Amplification of MVM(p) vectors through serial infection of a new packaging cell line

Vectors derived from the autonomous parvovirus MVM(p) [Minute Virus of Mice (prototype strain)] target the expression of transgenes to transformed eel Is and are therefore of interest for cancer gene therapy. Their production is however difficult and stocks are contaminated by wild-type MVM that is generated through recombination between cotransfected vector and helper DNA sequences, Integration of helper sequences into a packaging cell line has allowed to decrease recombination and to generate vector stocks with no det ectable helper virus. However, serial infection of this packaging cell line did not allow one to efficiently amplify recMVM, presumably because the in itial titres were too low. We have now generated a new packaging cell line that produces ten-fold higher stocks after transfection and that allows us to reach recMVM titres of up to 10(7) infectious units/ml after three to fo ur rounds of infection with no concentration procedure, Although undetectab le in the initial stocks obtained by transfection,wild-type MVM appeared du ring serial infections, This rapid and simple method should be easily scale d up, and will allow the production and purification of vectors suitable fo r in vivo testing of the therapeutic efficiency of recMVM vectors.