During the biopharmaceuticals' production processes, engineered bacteria or cells are commonly used as hosts. Residual nucleic acids from these hosts can pose potential safety risks. For instance, DNA residues from continuously passaged host cells may lead to uncontrolled proliferation in human cells, or causing infections due to nucleic acid residues from integrated viruses in the body. Due to these risks, both the World Health Organization (WHO) and national drug regulatory authorities strictly control the levels and fragment lengths of nucleic acids in residual hosts. Typically, residual DNA in vaccines and other biologics is controlled to 100pg/dose, with allows up to 10ng/dose in special circumstances, and residual DNA fragments must be less than 200 base pairs [1]. Saltonase, as a versatile nuclease, offers an effective solution for removing host nucleic acid contamination. However, during virus purification processes, host-cell DNA is highly condensed and wrapped around histones and other nucleoproteins. These processes lead to chromatin formation, which primarily leads to the following issues:

1. Protects genomic DNA (gDNA) from degradation
2. Frequently binds to chromatography media (i.e. anion-, cation-exchange, HIC and affinity resins) than the products they are intended to purify
3. Causes resin and filtration membrane fouling in chromatography 
4. Aggregates viral vectors which reduces yield during purification processes and may adversely affect vector transfection efficiency, biodistribution, and immunogenicity following in vivo administration

Higher salt conditions can effectively address these issues. High ionic strength enables nucleic acids to dissociate from targeted proteins and become accessible for efficient nucleolytic digestion. Also, it reduces product viral vector aggregation, inhibits the activity of many proteases’ and ultimately increases purification yield. Besides that, higher salt conditions are preferred in many chromatographic steps during the purification process like reducing non-specific interaction with resin, improving target binding, prevent fouling.

The method to remove nucleic acid contamination in high-salt buffer solutions remains a challenge. At higher salt concentrations, enzymatic activity from traditional nucleases are hard to maintain, posing challenges for both purification processes and costs.  BLIRT (Gdańsk), a leading enzyme manufacturer in Europe acquired by QIAGEN, has developed the versatile nuclease known as Saltonase which ensures high activity across a wide range of salt concentrations (0.1 – 1.1 M NaCl), effectively degrading nucleic acids to below 10 base pairs.

Figure 1: Comparison of saltonase with market leaders in activity over a broad range of salt concentrations

Saltonase exhibits higher tolerance to varying concentrations of Na+ while other market leaders lose activity tolerance beyond salt concentrations of >250 mM.

Figure 2: Saltonase is active in a wider range of salt environment (0.1 – 1.1 M NaCl)

In conclusion, Saltonase demonstrates broad applicability across a wide range of temperatures (15–55°C), pH levels (6.8–9.3), buffers, and additives while maintaining higher activity. It is highly versatile, easy to be deactivated during production and has excellent purification and quality control process which fundamentally address instability issues. From a long-term and cost perspective, it serves as an effective solution for removing host nucleic acids in biopharmaceutical production!

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[1] Luyao Yan. Research progress on detection of host cell residual DNA in biological products. International Journal of Biologicals, 2021, 44(3):5. DOI:10.3760/cma.j.cn311962-20200409-00039.

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