CRISPR might have taken the world by storm but what’s next for gene editing technology? Ashley Jacobi, senior staff scientist at Integrated DNA Technologies (IDT) examines what's next.
Gene editing
“We’re going to make the most of the time we have together,” Alexandra’s mother said to her. When Alexandra* was born, in the 1950s, her life expectancy was 12 to 13 years, like that of other babies born with β-thalassemia. From childhood, her mother told her to make the most of life but prepared her to not expect too much – like finishing or even starting high school, going to university, or getting married. β-thalassemia is a genetic blood disorder, where the β-protein chains of haemoglobin in red blood cells are either present at lower than normal levels or not synthesised at all. Individuals with β-thalassemia can suffer from severe anemia and other serious medical issues such as bone deformities, broken bones, and an enlarged spleen. Patients are treated with regular blood transfusions, but this can lead to the build-up of iron in the body, which can damage the heart and endocrine system.[1]
Spotlight on CRISPR
Since CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) gene editing was discovered in 2012, it has been taking the world by storm and generating excitement among diverse audiences including scientists, people suffering from currently untreatable diseases, patient advocates and the general public. CRISPR was one of the biggest and most important science stories in 2019. To put this into context, in 2011 there were fewer than 100 published papers on CRISPR. Today, there are almost 30,000 and that number keeps growing.[2]
With the first clinical trials underway and a broad range of possible applications for CRISPR, including disease-vector control as well as agricultural science, I wanted to reflect on the successes achieved to-date and share my predictions for where the technology is heading. Given the hype and progress made in a relatively short timeframe, I believe we will be hearing a lot more about CRISPR in 2020 and the years to come.
What is CRISPR Gene Editing?
CRISPR gene editing is a technique being investigated by scientists to make permanent and precise changes to DNA in animals and plants. It is promising since it offers scientists the possibility to target and then edit a single, specific stretch of DNA more precisely, quickly and cheaply than was previously possible.
Ashley Jacobi
Ashley Jacobi - senior staff scientist at Integrated DNA Technologies
However, while the technique is relatively simple, powerful and precise, it is not perfect. The goal of CRISPR gene editing is to target, and then edit, specific stretches of DNA. However, cleavage may occur at unintended sites with similar sequences to the target site. These are known as off-target effects (OTEs) and may account for more than 50% of editing accomplished with wild-type (WT) Cas9, the most widely used CRISPR enzyme.[3] There is always a risk that off-target editing may lead to unintended, adverse consequences.
A New Cas9 Enzyme
Numerous attempts have been made by scientists to improve the specificity of the Cas9 enzyme, including our team at Integrated DNA Technologies (IDT). By devising an unbiased bacterial mutagenesis screen to isolate Cas9 variants, we at IDT were able to develop a high-fidelity Cas9 enzyme, known as HiFi Cas9. HiFi Cas9 offers highly specific cleavage with minimal OTEs and on-target nuclease activity in line with that of WT Cas9. The results of this work were highlighted through the application of HiFi Cas9 in human stem cells, published in Nature Medicine in 2018.[4]
Due to its activity and specificity, HiFi Cas9 is ideal for use in clinical studies. This led IDT to partner with Aldevron to supply a Good Manufacturing Practice (GMP) grade of the enzyme for clinical use. The enzyme has also been singled out for use by researchers in their proposed clinical trials. One such researcher is Dr Matthew Porteus, professor of Paediatrics (Stem Cell Transplantation) at Stanford University, who has been using it in his preclinical studies and intends to use it in his proposed Phase I sickle cell disease (SCD) clinical trial. The trial is investigating the potential for CRISPR to correct the SCD-causing point mutation to the human beta-globin gene (HBB). Another researcher, Dr Katy Rezvani, professor of Medicine (Stem Cell Transplantation) at the University of Texas MD Anderson Cancer Centre, has also been using HiFi Cas9 in her translational cancer research and is looking to use it at GMP grade in protocols being developed for potential use in oncology clinical trials. While unknowns remain, we are beginning to see the first therapeutic applications of CRISPR being tested in human trials.
Clinical Applications of CRISPR
In 2018, news broke that the first cancer immunology clinical trial using CRISPR had been opened at the University of Pennsylvania; this was quickly followed by trials launched in 2019 for SCD and β-thalassemia. SCD and β-thalassemia are prime targets for CRISPR editing since there are no viable current treatments available and each disease is caused by a single-DNA base mutation which, in theory, could be corrected using this technology. However, assessing the success of these trials and treatments, as well as any side effects, will take many years as we are only just beginning to scratch the surface of both the potential and clinical applications.
Where Might the Future Take Us?
As we build our understanding of the technology, and fully understand the opportunities it may afford us, as well as begin to see the outcomes of early clinical trials, I would anticipate that we begin to broaden its use from diseases caused by single-DNA base mutations to more complex diseases. Furthermore, we might start to see applications being developed for in vivo use. These in vivo therapies might start out as highly targeted and localised treatments, for example therapies delivered to a specific site like the eye but could eventually become systemic in-vivo treatments. This will, of course, take many years of testing.
We will also likely witness the advent and application of other similar technologies. Following a presentation at the Cold Spring Harbor Laboratory in October this year, there was much excitement about the potential of “prime editing.” While this technology is exciting, it is still somewhat in its infancy, compared with the current predominant CRISPR technology. It will be important to evaluate its strengths and weaknesses and assess OTEs. No doubt there will be other discoveries that will show potential, but it remains to be seen which ones will lead to eventual therapies and other real-world applications.
Maintaining Momentum
While there is currently much hype about potential therapies and uses, how will we maintain public support once more clinical trials are being launched and outcomes from early-stage trials begin to emerge? CRISPR and other gene editing therapies offer patients suffering debilitating diseases hope that someday there will be a curative therapy for them. However, as we have seen with other scientific advancements, it will be critical for consumer awareness and education to keep pace with scientific progress to ensure people remain open to CRISPR’s potential and confident that enough regulatory oversight is being applied.
The dialogue will require participation from all strata of society: scientists, ethicists, patients, patient advocates, caregivers, journalists and policymakers. Only with a concerted effort will the technology continue to make progress at its current rate. The benefits cannot be understated, and neither can the risks if we fail to learn from previous shortcomings or fail to facilitate meaningful and informed conversations and debates. As leaders in the innovation and provision of CRISPR technologies, we are invested in supporting and encouraging endeavours aimed at raising awareness, education, and discussion regarding CRISPR technology among both multidisciplinary experts and the general public.
References
1] U.S. Centers for Disease Control and Prevention (CDC). Real Stories from People Living with Thalassemia. 2019. https://www.cdc.gov/ncbddd/thalassemia/stories.html (accessed November 2019).
[2] https://scholar.google.com/scholar?as_ylo=2018&q=crispr&hl=en&as_sdt=0,9
[3] Zhang, X. H., Tee, L. Y., Wang, X. G., Huang, Q. S., & Yang, S. H. Off-target effects in CRISPR/Cas9-mediated genome engineering. Mol. Ther. Nucleic. Acids. 17 (4), e264 (2015).
[4] Vakulskas CA, Dever DP, Rettig GR, Turk R, et al. A high-fidelity Cas9 mutant delivered as a ribonucleoprotein complex enables efficient gene editing in human hematopoietic stem and progenitor cells. Nat Med. 2018;24:1216–24.