Systematic Studies on Stabilization of AAV Vector Formulations by Lyophilization.

Adeno-associated virus (AAV) vectors have evolved as one of the most promising delivery systems for gene therapy. The current standard for AAV vector storage is deep-freezing below -60 °C. While this allows for long-term vector storage without loss of activity, it is inconvenient and involves high costs and logistical challenges. Therefore, there is a need for AAV formulations, such as freeze-dried formulations, that allow for long-term storage at 2-8 °C. A major challenge in developing a lyophilization process for complex biological structures like an AAV vector is to minimize the stress on the capsid during the lyophilization cycle. Here, we evaluated different conditions for freeze-drying of AAV8 vectors and found that undesirable instability can be significantly reduced if secondary drying is performed at lower temperatures, kept as short as possible, and the residual moisture is kept between 1.5 and 2%. In a next step, we explored formulations with different salt concentration or excipient compositions and found that a combination of 10 mM phosphate buffer, 5.67% (150 mM) trehalose, 5% hydroxyectoine and 0.1% poloxamer with a residual moisture of approx. 1.5% provided stable long-term storage at 2-8 °C and for at least 4 weeks at 25 °C. These results pave the way for future optimizations of freeze-drying processes for AAV vector-based gene therapy products.

Understanding opalescence measurements of biologics - A comparison study of methods, standards, and molecules.

Opalescence measurements are broadly applied to assess the quality and stability of biopharmaceutical products at all stages of development and manufacturing. They appear to be simple and straight forward but detect complex light scattering phenomena. Despite a routine calibration step, opalescence values obtained with the same biopharmaceutical sample but on different instruments and/or with different methods may vary significantly. Since the reasons for this high variability are generally not well understood, comparison of opalescence results from different biopharmaceutical laboratories is difficult. Here, we characterized a comprehensive set of biopharmaceutically relevant samples with five opalescence methods to illustrate fundamental differences in method performance and explore the reasons for poor comparability. In addition, we developed a high-throughput method for measuring opalescence in a conventional light scattering plate reader that yields opalescence values in the same range as compendial methods. The presented results underline the impact of sample properties, instrument type, and calibration standards on the determined opalescence value. Based on our findings we provide recommendations for the appropriate application of each method during biopharmaceutical drug product development. Overall, our study contributes to an improved understanding of opalescence measurements in the biopharmaceutical field.

Comparison of Different Liquid Chromatography-Based Purification Strategies for Adeno-Associated Virus Vectors.

Recombinant adeno-associated virus (rAAV) vectors have evolved as one of the most promising technologies for gene therapy due to their good safety profile, high transduction efficacy, and long-term gene expression in nondividing cells. rAAV-based gene therapy holds great promise for treating genetic disorders like inherited blindness, muscular atrophy, or bleeding disorders. There is a high demand for efficient and scalable production and purification methods for rAAVs. This is particularly true for the downstream purification methods. The current standard methods are based on multiple steps of gradient ultracentrifugation, which allow for the purification and enrichment of full rAAV particles, but the scale up of this method is challenging. Here, we explored fast, scalable, and universal liquid chromatography-based strategies for the purification of rAAVs. In contrast to the hydrophobic interaction chromatography (HIC), where a substantial amount of AAV was lost, the cation exchange chromatography (CEX) was performed robustly for multiple tested serotypes and resulted in a mixture of full and empty rAAVs with a good purity profile. For the used affinity chromatography (AC), a serotype dependence was observed. Anion exchange chromatography (AEX) worked well for the AAV8 serotype and achieved high levels of purification and a baseline separation of full and empty rAAVs. Depending on the AAV serotype, a combination of CEX and AEX or AC and AEX is recommended and holds promise for future translational projects that require highly pure and full particle-enriched rAAVs.

Intrinsic Differential Scanning Fluorimetry for Fast and Easy Identification of Adeno-Associated Virus Serotypes.

Recombinant adeno-associated virus (AAV) vectors have evolved as the most promising technology for gene therapy due to their good safety profile, high transduction efficacy, and long-term gene expression in non-dividing cells. AAV-based gene therapy holds great promise for treating genetic disorders like inherited blindness, muscular atrophy, or bleeding disorders. Multiple naturally occurring and engineered AAV serotypes exist, which differ in capsid sequence and as a consequence in cellular tropism. Individual AAV capsids differ in thermal stability and have a characteristic melting temperature (Tm), which enables serotype-specific discrimination of AAV vectors. Differential scanning fluorimetry (DSF) combined with a dye-like SYPRO Orange (SO-DSF), which binds to hydrophobic regions of unfolded proteins, has been successfully applied to determine the Tm of AAV capsids. Here, we present DSF measurement of intrinsic fluorescence signal (iDSF) as a simple alternative method for determination of AAV capsid Tm. The study demonstrates that DSF measurement of intrinsic fluorescence signal is a simple, accurate, and rapid alternative to SO-DSF, which enables characterization of AAV capsid stability with excellent precision and without the need of SO or any other dye.