Selecting the optimal AAV serotype is a primary determinant of therapeutic success and safety for ocular gene therapies. For intravitreal administration, AAV2 and AAV5 exhibit distinct retinal transduction profiles, with AAV2 primarily targeting inner retinal layers and AAV5 targeting outer retinal cells like photoreceptors. Non-human primate (NHP) models provide the most translationally relevant data for human clinical outcomes due to their anatomical and physiological similarity to the human eye. A comprehensive, comparative biodistribution study in NHPs is a core requirement for de-risking a development program and building a robust IND submission package, typically within an 18-24 month timeline.

Why are NHP models preferred for ocular AAV biodistribution studies?

NHP models are the industry standard for preclinical ocular studies because their eye structure, including the presence of a fovea, vitreous volume, and retinal cell layer organization, closely mimics that of humans. This anatomical fidelity provides highly predictive data on vector transduction efficiency, cellular tropism, and potential immune responses that cannot be accurately replicated in rodent or other models.

What are the primary retinal cell targets for AAV2 versus AAV5 after intravitreal injection?

Following intravitreal administration, AAV2 primarily transduces cells in the inner retina, most notably retinal ganglion cells (RGCs). In contrast, AAV5 demonstrates a strong tropism for the outer retina, efficiently transducing photoreceptor cells and the retinal pigment epithelium (RPE). This differential targeting is a key factor in selecting a serotype appropriate for a specific disease pathology.

How does vector shedding analysis inform the safety profile of intravitreal AAV administration?

Vector shedding analysis, which involves quantifying vector DNA in bodily fluids like tears, blood, and urine, is a GxP requirement for assessing the risk of vector transmission and systemic exposure. For ocular studies, it helps establish the degree to which the vector is contained within the eye versus escaping into systemic circulation, informing the overall safety and biodistribution profile.

How is vector biodistribution quantified in ocular and non-ocular tissues?

Vector distribution is assessed by quantifying vector DNA copies in collected tissue samples, providing quantitative data on the extent of vector dissemination. These findings are supported by qualitative histological analysis to visualize vector presence and transgene expression at a cellular level, confirming tropism and localization.

Precision in Sight: Ocular Biodistribution for AAV Gene Therapies

The therapeutic strategy for an ocular gene therapy is directly linked to the cellular tropism of the selected AAV serotype. For intravitreal delivery, AAV2 and AAV5 are two of the most characterized vectors, yet they possess fundamentally different transduction patterns within the complex architecture of the retina. Understanding these differences in a translationally relevant NHP model is a prerequisite for advancing a program toward clinical evaluation.

The choice between AAV2 and AAV5 depends entirely on the retinal cell population that must be targeted to address the underlying disease mechanism. AAV2’s affinity for retinal ganglion cells makes it suitable for conditions like glaucoma, while AAV5’s efficient transduction of photoreceptors is leveraged for inherited retinal diseases affecting these cells.

Our GxP-compliant preclinical facility, spanning over 100,000 square feet, includes dedicated NHP housing and specialized surgical suites for complex ocular administration studies.

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While the eye is considered immune-privileged, intravitreal administration does not guarantee complete vector containment. Assessing non-target tissue biodistribution is a core component of the safety evaluation. High-dose AAV administration studies have demonstrated that unintended systemic exposure can lead to significant toxicities, including sensory neuron damage (PMID: 29378426). This highlights the need to precisely map vector dissemination to distal tissues such as the liver, spleen, and dorsal root ganglia. This rigorous analysis establishes a clear safety profile and therapeutic window for the intended clinical dose.

“We started collaborating with UPenn Vector core in 2023 and the AAV vector which they manufactured laid a foundation for development of a gene therapy candidate which will enter soon preclinical studies. The key people from UPenn Vector Core joined Franklin Biolabs and our partnership transitioned without interruption from UPenn Vecor Core to Franklin Biolabs Research Vector Division. Franklin Biolabs is our trusted partner in our AAV-vector based gene therapy candidate development and we hope to continue the partnership for years to come.”
— Biotech Partner

Our commitment to the highest ethical standards in animal welfare, including the principles of the 3Rs (Replacement, Reduction, and Refinement), underpins our IND-enabling programs. This dedication to quality and ethics has contributed to a 100% IND approval success rate since 2019 for programs managed by our scientific leadership, with the Franklin Biolabs brand itself launching in 2024.