CRISPR

CRISPR: Where There Is Great Power There Is Great Responsibility

by Ryan Mateja, PhD

The idea of going into a cell and editing its genome is not new, what is new is how close we are to making this sci-fi idea a reality. As it turns out, we are closer than ever to complex genome editing using a modified version of the prokaryotic CRISPR/Cas system to target and cut DNA at a desired location and remove existing genes and/or add new ones. This very powerful technique to edit the genome was the American Association for the Advancement of Science’s breakthrough of the year winner in 2015.1 The financial and medical benefits that CRISPR promises are its greatest asset and also its greatest liability, creating significant roadblocks that must be overcome before its true potential can be realized by patients.

CRISPR

Crystal structure of Cas9 bound to PAM-containing DNA target (PDB: 4UN3)

The CRISPR-associated protein Cas9 is an RNA-guided endonuclease that cleaves double-stranded DNA bearing sequences complementary to a 20-nucleotide segment in the guide RNA. Cas9 has emerged as a versatile molecular tool for genome editing and gene expression control

Anders, C., Niewoehner, O., Duerst, A., Jinek, M., Structural Basis of Pam-Dependent Target DNA Recognition by the Cas9 Endonuclease, (2014) Nature 513: 569

Unequivocally, one of the major safety concerns with CRISPR-Cas9 editing, as it’s called, is off-target effects. The CRISPR-Cas9 system is directed to the intended location using a guide segment of RNA with a string of nucleotide repeats that match a patient’s DNA nucleotide repeats at the location of the target gene. A problem arises when there is an identical segment of DNA nucleotide repeats elsewhere in the genome, thereby causing it to be edited at an unintentional location. Even if the intended target gets edited, the enzyme can still continue to cut and edit other off-target segments of DNA. To reduce the probability of this occurring, scientists are using web-based algorithms to calculate the chances that their guide segments of RNA will have off-target binding. Yet there is a major limitation in utilizing these algorithms based on the fact that the DNA used comes from libraries of composite or reference DNA. Since every person has different DNA due to silent mutations and genetic variation, there is a chance a patient will experience off-target effects even though the algorithms suggest they will not. Why is unintentional binding and subsequent off-target effects such a big deal? Well, while an off-target effect may have no impact on a patient whatsoever, it could alternatively have a devastating impact by disabling a tumor-suppressing gene or activating a cancer causing gene. Remember, that regardless of how sure you are that an RNA segment will not have any unintended binding, you can only guarantee that an RNA guide will not bind unintended targets that you are aware of.

Putting the scientific concerns of CRISPR aside, there is also a very intense patent war going on between the University of California, Berkeley and the Broad Institute at MIT with respect to this technology. In fact, both sides are in the process of presenting their case to the United States Patent and Trademark Office (USPTO) to determine who deserves the patent on using CRISPR-Cas9 to edit genes. Since companies have already licensed these patents, they have a vested interest and are willing to spend a lot of time and money to fight it out for as long as it takes to win. Interestingly, rather than an academic battle about who deserves credit for this discovery, the commercial aspect appears to be the driving force behind these filings. Patent issues are not limited to the U.S. federal court, Berkeley is also hitting roadblocks in Europe. Their patents are facing multiple challenges under the European Patent Office’s opposition process due to different nuances in rules revolving around the patent application as compared to the USPTO.2

Somewhere between the science aspect and the legal aspect lies the real ethical concern. There is intense financial pressure to be the first company to get this technology through the regulations and out to patients. Scientists have already predicted a fierce battle between U.S. and China to dominate the CRISPR landscape, which puts pressure on both sides to not delay marketing authorization with too much regulatory red tape.3 In the rush for approval it is important for both companies and regulators to not get distracted by money or fame and keep their focus on whether the treatment is safe and efficacious. So while people are discussing and fighting for the great power of CRISPR, it is paramount that they don’t lose sight of their responsibility to the people who this technology will ultimately be used on, the patient.



[1]

Travis J (17 December 2015). “Breakthrough of the Year: CRISPR makes the cut”. Science Magazine. American Association for the Advancement of Science.

[2]

Ledford H. Titanic clash over CRISPR patent turns ugly. Nature. 2016 Sep 22;537(7621):460-1.

[3]

Adams, C. (2016, December 30). Is CRISPR the big deal everyone says it is? Retrieved from http://www.straightdope.com/columns/read/3321/is-crispr-the-big-deal-everyone-says-it-is