Disclosed herein are new defective Sindbis viral vectors made from wild typeAr-339 Sindbis virus, with differencesin replicase and envelope proteins between JT vectors and consensus Sindbisvirus sequences, and also between JT and Ar-339vectors. Also disclosed are plasmids used for the production of the vectors,methods for producing the vectors, methods for treatingmammals suffering from tumors and pharmaceutical formulations for use in thetreatment methods.