Example 2
Another example of a suitable vector is a retroviral vector. Retroviruses are RNA viruses that contain an RNA genome. The gag, pol, and env genes are flanked by long terminal repeat (LTR) sequences (or their corresponding proteins). The 5′ and 3′ LTR sequences promote transcription and polyadenylation of mRNAs.
The retroviral vector may provide a regulable transactivating element, an internal ribosome reentry site (IRES), a selection marker, and a target heterologous gene operated by a regulable promoter.
Alternatively, multiple sequences may be expressed under the control of multiple promoters. Finally, the retroviral vector may contain cis-acting sequences necessary for reverse transcription and integration. Upon infection, the RNA is reverse transcribed to DNA that integrates efficiently into the host genome. The recombinant retrovirus of this invention is genetically modified in such a way that some of the retroviral, infectious genes of the native virus have been removed and in certain instances replaced instead with a target nucleic acid sequence for genetic modification of the cell. The sequences may be exogenous DNA or RNA, in its natural or altered form.
