thebench.bio #1 Ecosystem for the Bio-Tech Industry
All Bioprocessing questions

Question 20 of 20 Advanced Practical

How would you design a viral clearance study for a monoclonal antibody process?

Short answer

Spike relevant and model viruses into qualified scale-down models of the steps expected to clear virus, measure log reduction for each, and combine only steps with different mechanisms. ICH Q5A(R2) favors two complementary dedicated steps, one effective against non-enveloped virus, with an effective step giving about 4 log10 or more.

Why

ICH Q5A(R2), revised in 2023, sets the framework. Viral clearance studies spike virus into process intermediates in a scale-down model and measure how much infectivity each step removes or inactivates. The scale-down model must be shown to represent the commercial step, with parameters such as bed height, flow rate, buffer, resin type, pH, temperature and conductivity matched.

Virus choice follows three categories: relevant viruses, specific model viruses such as murine leukemia virus for rodent retrovirus, and non-specific model viruses with diverse properties to show general robustness, favoring resistant ones. For a CHO antibody, a typical panel includes murine leukemia virus and a small non-enveloped virus. The guideline recommends two distinct, complementary clearance steps where feasible, one effective against non-enveloped virus.

It describes an effective step as giving reproducible reduction of about 4 log10 or more in at least two independent studies, while steps of 1 to 3 log10 can contribute. Reductions below 1 log10 are considered negligible and ignored unless justified, and adding steps with the same mechanism can overestimate clearance. Common steps are low-pH inactivation after Protein A, anion exchange and virus filtration.

Studies should test worst-case conditions and support resin reuse where relevant. Clearance studies contribute to safety but do not establish it alone, since spiked virus can behave differently from native virus.

How to work it through

  1. Identify which steps can plausibly remove or inactivate virus by different mechanisms.
  2. Build and qualify scale-down models that match the commercial steps' key parameters.
  3. Select relevant, specific model and non-specific model viruses, including a resistant non-enveloped virus.
  4. Spike each step's load, run at worst-case conditions, and titrate input and output to calculate log reduction.
  5. Repeat to show reproducibility and sum only steps that are at least 1 log10 and mechanistically distinct.
  6. Compare the total with the estimated retrovirus-like particle load per dose to justify the safety margin.

An example

For a CHO antibody, the team studies low-pH hold at pH 3.6 for 60 minutes, anion exchange flow-through and a 20 nm virus filter. Murine leukemia virus gives reduction factors of at least 5.0, 4.2 and at least 5.5 log10, totalling at least 14.7. A minute virus of mice model gives less than 1 log10 at low pH, which is ignored, 3.1 log10 on anion exchange and at least 4.8 log10 on the filter, totalling at least 7.9.

Low pH is run at the highest allowed pH and shortest time as the worst case. Retrovirus-like particle counts in harvest support a wide margin per dose.

Where the answer stops holding

Spiked laboratory virus can differ from native virus in aggregation and behavior. Small-scale models never perfectly reproduce commercial processing. Log reduction never reaches zero virus, and assay detection limits cap the reduction that can be claimed.

A strong answer covers

  • Qualified scale-down models of clearance steps
  • Relevant, specific model and non-specific model viruses
  • Two complementary steps, one for non-enveloped virus
  • About 4 log10 for an effective step, below 1 log10 ignored
  • Do not sum steps with the same mechanism

Common mistakes

  • Adding up reductions from steps that work by the same mechanism.
  • Counting steps with less than 1 log10 reduction toward the total.
  • Running studies at center-point conditions instead of worst case.