Distinct components of nucleoside-modified messenger RNA vaccines cooperate to instruct efficient germinal center responses

Nucleoside-modified mRNA vaccines elicit protective antibodies through their ability to promote T follicular helper (Tfh) cells. The lipid nanoparticle (LNP) component of mRNA vaccines possesses inherent adjuvant activity. However, to what extent the nucleoside-modified mRNA can be sensed and contribute to Tfh cell responses remains largely undefined. Herein, we deconvoluted the signals induced by LNP and mRNA that instruct dendritic cells (DCs) to promote Tfh cell differentiation. We demonstrated that the nucleoside-modified mRNA drives the production of type I interferons that act on DCs to induce their maturation and the induction of Th1-biased Tfh responses. Conversely, LNP favors the acquisition of a Tfh cell-inducing program in DCs, a stronger Th2 polarization in Tfh cells, and allows for rapid mRNA translation by DCs within the draining lymph node. Our work unravels distinct adjuvant features of mRNA and LNP necessary for the induction of Tfh cells, with implications for vaccine design. Overall design: We sought to evaluate the impact of the nucleoside-modified mRNA and LNP vaccine components on the transcriptional program of DCs and utilized the LIPSTIC system to probe this in relation to their antigen-presenting status. We created a construct consisting of the RBD of SARS-CoV-2 spike protein fused via a GS linker to the chicken ovalbumin peptide sequence recognized by OT-II CD4 T cells (RBD-OVA). Mice were immunized with either mRNA-LNP encoding RBD-OVA (mRNA_LNP), recombinant RBD-OVA mixed with empty LNP (protein_LNP), or recombinant RBD-OVA mixed with AddaVax (protein_Addavax) and DCs in the draining lymph nodes were analyzed 24-hours later.