Lentiviral vectors are commonly used in laboratory experiments to stably integrate transgenes into host genomes. It has long been observed that storage of virus stocks leads to a decrease in viral titer, but the mechanisms driving this decrease have yet to be identified. To that end, lentiviral vector stocks were generated and stored as follows: room temperature for less than one hour, -80ºC for 24 hours, 4ºC for three days and 4ºC for 7 days. These stocks were subsequently evaluated with regard to their transducing ability and their morphology, specifically particle diameter. The vector that was stored at room temperature served as the control with viral morphology similar to other VSV-G pseudotyped viruses. These stocks were able to transduce ~100% of HEK 293T cells. Particles were unstable under the storage conditions tested, as evidenced by the fact that all stocks stored at -80°C and 4°C required concentration with an ultracentrifuge to generate a preparation suitable for visualization with TEM. The vector stored at -80°C for 24 hours exhibited some morphological changes, but only a slight decrease in titer. The morphology of vectors stored at 4°C for 3 and 7 days was not significantly different from the room temperature control, although titer was reduced to 60% and 30-40%, respectively. Thus, the decrease in titer observed in the lentiviral stocks generated and stored during this investigation appears to be the result of viral particle instability rather than morphological changes to individual particles.
Rahman, H.; Taylor, Josephine; Clack, Beatrice; Stewart, R. S.; and Canterberry, Sarah C., "Effects of Storage Conditions on the Morphology and Titer of Lentiviral Vectors" (2013). Faculty Publications. Paper 94.