Considerations for Buffering Agent Selection for Frozen rAAV2 Mediated Gene Therapy Products

The buffering component selection is a key criterion for the formulation development process for biopharmaceuticals. This decision for recombinant adeno-associated virus (rAAV) mediated gene therapies is receiving special attention due to their rise in clinical trials which may require high concentration, frozen supply chain, and direct delivery to eye and central nervous system related sites. In the present study, we investigate the impact of rates of freezing and thawing on rAAV2 as a model serotype. It was observed that slow rate of thawing impacts rAAV2 colloidal stability in Phosphate based buffering system. Our pre-formulation workflow suggests that rAAV2 has maximum aggregation propensity between pH of 5.5 to 6.5. Thus, the overlap of maximum aggregation propensity pH range with acidic pH shift in Phosphate based buffering system during freezing and thawing appears to be responsible for 42-75% concentration drop noticed for rAAV2. This impact appears to be fully mitigated upon replacement of Phosphate based buffering system with an alternate buffer system such as Tris. The results reported in this study highlight associated risks and provide preliminary guidance on handling of early stage frozen rAAV mediated gene therapies.