Genome Editing—Potential and Risks
CRISPR-Cas and its Potential for Genome Editing
After the discovery of RNAi, another evolutionary important and highly conserved cellular system with large potential for basic research and clinical translational development was identified and characterized. The CRISPR-Cas system has the capacity for genome editing directly at the level of the DNA sequence and has already proven highly valuable for experimental research. In experimental studies, correction of single gene defects has been achieved by use of CRISPR-Cas technology.[210–232] Of interest for monogenetic CVD, the MYBPC.3 mutation causing hypertrophic cardiomyopathy has been successfully corrected in human embryonic cells using CRISPR-Cas9 technology.[233,234]
Despite the potential of this technology, two major remaining current obstacles need to be emphasized with regard to possible clinical translation. First, in vivo delivery of therapeutic CRISPR tools faces hurdles similar to adeno-associated virus (AAV)-based gene therapy, i.e. potentially low delivery efficacy or mis-targeting. Second, possible introduction of off-target mutations in the genome of the patient itself and all of its offspring requires novel safety precautions, e.g. advanced highly sensitive methods for the detection of genomic mutations[218,221,231] which are applicable in the setting of clinical trials. Importantly, different DNA repair mechanisms dominate in stem cells vs. somatic cells (e.g. cardiomyocytes) with up to 99% non-homologous end-joining (NHEJ) as compared to homology-directed-repair (HDR) during S and G2 phase of the cell cycle. While CRISPR tools have already proven valuable to identify myocardial disease mechanisms in human-induced pluripotent stem cells,[216,223,224]cardiac genome editing in vivo still faces the major obstacles of targeting and NHEJ vs. HDR. However, there are two classes of CRISPR-Cas systems with several subtypes most of which have not yet been exploited regarding their possible clinical therapeutic potential.[235,236] Further research in this field may therefore lead to expanded therapeutic options in the more remote future.
Epigenome Modulation Using CRISPR-Cas Technology
Notably, CRISPR-Cas may be therapeutically employed in multiple ways which do not irreversibly affect the genome and may be considered for clinical applications in the cardiovascular field. In haematology, there arises the clinically most advantageous option for ex vivo correction of haematopoietic stem cells carrying a monogenic defect, which then upon transplantation is capable to fully reconstitute the patient's bone marrow without affecting his/her germline.[238–241] This ex vivo option essentially circumvents the danger of entirely unforeseeable long-term and off-target effects which may result from manipulation of the human germline in vivo. These would not only affect the treated individual but also any offspring. In this ethical context, recent experimental studies are of major interest since they indicate approaches towards targeted modulation of the epigenome editing without alteration of the genomic DNA. Since pathophysiologically relevant epigenome alterations are increasingly appreciated in CVD, such options arising from CRISPR-Cas research may become increasingly relevant for cardiovascular research.[210–242]
Eur Heart J. 2020;41(40):3884-3899. © 2020 Oxford University Press
Copyright 2007 European Society of Cardiology. Published by Oxford University Press. All rights reserved.