Intracerebral Gene Transfer Using Viral Vectors

The recent development of recombinant viral vectors that are capable of transducing postmitotic cells may provide a powerful new tool for studying brain function, as well as ameliorative strategies in models of neurological disease. Some of these vectors have recently demonstrated direct expression of biologically relevant levels of protein expression (Mandel et al., 1997, 1998; Left et al., 1999; B16mer et al., 1998) for varying periods of time of up to 1 yr after direct intracerebral injection (Mandel et al., 1997, 1998; B16mer et al., 1997; Naldini et al., 1996a). Moreover, vectors injected into the nervous system have been shown, not only to be capable of expressing de novo transgenes, but also to be able to regionally suppress gene expression by delivery of antisense oligonucleotides (Xiao et al., 1997), by expression of a dominant-negative protein, by local knock-out of genes in transgenic animals carrying a transgene surrounded by lox-P sites (Donello et al., 1998), or by the production of molecules capable of inhibiting specific mRNAs, called ribozymes (Lewin et al., 1998). Thus, the use of viral vectors has great potential, not only for the study of gene therapy (GT), but also for the study of the molecular basis of certain brain functions. This chapter provides information about a range of practical issues involved in the use of recombinant vectors, and may be used as a guide for laboratories that intend to use viral vectors in their research. This chapter focuses on the three recombinant vectors that are among the most commonly currently used in the literature, i.e., recombinant adeno-associated virus (rAAV) vectors, recombinant adenovirus (rAd), and recombinant lentivirus (rLV) vectors. Other promising vector systems are under development for direct gene transfer, e.g., vectors based on herpes simplex virus (HSV) (During et al., 1994; Bowers et al., 1997). HSV vectors will not be discussed here, but this does not reflect any judgement on the quality or the potential of HSV vectors