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In the past there was concern over definition of a batch or lot but it is no longer an issue. A batch from a continuous process can be defined by batch duration and/or certain product amount. For early phase clinical production, one perfusion culture run is usually released as one lot – thus, harvest collections from different time points are processed to a stable intermediate and pooled later (after appropriate in process control testing is completed) to complete the rest of purification and release as one batch. For some long duration perfusion culture with good steady state and high productivity, it is feasible to split the product to multiple lots for release. In addition, multiple parallel, staggered or successive perfusion runs could be combined at a certain defined stage prior to drug substance final production and released as one lot.