Optimization of biomass and target protein yield for Phase III clinical trial to evaluate Angiotensin Converting Enzyme 2 expressed in lettuce chloroplasts to reduce SARS-CoV-2 infection and transmission

The goal of delivering therapeutic proteins in plant cells, free ofcold chain and expensive purification processes has been elusivefor several decades. Recently, Angiotensin Converting Enzyme 2(ACE2) expressed in lettuce chloroplasts for delivery via chewinggum (Daniell et al., 2022a,b) to prevent infection and transmis-sion of severe acute respiratory syndrome coronavirus (SARS-CoV-2) was approved by the FDA for a Phase I/II clinical trial (IND154897, NCT05433181, IRB 851459). Further product develop-ment, leading to a Phase III clinical trial in preparation forcommercial product launch, requires large-scale biomass produc-tion under optimal growth conditions, for maximal yield of thetarget protein drug. Although there are many reports onoptimization of lighting, nutrients and spacing to grow lettuceunder hydroponic conditions, they focus on biomass accumula-tion and metabolite levels, except in one report on a vaccineantigen (Lin et al., 2013; Okamura et al., 2014). Biomass andtarget protein yield are dramatically lower in lettuce plants grownunder hydroponic conditions when compared with the green-house (Daniell et al., 2020), but there are no reports on thecombined optimization of lighting, nutrients and spacing toimprove biomass and protein yields in hydroponically grownlettuce plants. Therefore, this study addresses this urgent need inmolecular farming.