Hyperacute Rejection After Lung Transplantation Caused by Undetected Low-titer Anti-HLA Antibodies

Pushing the Survival Bar Higher: Two Decades of Innovation in Lung Transplantation

Survival after lung transplantation has significantly improved during the last two decades. The refinement of the already existing extracorporeal life support (ECLS) systems, such as extracorporeal membrane oxygenation (ECMO), and the introduction of new techniques for donor lung optimization, such as ex vivo lung perfusion (EVLP), have allowed the extension of transplant indication to patients with end-stage lung failure after acute respiratory distress syndrome (ARDS) and the expansion of the donor organ pool, due to the better evaluation and optimization of extended-criteria donor (ECD) lungs and of donors after circulatory death (DCD). The close monitoring of anti-HLA donor-specific antibodies (DSAs) has allowed the early recognition of pulmonary antibody-mediated rejection (AMR), which requires a completely different treatment and has a worse prognosis than acute cellular rejection (ACR). As such, the standardization of patient selection and post-transplant management has significantly contributed to this positive trend, especially at high-volume centers. This review focuses on lung transplantation after ARDS, on the role of EVLP in lung donor expansion, on ECMO as a principal cardiopulmonary support system in lung transplantation, and on the diagnosis and therapy of pulmonary AMR.

Immunopathology of lung transplantation: from infection to rejection and vice versa

Lung transplantation offers a lifesaving option for patients with end-stage lung disease, but it is marred by a high risk of post-transplant infections, particularly involving multidrug-resistant bacteria, Cytomegalovirus, and fungal pathogens. This elevated infection rate, the highest among solid organ transplants, poses a significant challenge for clinicians, particularly within the first year post-transplantation, where infections are the leading cause of mortality. The direct exposure of lung allografts to the external environment exacerbates this vulnerability leading to constant immune stimulation and consequently to an elevated risk of triggering alloimmune responses to the lung allograft. The necessity of prolonged immunosuppression to prevent allograft rejection further complicates patient management by increasing susceptibility to infections and neoplasms, and complicating the differentiation between rejection and infection, which require diametrically opposed management strategies. This review explores the intricate balance between preventing allograft rejection and managing the heightened infection risk in lung transplant recipients.

Introduction to stem cell biology and its role in treating neurologic disorders

Regenerative medicine is an emerging and rapidly evolving field of research and therapeutics aimed to restore, maintain, and improve body functions. In the adult mammalian brain, very few neurons, if any, are generated after disease onset or an injury, and its ability to self-repair is therefore limited. Replacing neurons that are lost during neurodegenerative diseases or due to injury therefore represents one of the major challenges to modern medicine. In this introductory chapter, we describe the basic biology of stem cells and outline how stem cells and cell reprogramming can be utilized to create new neurons for therapeutic purposes that are discussed in detail in other chapters in this handbook.

Lung transplantation despite preformed donor-specific antihuman leukocyte antigen antibodies: a 9-year single-center experience

Pretransplant allosensitization to human leukocyte antigens (HLA) increases the recipient's waiting list time and mortality in lung transplantation. Rather than waiting for crossmatch-negative donors, since 2013, recipients with preformed donor-specific antiHLA antibodies (pfDSA) have been managed with repeated IgA- and IgM-enriched intravenous immunoglobulin (IgGAM) infusions, usually in combination with plasmapheresis before IgGAM and a single dose of antiCD20 antibody. This retrospective study presents our 9-year experience with patients transplanted with pfDSA. Records of patients transplanted between February 2013 and May 2022 were reviewed. Outcomes were compared between patients with pfDSA and those without any de novo donor-specific antiHLA antibodies. The median follow-up time was 50 months. Of the 1,043 patients who had undergone lung transplantation, 758 (72.7%) did not develop any early donor-specific antiHLA antibodies, and 62 (5.9%) patients exhibited pfDSA. Among the 52 (84%) patients who completed treatment, pfDSA was cleared in 38 (73%). In pfDSA vs control patients and at 8-year follow-up, respectively, graft survival (%) was 75 vs 65 (P = .493) and freedom from chronic lung allograft dysfunction (%) was 63 vs 65 (P = .525). In lung transplantation, crossing the preformed HLA-antibody barrier is safe using a treatment protocol based on IgGAM. Patients with pfDSA have a good 8-year graft survival rate and freedom from chronic lung allograft dysfunction, similar to control patients.

The Highly Sensitized Recipient: Pretransplant and Posttransplant Considerations

Highly sensitized patients, who are often black and Hispanic women, are less likely to be listed for lung transplant and are at higher risk for prolonged waitlist time and waitlist death. In this review, the authors discuss strategies for improving access to transplant in this population, including risk stratification of crossing pretransplant donor-specific antibodies, based on antibody characteristics. The authors also review institutional protocols, such as perioperative desensitization, for tailoring transplant immunosuppression in the highly sensitized population. The authors conclude with suggestions for future research, including development of novel donor-specific antibody-directed therapeutics.

First use of imlifidase desensitization in a highly sensitized lung transplant candidate: a case report

Lung transplant candidates who are highly sensitized against human leucocyte antigen present an ongoing challenge with regards to finding immunologically acceptable donors. Desensitization strategies aimed at reducing preformed donor-specific antibodies have a number of limitations. Imlifidase, an IgG-degrading enzyme derived from Streptococcus pyogenes, is a novel agent that has been used to convert positive crossmatches to negative in kidney transplant candidates, allowing transplantation to occur. We present the first case of imlifidase use for antibody depletion in a highly sensitized lung transplant candidate who went on to undergo a successful bilateral lung transplant.

Lung Allograft Rejection

Rejection is a major complication following lung transplantation. Acute cellular rejection (ACR), and antibody-mediated rejection (AMR) are risk factors for the subsequent development of chronic lung allograft dysfunction and worse outcomes after transplantation. Although ACR has well-defined histopathologic diagnostic criteria and grading, the diagnosis of AMR requires a multidisciplinary diagnostic approach. This article reviews the identification, clinical and pathologic features of, and therapeutic options for ACR and AMR.

The clinical utility and thresholds of Virtual and Halifaster Flow crossmatches in lung transplantation

INTRODUCTION

Immune sensitization, defined as the presence of alloreactive donor-specific antibodies (DSA), is associated with increased wait-times and inferior transplant outcomes. Identifying pre-transplant DSA with a physical cell-based assay is critical in defining immunological risk. However, improved solid phase antibody detection has provided the potential to forgo this physical assay. Here, we evaluated the association between DSA mean fluorescence intensity (MFI) and the recently introduced Halifaster Flow cytometry crossmatch (FXM) to determine if MFI could predict the outcome of FXM and whether a virtual crossmatch (VXM) would provide an accurate risk assessment.

METHODS

Sera from 134 waitlisted lung patients was retrospectively assessed by Halifaster FXM against lymphocytes preparations from 32 donors, resulting in 265 FXMs. HLA typing was performed to 2-field allelic level and Luminex single antigen beads (SAB) used to identify DSA. The association between FXM and Luminex MFI was calculated using ROC analysis. MFI threshold accuracy was confirmed using a separate validation cohort (174 recipient sera and 34 donors), whereby both virtual crossmatch (VXM) and FXMs were compared.

RESULTS

From the 265 FXM performed, 48 (18%) T-cell (TFXM) and 56 (21%) B-cell (BFXM) were positive. In the evaluation cohort, MFI thresholds of 2000 for HLA-A, B, DRB1 and >4000 for DQB1, were predictive of a positive FXM. The validation cohort of 233 paired FXM and VXM confirmed these MFI thresholds for both TFXM and BFXM with an accuracy of 91.4% and 89.3% respectively.

CONCLUSION

A positive VXM, defined with HLA-specific MFI thresholds predicts Halifaster FXM reactivity, and can potentially expedite organ allocation, by minimising the need for the more time-consuming flow cytometry crossmatch. This article is protected by copyright. All rights reserved.

Long-term outcomes of sensitized lung transplant recipients after peri-operative desensitization

The Toronto Lung Transplant Program has been using a peri-operative desensitization regimen of plasma exchange, intravenous immune globulin, and antithymocyte globulin in order to accept donor-specific antibody (DSA)-positive lung transplants safely since 2008. There are no long-term data on the impact of this practice on allograft survival or the development of chronic lung allograft dysfunction (CLAD). We extended our prior study to include long-term follow-up of 340 patients who received lung transplants between January 1, 2008 and December 31, 2011. We compared allograft survival and CLAD-free survival among patients in three cohorts: DSA-positive, panel reactive antibody (PRA)-positive/DSA-negative, and unsensitized at the time of transplant. The median follow-up time in this extension study was 6.7 years. Among DSA-positive, PRA-positive/DSA-negative, and unsensitized patients, the median allograft survival was 8.4, 7.9, and 5.8 years, respectively (p = .5908), and the median CLAD-free survival was 6.8, 7.3, and 5.7 years, respectively (p = .5448). This follow-up study confirms that long-term allograft survival and CLAD-free survival of patients who undergo DSA-positive lung transplants with the use of our protocol do not differ from other lung transplant recipients. Use of protocols such as ours, therefore, may improve access to transplant for sensitized candidates.

Imaging Course of Lung Transplantation: From Patient Selection to Postoperative Complications

Lung transplant is increasingly performed for the treatment of end-stage lung disease. As the number of lung transplants and transplant centers continues to rise, radiologists will more frequently participate in the care of patients undergoing lung transplant, both before and after transplant. Potential donors and recipients undergo chest radiography and CT as part of their pretransplant assessment to evaluate for contraindications to transplant and to aid in surgical planning. After transplant, recipients undergo imaging during the postoperative hospitalization and also in the long-term outpatient setting. Radiologists encounter a wide variety of conditions leading to end-stage lung disease and a myriad of posttransplant complications, some of which are unique to lung transplantation. Familiarity with these pathologic conditions, including their imaging findings and their temporal relationship to the transplant, is crucial to accurate radiologic interpretation. Knowledge of the surgical techniques and expected postoperative appearance prevents confusing normal posttransplant imaging findings with complications. A basic understanding of the indications, contraindications, and surgical considerations of lung transplant aids in imaging interpretation and protocoling and also facilitates communication between radiologists and transplant physicians. Despite medical and surgical advances over the past several decades, lung transplant recipients currently have an average posttransplant life expectancy of only 6.7 years. As members of the transplant team, radiologists can help maximize patient survival and hopefully increase posttransplant life expectancy and quality of life in the coming decades. ^©RSNA, 2021 An invited commentary by Bierhals is available online. Online supplemental material is available for this article.

Donor-specific antibodies in lung transplantation

PURPOSE OF REVIEW

The development of donor-specific antibodies (DSA) after lung transplantation has been recognized as an important risk factor for poor outcomes over the past 20 years. Recently, this has been a focus of intense research, and the purpose of this review is to summarize our current understanding of humoral responses and important recent findings as well as to identify areas of future research.

RECENT FINDINGS

Recent studies have identified donor-derived cell-free DNA (ddcfDNA) as an important biomarker associated with antibody-mediated rejection (AMR). Importantly, ddcfDNA levels are noted to be elevated approximately 3 months before the onset of clinical allograft dysfunction, making ddcfDNA a particularly appealing biomarker to predict the onset of AMR. Additional notable recent findings include the identification of an independent association between the isolation of Pseudomonas aeruginosa from respiratory specimens and the development of DSA. This finding provides potential insights into crosstalk between innate and alloimmune responses and identifies a potential therapeutic target to prevent the development of DSA.

SUMMARY

Progress in the field of humoral responses after lung transplantation has been slow, but ongoing and future research in this area are critically necessary to improve patient outcomes in the future.

A virtual crossmatch-based strategy for perioperative desensitisation in lung transplant recipients with preformed donor-specific antibodies: 3-year outcome

BACKGROUND

Preformed donor-specific antibodies (DSAs) are associated with worse outcome after lung transplantation (LTx) and migvaht limit access to LTx. A virtual crossmatch (CXM)-based strategy for perioperative desensitisation protocol has been used for immunised LTx candidates since 2012 at Foch hospital. We compared the outcome of desensitised LTx candidates with high DSA mean fluorescence intensity (MFI) and those with low or no preformed DSAs, not desensitised.

METHODS

For all consecutive LTx recipients (January-2012/March-2018), freedom from CLAD and graft survival were assessed by Kaplan-Meier analysis and Cox multivariate analysis.

RESULTS

We compared outcomes for desensitised patients with high preformed DSAs (n=39) and those with no (n=216) or low pre-formed DSAs (n=66). The desensitisation protocol decreased the level of immunodominant DSA (class I/II) at 1, 3, and 6 month post-LTx (p<0.001, p<0.01, p<0.001, respectively). Freedom from CLAD and graft survival at 3 years was similar in the desensitised group as a whole and other groups. Nevertheless, incidence of CLAD was higher with persistent high- than cleared high-level (p=0.044) or no DSAs (p=0.014). Conversely, graft survival was better with cleared high DSAs than persistent high-, low-level, and no pre-formed DSAs (p=0.019, p=0.025, and p=0.044, respectively). On multivariate analysis, graft survival was associated with cleared high DSAs (HR: 0.12 [95%CI: 0.02-0.85] versus no DSAs, p=0.035) and CLAD with persistent DSAs (HR: 3.04 [1.02-9.17] versus no preformed DSAs, p=0.048).

CONCLUSION

The desensitisation protocol in LTx recipients with high preformed DSAs was associated with satisfactory outcome, with cleared high pre-formed DSAs after desensitisation identified as an independent predictor of graft survival.

Desensitization and management of allograft rejection

PURPOSE OF REVIEW

Chronic lung allograft dysfunction (CLAD) limits the success of lung transplantation. Among the risk factors associated with CLAD, we recognize pretransplant circulating antibodies against the human leukocyte antigens (HLA), acute cellular rejection (ACR) and antibody-mediated rejection (AMR). This review will summarize current data surrounding management of desensitization, ACR, AMR, and CLAD.

RECENT FINDINGS

Strategies in managing in highly sensitized patients waiting for lung transplant include avoidance of specific HLA antigens and reduction of circulating anti-HLA antibodies at time of transplant. Several multimodal approaches have been studied in the treatment of AMR with a goal to clear circulating donor-specific antibodies (DSAs) and to halt the production of new antibodies. Different immunosuppressive strategies focus on influence of the host immune system, particularly T-cell responses, in order to prevent ACR and the progression of CLAD.

SUMMARY

The lack of significant evidence and consensus limits to draw conclusion regarding the impact of specific immunosuppressive regimens in the management of HLA antibodies, ACR, and CLAD. Development of novel therapeutic agents and use of multicenter randomized clinical trials will allow to better define patient-specific treatments and improve the length and quality of life of lung transplant recipients.

Strategies for Genetically Engineering Hypoimmunogenic Universal Pluripotent Stem Cells

Despite progress in developing cell therapies, such as T cell or stem cell therapies to treat diseases, immunoincompatibility remains a major barrier to clinical application. Given the fact that a host's immune system may reject allogeneic transplanted cells, methods have been developed to genetically modify patients' primary cells. To advance beyond this time-consuming and costly approach, recent research efforts focus on generating universal pluripotent stem cells to benefit a broader spectrum of patients. In this review, we first summarize current achievements to harness immunosuppressive mechanisms in cells to reduce immunogenicity. Then, we discuss several recent studies demonstrating the feasibility of genetically modifying pluripotent stem cells to escape immune attack and summarize the methods to evaluate hypoimmunogenicity. Although challenges remain, progress to develop genetically engineered universal pluripotent stem cells holds the promise of expediting their use in future gene and cell therapeutics and regenerative medicine.

Imaging indications and findings in evaluation of lung transplant graft dysfunction and rejection

Lung transplantation is a treatment option in end-stage lung disease. Complications can develop along a continuum in the immediate or longer post-transplant period, including surgical and technical complications, primary graft dysfunction, rejection, infections, post-transplant lymphoproliferative disorder, and recurrence of the primary disease. These complications have overlapping clinical and imaging features and often co-exist. Time of onset after transplant is helpful in narrowing the differential diagnosis. In the early post transplantation period, imaging findings are non-specific and need to be interpreted in the context of the clinical picture and other investigations. In contrast, imaging plays a key role in diagnosing and monitoring patients with chronic lung allograft dysfunction. The goal of this article is to review primary graft dysfunction, acute rejection, and chronic rejection with emphasis on the role of imaging, pathology findings, and differential diagnosis.

The role of the immune system in lung transplantation: towards improved long-term results

Over the past 35 years, lung transplantation has evolved from an experimental treatment to the treatment of choice for patients with end-stage lung disease. Beyond the immediate period after lung transplantation, rejection and infection are the leading causes of death. The risk of rejection after lung transplantation is generally higher than after other solid organ transplants, and this necessitates more intensive immunosuppression. However, this more intensive treatment does not reduce the risk of rejection sufficiently, and rejection is one of the most common complications after transplantation. There are multiple forms of rejection including acute cellular rejection, antibody-mediated rejection, and chronic lung allograft dysfunction. These have posed a vexing problem for clinicians, patients, and the field of lung transplantation. Confounding matters is the inherent effect of more intensive immunosuppression on the risk of infections. Indeed, infections pose a direct problem resulting in morbidity and mortality and increase the risk of chronic lung allograft dysfunction in the ensuing weeks and months. There are complex interactions between microbes and the immune response that are the subject of ongoing studies. This review focuses on the role of the immune system in lung transplantation and highlights different forms of rejection and the impact of infections on outcomes.

Generation of hypoimmunogenic human pluripotent stem cells

Polymorphic HLAs form the primary immune barrier to cell therapy. In addition, innate immune surveillance impacts cell engraftment, yet a strategy to control both, adaptive and innate immunity, is lacking. Here we employed multiplex genome editing to specifically ablate the expression of the highly polymorphic HLA-A/-B/-C and HLA class II in human pluripotent stem cells. Furthermore, to prevent innate immune rejection and further suppress adaptive immune responses, we expressed the immunomodulatory factors PD-L1, HLA-G, and the macrophage "don't-eat me" signal CD47 from the AAVS1 safe harbor locus. Utilizing in vitro and in vivo immunoassays, we found that T cell responses were blunted. Moreover, NK cell killing and macrophage engulfment of our engineered cells were minimal. Our results describe an approach that effectively targets adaptive as well as innate immune responses and may therefore enable cell therapy on a broader scale.

Pathology of Lung Rejection: Cellular and Humoral Mediated

Acute rejection is an important risk factor for bronchiolitis obliterans syndrome, the clinical manifestation of chronic airway rejection in lung allograft recipients. Patients with acute rejection might be asymptomatic or present with symptoms that are not specific and can be also seen in other conditions. Clinical tests such as pulmonary function tests and imaging studies among others usually are abnormal; however, their results are also not specific for acute rejection. Histopathologic features of acute rejection in adequate samples of transbronchial lung biopsy of the lung allograft are currently the gold standard to assess for acute rejection in lung transplant recipients. Acute alloreactive injury can affect both the vasculature and the airways. Currently, the guidelines of the 2007 International Society of Heart and Lung Transplantation consensus conference are recommended for the histopathologic assessment of rejection. There are no specific morphologic features recognized to diagnose antibody-mediated rejection (AMR) in lung allografts. Therefore, the diagnosis of AMR currently requires a “triple test” including clinical features, serologic evidence of donor-specific antibodies, and pathologic findings supportive of AMR. Complement 4d deposition is used to support a diagnosis of AMR in many solid organ transplants; however, its significance for the diagnosis of AMR in lung allografts is not entirely clear. This chapter discusses the currently recommended guidelines for the assessment of cellular rejection of lung allografts and summarizes our knowledge about morphologic features and immunophenotypic tests that might help in the diagnosis of AMR.

Acute Rejection and Antibody-Mediated Rejection in Lung Transplantation

Despite advances in immunosuppression over the past 25 years, acute cellular rejection remains a common complication early after lung transplantation. Although acute cellular rejection has often not resulted in clinical signs or symptoms of allograft dysfunction, it has been widely recognized as a strong independent risk factor for the development of chronic rejection, emphasizing its clinical significance. In recent years, the role of humoral immunity in lung rejection has been increasingly appreciated, and antibody-mediated rejection is now recognized as a form of rejection that may result in allograft failure.

Autologous and Allogenous Antibodies in Lung and Islet Cell Transplantation

The field of organ transplantation has undoubtedly made great strides in recent years. Despite the advances in donor-recipient histocompatibility testing, improvement in transplantation procedures, and development of aggressive immunosuppressive regimens, graft-directed immune responses still pose a major problem to the long-term success of organ transplantation. Elicitation of immune responses detected as antibodies to mismatched donor antigens (alloantibodies) and tissue-restricted self-antigens (autoantibodies) are two major risk factors for the development of graft rejection that ultimately lead to graft failure. In this review, we describe current understanding on genesis and pathogenesis of antibodies in two important clinical scenarios: lung transplantation and transplantation of islet of Langerhans. It is evident that when compared to any other clinical solid organ or cellular transplant, lung and islet transplants are more susceptible to rejection by combination of allo- and autoimmune responses.

Lung Transplantation

The therapeutic options for patients with advanced pulmonary parenchymal or vascular disorders are currently limited. Lung transplantation remains one of the few viable interventions, but on account of the insufficient donor pool only a minority of these patients actually undergo the procedure each year. Following transplantation there are a number of early and late allograft complications such as primary graft dysfunction, allograft rejection, infection, post-transplant lymphoproliferative disorder and late injury that is now classified as chronic lung allograft dysfunction. The pathologist plays an essential role in the diagnosis and classification of these myriad complications. Although the transplant procedures are performed in selected centers patients typically return to their local centers. When complications arise it is often the responsibility of the local pathologist to evaluate specimens. Therefore familiarity with the pathology of lung transplantation is important.

Antibody-mediated Rejection in Lung Transplantation

There has been increasing awareness of antibody-mediated rejection (AMR) as an important cause of graft failure after lung transplantation in recent years. However, the diagnostic criteria for pulmonary AMR are not well defined. All four tenets of AMR in kidney and heart transplantation, graft dysfunction, complement component deposition, circulating donor-specific antibodies (DSA), and histopathologic changes consistent with AMR, are infrequently present in lung transplantation. Nonetheless, the lung transplant community has made important progress recognizing cases of AMR and developing a definition. However, AMR is often refractory to therapy resulting in graft failure and death. In this review, we discuss the progress and challenges in the diagnosis and therapeutic options for pulmonary AMR. In addition, we briefly examine emerging paradigms of C4d-negative AMR and chronic AMR, and conclude that significant progress is needed to mitigate the effects of humoral immune responses after lung transplantation.

Influence of preformed donor-specific antibodies and C4d on early liver allograft function

INTRODUCTION. The impact of preformed donor-specific antibodies (DSA) is incompletely understood in liver transplantation. The incidence and impact of preformed DSA on early post liver transplant were assessed and these were correlated with compliment fragment C4d on allograft biopsy. METHODS. Pretransplant serum from 41 consecutive liver transplant recipients (brain dead donors; DBD = 27 and cardiac death donors; DCD = 14) were tested for class-specific anti-human leukocyte antigen (HLA) and compared against donor HLA types. Liver biopsies were taken during cold storage (t-1) and post-reperfusion (t0) stained with C4d and graded for preservation-reperfusion injury (PRI). RESULTS. Of the 41 recipients, 8 (20%) had anti-HLA class I/II antibodies pretransplant, 3 (7%) were confirmed preformed DSA; classes I and II (n=1) and class I only (n=2). No biopsies showed definite evidence of antibody-mediated rejection. Graft biopsies in overall showed only mild PRI with ischemic hepatocyte C4d pattern similar in both positive and negative DSA patients. One DSA-positive (33%) compared with four DSA-negative patients (10%) had significant early graft dysfunction; severe PRI causing graft loss from primary nonfunction was seen only in DSA-negative group. Allograft biopsy of preformed DSA-positive patient demonstrated only minimal PRI; however, no identifiable cause could be attributed to graft dysfunction other than preformed DSA. CONCLUSION. Preformed DSA are present in 5-10% liver transplant recipients. There is no association between anti-HLA DSA and PRI and C4d, but preformed DSA may cause early morbidity. Larger studies on the impact of DSA with optimization of C4d techniques are required.

Acute antibody-mediated rejection after lung transplantation

BACKGROUND

Antibody-mediated rejection (AMR) after lung transplantation remains enigmatic, and there is no consensus on the characteristic clinical, immunologic and histologic features.

METHODS

We performed a retrospective, single-center cohort study and identified cases of acute AMR based on the presence of circulating donor-specific human leukocyte antigen (HLA) antibodies (DSA), histologic evidence of acute lung injury, C4d deposition and clinical allograft dysfunction.

RESULTS

We identified 21 recipients with acute AMR based on the aforementioned criteria. AMR occurred a median 258 days after transplantation; 7 recipients developed AMR within 45 days of transplantation. All patients had clinical allograft dysfunction, DSA, histology of acute lung injury and capillary endothelial C4d deposition. Fifteen recipients improved clinically and survived to hospital discharge, but 6 died of refractory AMR. One survivor had bronchiolitis obliterans syndrome at the time of AMR diagnosis; 13 of the 14 remaining survivors developed chronic lung allograft dysfunction (CLAD) during follow-up. Overall, 15 recipients died during the study period, and the median survival after the diagnosis of AMR was 593 days.

CONCLUSIONS

Acute AMR can be a fulminant form of lung rejection, and survivors are at increased risk of developing CLAD. The constellation of acute lung injury, DSA and capillary endothelial C4d deposition is compelling for acute AMR in recipients with allograft dysfunction. This clinicopathologic definition requires validation in a multicenter cohort, but may serve as a foundation for future studies to further characterize AMR.

Antibody-Mediated Lung Transplant Rejection

Antibody-mediated rejection after lung transplantation remains enigmatic. However, emerging evidence over the past several years suggests that humoral immunity plays an important role in allograft rejection. Indeed, the development of donor-specific antibodies after transplantation has been identified as an independent risk factor for acute cellular rejection and bronchiolitis obliterans syndrome. Furthermore, cases of acute antibody-mediated rejection resulting in severe allograft dysfunction have been reported, and these demonstrate that antibodies can directly injure the allograft. However, the incidence and toll of antibody-mediated rejection are unknown because there is no widely accepted definition and some cases may be unrecognized. Clearly, humoral immunity has become an important area for research and clinical investigation.

Critical care management of the lung transplant recipient

Lung transplantation provides the prospect of improved survival and quality of life for patients with end stage lung and pulmonary vascular diseases. Given the severity of illness of such patients at the time of surgery, lung transplant recipients require particular attention in the immediate post-operative period to ensure optimal short-term and long-term outcomes. The management of such patients involves active involvement of a multidisciplinary team versed in common post-operative complications. This review provides an overview of such complications as they pertain to the practitioners caring for post-operative lung transplant recipients. Causes and treatment of conditions affecting early morbidity and mortality in lung transplant recipients will be detailed, including primary graft dysfunction, cardiovascular and surgical complications, and immunologic and infectious issues. Additionally, lung donor management issues and bridging the critically ill potential lung transplant recipient to transplantation will be discussed.

Fulminant hyperacute rejection after unilateral lung transplantation

Hyperacute rejection (HAR) is a well-known complication in renal and cardiac transplantation, but rare in lung recipients. We present a case of HAR of the lung graft with a fatal outcome of a male patient with preformed class II anti-HLA antibodies.

Increased erythrocyte C4D is associated with known alloantibody and autoantibody markers of antibody-mediated rejection in human lung transplant recipients

BACKGROUND

Immune responses to mismatched donor human leukocyte antigens (HLA) are important in the pathogenesis of chronic rejection. This study evaluated whether erythrocyte-bound C4d (E-C4d) is associated with known alloimmune and autoimmune markers of antibody-mediated rejection after human lung transplantation (LTx).

METHODS

Flow cytometry was used to analyze 22 LTx recipients and 15 healthy individuals for E-C4d. Development of antibodies to donor-mismatched HLA (donor-specific antibody [DSA]) and antibodies to HLA were determined using the solid-phase method by Luminex. Development of antibodies to self-antigens, K-alpha-1-tubulin (KA1T) and collagen V (Col-V), were measured by enzyme-linked immunosorbent assay. C3d deposition in lung biopsy specimens was determined by immunohistochemical staining.

RESULTS

Percent E-C4d (%E-C4d) levels were 19.9% in LTx patients vs 3.7% in healthy individuals (p = 0.02). DSA+ patients had higher E-C4d levels than DSA- patients (34.1% vs 16.7%, p = 0.02). In 5 patients with preformed anti-HLA, E-C4d levels were not significantly different vs 13 patients without detectable anti-HLA (p = 0.1). E-C4d levels were higher in patients who developed antibodies to KA1T (p = 0.02) and Col-V (p = 0.03). Recipients with C3d-positive tissue deposition had higher E-C4d levels than patients with C3d-negative biopsy results (p = 0.01).

CONCLUSIONS

Increased %E-C4d levels are found in patients with positive DSA, high antibody titers to KA1T and Col-V, and have C3d+ lung biopsy findings. Therefore, %E-C4d can serve as a potential marker for antibody-mediated rejection after LTx.

Acute rejection and humoral sensitization in lung transplant recipients

Despite the recent introduction of many improved immunosuppressive agents for use in transplantation, acute rejection affects up to 55% of lung transplant recipients within the first year after transplant. Acute lung allograft rejection is defined as perivascular or peribronchiolar mononuclear inflammation. Although histopathologic signs of rejection often resolve with treatment, the frequency and severity of acute rejections represent the most important risk factor for the subsequent development of bronchiolitis obliterans syndrome (BOS), a condition of progressive airflow obstruction that limits survival to only 50% at 5 years after lung transplantation. Recent evidence demonstrates that peribronchiolar mononuclear inflammation (also known as lymphocytic bronchiolitis) or even a single episode of minimal perivascular inflammation significantly increase the risk for BOS. We comprehensively review the clinical presentation, diagnosis, histopathologic features, and mechanisms of acute cellular lung rejection. In addition, we consider emerging evidence that humoral rejection occurs in lung transplantation, characterized by local complement activation or the presence of antibody to donor human leukocyte antigens (HLA). We discuss in detail methods for HLA antibody detection as well as the clinical relevance, the mechanisms, and the pathologic hallmarks of humoral injury. Treatment options for cellular rejection include high-dose methylprednisolone, antithymocyte globulin, or alemtuzumab. Treatment options for humoral rejection include intravenous immunoglobulin, plasmapheresis, or rituximab. A greater mechanistic understanding of cellular and humoral forms of rejection and their role in the pathogenesis of BOS is critical in developing therapies that extend long-term survival after lung transplantation.

Acute antibody-mediated rejection after lung transplantation

The role of humoral immunity after lung transplantation remains unclear. In this report, we describe the pathologic findings and clinical course of a case of acute antibody-mediated rejection (AMR) after lung transplantation. After an uncomplicated early course, a 31-year-old man with cystic fibrosis developed acute graft dysfunction 1 month after bilateral lung transplantation. Lung biopsies showed acute pneumonitis with capillary injury, neutrophilic infiltration and nuclear dust. Immunostaining for C4d demonstrated endothelial cell deposition, and circulating donor-specific human leukocyte antigen (HLA) antibodies were identified. Despite severe hypoxemic respiratory failure, he responded well to a regimen consisting of methylprednisolone, plasma exchange, intravenous immunoglobulin and rituximab therapy. He completely recovered clinically although donor-specific HLA antibodies have remained detectable. The incidence of acute AMR after lung transplantation is unknown, but this case fulfills all of the consensus diagnostic criteria, and we suggest that AMR could be an under-recognized cause of acute graft dysfunction.

Human leukocyte antigen antibodies and chronic rejection: from association to causation

Considerable research has established an association between human leukocyte antigen antibodies and chronic rejection. Two new major developments now provide evidence that this relationship is in fact causative. First, recent studies of serial serum samples of 346 kidney transplant patients from four transplant centers show that de novo antibodies, can be detected before rejection. Moreover, serial testing revealed that when antibodies were not present, 528 patient years of good function was demonstrable in 149 patients. Second, among 90 patients whose grafts chronically failed, 86% developed antibodies before failure. To assess the likelihood of a causal link, we applied the nine widely accepted Bradford Hill criteria and conclude that the evidence supports a causal connection between human leukocyte antigen antibodies and chronic rejection. The clinical implication is significant because we hope this review will stimulate centers to begin the one remaining task of showing that antibody removal will indeed prevent chronic failure.