Evaluation of retroviral production systems using quantitative analysis

Because of the low titer of retroviral supernatant, it is necessary to develop and optimize large-scale retroviral production systems. To quantitatively determine the effect of a given operating condition (e.g., temperature and serum content) on producer cells' retrovirus-producing capacity, a mathematical model was used to analyze the static retroviral production system described by three processes: viral diffusion, decay, and generation. The analytical solutions of the defined model equations were fitted with experimental data to determine the specific retroviral production rate constant, which represents the competence of a retroviral production system. Two different retroviral production systems, inducible production of vesicular stomatitis virus G glycoprotein (VSV-G) pseudotyped retrovirus from 293GPG/EGFP cells and constant production of ecotropic retrovirus from GP+E86/LNCX cells, were employed to demonstrate the feasibility of the engineering analysis. Our results indicated that the time-variant specific retroviral production rate of 293GPG/EGFP cells reached its maximum value of 5.7 x 10(-3) CFU/cm(2).h.cell, and the constant specific retroviral production rate of GP+E86/LNCX cells was 1.49 x 10(-2) CFU/cm(2).h.cell for the whole period of production. Furthermore, the effects of serum concentration and temperature on the ecotropic retroviral production system were examined separately. Our results suggest that producing ecotropic retroviruses with 10% fetal bovine serum at 37 degreesC is the optimal operating conditions for the long-term production system used here.