Lung Transplant Tolerance Research Articles

Regulatory T cells in lung disease and transplantation.

Pulmonary disease can refer to the disease of the lung itself or the pulmonary manifestations of systemic diseases, which are often connected to the malfunction of the immune system. Regulatory T (Treg) cells have been shown to be important in maintaining immune homeostasis and preventing inflammatory damage, including lung diseases. Given the increasing amount of evidence linking Treg cells to various pulmonary conditions, Treg cells might serve as a therapeutic strategy for the treatment of lung diseases and potentially promote lung transplant tolerance. The most potent and well-defined Treg cells are Foxp3-expressing CD4+ Treg cells, which contribute to the prevention of autoimmune lung diseases and the promotion of lung transplant rejection. The protective mechanisms of Treg cells in lung disease and transplantation involve multiple immune suppression mechanisms. This review summarizes the development, phenotype and function of CD4+Foxp3+ Treg cells. Then, we focus on the therapeutic potential of Treg cells in preventing lung disease and limiting lung transplant rejection. Furthermore, we discussed the possibility of Treg cell utilization in clinical applications. This will provide an overview of current research advances in Treg cells and their relevant application in clinics.

Lymphatic drainage from bronchus-associated lymphoid tissue in tolerant lung allografts promotes peripheral tolerance.

Tertiary lymphoid organs are aggregates of immune and stromal cells including high endothelial venules and lymphatic vessels that resemble secondary lymphoid organs and can be induced at nonlymphoid sites during inflammation. The function of lymphatic vessels within tertiary lymphoid organs remains poorly understood. During lung transplant tolerance, Foxp3+ cells accumulate in tertiary lymphoid organs that are induced within the pulmonary grafts and are critical for the local downregulation of alloimmune responses. Here, we showed that tolerant lung allografts could induce and maintain tolerance of heterotopic donor-matched hearts through pathways that were dependent on the continued presence of the transplanted lung. Using lung retransplantation, we showed that Foxp3+ cells egressed from tolerant lung allografts via lymphatics and were recruited into donor-matched heart allografts. Indeed, survival of the heart allografts was dependent on lymphatic drainage from the tolerant lung allograft to the periphery. Thus, our work indicates that cellular trafficking from tertiary lymphoid organs regulates immune responses in the periphery. We propose that these findings have important implications for a variety of disease processes that are associated with the induction of tertiary lymphoid organs.

Bacterial products in donor airways prevent the induction of lung transplant tolerance.

Although postoperative bacterial infections can trigger rejection of pulmonary allografts, the impact of bacterial colonization of donor grafts on alloimmune responses to transplanted lungs remains unknown. Here, we tested the hypothesis that bacterial products present within donor grafts at the time of implantation promote lung allograft rejection. Administration of the toll-like receptor 2 (TLR2) agonist Pam3 Cys4 to Balb/c wild-type grafts triggered acute cellular rejection after transplantation into B6 wild-type recipients that received perioperative costimulatory blockade. Pam3 Cys4 -triggered rejection was associated with an expansion of CD8+ T lymphocytes and CD11c+ CD11bhi MHC (major histocompatibility complex) class II+ antigen-presenting cells within the transplanted lungs. Rejection was prevented when lungs were transplanted into TLR2-deficient recipients but not when MyD88-deficient donors were used. Adoptive transfer of B6 wild-type monocytes, but not T cells, following transplantation into B6 TLR2-deficient recipients restored the ability of Pam3 Cys4 to trigger acute cellular rejection. Thus, we have demonstrated that activation of TLR2 by a bacterial lipopeptide within the donor airways prevents the induction of lung allograft tolerance through a process mediated by recipient-derived monocytes. Our work suggests that donor lungs harboring bacteria may precipitate an inflammatory response that can facilitate allograft rejection.

Pseudomonas Aeruginosa Infection of Lung Transplants Breaks Established Tolerance through B Cell-Intrinsic Innate Immune Signaling That Promotes Intragraft Plasma Cell Generation and Donor Specific Antibody Accumulation

Antibody mediated rejection (AMR) has become an increasingly recognized form of lung transplant rejection. Our group recently identified Pseudomonas aeruginosa infection as a risk factor for clinical AMR but whether infection is sufficient for donor specific antibody (DSA) production and AMR remains unknown. Here we ask in a mouse model of orthotopic lung allograft transplantation whether airway infection with P. aeruginosa promotes DSA generation and AMR. Balb/c lungs were transplanted into the following recipients: B6 WT (wildtype), uMT KO (No B cells), AID/uS KO (Have B cells but are unable to secrete Ig), CD19 Cre , CD19 Cre x TLR4fl/fl and CD19 Cre x MyD88fl/fl. Lung recipients were immunosuppressed with costimulatory blockade on post-operative day (POD) 0 (CD40L Ab) and POD 2 (CTLA4Ig) to induce allograft acceptance. On POD 21 recipients received intratracheal saline or 2 x 105 pfu/g body weight of live P. aeruginosa (clinical isolate M57-15) and then treated with ciprofloxacin from POD 22 to 25. On POD 42 peripheral blood was assessed for DSA and graft tissue evaluated for C4d deposition or quantitated for plasma cells (PC) by flow cytometric analysis (FACS). P. Aeruginosa infection stimulated high amounts of DSA generation and marked C4d deposition. In contrast, C4d deposition was nearly absent in uMT and AID/uS KO recipients. Infected recipients with TLR4 or MyD88 targeted-deficiency in B cells had sharply lower DSA when compared to WT controls. P. aeruginosa infection drove a 4-fold expansion of allograft resident PCs that was largely dependent on maintaining B cell TLR4-MyD88 signaling. In contrast, the spleen and bone marrow had only modest changes in PC abundance despite infection. Surprisingly, re-transplantation of P. aeruginosa-infected lung allografts into secondary uMT KO recipients revealed that lung allograft-resident PCs are capable of producing large amounts of DSA. Collectively, these data show that P. aeruginosa infection abrogates established lung transplant tolerance through engaging innate immune signaling pathways within the B cell compartment. Additionally, we make the novel observation that the lung is a suitable environment for PC development with implications for clinical AMR.

An obligatory role for club cells in preventing obliterative bronchiolitis in lung transplants.

Obliterative bronchiolitis (OB) is a poorly understood airway disease characterized by the generation of fibrotic bronchiolar occlusions. In the lung transplant setting, OB is a pathological manifestation of bronchiolitis obliterans syndrome (BOS), which is a major impediment to long-term recipient survival. Club cells play a key role in bronchiolar epithelial repair, but whether they promote lung transplant tolerance through preventing OB remains unclear. We determined if OB occurs in mouse orthotopic lung transplants following conditional transgene-targeted club cell depletion. In syngeneic lung transplants club cell depletion leads to transient epithelial injury followed by rapid club cell-mediated repair. In contrast, allogeneic lung transplants develop severe OB lesions and poorly regenerate club cells despite immunosuppression treatment. Lung allograft club cell ablation also triggers the recognition of alloantigens, and pulmonary restricted self-antigens reported associated with BOS development. However, CD8+ T cell depletion restores club cell reparative responses and prevents OB. In addition, ex-vivo analysis reveals a specific role for alloantigen-primed effector CD8+ T cells in preventing club cell proliferation and maintenance. Taken together, we demonstrate a vital role for club cells in maintaining lung transplant tolerance and propose a new model to identify the underlying mechanisms of OB.

IL-22 Regulates Induction of Foxp3-Rich Tertiary Lymphoid Organs in Tolerant Lung Allografts

Purpose Intragraft tertiary lymphoid organs (TLOs) are generally associated with the generation of deleterious immune responses. In contrast, we have shown that Foxp3+ cells residing within bronchus-associated lymphoid tissue (BALT), a pulmonary TLO, are required for maintenance of allograft tolerance. Here, we set out to define the cellular and molecular mechanisms that mediate the induction of BALT in tolerant lung allografts. Methods Balb/c lungs were transplanted into B6 wild-type (WT), RORγt-Cre AHR flox (Group 3 innate lymphoid cells (ILC3)-deficient), TCRδ−/− (γδ T cell-deficient), anti-IL23 antibody-treated mice and IL-22 KO mice (n≥4/group). Recipients received anti-CD40L (day 0) and CTLA4-Ig (day 2) to induce tolerance. 7 or 30 days after transplantation grafts were evaluated by histology, flow cytometry and RT-PCR. Results 30 days after transplantation into WT hosts BALT was present in all lung allografts, characterized by expression of PNAd, a marker of high endothelial venules, and lymphoid follicles rich in B cells and Foxp3+ cells (Fig. 1). Graft expression of IL-22 and IL-23 (p Conclusion IL-22 regulates the formation of BALT within tolerant lungs through a process mediated by graft-infiltrating ILC3s and γδ T cells. This is in contrast to previous findings that induction of TLOs is dependent on lymphotoxin or IL-17 signaling. Thus, our findings have important implications for strategies to induce lung transplant tolerance.

Neutrophil extracellular trap fragments stimulate innate immune responses that prevent lung transplant tolerance.

Neutrophil extracellular traps (NETs) have been shown to worsen acute pulmonary injury including after lung transplantation. The breakdown of NETs by DNAse-1 can help restore lung function, but whether there is an impact on allograft tolerance remains less clear. Using intravital 2-photon microscopy, we analyzed the effects of DNAse-1 on NETs in mouse orthotopic lung allografts damaged by ischemia-reperfusion injury. Although DNAse-1 treatment rapidly degrades intragraft NETs, the consequential release of NET fragments induces prolonged interactions between infiltrating CD4+ T cells and donor-derived antigen presenting cells. DNAse-1 generated NET fragments also promote human alveolar macrophage inflammatory cytokine production and prime dendritic cells for alloantigen-specific CD4+ T cell proliferation through activating toll-like receptor (TLR) - Myeloid Differentiation Primary Response 88 (MyD88) signaling pathways. Furthermore, and in contrast to allograft recipients with a deficiency in NET generation due to a neutrophil-specific ablation of Protein Arginine Deiminase 4 (PAD4), DNAse-1 administration to wild-type recipients promotes the recognition of allo- and self-antigens and prevents immunosuppression-mediated lung allograft acceptance through a MyD88-dependent pathway. Taken together, these data show that the rapid catalytic release of NET fragments promotes innate immune responses that prevent lung transplant tolerance.

(302) - Induction of Persistent Lung Transplant Tolerance by IL-2 Complex-Stimulated Regulatory T Cells In Vivo

(302) - Induction of Persistent Lung Transplant Tolerance by IL-2 Complex-Stimulated Regulatory T Cells In Vivo

(721) - VEGF-B Overexpression Enhances Ischemia-Reperfusion Injury and the Innate Immune Response in Rat Heart Transplants

s S265 period of 42 days in both groups. Long term survival of the animals is currently under investigation. Conclusion: Delayed administration of anti-CD4 antibody 3 days after lung transplantation appears to preferentially suppress the CD4+ effector arm rather than CD4+ regulatory T cells. This finding may be advantageous for promoting donor-specific tolerance in lung transplantation.

(723) - IL-25 Attenuates Obliterative Bronchiolitis By Regulating the Polarization of Macrophages in Murine Orthotopic Tracheal Transplantation Models

s S265 period of 42 days in both groups. Long term survival of the animals is currently under investigation. Conclusion: Delayed administration of anti-CD4 antibody 3 days after lung transplantation appears to preferentially suppress the CD4+ effector arm rather than CD4+ regulatory T cells. This finding may be advantageous for promoting donor-specific tolerance in lung transplantation.

(724) - Evidence That CTLA4Ig Attenuates Recall Alloantibody Responses By Interacting With Antibody Forming Cells

s S265 period of 42 days in both groups. Long term survival of the animals is currently under investigation. Conclusion: Delayed administration of anti-CD4 antibody 3 days after lung transplantation appears to preferentially suppress the CD4+ effector arm rather than CD4+ regulatory T cells. This finding may be advantageous for promoting donor-specific tolerance in lung transplantation.

Working toward immune tolerance in lung transplantation

Long-term allograft survival is a major challenge facing solid organ transplantation. Recent studies have shown a negative correlation between infiltration of memory T cells and allograft survival. Furthermore, blockade of leukocyte activation increases acceptance of transplanted organs, including heart, liver, and kidney. Lung allografts are associated with high rates of rejection, and therapies that increase acceptance of other transplanted organs have not translated into the lung. In this issue of the JCI, Krupnick and colleagues demonstrate in a murine model that lung allograft acceptance requires infiltration of a specific T cell population into the graft. This study highlights the unique immunobiology of the lung and the complexity of lung transplant tolerance.

Differential Rates of Apoptosis in Bronchoalveolar Lavage and Blood of Lung Transplant Patients

Lung transplant tolerance depends on effective control of T-cell proliferation and activation. Commonly used immunosuppressive agents promote peripheral blood-derived lymphocyte apoptosis and inhibit production of cytokines involved in lymphocyte proliferation and survival. However, there have been no studies of the effectiveness of immunosuppressive treatments on apoptosis of T cells derived from the airways of lung transplant recipients. Our main aim was to compare apoptosis of T cells derived from peripheral blood and bronchoalveolar lavage (BAL) from lung transplant recipients, with no evidence of chronic or acute cellular rejection, and healthy volunteers. Lung transplantation may also be associated with increased apoptosis of airway epithelial cells. To investigate this possibility, we also examined apoptosis of epithelial cells derived from bronchial brushing. BAL, blood, and bronchial brushings were obtained from lung transplant recipients (n = 9) and age-matched controls (n = 15). T cell and epithelial cell apoptosis, Fas, Bax, Bcl-2, and p53 were evaluated by flow cytometry. Increased apoptosis of peripheral blood T cells and decreased Bcl-2 were observed in the transplant patients. In contrast, there was no significant change in apoptosis of airway T cells or apoptosis-related proteins. Increased apoptosis and increased p53 were observed in the airway epithelial cells from the transplant recipients, possibly as a result of ineffective control of infiltrating cytotoxic T cells. Immunosuppressive agents may not be as effective in inducing apoptosis of airway-derived T cells as peripheral blood-derived T cells after lung transplantation. These findings may have implications on the outcome of the immune response in the airways after immunosuppressive therapy and may be particularly relevant to lung allograft rejection.