Systemic Examination of Simian Immunodeficiency Virus (SIV)–Based Lentivirus Vector for Retinal Gene Transfer in Non–Human Primates

Abstract

Abstract: : Purpose: Lentivirus vectors hold promise as a potential treatment modality for ocular diseases. However, the possible risks associated with the use of current human immunodeficiency virus (HIV)–based vectors slow their clinical application. We recently developed a novel lentivirus vector derived from the non–pathogenic simian immunodeficiency virus (SIVagm), to minimize these safety issues. Here, we report the acute systemic toxicity following intraocular administration of SIV–PEDF in Macaca fascicularis, as a preclinical safety study. Methods: Eleven Macaca fascicularis (body weight=2.35–5.63 kg) were enrolled in this study. Approximately 20 µl of SIV–PEDF (low titer: 2.5x10⁷ transducing units [TU]/ml, equal to clinically used titer, high titer: 2.5x10⁸ TU/ml, and max titer: 1.0x10⁹ TU/ml, n=3, respectively) or control (balanced salt solution: BSS, n=2) were injected into subretinal space via a glass capillary tube. We undertook a systemic examination including general body condition, vital sign, hematology, and blood and urine chemistry during experimental course (3 months), and assessed the histology of general organ and the dissemination of vector genome by PCR assay. Results: SIV vector was efficiently transferred mainly to the retinal pigment epithelium and transgene expression was detected within 3 months. Neither dead animal nor serious side effect was found during experimental course. Transient increase of GOT and CPK was observed in all animals, suggesting a result of operation. Transient increase of serum IL–6 was found in some animals, but not dose–dependent. No vector genome was detected by PCR assay using the sample of whole blood and general organ. Conclusions: The current study exhibited the acute systemic safety of intraocular administration of SIV–PEDF (up to 40–times higher titer than clinically available titer). We are now conducting the long–term safety study to assess the possibility of carcinogenesis in non–human primates.

Keywords: gene transfer/gene therapy • retinal degenerations: cell biology • neuroprotection