A rapid method for estimation of baculovirus titer based on viable cell size

Baculovirus protein expression system is a powerful tool for producing recombinant proteins. To optimize conditions for efficient recombinant protein expression, it is important to determine titer of virus stock for arriving at an optimal multiplicity of infection (MOI) that maximizes recombinant protein expression. Traditionally plaque assays have been used for titer determination. Other methods such as endpoint dilution, quantitative real-time polymerase chain reaction and flow cytometry have been developed to aid the determination of virus titers. However, most of these methods are time-consuming and labor intensive. In this regard, a simple and rapid method for determination of virus titers based on the cytopathic effects that lead to viable cell size increase following virus infection is presented in this paper. In this study, the Vi-CELL (Beckman Coulter) was used to measure cell-diameter over a range of virus dilutions, following infection. Applying statistical modeling techniques, the viable cell-diameter data was used to estimate the virus titer. The results indicated that the viable cell-diameter based titer estimation to be reliable and comparable to titers determined by the traditional plaque assay.