Ocular Gene Therapy: A Literature Review with Special Focus on Immune and Inflammatory Responses

Gene therapy has emerged as a research topic of choice in recent years. The eye in particular is one of few organs of the body for which gene therapy has received Food and Drug Administration approval, and it remains a field of great interest for gene therapy development. However, its associated immune and inflammatory reactions may render the treatment ineffective or harmful, which are of particular concern for the eyes due to their susceptibility to inflammation. The severity of immune and inflammatory reactions depends on the choice of vector and its route of administration. Furthermore, most preclinical and clinical studies have shown that the dose of vectors is correlated with the degree of humoral response and ocular inflammation. The route of administration directly impacts the degree of immune and inflammatory reaction. Subretinal delivery produces a weaker humoral response than the intravitreal route. However, some studies have demonstrated that the subretinal delivery induces a stronger inflammatory reaction. On the other hand, several instances of vision loss due to severe late onset intraocular inflammation were reported in a clinical trial involving intravitreal delivery of viral vectors. When compared with the intravitreal route, suprachoroidal gene delivery has been shown to produce weaker humoral response. However, unlike the subretinal space, the suprachoroidal space is not known to have immune privilege status. Inflammatory reactions following ocular gene therapy are typically mild and most clinical and preclinical studies have shown that they can be controlled with topical, local or systemic steroids. However, severe inflammatory responses may occur and require aggressive management to avoid permanent vision loss. Further investigations are required to elucidate and expand our knowledge of inflammatory reactions, and their optimal management, following ocular gene therapy.