CRISPR Nobel Prize Technology: “A tool for rewriting the code of life”
Jennifer A. Doudna and Emmanuelle Charpentier were awarded the 2020 Nobel Prize for Chemistry for their discovery of a technology, described by the Nobel Committee as “Genetic scissors: a tool for rewriting the code of life”. CRISPR (a wisely chosen acronym for Clustered Regularly Interspaced Short Palindromic Repeats) in combination with the enzyme Cas9 (CRISPR-associated protein 9), is a new breakthrough technology that can target a section of DNA, literally cut out a sequence of interest and insert a new sequence in its stead that is then incorporated during the process of DNA repair. There is no doubt that CRISPR/Cas9 represents a watershed moment in science, and applications for therapeutics and even cures of disorders once thought incurable are on the horizon. The Nobel Committee appropriately describes CRISPR as a “technology has had a revolutionary impact on the life sciences, is contributing to new cancer therapies and may make the dream of curing inherited diseases come true.”
In a publication by Ma et al. (Nature, 2017), researchers were able to take human preimplantation embryos and cut out and replace a disease-causing pathogenic variant, using the CRISPR/Cas9 gene-editing tool.
In anticipation of a fast-paced research trajectory, The American Society of Human Genetics (ASHG) brought together an international workgroup that included representatives from the following organizations
UK Association of Genetic Nurses and Counsellors
Canadian Association of Genetic Counsellors
International Genetic Epidemiology Society
US National Society of Genetic Counselors
The document was endorsed by
American Society for Reproductive Medicine
Asia Pacific Society of Human Genetics
British Society for Genetic Medicine
Human Genetics Society of Australasia
Professional Society of Genetic Counselors in Asia
Southern African Society for Human Genetics
The following positions are stated in this document:
(1) At this time, given the nature and number of unanswered scientific, ethical, and policy questions, it is inappropriate to perform germline gene editing that culminates in human pregnancy. (2) Currently, there is no reason to prohibit in vitro germline genome editing on human embryos and gametes, with appropriate oversight and consent from donors, to facilitate research on the possible future clinical applications of gene editing. (3) There should be no prohibition on making public funds available to support this research. (4) Future clinical application of human germline genome editing should not proceed unless, at a minimum, there is (a) a compelling medical rationale, (b) an evidence base that supports its clinical use, (c) an ethical justification, and (d) a transparent public process to solicit and incorporate stakeholder input.
What is CRISPR and How Does It Work?
History: Bacteria Defense System
In 1987, segments of short palindromic repeats were discovered in bacterial DNA
These repeats were actually part of an ancient system used by bacteria to defend themselves against viruses
Through a process of ‘acquired immunity’, bacteria were found to have ‘spacers’ between the repeats that were actually the same sequences found in threatening viral genomes
If a bacteria was found to have a specific viral sequence, they were protected from that particular virus
Over time, researchers discovered that
Cas (CRISPR-associated system) genes were identified near these repeat sequences, producing enzymes that can cut DNA
Bacteria can generate RNA that match the spacer sequences
The Cas enzymes circulate with these specialized RNA molecules that function as viral genome locators
If there is a matching viral sequence, the RNA molecule will lock on and the Cas enzymes will then cut through DNA preventing replication
Now: Genome Engineering and CRISPR/Cas9
Scientists modified the above system, found in nature, but the overall principles are the same
If one knows the sequence of interest in a particular gene, an RNA locator can be created that matches that sequence
The RNA locator sequence will bind to the sequence of choice
The Cas9 enzyme can then cut out the sequence of interest
Researchers can replace the missing sequence with another sequence of choice
The DNA will undergo repair and incorporate the new sequence
In the case of the recent paper in Nature, the authors applied CRISPR/Cas9 to embryos with a pathogenic variant (a deletion of just 4 base pairs – GAGT) in the MYBPC3 gene that causes hypertrophic cardiomyopathy
The pathogenic variant, inherited from the father, was replaced with a normal sequence from the mother
In theory, because hypertrophic cardiomyopathy is an autosomal dominant disorder, this procedure would be curative and a normal embryo could then be transferred to the mother
The authors of this research paper do not feel that this technique can be used clinically without further optimization because intrinsic mechanisms used to repair DNA introduce new deletions and insertions
In May 2020, the FDA gave emergency approval for the development of a CRISPR based test (under the guidance of Sherlock Biosciences) that can diagnose COVID-19 in around an hour
The test utilizes Cas13a (instead of Cas9 as discussed above), to identify the specific RNA sequence that is unique to COVID-19
In June 2020, researchers at Stanford University and Lawrence Berkeley National Laboratory announced in “Cell” that they created a way to disable COVID-19
The paper discusses a new technique called prophylactic antiviral CRISPR in human cells, or PAC-MAN, that is able to knock out the virus by using CRISPR to scramble the genetic code in COVID-19.
The researchers also found a way to deliver PAC-MAN to lung cells where COVID-19 does the most damage
How it works: PAC-MAN uses a guide RNA to direct Cas13d to target areas of the COVID-19 genome – cleaving the genetic sequences and inactivating the virus
Learn More – Primary Sources:
The ObG Project highly recommends you join the almost 2-million people who have viewed Dr. Jennifer Doudna’s TED talk. As a co-inventor of CRISPR/Cas9, she explains this groundbreaking technology in less than 20 minutes and makes the case for why this research must be done within an ethical framework.
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