Clinical-stage biotech company Gritstone has dosed the first participants in a Phase I clinical trial of its second-generation, self-amplifying mRNA (SAM) Covid-19 vaccine.

Named GRT-R910, the vaccine is expected to boost and expand first-generation Covid-19 vaccines’ immunogenicity in people aged 60 years and above.

The single-centre Phase I trial is being performed in alliance with The University of Manchester and Manchester University NHS Foundation Trust in the UK.

GRT-R910 utilises a SAM vector formulated with lipid nanoparticles to deliver antigens against both SARS-CoV-2 spike protein and highly conserved viral protein regions consisting of T cell epitopes.

The self-amplification, prolonged duration and extent of antigen generation with SAM vaccines could enable a decrease of vaccine doses or avoid repeat administrations, the company said.

Gritstone added that GRT-R910 may trigger robust, sustainable and wide immune responses against SARS-CoV-2 variants.

Gritstone co-founder, president and CEO Andrew Allen said: “Our SAM COVID vaccine is designed to drive robust CD8+ T cell responses, in addition to strong neutralising antibody responses, offering the promise of longer-lasting immunity, especially in more vulnerable populations.

“Additionally, since viral surface proteins like the spike protein are evolving and sometimes partially evading vaccine-induced immunity, we designed GRT-R910 to have broad therapeutic potential against a wide array of SARS-CoV-2 variants by also delivering highly conserved viral proteins that may be less prone to antigenic drift.”

Sponsored by Gritstone, the open-label, dose-escalation Phase I trial will initially enrol 20 participants.

It will evaluate GRT-R910’s ability to boost the immunogenicity of AstraZeneca‘s first-generation Covid-19 vaccine, AZD1222 (Vaxzevria), in healthy adults aged 60 years and above.

The trial will check the dose, safety, tolerability and immunogenicity of two GRT-R910 dose levels at a minimum of four months following the second administration of the initial vaccine.

Preliminary data from the Phase I trial are anticipated in the first quarter of next year.

In March 2021, the company began dosing in GRT-R910’s Phase I study supported by the US National Institute of Allergy and Infectious Diseases (NIAID).