Despite great progress with SARS-CoV-2 vaccines, there is still a need for more effective vaccine strategies in older adults, who tend to have weaker immune responses to vaccination.
In a new study from Boston Children’s Hospital, researchers described a protein-based vaccine, paired with custom adjuvants, that can be manufactured at scale.
In testing in immune cells from older adults, it showed efficacy potentially equivalent to that of current mRNA vaccines.
The formulation combines the part of the viral spike protein that binds to people’s cells, known as the receptor-binding domain (RBD), with two vaccine adjuvants, molecules that boost the immune response.
There are currently at least a half-dozen candidate protein vaccines against SARS-CoV-2, using different adjuvants.
The new study was unique in systematically screening multiple adjuvants and focusing on immune responses in aged human cells and aged mice.
The team recruited adults over age 65 across the Boston area, including members of Levy’s synagogue, to donate their white blood cells.
Aged mice were vaccinated at Boston Children’s and directly challenged with live SARS-CoV-2.
The team found that the RBD subunit formulated with the adjuvants aluminum hydroxide and CpG was a successful combination, equivalent to, and in some instances exceeding current mRNA vaccines.
CpG is known to stimulate Toll-like receptors in the innate immune system, sparking a larger immune response.
Aluminum hydroxide, the most commonly used adjuvant in current vaccines, also helps keep vaccine antigens in the body for a longer period of time so that the immune system can better detect them.
The formulation synergistically activated innate immune responses from mononuclear white blood cells from older adults, equivalent to responses in younger adults.
The team also found the immunized aged mice still had high levels of functional antibodies nearly a year later.
In addition to being much easier to manufacture at scale than mRNA vaccines, the new formulation is unlikely to need the extreme cold storage required by mRNA vaccines, which would enable its use in more settings.
The study is published in Science Translational Medicine. One author of the study is David Dowling, Ph.D.
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