Retrovirus vectors designed for efficient transduction of cytotoxic or cytostatic genes

It is difficult to establish stable packaging cell lines producing retrovir us vectors for the expression of anti-oncogenes with cytotoxic or cytostati c potential, because these genes would also affect the growth of the packag ing cell lines. To overcome this problem, we designed a transcriptional uni t pBabeLPL for vector RNA production, in which the transcription of the exo genous genes is completely suppressed by the presence of a preceding insert ion containing the puromycin resistance gene (puro) and a poly(A) addition signal. This insertion is flanked by a tandem pair of loxP, and is designed to be excised after the introduction of Cre recombinase, when transcriptio n of the exogenous gene will be started from the 5'-LTR. The transcriptiona l unit carrying LacZ or p53 as the exogenous gene was introduced into a pre viously constructed prepackaging cell lines PtG-S2, in which the expression of VSV-G is also designed to be initiated by the introduction of Cre recom binase, while the gag-pol gene is expressed continuously. After the introdu ction of Cre recombinase by an adenovirus vector, LacZ- or p53- expressing VSV-G-pseudotyped retrovirus vectors with the designed structure were produ ced at high virus titers. The p53 virus was shown to be able to transduce p 53 into the entire population of several human cancer cell lines and to ind uce their growth arrest at the GI phase, indicating that this vector-produc ing system will be advantageous for human gene therapy.