ASSESSMENT OF VIRUS PRODUCTION AND CHLORAMPHENICOL ACETYL TRANSFERASE EXPRESSION BY INSECT CELLS IN SERUM-FREE AND SERUM-SUPPLEMENTED MEDIA USING A TEMPERATURE-SENSITIVE BACULOVIRUS

Spodoptera frugiperda insect cells were grown in Sf-900 serum-free medium and two kinds of serum-supplemented media (IPL-41 and Grace's). The specific growth rates of uninfected cells were found to be 0.024, 0.035, and 0.034 h-1, respectively, at 33-degrees-C. The IPL-41 medium supported the highest maximum cell density (10.6 x 10(6) cells/mL) compared to 3.5 X 10(6) and 8.7 X 10(6) cells/mL with the Grace's and serum-free media, respectively. In temperature shift-down experiments with a temperature-sensitive baculovirus (Acts10YM1CAT), virus titer and chloramphenicol acetyl transferase (CAT) expression were highest in the IPL-41 (5.1 X 10(7) PFU/mL and 20000 U/mL). Use of Grace's medium gave higher virus titers than the serum-free medium (4.4 x 10(6) vs 4.1 x 10(5) PFU/mL) as well as higher CAT titers (7050 vs 1980 U/mL). Interestingly, in the three media used, the highest virus and CAT titers were obtained at MOI (multiplicity of infection) of 0.02. At MOI of 2.0 virtually no increase in virus or CAT titer was observed. This result is contrary to those obtained at constant-temperature (27-degrees-C) infection and cell culture, in which higher virus titers and recombinant protein expression are obtained at higher MOI.