Efficacy and safety analyses of a recombinant human immunodeficiency virustype 1 derived vector system

Lentiviruses infect both dividing and nondividing cells. In this study we c haracterized a lentiviral vector system consisting of a packaging vector (p HP) and a transducing vector (pTV) derived from a recombinant human immunod eficiency virus type I (HIV-I). In pHP, the long terminal repeats (LTRs), t he 5' untranslated leader and portions of env and nef genes were deleted. T he leader sequence of pHP was substituted with a modified Rous sarcoma viru s (RSV) 59 bp leader containing a mutated RSV gag AUG and a functional 5' s plice site. The pHP construct was found to direct Gag-Pol synthesis as effi ciently as wild-type HIV-1. The pTV construct contains sequences required f or PNA packaging, reverse transcription and integration, but lacks viral ge nes. Co-transfection of pHP, pTV and a vesicular stomatitis virus G (VSV-G) envelope plasmid produced vectors at titers of 10(5)-10(6) transducing uni ts per milliliter in 48 h. Replication-competent virus (RCV) was not detect ed when deletions were made in the env gene in pHP The ability of this vect or system to transduce dividing and nondividing cell in vitro and in vivo w as also demonstrated. Compared with a Moloney murine leukemia virus (MLV) v ector the HP/TV vectors transduced human muscle-, kidney-, liver-derived ce ll fines and CD34(+) primary hematopoietic progenitor cells more efficientl y. Although the levels of the PTV transgene expression were high soon after transduction, the expression tended to decrease with time due either to th e loss of proviral DNA or to the inactivation of promoter activity, which w as found to be cell type-dependent. Analyses of extrachromosomal DNA showed that the unintegrated proviral DNA of lentiviral vectors survived much lon ger than that of the retroviral vectors. We : demonstrate that the HP/TV ve ctor is capable of high efficiency transduction and that long-term expressi on of lentiviral Vectors is dependent on target cell type, the infernal pro moter and the transgene itself in the transducing vector.