Assessment of HIV-1 Pr55GagVLPs using TEM. (A) Freshly prepared VLPs resuspended in 1 × PBS. (B) An example where 50% or more VLPs have not retained their original appearance: VLPs retained in 1 × PBS stored at −20°C after 1 month; the white arrows indicate electron dense areas. (C) An example where all the VLPs (100%) have degraded: VLPs retained in 5% trehalose at 4°C after 1 month. Scale bars = 500 nm.