This manuscript describes the use of an analytical assay that combines transfection of mammalian cells and isotope dilution mass spectrometry (IDMS) for accurate quantification of antigen expression. Expired mRNA COVID-19 vaccine material was stored at 4 °C, room temperature (∼25 °C), and 56 °C over a period of 5 weeks. The same vaccine was also exposed to 5 freeze-thaw cycles. Every week, the spike protein antigenic expression in mammalian (BHK-21) cells was evaluated. Housekeeping proteins, β-actin and GAPDH, were simultaneously quantified to account for the variation in cell counts that occurs during maintenance and growth of cell cultures. Data show that vaccine stored at elevated temperatures results in reduced spike protein expression. Also, maintaining the vaccine in ultracold conditions or exposing the vaccine to freeze-thaw cycles had less effect on the vaccine's ability to produce the antigen in mammalian cells. We describe the use of IDMS as an antibody-free means to accurately quantify expressed protein from mammalian cells transfected with mRNA vaccine.
Published by Elsevier Ltd.