Immunization strategies that rapidly modulate appropriate and precise interactions between the innate and adaptive immune responses are essential to generate robust, durable, and protective immunity against pathogens. Here, we describe a novel vaccine platform, Spike Ferritin Protein Nanoparticle (SpFN) mixed with the adjuvant Army Liposome Formulation containing QS-21 (ALFQ) and assessed the vaccine-induced immune signatures.
C57BL/6 mice were vaccinated with SpFN formulated with either Alhydrogel (SpFN+AH) or ALFQ (SpFN+ALFQ) and immunological assessment from the vaccine draining lymph nodes (dLNs), lung and spleen was performed to assess cellular engagement and cytokine activation induced by the distinct vaccine-adjuvant combinations using ELISA, flow cytometry, multiplex cytokine assay, ELISPOT, Biacore, and immunohistochemistry-based methods.
SpFN+ALFQ significantly increased the recruitment and activation of classical and non-classical antigen presenting cells (APCs) with upregulated costimulatory molecules in the dLNs. Recruitment of highly activated APCs to the dLNs of SpFN+ALFQ vaccinated mice was associated with an increased frequency of polyfunctional spike-specific memory CD4+ T cells and Kb spike(539-546)-specific long-lived memory CD8+ T cells with effective cytolytic function and distribution to the lungs. Immunohistochemistry and/or flow cytometry showed that SpFN+ALFQ induced an increase in the frequency of IL-21 secreting T follicular helper (Tfh) cells and germinal center (GCs) B cells in the dLNs and spleen, and generated spike specific antibodies as early as day 5. Increased interaction of Tfh and B cells in the GCs of SpFN+ALFQ vaccinated mice was associated with higher frequency of spike specific long-lived plasma cells in the bone marrow. Longitudinal antibody analysis showed a 10-fold higher avidity which was maintained even at week 21 post-vaccination compared to SpFN+AH.
In conclusion, SpFN+ALFQ vaccine effectively recruited highly activated multifaceted APCs driving potent antigen-specific polyfunctional T cell responses. SpFN+ALFQ caused an increase in the size and frequency of GCs and early engagement of Tfh and B cells, leading to the generation of high titer, high avidity, durable binding and neutralizing antibody responses. Together, these findings highlight the importance of ALFQ in orchestrating the interplay of innate and adaptive immune responses. Currently, SpFN+ALFQ is being evaluated in a phase I human clinical trial.