Unlike Cognate, Sawston’s infrastructure supports autologous cell therapy at a commercial level, including storage, cryopreservation, and logistics which would all likely be needed for gaining approval.
Cognate was always about cellular manufacturing. Even in 2016 it was larger than Sawston is today (and Cognate had significant expansion after that). Cognate has made far more batches of -L than Advent has.
From the 2017 10-K:
Cognate BioServices’ manufacturing facility for clinical-grade cell products is located in Memphis, Tennessee. Cognate BioServices' facility is approximately 80,000 square feet and contains substantial buildout expansion space in addition to the portions currently built out and in use. The current manufacturing facilities are sufficient to produce DCVax for at least several thousand patients per year. The expansion space will allow us to procure significantly increasing capacity when needed for commercial readiness. We are also developing a facility for manufacturing in the U.K. for the European market. It is necessary for us to have manufacturing operations in Europe to meet the logistical requirements for European patients relating to the collection, delivery and processing of the patient’s blood draw containing the immune cells (for which the time window is too limited to reach the US manufacturing facility).