The first gene therapy trials in three distinct laboratories are underway using the IQSEC2 minigene
Adeno-associated virus (AAV) has recently been demonstrated to successfully deliver a replacement copy of a defective gene for several diseases in humans. The FDA, the major licensing body in the USA that has been given the task of ensuring that new therapeutics are safe and effective, has approved the use of AAV in humans. There are now many clinical trials underway for other genetic diseases.
Applying AAV to deliver a “good” copy of the gene, as we wrote in October, has two major hurdles for a given gene. First, the way that we deliver gene therapy with AAV is by replacing the genes that normally appear in the virus with our gene of interest (in our case IQSEC2). The problem is that the size of the gene that can fit in the AAV has to be small and over half of all genes are too big. IQSEC2 is way too big to fit in an AAV. The second problem is providing specificity for where the gene is delivered and how it gets into the brain.
The IQSEC2 gene is only used in brain neurons and getting into the brain is challenging due to the existence of a barrier between the rest of the body and the brain (known as the blood brain barrier or BBB). The purpose of the BBB is to block the ability of molecules that get into our blood from our diet, or from other entry points, from getting into the brain.
Over the past few months we have surmounted these problems. First, we have found a way to reduce the size of the IQSEC2 gene so that it can fit within the AAV virus. This has entailed reducing the size of the IQSEC2 gene by over 40%. This was possible based on our ability to model the molecular structure of the protein made by the IQSEC2 gene (see our new paper in Journal of Biomolecular Structure and Dynamics). We were then able to identify regions in the IQSEC2 protein which were not important in its function per se; rather their function was merely to connect functional regions of the protein. An appropriate analogy might be when you look at a map of a country you see big cities connected by lines (highways). The cities provide the function to the country: factories, major places of employment, services, whereas the highways serve to connect the cities. Each city has its own function and together the network of highways serves to connect all the functions to work together. All of the reduction in IQSEC2 which we have achieved has been in its highways or connectors between the functional domains of IQSEC2. We have created a new way to reconnect the domains using a very short stretch of the simplest amino acid glycine. We have studied this miniature IQSEC2 (hereafter referred to as miniIQSEC2) in terms of its function in a virtual and experimental setting and found that the miniIQSEC2 gene is similar, if not identical, to the normally existing IQSEC2 gene in terms of the protein that is produced and its functionality in multiple different measurements.
The second problem – one of specificity – has been surmounted by inserting control regions in front of the IQSEC2 gene that will only allow it to be made in neurons. Finally, the ability of the AAV to cross the BBB has been recently been shown to be possible.
Therefore, we are excited to say that the first gene therapy trials in three distinct laboratories are underway using the IQSEC2 minigene. All three labs will be using the same AAV construct to see if it can prevent IQSEC2 disease in mice with different IQSEC2 mutations. These experiments will be examining the ability of the AAV with the IQSEC2 minigene to prevent seizures, to improve learning, and to correct abnormalities in behavior (including speech). In science it is extremely important to show that results are reproducible and thus having three different labs working on the same problems will be extremely helpful in providing confidence that the approach will work. We are hoping to know by this fall if the AAV with the IQSEC2 minigene is effective.
This is a major step forward. We are hopeful, but also realistic, that the AAV we create may need to be refined and may only be effective for a subset of IQSEC2 mutations. However, the current studies underway are the translational bridge for our previous basic science studies and the establishment of clinical trials in children with IQSEC2 disease.
If we are able to demonstrate benefit with the IQSEC2 minigene AAV our next step would be in clinical trials. We hope to come back to you soon with an update!
Andy Levy
Technion Israel Institute of Technology
Haifa, Israel
