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