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40 Pharmaceutical Technology ® Trends in Formulation 2022 eBook PharmTech.com frequently undergo freeze/thaw cycles, possible pH changes, and shear stress. Better characterization and optimization of excipients under storage and in stressed conditions will greatly improve the clinical applications of these products. Importance of buffer quality Buffers are critical to the entire viral manufacturing pipeline. The composition can affect every step, from transfection efficiency to product stability, and they must be optimized for ideal purified material recov- ery. Buffers must be formulated to reduce salinity to avoid loss of viral activity, particularly as the addition of desalting steps further reduces yield. The goal is to move toward fewer, more universal buffers that can be used for multiple steps of production, and to which various excipients can be added to maintain or improve performance for the product of interest. The quality of the buffer component is critical as, for example, free radical impurities in buffer can oxidize and alter the safety and efficacy of the product. Finding a balance with salts Although reduced salinity is necessary to prevent viral activity loss, the addition of some salts can improve viral titers and stability. However, increased salt con- tent can also result in increased impurities, and thus necessitate the need for additional purification. As mentioned above, salts can have a destabilizing ef- fect as well, and these effects are all dependent on the solution pH, concentration, and type of salt. Therefore, there is a balance to be navigated when modulating salt conditions and should be carefully considered with respect to the specifics of the viral product and manufacturing process. Achieving cell lysis Improvements in surfactant type and usage for cell lysis in AAV vector manufacturing will also be neces- sary, as the current standard, Triton X-100, is prohib- ited from use due to toxicity concerns. While alternate chemical cell lysis tools are under investigation and show improved product yield (10,11), a challenge is that lysis efficiency must be balanced with the ability to re- move the solution's components from the downstream product though the purification. Alternatively, cell lysis may be achieved through fil- tration methods, such as dead-end and depth filters or membrane devices (pore sizes ranging from 0.2 to 3 µm), which have produced recovery yields ranging from 85–93% (10) though more improvement will be needed to meet CGMP criteria and make filtration methods cost effective. Surfactants are also critical to prevent vector surface absorption as well as aggre- gation and precipitation due to shear stress during manufacturing, transport, and use (6,11). Conclusion While the challenges facing viral vector manufacturers are significant, they should not be surprising. Many of the challenges in the viral vector space today parallel those of the early days of monoclonal antibodies (mAbs). In sharp contrast to mAbs, the small patient population for viral vector therapies will prevent the need for most therapeutic workflows to be manufactured at the same scale, requiring suppliers to develop new product initia- tives to meet the field's unique demands. These challenges are natural for emerging technolo- gies, and today's evolving biopharmaceutical industry has the potential to overcome these challenges through collaboration between viral vector manufacturers and their suppliers. 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