Patent ID: 7252991

Claim:
A retroviral packaging plasmid for the production of high titers of recombinant retrovirus in human cells comprising one retroviral helper DNA sequence derived from a replication-incompetent retroviral genome encoding in trans all virion proteins required for packaging a replication-incompetent retroviral vector and for producing virion proteins capable of packaging said replication-incompetent retroviral vector at high titer, without the production of replication-competent helper virus, said retroviral helper DNA sequence lacking the region encoding the native enhancer and/or promoter of the viral 5′LTR of said virus and lacking both the psi function sequence responsible for packaging helper genome and the 3′LTR, and encoding a foreign enhancer and/or promoter functional in a selected mammalian cell, and a foreign polyadenylation site, wherein said helper DNA sequence codes for ecotropic MMLV gag and pol and an envelope protein selected from a xenotropic, amphotropic, ecotropic or polytropic envelope protein.