[40] Use of retroviral vectors for gene transfer and expression

This chapter discusses the use of retroviral vectors for gene transfer and expression. Retroviruses have evolved a highly efficient gene transfer capability that provides the basis for one of the most effective gene transfer systems available to date. The retroviral vector system has proved useful for the transfer of genes into many cell types, such as hematopoietic cells and other primary cells that are difficult to transduce by using other methods. Most attempts to make virus from a particular vector have been straightforward, resulting in high-titer virus carrying the unrearranged vector. In some cases, it has proved difficult to generate high-titer virus from vectors carrying specific genes or cDNAs. However, the presence of the intron in reverse orientation resulted in aberrant vector transcription and low vector titers. Some reports suggest that the titer of retroviral vectors can be dramatically increased by the cocultivation of a vector-producing cell line with a packaging cell line having a different host range. However, no more than a 2- to 10-fold increase has been found in titer by using this method, with the disadvantages of increased probability of helper virus generation and vector rearrangement.