APOPTOSIS-MEDIATED REGULATION OF RECOMBINANT HUMAN GRANULOCYTE-COLONY-STIMULATING FACTOR PRODUCTION BY GENETICALLY-ENGINEERED FIBROBLASTS

We investigated the feasibility of an inducible apoptosis system to re gulate cells genetically engineered for ectopic cytokine production. I n a previous study, cDNA encoding the ligand-binding domain of the rat e estrogen receptor was fused to the sequence for murine Fas transmemb rane and cytoplasmic regions, and expression of the fusion protein (Mf asER) in L929 fibroblasts resulted in estrogen-dependent apoptosis. We applied this MfasER/estrogen strategy to apoptosis-mediated regulatio n of cytokine production, using the human granulocyte colony-stimulati ng factor (G-CSF) as a model. Upon estrogen treatment, the G-CSF produ cers expressing MfasER showed an apoptotic phenotype and died in sever al hours, with termination of G-CSF production. This estrogen-induced apoptosis: was not influenced by whether the target cells were prolife rating or resting, unlike a conventional suicide system involving the herpes simplex virus I thymidine kinase (HSVtk). That is, estrogen ind uced prompt and extensive apoptosis in the resting cells which express ed MfasER, while ganciclovir treatment induced only partial reduction of the resting cells which expressed HSVtk. These results imply the fe asibility of apoptosis-mediated regulation of cytokine production by g enetically modified cells for supplement gene therapy.