Physical Characterization and Stabilization of a Lentiviral Vector Against Adsorption and Freeze-Thaw

A replication-deficient lentiviral vector encoding the tumor antigen gene NY-ESO-1 was characterized in terms of vector morphology, particle size range, concentration, and zeta potential using a variety of physical methods. Environmentally stressed vector samples were then evaluated in terms of viral vector particle size and concentration by nanoparticle tracking analysis (NTA). These NTA stability results correlated reasonably well with a quantitative polymerase chain reaction assay for quantitation of viral genome copy number (r² = 0.80). Approximately 40 pharmaceutical excipients were examined for their ability to stabilize the vector against exposure to an adsorptive container surface (glass) as well as freeze-thaw cycling using NTA as the screening method. Stabilizing additives that inhibited viral vector particle loss under these conditions included proline, lactose, and mannitol. Several candidate frozen liquid formulations that contained a combination of these lead excipients and various buffering agents were further evaluated for their ability to stabilize the viral vector. The additional benefit of lowering the Tris buffer concentration was observed. This study highlights the use of physical particle assays such as NTA for initial screening of stabilizing excipients to minimize vector loss due to container adsorption and freeze-thaw cycling to facilitate early formulation development of viral vector candidates in frozen liquid formulations.