Researchers at the University of North Carolina, USA, and its Gene Therapy Center have published findings exploring the potential of a new gene therapy for Sanfilippo type C, a type of childhood dementia caused by a deficiency of the enzyme HGSNAT.
A deficiency of one of four enzymes that work in the lysosome leads to Sanfilippo syndrome. The enzymes associated with subtypes A, B, and D float freely inside the lysosome and can even be released from the cell.
This enzyme release can be harnessed in gene therapy for these three subtypes, so an enzyme produced by a gene in one cell can enter and work in neighbouring cells. Known as cross-correction, or a bystander effect, this helps to increase the effectiveness of a gene therapy and lower the therapy’s required dose, reducing the potential for unwanted side effects.
However, HGSNAT does not float freely inside the lysosome. Instead, it sits on the membrane border separating the lysosome from the inside of the cell and is not naturally released from the cell. This means the current gene therapy approaches used for other Sanfilippo subtypes cannot treat Sanfilippo type C effectively, and the high doses required to produce the enzyme in the majority of cells may cause safety concerns.
A team of US researchers, led by gene therapy and Sanfilippo researcher Associate Professor Haiyan Fu, engineered a gene therapy so HGSNAT could leave the cell via specialised export compartments and cross-correct neighbouring cells. These compartments, called extracellular vesicles (EVs), are involved in cell communication and are normally released by all cell types.
EVs will package up proteins that contain an EV signalling tag, so the team coded the EV signalling tag onto the end of the genetic information for a correct HGSNAT enzyme.
In the laboratory, they delivered the gene therapy for HGSNAT with the EV tag into skin cells sourced from patients with Sanfilippo type C. Delivery methods included a non-viral method (using a special electric pulse) and a viral method (using an AAV2 delivery vehicle).
Forty-eight hours post-delivery, HGSNAT enzyme levels in cells that received the therapy were significantly greater, with levels 107 or 23 times higher for the non-viral and viral delivery methods, respectively. The waste material (GAGs) that typically build up in cells in Sanfilippo was also cleared. Importantly, there was no cell death as a result of the therapy.
The team collected the liquid around the treated cells and added it to skin cells that didn’t receive the gene therapy. After 48 hours, the HGSNAT levels increased in these cells and GAG levels reduced to normal. This indicates the tagged HGSNAT in the EVs released from the cell could enter and work in other cells.
Results from this study support further investigation into the use of EV signalling tags to increase the efficiency of gene therapy for Sanfilippo type C. Future studies in animal models are needed, which will provide a greater indication of its therapeutic potential in patients.
Funding for the study included a research grant from the USA Government’s National Institutes of Health.
