Reducing cytotoxicity induced by Sindbis viral vectors.
Sindbis virus has been recognized as a potentially useful virus vector for gene therapy. In an effort to improve its utility and provide cell-targeting capability to gene therapy vectors, we recently developed Sindbis virus vectors possessing chimeric envelopes with cell-specific targeting ability [K. Ohno et al. Nature Biotechnol 15:763-767, 1997; K. Sawai et al. Biochem Biophys Res Commun 248:315-323, 1998]. However, a residual problem associated with Sindbis virus vectors is the apoptotic effect of this virus on infected cells. To address this issue, we have studied the possible role of bcl-2 expression. Bcl-2 expression has been postulated to facilitate the establishment of persistent Sindbis viral infection by blocking virus-induced apoptosis. In this study we produced a Sindbis virus vector capable of expressing human bcl-2 and the reporter gene, lacZ. This chimeric virus (SinRep/lacZ/bcl-2/DH-BB) showed a marked reduction in induced apoptosis in infected cells. For example, after infection with this vector, cell proliferation of BHK cells was 55% of that of uninfected cells 2 days after infection and 40% 3 days after infection. While this reflected a significant degree of apoptosis, the effect was much less pronounced than that seen with wild-type Sindbis virus. Cell proliferation was reduced to 26% 2 days after wild-type virus infection of BHK cells and to only 7% 3 days after infection. Although additional work will be required to eliminate apoptosis induced by Sindbis virus vectors, the studies reported here suggest that such a goal may be achievable after additional modification of the vectors.