Estimating viral titres in solutions with low viral loads

Area of Science:

• Biotechnology
• Virology
• Process Engineering

Background:

• Assessing virus reduction in manufacturing is crucial for product safety.
• Cell-based infectivity assays are standard for determining viral titres.
• Common methods include Spearman-Kärber (SK) and Maximum Likelihood (ML) estimation.

Purpose of the Study:

• To compare the accuracy of SK and ML methods for viral titre estimation.
• To identify conditions under which each method may be biased.
• To provide recommendations for optimal viral titre estimation in process validation.

Main Methods:

• Bench-scale models simulating manufacturing steps were used.
• Process intermediates were spiked with virus.
• Viral titres of input and output samples were determined using cell-based infectivity assays.
• Comparison of Spearman-Kärber (SK) and Maximum Likelihood (ML) estimation methods.

Main Results:

• Both SK and ML methods showed similar performance across most virus concentrations.
• The SK method demonstrated an upward bias in estimating viral titres at low, measurable virus concentrations.
• ML estimation provided more accurate results at low viral titres.

Conclusions:

• ML estimation is recommended over SK for viral titre determination at low virus concentrations.
• Both ML and SK can be used at higher virus concentrations.
• Accurate viral titre estimation is essential for validating virus reduction in manufacturing processes.