Researchers have developed a nanoparticle vaccine that elicits a virus-neutralising antibody response after a single dose. The team, including Peter Kim from Stanford University in the US, said that the primary target for Covid-19 vaccines is the spike protein, which is necessary for SARS-CoV-2's entry into cells.
Both of the vaccines are mRNA vaccines that cause human cells to temporarily produce the spike protein, triggering an immune response and antibody production.
For the study, published in the ACS Central Science journal, the team wanted to try a different approach: a vaccine consisting of multiple copies of the spike protein displayed on ferritin nanoparticles, in a mice-based experiment.
Ferritin is an iron storage protein found in many organisms that self-assembles into a larger nanoparticle. Other proteins, such as viral antigens, can be fused to ferritin so that each nanoparticle displays several copies of the protein, which might cause a stronger immune response than a single copy.
The researchers spliced spike protein and ferritin DNA together and then expressed the hybrid protein in cultured mammalian cells. The ferritin self-assembled into nanoparticles, each bearing eight copies of the spike protein trimer. The team purified the spike/ferritin particles and injected them into mice.
After a single immunisation, mice produced neutralising antibody titers that were at least two times higher than those in convalescent plasma from Covid-19 patients, and significantly higher than those in mice immunized with the spike protein alone.
A second immunisation 21 days later produced even higher antibody levels.
Although these results must be confirmed in human clinical trials, they suggest that the spike/ferritin nanoparticles may be a viable strategy for single-dose vaccination against Covid-19, the researchers said.