Lipid nanoparticle adjuvants for mRNA vaccines: composition-function relation and mechanism of action

ABSTRACT Vaccines are one of the cornerstones of modern medicine, saving millions of lives every year by preventing or attenuating multiple life-threatening diseases. The nucleoside-modified mRNA-lipid nanoparticle (LNP) vaccine platform proved to be very successful during the COVID-19 pandemic. We now know that this revolutionary platform technology can be effectively deployed for infectious disease vaccine development in preclinical and clinical settings. However, our knowledge about the mechanism of action of modified mRNA-LNP vaccines is still limited. We were successful in demonstrating that the LNP component of modified mRNA-LNP vaccines possesses a potent, intrinsic adjuvant activity and promotes T follicular helper cell and germinal center responses, which are necessary for the effective production of antibodies against pathogens. However, we still have an incomplete understanding of the mechanisms by which the immune system senses LNPs, and of how LNPs can be manipulated to fine-tune their adjuvant activity and reactogenicity. In this proposal, we will focus on two critical, yet poorly investigated aspects of LNP adjuvants with the following 2 specific aims: AIM 1. Evaluating the adjuvanticity and reactogenicity of LNPs with different compositions. In this aim, we will generate multiple LNPs, screen their ability to elicit robust cellular and humoral immune responses in mice, and examine the cellular and molecular determinants that contribute to the immunostimulatory profile of various LNPs. Both the quality and quantity of germinal center and antibody responses will be investigated, in detail. Additionally, we will set out to assess the reactogenicity of LNP adjuvants in a relevant mouse model to better predict the tolerability of LNPs in humans. AIM 2. Understanding how LXRs sense LNPs to promote effective cellular and humoral responses. In this aim, we will explore the hypothesis that the nuclear receptors Liver X Receptors (LXRs), which are key sensors of intracellular cholesterol-derived oxysterols, play a fundamental role in LNP sensing mechanisms and in the regulation of immune responses following immunization with LNP-containing vaccines. Moreover, we will determine the importance of the LNP-oxysterol axis in the regulation of the LXR pathway triggered by LNPs. The proposed studies will pave the way to the development of LNPs with a more potent adjuvant activity and to the targeted manipulation of LXRs to fine-tune the magnitude and quality of LNP-driven B cell responses. These deliverables are technically and conceptually innovative and have an immediate translational potential, including for mRNA-LNP vaccine candidates on the market or currently in clinical development.