Bulk production of the antiviral lectin griffithsin

Fuqua, Joshua L.; Hamorsky, Krystal; Khalsa, Guruatma; Matoba, Nobuyuki; Palmer, Kenneth E.

The theoretical lack of impact of upstream cost-saving measures on the overall cost of goods has limited their investigation in side-by-side comparator studies of multiple expression systems. However, upstream methodologies can impact downstream processing costs and have a multiplicative effect on the overall cost-savings. Changing the upstream expression methodology could result in significant cost-savings, but have not been investigated because of limitations on time and the necessity for immediate GRFT production. Upstream expression technologies such as Agrobacterium infiltration (agroinfiltration)-based transient expression and stable transgenic expression methods could reduce cost by increasing yield per biomass or reducing the complexity of downstream processing. Expression systems requiring reduced biomass processing for similar yield can have a significant cost-saving effect. Buyel and Fischer (2012) demonstrated that reducing the amount of material processed by harvesting specific leaves can have a significant cost-saving impact by reducing the total process volume which reduces downstream processing costs (Buyel and Fischer, 2012) . Expression technologies that provide significantly higher yield per biomass have the potential to reduce both upstream and downstream processing. Additionally, expression technologies that reduce the need for downstream processing can have a substantial impact on overall cost of goods. For example, transgenic plants would have a modest impact on the upstream costs by removing the continual need for transient expression systems, but have the potential to simplify downstream processing by limiting transient expression system-derived contaminants such as TMV coat protein, in rTMVbased systems and endotoxin, in agroinfiltration-based systems. In the cost assessment of PMP products, the upstream and downstream costs are not fixed relative to each other and upstream processes can significantly influence downstream costs. Currently multiple systems can be used to produce GRFT in plants: Agrobacterium-based, rTMV-based, transplastomics, amongst others (Fuqua et al., 2015; Hahn et al., 2015; O'Keefe et al., 2009; Vafaee et al., 2014) . Transgenic lines with inducible expression systems provide interesting new potentials for optimizing upstream expression costs (Werner et al., 2011) . All of these alternative expression systems would have varying degrees of impact on GRFT's production costs. In targeting GRFT to resource-limited settings we need to reduce its overall cost, but this will require data from multiple expression systems coupled with optimization of purification methodologies to develop proper economic models related to overall cost. To validate economic models related to the cost of GRFT, it will then be necessary to scale the processes and verify the predicted outcomes in head-tohead comparisons at pilot manufacturing scale.