Assessing the tropism of adeno-associated virus serotypes in the primate retina for gene therapy

Abstract

Purpose: The success of gene therapy largely depends on delivery of the therapeutic molecule to the target tissue or cell type. Efficient gene delivery can be achieved using viral vectors such as adeno-associated viruses (AAV). There are many naturally occurring AAV (1-9) serotypes with distinct tropisms to different cell and tissue types and in addition, mutations made to the AAV capsid can enhance or alter cellular tropism. We are interested in identifying the tropism of AAV serotypes in the non-human primate (NHP) retina that will be applicable to gene therapy.

Methods: To assess the tropism of the various AAV serotypes in NHPs, we delivered various AAV serotypes including two novel AAVs expressing a reporter gene (eGFP) from a cytomegalovirus (CMV) promoter/chicken β-actin enhancer in “recycled” NHPs. We used two delivery routes and different doses to assess the efficacy and tropism of the different AAVs in the retina. We also screened the serum and ocular fluid for anti-AAV neutralizing antibodies using an in vitro assay.

Results: The novel AAVs tested efficiently transduced the photoreceptors, ganglion cells and retinal pigment epithelium. One AAV also targeted anterior segment structures. The optic nerve was transduced with both novel AAVs. It remains to be determined if the ocular pathways in the CNS were transduced. There was no inflammation observed at the selected doses.

Conclusions: AAV serotype analyses have been carried out extensively in the mouse retina. However, AAV can display altered cellular tropism across different species. For translational studies, it is important to determine AAV transduction characteristics in the NHP retina, as that is most similar anatomically and immunologically to human retina. These studies will be directly applicable to determining AAV gene delivery approaches for many human retinal diseases.