Enhanced transduction efficiency of retroviral vectors coprecipitated with calcium phosphate

Retroviral vectors are being used increasingly in clinical gene therapy protocols but low transduction frequencies are presenting a significant obstacle to progress. In this paper we report a simple method to enhance the efficiency of ex vivo retroviral gene transfer. Calcium chloride is added to the vector stock and calcium phosphate precipitates out of solution in complex with the retroviral vectors. When such coprecipitated vectors were used for gene transfer, the vector titres were increased at least five-fold and as much as 50-fold compared with the titres obtained in standard polybrene-enhanced infection protocols. Titre enhancement was not dependent on the starting concentration of vector, was equally effective for ecotropic and amphotropic vectors on a variety of mouse and human cells, and was not associated with any alteration in vector host range properties. The method may be of value to concentrate retroviral vectors and to enhance the efficiency of gene transfer in selected human gene therapy protocols.