RESEARCH ARTICLE Simian immunodeficiency virus-based lentivirus vector for retinal gene transfer: a preclinical safety study in adult rats Y Ikeda 1,2,6 , Y Goto 3,6 , Y Yonemitsu 1 , M Miyazaki 1,2 , T Sakamoto 4 , T Ishibashi 2 , T Tabata 5 , Y Ueda 5 , M Hasegawa 5 , S Tobimatsu 3 and K Sueishi 1 1 Division of Pathophysiological and Experimental Pathology, Department of Pathology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan; 2 Department of Ophthalmology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan; 3 Department of Clinical Neurophysiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan; 4 Department of Ophthalmology, Kagoshima University, Kagoshima, Japan; and 5 DNAVEC Research Inc., Tsukuba-city, Ibaraki, Japan Although lentivirus vectors hold promise for ocular gene therapy, they also have potential safety issues, particularly in the case of the current human immunodeficiency virus-based vectors. We recently developed a novel lentivirus vector derived from the nonpathogenic simian immunodeficiency virus from African green monkeys (SIVagm) to minimize these potentials. In this preclinical study, we evaluated whether SIV vector could be efficiently and safely applicable to retinal gene transfer by assessing the transgene expres- sion, retinal function and histology over a 1-year period following subretinal injection in adult rats. The functional assessment via electroretinogram after both titers of SIV- lacZ (2.5  10 7 or 2.5  10 8 transducing units/ml) injection revealed both the dark and light adaptations to soon be impaired, in a dose-dependent manner, after a buffer injection as well, and all of them recovered to the control range by day 30. In both titers tested, the retinas demon- strated a frequent transgene expression mainly in the retinal pigment epithelium; however, the other retinal cells rarely expressed the transgene. Retinas exposed to a low titer virus showed no significant inflammatory reaction throughout the observation period, and also maintained the transgene expression over a 1-year period. In the retinas exposed to a high titer virus, however, mononuclear cell infiltration persisted in the subretinal area, and the retina that corresponded to the injected area finally underwent degen- eration by around day 90. No retinal neoplastic lesions could be found in any animals over the 1-year period. We thus propose that SIV-mediated stable gene transfer might be useful for ocular gene transfer; however, more attention should be paid to avoiding complications when administering high titer lentivirus to the retina. Gene Therapy (2003) 10, 1161–1169. doi:10.1038/ sj.gt.3301973 Keywords: lentivirus; simian immunodeficiency virus; retina; electroretinogram Introduction Retinitis pigmentosa (RP) is an inherited disease, affecting approximately one in 3500 individuals. 1,2 Night blindness and a progressive loss of peripheral visual field are the typical symptoms of RP and a degeneration of photoreceptor cells, such as rods and subsequently cones, also results in a loss of central vision. RP is caused by a mutation in various genes, including rhodpsin, cGMP phosphodiesterase b-subunit (PDE-b), and rds/peripherin, which are expressed in photoreceptor cells. 3–5 Despite clinical treatments, RP is intractable and still remains a major cause of blindness in adults. Recently, retinal gene transfer has been suggested as a possible therapeutic strategy for RP. There are basically two concepts for this strategy; one is normal gene supplementation directly to photoreceptor cells, and the other is the gene transfer of secreting neurotrophic factors to the surrounding cells indirectly to prevent photoreceptor cell degeneration. Some investigators have tested several vectors in animal models of RP. In early studies, a recombinant adenovirus was employed for in vivo retinal gene transfer, and showed a transient rescue of photoreceptor cells in rd mice. 6–8 However, adenoviral vector could evoke a host immune response resulting in a transient gene expression. As a result, it is most likely not suitable as a treatment for human subjects. Further- more, a transient impairment of the retinal function as assessed by electroretinograms (ERGs) was apparently found, and closely correlated to the degree of histological inflammatory reaction following adenovirus injection. 9 ERGs might therefore be an important sensitive assess- ment technique to detect retinal damage because of vector injection, as well as to identify photoreceptor degeneration. Received 5 August 2002; accepted 23 November 2002 Correspondence: Dr Y Yonemitsu, Division of Pathophysiological and Experimental Pathology, Department of Pathology, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan 6 Contributed equally to this work. Gene Therapy (2003) 10, 1161–1169 & 2003 Nature Publishing Group All rights reserved 0969-7128/03 $25.00 www.nature.com/gt