Monoclonal antibody interchain disulfide bond reduction was observed in a ChineseHamster Ovary manufacturing process that used single-use technologies. A similar reduction has been reported for processes that involved high mechanical shear recovery unit operations, such as continuous flow centrifugation and when the clarified harvest was stored under low dissolved oxygen (DO) conditions (Trexler-Schmidt et al., 2010. Biotechnology and Bioengineering, 106(3), 452-461). The work described here identifies disposable depth filtration used during cell culture harvest operations as a shear-inducing unit operation causing cell lysis. As a result, reduction of antibody interchain disulfide bonds was observed through the same mechanisms described for continuous flow centrifugation. Small-scale depth-filtration models were developed, and the differential pressure (ΔP) of the primary depth filter was identified as the key factor contributing to cell lysis. Strong correlations of ΔP and cell lysis were generated by measuring the levels of lactate dehydrogenase and thiol in the filtered harvest material. A simple risk mitigation strategy was implemented during manufacturing by providing an air overlay to the headspace of a single-use storage bag to maintain sufficient DO in the clarified harvest. In addition, enzymatic characterization studies determined that thioredoxin reductase and glucose-6phosphate dehydrogenase are critical enzymes involved in antibody reduction in a nicotinamide adenine dinucleotide phosphate (NADP + )/NADPH-dependent manner. K E Y W O R D Sair overlay, antibody, cell lysis, depth filtration, differential pressure, dissolved oxygen, disulfide reduction 1 | INTRODUCTION Monoclonal antibodies (mAbs) are commonly manufactured with fed-batch or perfusion mammalian cell culture processes. In such manufacturing processes, the mAb, which is expressed and secreted from the cell, accumulates in the cell culture fluid and is recovered using centrifugation and/or filtration. With the advent of high productivity (>5 g/L) cell culture processes and the availability of improved disposable technologies, the implementation of single-use systems, such as bioreactors, depth filters, columns, membranes, and bioprocess storage bags in the production of biologics has become standard industry practice (Liu, 2005).