Questions & Answers About The Future Of Genome Editing
By Anna Rose Welch, Editorial & Community Director, Advancing RNA
It was almost fate that, the same week I happened to stumble upon the University of Illinois news in the previous post about TALEN vs. CRISPR, I was able to attend a webinar put on by Scientific American Custom Media entitled “Curing The Incurable: The Promises Of Gene Editing.” This webinar featured a couple of high-profile folks whose opinions I was especially keen to hear, including: Andre Choulika, CEO of Cellectis, George Church of Harvard Medical School, and Matthew Porteus, Stanford University School of Medicine.
Since it can be hard to fit in all of the virtual things we want to attend, I’ve boiled down the hour-plus-long event down into a handful of points that were the most “need-to-know” about how we got to where we are with the current generations of these tools and what the future holds for them.
How did we get here? No surprise here, Cellectis’ Andre Choulika credits the arrival of CRISPR in 2012 as one of the primary reasons we see such emphasis being placed on gene editing today. As he explained, ease of access to and use of the technology led pretty much every lab — even those with absolutely no history of gene editing or protein engineering — to become gene editors overnight. This “viral contamination of the life science planet [to commence] gene editing” is what has turned the 21st century into what Choulika has termed the “Synthetic Biology Century.”
What tools do we have to work with now? There are four primary “families of tools,” including meganucleases, zinc-finger nucleases, TALEN, and CRISPR. However, there has also been some crossbreeding of these technologies, for example megaTAL (a combination of meganucleases and TALEN).
What vision are we striving to achieve with genome editing? Historically, it has been rare to see medicines coming onto the market that produce an actual cure; most benefit patients by modifying a disease to improve quality of life. But as Matthew Porteus explained, we have seen cures of some blood and immune system diseases thanks to allogenic stem cell transplantation (another Nobel Prize-winning strategy, btw). However, given the complexity and toxicity of such a treatment approach — not to mention it can only benefit a limited number of patients — this treatment strategy has served more as a jumping-off point for the cell and gene industry. Instead of seeking out stem cells from healthy donors, the goals now are to use these genome editing tools to edit a patient’s own stem cells ex-vivo.
We’re right on the cusp of this vision, Porteus explained. So far, only a small handful of patients have been treated with their own gene-edited stem cells. In the next few years, Porteus hopes to see gene editing used to correct certain disease-causing mutations altogether.
What are the long-term considerations or concerns for these tools? Immune responses, graft-vs.-host disease, and off-target effects are some of the biggest challenges the field is watching. To George Church, this only re-emphasizes the (often underemphasized) importance of sequencing — both prior to and post-edits.
However, the challenge will not just be assessing the potential off-target effects of a specific gene editing tool, but the impact these tools have in the overall context of the body. As Porteu pointed out, our genome naturally changes every day, introducing 10s to 100s of new (albeit scattered) mutations. How the changes made using gene editing tools jive with the changes occurring naturally in the body will be a large piece of the puzzle of gene editing moving forward.
What’s the skinny on germline editing? This is obviously a big, messy, and complicated question that will in no way be answered here — let alone in the next few years. Long-story-short, both Porteu and Church agreed that there is currently no clearly defined clinical need to take this approach — especially given other tools like genetic counseling, somatic gene therapies, and in-vitro fertilization which can enable couples to have children without genetic diseases.
Porteu summed up the morale question and how it should be approached in the future quite nicely. When the genome is intentionally altered and that change is passed on to future generations, that change is effectively impacting all of humanity.
‘That decision is not to be made just by scientists but needs to be made by a broad swath of people… with a diverse number of perspectives to say this is a line we want to cross,’ said Porteu. ‘This is not just a scientific and technical decision, this is a decision that has to be made by politicians, scientists, [medical experts], and the public; all of humanity has to buy into this concept.’
What are some of the tools (besides MNs, ZFs, TALEN, and CRISPR) we should be watching? In particular, Church highlighted recombinases, integrases, transposases, and deaminases. Scientists are currently exploring these enzymes’ potentials in making multiple, precise edits within larger pieces of DNA.
What will next-gen edited CAR-Ts look like? For the first-gen CAR-T therapies, the goals have been to prevent/treat graft vs. host by knocking out the TCR-alpha gene, as well as host vs. graft using a preconditioning monoclonal antibody treatment and a series of edits to knock out CD52 inside the T-cell.
We’re now looking at the next generation of off-the-shelf CAR-Ts. Choulika was particularly excited about some of the efforts being done to replace specific genes within T-cells to provoke new activity within the T-cell (i.e., replace CD20 with an effector gene like IL-12 or IL-2). Choulika sees such efforts as being CAR-T’s “foot in the door” into the world of synthetic biology.