Breadth of immunity
Among ‘pan-variant’ vaccines with some cross-clade potential, a few candidates are farther along. The Walter Reed Army Institute of Research in Silver Spring, Maryland, for example, is developing an adjuvanted nanoparticle vaccine candidate, prepared by conjugating a self-oligomerizing protein called ferritin to prefusion-stabilized versions of the SARS-CoV-2 spike protein. Results from a 29-person phase I study are expected in the coming weeks.
Army researchers call it a pan-coronavirus vaccine because in mouse and monkey studies the shot elicited robust humoral and cell-mediated immune responses against SARS-CoV-2 variants of concern and SARS-CoV-1. When given as a booster after two priming doses of first-generation COVID-19 vaccines, the scope of immunity might be even greater.
Immunologists Barton Haynes and Kevin Saunders from Duke University demonstrated as much last year when they administered their own ferritin nanoparticle shot to monkeys primed with an mRNA vaccine. (Duke’s vaccine candidate uses a more modular manufacturing protocol as well as RBD antigens based on an early Washington state isolate instead of full-length spike proteins derived from the original Wuhan strain, but is otherwise quite similar to the Army’s candidate.) “With the boost, you get all this breadth,” Haynes says.
“We were hitting bat viruses, pangolin viruses, SARS-CoV-1,” he continues. “Not MERS because the RBD is very different, but everything within the sarbecovirus group.” As measured by antibody binding titres, the immune responses achieved with a nanoparticle design were greater than those achieved with a soluble RBD vaccine comparator. A recent preprint suggests that the type of adjuvant formulation also matters.
