Neuronal and glial cell type-specific promoters within adenovirus recombinants restrict the expression of the apoptosis-inducing molecule Fas ligand to predetermined brain cell types, and abolish peripheral liver toxicity

Gene therapy using Fas ligand (FasL) for treatment of tumours and protectio n of transplant rejection is hampered because of the systemic toxicity of F ast. In the present study, recombinant replication-defective adenovirus vec tors (RAds) encoding Fast under the control of either the neuronal-specific neuronal-specific enolase (NSE) promoter or the astrocyte-specific glial f ibrillary acidic protein (GFAP) promoter have been constructed. The cell ty pe-specific expression of Fast in both neurons and glial cells in primary c ultures, and in neuronal and glial cell lines is demonstrated, Furthermore, transgene expression driven by the neuronal and glial promoter was not det ected in fibroblastic or epithelial cell lines. Expression of Fast driven b y a major immediate early human cytomegalovirus promoter (MIEhCMV) was, how ever, achieved in all cells tested. As a final test of the stringency of tr ansgene-specific expression, the RAds were injected directly into the blood stream of mice. The RAds encoding Fast under the control of the non-cell ty pe-specific MIEhCMV promoter induced acute generalized liver haemorrhage wi th hepatocyte apoptosis, while the RAds containing the NSE or GFAP promoter sequences were completely non-toxic. This demonstrates the specificity of transgene expression, enhanced safety during systemic administration, and t ightly regulated control of transgene expression of highly cytotoxic gene p roducts, encoded within transcriptionally targeted Rads.