Virofection: a one-step procedure for using replication-defective retrovirus vectors.

Virofection is a simple new way to use replication-defective vectors. It consists of the cotransfection of two plasmids: one plasmid bearing the genome of the replication-defective retrovirus vector and a second "helper" plasmid expressing the gag, pol, and env retrovirus sequences. It provides stable integration into the chromosome and long-term expression of only vector-borne sequences. We present here several helper plasmids derived from avian leukosis viruses, which we have used for the virofection of the lacZ reporter gene in chicken cell cultures. Expression can be stabilized at a very high rate in both chicken fibroblasts and blastoderm cells, without giving rise to replication-competent virus.