Gritstone bio has reported positive results from the first cohort of Phase I CORAL-BOOST clinical trial of its CORAL self-amplifying mRNA (samRNA) vaccine for Covid-19.

Findings showed that the 10µg vaccine dose offered robust neutralising antibody responses to Spike and strong CD8+ T cell responses.

One of four trials of the CORAL programme, CORAL-BOOST is assessing the reactogenicity, safety and immunogenicity of the vaccine directed against Spike and highly conserved non-Spike T cell epitopes (TCE) as a Covid-19 booster shot.

This ongoing trial in the UK enrolled healthy adult subjects aged 60 years or above and were vaccinated with two doses of AstraZeneca’s AZD1222 (Vaxzevria) Covid-19 vaccine.

New CD8+ T cell responses across a wide range of non-spike epitopes, including several established T cell targets, were observed in the trial, which indicates the vaccine’s variant-proof immunity potential.

The vaccine was also found to be well-tolerated in the trial.

It also showed an encouraging safety profile without any grade 3/4 side effects or unexpected reactogenicity or safety issues noted in ten healthy trial adult subjects.

Gritstone bio co-founder, president and CEO Andrew Allen said: “We designed our Covid-19 vaccines to drive broad CD8+ T cell immunity, an additional key layer of protection against viruses.

“This innovation enables the inclusion of a wide array of highly conserved viral epitopes, potentially creating an immune state that may offer more robust clinical protection against current and future SARS-CoV-2 variants and be a first step toward developing a pan-coronavirus vaccine.”

Presently, the trial dose-escalated to a 30mg dose of the vaccine.

With the latest development, the company is modifying the trial to raise the subject enrolment to 120 and assess the inclusion of a second samRNA-Spike-TCE dose of the shot.

Last September, Gritstone dosed the first subjects in a Phase I trial of a self-amplifying mRNA Covid-19 vaccine.