RESUMEN
While mRNA vaccines have been highly effective over the past 2 years in combating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), waning of vaccine-induced antibody responses and lack of induction of respiratory tract immunity contribute to ongoing infection and transmission. However, intranasally (i.n.) administered vaccines may induce mucosal immunity at the site of respiratory virus infection and may thus boost protection. In this work, we present an i.n. administered SARS-CoV-2 self-amplifying RNA (saRNA) vaccine, delivered by a nanostructured lipid carrier (NLC), which induces both potent respiratory mucosal and systemic immune responses. Following prime-boost immunization in C57BL/6 mice, i.n. vaccination induces serum neutralizing antibody titers, bone marrow resident IgG-secreting cells, and robust systemic polyfunctional T cells, similar to intramuscular (i.m.) vaccination. The intranasal vaccine additionally induces key SARS-CoV-2-reactive lung-resident polyfunctional memory and lung-homing T cell populations. As a booster following i.m. administration, the i.n. vaccine also elicits robust mucosal and systemic immunity, exceeding an i.m. booster, durable for at least 4 months. This i.n. saRNA vaccines potent mucosal and systemic immunogenicity may be key for combating SARS-CoV-2 and other respiratory pathogens.
RESUMEN
mRNA vaccines were the first to be authorized for use against SARS-CoV-2 and have since demonstrated high efficacy against serious illness and death. However, limitations in these vaccines have been recognized due to their requirement for cold storage, short durability of protection, and lack of access in low-resource regions. We have developed an easily-manufactured, potent self-amplifying RNA (saRNA) vaccine against SARS-CoV-2 that is stable at room temperature. This saRNA vaccine is formulated with a nanostructured lipid carrier (NLC), providing enhanced stability, improved manufacturability, and protection against degradation. In preclinical studies, this saRNA/NLC vaccine induced strong humoral immunity, as demonstrated by high pseudovirus neutralization titers to the Alpha, Beta, and Delta variants of concern and induction of long-lived bone marrow-resident antibody secreting cells. Robust Th1-biased T-cell responses were also observed after prime or homologous prime-boost in mice. Notably, the saRNA/NLC platform demonstrated thermostability at room temperature for at least 6 months when lyophilized. Taken together, this saRNA delivered by NLC represents a potential improvement in RNA technology that could allow wider access to RNA vaccines for the current COVID-19 and future pandemics.
RESUMEN
We assessed if immune responses are enhanced in CD-1 mice by heterologous vaccination with two different nucleic acid-based COVID-19 vaccines: a next-generation human adenovirus serotype 5 (hAd5)-vectored dual-antigen spike (S) and nucleocapsid (N) vaccine (AdS+N) and a self-amplifying and -adjuvanted S RNA vaccine (SASA S) delivered by a nano-lipid carrier. The AdS+N vaccine encodes S modified with a fusion motif to increase cell-surface expression. The N antigen is modified with an Enhanced T-cell Stimulation Domain (N-ETSD) to direct N to the endosomal/lysosomal compartment and increase MHC class I and II stimulation potential. The S sequence in the SASA S vaccine comprises the D614G mutation, two prolines to stabilize S in the prefusion conformation, and 3 glutamines in the furin cleavage region to increase cross-reactivity across variants. CD-1 mice received vaccination by homologous and heterologous prime > boost combinations. Humoral responses to S were the highest with any regimen including the SASA S vaccine, and IgG bound to wild type and Delta (B.1.617.2) variant S1 at similar levels. An AdS+N boost of an SASA S prime particularly enhanced both CD4+ and CD8+ T-cell responses to both wild type and Delta S peptides relative to all other vaccine regimens. Sera from mice receiving SASA S homologous or heterologous vaccination were found to be highly neutralizing of all pseudovirus strains tested: Wuhan, Beta, Delta, and Omicron strain. The findings here support the clinical testing of heterologous vaccination by an SASA S > AdS+N regimen to provide increased protection against emerging SARS-CoV-2 variants.