What distinguishes upstream and downstream processing?

Why

For a monoclonal antibody process, upstream includes cell banking, inoculum expansion, bioreactor culture and harvest preparation. Downstream begins with recovery and clarification, proceeds through capture and polishing chromatography, virus-related clearance steps where applicable, and filtration or concentration before formulation. The goal is not simply to maximize antibody titer at the reactor.

Culture conditions influence cell lysis, host-cell proteins, glycosylation, aggregates and other properties that determine downstream difficulty. A high-titer batch that plugs filters or carries unacceptable aggregates may deliver less useful purified product than a lower-titer batch. Review mass balance, step recoveries, removal of impurities and product CQAs across the whole chain.

The workflow differs across secreted antibodies, intracellular products, viral vectors and cell therapies. Therefore explain the principle first and then specify the actual platform and its risks.