Carbohydrate fatty acid monosulphate ester adjuvant enhances the immunogenicity of influenza antigens

Introduction: Subunit influenza vaccines require potent adjuvants to elicit robust and broad immune responses, particularly against emerging pandemic strains such as H7N9. However, currently approved adjuvants often fail to induce durable and broadly protective immunity. Carbohydrate fatty acid monosulphate ester (CMS), a synthetic glycolipid incorporated into a squalane-in-water emulsion, has demonstrated promising immunostimulatory properties and is currently undergoing phase I clinical evaluation. However, the molecular mechanisms underlying its adjuvanticity in human immune cells remain incompletely understood. We therefore investigated the immunological and molecular mechanisms by which CMS enhances influenza hemagglutinin (HA) immunogenicity. Methods: Human peripheral blood mononuclear cells (PBMCs) and monocyte-derived dendritic cells (DCs) from healthy donors were stimulated with influenza HA antigen alone or in combination with CMS. Antigen-specific T cell responses were assessed using activation-induced marker assays and intracellular cytokine staining. DC maturation markers and cytokine secretion were analyzed by flow cytometry and ELISA. Antigen uptake was evaluated by fluorescence microscopy and flow cytometry. Bulk RNA sequencing of CMS-stimulated DCs was performed to identify differentially expressed genes and enriched pathways. Toll-like receptor (TLR) involvement was validated using THP-1 reporter assays and pharmacological inhibition in DCs. Results: CMS significantly enhanced antigen-specific CD4⁺ and CD8⁺ T cell responses in PBMCs. While recombinant H7N9 HA alone poorly activated DCs, co-formulation with CMS induced robust upregulation of co-stimulatory molecules and pro-inflammatory cytokines, leading to a polyfunctional T helper cell response. Transcriptomic profiling revealed strong enrichment of TLR, NF-κB, JAK-STAT, and interferon signaling pathways. Functional studies confirmed that CMS-induced activation depends on TLR4 and TLR2 engagement. Discussion: CMS enhances influenza antigen immunogenicity by promoting TLR4/2-dependent DC activation, inflammatory signaling, and improved antigen presentation. These findings define the mechanistic basis of CMS adjuvanticity and support its development as a promising adjuvant platform for next-generation influenza vaccines targeting emerging pandemic strains.