Researchers increased the production of lentiviral vectors by host cells by co-expressing the proteins SPSB1 or Tax. Mechanistically, this was shown to have a range of effects, including increased activity of the HIV-1 and cytomegalovirus promoters, the latter being used for many lentiviral constructs. This approach enables greater ability to generate sufficiently large quantities of viruses for use as vectors for transferring genes into a variety of cells, which has to date been expensive and laborious.