The mobile transgene constructs of most human immunodeficiency virus (HIV)-
based lentivirus vectors currently in use contain viral long terminal repea
ts, a 5' untranslated region, gag sequences, and env sequences that include
the Rev-responsive element (RRE). In this study, we examined the possibili
ty of deleting HIV splice sites and gag and env sequences from an HN type 1
recombinant vector established in our laboratory as part of our ongoing ef
forts to improve this vector system. Mutations in the major splice donor si
te (SD) markedly reduced viral RNA expression but had little effect on vect
or titer. Deletion of gag or env sequences, excluding RRE, led to a moderat
e reduction in vector titer. Interestingly, deletion of RRE slightly reduce
d viral RNA expression but markedly impaired vector function. Combined dele
tions of RRE, gag (except for the first 40 nucleotides), env, and the SD mu
tation resulted in a twofold increase in cytoplasmic viral RNA expression a
nd a recovery of vector efficiency to similar to 50% of the wild-type level
. This increase in cytoplasmic RNA levels is likely to be due, at least in
part, to effects of the TE671 host cells, a human rhabdomyosarcoma cell lin
e used for vector production in our system, on the cytoplasmic distribution
of spliced and unspliced viral RNA. These results show that optimal lentiv
irus vector function can be maintained in the absence of multiple essential
viral elements.