Blocking the CD28-B7 T-cell costimulatory pathway abrogates the development of obliterative bronchiolitis in a murine heterotopic airway model

Effect of CTLA4-Ig on Obliterative Bronchiolitis in a Mouse Intrapulmonary Tracheal Transplantation Model

Objectives: One of the serious problems after lung transplantation is chronic lung allograft dysfunction (CLAD). Most CLAD patients pathologically characterized by obliterative bronchiolitis (OB). Cytotoxic T-lymphocyte-associated antigen 4 (CTLA4)-Ig is a combination protein of the Fc fragment of human IgG1 linked to the extracellular domain of CTLA4. The aim of the study was to examine the effect of CTLA4-Ig therapy on OB using a mouse intrapulmonary tracheal transplantation (IPTT) model.

Methods: IPTT was performed between BALB/c (donor) and C57BL/6 (recipient) mice. Abatacept, which is a commercially available form of CTLA4-Ig, was intraperitoneally injected in recipient mice immediately after surgery, on days 7, 14, and 21. The mice in the control group received human IgG.

Results: We performed semi-quantitative analysis of graft luminal obliteration at post-transplant day 28. We calculated the obliteration ratio of the lumen of the transplanted trachea in each case. The obliteration ratio was significantly lower in the CTLA4-Ig group than that in the control group (91.2 ± 2.1% vs. 47.8 ± 7.9%, p = 0.0008). Immunofluorescent staining revealed significantly decreased lymphoid neogenesis in the lung.

Conclusions: CTLA4-Ig therapy attenuated tracheal obliteration with fibrous tissue in the mouse IPTT model. The attenuation of fibrous obliteration was correlated with the inhibition of lymphoid neogenesis.

HSCT-Based Approaches for Tolerance Induction in Renal Transplant

Renal transplantation has become the preferred treatment for end stage kidney failure. Although short-term graft survival has significantly improved as advances in immunosuppression have occurred, long-term patient and graft survival have not. Approximately only 50% of renal transplant recipients are alive at 10 years due to the toxicities of immunosuppression and alloimmunity. Emerging research on cell-based therapies is opening a new door for patients to receive the organs they need without sacrificing quality of life and longevity because of drug-based immunosuppression. Research has focused on inducing tolerance, a state in which the body accepts the transplant and graft function is stable. Cell-based therapies to facilitate chimerism and achieve tolerance in major histocompatibility disparate recipients have been developed in mouse, swine, canine, and nonhuman primate models. These findings are now being translated into the clinic in several trials currently underway. Protocols that use a combination of traditional therapeutic agents paired with cell populations including hematopoietic stem cells, regulatory T cells, and facilitating cells are being conducted with the objective to harness the donor immune system to protect the transplanted tissue. The benefits and feasibility of the clinical application of cell-based therapy has been demonstrated, and promising results have been achieved. Here we discuss the preclinical work that has led to the clinical application of the various approaches and a summary of the most current clinical data from groups throughout the world.

Belatacept for renal rescue in lung transplant patients

Renal failure causes morbidity and mortality after lung transplantation and is aggravated by exposure to nephrotoxic immunosuppressant (IS) drugs. We report an off-label experience using belatacept for lung transplant recipients with severe renal insufficiency to reduce nephrotoxic IS exposure. We analyzed data retrospectively from a consecutive series of lung transplant patients with renal insufficiency in whom belatacept treatment was initiated between June 2012 and June 2014 at the University of Maryland Medical Center. Eight patients received belatacept because of acute or chronic renal insufficiency (median) GFR 24 (IQR 18-26). Glomerular filtration rate (GFR) remained stable in two patients and increased in five. One patient with established renal and respiratory failure received only the induction dose of belatacept and died 4 months later of respiratory and multisystem organ failure. Calcineurin inhibitor or sirolimus exposure was safely withheld or reduced without moderate or severe acute rejection during ongoing belatacept in the other seven patients. FEV1 remained stable over the 6-month study interval. Belatacept use appears to permit safe transient reduction in conventional immunosuppressive therapy and was associated with stable or improved renal function in a small retrospective series of lung transplant recipients with acute or chronic renal insufficiency.

Blockade of both B7-H4 and CTLA-4 co-signaling pathways enhances mouse islet allograft survival

Costimulation blockade is an effective way to prevent allograft rejection. In this study, we tested the efficacy of two negative co-signaling molecules in protecting islet allograft function. We used local expression of B7-H4 by adenoviral transduction of islets (Ad-B7-H4) and systemic administration of CTLA-4.Ig to investigate the outcomes of allograft survival. Five groups of streptozotocin-induced diabetic C57BL/6 mice received 400 islets each from BALB/c donors. The groups consisted of control (G1); CTLA-4.Ig (G2); Ad-LacZ (G3); Ad-B7-H4 (G4); and Ad-B7-H4 and CTLA-4.Ig combined (G5). G1 and G3 developed graft failure on average of two weeks. G2, G4 and G5 survived for 43.8 ± 34.8, 54.7 ± 31.2 and 77.8 ± 21.5 d, respectively. Activated T and B cells in the lymph nodes were significantly controlled by CTLA-4.Ig treatment. Significantly reduced infiltrates were also detected in the allografts of G2 compared with G1. By contrast, B7-H4 significantly inhibited Th1-associated IFN-gamma secretion in the early stage and increased Foxp3 (+) T cells in the long-term surviving allografts. Our study suggests that CTLA-4 and B7-H4 inhibit alloimmune responses through distinct mechanisms, and that combination therapy which activates two negative co-signaling pathways can further enhance islet allograft survival.

Bronchiolitis obliterans in lung transplantation: the good, the bad, and the future

Lung transplantation remains the hope for many incurable pulmonary diseases, such as cystic fibrosis, pulmonary fibrosis, and chronic obstructive pulmonary disease. Remarkable progress has been made in improving outcomes, although the incidence of acute rejection remains more than 50% in the 1st year, and the 5-year graft survival is still less than 50% primarily because of the development of chronic rejection and graft dysfunction. Chronic rejection is characterized by the development of obliterative bronchiolitis in allografts and manifests as bronchiolitis obliterans syndrome in humans with no effective treatment. Previous studies support a role for alloreactive T cells in the development of bronchiolitis obliterans syndrome, but the specific mechanisms are unknown. One major stumbling block to research in the field of lung transplantation has been the lack of physiologic models to study the disease in the laboratory. We will review the current understanding of the immunology of the pathogenesis of obliterative bronchiolitis and will discuss exciting new advances from the laboratory as well as the implications for future research in lung transplantation.

Science of composite tissue allotransplantation

The science of composite tissue allotransplantation (CTA) is rooted in progressive thinking by surgeons, fueled by innovative solutions, and aided by understanding the immunology of tolerance and rejection. These three factors have allowed CTA to progress from science fiction to science fact. Research using preclinical animal models has allowed an understanding of the antigenicity of complex tissue transplants and mechanisms to promote graft acceptance. As a result, translation to the clinic has shown that CTA is a viable treatment option well on the way of becoming a standard of care for those who have lost extremities and suffered large tissue defects. The field of CTA has been progressing exponentially over the past decade. Transplantation of hands, larynx, vascularized knee, trachea, face, and abdominal wall has been performed. Several important observations have emerged from translation to the clinic. Although it was predicted that rejection would pose a major limitation, this has not proven true. In fact, steroid-sparing protocols for immunosuppression that have been successfully used in renal transplantation are sufficient to prevent rejection of limbs. Although skin is highly antigenic when transplanted alone in animal models, when part of a CTA, it has not proven to be. Chronic rejection has not been conclusively demonstrated in hand transplant recipients and is difficult to induce in rodent models of CTA. This review focuses on the science of CTA, provides a snapshot of where we are in the clinic, and discusses prospects for the future to make the procedures even more widely available.

Animal models for bronchiolitis obliterans syndrome following human lung transplantation

Lung transplantation is the only viable treatment option that can improve survival and enhance the quality of life of patients with end-stage lung diseases such as emphysema, cystic fibrosis, idiopathic pulmonary fibrosis, and primary pulmonary hypertension. However, the long-term survival of lung allografts is still limited by the development of bronchiolitis obliterans syndrome (BOS), an irreversible condition unresponsive to therapy. BOS is the most significant cause of long-term morbidity and mortality after lung transplantation. Over the past decade, several animal models have been developed to investigate BOS. These are valuable to elucidate the immunologic and pathologic mechanisms that lead to BOS and to test treatment options for BOS. In this review, we discuss the advantages and disadvantages of different animal models and highlight work that has been done with each model.

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.

Integrity of airway epithelium is essential against obliterative airway disease in transplanted rat tracheas

BACKGROUND

The pathogenesis of obliterative bronchiolitis after lung transplantation requires further elucidation. In this study we used rat trachea transplantation to examine the role of epithelium in the progression of obliterative airway disease.

METHODS

Normal and denuded (i.e., epithelium removed) trachea grafts from Lewis (LEW) and Brown Norway (BN) rats were transplanted sub-cutaneously into LEW rats. Viable trachea epithelial cells (to recover epithelium) were seeded into the lumen of some of the denuded tracheas. Grafts were removed at different time-points between 2 days and 8 weeks after transplantation. Histologic analysis was performed to evaluate cellular infiltration of inflammatory cells, loss of epithelium, and obliteration of trachea lumen.

RESULTS

Obliteration was found to occur in trachea transplants after loss of epithelium, caused by rejection in allografts or by enzymatic denudation in isografts. In these situations, fibroblasts started to proliferate and migrate into the lumen in the second week after transplantation. Obliteration could be prevented when epithelial integrity was restored by seeding epithelial cells; no obliteration occurred when denuded trachea isografts were seeded with epithelial cells, whereas non-seeded denuded tracheas were obliterated at Day 6 after transplantation.

CONCLUSIONS

We conclude that integrity of airway epithelium is essential for rat trachea transplants to be safeguarded from obliterative airway disease. For clinical lung transplantation the results of our study suggest that protection of the integrity of airway epithelium may be important in preventing the development of obliterative bronchiolitis.

Blockage of the macrophage migration inhibitory factor expression by short interference RNA inhibited the rejection of an allogeneic tracheal graft

We investigated the inhibitory effect of blocking the macrophage migration inhibitory factor (MIF) on the fibrous obstruction of a transplanted allograft in a murine model of obstructive bronchiolitis (OB). Tracheal grafts from C57BL/6 mice were transplanted into a subcutaneous pouch of BALB/c. Three days after transplantation, liposome including short interference (si) RNA for MIF was injected into the lumen of the grafts. The allografts were then harvested 7, 14 or 28 days after transplantation for an evaluation of the morphological changes. The MIF expression, which was ubiquitously recognized in the epithelium of allografts, decreased after the in vivo transfection of MIF siRNA. OB formation was therefore inhibited significantly more by the treatment with MIF siRNA than the allografts injected with empty liposome on the 14th day, however, no difference was observed between them on the 28th day. Treatment with MIF siRNA inhibits the destruction of tracheal allografts and OB formation in the early phase, and MIF was thus found to be one of the major cytokines involved in the rejection of the allogeneic trachea.

Combined donor specific transfusion and anti-CD154 therapy achieves airway allograft tolerance

BACKGROUND

The state of tolerance allows long term graft survival without immunosuppressants. Lung transplantation tolerance has not been consistently achieved in either small or large animal models.

METHODS

The mechanisms and effectiveness of a tolerance induction protocol consisting of donor specific transfusion (DST; day 0) and a short course of co-stimulatory blockade (anti-CD154 antibody; days -7, -4, 0 and +4) were studied in the mouse heterotopic tracheal transplant model of chronic lung rejection. C57BL/6 mice received BALB/c tracheal grafts (day 0) and were treated with DST alone, anti-CD154 alone, the combination (DST/anti-CD154), or no treatment. No non-specific immunosuppressants were used.

RESULTS

DST/anti-CD154 in combination, but neither treatment alone, markedly prolonged the lumen patency and survival (>100 days) of fully histo-incompatible allografts (p<0.05 versus control allografts at every time point studied up to 16 weeks) without immunosuppression. This protocol was donor antigen specific as third party grafts (C3H) were promptly rejected. In addition, DST/anti-CD154 did not result in mixed chimerism but induced transplantation tolerance via a peripheral mechanism(s), which included significantly reduced cytotoxic T cell activity (p<0.001) and a significantly increased percentage of CD4+CD25+ cells (p = 0.03).

CONCLUSIONS

The DST/anti-CD154 protocol successfully induced and maintained long term, donor specific tolerance in the mouse heterotopic airway graft model of chronic lung rejection. This finding may lead us closer to successful tolerance induction in lung transplantation.

The effects of pretreatment with donor antigen and immunosuppressive agents on fully allogenic tracheal graft

BACKGROUND

Obliterative bronchiolitis is a major clinical problem in cases involving a transplanted lung. We examined drug-induced tolerance to a fully allogenic tracheal graft in a murine heterotopic transplantation model.

MATERIALS AND METHODS

Recipient mice (C57BL/6) were primed iv with 1 x 10(8) splenocytes of donor mice (BALB/c). Day 0 was the day of the splenocyte injection. Cyclophosphamide and Busulfan were injected intraperitoneally on day 2. On day 3, 1 x 10(7) donor bone marrow cells were intravenously injected. On day 28, a donor tracheal graft was implanted into a subcutaneous pocket. Grafts were harvested at 3-week intervals, and the degree of obstruction of the inner cavity, the condition of epithelium, and the viability of chondrocytes were examined.

RESULTS

All of the isograft controls (BALB/c) and grafts implanted in the T cell-free recipients (BALB/c-nu) showed patent, lined epithelium and viable chondrocytes. All allografts tested showed total luminal occlusion by granulative tissue and inflammatory cells, and the epithelium was totally absent. Five of 11 drug-treated grafts were completely patent, although the epithelium was almost absent and the chondrocytes were substantially destroyed. However, when the chimerism was analyzed by flow cytometry analysis of the recipient T cells, approximately 90% of the donor cells were recognized.

CONCLUSIONS

Even by this pre-treatment-induced chimerism, a transplanted allogenic trachea was not completely preserved. The present results suggest that a non-allogenic response might have contributed to the rejection.

Combined gene therapy with adenovirus vectors containing CTLA4Ig and CD40Ig prolongs survival of composite tissue allografts in rat model

BACKGROUND

The blockade of costimulatory signal pathway by anti-CD40 ligand antibody or cytotoxic T lymphocyte antigen 4 immunoglobulin (CTLA4Ig) prolongs allograft survival in various vascularized organ transplantations. Because of the short half life of these agents, repeated administration of proteins is required to achieve significant graft survival. Furthermore, there is limited information regarding the effect of cosimulatory blockade on the survival of composite tissue allografts. Therefore, we examined the effect of adenovirus-mediated gene transfer of CTLA4Ig or CD40Ig gene or both in composite tissue allotransplantation.

METHODS

The hind limbs removed from male ACI rats (RT1 ) were transplanted into female Lewis rats (RT1 ) heterotopically. The recombinant adenovirus carrying CTLA4Ig (AxCTLA4Ig) or CD40Ig (AxCD40Ig) was intravenously administered after limb transplantation.

RESULTS

Limb allograft survival was significantly prolonged by either AxCTLA4Ig or AxCD40Ig treatment at 1 x 10 plaque forming unit (mean survival time [MST] of 39.4+/-6.0 and 13.0+/-2.9, respectively) compared with the adenovirus vector containing beta-galactosidase-treated group (MST of 4.8+/-0.8). Combination of AxCTLA4Ig and AxCD40Ig led to significant prolongation of graft survival (MST of 49.2+/-6.6). Serum levels of CD40Ig were higher in rats treated with combination therapy than those treated with AxCD40Ig alone, whereas the serum levels of CTLA4Ig in rats treated with AxCTLA4Ig alone and AxCTLA4Ig and AxCD40Ig combined were very similar.

CONCLUSION

This study indicates that an adenovirus-mediated gene therapy of CTLA4Ig or CD40Ig has a therapeutic potential for preventing rejection in composite tissue transplantation. Furthermore, a combination therapy of AxCTLA4Ig and AxCD40Ig was even more effective in preventing acute rejection and prolonging the survival of allografted limbs without apparent complication.

Airway-directed gene transfer of interleukin-10 using recombinant Sendai virus effectively prevents post-transplant fibrous airway obliteration in mice

Bronchiolitis obliterans (BO) after lung transplantation prevents a satisfactory prognosis, and recent studies suggested that interleukin-10 (IL-10) gene transfer to distant organs could inhibit BO in rodent models. Although delivery of the therapeutic gene to a local airway would be favored to minimize systemic effects, current limitations include lower gene transfer efficiency to airway epithelium. As recombinant Sendai virus (SeV) can produce dramatically efficient gene transfer to airway epithelium, we determined if SeV-mediated IL-10 gene transfer to the local airway would inhibit bronchial fibrous obliteration in murine tracheal allografts. Administration of cyclosporine A (CsA) significantly promoted not only recovery of the injured airway epithelium but also SeV-mediated IL-10 expression (CsA- versus CsA+ =228+/-78 versus 3627+/-1372 pg/graft with 5 x 10(7) pfu), thereby suggesting the requirement of epithelia for efficient gene transfer. Even at the highest expression, no significant leakage of IL-10 was evident in the systemic circulation, and the induction of interferon-gamma was completely diminished on day 7 by IL-10 gene transfer. As a result, luminal loss was significantly prevented in allografts treated with SeV-IL-10 (luminal opening, all control groups: 0% respectively, and SeV-IL-10 5 x 10(7) pfu: 25.7+/-10.5%), an effect that was enhanced by short-term CsA treatment (SeV-IL-10 5 x 10(7) pfu with CsA: 63.7+/-12.7%). We propose that SeV is a useful vector that can target airway epithelium to prevent BO avoiding putative systemic effect.

Combination treatment with FTY720 and CTLA4IgG preserves the respiratory epithelium and prevents obliterative disease in a murine airway model

BACKGROUND

Mouse heterotopic tracheal transplantation offers a reproducible model of obliterative bronchiolitis after lung transplantation. CTLA4IgG inhibits signaling of the CD28/B7 pathway and induces antigen-specific T-cell unresponsiveness. FTY720 induces T-cell apoptosis and sequestration of circulating mature lymphocytes. We previously found that CTLA4IgG could prevent the development of obliterative airway disease but could not preserve the respiratory epithelium of grafted tracheae. We evaluated whether treatment with either FTY720 or CTLA4IgG, or with combination FTY720 and CTLA4IgG could preserve the respiratory epithelium and inhibit the development of obliterative airway disease.

METHODS

Tracheae with main bronchi from C3H/He mice were transplanted heterotopically into BALB/C mice and harvested on Day 35. Recipient mice received either no treatment or treatment with intraperitoneal FTY720, CTLA4IgG, or the combination of the 2.

RESULTS

Either FTY720 or CTLA4IgG alone significantly inhibited the development of obliterative airway disease. However, normal ciliated columnar respiratory epithelial cells were lost in the allografts. In contrast, combination therapy preserved the respiratory epithelium of the allografted tracheae. FTY720 concentration in the tissue was very high; treatment with FTY720 inhibited mixed lymphocyte reactions and augmented T-cell apoptosis.

CONCLUSION

Combination treatment with FTY720 and CTLA4IgG may prevent obliterative airway disease.

Blockade of CD28/B7-2 costimulation inhibits experimental obliterative bronchiolitis in rat tracheal allografts: suppression of helper T cell type1-dominated immune response

T cell activation is a proximal event in the initiation of chronic rejection that may ultimately lead to obliterative bronchiolitis (OB) after lung transplantation. In addition to primary signals generated by the T cell receptor, T cell activation relies on costimulatory signals, of which the most important are mediated via interaction between CD28 and its ligands B7-1 and B7-2. In nontreated rat tracheal allografts, B7-2, but not B7-1, expression peaked 10 d after transplantation, unlike in syngeneic grafts, where no B7-2 upregulation was observed. Selective blockade of the CD28/B7-1 T cell costimulatory pathway by a mutant form of CTLA4Ig (cytotoxic T lymphocyte antigen 4 immunoglobulin), CTLA4IgY100F, did not affect epithelial injury or degree of luminal occlusion in rat tracheal allografts. Treatment with CTLA4Ig fusion protein, which blocks both CD28/B7-1 and CD28/B7-2 interaction, significantly delayed the development of epithelial injury and airway occlusion. Immunohistochemical analyses of allografts showed that selective inhibition of the CD28/B7-1 pathway did not affect cytokine expression. In contrast, treatment with CTLA4Ig was associated with a significant decrease in the intragraft production of tumor necrosis factor alpha, interleukin 2, and interferon gamma, as well as slightly increased intragraft expression of interleukin 10. In conclusion, CTLA4Ig-mediated costimulatory blockade delays epithelial injury and attenuates obliterative changes and is associated with marked suppression of helper T cell type 1 (Th1)-dominated cytokine response. These observations emphasize the role of the CD28/B7-2 costimulatory pathway in regulating proinflammatory and Th1 cytokine responses and thereby in the development of epithelial and graft injury gradually leading to obliteration of the airway lumen.

Prevention of acute lung allograft rejection in rat by CTLA4Ig

CTLA4 immunoglobulin (CTLA4Ig), which binds with a high affinity to B7-1 and B7-2, interrupts T-cell activation by inhibiting costimulatory signal. CTLA4Ig has been used in hopes of achieving antigen-specific tolerance induction in several solid organ transplants. In lung allograft rejection, however, its use has been controversial in terms of its effect on prevention of rejection. In the present study, the effect of murine CTLA4Ig on rat-lung allograft rejection was investigated. Rat left-lung transplantation was performed in an RT1 incompatible donor (Brown Norway; BN)-recipient (F344) combination. All allografts (n = 12) without any treatment were rejected within 7 days after transplantation. A single injection of murine form CTLA41g at a dose of 100 microg intraperitoneally (ip) or intravenously (iv) on day 1 post-transplantation achieved long-term graft survival (>90days) in 2/5 (40%) and 3/8 (38%), respectively. Moreover, 6/7 (86%) allografts in rats that received iv injection of 500 microg CTLA4Ig survived more than 90days. Allograft survival in the CTLA4Ig 500 microg iv recipient group was significantly longer than that in the no-treatment control or control immunoglobulin group (p <0.01). Four out of seven recipients bearing functional allografts for more than 90 days with the CTLA4Ig treatment accepted donor-specific skin grafts, whereas all third-party skin grafts (n=3) were rejected. Prevention of rat-lung allograft rejection could be achieved by intravenous administration of CTLA4Ig, resulting in long-term allograft survival with acceptance of donor-specific skin grafts.

Dependence of murine obstructive airway disease on CD40 ligand

BACKGROUND

Human lung transplantation carries a poor prognosis because of chronic rejection in the form of obliterative bronchiolitis syndrome (OBS). Using the mouse model of heterotopic tracheal transplantation, we examined the role of costimulation in the allograft rejection that characterizes obstructive airway disease (OAD).

METHODS

C57BL/6 or BALB/c tracheae were implanted into wild-type control, CD28-/-, muMT (B-cell deficient), or CD40L-/- recipient mice. Grafts were explanted from 7 to 42 days posttransplantation and evaluated.

RESULTS

Thickening of the basement membrane and a decrease in patent luminal area were first noted at 2 weeks in wild-type allogeneic trachea recipients and to a slightly lesser degree in CD28-/- recipients. In contrast, CD40L-/- recipient mice showed no evidence of cellular infiltrates or fibrosis in transplanted tracheae. To determine whether CD40L interacted with host or donor CD40, CD40-deficient tracheae were transplanted into CD40L+/+, CD40+/+ wild-type mice. Wild-type mice rejected CD40-/- tracheae. Tracheae were transplanted into B-cell-deficient mice to determine the role of B-cell CD40 in chronic pulmonary allograft rejection. The OAD reaction was identical in wild-type and B-cell-deficient mice.

CONCLUSIONS

Development of OAD in the mouse trachea transplant model is primarily dependent on CD40L and is relatively CD28 independent. The ability of mice to reject CD40-/- tracheae demonstrated that host, not donor, CD40 is required for rejection. Furthermore, the ability of B-cell-deficient mice to reject allogeneic tracheae demonstrated that B-cell CD40-mediated responses are not required for the development of OAD.

Prolonged inhibition of obliterative airway disease in murine tracheal allografts by brief treatment with anti-leukocyte function-associated antigen-1 (CD11a) monoclonal antibody

BACKGROUND

We have previously shown that anti-leukocyte function-associated antigen (LFA)-1 (CD11a) monoclonal antibody (mAb) prevents acute rejection and produces donor-specific unresponsiveness in murine recipients of heterotopic heart allografts. Here, we investigate the ability of this mAb to prevent the development of obliterative airway disease (OAD) in murine recipients of tracheal allografts.

METHODS AND RESULTS

BALB/c tracheae were heterotopically transplanted into C3H mice. OAD developed by day 28 after transplantation and was characterized histologically by a loss of epithelial cell coverage and luminal obliteration of the tracheal allograft with a proliferation of fibrogenic mesenchymal cells, which is a lesion comparable to obliterative bronchiolitis in human lung transplant recipients. Monotherapy with anti-LFA-1 mAb preserved graft epithelium, prevented the development of OAD, and maintained unresponsiveness to donor antigen for more than 42 days after the final mAb administration.

CONCLUSION

These findings suggest the potential for anti-LFA-1 mAb therapy to suppress both acute and chronic rejection in clinical lung transplantation.

The heterotopic tracheal allograft as an animal model of obliterative bronchiolitis

Heterotopic tracheal allografts in small rodents have been shown to share many characteristics with the development of obliterative bronchiolitis (OB) in the clinic and therefore provide a suitable animal model for the study of OB. The model facilitates the examination of the pathogenesis of the disease and the elucidation of the cellular and molecular mechanisms involved in its development. The model provides a less technically demanding alternative to whole lung transplantation in small rodents and should lead to a speedier identification of new treatments that might prevent the development of post-transplantation OB in the clinic.