High-precision quantitation of a tuberculosis vaccine antigen with capillary-gel electrophoresis using an injection standard

Analysis of proteinogenic vaccine antigens in a quality control environment requires an accurate, precise, and reliable method for protein separation and quantitation. While having multiple advantages over the classical SDS-PAGE, capillary gel electrophoresis (CGE) has not yet become a standard tool in vaccine antigen analysis. Here we report on development of a CGE-based method for quantitative analysis of a tuberculosis vaccine fusion antigen protein, H4, currently in clinical trials. We demonstrate that our method can monitor antigen purity and relative quantity with greater precision and accuracy versus SDS-PAGE. In addition, due to use of direct light-absorbance detection, the CGE method is suitable for absolute quantitation, an application for which SDS-PAGE is limited due to the need for staining and limited dynamic range of detection. To further improve the performance of our quantitation method, we introduced Bovine Serum Albumin (BSA) as an injection standard to correct for signal variance associated with the injected sample volume. We found that, for our specific application, BSA was more appropriate as an injection standard versus one provided in a commercial kit, in terms of precision and accuracy for quantitation of H4. In addition to providing better method performance versus SDS-PAGE, CGE is also faster and less resource-intensive. We conclude that CGE should be considered as a replacement for traditional SDS-PAGE methods for vaccine antigen quantitation in a quality-control environment.