Amit I. Bery

The consequence of lymphatic disruption during transplantation of solid organs remains unknown. Long-term survival after organ transplantation is limited by chronic rejection, a poorly understood process involving fibrotic remodeling and functional decline of the graft. Here, we found that transplanted human lungs and hearts with chronic rejection exhibited fibrosis distributed along dysmorphic lymphatics in areas densely concentrated with hyaluronan, an interstitial glycosaminoglycan that depends on lymphatic drainage for clearance. We illustrated similar findings in transplanted mouse lungs and hearts, which were accompanied by lymphographic findings of graft lymphedema. Using unsupervised clustering, we found a subset of stromal cells present in fibrotic syngeneic mouse lung grafts and human lung and heart grafts with chronic rejection that coexpressed hyaluronan synthase 1 and interleukin-1 receptor 1. Shortly after reperfusion of syngeneic mouse lung grafts, we identified neutrophilic expression of interleukin-1 β ( Il1b ) as a driver of hyaluronan synthase 1 up-regulation. We found interleukin-1–mediated hyaluronan accumulation as a mechanism driving fibrosis that occurred independent of alloimmunity in the setting of lymphatic disruption after transplantation. Development of fibrotic remodeling in transplanted mouse lungs was inhibited by preventing hyaluronan synthesis through the administration of 4-methylumbilliferone, accelerating lymphangiogenesis with pharmacologic activation of VEGF (vascular endothelial growth factor) receptor-3, or inhibiting interleukin-1 receptor 1 signaling in the graft. These therapeutic interventions lay the foundation for future clinical strategies to prevent chronic rejection.

Mechanisms that mediate allograft tolerance differ between organs. We have previously shown that Foxp3 ⁺ T cell–enriched bronchus-associated lymphoid tissue (BALT) is induced in tolerant murine lung allografts and that these Foxp3 ⁺ cells suppress alloimmune responses locally and systemically. Here, we demonstrated that Foxp3 ⁺ cells that reside in tolerant lung allografts differed phenotypically and transcriptionally from those in the periphery and were clonally expanded. Using a mouse lung retransplant model, we showed that recipient Foxp3 ⁺ cells were continuously recruited to the BALT within tolerant allografts. We identified distinguishing features of graft-resident and newly recruited Foxp3 ⁺ cells and showed that graft-infiltrating Foxp3 ⁺ cells acquired transcriptional profiles resembling those of graft-resident Foxp3 ⁺ cells over time. Allografts underwent combined antibody-mediated rejection and acute cellular rejection when recruitment of recipient Foxp3 ⁺ cells was prevented. Finally, we showed that local administration of IL-33 could expand and activate allograft-resident Foxp3 ⁺ cells, providing a platform for the design of tolerogenic therapies for lung transplant recipients. Our findings establish graft-resident Foxp3 ⁺ cells as critical orchestrators of lung transplant tolerance and highlight the need to develop lung-specific immunosuppression.

Neutrophils are the primary cell type involved in lung ischemia-reperfusion injury (IRI), which remains a frequent and morbid complication after organ transplantation. Endogenous lipid mediators that become activated during acute inflammation-resolution have gained increasing recognition for their protective role(s) in promoting the restoration of homeostasis, but their influence on early immune responses following transplantation remains to be uncovered. Resolvin D1, 7 S ,8 R ,17 S -trihydroxy-4 Z ,9 E ,11 E ,13 Z ,15 E ,19 Z -docosahexaenoic acid (RvD1), is a potent stereoselective mediator that exhibits proresolving and anti-inflammatory actions in the setting of tissue injury. Here, using metabololipidomics, we demonstrate that endogenous proresolving mediators including RvD1 are increased in human and murine lung grafts immediately following transplantation. In mouse grafts, we observe lipid mediator class switching early after reperfusion. We use intravital two-photon microscopy to reveal that RvD1 treatment significantly limits early neutrophil infiltration and swarming, thereby ameliorating early graft dysfunction in transplanted syngeneic lungs subjected to severe IRI. Through integrated analysis of single-cell RNA sequencing data of donor and recipient immune cells from lung grafts, we identify transcriptomic changes induced by RvD1. These results support a role for RvD1 as a potent modality for preventing early neutrophil-mediated tissue damage after lung IRI that may be therapeutic in the clinics.

Tertiary lymphoid organs (TLOs) are collections of immune cells resembling secondary lymphoid organs (SLOs) that form in peripheral, non-lymphoid tissues in response to local chronic inflammation. While their formation mimics embryologic lymphoid organogenesis, TLOs form after birth at ectopic sites in response to local inflammation resulting in their ability to mount diverse immune responses. The structure of TLOs can vary from clusters of B and T lymphocytes to highly organized structures with B and T lymphocyte compartments, germinal centers, and lymphatic vessels (LVs) and high endothelial venules (HEVs), allowing them to generate robust immune responses at sites of tissue injury. Although our understanding of the formation and function of these structures has improved greatly over the last 30 years, their role as mediators of protective or pathologic immune responses in certain chronic inflammatory diseases remains enigmatic and may differ based on the local tissue microenvironment in which they form. In this review, we highlight the role of TLOs in the regulation of immune responses in chronic infection, chronic inflammatory and autoimmune diseases, cancer, and solid organ transplantation.