Incorporation of 5 methylcytidine alleviates innate immune response to self-amplifying RNA vaccine (preprint)

In order to improve vaccine effectiveness and safety profile of existing synthetic RNA-based vaccines, we have developed a self-amplifying RNA (saRNA)-based vaccine expressing membrane-anchored receptor binding domain (RBD) of SARS-CoV-2 S protein (S-RBD) and have demonstrated that a minimal dose of this saRNA vaccine elicits robust immune responses. Results from a recent clinical trial with 5-methylcytidine (5mC) incorporating saRNA vaccine demonstrated reduced vaccine-induced adverse effects while maintaining robust humoral responses. In this study, we investigate the mechanisms accounting for induction of efficient innate and adaptive immune responses and attenuated adverse effects induced by the 5mC-incorporated saRNA. We show that the 5mC-incorporating saRNA platform leads to prolonged and robust expression of antigen, while induction of type-I interferon (IFN-I), a key driver of reactogenicity, is attenuated in peripheral blood mononuclear cells (PBMCs), but not in macrophages and dendritic cells. Interestingly, we find that the major cellular source of IFN-I production in PBMCs is plasmacytoid dendritic cells (pDCs), which is attenuated upon 5mC incorporation in saRNA. In addition, we demonstrate that monocytes also play an important role in amplifying proinflammatory responses. Furthermore, we show that the detection of saRNA is mediated by a host cytosolic RNA sensor, RIG-I. Importantly, 5mC-incorporating saRNA vaccine candidate produced robust IgG responses against S-RBD upon injection in mice, thus providing strong support for the potential clinical use of 5mC-incorporating saRNA vaccines.

Safety and immunogenicity of VLPCOV-02, a SARS-CoV-2 self-amplifying RNA vaccine with a modified base, 5-methylcytosine, in healthy individuals (preprint)

Continuing emergence of variants of concern resulting in reduced SARS-CoV-2 vaccine efficacy necessitates additional prevention strategies. The structure of VLPCOV-01, a lipid nanoparticle-encapsulated, self-amplifying RNA COVID-19 vaccine with a comparable immune response to BNT162b2, was revised by incorporating a modified base, 5-methylcytosine to reduce reactogenicity, and an updated receptor-binding domain derived from Brazil (gamma) variant. Interim analyses of a phase 1 dose-escalation booster vaccination study with the resulting construct, VLPCOV-02, in healthy, previously vaccinated Japanese individuals (N=96) are reported (jRCT2051230005). A dose-related increase in solicited local and systemic adverse events was observed, which were generally rated mild or moderate. The most commonly occurring events were tenderness, pain, fatigue, and myalgia. Serum SARS-CoV-2 immunoglobulin titers increased during the 4 weeks post-immunization. VLPCOV-02 demonstrated a favorable safety profile compared with VLPCOV-01, with a lower frequency of adverse events and fewer fever events at an equivalent dose. These findings support further study of VLPCOV-02.

Safety and immunogenicity of SARS-CoV-2 self-amplifying RNA vaccine expressing anchored RBD: a randomised, observer-blind, phase 1 study (preprint)

BACKGROUND VLPCOV-01 is a lipid nanoparticle-encapsulated self-amplifying (sa) RNA vaccine that expresses a membrane-anchored receptor-binding domain (RBD) derived from the SARS-CoV-2 spike protein. METHODS A phase 1 study of VLPCOV-01 was conducted at Medical Corporation Heishinkai OPHAC Hospital, Japan. The investigational vaccines were administered to participants, between February 16, 2022, and March 17, 2022. Participants aged 18 to 55 or [≥]65 years who had completed two doses of the BNT162b2 mRNA vaccine 6 to 12 months previously were randomised to receive one intramuscular vaccination of 0{middle dot}3, 1{middle dot}0, or 3{middle dot}0 {micro}g VLPCOV-01, 30 {micro}g BNT162b2, or placebo. Solicited adverse events were collected up to 6 days post-administration, with follow-up on all adverse events until week 4. Interim immunogenicity analyses following data cutoff at day 29 included SARS-CoV-2 IgG and neutralising antibody titres. (The trial is registered: jRCT2051210164). FINDINGS 92 healthy adults were enrolled, with 60 participants receiving VLPCOV-01. No serious adverse events were reported up to 26 weeks, and no prespecified trial-halting events were met. VLPCOV-01 induced robust IgG titres against SARS-CoV-2 RBD protein that were maintained up to 26 weeks in non-elderly participants, with geometric means ranging from 5037 (95% CI 1272-19,940) at 0{middle dot}3 {micro}g to 12,873 (95% CI 937-17,686) at 3 {micro}g, in comparison to 3166 (95% CI 1619-6191) with 30 {micro}g BNT162b2. Among elderly participants, IgG titres at 26 weeks post-vaccination with 3 {micro}g VLPCOV-01 were 9865 (95% CI 4396-22138) compared to 4183 (95% CI 1436-12180) following vaccination with 30 {micro}g BNT162b2. Pseudovirus-Neutralising antibody responses were observed against multiple SARS-CoV-2 variants and strongly correlated with anti-SARS-CoV-2 IgG (r=0{middle dot}950, p<0{middle dot}001). INTERPRETATION VLPCOV-01 is immunogenic following low dose administration, with anti-SARS-CoV-2 immune responses comparable to BNT162b2. These findings support further development of VLPCOV-01 as a COVID-19 booster vaccine and the potential for saRNA vectors as a vaccine platform. FUNDING Supported by AMED, Grant No. JP21nf0101627.