Temperature significantly affects retroviral vector production and deactivation rates, and thereby determines retroviral titers

The retroviral titer obtained from the pMFG/psi CRIP producer cell line is determined by a dynamic interplay of vector production and deactivation rat es. Both these rates are influenced by temperature. It was determined that; (i) the retroviral half-lives are strongly influenced by temperature and t he temperature dependency can be described by the Arrhenius equation with a n activation energy of 39 kcal/gmol; (ii) the actual retroviral vector prod uctivity per cell is highest at 37 degrees C with retroviral production rat e of 24.4(+/-7.0; +/- standard deviation) colony forming unit (CFU)/cell/da y; (iii) the dynamic interplay of these two factors produces an optimal tem perature of 34 degrees C for pMFG/psi CRIP cells under the culture conditio ns used; and (iv) the cellular growth rate is highest at 37 degrees C at 26 .8 hr doubling time. Taken together, these parameters can be used to optimi ze a two-step retroviral production protocol, where the cells are first gro wn under optimal growth conditions (37 degrees C) and second, the virus is produced at 34 degrees C to yield the highest titer. These results have sig nificant implications for optimal retroviral production protocols.