National conference to assess antibody-mediated rejection in solid organ transplantation

Retransplant candidates have donor-specific antibodies that react with structurally defined HLA-DR,DQ,DP epitopes

This report describes a detailed analysis how donor-specific HLA class II epitope mismatching affects antibody reactivity patterns in 75 solid organ transplant recipients with an in situ allograft and who were considered for retransplantation. Sera were tested for antibodies in a sensitive antigen-binding assay (Luminex) with single class II alleles. Their reactivity was analyzed with HLAMatchmaker, a structural matching algorithm that considers so-called eplets to define epitopes recognized by antibodies. Only 24% of the patients showed donor-specific anti-DRB1 antibodies and there was a significant correlation with a low number of mismatched DRB1 eplets. This low detection rate of anti-DRB1 antibodies may also be due to allograft absorption. In contrast, antibodies to DRB3/4/5 mismatches were more common. Especially, 83% of the DRB4 (DR53) mismatches resulted in detectable antibodies against an eplet uniquely found on DR53 antigens. Donor-specific DQB mismatches led to detectable anti-DQB antibodies with a frequency of 87%. Their specificity correlated with eplets uniquely found on DQ1-4. The incidence of antibodies induced by 2-digit DQA mismatches was 64% and several eplets appeared to play a dominant role. These findings suggest that both alpha and beta chains of HLA-DQ heterodimers have immunogenic epitopes that can elicit specific antibodies. About one-third of the sera had anti-DP antibodies; they reacted primarily with two DPB eplets and an allelic pair of DPA eplets. These data demonstrate that HLA class II reactive sera display distinct specificity patterns associated with structurally defined epitopes on different HLA-D alleles.

Antibody-mediated rejection of the kidney after simultaneous pancreas-kidney transplantation

The prevalence, risk factors, and outcome of antibody-mediated rejection (AMR) of the kidney after simultaneous pancreas-kidney transplantation are unknown. In 136 simultaneous pancreas-kidney recipients who were followed for an average of 3.1 yr, 21 episodes of AMR of the kidney allograft were identified. Eight episodes occurred early (</=90 d) after transplantation, and 13 occurred later. Histologic evidence of concomitant acute cellular rejection was noted in 12 cases; the other nine had evidence only of humoral rejection. In 13 cases, clinical rejection of the pancreas was diagnosed simultaneously, and two of these were biopsy proven and were positive for C4d immunostaining. Multivariate analysis identified only one significant risk factor: Female patients were three times more likely to experience AMR. Nearly all early episodes resolved with treatment and did not predict graft loss, but multivariate Cox models revealed that late AMR episodes more than tripled the risk for kidney and pancreas graft loss; therefore, new strategies are needed to prevent and to treat late AMR in simultaneous pancreas-kidney transplant recipients.

Mechanisms of chronic rejection in cardiothoracic transplantation

Despite significant improvements in early post-transplantation survival rates, long-term patient and graft survival have remained poor, due in large part to the vexing problem of chronic allograft rejection. Attempts to combat this problem with intensification of immunosuppression have led to concomitant increases in the rates of fatal malignancies and infections. In cardiac transplantation, chronic rejection is manifested primarily by a disease entity known as cardiac allograft vasculopathy, an occlusive narrowing of the coronary vessels. In lung transplantation, chronic rejection is typified by obliterative bronchiolitis, an airflow limiting narrowing of the bronchioles. From an immunologic standpoint, chronic rejection is believed to be the end result of repeated immune and non-immune insults to the graft. This review examines the pathophysiology of heart and lung chronic, with emphasis on both immune and non-immune causes.

In vitro detection of C4d-fixing HLA alloantibodies: associations with capillary C4d deposition in kidney allografts

Capillary C4d deposition is a valuable marker of antibody-mediated rejection (AMR). In this analysis, flow cytometric detection of alloantibody-triggered C4d deposition to HLA antigen-coated microparticles ([C4d]FlowPRA) was evaluated for its value as a marker for C4d deposition in renal allografts. For comparative analysis, 105 first renal biopsies performed for graft dysfunction and an equal number of concurrent sera were subjected to immunohistochemistry and [C4d] plus standard [IgG]FlowPRA, respectively. C4d deposition/fixation was detected in 17 biopsies and, applying [C4d]FlowPRA HLA class I and II screening, also in a small number of corresponding sera (N = 20). IgG reactivity detected by standard [IgG]FlowPRA was more frequent (49% of sera). Comparing [C4d]FlowPRA screening with capillary C4d staining, we found a high level of specificity (0.92 [95% confidence interval: 0.86-0.98]), which far exceeded that calculated for [IgG]FlowPRA (0.60 [0.50-0.70]). [IgG]FlowPRA screening, however, turned out to be superior in terms of sensitivity (0.94 [0.83-1.05] vs. 0.76 [0.56-0.97] calculated for C4d-fixing panel reactivity). Remarkably, posttransplant single antigen testing for identification of complement-fixing donor-specific alloreactivities failed to improve the predictive value of FlowPRA-based serology. In conclusion, our results suggest that detection of complement-fixing HLA panel reactivity could provide a specific tool for monitoring of C4d-positive AMR.

Analysis of subcutaneous (SQ) alemtuzumab induction therapy in highly sensitized patients desensitized with IVIG and rituximab

Here we report on our experience with subcutaneous (SQ) Alemtuzumab in an uncontrolled study in highly HLA-sensitized patients (HS). From 3/05-4/07, 54 HS patients received Alemtuzumab 30 mg SQ as induction. Patient and graft survival, AR episodes, serum creatinines, absolute lymphocyte counts, monthly PCR monitoring for viruses, AE/SAEs and infectious complications were monitored. No patient to date has developed acute injection-related reactions after SQ Alemtuzumab; however, bone marrow suppression was occasionally seen requiring reduction or elimination of mycophenolate mofetil approximately 1-2 months posttransplant. Patient and graft survival at 12 M was 98%/96%, respectively. AR episodes occurred in 35% with 20% being C4d+ AMR. Mean SCrs at 12 M were 1.4 +/- 0.3 mg/dL. The nadir ALC was 0.17 +/- 0.19 within 24 h and sustained up to 365 days posttransplant. Infections occurred in eight patients (five with polyoma BK viremia [PBK], one CMV/PBK and two CMV viremia). SQ Alemtuzumab was well tolerated and resulted in prolonged lymphocyte depletion. Compared to our previous experience with daclizumab and rabbit ATG induction in HS patients, single-dose SQ Alemtuzumab was more cost effective, showed similar infection rates and did not reduce the AMR rates posttransplant. Although uncontrolled, these observations suggest that induction therapy with Alemtuzumab appears feasible and indeed promising, but awaits more definitive study.

Quantitation of alloantibody concentration can predict patient sensitivity to intravenous immunoglobulin desensitization

Despite the success of intravenous immunoglobulin (IVIg) desensitization to reduce anti-human leukocyte antigen antibodies, its high failure rate and expense limit its usefulness. We speculated that quantitation of alloantibody concentration could allow early identification of IVIg resistant patients. Patients were described as nonresponders (n=3) or responders (n=8). Panel reactive antibodies (PRA) were determined using Flowbeads and concentration calculated as molecules of equivalent soluble fluorochrome (MESF). PRA was equivalent between nonresponders and responders before (97+/-3% vs. 76+/-20%, P=NS) and after 3 IVIg/plasmapheresis (PP) treatments but lower among responders at end-of-treatment (76+/-20% vs. 44+/-15%, P<0.01). In contrast, pretreatment MESFs were higher (333,640+/-241,352 vs. 38,741+/-5,133, P=0.006) among nonresponders than responders. During treatment, MESFs decreased (P<0.05) in 0 of 3 nonresponders vs. 8 of 8 responders. Final MESFs were higher among nonresponders than responders. We report that quantitation of MESFs allows early identification of IVIg/PP resistant patients. This sensitive and inexpensive technique should allow more effective patient selection and reduce the costs associated with desensitization.

Re-exposure to mismatched HLA class I is a significant risk factor for graft loss: multivariable analysis of 259 kidney retransplants

BACKGROUND

Kidney retransplants carry increased immunologic risk. One possible contributor to this risk may be re-exposure to human leukocyte antigens (HLA) common to a previous donor but foreign to the recipient. Conflicting publications have assessed this risk, so to examine our experience 259 kidney retransplants were analyzed.

METHODS

A retrospective cohort of retransplant patients from 1973 to 2005 with minimum 12 months follow up was examined. Using multivariable modeling, important confounders were controlled for identifying factors significantly affecting graft survival.

RESULTS

Re-exposure to HLA class I (HLA-A or B) antigens, peak panel reactive antibodies and donor source were the most important determinants of allograft survival, despite a negative conventional or anti-human globulin-augmented T cell crossmatch. We failed to demonstrate that recipient re-exposure to HLA class II (HLA-DR) or positive B cell crossmatch were associated with adverse outcomes. Sample size and molecular versus serologic methods may have influenced the former, while inability to determine antibody specificities may have influenced the latter. Controlling for other variables, the adjusted risk of graft loss associated with re-exposure to HLA class I increased by 71% (P=0.006) and occurred early, consistent with recall of memory cytotoxic T lymphocyte or antibody responses.

CONCLUSIONS

Kidney recipients re-exposed to mismatched HLA class I antigens appear to be at heightened risk of early graft loss. Such patients may benefit from pretransplant identification of donor specific antibodies using solid phase methods and heightened vigilance for acute rejection. Future studies may indicate whether more intensive immunosuppression for these patients is warranted.

Synergistic deposition of C4d by complement-activating and non-activating antibodies in cardiac transplants

The role of non-complement-activating alloantibodies in humoral graft rejection is unclear. We hypothesized that the non-complement-activating alloantibodies synergistically activate complement in combination with complement-activating antibodies. B10.A hearts were transplanted into immunoglobulin knock out (Ig-KO) mice reconstituted with monoclonal antibodies to MHC class I antigens. In allografts of unreconstituted Ig-KO recipients, no C4d was detected. Similarly, reconstitution with IgG1 or low dose IgG2b alloantibodies did not induce C4d deposition. However, mice administered with a low dose of IgG2b combined with IgG1 had heavy linear deposits of C4d on vascular endothelium. C4d deposits correlated with decreased graft survival. To replicate this synergy in vitro, mononuclear cells from B10.A mice were incubated with antibodies to MHC class I antigens followed by incubation in normal mouse serum. Flow cytometry revealed that both IgG2a and IgG2b synergized with IgG1 to deposit C4d. This synergy was significantly decreased in mouse serum deficient in mannose binding lectin (MBL) and in serum deficient in C1q. Reconstitution of MBL-A/C knock out (MBL-KO) serum with C1q-knock out (C1q-KO) serum reestablished the synergistic activity. This suggests a novel role for non-complement-activating alloantibodies and MBL in humoral rejection.

Antibody-Mediated Rejection of Cardiac Allografts in CCR5-Deficient Recipients

Rejected MHC-mismatched cardiac allografts in CCR5(-/-) recipients have low T cell infiltration, but intense deposition of C3d in the large vessels and capillaries of the graft, characteristics of Ab-mediated rejection. The roles of donor-specific Ab and CD4 and CD8 T cell responses in the rejection of complete MHC-mismatched heart grafts by CCR5(-/-) recipients were directly investigated. Wild-type C57BL/6 and B6.CCR5(-/-) (H-2(b)) recipients of A/J (H-2(a)) cardiac allografts had equivalent numbers of donor-reactive CD4 T cells producing IFN-gamma, whereas CD4 T cells producing IL-4 were increased in CCR5(-/-) recipients. Numbers of donor-reactive CD8 T cells producing IFN-gamma were reduced 60% in CCR5(-/-) recipients. Day 8 posttransplant serum titers of donor-specific Ab were 15- to 25-fold higher in CCR5(-/-) allograft recipients, and transfer of this serum provoked cardiac allograft rejection in RAG-1(-/-) recipients within 14 days, whereas transfer of either serum from wild-type recipients or immune serum from CCR5-deficient recipients diluted to titers observed in wild-type recipients did not mediate this rejection. Wild-type C57BL/6 and B6.CCR5(-/-) recipients rejected A/J cardiac grafts by day 11, whereas rejection was delayed (day 12-60, mean 21 days) in muMT(-/-)/CCR5(-/-) recipients. These results indicate that the donor-specific Ab produced in CCR5(-/-) heart allograft recipients is sufficient to directly mediate graft rejection, and the absence of recipient CCR5 expression has differential effects on the priming of alloreactive CD4 and CD8 T cells.

Inhibition of Terminal Complement Components in Presensitized Transplant Recipients Prevents Antibody-Mediated Rejection Leading to Long-Term Graft Survival and Accommodation

Ab-mediated rejection (AMR) remains the primary obstacle in presensitized patients following organ transplantation, as it is refractory to anti-T cell therapy and can lead to early graft loss. Complement plays an important role in the process of AMR. In the present study, a murine model was designed to mimic AMR in presensitized patients. This model was used to evaluate the effect of blocking the fifth complement component (C5) with an anti-C5 mAb on prevention of graft rejection. BALB/c recipients were presensitized with C3H donor skin grafts 7 days before heart transplantation from the same donor strain. Heart grafts, transplanted when circulating anti-donor IgG Abs were at peak levels, were rejected in 3 days. Graft rejection was characterized by microvascular thrombosis and extensive deposition of Ab and complement in the grafts, consistent with AMR. Anti-C5 administration completely blocked terminal complement activity and local C5 deposition, and in combination with cyclosporine and short-term cyclophosphamide treatment, it effectively prevented heart graft rejection. These recipients achieved permanent graft survival for >100 days with normal histology despite the presence of systemic and intragraft anti-donor Abs and complement, suggesting ongoing accommodation. Furthermore, double-transplant experiments demonstrated that immunological alterations in both the graft and the recipient were required for successful graft accommodation to occur. These data suggest that terminal complement blockade with a functionally blocking Ab represents a promising therapeutic approach to prevent AMR in presensitized recipients.

Mortality and Morbidity in Pre-sensitized Pediatric Heart Transplant Recipients With a Positive Donor Crossmatch Utilizing Peri-operative Plasmapheresis and Cytolytic Therapy

BACKGROUND

The difficulty in obtaining a prospective negative donor/recipient crossmatch limits the ability to successfully transplant pediatric heart transplant candidates who show evidence of antibodies to multiple human leukocyte antigens (pre-sensitized patients).

METHODS

We utilized a protocol that included peri-operative plasmapheresis, thymoglobulin and cyclophosphamide in 17 pre-sensitized (panel-reactive antibodies [PRA] >10%) pediatric patients to accept donors for these patients without a prospective crossmatch between 1995 and 2005. A retrospective review of survival, rejection and infection was performed, comparing the frequency of rejection and infection in our patients who were transplanted with a complement-dependent cytotoxic (CDC)-positive donor/recipient crossmatch to those patients transplanted with a negative crossmatch.

RESULTS

Thirteen of 17 patients were found to have a CDC-positive crossmatch. Actuarial survival after transplantation was 85% at 1 year and 73% at 3 years. Twelve of 13 (92%) of these patients experienced rejection, and 5 of 13 (38%) had recurrent rejection, generally in the first 2 months after transplantation. Rejection was associated with hemodynamic compromise in 58% of first rejection episodes and 67% of episodes of recurrent rejection. The frequency of rejection in these patients was significantly greater than the frequency in patients with a negative crossmatch in the first 6 months after transplantation, but not afterward. The frequency of infection episodes was not significantly different between the groups.

CONCLUSIONS

Heart transplantation in pre-sensitized pediatric recipients with a CDC-positive donor/recipient crossmatch may result in reasonable short-term survival, but with a high frequency of early rejection, often with hemodynamic compromise.

Acute antibody-mediated rejection following heart transplantation

Acute antibody-mediated rejection (AMR) in heart transplantation is often associated with hemodynamic compromise, and is associated with increased mortality and development of accelerated transplant coronary artery disease (TCAD). The diagnosis of AMR has historically been controversial and outcomes with aggressive immunosuppressive therapy including plasmapheresis and cyclophosphamide are poor. Advances in diagnostic techniques like the demonstration of immunopathologic evidence for antibody-mediated rejection by deposition of the complement split product C4d in tissue and detection of anti-HLA antibodies by flow cytometry will assist in further characterizing AMR. Immunosuppression targeting B-lymphocytes and use of m-TOR inhibitors to alter the predilection to develop TCAD and improve survival in AMR remains to be proven.

Acute antibody-mediated rejection of renal transplant: pathogenetic and diagnostic considerations

CONTEXT

Acute antibody-mediated rejection (AMR) has emerged recently as an important cause of graft failure.

OBJECTIVE

To review the pathogenetic, clinicopathologic, and diagnostic considerations of AMR.

DATA SOURCES

Review of literature and the authors' experience.

CONCLUSIONS

Acute antibody-mediated rejection is mediated by antibodies specific for donor antigens, which bind to target antigens and activate the complement system, culminating in tissue injury. The clinical manifestation of AMR is not specific, and transplant biopsy is needed for diagnosis. The glomeruli show thrombosis or neutrophils or mononuclear leukocytes in capillary lumens. The tubulointerstitial compartment shows edema, hemorrhage, necrosis, mild inflammation, and neutrophils or mononuclear leukocytes in the peritubular capillary lumens. The blood vessels show thrombosis, thrombotic microangiopathy, fibrinoid necrosis, or transmural vasculitis. Strong staining for C4d in the peritubular capillaries is characteristic. A definitive diagnosis of AMR requires (1) morphologic evidence of acute tissue injury, (2) immunopathologic evidence for antibody action, and (3) serologic evidence of circulating donor-specific antibodies. Acute antibody-mediated rejection should be suspected if some but not all 3 criteria are met. Since effective treatment is currently available, accurate and timely diagnosis of AMR is essential.

Pathology of lung transplantation

The International Society for Heart and Lung Transplantation has a standardized nomenclature for the evaluation of lung allografts. Rejection of the lung allograft is divided into acute and chronic forms. Acute cellular rejection is characterized by perivascular accumulations of mononuclear cells and eosinophils; bronchiolar inflammation is also included in the grading scheme. Acute antibody-mediated rejection in lung allografts is not well defined. Chronic rejection is manifest by fibrous scarring narrowing the lumen of bronchioles, arteries, and veins. The diagnosis of rejection requires the exclusion of infection and other pathology in the allograft.

HLA-specific B cells: I. A method for their detection, quantification, and isolation using HLA tetramers

BACKGROUND

The development of highly sensitive and specific assays for detecting and characterizing HLA-specific antibodies has contributed to an appreciation of the extensive involvement of those antibodies in graft injury and dysfunction. However, understanding the regulatory processes of the humoral response to transplantation and the mechanisms underlying therapeutic agents and protocols for preventing and treating sensitization requires a way to study HLA-specific B cells.

METHODS

Lymphocyte preparations enriched for B cells were stained with one or more of three different HLA tetramers. Tetramer-positive (tet+) B cells were enumerated and evaluated for an association of their frequencies with known sensitization. In some cases, tet+ B cells were isolated and placed in culture with supplements known to activate B cells in a nonspecific fashion.

RESULTS

For all tetramers used, the frequencies of tet+ B cells were significantly higher (4.1%-5.5%) among sensitized patients than among nonsensitized patients (1.6%-3.2%, P<0.001). Binding of the tetramers occurred by the surface immunoglobulin antigen receptor with little or no binding to antibody captured in the Fc receptor. Cultured tet+ B cells produced antibodies specific for epitopes of the tetramer antigen. There appeared to be a certain amount of crossreactivity in the binding of tetramers. The frequency of CD27+ cells among tet+ B cells was higher, on average (34.4%-38.8%) than among all B cells (26.2%) whereas the frequencies of CD38 were comparable in the two groups.

CONCLUSIONS

Staining with HLA tetramers provides a means for identifying, quantifying, and isolating HLA-specific B cells.

Lymphoid cell proliferation in renal transplants: biologic and diagnostic implications

It is unclear whether alloreaction develops in peripheral lymphoid organs and effector cells being recruited to the target organs, or the entire process of alloreaction can happen within the transplanted kidneys. Interstitial inflammatory cell (IIC) proliferation was evaluated by MIB-1 antigen immunostain and the rate expressed as positive cells/1000 cells. This rate was higher in acute cell-mediated rejection (ACR) (25.7, n = 14) compared with normal kidney (0.4, n = 8), acute tubular necrosis (1.2, n = 8), chronic allograft nephropathy (CAN, 2.4, n = 20), and native kidneys with diverse diseases (9.2, n = 63); but was comparable to that in CAN with significant IIC (20.6, n = 16). 10.1% and 8.3% of T lymphocytes underwent proliferation in ACR with or without CAN, whereas only rare B lymphocytes or macrophages showed this change (<1.2%), regardless of diagnostic categories. All biopsies diagnosed as ACR in conjunction with a high rate of MIB-1 + IIC and 9/12 biopsies with CAN and significant IIC in which ACR was diagnosed due to a high rate of MIB-1 + IIC, responded to anti-rejection therapy. Proliferation of IIC involves predominantly T lymphocytes. These observations provide support for the concept of in situ alloimmunization, and facilitate the diagnosis of ACR.

The immunology of composite tissue transplantation

Composite tissue allotransplantation holds great potential for reconstructive surgery. That these procedures can be successful has been clearly demonstrated by the success of hand, face, and larynx transplants around the world. Although the immunology of composite tissue allotransplantation mirrors that of any allogeneic organ transplant, there are several unique aspects to these grafts. This article reviews the immunology of transplantation, histocompatibility testing for composite tissue allotransplantation, graft rejection, immunosuppression, and specific immunologic considerations of composite tissue allotransplantation.

Antibody-Mediated Rejection

The introduction of both complement 4d (C4d) staining in renal allograft biopsies and sensitive methods to detect anti-human leukocyte antigen antibodies, such as single antigen bead flow assays, into tissue-typing techniques have shown the importance of antibody-mediated alloimmune response in kidney transplantation. The use of these sensitive methods, combined with the increased number of transplants in highly sensitized patients with donor-specific antibodies, or patients receiving desensitization protocols, have increased the awareness and thus the incidence of acute antibody-mediated rejection. Chronic rejection also can be mediated through alloantibodies, and the term chronic antibody-mediated rejection recently was proposed. In this review article we summarize the current knowledge of the role of alloantibodies in transplantation, the diagnosis and treatment of acute and chronic antibody-mediated rejection, and their effect on graft function and outcome.

C4d immunopositivity is uncommon in ABO-compatible liver allografts, but correlates partially with lymphocytotoxic antibody status

AIMS

To determine whether C4d immunopositivity helps recognition of humoral rejection in dysfunctional liver allografts.

METHODS AND RESULTS

C4d immunopositivity was retrospectively evaluated in liver allografts. There were three staining patterns: portal venular plexus, sinusoidal and hepatocellular. The latter was related to ischaemic necrosis and not scored as positive. C4d immunopositivity was not encountered in 10 preperfusion or 15 consecutive early protocol biopsies. However, three of 12 early protocol biopsy specimens from crossmatch-positive patients were C4d+, two showing repeated positivity on at least one further biopsy specimen, while others remained negative. C4d was also positive in 2/16 early moderate acute cellular rejections, 3/14 cases of centrilobular necroinflammation, 3/11 biliary obstructions, 3/13 chronic rejections and 1/10 primary non-functional allografts.

CONCLUSION

C4d immunopositivity is uncommon in liver allografts. There is a weak positive correlation with a positive lymphocytotoxic crossmatch and some patterns of allograft dysfunction. The morphological associations resemble those reported in lymphocytotoxic crossmatch-positive patients, plus occasional sinusoidal and hepatocellular injury. Although the practical utility of C4d immunohistochemistry seems limited, it may identify a small subgroup of individuals in whom chronic humoral microvascular injury contributes to allograft dysfunction.

Significance of C4d staining in ABO-identical/compatible liver transplantation

Complement degradation product C4d has become an important marker of humoral or antibody-mediated rejection in renal and heart allograft biopsies. Although there have been several reports on the detection of C4d in liver allografts, the significance of C4d in liver transplantation and its relationship with humoral rejection are still not clear. We investigated the frequency and pattern of C4d staining in liver allograft biopsies with reference to preoperative lymphocyte crossmatch tests, which detect donor-reactive lymphocyte antibody. Survival rates at 5 years were 77% for crossmatch-negative patients and 53% for crossmatch-positive patients (P=0.009). In crossmatch-negative patients, reproducible positive staining was obtained in 28 of 86 (33%) biopsies taken within 90 days after transplantation and 33 of 96 (34%) biopsies 90 days or after transplantation. Most C4d staining was observed in the portal areas, and no clear correlation was observed between C4d positivity and histological diagnosis. In crossmatch-positive patients, 9 of 11 (82%) biopsies showed positivity for C4d. C4d stained perivenular areas as well as portal areas. Histology of crossmatch-positive patients included acute rejection and cholangitis, but did not include periportal changes that were seen in humoral rejection in ABO-incompatible liver transplantation. In summary, focal C4d deposition was seen in various types of liver allograft injury and had little clinical impact on crossmatch-negative patients, but extensive C4d staining in crossmatch-positive patients may be associated with humoral rejection and poor graft survival.

Posttransplant monitoring of pediatric lung transplant recipients

PURPOSE OF REVIEW

This article reviews current trends in pediatric lung posttransplant management, reveals pitfalls that exist, and introduces additional parameters that may have an impact on long-term survival.

RECENT FINDINGS

A number of parameters are monitored after transplantation to prevent or identify early complications related to lung transplantation in hope of reducing morbidity and mortality. These include routine laboratory studies, imaging, and monitoring of drug levels and lung function. Drug monitoring allows individualization of a patient's immunosuppressive therapy; however, drug levels alone may not reflect the patient's immune status. ImmuKnow is a general immune-monitoring assay that may help guide therapy. Two major complications are rejection and infection, and bronchoscopy is used to differentiate these two entities. Silent rejection may occur and increase the chance of developing bronchiolitis obliterans; therefore, many centers perform surveillance bronchoscopies. Recently, de-novo anti-histocompatibility locus antigen antibodies and gastroesophageal reflux have been associated with poor outcomes, and many centers are monitoring these entities as part of care following lung transplant.

SUMMARY

There has been little improvement in long-term outcomes of lung transplantation. Current monitoring methods are utilized to maintain or improve outcomes and recently additional monitoring parameters have been identified which hopefully will improve long-term outcomes.

Accommodation of grafts: implications for health and disease

Accommodation refers to the acquired resistance of a graft to immune-mediated injury. It is typically observed after antibodies that would cause rejection of a graft are removed from a recipient and then later return. In addition to being induced in this manner, accommodation can occur spontaneously, without depleting antibodies. Indeed, we postulate spontaneous accommodation may be the most common outcome of clinical organ transplantation. The paper reviews the current understanding of accommodation, emphasizing recent advances and important questions. Among the recent advances are the discoveries of potentially broader relevance of accommodation for biology and immunology and pathways by which accommodation may be achieved. To investigate these pathways and to understand how accommodation begins and how it evolves, clinical organ transplants might offer a useful and incisive model.

Posttransplant prophylactic intravenous immunoglobulin in kidney transplant patients at high immunological risk: a pilot study

The effects of posttransplant prophylactic intravenous immunoglobulin (IVIg) were investigated in renal transplant recipients at high immunological risk. Thirty-eight deceased-donor kidney transplant recipients with previous positive complement-dependent cytotoxicity crossmatch (n=30), and/or donor-specific anti-HLA antibodies (n=14) were recruited. IVIg (2 g/kg) was administrated on days 0, 21, 42 and 63 with quadruple immunosuppression. Biopsy-proven acute cellular and humoral rejection rates at month 12 were 18% and 10%, respectively. Glomerulitis was observed in 31% and 60% of patients at months 3 and 12, respectively, while allograft glomerulopathy rose from 3% at month 3 to 28% at 12 months. Interstitial fibrosis/tubular atrophy increased from 18% at day 0 to 51% and 72% at months 3 and 12 (p<0.0001). GFR was 50 +/- 17 mL/min/1.73 m(2) and 48 +/- 17 mL/min/1.73 m(2) at 3 and 12 months. PRA decreased significantly after IVIg (class I: from 18 +/- 27% to 5 +/- 12%, p<0.01; class II: from 25 +/- 30% to 7 +/- 16%, p<0.001). Patient and graft survival were 97% and 95%, respectively and no graft was lost due to rejection (mean follow-up 25 months). In conclusion, prophylactic IVIg in high-immunological risk patients is associated with good one-year outcomes, with adequate GFR and a profound decrease in PRA level, but a significant increase in allograft nephropathy.

Determinants of poor graft outcome in patients with antibody-mediated acute rejection

This study analyzes the incidence and course of antibody-mediated rejection (AMR) in a cohort of 237 renal transplant patients followed for 30 +/- 20 months. Among these, 32 patients were considered to be at risk for AMR and received intravenous immunoglobulin (IVIg), either as preconditioning (Group A, n = 18) or at the time of transplant (Group B, n = 14). The prevalence of AMR was 27.8% in Group A, 57.1% in Group B and 3.9% in the remainder of the population. Although graft loss remains greater among AMR than for acute cellular rejection (ACR) or the overall transplant population, we have identified a good outcome group (GFR > 15 mL/min/1.73 m(2)) (n = 13), whose renal function at the end of follow-up was comparable to that of the general transplant population. The factors associated with bad outcome are: (1) immunologic: presence and/or persistence of donor-specific anti-HLA antibodies post-transplantation and (2) histologic: neutrophilic glomerulitis, peritubular capillary dilatation with neutrophil infiltrates and interstitial edema at the time of first biopsy; and at the time of late biopsy (3-6 months): lesions of vascular rejection, and monocyte/macrophage infiltrates in glomeruli and dilated peritubular capillaries. Persistence of C4d does not predict outcome. This study outlines for the first time the immunologic and histologic profiles of AMR patients with poor prognosis.

Antibody-mediated renal allograft rejection: diagnosis and pathogenesis

Alloantibodies to HLA class I or II and other antigens expressed by endothelium cause a variety of effects on renal transplants, ranging from acute to chronic rejection, and even apparent graft acceptance (accommodation). Recognition of these conditions and appropriate therapy requires demonstration of C4d in biopsies, commonly confirmed by tests for circulating alloantibody. Substantial practical experience by pathologists in the interpretation and pitfalls of C4d stains are reviewed along with considerations of the clinical significance and pathologic mechanisms of the different effects of antibody on the endothelium of the renal allograft. Clinical trials will be needed to ascertain the optimal treatment for the newly appreciated conditions chronic humoral rejection and accommodation.

Subclinical acute antibody-mediated rejection in positive crossmatch renal allografts

Subclinical antibody-mediated rejection (AMR) has been described in renal allograft recipients with stable serum creatinine (SCr), however whether this leads to development of chronic allograft nephropathy (CAN) remains unknown. We retrospectively reviewed data from 83 patients who received HLA-incompatible renal allografts following desensitization to remove donor-specific antibodies (DSA). Ten patients had an allograft biopsy showing subclinical AMR [stable SCr, neutrophil margination in peritubular capillaries (PTC), diffuse PTC C4d, positive DSA] during the first year post-transplantation; 3 patients were treated with plasmapheresis and intravenous immunoglobulin. Three patients had a subsequent rise in SCr and an associated biopsy with AMR; 5 others showed diagnostic or possible subclinical AMR on a later protocol biopsy. One graft was lost, while remaining patients have normal or mildly elevated SCr 8-45 months post-transplantation. However, the mean increase in CAN score (cg + ci + ct + cv) from those biopsies showing subclinical AMR to follow-up biopsies 335 +/- 248 (SD) days later was significantly greater (3.5 +/- 2.5 versus 1.0 +/- 2.0, p = 0.01) than that in 24 recipients of HLA-incompatible grafts with no AMR over a similar interval (360 +/- 117 days), suggesting that subclinical AMR may contribute to development of CAN.

Banff '05 Meeting Report: differential diagnosis of chronic allograft injury and elimination of chronic allograft nephropathy ('CAN')

The 8th Banff Conference on Allograft Pathology was held in Edmonton, Canada, 15-21 July 2005. Major outcomes included the elimination of the non-specific term "chronic allograft nephropathy" (CAN) from the Banff classification for kidney allograft pathology, and the recognition of the entity of chronic antibody-mediated rejection. Participation of B cells in allograft rejection and genomics markers of rejection were also major subjects addressed by the conference.

Guidelines on the use of therapeutic apheresis in clinical practice—Evidence-based approach from the apheresis applications committee of the American society for apheresis

The American Society for Apheresis (ASFA) Apheresis Applications Committee is charged with a review and categorization of indications for therapeutic apheresis. This elaborate process had been undertaken every 7 years resulting in three prior publications in 1986, 1993, and 2000 of "The ASFA Special Issues." This article is the integral part of the Fourth ASFA Special Issue. The Fourth ASFA Special Issue is significantly modified in comparison to the previous editions. A new concept of a fact sheet has been introduced. The fact sheet succinctly summarizes the evidence for the use of therapeutic apheresis. A detailed description of the fact sheet is provided. The article consists of 53 fact sheets devoted to each disease entity currently categorized by the ASFA. Categories I, II, and III are defined as previously in the Third Special Issue. However, a few new therapeutic apheresis modalities, not yet approved in the United States or are currently in clinical trials, have been assigned category P (pending) by the ASFA Clinical Categories Subcommittee. The diseases assigned to category IV are discussed in a separate article in this issue.

The classification and treatment of antibody-mediated renal allograft injury: Where do we stand?

Since the acceptance of the detection of C4d in allografts as a reliable tool to mark a humoral alloresponse, de novo antibody-induced graft injury has attracted much attention. Antibodies and B cells are the new frontier in transplantation. At this juncture carefully designed studies are critical in order to gain solid diagnostic, therapeutic, and prognostic knowledge about the role of antibodies in graft injury and to avoid any confusion and misconception. One prerequisite is the strict adherence to refined classification systems of renal transplant rejection that carefully split and categorize different phenotypes of humoral mediated graft damage and ideally also include information on anti-donor antibody specificity and titers. Sun and colleagues follow this concept and provide evidence that mixed cellular and antibody-mediated graft rejection can respond favorably to intensified immunosuppression with tacrolimus and mycophenolate mofetil. What will the future bring to treat rejection episodes with a dominant, co-dominant, or minor antibody response?

Contemporary Concepts in Noncellular Rejection

Acute rejection is the major cause of morbidity and mortality in the first year after cardiac transplantation. Cellular rejection is the most common form of rejection observed; however, noncellular rejection is being seen more often. This noncellular rejection is mostly a result of less well-characterized antibody-mediated mechanisms. Antibody-mediated rejection is associated more commonly with hemodynamic compromise, increased graft loss, cardiac allograft vasculopathy, and increased mortality. Histologic, immunofluorescence, and immunoperoxidase studies of endomyocardial biopsies from such patients often reveal intravascular macrophages and immunoglobulin and complement deposition in capillaries, in the absence of lymphoid infiltrates. Severely ill patients require intense therapy, which includes high-dose corticosteroids, cytolytic agents, intravenous heparin, intravenous gamma globulin, plasmapheresis, and/or antiproliferative agents. Further understanding of noncellular rejection will lead to more effective therapy.

Immunoadsorption in severe C4d-positive acute kidney allograft rejection: a randomized controlled trial

Antibody-mediated rejection (AMR) frequently causes refractory graft dysfunction. This randomized controlled trial was designed to evaluate whether immunoadsorption (IA) is effective in the treatment of severe C4d-positive AMR. Ten out of 756 kidney allograft recipients were included. Patients were randomly assigned to IA with protein A (N = 5) or no such treatment (N = 5) with the option of IA rescue after 3 weeks. Enrolled recipients were subjected to tacrolimus conversion and, if indicated, 'anti-cellular' treatment. All IA-treated patients responded to treatment. One death unrelated to IA occurred after successful reversal of rejection. Four control subjects remained dialysis-dependent. With the exception of one patient who developed graft necrosis, non-responders were subjected to rescue IA, however, without success. Because of a high graft loss rate in the control group the study was terminated after a first interim analysis. Even though limited by small patient numbers, this trial suggests efficiency of IA in reversing severe AMR.

Isolated donor specific alloantibody-mediated rejection after ABO compatible liver transplantation

Antibody-mediated rejection (AMR) after liver transplantation is recognized in ABO incompatible and xeno-transplantation, but its role after ABO compatible liver transplantation is controversial. We report a case of ABO compatible liver transplantation that demonstrated clinical, serological and histological signs of AMR without evidence of concurrent acute cellular rejection. AMR with persistently high titers of circulating donor specific antibodies resulted in graft injury with initial centrilobular hepatocyte necrosis, fibroedematous portal expansion mimicking biliary tract outflow obstruction, ultimately resulting in extensive bridging fibrosis. Immunofluorescence microscopy demonstrated persistent, diffuse linear C4d deposits along sinusoids and central veins. Despite intense therapeutic intervention including plasmapheresis, IVIG and rituximab, AMR led to graft failure. We present evidence that an antibody-mediated alloresponse to an ABO compatible liver graft can cause significant graft injury independent of acute cellular rejection. AMR shows distinct histologic changes including a characteristic staining profile for C4d.

Preformed antibody, not primed T cells, is the initial and major barrier to bone marrow engraftment in allosensitized recipients

Multiply-transfused individuals are at higher risk for BM rejection. We show that whereas allosensitization resulted in the priming of both cellular and humoral immunity, preformed antibody was the major barrier to engraftment. The generation of cross-reactive alloantibody led to rejection of BM of a different MHC-disparate strain. Imaging studies indicated that antibody-mediated rejection was very rapid (<3 hours) in primed recipients, while T-cell-mediated rejection in nonprimed mice took more than 6 days. Antibody-mediated BM rejection was not due to a defect in BM homing as rejection occurred despite direct intra-BM infusion of donor BM. Rejection was dependent upon host FcR+ cells. BM cells incubated with serum from primed mice were eliminated in nonprimed recipients, indicating that persistent exposure to high-titer antibody was not essential for rejection. High donor engraftment was achieved in a proportion of primed mice by mega-BM cell dose, in vivo T-cell depletion, and high-dose immunoglobulin infusion. The addition of splenectomy to this protocol only modestly added to the efficacy of this combination strategy. These data demonstrate both rapid alloantibody-mediated elimination of BM by host FcR+ cells and priming of host antidonor T cells and suggest a practical strategy to overcome engraftment barriers in primed individuals.

Effect of induction therapy protocols on transplant outcomes in crossmatch positive renal allograft recipients desensitized with IVIG

Here we retrospectively examine the efficacy of two antibody induction regimens using Zenapax or Thymoglobulin in patients with positive complement-dependent cytotoxicity crossmatches (CDC-CMXs) desensitized with IVIG (intravenous immunoglobulin). Between January 1999 and March 2005, 97 patients with (+) CDC-CMXs received kidney transplants (43 deceased donors/54 living donors). All patients received at least 2 g/kg IVIG (maximum four doses) until an acceptable CMX was obtained. Patients were divided into two groups: 1. IVIG + Zenapax (n = 58), 2. IVIG + Thymoglobulin (n = 39). A total of 94% of patients in Group 1 and 84% in G2 have at least 2 years of follow up. Patient and graft survival was 96%/84% in Group 1 and 100%/90% in Group 2, p = NS. The number and severity of AR episodes were similar (36% Group 1 vs. 31% Group 2, p = NS) as was the incidence of C4d (+) antibody-mediated rejection (AMR) (Banff Grade II/III) (22% Group 1 vs. 21% Group 2). Mean serum creatinines (SCrs) at 24 months were similar (Group 1: 1.4 +/- 0.7 vs. G2: 1.5 +/- 0.7 mg/dL). Induction therapy with Zenapax or Thymoglobulin results in excellent patient, graft survival and graft function at 2 years. There was no increased risk of viral infections or malignancies with either agent. Neither agent was effective in reducing the incidence of AMR.

Biomarkers in transplantation: Prospective, blinded measurement of predictive value for the flow cytometry crossmatch after negative antiglobulin crossmatch in kidney transplantation

This prospective, blinded observational study was conducted to measure the predictive value the of flow cytometric crossmatch for biopsy-proven acute rejection, graft loss, or death following kidney transplantation. Patients were selected for renal transplantation on the basis of a conventional antihuman globulin cytotoxic T-cell crossmatch. Flow crossmatch was performed simultaneously, but the results were not disclosed to the transplant team. A total of 257 kidney transplant recipients were enrolled in the study; 78 patients experienced biopsy-proven rejection in the first post-transplant year, and 41 patients lost their graft or died during the period of follow-up (mean: 2046 days). Kaplan-Meier estimates of rejection, graft loss, or patient death did not differ between subjects with a positive or negative flow crossmatch. Cox analyses showed no influence of the flow crossmatch on the risk of biopsy-proven acute rejection (P = 0.987). The sensitivity and specificity of the flow crossmatch for prediction of biopsy-proven rejection were 0.128 and 0.883, and the positive and negative post-test probabilities were 0.323 and 0.301, respectively. The magnitude of the channel shift did not influence the multivariate Cox regression model. The area under the receiver operating characteristic curve of the flow crossmatch was 0.483 (P = 0.71) and 0.572 (P = 0.38), respectively for the living and cadaver transplant recipients, indicating no discriminative value in this study population. Flow crossmatch appears to have no significant incremental value in predicting biopsy-proven acute rejection, graft loss, or death following kidney transplantation in patients who have a negative antihuman globulin cytotoxic T-cell crossmatch against their donor.

Treatment of early mixed cellular and humoral renal allograft rejection with tacrolimus and mycophenolate mofetil

This prospective study investigated the efficiency of the tacrolimus (Tac) combined with mycophenolate mofetil (MMF) alone without immunoadsorption (IA) or plasmapheresis (PPH) as treatment for early (within 2 weeks) acute humoral rejection (AHR) in non-sensitized renal allograft recipients. Of 160 patients enrolled in this prospective study, 11 patients had histologically and clinically confirmed early steroid-resistant acute rejection with an antibody response and received Tac-MMF therapy. No other aggressive rescue methods such as IA, PPH were used, according to the study design. Patients (n=11) were followed for 13.8+/-3.5 months; nine were females. The complement-dependent cytotoxicity crossmatch was negative before transplantation in all patients and only positive for panel-reactive antibody in one patient. Most of the rejection episodes were mixed with cellular rejection (four patients met Banff IIA criteria, five patients met Banff IIB, one patient met Banff IB, and one patient met Banff borderline). After 16.19+/-6.16 days of treatment, all rejection episodes were successfully reversed and all graft functions were stable, with a mean serum creatinine level of 1.12+/-0.32 mg/dl during follow-up. No patient suffered from severe infectious complications (except one case of urinary infection). Our investigation suggests that Tac combined with MMF alone is adequate to reverse early mixed cellular and humoral C4d-positive rejection in non-sensitized renal allograft recipients.