New tools for immunologists: models of lymph node function from cells to tissues

Abstract

The lymph node is a highly structured organ that mediates the body’s adaptive immune response to antigens and other foreign particles. Central to its function is the distinct spatial assortment of lymphocytes and stromal cells, as well as chemokines that drive the signaling cascades which underpin immune responses. Investigations of lymph node biology were historically explored in vivo in animal models, using technologies that were breakthroughs in their time such as immunofluorescence with monoclonal antibodies, genetic reporters, in vivo two-photon imaging, and, more recently spatial biology techniques. However, new approaches are needed to enable tests of cell behavior and spatiotemporal dynamics under well controlled experimental perturbation, particularly for human immunity. This review presents a suite of technologies, comprising in vitro, ex vivo and in silico models, developed to study the lymph node or its components. We discuss the use of these tools to model cell behaviors in increasing order of complexity, from cell motility, to cell-cell interactions, to organ-level functions such as vaccination. Next, we identify current challenges regarding cell sourcing and culture, real time measurements of lymph node behavior in vivo and tool development for analysis and control of engineered cultures. Finally, we propose new research directions and offer our perspective on the future of this rapidly growing field. We anticipate that this review will be especially beneficial to immunologists looking to expand their toolkit for probing lymph node structure and function.

Recapitulating memory B cell responses in a Lymphoid Organ-Chip to evaluate mRNA vaccine boosting strategies

“…Therefore, the LO chip recapitulates some important features of GC, but not all of them, and may be further improved, for instance by the inclusion of stromal cells that would structure lymphoid tissue territories through the secretion of chemokines (10). The current LO chip model retains the advantage of providing CD4+ T cell help in an Ag-specific fashion, in contrast to systems requiring superantigen stimulation, CD40L-expressing fibroblasts, or exogenous cytokine addition (15,16,27). This may be one reason why immune response analysis in LO chips was not hampered by spontaneous CD4+ T cell or B cell activation, as shown by low/undetectable responses upon stimulation with the irrelevant BSA Ag.…”

“…3D cultures based on peripheral blood mononuclear cells (PBMC) have the decisive advantage of allowing the assessment of human immune responses in large cohorts of vaccinated volunteers, without the need for invasive lymphoid tissue sampling. A 3D environment mimicking a lymphoid-like architecture can be provided by porous synthetic scaffolds or by a variety of hydrogels which are enriched in extracellular matrix (ECM) components such as collagen or fibrin (15,16). Researchers who focused on modeling the early steps of antigenic priming developed tissue-like 3D cultures where primed monocytes mature into dendritic cells (DC) upon Ag stimulation and emigrate through an endothelial barrier, before being collected and cocultured with purified T and/or B lymphocytes (17,18).…”

“…Microfluidic systems that ensure a continuous perfusion of 3D cultures further increase cell adhesion, migration, and differentiation (24), as physiological levels of shear stress promote integrin function and chemokine production (25,26). In addition, the continuous renewal of nutrients and controlled oxygenation levels in microfluidic devices enable cultures at high cellular densities that approach those observed in lymphoid organs (16) (15). Both the increased migration capacity and high cellular density facilitate the encounter of rare Ag-specific CD4+ T cells and B cells, emphasizing the potential of microfluidic systems for mimicking the GC environment.…”

Targeting lymph nodes for enhanced cancer vaccination: From nanotechnology to tissue engineering

“…The multiple types of immune cells in LNs, together with the peripheral lymphocytes that can migrate to LNs, form a massive and dynamic system that monitors the entrance of immunogenic foreign substances into the body [ 1 , 2 ]. Foreign substances will be carried by interstitial flow or by migratory dendritic cells (DCs) to LNs, where they will be further processed to evoke cognate immune responses [ 3 , 4 ]. In antitumor immune responses, LNs are essential tissues sensing and regulating the progression of cancer.…”

Tonsil explants as a human in vitro model to study immune responses to vaccines

“…Human organoids or engineered tissue approaches are emerging as promising tools to overcome interspecies differences for more accurate vaccine testing. Different strategies have been developed to recapitulate salient features of secondary lymphoid organs and drive B cell responses 18 . Engineered in vitro models need to include multiple heterogeneous cell populations derived from humans or mice, seeded into scaffolds that allow the spatial organization and interactions of cells to mimic a tissue 19 .…”