The Rollercoaster Ride of Gene TherapyDecember 21, 2018

Gene therapy has had several ups and downs since the idea of editing genes for therapy was first published in 1972. While there have been several instances of successful attempts of treatment in humans, there have also been cases failures which have, at times, temporarily halted clinical studies.

One of the main issues with gene therapy has been the targeting of the molecular machinery to where it is needed and to avoid places it is not. The off-targeting of gene therapy is perhaps the biggest issue that needs to be addressed as it directly relates to patient safety. In the past few years, this issue has been addressed using various nuclease systems, such as Zinc Fingers, TALENS, and CRISPR. These systems have improved not only targeting, but also the efficiency of making changes to chromosomes.

However, these systems also have their drawbacks. For example, the most commonly used CRISPR system can only target about 10% of the genome. It has also been disclosed this year that, contrary to initial studies, CRISPR may have more off-targeting than originally thought. Additionally, a lab in Germany recently has shown that the immune system of most of the healthy volunteers for the study could produce antibodies against the CRISPR nuclease when it was injected. This immunity is likely to run across most forms of the CRISPR nuclease and across multiple species as the nuclease is highly conserved. These studies have shown that the current system has a number of limitations.

These limitations highlight the need of continual innovation in this area. Researchers have already shown some improvements to the nuclease itself. This year a lab at MIT used computation prediction to look for CRISPR nucleases that might be less site restrictive than the most commonly used one. By testing their predictions, they were able to find a nuclease which targets up to half of the genome, five times what the commonly used nuclease can target.

This shows that future innovations may create synthetic nucleases that could target anywhere in the genome by changing how the nuclease interacts with nucleic acid. Additionally, further innovation is needed to decrease the off-targeting of these systems and to hide them from the host’s immune system to improve their safety and efficacy for patients.

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