FRC transplantation restores lymph node conduit defects in laminin α4–deficient mice

Abstract

Fibroblastic reticular cells (FRCs) play important roles in tolerance by producing laminin α4 (Lama4) and altering lymph node (LN) structure and function. The present study revealed the specific roles of extracellular matrix Lama4 in regulating LN conduits using FRC-specific KO mouse strains. FRC-derived Lama4 maintained conduit fiber integrity, as its depletion altered conduit morphology and structure and reduced homeostatic conduit flow. Lama4 regulated the lymphotoxin β receptor (LTβR) pathway, which is critical for conduit and LN integrity. Depleting LTβR in FRCs further reduced conduits and impaired reticular fibers. Lama4 was indispensable for FRC generation and survival, as FRCs lacking Lama4 displayed reduced proliferation but upregulated senescence and apoptosis. During acute immunization, FRC Lama4 deficiency increased antigen flow through conduits. Importantly, adoptive transfer of WT FRCs to FRC Lama4–deficient mice rescued conduit structure, ameliorated Treg and chemokine distribution, and restored transplant allograft acceptance, which were all impaired by FRC Lama4 depletion. Single-cell RNA sequencing analysis of LN stromal cells indicated that the laminin and collagen signaling pathways linked crosstalk among FRC subsets and endothelial cells. This study demonstrated that FRC Lama4 is responsible for maintaining conduits by FRCs and can be harnessed to potentiate FRC-based immunomodulation.

Fibril-Guided Three-Dimensional Assembly of Human Fibroblastic Reticular Cells

“…In mice transplanted with heart allografts, infusion of FRCs restores the capacity of CD40L blockade to induce long-term graft tolerance mediated by expansion of Tregs . Infusion of healthy FRCs into laminin α4-deficient mice restores tolerance to allografts . There is also direct evidence supporting the use of FRCs as cell therapies.…”

“…In vitro and in vivo evidence indicates that FRCs possess the capacity to inhibit the expansion of effector T cells during an immune response . In murine models of graft versus host disease (GVHD), FRCs have been found as hubs for the proliferation of Tregs, , and de novo conversion of conventional T cells to Tregs. ,,, Acute GVHD damages the FRC network and reduces the presentation of PTAs, which is essential for deleting autoreactive T cells . In rodents, repetitive allograft transplantations drove FRCs to deposit excessive collagens, resulting in an altered lymph node microarchitecture coinciding with decreased Tregs and graft rejection.…”

“…24 Infusion of healthy FRCs into laminin α4-deficient mice restores tolerance to allografts. 23 There is also direct evidence supporting the use of FRCs as cell therapies. Fletcher et al…”

“…Fletcher et al showed that a single dose of mouse FRCs given intraperitoneally reduced mortality in mice undergoing sepsis . Transfer of FRCs restored normal architecture and reduced fibrosis in kidney draining lymph nodes damaged by infusion-related injury . While human FRCs can be isolated from routine lymph node biopsy, few studies have investigated the potential for delivering the cells as therapeutics.…”

“… 14 , 19 , 21 , 22 Acute GVHD damages the FRC network and reduces the presentation of PTAs, which is essential for deleting autoreactive T cells. 23 In rodents, repetitive allograft transplantations drove FRCs to deposit excessive collagens, 24 resulting in an altered lymph node microarchitecture coinciding with decreased Tregs and graft rejection. In mice transplanted with heart allografts, infusion of FRCs restores the capacity of CD40L blockade to induce long-term graft tolerance mediated by expansion of Tregs.…”