**5. Conclusion**

It has become increasingly clear that parvovirus-based vectors are a potentially safe and useful alternative to the more commonly used retroviral and adenoviral vectors. Gene transfer vectors based on the replication-defective (adeno-associated virus) and autonomous parvoviruses are emerging as promising vehicles for gene therapeutic approaches. AAV has been exploited as a gene delivery vector due to its unique characteristics like small size, simple genetic composition, lack of inflammatory response, and ability to transduce both dividing and non-dividing cells followed by persistence for the lifetime of the cell. AAV-based vectors are nonpathogenic and possess an extremely wide host and tissue range. Unlike AAV, autonomous parvoviruses do not integrate. However, their tropism for transformed tissues and innate oncolytic properties may permit rapid in situ therapies. As a consequence, APVs, including MVM and H-1 virus, have been developed as antitumor vectors with the aim of strengthening the antineoplastic effect of the natural parvoviruses. With the emergence of clinically approved products in the global market and more and more successful clinical trials being conducted, AAV is at the forefront of gene therapy, but *Parvovirus Vectors: The Future of Gene Therapy DOI: http://dx.doi.org/10.5772/intechopen.105085*

its smaller genome and neutralizing antibodies limit its application in many diseases. Present research suggests that the genetic modification of AAV vectors may further increase the success of AAV gene therapy. Vector can be engineered to increase AAV transduction efficiency by optimizing the transgene cassette. Moreover, capsid engineering can enhance vector tropism and the ability of the capsid and transgene to avoid the host immune response. Genetic manipulation of these components to optimize the large-scale production of AAV is also being explored.

APVs can prove to be superior alternative to more established vectors for gene transfer, particularly with respect to their potential use in cancer therapy. Based on the natural diversity of APVs and the ability to generate pseudo types with capsids from closely related members of the group, they should complement AAV vectors as well as offer various advantages like circumventing immune responses and exploiting tissue tropisms. However, substantial work is required to completely explore the pros and cons of these vectors, especially in context of mechanisms of transduction and the range of tissues that can be transduced in vivo by vectors with alternative, or modified, capsids. A significant preclinical evaluation of these vectors should lead to their application in future clinical cancer gene therapy trials.
