The Quantification of Spike Proteins in the Inactivated SARS-CoV-2 Vaccines of the Prototype, Delta, and Omicron Variants by LC–MS

Abstract

Developing variant vaccines or multivalent vaccines is a feasible way to address the epidemic as the SARS-CoV-2 variants of concern (VOCs) posed an increased risk to global public health. The spike protein of the SARS-CoV-2 virus was usually used as the main antigen in many types of vaccines to produce neutralizing antibodies against the virus. However, the spike (S) proteins of different variants were only differentiated by a few amino acids, making it difficult to obtain specific antibodies that can distinguish different VOCs, thereby challenging the accurate distinction and quantification of the variants using immunological methods such as ELISA. Here, we established a method based on LC–MS to quantify the S proteins in inactivated monovalent vaccines or trivalent vaccines (prototype, Delta, and Omicron strains). By analyzing the S protein sequences of the prototype, Delta, and Omicron strains, we identified peptides that were different and specific among the three strains and synthesized them as references. The synthetic peptides were isotopically labeled as internal targets. Quantitative analysis was performed by calculating the ratio between the reference and internal target. The verification results have shown that the method we established had good specificity, accuracy, and precision. This method can not only accurately quantify the inactivated monovalent vaccine but also could be applied to each strain in inactivated trivalent SARS-CoV-2 vaccines. Hence, the LC–MS method established in this study can be applied to the quality control of monovalent and multivalent SARS-CoV-2 variation vaccines. By enabling more accurate quantification, it will help to improve the protection of the vaccine to some extent.

The Immunogenicity of CpG, MF59-like, and Alum Adjuvant Delta Strain Inactivated SARS-CoV-2 Vaccines in Mice

“…The Delta (B.1.617.2) strain virus of SARS-CoV-2 was isolated from a COVID-19 patient and an adaptive subculture on Vero cells was cultured. Preparation of the inactivated Delta vaccine bulk was consistent with previous reports [9,11]. Briefly, the Delta strain virus was propagated in Vero cells (Obtained from WHO) for large-scale culture, and β propiolactone was added to the culture product at a ratio of 1:4000 for virus inactivation.…”

“…The receptor-binding domain (RBD) situated on the S1 subunits attaches to the angiotensin-converting enzyme 2 (ACE2) receptor in the host, while the S2 subunits facilitate the virus penetration into the host cells. Therefore, despite the N protein being the most abundant, the S protein is the primary target for the action of neutralizing antibodies [ 6 , 7 , 8 , 9 ].…”

“…The receptor-binding domain (RBD) situated on the S1 subunits attaches to the angiotensin-converting enzyme 2 (ACE2) receptor in the host, while the S2 subunits facilitate the virus penetration into the host cells. Therefore, despite the N protein being the most abundant, the S protein is the primary target for the action of neutralizing antibodies [6][7][8][9]. In response to the urgent public health crisis presented by the COVID-19 pandemic, there has been a concerted global effort to expedite research and development processes for a vaccine.…”