by Monica Coenraads
I am delighted to give you a brief update on the MECP2 Gene Therapy Consortium, the collaboration of four elite labs that RSRT launched earlier this year. As you know, the Consortium is charged with developing gene therapy techniques that could treat or significantly reverse the symptoms of Rett. Our goal is to get to clinical trials. The project is grounded in work done last year by Consortium members Gail Mandel and Brian Kaspar that showed for the first time reversal of Rett symptoms in mice using gene therapy techniques that have the potential to be used in humans. The reversal of symptoms in mice was quite remarkable, but there are many challenges to translating that to a reversal in girls and women with Rett. The Consortium is attacking these challenges head on.
Earlier this month members of the Consortium met in the boardroom of a JFK Airport hotel in New York (we did not want to waste any of our meeting time traveling to and from a hotel in Manhattan). In addition to Gail Mandel, other members of the Consortium are Stuart Cobb (University of Glasgow), Steven Gray (University of North Carolina at Chapel Hill), and Brian Kaspar (Nationwide Children’s Hospital). The Consortium has a timeline of 3 years and a budget of $1.5 million. RSRT hosts in-person Consortium meetings twice a year as well as regularly scheduled conference calls.
The advantages gained by labs working collaboratively are clear: speed (four labs contributing to the work that has to be done), real time sharing of information means more brainpower and broader perspectives for problem solving. This is an obvious example of more heads are better than one.
Three facts make Rett Syndrome an attractive disease for gene therapy: it is monogenic; it is remarkably reversible in animal models; delivering MECP2 does not require understanding its function.
There are several hurdles to overcome. There is a requirement for MECP2 in every part of the brain so the gene will need to be broadly delivered. Also, the MECP2 Duplication Syndrome suggests that too much MECP2 is bad. It is difficult in gene therapy to regulate how many copies of a gene enter a cell and how much protein is made so the issue of MECP2 dosage must be carefully explored. We know that having too much MECP2 from conception and through early development causes serious symptoms. But does the same hold true if extra MECP2 is delivered later in life? Also, is it possible that females tolerate greater amounts of this protein than males? These questions must be answered before a clinical trial can be proposed.
Consortium members are also working on the following key issues:
1) Vector optimization – The vector is the Trojan horse that delivers the gene into a cell. There are many types of vectors in use and many more under development. For Rett we need a vector that can get into the brain and spread efficiently throughout the organ. The delivery route will affect the vector of choice. For example, if you deliver intravenously (via the blood stream) there is concern that a large amount of vector will end up in the liver potentially causing toxicity. To get around this problem a vector that de-targets the liver would be very useful. If dosage of MECP2 turns out to be problematic vectors that can be turned off will be required.
2) MEPC2 optimization – There are limits to the amount of DNA that can be packaged into a vector. The entire MECP2 gene does not fit. Scientists therefore have to select the parts of the gene they think are the most important. In essence they need to design a “mini-MECP2 gene’. Similar “mini-gene” work is also underway in the lab of Adrian Bird and will be shared with the Consortium.
3) Delivery route optimization – Gene therapy can be delivered via the blood stream, intrathecally into the spinal cord (like an epidural), or directly to the brain. Each route has its own advantages and disadvantages.
4) Optimizing how much gene therapy to deliver – the scientists are delivering low, medium and high dosages in an attempt to see how much is needed to get a therapeutic effect without generating toxic side effects.
We thank our precious donors who make this critical research possible!
In Their Own Words
It is very stimulating to be part of such a focused group of experts on gene therapy approaches towards Rett. The previous studies that we performed in collaboration with the Kaspar group were promising in showing that expression of a good copy of MeCP2, delivered systemically with AAV9, ameliorated Rett-like symptoms in female mice and prolonged survival significantly in affected males. Most surprisingly, but importantly, although we did not achieve a large amount of expression of the good MeCP2 in brains of the treated mice, we still saw behavioral benefits. We are now trying to improve the expression level of delivered MeCP2 by redesigning the vector, according to ideas and experimental results presented at the Consortium meetings. The openness of the investigators propels our studies and makes for a productive venture that would not be possible by any one individual laboratory. Additionally, it saves time because we can move on from doing obvious experiments that were done already in another laboratory. Finally, for those crucial experiments that had positive results, we have the ability to reproduce them in a different laboratory to insure that the results are solid.
– Gail Mandel
The Kaspar Laboratory is extremely excited about the potential to deliver gene therapies to the CNS. We are encouraged with our delivery studies to target cells efficiently in the brain, where one requires the proper expression of MECP2. Furthermore, our clinical trial in Spinal Muscular Atrophy has to date demonstrated the safety of this gene therapeutic in children which is excellent news for development of gene therapeutics in diseases, such as Rett. As a laboratory, we have bolstered our Rett efforts and are making great progress in testing the safety and developing the pre-clinical data necessary for developing a treatment. Our approach is building off the success of our collaboration with Dr. Gail Mandel. We are thankful for her continued support on our steep learning curve of Rett. This Consortium allows us to learn from each other’s studies. It’s a great group of scientists and I’m privileged to be a part of it. I see the progress we are collectively making and the commitment to the development of a therapy for Rett patients. The path is starting to look much clearer to get there.
– Brian Kaspar
The Cobb lab shares Brian’s excitement about the consortium’s efforts and the potential for gene therapy to counteract the root cause of Rett Syndrome. The project is progressing on multiple fronts from vector design/optimization to assessing best delivery methods and testing for efficacy and safety. Whilst the concept of gene therapy is a very simple one, the route to developing a safe and effective therapy is not at all straightforward. A key element of the consortium is that it enables us to share ideas and to discuss and act on emerging results from the four labs in real time. This will inevitably lead to more rapid progress in addressing the various challenges. As well as coordinating efforts, the consortium also enables us to cross validate key experiments to ensure findings are robust and reproducible across laboratories. After our Consortium meeting Kamal and I traveled to visit Steve Gray’s lab at UNC Chapel Hill. It was an extremely valuable few days as we were able to not only observe but also practice various delivery route methods. We also were able to compare and standardize how we score neurological features seen in the mice. Spending time together also provided an opportunity to further discuss vector development. Our trip to the US for both the Consortium meeting and visit to UNC was very productive.
– Stuart Cobb
Our efforts to treat Rett syndrome are built on 7 years of experience with the Rett community along with “bench to bedside” approaches that we are taking for six other inherited diseases. Our gene therapy clinical trial for Giant Axonal Neuropathy laid an important foundation for a similar approach to be taken with Rett syndrome. Gene therapy for Rett is an enormous challenge, but the last few years have garnered a great deal of excitement based on the similar positive findings published by all 4 laboratories in this consortium in 2 seminal papers. We are excited to be part of this group, and together we can accomplish much more than my lab alone. When Dr. Cobb visited our lab recently he provided critical expertise in a short visit that saved us an enormous amount of time and effort if we had been working alone. This is a small example of the many benefits we have had from working together in a collaborative fashion.
– Steve Gray