Ex vivo Model of Functioning Human Lymph Node Reveals Pivotal Role for Innate Lymphoid Cells and Stromal Populations in Response to Vaccine Adjuvant

Immunological processes that underpin the administration of therapeutics and vaccines are poorly defined due to a lack of models which faithfully recapitulate human immune responses. Inbred mice lack the diversity inherent to people, while the microanatomical organisation of human tissue is lost in isolated cell suspensions. We describe precision-cut human lymph node (LN) slices as architecturally-preserved, functioning lymphoid tissue model system, and explore early inflammatory responses to a potent vaccine liposomal adjuvant containing a TLR4-agonist and QS21 saponin. Combining scRNA-seq, multiplexed immunofluorescence and secretome analysis, we dissect direct and indirect signalling pathways in both leukocytes and stromal cells to reveal communication networks linking innate and adaptive immunity. Application of molecular inhibitors reveals that secretion of IL- 1b, but not IL-18, is TLR4-dependent in human LN. Retaining donor-to-donor immune variation, this ex vivo LN model system enables the study of pathways previously difficult to observe in humans, paving the way towards precision medicine.