Researchers are making strides in improving gene therapies for genetic diseases, particularly chronic kidney disease, using adeno-associated virus, or AAV, vectors. While AAV-based treatments have shown promise, delivering these therapies effectively to the kidneys has remained a challenge — until now.
There are many different types of AAV capsids — the protein shells of virus particles — that have been used to deliver genes to cells, each with unique effects. Most commonly, AAV capsids are delivered into the body via intravenous injection, but this method has limited success in targeting kidney cells and can sometimes cause harmful side effects, especially to the liver.
New research by Oregon Health & Science University scientists, however, has uncovered multiple factors to improve gene delivery to the kidney, including AAV capsids, delivery routes such as IV injection or direct injection into the renal vein or renal pelvis — areas closer to the kidneys — and kidney disease conditions.
The study results were published today in Nature Communications.
Hiroyuki Nakai, M.D., Ph.D., OHSU School of Medicine Distinguished Professor in Molecular Medicine, Department of Molecular and Medical Genetics, and colleagues tested 47 different AAV capsids in mice, examining the effects of various delivery routes. One capsid, AAV-KP1, stood out as particularly effective when administered directly to the kidneys via the renal vein or pelvis, reaching kidney cells with minimal impact on the liver. In contrast, AAV9, which is not an effective capsid in healthy kidneys, showed better kidney targeting when injected intravenously in cases of chronic kidney disease.
The team's research suggests that these local injections may improve the targeting of kidney cells and reduce unwanted side effects, while IV injection emerges as an effective approach to deliver genes to the kidney when the kidney is diseased, but not when it is healthy.
"There was a misconception based on the literature already out there that AAV doesn't work well on the kidney," said Nakai, senior author of the paper. "Our study shows that we can deliver genes to renal tubules and podocytes [highly specialized cells] in the kidney, the two important target cell types for gene therapy, and while there is a significant barrier, we now know that it is possible, especially for certain types of kidney diseases."
Taisuke Furusho, M.D., Ph.D., lead author of the paper, was a postdoctoral scholar in Nakai's lab when they worked on this study. His expertise as a clinical nephrologist helped identify the combinations of AAV capsids and delivery routes that turned out to be most effective.
"The kidney is difficult to target with gene therapy because it is composed of many different cell types and shows structural complexity, compared to other organs," he said. "Genetic kidney diseases were considered mainly to be found in pediatric patients, but recent studies have shown that genetic causes are more commonly found than previously thought in both children and adults with chronic kidney diseases. If we can correct that gene expression in those cases, that would be a huge potential."
One of the most significant findings of the study was that the two capsids behave differently in terms of how they accumulate in the injection site and spread in the body. The researchers discovered that injecting AAV-KP1 directly into the kidney resulted in effective and specific targeting of kidney cells, while AAV9 spread all over the body even by local delivery.
The study also highlighted an important point: The results varied significantly between species, showing big differences between mice and nonhuman primates in how the virus enters kidney cells following injection into the renal pelvis. The cell entry mechanism found in nonhuman primates enabled AAV vectors to enter kidney cells in the presence of anti-AAV-neutralizing antibodies, overcoming pre-existing immunity in nonhuman primates, which was not the case in mice. These observations underlined the need for careful selection of the right AAV capsid and injection method, depending on the species and the disease condition.
Nakai said this research provides valuable insights into how to optimize AAV-based gene delivery to the kidney in both basic research and gene therapy. It shows that the best results come not just from choosing the right virus capsid, but also from carefully considering how and where to administer it, depending on the disease condition. These findings could pave the way for more effective treatments for people suffering from kidney diseases in the future.
In addition to Nakai and Furusho, OHSU co-authors include: Ranjan Das, Ph.D., Hideyuki Hakui, M.D., Ph.D., Anusha Sairavi, M.S., Kei Adachi, Ph.D., Mia S. Galbraith-Liss, B.S., Pratheppa Rajagopal, Ph.D., Masahiro Horikawa, M.D., M.B.A., Shuhua Luo, B.S., Lena Li, M.D., Kentaro Yamada, M.D., Ph.D., Nicole Andeen, M.D., Gregory A. Dissen, Ph.D.
In our interest of ensuring the integrity of our research and as part of our commitment to public transparency, OHSU actively regulates, tracks and manages relationships that our researchers may hold with entities outside of OHSU. In regard to this research, OHSU's Nakai and Adachi receive a royalty of AAV-related technologies licensed by Takara Bio Inc. and Capsigen Inc. Nakai serves as a consultant for biotech companies, is a co-founder of Capsigen Inc., and holds shares of Capsigen Inc. and Sphere Gene Therapeutics.
This research was supported by a Sponsored Research Fund from Otsuka Pharmaceutical Co., Ltd., and National Institutes of Health Grant P51 OD011092, which supports the Oregon National Primate Research Center. This work used the Extreme Science and Engineering Discovery Environment, which is supported by National Science Foundation grant number ACI-1548562. Specifically, it used the Bridges-2 system, which is supported by NSF award number ACI-1928147, at the Pittsburgh Supercomputing Center. The ONPRC Molecular Virology Core, supported by P51 OD011092, provided neutralizing antibody assays for NHPs. The content is solely the responsibility of the authors and does not necessarily represent the official views of any funders.
All research involving animal subjects at OHSU must be reviewed and approved by the university's Institutional Animal Care and Use Committee (IACUC). The IACUC's priority is to ensure the health and safety of animal research subjects. The IACUC also reviews procedures to ensure the health and safety of the people who work with the animals. The IACUC conducts a rigorous review of all animal research proposals to ensure they demonstrate scientific value and justify the use of live animals.
