Viral vectors have shown great promise in various areas of gene therapy and have led to major breakthroughs in the development of therapies for rare diseases such as severe combined immune deficiency (SCID-X) and hemophilia. Currently, adeno-associated virus (AAV), adenovirus, and lentiviral vectors are frequently used. However, the less commonly used alphavirus vectors offer interesting properties for gene therapy applications and are expected to contribute to the development of gene therapies for rare cancers. Alphaviruses are a class of RNA viruses that can replicate in large numbers within the cytoplasm of the host cell. The replacement of structural protein genes with exogenous genes in an alphavirus vector still has many of the biological properties of an alphavirus such as a broad host spectrum of infection, the ability to self-replicate, and induce apoptosis in transfected cells, while being able to express exogenous genes in large numbers and not integrating easily with the host genome. Currently, Sindbis virus (SIN), Semliki forest virus (SFV), and Venezuelan equine encephalitis virus (VEE) have been developed as expression vectors and are widely used in gene therapy and molecular biology research.