The human lymph node microenvironment unilaterally regulates T-cell activation and differentiation

Abstract

The microenvironment of lymphoid organs can aid healthy immune function through provision of both structural and molecular support. In mice, fibroblastic reticular cells (FRCs) create an essential T-cell support structure within lymph nodes, while human FRCs are largely unstudied. Here, we show that FRCs create a regulatory checkpoint in human peripheral T-cell activation through 4 mechanisms simultaneously utilised. Human tonsil and lymph node–derived FRCs constrained the proliferation of both naïve and pre-activated T cells, skewing their differentiation away from a central memory T-cell phenotype. FRCs acted unilaterally without requiring T-cell feedback, imposing suppression via indoleamine-2,3-dioxygenase, adenosine 2A Receptor, prostaglandin E2, and transforming growth factor beta receptor (TGFβR). Each mechanistic pathway was druggable, and a cocktail of inhibitors, targeting all 4 mechanisms, entirely reversed the suppressive effect of FRCs. T cells were not permanently anergised by FRCs, and studies using chimeric antigen receptor (CAR) T cells showed that immunotherapeutic T cells retained effector functions in the presence of FRCs. Since mice were not suitable as a proof-of-concept model, we instead developed a novel human tissue–based in situ assay. Human T cells stimulated using standard methods within fresh tonsil slices did not proliferate except in the presence of inhibitors described above. Collectively, we define a 4-part molecular mechanism by which FRCs regulate the T-cell response to strongly activating events in secondary lymphoid organs while permitting activated and CAR T cells to utilise effector functions. Our results define 4 feasible strategies, used alone or in combinations, to boost primary T-cell responses to infection or cancer by pharmacologically targeting FRCs.

Role of lymph node stroma and microenvironment in T cell tolerance

“…22 Ex vivo expanded allogeneic FRCs were successfully used as an anti-inflammatory therapy for murine sepsis. 13 FRC administration is associated with reduced mortality, lower levels of pro-inflammatory cytokines, and reduction in bacteremia. 6 In a kidney ischemia-reperfusion injury (IRI) model, FRC depletion hindered T cell activation in the kidney dLN and ameliorated renal injury in acute IRI.…”

“…LN SCs, including FRCs, blood endothelial cells (BECs) and LECs form special niches that support T cell and B cell activation. 13 There are likely many further distinct SC subsets, including FRC. 12 FRCs provide the three-dimensional scaffold in the LN microenvironment, and are characterized by expressing podoplanin (gp38) and extracellular matrix proteins such as laminins, ER-TR7 and collagen.…”

“…6 FRCs affect T cell migration, survival, activation and function, thereby regulating immune responses. 13 There are likely many further distinct SC subsets, including FRC. LN SCs subsets can be defined by differential cell surface markers' expression (…”

“…PD-1/PD-L1 signaling is employed by FRCs for immune suppression 47,48. Human LN FRC constrain naïve T cell proliferation and differentiation through indoleamine-2,3-dioxygenase, adenosine 2A receptor, prostaglandin E2, and transforming growth factor beta receptor (TGFβR) 13. LTβR signaling regulates FRC homeostasis and blocking this signaling upregulates FRC expression of inflammatory cytokines and causes inflammation in allografts 15.…”

“…T cells rely on specific trafficking to blood and tissues to fulfill their functions and regulate immune responses. Ex vivo expanded allogeneic FRCs were successfully used as an anti-inflammatory therapy for murine sepsis 13. Alternatively, T cells from peripheral tissues can also be guided to tissue dLNs through afferent lymphatics.…”