New DNA delivery system potential

03 August 2022

Bristol scientists have developed a new DNA delivery system that may enable future editing of genes damaged in kidney disease.

In healthy people, specialised kidney cells called podocytes prevent proteins from leaking into urine. Podocytes have filtration slits that are made up of proteins, one of which is called podocin. The protein podocin is produced by the podocin gene. If a change or mutation in the podocin gene occurs, podocin protein can become faulty, causing damage to the podocyte, and protein can leak into urine. This can lead to chronic illness and a kidney disease known as steroid-resistant nephrotic syndrome (SRNS). SRNS is a devastating disease and is one of the most common and difficult to manage kidney diseases in children. A significant proportion of children affected have a genetic form of the disease which could possibly be treated using gene therapy approaches.

New research

In new research published in the journal Nucleic Acids Research, a team led by Dr Francesco Aulicino and Professor Imre Berger at the School of Biochemistry, University of Bristol, and Dr Ruth Rollason, Professor Moin Saleem and Professor Gavin Welsh from Bristol Renal, University of Bristol have collaborated to explore a process known as gene editing, which simply means to change DNA.

A podocyte

This change can be to add, remove or alter DNA at a particular location in a gene. This edit can potentially correct changes (mutations) in the DNA of patients with genetic forms of nephrotic syndrome (NS). There are several technologies that can successfully achieve this editing, the most popular being the CRISPR/Cas machinery. Compared to other gene editing technologies, CRISPR/Cas is faster, cheaper, more accurate and more efficient so is usually the technology of choice; it is much more “CRISP”.

If a patient’s DNA has mutated, and this mutation is found to be harmful, CRISPR/Cas9 might help to fix this by acting like “scissors” and cutting out the damaged part of the DNA. When that part is removed, the patient’s own cell can either repair it or a healthy DNA variant can be delivered to the gene, potentially preventing or curing the disease.

Current gene therapy approaches use human viruses as a “trojan horse” to infect cells that are carrying genetic errors, in order to correct those errors. However, these viruses are very limited in the amount of cargo they can deliver, significantly limiting their application in gene therapy. Think of it like an elevator delivering individuals to a floor in a building. These elevators usually have a capacity of a certain number of people. Exceeding this number can lead to operational problems and could cause harm.

Increasing the capacity of the vector

The Bristol team set out to develop a new system to push past existing limitations and edit genes more efficiently. They redesigned a virus that is harmless to humans called baculovirus, to create a potentially game changing gene therapy delivery tool that is no longer constrained by limited ‘cargo capacity’. In effect, they made an elevator that is not limited to the number of people it can carry.

Using this new tool and an NS patient podocyte cell line that carried the disease-causing error in the podocin gene, the team were able to deliver a healthy copy of the podocin gene into the genome, correcting the error and reversing its effect. These encouraging results showed that:

Baculovirus vector was safe to use to edit genes in cells.
It could be used to deliver tools to search for, and replace, faulty genes.
It was highly efficient in gene editing and overcame the limitation of current CRISPR/Cas9 delivery systems.

Professor Welsh, recipient of a Kidney Research UK paediatric research project grant which helped fund the work said:

“With support from Kidney Research UK, we have been able to develop this new approach which is very encouraging and holds promise for not only SRNS, but for a range of other kidney diseases. This work will now be further developed to determine whether this novel system is suitable for clinical use, to treat genetic forms of kidney disease”.

Dr Aisling McMahon, executive director of research, innovation and policy at the charity said: “We are delighted to see researchers from different specialties collaborating to develop better technology and accelerate research to help children and adult kidney patients faster. We look forward to the translation of these findings into clinical settings”.