No abstract

Adjuvants are critical for improving the quality and magnitude of adaptive immune responses to vaccination. Lipid nanoparticle (LNP)-encapsulated nucleoside-modified mRNA vaccines have shown great efficacy against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), but the mechanism of action of this vaccine platform is not well-characterized. Using influenza virus and SARS-CoV-2 mRNA and protein subunit vaccines, we demonstrated that our LNP formulation has intrinsic adjuvant activity that promotes induction of strong T follicular helper cell, germinal center B cell, long-lived plasma cell, and memory B cell responses that are associated with durable and protective antibodies in mice. Comparative experiments demonstrated that this LNP formulation outperformed a widely used MF59-like adjuvant, AddaVax. The adjuvant activity of the LNP relies on the ionizable lipid component and on IL-6 cytokine induction but not on MyD88-or MAVS-dependent sensing of LNPs. Our study identified LNPs as a versatile adjuvant that enhances the efficacy of traditional and next-generation vaccine platforms.

Highlights d T-bet + B cells are a separate and durable memory subset in mice and humans d T-bet hi memory B cells are absent from the lymphatic circulation d Influenza-specific T-bet hi memory B cells are spleen-resident in mice d B cell-intrinsic T-bet is required for >90% of flu-and HA stalkspecific antibodies

The T-box transcription factors T-bet and Eomesodermin (Eomes) have been well defined as key drivers of immune cell development and cytolytic function. While the majority of studies have defined the roles of these factors in the context of murine T-cells, recent results have revealed that T-bet, and possibly Eomes, are expressed in other immune cell subsets. To date, the expression patterns of these factors in subsets of human peripheral blood mononuclear cells beyond T-cells remain relatively uncharacterized. In this study, we used multiparametric flow cytometry to characterize T-bet and Eomes expression in major human blood cell subsets, including total CD4+ and CD8+ T-cells, γδ T-cells, invariant NKT cells, natural killer cells, B-cells, and dendritic cells. Our studies identified novel cell subsets that express T-bet and Eomes and raise implications for their possible functions in the context of other human immune cell subsets besides their well-known roles in T-cells.

Summary B cells expressing the transcription factor T‐bet have emerged as participants in a number of protective and pathogenic immune responses. T‐bet+ B cells characteristically differentiate in response to combined Toll‐like receptor and cytokine signaling, contribute to protective immunity against intracellular pathogens via IgG2a/c production and antibody‐independent mechanisms, and are prone to produce autoantibodies. Despite recent advances, a number of questions remain regarding the basic biology of T‐bet+ B cells and their functional niche within the immune system. Herein, we review the discovery and defining characteristics of the T‐bet+ B cell subset in both mice and humans. We further discuss their origins, the basis for their persistence, and their potential fate in vivo. Evidence indicates that T‐bet+ B cells represent a distinct, germinal center‐derived memory population that may serve as an important therapeutic target for the improvement of humoral immunity and prevention of autoimmunity.