CRISPR/Cas9 is a versatile genome-editing technology that is widely used for studying the functionality of genetic elements, creating genetically modified organisms as well as preclinical research of genetic disorders. However, the high frequency of off-target activity (≥50%)—RGEN (RNA-guided endonuclease)-induced mutations at sites other than the intended on-target site—is one major concern, especially for therapeutic and clinical applications. Here, we review the basic mechanisms underlying off-target cutting in the CRISPR/Cas9 system, methods for detecting off-target mutations, and strategies for minimizing off-target cleavage. The improvement off-target specificity in the CRISPR/Cas9 system will provide solid genotype–phenotype correlations, and thus enable faithful interpretation of genome-editing data, which will certainly facilitate the basic and clinical application of this technology.

Off-target Effects in CRISPR/Cas9-mediated Genome Engineering

Genetic diseases of blood cells are prime candidates for treatment through ex vivo gene editing of CD34+ hematopoietic stem/progenitor cells (HSPCs), and a variety of technologies have been proposed to treat these disorders. Sickle cell disease (SCD) is a recessive genetic disorder caused by a single-nucleotide polymorphism in the β-globin gene (HBB). Sickle hemoglobin damages erythrocytes, causing vasoocclusion, severe pain, progressive organ damage, and premature death. We optimize design and delivery parameters of a ribonucleoprotein (RNP) complex comprising Cas9 protein and unmodified single guide RNA, together with a single-stranded DNA oligonucleotide donor (ssODN), to enable efficient replacement of the SCD mutation in human HSPCs. Corrected HSPCs from SCD patients produced less sickle hemoglobin RNA and protein and correspondingly increased wild-type hemoglobin when differentiated into erythroblasts. When engrafted into immunocompromised mice, ex vivo treated human HSPCs maintain SCD gene edits throughout 16 weeks at a level likely to have clinical benefit. These results demonstrate that an accessible approach combining Cas9 RNP with an ssODN can mediate efficient HSPC genome editing, enables investigator-led exploration of gene editing reagents in primary hematopoietic stem cells, and suggests a path toward the development of new gene editing treatments for SCD and other hematopoietic diseases.

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Selection-free genome editing of the sickle mutation in human adult hematopoietic stem/progenitor cells.

The field of gene therapy is striving more than ever to define a path to the clinic and the market. Twenty gene therapy products have already been approved and over two thousand human gene therapy clinical trials have been reported worldwide. These advances raise great hope to treat devastating rare and inherited diseases as well as incurable illnesses. Understanding of the precise pathomechanisms of diseases as well as the development of efficient and specific gene targeting and delivery tools are revolutionizing the global market. Currently, human cancers and monogenic disorders are indications number one. The elevated prevalence of genetic disorders and cancers, clear gene manipulation guidelines and increasing financial support for gene therapy in clinical trials are major trends. Gene therapy is presently starting to become commercially profitable as a number of gene and cell-based gene therapy products have entered the market and the clinic. This article reviews the history and development of twenty approved human gene and cell-based gene therapy products that have been approved up-to-now in clinic and markets of mainly North America, Europe and Asia.

/pdf/development-and-clinical-translation-of-approved-gene-4jopgxr1hh.pdf

Development and Clinical Translation of Approved Gene Therapy Products for Genetic Disorders.

Genetic treatment of a molecular disorder: gene therapy approaches to sickle cell disease

Human induced pluripotent stem cells (hiPSCs) have revolutionized the field of human disease modeling, with an enormous potential to serve as paradigm shifting platforms for preclinical trials, personalized clinical diagnosis, and drug treatment. In this review, we describe how hiPSCs could transition cardiac healthcare away from simple disease diagnosis to prediction and prevention, bridging the gap between basic and clinical research to bring the best science to every patient.

Human Induced Pluripotent Stem Cells as a Platform for Personalized and Precision Cardiovascular Medicine

http://bushmanlab.org/assets/pdf/publications/25943494.pdf

Genome editing technologies: defining a path to clinic.

The National Institutes of Health (NIH) oversight of human gene transfer research, which is defined as the deliberate transfer of recombinant and/or synthetic nucleic acid molecules to humans, originates with the NIH Guidelines for Research Involving Recombinant or Synthetic Nucleic Acid Molecules (NIH Guidelines). The NIH Guidelines, which were first published in the Federal Register almost 40 years ago, have been amended numerous times to remain responsive to scientific progress and to clearly define the responsibilities of NIH, the Recombinant DNA Advisory Committee (RAC), investigators, and institutions. Human gene transfer trials conducted at clinical sites in the United States (USA) are subject to the NIH Guidelines if they are conducted at, or sponsored by, an institution that receives any support for recombinant or synthetic nucleic acid research from the NIH. Human gene transfer trials conducted either in the USA or abroad are also subject to the NIH Guidelines if the investigational agent was developed with NIH funds and the institution that developed the investigational materials sponsors or participates in these projects. Trials are registered with the NIH Office Biotechnology Activities (OBA) and there are ongoing reporting requirements. Each new trial is reviewed by the RAC, and those that are novel or raise unique ethical or social issues are selected for review at quarterly public RAC meetings. The RAC also advises the NIH on policy and other matters relating to clinical gene transfer research and biosafety.

Morad Hassani

Papers

Genome editing technologies: defining a path to clinic.

The National Institutes of Health Oversight of Human Gene Transfer Research: Enhancing Science and Safety