Distinct components of mRNA vaccines cooperate to instruct efficient germinal center responses.

Nucleoside-modified messenger RNA (mRNA) vaccines elicit protective antibodies through their ability to promote T follicular helper (Tfh) cell differentiation. The lipid nanoparticles (LNPs) of mRNA vaccines possess inherent adjuvant activity. However, the extent to which the nucleoside-modified mRNA is sensed and contributes to Tfh cell responses remains undefined. Herein, we deconvolute the signals induced by LNPs and mRNA that instruct dendritic cells (DCs) to promote Tfh cell differentiation. We demonstrate that the mRNA drives the production of type I interferons, which act on DCs to enhance their maturation and Tfh cell differentiation, and favors plasma cells and memory B cell responses. In parallel, LNPs, which allow for mRNA uptake by DCs within the draining lymph node, also modulate Tfh cell responses by shaping the localization of CD25(+) DCs. Our work unravels distinct adjuvant features of mRNA and LNPs necessary for the induction of Tfh cells, with implications for rational vaccine design.