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CRISPR-Cas9 in Heart Failure and Transplantation


Diana Kim
Howard Eisen, MD

Heisen@drexelmed.edu
Drexel University College of Medicine
Philadelphia, PA, USA



It has been on the cover of Time magazine. So, to help you answer questions that your patients may raise after reading that article, we will review the important, developing field of gene editing.

As we think about the future of heart failure and transplantation, it is important to maintain a keen eye for technologies that will impact our future patients. The foresight to anticipate and be ready for changes in heart failure and transplantation comes from understanding the scientific underpinnings and potential for new therapies. In this context, molecular biologists have recently discovered one of the most potentially transformative technologies seen in years. The Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 technology, a bacterial-derived technology that confers bacteria protection against viruses and plasmids, has been harnessed in order to edit the genomes of eukaryotes (Figure 1). In brief, this technology takes advantage of the Cas9 endonuclease, which is specifically targeted to a gene sequence of interest through a guide RNA molecule that is complementary to the intended sequence. Cas9 then introduces a site-specific double-stranded DNA break, which can either be rejoined through non-homologous end joining or replaced with a new sequence through homologous recombination from a donor sequence (1,2). As a result, gene sequences can be removed or replaced with high specificity in eukaryotic cells.

It is important to recognize the advantage that CRISPR-Cas9 has compared to other gene editing mechanisms such as Zinc Finger Nucleases (ZNFs), TALENS, or RNAi. First, CRISPR-Cas9 design is simple and only requires design of the guide RNA. It also confers high specificity, reducing effects of insertional mutagenesis (3). Unlike RNAi, CRISPR-Cas9 achieves knockout rather than knockdown, which is a permanent, sustained effect rather than a transient one.

The clinical implications of CRISPR-Cas9 are tremendous, and this is no less true in the context of heart failure and transplant. Previous attempts have validated genetic targets like SERCA2a, a sarcoplasmic reticulum Ca2+ ATPase, which can improve function in heart failure and has made it to as far as phase II of clinical gene therapy trials (4). Other potential targets such as the threonine/serine phosphatase PP1 which is an inhibitory regulator of beta-adrenergic receptors and PLN, a regulator of SERCA2a can exert adverse effects in heart failure and would benefit from efficient silencing in the heart (5). In the context of transplantation, modulation of the immune system or targets of the immune system could be achieved through specific targeting of the T cell response in acute or chronic graft rejection. One of the most recent CRISPR-Cas9 targets is class II major histocompatibility complex (MHC) molecules, which mitigate the CD4+ helper T lymphocyte response during acute allograft rejection (6). Editing of the donor allo-immune targets like the MHC antigens could effectively "cloak" the donor organ from the recipient immune system, akin to the cloaking of Romulan warbirds of Star Trek lore (Figure 2). CRISPR-Cas9 also has potential to identify new drug targets by creating animal allelic knockouts and characterizing phenotypes in the context of heart failure and transplant.

As physicians, we should continue to think about how these technologies can and might be utilized and their limitations. A fundamental understanding of these processes then will go a long way in the bench to bedside translation of this therapy. First, we should achieve better understandings of the genomic underpinnings that lead to unique heart failure or transplant technologies, perhaps taking advantage of GWAS or whole genome sequencing to find pathologic genetic variants that may benefit from CRISPR-Cas9 translation. Moreover, we should think about the delivery route and timing for these therapies. Do we want permanent gene editing? Do we want to target the heart or a different organ such as the bone marrow or thymus in the case of immunogenic modulation? How many administrations of CRISPR-Cas9 are needed to achieve enough gene editing towards a measurable, significant outcome? Importantly, we should give equal weight to side effects and toxicities. How will CRISPR-Cas9 be delivered? If viral, we should be wary of the immunogenicity that viruses introduce when administered systemically. If some other route, such as nanoparticle and electroporation, there are well-described cytotoxicities (7) that we should be concerned about as well. These approaches will need to be investigated initially in rodents and then in large animal models of solid organ transplantation.

As we move forward with this technology, it is highly likely that CRISPR-Cas9 will find its way into heart failure and transplant. To fully reach its potential, physicians and scientists need to be on the same page and that comes from an understanding of the molecular biology, the clinical needs, but also the limitations. With these in mind, we can hopefully move towards robust, improved clinical outcomes from CRISPR-Cas9 gene editing in the future. ■

Disclosure Statement: The authors have no conflicts of interest to disclose except that Dr. Eisen is a longtime (50 years) fan of Star Trek.


References:

  1. oudna, J. A. & Charpentier, E. Genome editing. The new frontier of genome engineering with CRISPR-Cas9. Science 346 (2014).
  2. Didovyk, A., Borek, B., Tsimring, L. & Hasty, J. Transcriptional regulation with CRISPR-Cas9: principles, advances, and applications. Curr Opin Biotechnol. 40, 177-184 (2016).
  3. Mohr, S. E. et al. CRISPR guide RNA design for research applications. FEBS J. (2016).
  4. Rincon, M. Y., VandenDriessche, T. & Chuah, M. K. Gene therapy for cardiovascular disease: advances in vector development, targeting, and delivery for clinical translation. Cardiovasc. Res. 108, 4-20 (2015).
  5. Raake, P. W. J. et al. Gene therapy targets in heart failure: the path to translation. Clin. Pharmacol. Ther. 90, 542-53 (2011).
  6. Abrahimi, P. et al. Blocking MHC class II on human endothelium mitigates acute rejection. JCI insight 1 (2016).
  7. Kong, B., Seog, J. H., Graham, L. M. & Lee, S. B. Experimental considerations on the cytotoxicity of nanoparticles. Nanomedicine (Lond). 6, 929-41 (2011).



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