US scientists have developed an adjuvant vaccine based on the RBD domain SARS-CoV-2 
US researchers have developed a coronavirus vaccine based on receptor-binding (RBD) domain of the S-protein SARS-CoV-2 and in the course of studies on mice selected the most effective adjuvants for it – aluminum hydroxide and protein CpG. The new drug has shown efficacy similar to mRNA vaccines and, according to the researchers, whose article was published in the journal Science Translational Medicine, is intended primarily for the elderly.
“RBD is a key target of SARS-CoV-2 vaccines, but RBD itself is weakly immunogenic. This is why (in other vaccines – Lenta.ru's note) they used total S-protein, which is more difficult to mass produce, ”explains lead author David Dowling of Harvard Medical School. In order to find the best adjuvants – substances that enhance the effect of vaccines – the researchers tested various combinations of them with the vaccine on young mice. The rodents were given two doses and their humoral – antibody-linked – immune response was measured.
“We found that the combination of RBD with two adjuvants – aluminum hydroxide and (image-recognizing receptor – approx.“ Lenta.ru ”) CpG was successful. It was equivalent, and in some cases superior to existing mRNA vaccines, ”said one of the scientists, Etsuro Nanishi. Aluminum hydroxide is the most common adjuvant in the world and helps the vaccine antigens stay in the body longer. CpG, on the other hand, is known to stimulate Toll-like receptors of the innate immune system, thereby inducing a stronger immune response.
In experiments, the mixture activated an innate immune response in leukocytes of older people, similar to that of younger people. After administration of the mixture to mice, a high titer of neutralizing antibodies was recorded in all age groups. The adjuvant vaccine completely protected 14 months old mice from SARS-CoV-2 infection. The developers emphasize that their drug, unlike mRNA vaccines, does not need a cold chain.