Ex vivo Model of Functioning Human Lymph Node Reveals Role for Innate Lymphocytes and Stroma in Response to Vaccine Adjuvant

Immunological processes that underpin human immune responses to therapeutics and vaccine components, such as vaccine adjuvants, remain poorly defined due to a paucity of models that can faithfully recapitulate immune activation in lymphoid tissues. We describe precision-cut human lymph node (LN) slices as a functioning, architecturally-preserved, full-organ cross-sectional model system. Using single cell transcriptomics and multiplexed imaging we explored early inflammatory response to a potent, clinically-relevant liposomal vaccine adjuvant containing a TLR4-agonist and QS-21 saponin. Both TLR4 and NLRP3 inflammasome activation were involved in the direct initiation of the inflammatory response to adjuvant by monocytes and macrophages (Mon./Mac.) with secretion of IL-1b, but not IL-18, found to be TLR4-dependent. Innate lymphoid cells, including NK cells, were indirectly activated by Mon./Mac.-produced cytokines, signalling downstream to B cells via IFNg secretion. Resident LN stromal populations were primed both directly and indirectly by vaccine adjuvant and were instrumental in mediating inflammatory cell recruitment, particularly neutrophils. Overall design: Healthy human cystic lymph nodes, obtained from routine cholecystectomy, enzymatically digested and sorted to remove dead (fixable live/dead-, 7AAD-) and red blood cells (CD235a+) and to deplete the majority of T (CD20-CD3+) and B (CD20+CD3-) cells which were spiked back at a 1:20 ratio. Lymph nodes were processed either as whole organs or precision cut slices cultured for 20 hours with or without adjuvant LMQ, a liposome-based adjuvant containing a synthetic toll-like receptor 4 (TLR4) agonist 3D-6-acyl-PHAD and QS-21 saponin.