Enhancing the Effect of Protein-Based COVID-19 Vaccines
Ironically, some vaccines need their own “boosters.” An ingredient called an adjuvant can be added to vaccines to help elicit a more robust immune response, better training the body to fight a pathogen. Scientists report a substance that boosted the immune response to an experimental COVID-19 shot in mice by 25 times, compared to injection with the vaccine alone. Details of the research are described in a new paper published today (August 31, 2022) in the journal ACS Infectious Diseases.
An adjuvant is an ingredient used in some vaccines, which helps recipients of the vaccine develop a greater immunological response. Adjuvants, in other words, make vaccinations more effective.
Even though the first COVID-19 shots authorized in the U.S. apply cutting-edge mRNA genetic technology, the tried-and-true strategy of using proteins from the pathogen can produce vaccines that are less expensive to make and easier to store. So far, the U.S. Food and Drug Administration (FDA) has authorized only one protein-based vaccine, made by Novavax, against SARS-CoV-2. However, many currently available inoculations against other diseases depend on proteins or pieces of them, and these shots contain adjuvants to boost their effectiveness.
Scientists have discovered that molecules derived from α-galactosylceramide (αGC), a compound from marine sponges, can act as adjuvants. They work by stimulating a small population of immune cells that are important for defending the body against viral infections. Rui Luo, Zheng Liu, and their colleagues wanted to see if they could devise a version of αGC to significantly enhance the immune response elicited by a protein-based COVID-19 vaccine.
Four analogs of αGC were made by the team. They added each to an experimental vaccine containing a piece of SARS-CoV-2’s spike protein, which the virus uses to infect cells. Mice were given three injections over 29 days and the researchers tracked their immune response out to 35 days.
To measure the effects of the adjuvants, the scientists scrutinized various aspects of immune function, including two ways the immune system eliminates pathogens: through T cells, which kill diseased cells, and antibodies, which are immune proteins that latch onto an invader.
None of the four meaningfully boosted the T cell response, but all of them produced antibodies with a much greater capacity for interfering with the virus. The analog called αGC-CPOEt led to the production of antibodies with the greatest neutralizing capacity — 25 times greater than what the vaccine could elicit without an adjuvant.
According to the researchers, these results suggest αGC-CPOEt merits further investigation as a potential adjuvant to fight COVID-19 and other infectious diseases.
Reference: “A new iNKT-cell agonist-adjuvanted SARS-CoV-2 subunit vaccine elicits robust neutralizing antibody responses” 31 August 2022, ACS Infectious Diseases.
The authors acknowledge funding from National Natural Science Foundation of China, Central China Normal University, Fundamental Research Funds for the Central Universities from Huazhong Agricultural University, and the Program of Introducing Talents of Discipline to Universities of China.