Over the past decade, human therapeutic proteins (HTPs) have become far more potent, and consequently, their acceptable exposures have decreased substantially. That has led to commensurately lower acceptance limits for biological process residues. Simultaneously, host-cell and other protein concentrations have increased considerably, thereby making process equipment potentially more difficult to clean. These trends have made biopharmaceutical cleaning validation more challenging. For example, the acceptance limits for many HTPs — based on acceptable exposures of active proteins — are on the…