The SARS-CoV-2 pandemic and the emergence of novel virus variants have had a dramatic impact on public health and the world economy, underscoring the need for detailed studies that explore the high efficacy of additional vaccines in animal models. In this study, we confirm the pathogenicity of the SARS-CoV-2/Leiden_008 isolate (GenBank accession number MT705206.1) in K18-hACE2 transgenic mice. Using this isolate, we show that a vaccine consisting of capsid virus-like particles (cVLPs) displaying the receptor-binding domain (RBD) of SARS-CoV-2 (Wuhan strain) induces strong neutralizing antibody responses and sterilizing immunity in K18-hACE2 mice. Furthermore, we demonstrate that vaccination with the RBD-cVLP vaccine protects mice from both a lethal infection and symptomatic disease. Our data also indicate that immunization significantly reduces inflammation and lung pathology associated with severe disease in mice. Additionally, we show that the survival of naïve animals significantly increases when sera from animals vaccinated with RBD-cVLP are passively transferred, prior to a lethal virus dose. Finally, the RBD-cVLP vaccine has a similar antigen composition to the clinical ABNCOV2 vaccine, which has shown non-inferiority to the Comirnaty mRNA vaccine in phase I-III trials. Therefore, our study provides evidence that this vaccine design is highly immunogenic and confers full protection against severe disease in mice.

Circadian rhythms regulate diverse immune processes, yet how they influence memory CD8 ⁺ T cell differentiation remains unclear. Here, we show that the time of day of antigen encounter shapes CD8 ⁺ T cell fate and antiviral immunity. Immunization during the active phase promotes the generation of progenitor-like memory CD8 ⁺ T cells and enhances T cell-mediated protection upon viral challenge. Mechanistically, dendritic cell-intrinsic circadian clocks regulate expression of the costimulatory ligand CD70, thereby directing T cell differentiation. These findings uncover a dendritic cell-mediated circadian mechanism that governs memory T cell fate decisions and suggest that aligning immune priming with circadian time may be leveraged to optimize T cell immunity.