GRT-R910: a self-amplifying mRNA SARS-CoV-2 vaccine boosts immunity for ≥6 months in previously-vaccinated older adults

Christine D. Palmer, Ciaran D. Scallan, Lauren D. Kraemer Tardif, Melissa A. Kachura, Amy R. Rappaport, Daniel O. Koralek, Alison Uriel, Leonid Gitlin, Joshua Klein, Matthew J. Davis, Harshni Venkatraman, Meghan G. Hart, Jason R. Jaroslavsky, Sonia Kounlavouth, Martina Marrali, Charmaine N. Nganje, Kyounghwa Bae, Tiffany Yan, Katharyn Leodones, Milana Egorova, Sue-Jean Hong, Jenchun Kuan, Silvia Grappi, Pedro Garbes, Karin Jooss () and Andrew Ustianowski
Additional contact information
Christine D. Palmer: Gritstone bio, Inc.
Ciaran D. Scallan: Gritstone bio, Inc.
Lauren D. Kraemer Tardif: Gritstone bio, Inc.
Melissa A. Kachura: Gritstone bio, Inc.
Amy R. Rappaport: Gritstone bio, Inc.
Daniel O. Koralek: Gritstone bio, Inc.
Alison Uriel: North Manchester General Hospital & University of Manchester
Leonid Gitlin: Gritstone bio, Inc.
Joshua Klein: Gritstone bio, Inc.
Matthew J. Davis: Gritstone bio, Inc.
Harshni Venkatraman: Gritstone bio, Inc.
Meghan G. Hart: Gritstone bio, Inc.
Jason R. Jaroslavsky: Gritstone bio, Inc.
Sonia Kounlavouth: Gritstone bio, Inc.
Martina Marrali: Gritstone bio, Inc.
Charmaine N. Nganje: Gritstone bio, Inc.
Kyounghwa Bae: Gritstone bio, Inc.
Tiffany Yan: Gritstone bio, Inc.
Katharyn Leodones: Gritstone bio, Inc.
Milana Egorova: Gritstone bio, Inc.
Sue-Jean Hong: Gritstone bio, Inc.
Jenchun Kuan: Gritstone bio, Inc.
Silvia Grappi: VisMederi Srl.
Pedro Garbes: Gritstone bio, Inc.
Karin Jooss: Gritstone bio, Inc.
Andrew Ustianowski: North Manchester General Hospital & University of Manchester

Nature Communications, 2023, vol. 14, issue 1, 1-17

Abstract: Abstract SARS-CoV-2 has resulted in high levels of morbidity and mortality world-wide, and severe complications can occur in older populations. Humoral immunity induced by authorized vaccines wanes within 6 months, and frequent boosts may only offer transient protection. GRT-R910 is an investigational self-amplifying mRNA (samRNA)-based SARS-CoV-2 vaccine delivering full-length Spike and selected conserved non-Spike T cell epitopes. This study reports interim analyses for a phase I open-label dose-escalation trial evaluating GRT-R910 in previously vaccinated healthy older adults (NCT05148962). Primary endpoints of safety and tolerability were assessed. Most solicited local and systemic adverse events (AEs) following GRT-R910 dosing were mild to moderate and transient, and no treatment-related serious AEs were observed. The secondary endpoint of immunogenicity was assessed via IgG binding assays, neutralization assays, interferon-gamma ELISpot, and intracellular cytokine staining. Neutralizing antibody titers against ancestral Spike and variants of concern were boosted or induced by GRT-R910 and, contrasting to authorized vaccines, persisted through at least 6 months after the booster dose. GRT-R910 increased and/or broadened functional Spike-specific T cell responses and primed functional T cell responses to conserved non-Spike epitopes. This study is limited due to small sample size, and additional data from ongoing studies will be required to corroborate these interim findings.

Date: 2023
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DOI: 10.1038/s41467-023-39053-9

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