Saturday, October 29, 2016

Genome Editing Potential for Cystic Fibrosis

People always ask what new information from NACFC excites me the most. I've listed my top 3 below, and will go into further detail about one of those--Gene Editing, as the topic of this entry.

Rebecca's Top 3 from the NACFC

1) The sheer number of new correctors and potentiators appearing in clinical research has exploded! There are almost too many of them to even keep track...and they are certainly NOT all coming from Vertex. There is a robust pipeline and a competetive surge to get these compounds on the market.

2) The development of new ways to measure CFTR function and personalized drug response. Small "organoids" can be grown from rectal tissue biopsy, nasal brushings (nasopheres), or bronchial tissue (bronchospheres). Once harvested, these cells can allow researchers to test whether or not an individual might respond to a drug treatment. As the number of new CFTR modulators increases, and as we try to treat patients with rare mutations, these techniques could prove to be extremely valuable. Once the cells are harvested, they can be reproduced indefinitely outside of the body, and drugs can be tested on a person's organoids in the lab as a good predictor of a clinical response in that individual. This kind of testing could streamline early phase clinical trials, and provide the safety of testing drugs in the lab vs. in vivo. 

3) Gene therapy strategies as a potential CURE for ANY mutation of cystic fibrosis. Investigators are examining several different techniques, as seen in the slide below. This entry will focus on CFTR gene editing using the CRISPR/Cas9 system.

One method of gene editing utilizes a system call CRISPR Cas9. CRISPR stands for clustered regularly interspaced short palindromic repeats--specific targets on a gene, containing short repetitions of base sequences, followed by short segments of "spacer" DNA. Cas9 is a single DNA targeting enzyme that serves to "code" for proteins related to CRISPRS.  In simpler terms, the CRISPR can be thought of as the specific portion of DNA targeted for alteration (the section where we find the presence of the CF mutation).  Cas9 can be thought of as a tiny pair of scissors, programmed to make a cut in the strand of DNA at precisely the right spot. This is a complicated process, but is explained nicely in this video produced by the CFF and shown during the first Plenary Session. 

Dr. Hao Yin from the Massachusetts Institute of Technology in Cambridge, MA gave a talk on Thursday afternoon entitled: 

In Vivo Genome Editing: From Proof-of-Concept to Therapeutic Delivery. 

Dr Yin's study utilized mice with a hereditary liver disease (tyrosinemia type I)
caused by a genetic mutation. He was able to demonstrate that CRISPR cas9 mediated correction of a genetic mutation in live mammals was truly possible, and has the potential for correction of human genetic diseases like CF.  As seen in the video, gene editing is a complex process. In this study, Dr. Yin combined lipid (fat) nanoparticle mediated delivery of Cas9 mRNA (messenger RNA) with adeno-associated viruses, and a repair template to induce gene repair in living mice. He was able to show that the mice exhibited short-term expression of the Cas9 nuclease by in vivo mRNA delivery, which provided efficienct on-target genome editing, and reduced off-target editing (altering the genome at unintended sites can obviously be problematic!). 

This proof-of-concept study is extremely exciting, but several challenges still remain. Two primary issues that investigators have always struggled with in regard to gene therapy strategies are the precision and specificity of targeting, and the method of delivery inside the nucleus of cells.

One method of getting information through the cell membrane to the inside of the cell is to use a modified virus to sort of "infect" cells with new information.  

It is profound that investigators have shown gene editing techniques may be successfully performed in living mammals, but there is still considerable progress to be made before we see these therapies in humans. At last year's NACFC, I also shared my excitement about development of these new gene therapy techniques. I'm really optimistic that progress will continue to accelerate in the coming year, and more exciting trials will be reported in 2017! 

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