[rhDNase: scientific background, cloning and production].

Despite the hopes raised by the first attempts in gene therapy, direct correction of the defect in CFTR protein associated with cystic fibrosis is still beyond clinical reach. Therefore we have to set upon the consequences of the defect. Respiratory distress and progressive lung destruction in cystic fibrosis can be accounted for by infectious exacerabations and the accumulation of viscous purulent secretions in the airways. For a long time we have known that purulent secretions that accumulate in the airways of patients with cystic fibrosis contain large amounts of DNA, a complex macromolecule that contributes mostly to the viscosity and hinders the mucociliary function. Hence we hypothesized that enzymatic cleaving of DNA molecules by desoxyribonuclease (DNase) should reduce the viscosity of sputum, and slow or prevent the deterioration of pulmonary function. Using the techniques of molecular biology and genetic engineering, we identified the gene of human DNase I, which was cloned in mammalian cells to produce large amounts of a glycosylated protein for therapeutic use. Catalytic amounts of rhDNase greatly reduce the viscosity of purulent cystic fibrosis sputum, transforming it within minutes from a nonflowing viscous gel to a flowing liquid. This effect was associated with a decrease in size of DNA fragments in the sputum. Our studies suggested that inhalation of a rhDNase aerosol might be a simple direct approach to reduce the viscosity of purulent secretions and thereby help patients with cystic fibrosis clear their airways and breathe more easily.