Vector platforms for gene therapy of inherited retinopathies

Abstract

Inherited retinopathies (IR) are common untreatable blinding conditions. Most of them are inherited as monogenic disorders, due to mutations in genes expressed in retinal photoreceptors (PR) and in retinal pigment epithelium (RPE). The retina's compatibility with gene transfer has made transduction of different retinal cell layers in small and large animal models via viral and non-viral vectors possible. The ongoing identification of novel viruses as well as modifications of existing ones based either on rational design or directed evolution have generated vector variants with improved transduction properties. Dozens of promising proofs of concept have been obtained in IR animal models with both viral and non-viral vectors, and some of them have been relayed to clinical trials. To date, recombinant vectors based on the adeno-associated virus (AAV) represent the most promising tool for retinal gene therapy, given their ability to efficiently deliver therapeutic genes to both PR and RPE and their excellent safety and efficacy profiles in humans. However, AAVs' limited cargo capacity has prevented application of the viral vector to treatments requiring transfer of genes with a coding sequence larger than 5 kb. Vectors with larger capacity, i.e. nanoparticles, adenoviral and lentiviral vectors are being exploited for gene transfer to the retina in animal models and, more recently, in humans. This review focuses on the available platforms for retinal gene therapy to fight inherited blindness, highlights their main strengths and examines the efforts to overcome some of their limitations.

Keywords: Adeno-associated virus; Adenovirus; Gene therapy; Inherited retinopathies; Lentivirus; Non-viral vectors.

Fig. 1

Retinal tropism of AAV, Ad, and LV. Arrows point at target cells (in bold) transduced after subretinal injection of the vectors indicated in the corresponding rows of the adjacent table. *: transduces the indicated cell type after intravitreal injection. **: transduces the indicated cell type after both intravitreal or subretinal injection. Tyr: tyrosine. References cited in the figure: 1. Auricchio et al., 2001; 2. Rabinowitz et al., 2002; 3. Weber et al., 2003; 4. Yang et al., 2002; 5. Dalkara et al., 2013; 6. Petrs-Silva et al., 2009; 7. Petrs-Silva et al., 2011; 8. Allocca et al., 2007; 9. Lotery et al., 2003; 10. Lebherz et al., 2008; 11. Mussolino et al., 2011a; 12. Vandenberghe et al., 2011; 13. Stieger et al., 2008; 14. Igarashi et al., 2013; 15. Hellstrom et al., 2009; 16. Klimczak et al., 2009; 17. Bainbridge et al., 2001; 18. Bemelmans et al., 2005; 19. Miyoshi et al., 1997; 20. Lipinski et al., 2014; 21. Greenberg et al., 2007; 22. Puppo et al., 2014; 23. Cheng et al., 2005; 24. Lotery et al., 2002; 25. Duisit et al., 2002; 26. Ikeda et al., 2003; 27. Miyazaki et al., 2003; 28. Molina et al., 2004b; 29. Takahashi et al., 2002; 30. Balaggan et al., 2006; 31. Binley et al., 2013; 32. Zallocchi et al., 2014; 33. Bennett et al., 1994; 34. Li et al., 1994; 35. Kreppel et al., 2002; 36. Lamartina et al., 2007; 37. Cashman et al., 2007; 38. Jomary et al., 1994; 39. Mallam et al., 2004; 40. Von Seggern et al., 2003; 41. Sweigard et al., 2010; 42. Wu et al., 2011; 43. Ikeda et al., 2009b.

Fig. 2

Schematic representation of AAV-based strategies for large gene transduction. X shows overlapping regions for homologous recombination. The striped boxes depict the exogenous recombinogenic sequence used in the dual hybrid approach. CDS: coding sequence; SD: splicing donor signal; SA: splicing acceptor signal; polyA: poly-adenylation signal.