Antibody-Mediated Rejection

Assessment of Rapid Optimized 96-well Tray Flow Cytometric Crossmatch (Halifax-FCXM) with Luminex Single Antigen Test

INTRODUCTION

Flow cytometric crossmatch assay (FCXM) is a sensitive cell-based method for evaluating the presence of donor-specific antibodies (DSA) before transplantation. Recently, 96-well tray FCXM protocol (Halifax FCXM) with improved test efficiency has been introduced. The objective of the present study was to assess the performance of Halifax FCXM by correlating with DSA results based on single antigen bead (SAB) assays (virtual crossmatch, VXM).

METHODS

A total of 341 FCXMs were evaluated for the detection of HLA-DSA. A positive VXM was defined as having at least one HLA - DSA (HLA-A, B, Cw, DR, DQB1) with ≥ 1000 MFI (mean fluorescence intensity) identified by SAB assay.

RESULTS

Of a total 341 cases, 113 showed class I VXM (+) with class I DSA MFI ≥ 1000 exclusively against one or more donor HLA class I antigens (HLA-A, B, Cw), 72 had class I-/II + DSA, and 156 had VXM(-). Halifax T-FCXM showed a sensitivity of 87.6% (99/113) and a specificity of 98.2% (224/228) for detecting class I VXM (+). The concordance between T-FCXM and class I VXM was 94.7% (323/341). Halifax B-FCXM showed a sensitivity of 58.3% (42/72) and a specificity of 98.7% (154/156) for detecting class I-/II + DSAs. The concordance between B-FCXM and class I-/II + VXM was 86.0% (196/228). When we separately analyzed data, B-FCXM detected HLA-DR (+) (68.8%) and HLA-DQ (+) DSAs (71.0%) similarly (P > 0.05). T-FCXM detected 87.6%, 97.2%, and 98.2% of class I DSA-positive cases with MFI values (sumDSA) ≥ 1000, ≥ 3000, and ≥ 5000, respectively. B-FCXM detected 58.3% of class I-II + DSA -positive (≥1000) cases, but detected 76.7% (33/43) and 89.2% (33/37) of class I-II + DSAs if MFI values of sumDSA and immunodominant DSA (iDSA) were above 5000, respectively. Halifax FCXM had sensitivities of 91.5% and 96.2% for detecting VXM (+) having MFI values above 5000 for class I or class II sumDSA and iDSA, respectively.

CONCLUSION

Halifax FCXM showed a good correlation, especially with SAB assay-based high MFI DSA or sumDSA. Concurrent application of FCXM with VXM can improve pre-transplant risk assessment and progress organ allocation efficiency.

HLA antibody repertoire in infants suggests selectivity in transplacental crossing

Problem

Late in pregnancy, women produce and transfer high amounts of antibodies to the foetus. During gestation, women produce antibodies against human leukocyte antigens (HLA), including antibodies directed at foetal HLA. There is paucity of data on transplacental crossing, specificity and role of HLA antibodies in pregnancy and new‐borns.

Method of study

Using highly sensitive Luminex technology, we measured prevalence of IgG HLA antibodies in 30 mother‐infant pairs six weeks post‐partum. Additionally, in six pregnant women, we measured HLA antibodies longitudinally and HLA‐typed infant DNA to assess whether maternal HLA antibodies were directed at infant specificities.

Results

Overall, 68% of mothers and 44% of infants expressed HLA‐I antibodies and 56% of mothers and 52% of infants expressed HLA‐II antibodies. Infants shared up to 78% of antibodies with their mothers, suggesting that the remaining antibodies were self‐made. Less than 25% of maternal HLA antibodies were detected in infants, possibly due to selection in transplacental crossing. We detected complement‐fixing HLA antibodies in mothers and at low levels in infants. In a third of our pregnant subjects, we detected infant‐directed HLA antibodies.

Conclusion

Our findings raise the possibility of selection in transplacental crossing of HLA antibodies. As HLA antibodies may act as autoantibodies in the neonate, the mechanism of a selective transfer may give important insights into immune tolerance. Findings also suggest that infants start producing their own HLA antibodies in the first weeks of life, which, together with maternally derived antibodies may impact the infant's immune reaction to HLA proteins.

The effect of histopathologic and clinical features on allograft survival in renal transplant patients with antibody-mediated rejection

Background: Antibody-mediated rejection is a frequent cause of graft failure; however, prognostic indications of this complication have not been well defined. The aim of this study was to evaluate the association of histopathological and clinical features and to determine the effect of these findings on allograft survival in patients with AMR.

Methods: Fifty-two patients suffered from AMR (30 male; mean age 39 ± 11 years) were included in the study. Data were investigated retrospectively and graft survival was analyzed. All transplant biopsies were evaluated according to Banff 2009 classification.

Results: Of the 52 cases, 45 were transplanted from living-donors. Twenty-one patients were diagnosed in the first 3-months after transplantation. Graft survival was 65% at 12 months and 54% at 36 months. Mean serum creatinine at time of biopsy was 3.8 ± 3.6 mg/dL. Thirty-five of the 52 cases showed diffuse C4d positivity, 12 cases showed focal and 5 remained C4d negative. One of the patients died, 13 experienced graft loss and 38 survived with functioning grafts. Serum creatinine levels at time of biopsy were correlated with graft survival (p = .021: OR = 1.10: 95 % CI = 1.015–1.199). In terms of the impact of pathological findings; tubulitis (p=.007: OR = 2.62: 95 % CI = 1.301–5.276), intimal arteritis (p=.017: OR = 2.85: 95% CI = 1.205–6.744) and interstitial infiltration (p=.004: OR = 3.37: 95% CI = 1.465–7.752) were associated with graft survival.

Conclusions: Serum creatinine at time of biopsy, tubulitis, intimal arteritis and interstitial infiltration were significantly associated with graft survival. Antibody-mediated rejection is associated with reduced long-term graft survival.

Increased intragraft rejection-associated gene transcripts in patients with donor-specific antibodies and normal biopsies

We investigated why some donor-specific antibody-positive patients do not develop antibody-mediated rejection. Of 71 donor-specific antibody-positive patients, 46 had diagnosis of antibody-mediated rejection and 25 had normal biopsies. Fifty donor-specific antibody-negative patients with normal biopsies were used as a control group. A subgroup of 61 patients with available biopsy and 64 with blood samples were analyzed by microarrays. Both donor-specific antibody-positive/antibody-mediated rejection-positive and negative biopsies showed increased expression of gene transcripts associated with cytotoxic T cells, natural killer cells, macrophages, interferon-gamma, and rejection compared to donor-specific antibody-negative biopsies. Regulatory T-cell transcripts were upregulated in donor-specific antibody-positive/antibody-mediated rejection-positive and B-cell transcripts in donor-specific antibody-positive/antibody-mediated rejection-negative biopsies. Whole-blood gene expression analysis showed increased immune activity in only donor-specific antibody-positive/antibody-mediated rejection-positive but not negative patients. During a median follow-up of 36 months, 4 donor-specific antibody-positive/antibody-mediated rejection-negative patients developed antibody-mediated rejection, 12 continued to have donor-specific antibody, but 9 lost their donor-specific antibody. Gene expression profiles did not predict the development of antibody-mediated rejection or the persistence of donor-specific antibody. Thus, donor-specific antibody-positive/antibody-mediated rejection-negative patients had increased rejection-associated gene transcripts in their allografts despite no histologic findings of rejection but not in their blood. This was found in both biopsy and blood samples of donor-specific antibody-positive/antibody-mediated rejection-positive patients.

Interleukin-2 gene polymorphism in Turkish patients with Behçet's disease and its association with ocular involvement

Behçet's disease (BD) is a chronic immune-mediated systemic disease, characterized by oral and genital lesions and ocular inflammation. Several cytokine genes may play crucial roles in host susceptibility to BD, because the cytokine production capacity varies among individuals and depends on the cytokine gene polymorphisms. The association of the interleukin (IL)-2 gene polymorphisms with the susceptibility to BD was investigated in this study. DNA samples were obtained from a Turkish population of 97 patients with BD and 76 healthy control subjects. Polymorphisms of IL-2 gene at position -330 and +166 were determined using the polymerase chain reaction with sequence-specific primers. In the patients with BD, there was a significantly increased frequency of IL-2 -330 GT genotype. Interestingly, we demonstrated that the frequencies of IL-2 -330 GT and IL-2 + 166 GG genotypes were increased in BD patients with ocular involvement, whilst IL-2 -330 TT genotype was significantly decreased. Also, analysis of allele frequency demonstrated that the presence of G allele at position +166 of IL-2 seems to be a risk factor for ocular involvement. These results reveal that IL-2 -330 GT genotype may be a susceptibility factor for BD, whereas IL-2 -330 TT genotype seems to display a protective association with BD. Additionally, IL-2 gene polymorphisms might be associated with ocular involvement in BD.

Desensitization protocols and their outcome

In the last decade, transplantation across previously incompatible barriers has increasingly become popular because of organ donor shortage, availability of better methods of detecting and characterizing anti-HLA antibodies, ease of diagnosis, better understanding of antibody-mediated rejection, and the availability of effective regimens. This review summarizes all manuscripts published since the first publication in 2000 on desensitized patients and discusses clinical outcomes including acute and chronic antibody-mediated rejection rate, the new agents available, kidney paired exchange programs, and the future directions in sensitized patients. There were 21 studies published between 2000 and 2010, involving 725 patients with donor-specific anti-HLA antibodies (DSAs) who underwent kidney transplantation with different desensitization protocols. All studies were single center and retrospective. The patient and graft survival were 95% and 86%, respectively, at a 2-year median follow-up. Despite acceptable short-term patient and graft survivals, acute rejection rate was 36% and acute antibody-mediated rejection rate was 28%, which is significantly higher than in nonsensitized patients. Recent studies with longer follow-up of those patients raised concerns about long-term success of desensitization protocols. The studies utilizing protocol biopsies in desensitized patients also reported higher subclinical and chronic antibody-mediated rejection. An association between the strength of DSAs determined by median fluorescence intensity values of Luminex single-antigen beads and risk of rejection was observed. Two new agents, bortezomib, a proteasome inhibitor, and eculizumab, an anti-complement C5 antibody, were recently introduced to desensitization protocols. An alternative intervention is kidney paired exchange, which should be considered first for sensitized patients.

Trends in HLA antibody screening and identification and their role in transplantation

HLA testing has been a staple in transplantation since the recognition that antibodies, directed against lymphocytes, were associated with allograft failure. This seminal finding led to the discovery of the MHC and the appreciation of the importance of HLA testing in transplantation. Early approaches focused on the importance of HLA matching, and were an important aspect of deceased organ donor allocation. More recently, and as a direct result of improvements in immunosuppression, there has been a movement away from 'matching' as the driving force in organ allocation. By contrast, we are now challenged with selecting donor-recipient pairs based on acceptable mismatches. For patients devoid of HLA antibodies, this is not an issue. However, for patients with HLA alloantibodies, that is, the sensitized patient, we face significant challenges in assessing the repertoire of the HLA antibody reactivity they possess. Over the past several years, significant advances in HLA antibody detection have occurred. Solid-phase, multiplex testing platforms have replaced traditional cell-based assays, and have provided better sensitivity and specificity in antibody detection. As a direct result of improved antibody identification, many programs are moving into the realm of the 'virtual crossmatch'. The virtual crossmatch has proven to be successful in renal, cardiac and lung transplantation, and has resulted in a greater percentage of sensitized patients gaining access to transplantation. This review will be devoted to highlighting the latest developments in antibody assessments and discussing their utilization in transplant testing.

A case of accelerated acute rejection after ABO-compatible living unrelated kidney transplantation

A 59-yr-old Japanese woman with chronic renal failure caused by IgA nephropathy and antineutrophil cytoplasmic antibody (ANCA)-related glomerulonephritis underwent kidney transplantation from a living unrelated spousal donor. The blood type was compatible, while the human leukocyte antigen (HLA) typing showed a 5/6 locus mismatch. She had become pregnant twice by her donor and had never received blood transfusions. Complement-dependent cytotoxicity cross-match, flow cytometry cross-match (FCXM), and flow panel reactive antibody (PRA) were negative. She initially underwent one week of immunosuppression with mycophenolate mofetil (MMF) and double filtration plasmapheresis (DFPP) immediately before transplantation to reduce the risk of antibody-mediated rejection. Induction therapy consisted of MMF, tacrolimus (TAC), methylprednisolone (MP), and basiliximab. The allograft function was excellent immediately after the operation. However, the urine output and platelet count declined rapidly on post-operative day (POD) 3, while the serum creatinine (sCr) and lactate dehydrogenase levels rose gradually. Subsequently, we could not detect the diastolic arterial flow on Doppler sonography. We diagnosed accelerated acute rejection and treated her with plasma exchange (PEX), intravenous MP pulse therapy, and rituximab. The first episode biopsy on POD 7 revealed acute vascular rejection and acute antibody-mediated rejection (Banff score AMR II). Her urinary excretion increased beginning on POD 13, while the sCr level decreased gradually and reached 0.9 mg/dL on POD 22. In our retrospective analysis, the LAB screen detected donor-specific antibody (DSA). This case suggested that, for successful kidney transplantation in highly sensitized recipients, such as husband-to-wife spousal kidney transplantation with a history of pregnancy, we should keep the risk of AMR in mind, even if the sensitive antibody detection tests are negative.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Endothelial cells in allograft rejection

In organ transplantation, blood borne cells and macromolecules (e.g., antibodies) of the host immune system are brought into direct contact with the endothelial cell lining of graft vessels. In this location, graft endothelial cells play several roles in allograft rejection, including the initiation of rejection responses by presentation of alloantigen to circulating T cells; the development of inflammation and thrombosis; and as targets of injury and agents of repair.

Immunosuppression minimization protocols: how should they be monitored?

This Practice Point commentary discusses the experience of Shapiro et al. with renal allograft recipients at a single center who underwent significant minimization of immunosuppressive treatment with alemtuzumab induction and tacrolimus monotherapy (weaned to three times weekly by 1 year after transplantation). Donor-specific antibodies (DSAs) against human leukocyte antigen were monitored after transplantation in some patients. Although 44% of patients did not develop acute rejection or DSAs and had excellent 2-year graft survival (96%), spaced weaning was not attempted in 20% of patients, generally those with early rejection and poor allograft function. During tapering, 20% of patients developed acute rejection and 15% developed DSAs. Two-year graft survival was 63% in patients for whom weaning was not attempted and 78% in patients who experienced acute rejection. Alemtuzumab preconditioning with tacrolimus monotherapy and spaced weaning increased the risk of acute rejection and development of DSAs. Patients should be carefully selected for this protocol and monitored closely for DSAs. Results of a long-term controlled trial that includes protocol biopsies are required to reach more-definitive conclusions.