Improved titers of HIV-based lentiviral vectors using the SRV-1 constitutive transport element

The development of lentiviral vectors that use Rev-independent mechanisms o f nuclear export for their genomic RNA could facilitate the construction of novel anti-HIV vectors. We have improved the titers of Rev-independent len tiviral vectors having the SRV-1 CTE by mutating the major splice donor and acceptor sites present in the vector and by relocalization of the CTE sequ ences adjacent to the HIV-I 3'LTR. These two modifications have additive be neficial effects on vector titers and packaging efficiency. Packaging these CTE+ vectors expressing marker genes with a Rev-dependent HIV-1 helper vec tor yields higher titers than are obtained using a Rev-dependent lentiviral vector.