Inhibition of obliterative airway disease development following heterotopic murine tracheal transplantation by costimulatory molecule blockade using anti-CD40 ligand alone or in combination with donor bone marrow

The need for a new animal model for chronic rejection after lung transplantation

The single most important cause of late mortality after lung transplantation is obliterative bronchiolitis (OB), clinically characterized by a decrease in lung function and morphologically by characteristic changes. Recently, new insights into its pathogenesis have been acquired: risk factors have been identified and the use of azithromycin showed a dichotomy with at least 2 different phenotypes of bronchiolitis obliterans syndrome (BOS). It is clear that a good animal model is indispensable to further dissect and unravel the pathogenesis of BOS. Many animal models have been developed to study BOS but, so far, none of these models truly mimics the human situation. Looking at the definition of BOS, a good animal model implies histological OB lesions, possibility to measure lung function, and airway inflammation. This review sought to discuss, including pros and cons, all potential animal models that have been developed to study OB/BOS. It has become clear that a new animal model is needed; recent developments using an orthotopic mouse lung transplantation model may offer the answer because it mimics the human situation. The genetic variants among this species may open new perspectives for research into the pathogenesis of OB/BOS.

Prevention of airway allograft tolerance by polyinosinic:polycytidylic acid requires type I interferon responsiveness for mouse airway obliteration

BACKGROUND

Respiratory RNA viruses are associated with bronchiolitis obliterans syndrome (BOS) in lung transplant recipients (LTRS); however, the immune mechanisms that regulate airway obliteration remain incompletely understood.

METHODS

Using the mouse heterotopic tracheal transplant model of obliterative airway disease (OAD), we studied the role of double-stranded (ds)RNA using polyinosinic:polycytidylic acid (poly[I:C]), a synthetic analog of viral dsRNA, in abrogating airway allograft tolerance established with donor-specific transfusion (DST) and anti-CD154 monoclonal antibody therapy.

RESULTS

Wild-type (WT) B6 recipients of accepted BALB/c airway grafts demonstrated significantly reduced intragraft CD8+ T cells, with markedly impaired allospecific interferon (INF)-γ and tumor necrosis factor-α secretion, uncoupled from an activated phenotype, and evidence of proliferation. Administration of poly(I:C) to DST/anti-CD154-treated recipients restored OAD pathology and CD8+ alloeffector responses to levels observed in untreated mice. However, B6 type I IFN receptor-deficient (IFN-αβR(-/-)) recipients were resistant to the abrogation of tolerance mediated by poly(I:C) and did not develop CD8+ alloeffector responses or OAD. Further, adoptive transfers of WT CD8+ T cells or CD11c+ dendritic cells alone into B6 IFNαβR(-/-) recipients treated with poly(I:C) and DST/anti-CD154 were incapable of abrogating airway graft tolerance.

CONCLUSIONS

Together, these data indicate abrogation of DST/anti-CD154-induced airway allograft tolerance via dsRNA requires type-I IFN responsiveness for mouse airway obliteration.

Ovariectomy expands murine short-term hemopoietic stem cell function through T cell expressed CD40L and Wnt10B

Estrogen deficiency expands hemopoietic stem and progenitor cells (HSPCs) and mature blood lineages, but the involved mechanism and the affected HSPC populations are mostly unknown. Here we show that ovariectomy (ovx) expands short-term HSPCs (ST-HSPCs) and improves blood cell engraftment and host survival after bone marrow (BM) transplantation through a dual role of the T-cell costimulatory molecule CD40 ligand (CD40L). This surface receptor is required for ovx to stimulate T-cell production of Wnt10b, a Wnt ligand that activates Wnt signaling in HSPCs and stromal cells (SCs). Moreover, CD40L is required for ovx to increase SC production of the hemopoietic cytokines interleukin (IL)-6, IL-7, and granulocyte macrophage-colony-stimulating factor. Attesting to the relevance of CD40L and Wnt10b, ovx fails to expand ST-HSPCs in CD40L-null mice and in animals lacking global or T-cell expression of Wnt10b. In summary, T cells expressed CD40L, and the resulting increased production of Wnt10b and hemopoietic cytokines by T cells and SCs, respectively, plays a pivotal role in the mechanism by which ovx regulates hemopoiesis. The data suggest that antiestrogens may represent pharmacological targets to improve ST-HSPC function through activation of the microenvironment.

Ovariectomy disregulates osteoblast and osteoclast formation through the T-cell receptor CD40 ligand

The bone loss induced by ovariectomy (ovx) has been linked to increased production of osteoclastogenic cytokines by bone marrow cells, including T cells and stromal cells (SCs). It is presently unknown whether regulatory interactions between these lineages contribute to the effects of ovx in bone, however. Here, we show that the T-cell costimulatory molecule CD40 ligand (CD40L) is required for ovx to expand SCs; promote osteoblast proliferation and differentiation; regulate the SC production of the osteoclastogenic factors macrophage colony-stimulating factor, receptor activator of nuclear factor-κB ligand, and osteoprotegerin; and up-regulate osteoclast formation. CD40L is also required for ovx to activate T cells and stimulate their production of TNF. Accordingly, ovx fails to promote bone loss and increase bone resorption in mice depleted of T cells or lacking CD40L. Therefore, cross-talk between T cells and SCs mediated by CD40L plays a pivotal role in the disregulation of osteoblastogenesis and osteoclastogenesis induced by ovx.

CD154 deficiency uncouples allograft CD8+ T-cell effector function from proliferation and inhibits murine airway obliteration

Obliterative bronchiolitis (OB) limits the long-term success of lung transplantation, while T-cell effector mechanisms in this process remain incompletely understood. Using the murine heterotopic tracheal transplant model of obliterative airway disease (OAD) to characterize airway allograft rejection, we previously reported an important role for CD8(+) T cells in OAD. Herein, we studied the role of CD154/CD40 costimulation in the regulation of allospecific CD8(+) T cells, as airway rejection has been reported to be CD154-dependent. Airway allografts from CD154(-/-) recipients had significantly lower day 28 OAD scores compared to wild-type (WT) recipients, and adoptive transfer of CD8(+) T cells from WT recipients, but not CD154(-/-) recipients, were capable of airway rejection in fresh CD154(-/-) allograft recipients. Intragraft CD8(+) T cells from CD154(-/-) mice showed similar expression of the surface markers CD69, CD62L(low) CD44(high) and PD-1, but markedly impaired IFN-gamma and TNF-alpha secretion and granzyme B expression versus WT controls. Unexpectedly, intragraft and systemic CD8(+) T cells from CD154(-/-) recipients demonstrated robust in vivo expansion similar to WT recipients, consistent with an uncoupling of proliferation from effector function. Together, these data suggest that a lack of CD154/CD40 costimulation results in ineffective allospecific priming of CD8(+) T cells required for murine OAD.

MMP-8 promotes polymorphonuclear cell migration through collagen barriers in obliterative bronchiolitis

Increased levels of MMP-8 (neutrophil collagenase) have been reported in OB, but the biological role of MMP-8 in OB is not known. MMP-8 is an interstitial collagenase highly expressed by polymorphonuclear leukocytes, which are prominent in early OB. Here, we show that MMP-8 promotes migration of PMNs through the collagen-rich matrix in a mouse heterotopic airway transplant model of OB. Overall, MMP-8(-/-) mice had significantly fewer PMNs in the airway lumen 2 and 14 days post-transplantation, and the percentage of PMNs traversing the matrix to the lumen was decreased markedly in the MMP-8(-/-) compared with WT mice at 14 days. There were significantly more PMNs outside of the lumen in the ECM in the MMP-8(-/-) mice compared with WT mice. In vitro, significantly fewer MMP-8(-/-) PMNs migrated through 3D cross-linked collagen gels than WT PMNs. MMP inhibitor GM6001 was also able to impede migration of WT PMNs through collagen gels. The decreased migration was likely a result of pericollagenase activity of MMP-8, as WT PMNs expressing MMP-8 were not able to migrate effectively through collagen that was resistant to the collagenase. Protection from OB was seen in the MMP-8(-/-) mice, as the airway lumen had significantly less obliteration and collagen deposition, suggesting that MMP-8 plays an important role in the pathogenesis of OB.

Chimerism and bone marrow based therapies in transplantation

Composite tissue allotransplantation holds a great potential for providing increased knowledge of anatomy and microsurgical experience for life-enhancing reconstructions. Many transplant cases around the world have made this a clinical reality at the present time. Composite tissue allotransplants contain multiple tissue types, including bone, muscle, vessels, nerves, skin, and immune cells and bear a huge antigenic load. Although immunosuppressive drugs are applied successfully to prevent allograft rejection, their side effects pose a barrier to worldwide use. Bone marrow therapy in many tolerance induction protocols, therefore, provides a guide to reaching the target of permanent immunotolerance. Multiple studies suggest that bone marrow is immunomodulatory and may facilitate allograft acceptance. In this review, bone marrow based therapy protocols of clinical and experimental models are presented in two major categories: solid organ and composite tissue transplantation.

Allopeptide-specific CD4(+) T cells facilitate the differentiation of directly alloreactive graft-infiltrating CD8(+) T Cells

To investigate the mechanism of CD4(+) T-cell help during the activation and differentiation of directly alloreactive CD8(+) T cells, we examined the development of obliterative airways disease (OAD) following transplantation of airways into fully mismatched recipient mice deficient in CD4(+) T cells. BALB/c trachea allografts became fibrosed significantly less frequently in B6 CD4(-/-) recipients as compared to wildtype controls. Furthermore, class I-directed cytotoxicity failed to develop in the absence of CD4(+) T cells. The infiltration of graft tissue by primed L(d)-specific directly alloreactive 2C CD8(+) T cells was not found to depend on the presence of CD4(+) T cells. Nevertheless, graft-infiltrating 2C CD8(+) T cells failed to express CD69 and granzyme B when CD4(+) T-cell help was unavailable. Importantly, reconstitution of B6 CD4(-/-) recipient mice with graft peptide-specific TCR-Tg CD4(+) T cells (OT-II or TEa) capable of recognizing antigen only on recipient APC allowed for full expression of CD69 and granzyme B by the directly alloreactive CD8(+) T cells and restored the capacity of recipients to reject their allografts. These results demonstrate that indirectly alloreactive CD4(+) T cells ensure the optimal activation and differentiation of graft-infiltrating directly alloreactive CD8(+) T cells independent of donor APC recognition.

Human and murine obliterative bronchiolitis in transplant

Obliterative bronchiolitis is a devastating illness that limits the long-term success of lung transplantation. Its high prevalence and overall poor response to current therapeutic measures demands further research to elucidate pathogenic mechanisms. Toward this goal, there is a role for animal models to study the mechanisms of obliterative bronchiolitis, such as the murine heterotopic tracheal allograft model. This review compares the tracheal allograft model to human obliterative bronchiolitis pathology and highlights the important mechanisms of airway rejection described using this model. Although certain limitations exist, the pursuit of proof-of-concept studies in this model, as well as other animal models, can provide the basis for genetic and cellular translational human studies directed toward post-transplant obliterative bronchiolitis pathogenesis. To meet these challenges, we call for the establishment of a National Institutes of Health-supported Lung Transplant Network to better orchestrate translational research efforts in obliterative bronchiolitis pathogenesis and treatment, and to advance the field of lung transplantation.