Newly-developed Sendai virus vector for retinal gene transfer: Reduction of innate immune response via deletion of all envelope-related genes

Background: Recombinant Sendai virus vectors (rSeV) constitute a new class of cytoplasmic RNA vectors that have shown efficient gene transfer in various organs, including retinal tissue; however, the related immune responses remain to be overcome in view of clinical applications. We recently developed a novel rSeV from which all envelope-related genes were deleted (rSeV/dFdMdHN) and, in the present study, assess host immune responses following retinal gene transfer. Methods: rSeV/dFdMdHN or conventional F-gene deleted rSeV (rSeV/dF) was injected into subretinal space of adult Wistar rats or C57BL/6 mice. The transgene expression and histopathological findings were assessed at various time points. Immunological assessments, including the expression of proinflammatory cytokines, natural killer (NK)-cell activity, as well as SeV-specific cytotoxic T lymphocytes (CTLs) and antibodies, were performed following vector injection. Results: rSeV/dFdMdHN showed high gene transfer efficiency into the retinal pigment epithelium at an equivalent level to that seen with rSeV/ dF. In the early phase, the upregulation of proinflammatory cytokines, local inflammatory cell infiltration and tissue damage that were all prominently seen in rSeV/dF injection were dramatically diminished using rSeV/dFdMdHN. NK cell activity was also decreased, indicating a reduction of the innate immune response. In the later phase, on the other hand, CTL activity and anti-SeV antibodies were similarly induced, even using rSeV/dFdMdHN, and resulted in transient transgene expression in both vector types. Conclusions: Deletion of envelope-related genes of rSeV dramatically reduces the vector-induced retinal damage and may extend the utility for ocular gene transfer; however, further studies regulating the acquired immune response are required to achieve long-term transgene expression of rSeV.