Use of sodium butyrate to enhance production of retroviral vectors expressing CFTR cDNA.

Previously, we constructed a retrovirus vector (LCFSN) for transduction and expression of the cDNA encoding the normal human cystic fibrosis transmembrane conductance regulator (CFTR). The titer of virus from amphotropic packaging cells producing the LCFSN vector was low (10(3)-10(4) infectious units/ml). In an attempt to increase virus production, we used sodium butyrate (NaB) to treat murine retrovirus packaging cells producing this vector. NaB treatment increased the production of LCFSN from between 20-fold to greater than 1,000-fold, depending upon the producer clone, thereby resulting in virus titers up to about 1 x 10(7) infectious units/ml. This induction of virus titer could be accounted for, at least in part, by an increase in steady-state levels of full-length vector RNA within the producer cells. With some clonal producer cell lines, lowering the temperature of the virus harvest in combination with NaB treatment resulted in an apparent synergistic increase in virus production. The production of retrovirus vectors containing genes other than CFTR could also be increased by NaB treatment, although the enhancement in titer was modest (2-fold to 10-fold). The increase in virus production was not accompanied by an induction of replication-competent helper virus. NaB treatment also increased the transient production of retroviral vectors following DNA-mediated transfection into packaging cells such that virus titers of greater than 10(6) infectious units/ml could be readily attained.