304. Particle Titer Determination and Characterization of rAAV Molecules Using Nanoparticle Tracking Analysis

The development and commercialization of a biological pharmaceutical, such as recombinant adeno associated virus (rAAV), requires rigorous quantitative and qualitative testing. An accurate particle titer measurement is important for the development of purification processes. Current methods for titering rAAV include qPCR, for measuring genome copy titer, and ELISA, for measuring particle titer. Additionally, methods such as dynamic light scattering (DLS) have been considered for assessment of particle size and aggregation but with limited success for rAAV. Here, a novel method is described called Nanoparticle Tracking Analysis (NTA), to provide rAAV titer (concentration) within minutes, as opposed to hours or days required by traditional techniques. NTA characterization was enabled by a gold labeling technique to increase the light scattered from rAAVs. With a purified gold labelled rAAV sample, NTA results indicated a monodisperse size distribution and a measured rAAV particle titer equivalent to the concentration based on genome copies by qPCR. Particle titer determination can also be relevant for assessment of product stability. NTA was used to assess the stability of rAAV over a 3 month thermal stress test. The NTA method enabled the detection of a reduction of the primary rAAV particle peak within 1 month, as well as further reductions over time. These initial results demonstrate the potential uses of NTA for product characterization.