Distinct innate immune activation profiles of an mRNA-lipid nanoparticle vaccine compared to the empty lipid nanoparticle

Background: While messenger RNA- RNA-lipid nanoparticle (mRNA-LNP) vaccines are known to be immunogenic, the specific innate immune cells activated and the distinct contributions of the LNP and mRNA to the immune response remain unclear. Methods: Using spectral flow cytometry and a multiplex cytokine assay, we define the change in expression of co-stimulatory molecules in specific innate immune cell populations and cytokine production from healthy human peripheral blood mononuclear cells (PBMCs) in response to LNP and mRNA-LNP. Results: Our data reveal distinct activation profiles induced by the BNT162b2 vaccine formulation LNP and mRNA-LNP. The LNP component primarily activated monocytes, upregulating antigen presentation and costimulatory molecules, and also induced costimulatory molecule expression on type 1 conventional dendritic cells (cDC1) and plasmacytoid DCs (pDCs) independently of the presence of mRNA. The mRNA-LNP activated B cells in contrast to empty LNP and induced cDC2 responses. The presence of mRNA enhanced GM-CSF and IL-10 production in culture but did not induce classic proinflammatory cytokines like TNF-α, IL-1β, or IL-6. Conclusion: This study defines the innate immune responses induced by the BNT162b2 vaccine formulation LNP and mRNA-LNP. Upregulation of proteins that support antigen presentation and communication with lymphocytes on monocytes and B cells were reflective of LNP and mRNA-LNP stimulation. Cytokine production was relatively modest with GM-CSF and IL-10 predominating. These findings provide insights into the mechanisms underlying immune responses to mRNA-LNP vaccine components.