Enhancing protective immunity against SARS-CoV-2 with a self-amplifying RNA lipid nanoparticle vaccine.

RNA-based vaccines against SARS-CoV-2 have demonstrated promising protective immunity against the global COVID-19 epidemic. Enhancing the intensity and duration of mRNA antigen expression is anticipated to markedly boost antiviral immune responses. Self-amplifying RNA (saRNA) represents a next-generation platform for RNA-based vaccines, amplifying transcripts in situ to augment the expression of encoded immunogens. Here, we develop a saRNA nanovaccine, formulated with a mutated saRNA encoding the receptor-binding domain (RBD) of the SARS-CoV-2 spike glycoprotein, encapsulated within a lipid nanoparticle (LNP-saRNA-RBD). This LNP-saRNA vaccine platform enables efficient delivery of saRNA-RBD, inducing enhanced and prolonged expression of the RBD antigen. LNP-saRNA-RBD vaccination stimulated the generation of antigen-specific T cells, promoting their differentiation into a long-lived effector memory phenotype. Immunization with LNP-saRNA-RBD induced a germinal center response in draining lymph nodes, leading to the production of anti-RBD IgG antibodies with the ability to neutralize SARS-CoV-2 pseudovirus. Furthermore, prime-boost immunizations with LNP-saRNA-RBD conferred protection to mice against SARS-CoV-2 challenge by suppressing viral infection and replication, as well as pulmonary inflammatory responses and associated damage. Taken together, these findings provide strong support for advancing the development of LNP-saRNA-RBD as a safe and efficacious vaccine candidate against SARS-CoV-2 infection.