Optimized conditions for the production of recombinant amphotropic retroviral vector preparations.

The production and stability of recombinant retroviral vectors was examined at various temperatures. The two studied recombinant retroviral vectors, based on different packaging cell lines, exhibited a four-fold increased half-life at 32 degrees C as compared to 37 degrees C. Surprisingly, this increased stability at 32 degrees C was only observed within a very narrow temperature window. At 30 degrees C and 34 degrees C, retroviral vector half-lives were quite similar to that at 37 degrees C. Regardless of the vector half-life, retroviral vectors accumulated in the culture medium for a period of 48 h before an equilibrium was reached between retroviral vector production and decay. Maximal accumulated recombinant retroviral titers were five- to ten-fold increased after a medium incubation at 32 degrees C as compared to 37 degrees C. Furthermore, multiple cycles of freezing and thawing of retroviral vector supernatants hardly affected the recombinant retroviral vector titer, independent of the presence of serum. This knowledge on characteristics of recombinant retroviral vectors has practical implications for the manufacturing of these viruses for clinical gene therapy protocols.