We have evaluated a chimeric, two-component Sindbis virus packaging system. As expected, use of this combination of two modified helper RNA species prevented formation of infection competent Sindbis viruses as analyzed by serial passaging. We observed, however, that vectors produced using this method were able to spread in BHK cell cultures and formed clusters of transgene positive cells that did not display cytopathic effects for up to 3 days post-transduction. Formation of spreading Sindbis virus vectors required only one of the helper components - the chimera with a deleted Ross River virus capsid and the Sindbis virus envelope glycoproteins. Spreading was also demonstrated in two rat glioma cell lines, 9L and BT4C, showing that this phenomenon was not limited to BHK cells. Our results warrant further characterization of split helper Sindbis virus vectors and imply their utility in gene therapy approaches where spreading of transgene expression and consequently high gene transfer rate could be beneficial.

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