Abstract
Baculovirus has emerged as a promising vector for in vivo or ex vivo gene therapy. To date, the infectious titer (IT) and multiplicity of infection (MOI) based on the ability of baculovirus to infect insect cells are commonly adopted to indicate the virus dosage. However, the infectious titer and MOI do not reliably represent the baculovirus transducing ability, making the comparison of baculovirus-mediated gene transfer difficult. To determine the baculovirus transducing ability more rapidly and reliably, we developed a protocol was called “transducing titration” to evaluate the transducing titers (TT) of baculovirus stocks. Comparing to the IT, the determination of TT is more reproducible and faster. More importantly, we demonstrated that baculoviruses with higher TT could transduce cells at higher efficiency and yield stronger and longer transgene expression, confirming that the TT was representative of the baculovirus transducing ability. In this regard, transducing titration provides a simple, fast and reliable measure to evaluate the quality of virus stocks during virus production and purification, and is helpful to predict the performance of vector supernatants and ensure reproducible gene delivery experiments. After the development of transducing titration, in order to optimize baculovirus production and storage protocols for gene therapy, several parameters were re-investigated by using TT. We found that these data reveal a general agreement between the optimal conditions based on the IT or TT measurements, and are significant because researchers do not need to alter the production and storage conditions they have been adopting. The reason why IT is at times unreliable to indicate the virus dosage in gene transfer as well as the implications of TT in baculovirus production, storage, and potentially purification processes are discussed.