By Akash Bhattacharya, Senior Application Scientist at Beckman Coulter Life Sciences
Gene therapy holds enormous potential to cure and prevent a range of diseases, from inherited disorders to cancers to viral infections. The first gene therapy product was approved by the Food and Drug Administration in the US in 2017, and since then, approvals have followed on a regular basis. Even more encouraging is that the life sciences industry, including companies like Beckman Coulter Life Sciences, has made great strides in advancing the technologies that make gene therapy possible, which results in more effective, safer, and more affordable products.
That said, gene therapy is still comparatively new and faces certain hurdles before it’s more widely available to patients. Two key challenges are safety and cost, as they often are in medicine.
Luckily, there are promising strategies to overcome them. Two related methods are ultracentrifugation and analytical ultracentrifugation (AUC), which can, respectively, purify and characterise a gene therapy product.
Gene therapy generally involves inserting genetic material into cells via a viral vector that ‘infects’ the cell and delivers the genetic payload. One of the most popular carriers for gene therapy has been the adeno-associated virus (AAV), which was originally chosen for its efficiency as a gene delivery vector and for its low pathogenicity. Recombinant AAV, which is the leading platform for gene therapy today has been modified from the wild type to optimize its efficiency as a carrier of a therapeutic gene and to minimise its potential to cause disease. Although the AAV itself is harmless, at the end of the day, it is still foreign material, so it can trigger an immune reaction in the patient. Packaging efficiency becomes a major consideration when a larger dosage of the payload gene is injected in hopes of a greater therapeutic effect. Specifically, if the efficiency of the packaging is very poor, for instance, if eight of 10 viral packages are empty or only partially loaded, then in order to deliver the target dose of the payload gene, you may have to dose the patient with a proportionately higher dose of total vector. This process may trigger an allergic response. The FDA has issued guidance for clinical trials, which addresses the importance of this very issue.
One way to minimise the safety risk is to maximise the amount of therapeutic gene payload being delivered with each vector, which requires high-level purification. As mentioned, ultracentrifugation does this by using density gradients to allow for the extraction of gene therapy products. There are other instruments that attempt the same thing (standard chromatography setups), but the ultracentrifugation technique is growing in popularity to obtain pure product.
The corollary to the method is analytical ultracentrifugation (AUC), which can help characterise (that is, determine the packaging efficiency of) the product you’ve just purified. In short, you can take a very small amount of purified product and place it in the AUC, which employs sophisticated detectors, and processes the data via highly complex mathematics, which are, thankfully, automated. The end point is that AUC data gives an answer about what percent of the viral particles are loaded, which ultimately could minimise patient risk. The ultracentrifugation process is an excellent method to get as good a drug product as you can; and the analytic version of the instrument is an excellent method to evaluate your success.
Although ultracentrifugation and AUC have both been around for many years, the technology is advancing rapidly—the analytical ultracentrifugation instrument itself has a small foot print with superior capabilities and a more user friendly interface than its predecessor. The industry will keep updating the instruments as well as the workflow, to get to a place where the entire experiment and analysis process conforms to current good manufacturing practices. We also hope to further reduce time and costs by being able to analyse ‘dirtier’ samples—in other words, samples that are closer to the bioreactor, before multiple rounds of purification.
All of this work takes deep collaboration across disciplines. Our virology colleagues are working on ways to scale up triple transfection, the beautifully elegant process by which the AAV itself is made. Gene therapy is a powerful step in the direction of eradicating a disease, which has been exceedingly rare historically. Eliminating macular degeneration or neurodegeneration would be monumental but will one day be possible. Simplifying workflows, and increasing purity and packaging efficiency, are all integral steps in the process, and will ultimately allow gene therapy to reach a greater number of people, safely and affordably.
Volume 22, Issue 1 – Winter 2020/21
About the author
Akash Bhattacharya joined Beckman Coulter Life Sciences in October 2018. He works in the Colorado R&D centre developing AUC applications for novel systems in biotech and materials science. Bhattacharya holds a BSc in Physics from Presidency College, a MS in Physics from the Indian Institute of Science and a PhD in Biophysics from the University of Michigan.