A custom-made time-resolved fluoroimmunoassay for the quantitation of the host cell protein of Vero in rabies vaccine

Host cell proteins (HCPs) are the process-specific and inevitable impurities during the manufacture via a host cell, which affect the safety or efficacy of the bio-product. However, the commercial HCP enzyme-linked immunosorbent assay (ELISA) kits may not apply to specific products such as rabies vaccine from Vero cells. More advanced and process-specific assay methods are needed in the quality control of rabies vaccine throughout the whole manufacturing process. Therefore, a novel time-resolved fluoroimmunoassay (TRFIA) for the detection of process-specific HCP of Vero cells in rabies vaccine was established in this study. Liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) was used during the preparation of HCP antigen. Based on a sandwich-type immunoassay format, analytes in samples were captured by one antibody coating in the wells and "sandwiched" by another antibody labeled with europium chelates. Due to the complex composition of HCP, both the capture and detected antibodies are polyclonal antibodies from the same anti-HCP antibodies pool. Multiple experiments have identified the optimal conditions to allow the valid and reliable detection of HCP in rabies vaccine. The TRFIA had a satisfactory limit of detection value (0.011 μg/ml) under optimal conditions, with the linear range from 0.0375 to 2.4 μg/ml of HCP. The coefficient variations (CVs) were all < 10%, and the recoveries were in the range of 97.00-102.42%. All the test results of Vero cell protein reference substance were included in the expected concentration, which demonstrated that the present method was available for the test of HCP in rabies vaccine. Based on these results, the novel TRFIA to detect HCP appears to be important for application in modern vaccine quality control during the whole manufacturing process.