-hyaluronic acid (PAHA) coat was combined with T-HSPs (PT-HSPs). PT-HSP NPs exhibited multi-layered morphologies and good stability against plasma protein adsorption. The release of paclitaxel (PTX) from PT-HSP NPs was negligible at physiological pH. Under conditions similar to the TME (acidic pH and overexpressed hyaluronidase (HAase)), the PAHA coat deshielded from PT-HSP NPs because of two factors: charge reversal and HAase degradation. Once the PAHA coat was shed, the size of the NPs decreased; its surface charge became positive; and remarkable drug release was triggered. Cellular experiments indicated that the CIA of PT-HSPs was shielded in the microenvironment of normal cells and recovered in that of tumour cells. In vivo imaging exhibited that the PT-HSP NPs had an impressive tumour targeting ability compared with the uncoated controls. The antitumor efficacy in vivo demonstrated that tumour-bearing mice treated with PTX-loaded PT-HSP NPs achieved better anti-tumour effects and safety than the Taxol formulation. In summary, this study provided Mj-sHSP NPs with coats that could be shed in response to the particular pH and enzymes in the TME, which improved the efficacy of tumour therapy. STATEMENT OF SIGNIFICANCE: This study reports on tumor microenvironment-targeting protein-based nanoparticles (PT-HSP NPs) for targeted tumor therapy. The NPs had a multilayered structure: a protein cage, a TAT cationic layer, and a dual-sensitive coat. PT-HSP NPs exhibited multilayered morphology, with good stability against plasma protein adsorption, and PTX release negligible at physiological pH. Under the tumor microenvironment (acidic pH and overexpressed HAase), PAHA coat deshielded from PT-HSP NPs due to two factors: the charge reversal induced by protonation of piperidines in PAHA and HAase degradation. The results of cellular uptake, cytotoxicity, in vivo imaging, and tumor inhibition experiments confirmed that PT-HSP NPs exhibited promising tumor targeting efficacy in vitro and in vivo.

Insights into Ebola Virus VP35 and VP24 Interferon Inhibitory Functions and their Initial Exploitation as Drug Targets

Upon viral infection, the interferon (IFN) system triggers potent antiviral mechanisms limiting viral growth and spread. Hence, to sustain their infection, viruses evolved efficient counteracting strategies to evade IFN control. Ebola virus (EBOV), member of the family Filoviridae, is one of the most virulent and deadly pathogen ever faced by humans. The etiological agent of the Ebola Virus Disease (EVD), EBOV can be undoubtedly considered the perfect example of a powerful inhibitor of the host organism immune response activation. Particularly, the efficacious suppression of the IFN cascade contributes to disease progression and severity. Among the EBOVencoded proteins, the Viral Proteins 35 (VP35) and 24 (VP24) are responsible for the EBOV extreme virulence, representing the core of such inhibitory function through which EBOV determines its very effective shield to the cellular immune defenses. VP35 inhibits the activation of the cascade leading to IFN production, while VP24 inhibits the activation of the IFN-stimulated genes. A number of studies demonstrated that both VP35 and VP24 is validated target for drug development. Insights into the structural characteristics of VP35 and VP24 domains revealed crucial pockets exploitable for drug development. Considered the lack of therapy for EVD, restoring the immune activation is a promising approach for drug development. In the present review, we summarize the importance of VP35 and VP24 proteins in counteracting the host IFN cellular response and discuss their potential as druggable viral targets as a promising approach toward attenuation of EBOV virulence.

Genome editing in wheat microspores and haploid embryos mediated by delivery of ZFN proteins and cell-penetrating peptide complexes

Recent advances in genome engineering technologies based on designed endonucleases (DE) allow specific and predictable alterations in plant genomes to generate value-added traits in crops of choice. The EXZACT Precision technology, based on zinc finger nucleases (ZFN), has been successfully used in the past for introduction of precise mutations and transgenes to generate novel and desired phenotypes in several crop species. Current methods for delivering ZFNs into plant cells are based on traditional genetic transformation methods that result in stable integration of the nuclease in the genome. Here, we describe for the first time, an alternative ZFN delivery method where plant cells are transfected with ZFN protein that eliminates the need for stable nuclease genomic integration and allows generation of edited, but not transgenic cells or tissues. For this study, we designed ZFNs targeting the wheat IPK1 locus, purified active ZFN protein from bacterial cultures, complexed with cell-penetrating peptides (CPP) and directly transfected the complex into either wheat microspores or embryos. NGS analysis of ZFN-treated material showed targeted edits at the IPK1 locus in independent experiments. This is the first description of plant microspore genome editing by a ZFN when delivered as a protein complexed with CPP.

TALEN mediated gene editing in a mouse model of Fanconi anemia

The promising ability to genetically modify hematopoietic stem and progenitor cells by precise gene editing remains challenging due to their sensitivity to in vitro manipulations and poor efficiencies of homologous recombination. This study represents the first evidence of implementing a gene editing strategy in a murine safe harbor locus site that phenotypically corrects primary cells from a mouse model of Fanconi anemia A. By means of the co-delivery of transcription activator-like effector nucleases and a donor therapeutic FANCA template to the Mbs85 locus, we achieved efficient gene targeting (23%) in mFA-A fibroblasts. This resulted in the phenotypic correction of these cells, as revealed by the reduced sensitivity of these cells to mitomycin C. Moreover, robust evidence of targeted integration was observed in murine wild type and FA-A hematopoietic progenitor cells, reaching mean targeted integration values of 21% and 16% respectively, that were associated with the phenotypic correction of these cells. Overall, our results demonstrate the feasibility of implementing a therapeutic targeted integration strategy into the mMbs85 locus, ortholog to the well-validated hAAVS1, constituting the first study of gene editing in mHSC with TALEN, that sets the basis for the use of a new safe harbor locus in mice.

Reduce and Control: A Combinatorial Strategy for Achieving Sustained HIV Remissions in the Absence of Antiretroviral Therapy

Human immunodeficiency virus (HIV-1) indefinitely persists, despite effective antiretroviral therapy (ART), within a small pool of latently infected cells. These cells often display markers of immunologic memory and harbor both replication-competent and -incompetent proviruses at approximately a 1:100 ratio. Although complete HIV eradication is a highly desirable goal, this likely represents a bridge too far for our current and foreseeable technologies. A more tractable goal involves engineering a sustained viral remission in the absence of ART––a “functional cure.” In this setting, HIV remains detectable during remission, but the size of the reservoir is small and the residual virus is effectively controlled by an engineered immune response or other intervention. Biological precedence for such an approach is found in the post-treatment controllers (PTCs), a rare group of HIV-infected individuals who, following ART withdrawal, do not experience viral rebound. PTCs are characterized by a small reservoir, greatly reduced inflammation, and the presence of a poorly understood immune response that limits viral rebound. Our goal is to devise a safe and effective means for replicating durable post-treatment control on a global scale. This requires devising methods to reduce the size of the reservoir and to control replication of this residual virus. In the following sections, we will review many of the approaches and tools that likely will be important for implementing such a “reduce and control” strategy and for achieving a PTC-like sustained HIV remission in the absence of ART.

Selection and Characterization of DNA Aptamers Against FokI Nuclease Domain

Genome editing with site-specific nucleases (SSNs) may be effective for gene therapy, as SSNs can modify target genes. However, the main limitation of genome editing for clinical use is off-target effects by excess amounts of SSNs within cells. Therefore, a controlled delivery system for SSNs is necessary. Previously we have reported on a zinc finger nuclease (ZFN) delivery system, which combined DNA aptamers against FokI nuclease domain (FokI) and nanoneedles. Here, we describe how DNA aptamers against FokI were selected and characterized for genome editing applications.

Microenvironment-Responsive Delivery of the Cas9 RNA-Guided Endonuclease for Efficient Genome Editing

Successful and efficient delivery of Cas9 protein and gRNA into cells is critical for genome editing and its therapeutic application. In this study, we developed an improved supercharged polypeptide (SCP) mediated delivery system based on dithiocyclopeptide linker to realize the effective genome editing in tumor cells. The fusion protein Cas9-linker-SCP (Cas9-LS) forms positively charged complexes with gRNA in vitro to provide possibilities for gRNA delivery into cells. Under the microenvironment of tumor cells, the dithiocyclopeptide linker, containing matrix metalloproteinase 2 (MMP-2) sensitive sequence and an intramolecular disulfide bond, can be completely disconnected to promote the release of Cas9 protein with the nuclear localization sequence (NLS) in the cytoplasm and transfer to the cell nucleus for highly efficient genome editing, resulting in an obvious increase of indel efficiency in comparison to fusion protein without dithiocyclopeptide linker (Cas9-SCP). Furthermore, Cas9-LS shows no significant cytotoxicity and minimal hemolytic activity. We envision that the microenvironment-responsive Cas9 protein delivery system can facilitate more efficient genome editing in tumor cells.

65 YEARS OF THE DOUBLE HELIX: The advancements of gene editing and potential application to hereditary cancer

Hereditary cancer predisposition syndromes are associated with germline mutations that lead to increased vulnerability for an individual to develop cancers. Such germline mutations in tumour suppressor genes, oncogenes and genes encoding for proteins essential in DNA repair pathways and cell cycle control can cause overall chromosomal instability in the genome and increase risk in developing cancers. Gene correction of these germline mutations to restore normal protein functions is anticipated as a new therapeutic option. This can be achieved through disruption of gain-of-function pathogenic mutation, restoration of loss-of-function mutation, addition of a transgene essential for cell function and single nucleotide changes. Genome editing tools are applicable to precise gene correction. Development of genome editing tools comes in two waves. The first wave focuses on improving targeting specificity and editing efficiency of nucleases, and the second wave of gene editing draws on innovative engineering of fusion proteins combining deactivated nucleases and other enzymes that are able to create limitless functional molecular tools. This gene editing advancement is going to impact medicine, particularly in hereditary cancers. In this review, we discuss the application of gene editing as an early intervention and possible treatment for hereditary cancers, by highlighting a selection of highly penetrant cancer syndromes as examples of how this may be achieved in clinical practice.

Human transbodies that interfere with the functions of Ebola virus VP35 protein in genome replication and transcription and innate immune antagonism

Small molecular inhibitors and passive immunization against Ebola virus disease (EVD) have been tested in animal models, including rodents and non-human primates, as well as in clinical trials. Nevertheless, there is currently no Food and Drug Administration (FDA)-approved therapy, and alternative strategies must be pursued. The aim of this study was to produce cell-penetrable human single-chain antibodies (transbodies) that are able to interfere with the activities of interferon inhibitory domain (IID) of the VP35 protein, a multifunctional virulence factor of Ebola virus (EBOV). We speculated that effective VP35-IID-specific transbodies could inspire further studies to identify an alternative to conventional antibody therapies. Phage display technology was used to generate Escherichia coli-derived human single-chain antibodies (HuscFvs) that bind to IID. HuscFvs were linked to nona-arginine (R9) to make them cell penetrable. Transbodies of transformed E. coli clones 13 and 3, which were predicted to interact with first basic patch residues (R9-HuscFv13), central basic patch, and end-cap residues (R9-HuscFv3), effectively inhibited EBOV minigenome activity. Transbodies of E. coli clones 3 and 8 antagonized VP35-mediated interferon suppression in VP35-transduced cells. We postulate that these transbodies formed an interface contact with the IID central basic patch, end-cap, and/or residues that are important for IID multimeric formation for dsRNA binding. These transbodies should be evaluated further in vitro using authentic EBOV and in vivo in animal models of EVD before their therapeutic/prophylactic effectiveness is clinically evaluated.

Transduction Methods for Cytosolic Delivery of Proteins and Bioconjugates into Living Cells

The human organism and its constituting cells rely on interplay between multiple proteins exerting specific functions. Progress in molecular biotechnologies has facilitated the production of recombinant proteins. When administrated to patients, recombinant proteins can provide important healthcare benefits. To date, most therapeutic proteins must act from the extracellular environment, with their targets being secreted modulators or extracellular receptors. This is because proteins cannot passively diffuse across the plasma membrane into the cytosol. To expand the scope of action of proteins for cytosolic targets (representing more than 40% of the genome) effective methods assisting protein cytosolic entry are being developed. To date, direct protein delivery is extremely tedious and inefficient in cultured cells, even more so in animal models of pathology. Novel techniques are changing this limitation, as recently developed in vitro methods can robustly convey large amount of proteins into cell cultures. Moreover, advances in protein formulation or protein conjugates are slowly, but surely demonstrating efficiency for targeted cytosolic entry of functional protein in vivo in tumor xenograft models. In this review, various methods and recently developed techniques for protein transport into cells are summarized. They are put into perspective to address the challenges encountered during delivery.

Efficient therapeutic delivery by a novel cell-permeant peptide derived from KDM4A protein for antitumor and antifibrosis

Cell-penetrating peptide (CPP) based delivery have provided immense potential for the therapeutic applications, however, most of nonhuman originated CPPs carry the risk of possible cytotoxicity and immunogenicity, thus may restricting to be used. Here, we describe a novel human-derived CPP, denoted hPP10, and hPP10 has cell-penetrating properties evaluated by CellPPD web server, as well as In-Vitro and In-Vivo analysis. In vitro studies showed that hPP10-FITC was able to penetrate into various cells including primary cultured cells, likely through an endocytosis pathway. And functionalized macromolecules, such as green fluorescent protein (GFP), tumor-specific apoptosis inducer Apoptin as well as biological active enzyme GCLC (Glutamate-cysteine ligase, catalytic subunit) can be delivered by hPP10 in vitro and in vivo. Collectively, our results suggest that hPP10 provide a novel and versatile tool to deliver exogenous proteins or drugs for clinical applications as well as reprogrammed cell-based therapy.

Oligonucleotide modifications enhance probe stability for single cell transcriptome in vivo analysis (TIVA)

Single cell transcriptomics provides a powerful discovery tool for identifying new cell types and functions as well as a means to probe molecular features of the etiology and treatment of human diseases, including cancer. However, such analyses are limited by the difficulty of isolating mRNA from single cells within biological samples. We recently introduced a photochemical method for isolating mRNA from single living cells, Transcriptome In Vivo Analysis (TIVA). The TIVA probe is a "caged" polyU : polyA oligonucleotide hairpin designed to enter live tissue, where site-specific activation with 405 nm laser reveals the polyU-biotin strand to bind mRNA in a target cell, enabling subsequent mRNA isolation and sequencing. The TIVA method is well suited for analysis of living cells in resected tissue, but has not yet been applied to living cells in whole organisms. Adapting TIVA to this more challenging environment requires a probe with higher thermal stability, more robust caging, and greater nuclease resistance. In this paper we present modifications to the original TIVA probe with multiple aspects of enhanced stability. These newer probes utilize an extended 22mer polyU capture strand with two 9mer polyA blocking strands ("22/9/9") for higher thermal stability pre-photolysis and improved mRNA capture affinity post-photolysis. The "22/9/9 GC" probe features a terminal GC pair to reduce pre-photolysis interactions with mRNA by more than half. The "PS-22/9/9" probe features a phosphorothioated backbone, which extends serum stability from <1 h to at least 48 h, and also mediates uptake into cultured human fibroblasts.

Human single chain-transbodies that bound to domain-I of non-structural protein 5A (NS5A) of hepatitis C virus

A safe and broadly effective direct acting anti-hepatitis C virus (HCV) agent that can withstand the viral mutation is needed. In this study, human single chain antibody variable fragments (HuscFvs) to conserved non-structural protein-5A (NS5A) of HCV were produced by phage display technology. Recombinant NS5A was used as bait for fishing-out the protein bound-phages from the HuscFv-phage display library. NS5A-bound HuscFvs produced by five phage transfected-E. coli clones were linked molecularly to nonaarginine (R9) for making them cell penetrable (become transbodies). The human monoclonal transbodies inhibited HCV replication in the HCVcc infected human hepatic cells and also rescued the cellular antiviral immune response from the viral suppression. Computerized simulation verified by immunoassays indicated that the transbodies used several residues in their multiple complementarity determining regions (CDRs) to form contact interface with many residues of the NS5A domain-I which is important for HCV replication complex formation and RNA binding as well as for interacting with several host proteins for viral immune evasion and regulation of cellular physiology. The human monoclonal transbodies have high potential for testing further as a new ramification of direct acting anti-HCV agent, either alone or in combination with their cognates that target other HCV proteins.

Targeted gene knock-in by homology-directed genome editing using Cas9 ribonucleoprotein and AAV donor delivery

Realizing the full potential of genome editing requires the development of efficient and broadly applicable methods for delivering programmable nucleases and donor templates for homology-directed repair (HDR). The RNA-guided Cas9 endonuclease can be introduced into cells as a purified protein in complex with a single guide RNA (sgRNA). Such ribonucleoproteins (RNPs) can facilitate the high-fidelity introduction of single-base substitutions via HDR following co-delivery with a single-stranded DNA oligonucleotide. However, combining RNPs with transgene-containing donor templates for targeted gene addition has proven challenging, which in turn has limited the capabilities of the RNP-mediated genome editing toolbox. Here, we demonstrate that combining RNP delivery with naturally recombinogenic adeno-associated virus (AAV) donor vectors enables site-specific gene insertion by homology-directed genome editing. Compared to conventional plasmid-based expression vectors and donor templates, we show that combining RNP and AAV donor delivery increases the efficiency of gene addition by up to 12-fold, enabling the creation of lineage reporters that can be used to track the conversion of striatal neurons from human fibroblasts in real time. These results thus illustrate the potential for unifying nuclease protein delivery with AAV donor vectors for homology-directed genome editing.

Cell-penetrating peptides and their utility in genome function modifications (Review)

For almost 30 years, studies have confirmed the effectiveness of cell-penetrating peptides (CPPs) in the facilitation of the intracellular delivery of various cargo molecules, including RNA, DNA, plasmids, proteins or nanoparticles, under in vitro and in vivo conditions. The cellular uptake of CPPs occurs via energy-dependent, as well as -independent mechanisms. In this relatively new direction of research, studies have attempted to introduce genome modification systems into cells by CPPs. Cellular uptake of CPPs carrying either covalently bound or electrostatically conjugated cargo, has several advantages over viral delivery systems, as it does not lead to any significant cytotoxicity or immunogenicity, and simultaneously it is more efficient than other non-viral systems. So far, CPPs have been successfully used to introduce Cre recombinase, zinc finger nucleases, transcription activator-like effector nucleases and clustered regularly interspaced short palindromic repeats systems into cells. The present article systematically reviewed the information obtained from studies on CPPs and assessed their utility with regard to their effectiveness and safety of use.

Hit-and-run programming of therapeutic cytoreagents using mRNA nanocarriers

Therapies based on immune cells have been applied for diseases ranging from cancer to diabetes. However, the viral and electroporation methods used to create cytoreagents are complex and expensive. Consequently, we develop targeted mRNA nanocarriers that are simply mixed with cells to reprogram them via transient expression. Here, we describe three examples to establish that the approach is simple and generalizable. First, we demonstrate that nanocarriers delivering mRNA encoding a genome-editing agent can efficiently knock-out selected genes in anti-cancer T-cells. Second, we imprint a long-lived phenotype exhibiting improved antitumor activities into T-cells by transfecting them with mRNAs that encode a key transcription factor of memory formation. Third, we show how mRNA nanocarriers can program hematopoietic stem cells with improved self-renewal properties. The simplicity of the approach contrasts with the complex protocols currently used to program therapeutic cells, so our methods will likely facilitate manufacturing of cytoreagents.Current widely used viral and electroporation methods for creating therapeutic cell-based products are complex and expensive. Here, the authors develop targeted mRNA nanocarriers that can transiently program gene expression by simply mixing them with cells, to improve their therapeutic potential.

HIV-1 Latency and Eradication: Past, Present and Future

BACKGROUND

It is well established that antiretroviral therapy (ART), while highly effective in controlling HIV replication, cannot eliminate virus from the body. Therefore, the majority of HIV-1-infected individuals remain at risk for developing AIDS due to persistence of infected reservoir cells serving as a source of virus re-emergence. Several reservoirs containing replication competent HIV-1 have been identified, most notably CD4+ T cells. Cells of the myeloid lineage, which are the first line of defense against pathogens and participate in HIV dissemination into sanctuary organs, also serve as cellular reservoirs of HIV-1. In latently infected resting CD4+ T cells, the integrated copies of proviral DNA remain in a dormant state, yet possess the ability to produce replication competent virus after cellular activation. Studies have demonstrated that modification of chromatin structure plays a role in establishing persistence, in part suggesting that latency is, controlled epigenetically.

CONCLUSION

Current efforts to eradicate HIV-1 from this cell population focus primarily on a &amp;quot;shock and kill&amp;quot; approach through cellular reactivation to trigger elimination of virus producing cells by cytolysis or host immune responses. However, studies revealed several limitations to this approach that require more investigation to assess its clinical application. Recent advances in gene editing technology prompted use of this approach for inactivating integrated proviral DNA in the genome of latently infected cells. This technology, which requires a detailed understanding of the viral genetics and robust delivery, may serve as a powerful strategy to eliminate the latent reservoir in the host leading to a sterile cure of AIDS.

TALEN based HPV-E7 editing triggers necrotic cell death in cervical cancer cells

Human Papillomavirus E7 and E6 oncoproteins have been considered as suitable candidate anti-viral targets since they cause malignant conversion in cervical cancers. Transcription Activator-Like Effector Nucleases (TALENs) are recent editing tools to knockout genes by inducing double stranded breaks at specific sites in the genome. In here, we have designed specific TALENs to target E7 and analyzed their efficiency in inducing cell death in cervical cancer cells. We found that designed TALENs could yield about 10–12% editing activity as observed from T7E1 and nuclease resistance assays. Down-regulation of E7 and E6 was further evident at the transcript as well as proteins levels indicating that the selected TALENs were effective. TALEN-mediated E7 editing led to cell death as ascertained by cell cycle and Annexin V assays. Annexin profiling suggested that cell death could be due to necrosis as observed by upregulation of necrotic markers such as LDH A, Rip-1, and Cyclophilin A. Necrosis appears to be a better therapeutic response as it could further activate pro-inflammatory cytokines to attract immune cells to eliminate HPV-integrated cells and therefore TALEN editing strategy has the potential to be a promising tool as an adjuvant therapy in cervical cancer along with surgery.

Therapeutic gene editing: delivery and regulatory perspectives

Gene-editing technology is an emerging therapeutic modality for manipulating the eukaryotic genome by using target-sequence-specific engineered nucleases. Because of the exceptional advantages that gene-editing technology offers in facilitating the accurate correction of sequences in a genome, gene editing-based therapy is being aggressively developed as a next-generation therapeutic approach to treat a wide range of diseases. However, strategies for precise engineering and delivery of gene-editing nucleases, including zinc finger nucleases, transcription activator-like effector nuclease, and CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats-associated nuclease Cas9), present major obstacles to the development of gene-editing therapies, as with other gene-targeting therapeutics. Currently, viral and non-viral vectors are being studied for the delivery of these nucleases into cells in the form of DNA, mRNA, or proteins. Clinical trials are already ongoing, and in vivo studies are actively investigating the applicability of CRISPR/Cas9 techniques. However, the concept of correcting the genome poses major concerns from a regulatory perspective, especially in terms of safety. This review addresses current research trends and delivery strategies for gene editing-based therapeutics in non-clinical and clinical settings and considers the associated regulatory issues.

The Argi system: one-step purification of proteins tagged with arginine-rich cell-penetrating peptides

The discovery of cell penetrating peptides (CPPs) opened new perspectives for the delivery of proteins into human cells. It is considered that in the future CPP-mediated transport of therapeutic proteins may find applications in the treatment of human diseases. Despite this fact a fast and simple method for the purification of CPP-tagged proteins, free of additional tags, was not available to date. To fill this gap we developed the Argi system for one-step purification of proteins tagged with arginine rich CPPs.

Cell-penetrating peptides (CPPs): From delivery of nucleic acids and antigens to transduction of engineered nucleases for application in transgenesis

Cell-penetrating peptides (CPPs) have been studied for their capacity to translocate across the lipid membrane of several cell types. In membrane translocation, these peptides can remarkably transport biologically active hydrophilic molecules, such as pharmaceuticals, nucleic acids (DNA and RNA) and even high-molecular-weight proteins, Fig. 3 into the cell cytoplasm and organelles. The development of CPPs as transduction agents includes the modification of gene and protein expression, the reprogramming and differentiation of induced pluripotent stem cells and the preparation of cellular vaccines. A relatively recent field of CPP application is the transduction of plasmid DNA vectors and CPP-fusion proteins to modify genomes and introduce new traits in cells and organisms. CPP-mediated transduction of components for genome editing is an advantageous alternative to viral DNA vectors. Engineered site-specific nucleases, such as Cre recombinase, ZFN, TALENs and CRISPR associated protein (Cas), have been coupled to CPPs, and the fused proteins have been used to permeate targeted cells and tissues. The functionally active fusion CPP-nucleases subsequently home to the nucleus, incise genomic DNA at specific sites and induce repair and recombination. This review has the objective of discussing CPPs and elucidating the prospective use of CPP-mediated transduction technology, particularly in genome modification and transgenesis.

Cell-Penetrating Peptide-Mediated Delivery of Cas9 Protein and Guide RNA for Genome Editing

The clustered, regularly interspaced, short palindromic repeat (CRISPR)-associated (Cas) system represents an efficient tool for genome editing. It consists of two components: the Cas9 protein and a guide RNA. To date, delivery of these two components has been achieved using either plasmid or viral vectors or direct delivery of protein and RNA. Plasmid- and virus-free direct delivery of Cas9 protein and guide RNA has several advantages over the conventional plasmid-mediated approach. Direct delivery results in shorter exposure time at the cellular level, which in turn leads to lower toxicity and fewer off-target mutations with reduced host immune responses, whereas plasmid- or viral vector-mediated delivery can result in uncontrolled integration of the vector sequence into the host genome and unwanted immune responses. Cell-penetrating peptide (CPP), a peptide that has an intrinsic ability to translocate across cell membranes, has been adopted as a means of achieving efficient Cas9 protein and guide RNA delivery. We developed a method for treating human cell lines with CPP-conjugated recombinant Cas9 protein and CPP-complexed guide RNAs that leads to endogenous gene disruption. Here we describe a protocol for preparing an efficient CPP-conjugated recombinant Cas9 protein and CPP-complexed guide RNAs, as well as treatment methods to achieve safe genome editing in human cell lines.

In vitro and in vivo delivery of therapeutic proteins using cell penetrating peptides

The failure of proteins to penetrate mammalian cells or target tumor cells restricts their value as therapeutic tools in a variety of diseases such as cancers. Recently, protein transduction domains (PTDs) or cell penetrating peptides (CPPs) have been shown to promote the delivery of therapeutic proteins or peptides into live cells. The successful delivery of proteins mainly depends on their physicochemical properties. Although, linear cell penetrating peptides are one of the most effective delivery vehicles; but currently, cyclic CPPs has been developed to potently transport bioactive full-length proteins into cells. Up to now, several small protein transduction domains from viral proteins including Tat or VP22 could be fused to other peptides or proteins to entry them in various cell types at a dose-dependent approach. A major disadvantage of PTD-fusion proteins is primary uptake into endosomal vesicles leading to inefficient release of the fusion proteins into the cytosol. Recently, non-covalent complex formation (Chariot) between proteins and CPPs has attracted a special interest to overcome some delivery limitations (e.g., toxicity). Many preclinical and clinical trials of CPP-based delivery are currently under evaluation. Generally, development of more efficient protein transduction domains would significantly increase the potency of protein therapeutics. Moreover, the synergistic or combined effects of CPPs with other delivery systems for protein/peptide drug delivery would promote their therapeutic effects in cancer and other diseases. In this review, we will describe the functions and implications of CPPs for delivering the therapeutic proteins or peptides in preclinical and clinical studies.

Genome-Editing Technologies: Principles and Applications

Targeted nucleases have provided researchers with the ability to manipulate virtually any genomic sequence, enabling the facile creation of isogenic cell lines and animal models for the study of human disease, and promoting exciting new possibilities for human gene therapy. Here we review three foundational technologies-clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9), transcription activator-like effector nucleases (TALENs), and zinc-finger nucleases (ZFNs). We discuss the engineering advances that facilitated their development and highlight several achievements in genome engineering that were made possible by these tools. We also consider artificial transcription factors, illustrating how this technology can complement targeted nucleases for synthetic biology and gene therapy.

DNA aptamers against FokI nuclease domain for genome editing applications

Genome editing with site-specific nucleases (SSNs) can modify only the target gene and may be effective for gene therapy. The main limitation of genome editing for clinical use is off-target effects; excess SSNs in the cells and their longevity can contribute to off-target effects. Therefore, a controlled delivery system for SSNs is necessary. FokI nuclease domain (FokI) is a common DNA cleavage domain in zinc finger nuclease (ZFN) and transcription activator-like effector nuclease. Previously, we reported a zinc finger protein delivery system that combined aptamer-fused, double-strand oligonucleotides and nanoneedles. Here, we report the development of DNA aptamers that bind to the target molecules, with high affinity and specificity to the FokI. DNA aptamers were selected in six rounds of systematic evolution of ligands by exponential enrichment. Aptamers F6#8 and #71, which showed high binding affinity to FokI (K_d=82nM, 74nM each), showed resistance to nuclease activity itself and did not inhibit nuclease activity. We immobilized the ZFN-fused GFP to nanoneedles through these aptamers and inserted the nanoneedles into HEK293 cells. We observed the release of ZFN-fused GFP from the nanoneedles in the presence of cells. Therefore, these aptamers are useful for genome editing applications such as controlled delivery of SSNs.

Virus-Like Particles Derived from HIV-1 for Delivery of Nuclear Proteins: Improvement of Production and Activity by Protein Engineering

Virus-like particles (VLPs) derived from retroviruses and lentiviruses can be used to deliver recombinant proteins without the fear of causing insertional mutagenesis to the host cell genome. In this study we evaluate the potential of an inducible lentiviral vector packaging cell line for VLP production. The Gag gene from HIV-1 was fused to a gene encoding a selected protein and it was transfected into the packaging cells. Three proteins served as model: the green fluorescent protein and two transcription factors-the cumate transactivator (cTA) of the inducible CR5 promoter and the human Krüppel-like factor 4 (KLF4). The sizes of the VLPs were 120-150 nm in diameter and they were resistant to freeze/thaw cycles. Protein delivery by the VLPs reached up to 100% efficacy in human cells and was well tolerated. Gag-cTA triggered up to 1100-fold gene activation of the reporter gene in comparison to the negative control. Protein engineering was required to detect Gag-KLF4 activity. Thus, insertion of the VP16 transactivation domain increased the activity of the VLPs by eightfold. An additional 2.4-fold enhancement was obtained by inserting nuclear export signal. In conclusion, our platform produced VLPs capable of efficient protein transfer, and it was shown that protein engineering can be used to improve the activity of the delivered proteins as well as VLP production.

Chemical Biology Approaches to Genome Editing: Understanding, Controlling, and Delivering Programmable Nucleases

Programmable DNA nucleases have provided scientists with the unprecedented ability to probe, regulate, and manipulate the human genome. Zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and the clustered regularly interspaced short palindromic repeat-Cas9 system (CRISPR-Cas9) represent a powerful array of tools that can bind to and cleave a specified DNA sequence. In their canonical forms, these nucleases induce double-strand breaks at a DNA locus of interest that can trigger cellular DNA repair processes that disrupt or replace genes. The fusion of these programmable nucleases with a variety of other protein domains has led to a rapidly growing suite of tools for activating, repressing, visualizing, and modifying loci of interest. Maximizing the usefulness and therapeutic relevance of these tools, however, requires precisely controlling their activity and specificity to minimize potentially toxic side effects arising from off-target activities. This need has motivated the application of chemical biology principles and methods to genome-editing proteins, including the engineering of variants of these proteins with improved or altered specificities, and the development of genetic, chemical, optical, and protein delivery methods that control the activity of these agents in cells. Advancing the capabilities, safety, effectiveness, and therapeutic relevance of genome-engineering proteins will continue to rely on chemical biology strategies that manipulate their activity, specificity, and localization.

Non-viral delivery of genome-editing nucleases for gene therapy

Manipulating the genetic makeup of mammalian cells using programmable nuclease-based genome-editing technology has recently evolved into a powerful avenue that holds great potential for treating genetic disorders. There are four types of genome-editing nucleases, including meganucleases, zinc finger nucleases, transcription activator-like effector nucleases and clustered, regularly interspaced, short palindromic repeat-associated nucleases such as Cas9. These nucleases have been harnessed to introduce precise and specific changes of the genome sequence at virtually any genome locus of interest. The therapeutic relevance of these genome-editing technologies, however, is challenged by the safe and efficient delivery of nuclease into targeted cells. Herein, we summarize recent advances that have been made on non-viral delivery of genome-editing nucleases. In particular, we focus on non-viral delivery of Cas9/sgRNA ribonucleoproteins for genome editing. In addition, the future direction for developing non-viral delivery of programmable nucleases for genome editing is discussed.

Use of genome-editing tools to treat sickle cell disease

Recent advances in genome-editing techniques have made it possible to modify any desired DNA sequence by employing programmable nucleases. These next-generation genome-modifying tools are the ideal candidates for therapeutic applications, especially for the treatment of genetic disorders like sickle cell disease (SCD). SCD is an inheritable monogenic disorder which is caused by a point mutation in the β-globin gene. Substantial success has been achieved in the development of supportive therapeutic strategies for SCD, but unfortunately there is still a lack of long-term universal cure. The only existing curative treatment is based on allogeneic stem cell transplantation from healthy donors; however, this treatment is applicable to a limited number of patients only. Hence, a universally applicable therapy is highly desirable. In this review, we will discuss the three programmable nucleases that are commonly used for genome-editing purposes: zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9). We will continue by exemplifying uses of these methods to correct the sickle cell mutation. Additionally, we will present induction of fetal globin expression as an alternative approach to cure sickle cell disease. We will conclude by comparing the three methods and explaining the concerns about their use in therapy.