Cell Type-Specific AAVs: An Exploration of Reward and Cognition

A multidisciplinary research team from the University of Pittsburgh and Carnegie Mellon University was awarded a National Institutes of Health U01 grant to explore the specific targeting capabilities of Adeno-Associated Viruses (AAVs) in neuroscience studies. This project is directed by principal investigators William Richard Stauffer, PhD (Pitt), Andreas Robert Pfenning, PhD (CMU), Afonso Silva, PhD (Pitt), and Leah Byrne, PhD, from the Department of Ophthalmology at the University of Pittsburgh, who specializes in developing gene therapies for retinal diseases using adeno-associated viral vectors (AAVs) and gene editing approaches using CRISPR/Cas9 and proprietary tools.

In 2022, Dr. Byrne co-founded Avista Therapeutics (and serves as its chief scientific officer) with University of Pittsburgh Department of Ophthalmology chair José-Alain Sahel, MD, and Paul Sieving, MD, PhD, from UC Davis. Avista’s mission is to develop innovative gene therapies for retinal diseases that leverage its computationally guided scAAVengr platform to generate and validate a toolkit of proprietary AAV vectors to rapidly translate new gene therapies to the clinic. Shortly after Avista’s launch, they struck a partnership with Roche Pharmaceuticals to further this work.

In 2023, Dr. Byrne received the University of Pittsburgh’s 2023 Emerging Innovator Award for her ongoing work in gene editing approaches and developing viral vectors capable of delivering gene-based therapies and in early 2024 became a Senior Member of the National Academy of Inventors.

AAVs and Their Importance to Gene-Based Therapies

AAVs are small, non-enveloped viruses that are not known to cause disease in humans. AAVs have gained significant attention in the field of gene therapy due to their unique properties. They can deliver a piece of genetic material to target cells without integrating it into the host genome, reducing the risk of potentially harmful mutations. This makes AAVs an appealing vector for delivering modified genes to cells for therapeutic purposes.

U01 Grant Details and Aims

While AAVs are widely recognized for their role as gene delivery vectors in both laboratory animals and in clinical trials in humans, one of the challenges has been that these viruses are not inherently specific to particular types of cells.

Such nonspecificity can pose limits to their utility, especially when studying circuit functions in nonhuman primates (NHPs), which share significant physiological similarities with humans.

The team’s U01 research is aimed at developing cell type-specific AAVs, addressing this current limitation. The team plans to identify and leverage cell type-specific enhancers – regulatory elements believed to guide AAVs to target cell types more accurately. Prior studies conducted by the team showed enhancer-driven expression in certain cell compartments of the striatum, which plays a role in reward processing in the brain.

One of the primary objectives of the grant involves expanding the current multi-omic single cell database with data from several types of NHPs. This addition of this data will help the research team identify cell type specific enhancers that can effectively drive gene expression. Additionally, the research will screen AAV variants to see if any demonstrate a natural predilection towards certain cell types in the brain's cognitive and reward systems.

To ensure the effectiveness of these refined AAVs, the research team will use fluorescent in situ hybridization (FISH) for validation. FISH is a molecular technique that uses fluorescent probes to detect and locate specific DNA sequences on chromosomes. By binding these probes to complementary target sequences and visualizing them under a fluorescence microscope, FISH can identify chromosomal abnormalities, and pinpoint gene locations, making it a valuable tool in both clinical diagnostics and research settings.

Additionally, the grant will support developing a high-resolution MRI-based atlas of the rhesus macaque brain, providing an unparalleled resource for the global research community. These vectors will be housed and disseminated by the University of Pittsburgh BioForge Initiative, ensuring their wide availability for further study and application.

Dr. Byrne and colleagues research has a number of important implications. Not only does it offer the promise of enhancing our understanding of the complex cognitive and reward systems in primate brains, but it also sets the stage for further translational and development of effective AAVs and AAV-delivered gene therapies.

Further Reading

Learn more about the grant, Dr. Byrne’s research and laboratory, the Department of Ophthalmology, Avista Therapeutics, and the University of Pittsburgh Bioforge Initiative.