Marburg self-amplifying mRNA-lipid nanoparticle vaccine: differential effects when co-formulated with Toll-like Receptor agonists

Abstract

The emergence of Marburg disease in parts of Africa poses a global threat, with the potential to spread to other regions. This requires rapid development of effective vaccines to be used as countermeasures in case of Marburg virus outbreak. This study evaluates the impact of Toll-like Receptor (TLR) agonists on the adaptive immune response to a self-amplifying mRNA (saRNA) vaccine targeting the Marburg virus glycoprotein (GP), delivered via lipid nanoparticles (LNPs). The base saRNA-LNP formulation demonstrated high encapsulation efficiency, stability, and immunogenicity in mice, confirming its potential as a vaccine candidate. To investigate changes in immune responses, three TLR agonists—MPLA (TLR4), CpG ODN (TLR9), and Telratolimod (TLR7)—were co-formulated with the saRNA-LNPs. Each agonist required tailored formulation strategies due to its distinct physicochemical properties, achieving >90% encapsulation efficiency and maintaining critical quality attributes. CryoEM revealed structural variations, including blebbing in CpG and Telratolimod formulations. In vivo studies showed that MPLA significantly enhanced B-cell responses, whereas Telratolimod and CpG had minimal impact on IgG levels. T-cell analysis revealed that Telratolimod and MPLA suppressed IFN-γ responses. Overall, these findings demonstrate that co-formulation with TLR agonists resulted in differential immune responses, where MPLA augmented humoral responses, the TLR9 agonist CpG provided no benefit and the TLR7 agonist Telratolimod inhibited responses, particularly with respect to cellular immunity.