The CombE-IDMS Assay as an Alternate Potency Method for Adjuvanted Quadrivalent Influenza Vaccines

The potency of all currently licensed inactivated influenza viral vaccines is assayed by the single radial immunodiffusion (SRID) method. SRID relies upon antisera and reference antigen reagents which are produced, standardized, and distributed in the mass quantities needed for vaccine manufacturers only after a significant amount of time has elapsed from the seasonal strain recommendations issued by the WHO; this time delay is exacerbated under conditions of an emerging pandemic. Previously, the limited trypsin digestion isotope dilution mass spectrometry (LTD-IDMS) method, which does not require antisera or reference antigens, demonstrated comparable quantitation of immunologically active hemagglutinin, the primary viral antigen, to SRID in stressed vaccine materials. Here, we demonstrate a streamlined improvement to the LTD-IDMS method by eliminating the need for its precipitation and washing steps, saving time and labor in the sample preparation process while paving the way for plate-based high-throughput analysis. This is accomplished using dissimilar proteases in the pretreatment (a combination of chymotrypsin and elastase) and analytical (trypsin) digestion steps so that any pretreatment digests will not cause interference while monitoring analytical tryptic digests by IDMS. The combination of enzymes (CombE)-IDMS method is tested alongside LTD-IDMS and SRID for the first time on MF59 adjuvanted seasonal cell-based quadrivalent influenza vaccines (aQIVc) under stressed conditions of heating, oxidation, lowered and elevated pH, and freeze-thaw. Overall, a correlation in the degradation trend is observed between CombE-IDMS and SRID in the four strains of the quadrivalent formulation, highlighting the method's stability indicating capability as a rapid alternate potency assay in a highly complex formulation of aQIVc.