DNA concentration in harvest affects retrovirus clearance capabilities of protein A chromatography

Protein A chromatography is a key unit operation in biopharmaceutical purification, widely used to capture monoclonal antibodies (mAbs) from harvest cell culture fluid (HCCF). In addition to its primary function, protein A chromatography is also frequently tested for its ability to remove viruses. Although protein A specifically binds mAbs and should not interact with viruses, some studies have shown that logarithmic reduction values (LRVs) can vary between 1 and 4 log₁₀ for retroviruses. This variance has been shown to depend on the mAb and feedstock compositions. However, it has not been evaluated so far which feedstock ingredients affect virus removal. To address this knowledge gap, a data set of virus spiking studies was analyzed and revealed a potential correlation between DNA content in HCCF and LRV of protein A chromatography. To evaluate this hypothesis, experiments with murine leukemia virus (MuLV) and retrovirus like particles (RVLP) spiked starting materials of three different mAbs were performed. In general, higher HCCF DNA levels were found to enhance LRV for both virus particles. A trend that was confirmed with RVLP spiked pure mAb. In addition, protein A chromatography washing buffers containing a detergent or a reducing agent were shown to improve LRV in RVLP spiked experiments. This study demonstrates the effect of DNA concentration on the virus removal capabilities of protein A chromatography. Findings that are especially useful when DNA is removed at early stages of the downstream process, for example by using functionalized depth filters or precipitation.