Abstract: The present invention provides viral vector compositions of high titre and purity, as well as methods for production of said compositions. The methods of the invention incorporate multiple features, such as production of viral vector particles in serum free media and multiple harvesting steps following transduction of the producer cell which provides for enhanced production of said viral vectors. The viral vector compositions of the invention, by virtue of their high titre and purity, minimize the deleterious phenotypic changes that typically occur following transduction of target cells, such as loss of a sub-populations of transduced cells, and effects on proliferation, differentiation, reprogramming or functionality of transduced cells.