The detection and role of circulating antibodies in rejection:

Detection of donor-specific HLA antibodies: A retrospective observation in 350 renal transplant cases

BACKGROUND

The main objective of this study was to determine the results of the cell-based assay (CDC-XM and FC-XM), and correlate with the results of solid phase assay (L-SAB).

METHODS

In this retrospective study, 350 prospective renal transplant recipients were tested for the presence of HLA antibodies by CDC-XM, FC-XM and L-SAB screening with their corresponding donor.

RESULTS

T-cell-FC-XM showed a sensitivity of 71.43% and a specificity of 91.50% for detecting class I L-SAB (+), while B-cell-FCXM showed a sensitivity of 94.94% and a specificity of 61.99% for detecting class II L-SAB (+). On the other hand, T-CDC-XM showed a sensitivity of 32.14% and a specificity of 98.64% for detecting class I L-SAB (+), while B-CDC-XM showed a sensitivity of 44.30% and a specificity of 94.83% for detecting class II L-SAB (+). In this study, the results indicated that DSA class I MFI value of 2845 and above significantly (p ≤0.001) correlated with T-cell-FC-XM positivity, while MFI value of 4585 and above (p ≤0.001) showed strong predictive accuracy of a positive T-cell-CDC-XM. However, DSA class II MFI cut-off of 1988 and above significantly (p ≤0.001) correlated with B-cell-FC-XM positivity, while MFI value of 5986 and above (p ≤0.001) showed strong predictive accuracy of a positive B-cell-CDC-XM.

CONCLUSIONS

Our study showed that CDC-XM has poor sensitivity, while FC-XM has poor specificity to detect DSA. L-SAB has good correlation with T-cell-FC-XM (p < 0.0001) but not with B-cell-FC-XM (P = 0.31). DSA strength >2845 and > 1988 significantly correlated with T-cell-FC-XM positivity and B-cell-FC-XM positivity, respectively. While, a MFI value of >4585 and > 5986 significantly correlated with T-cell-CDC-XM positivity and B-cell-CDC-XM positivity, respectively. These MFI cut-off values could serve as a surrogate marker for CDC-XM and FC-XM tests and may help in resolving the limitations of cell-based techniques. In conclusion, we found that L-SAB is more sensitive and specific than CDC-XM and FC-XM and therefore may be used as a test of choice.

Effects of different sensitization events on HLA alloimmunization in renal transplant cases; a retrospective observation in 1066 cases

BACKGROUND

Patients awaiting solid organ transplantation may develop anti-HLA antibodies after sensitization events such as transfusions, pregnancies, or previous transplantations. However, the effects of a particular sensitization event on HLA alloimmunization have not been well studied in parallel using cell-based assays and solid-phase assays. In this study, we evaluated and compare how different sensitization events affect the HLA antibody screening (HLA-Ab) and donor specific antibody (DSA) status in solid renal organ transplantation patients.

METHODS

HLA antibody (HLA-Ab) screening tests like complement-dependent cytotoxicity crossmatch (CDC-XM), flow cytometry crossmatch (FC-XM) & Luminex panel-reactive antibody (L-PRA) were performed in all 1066 patients (635 males and 431 females). If any of these tests turned out to be positive, a Luminex single antigen bead (L-SAB) assay was performed for DSA identification. Test positive rates and antibody strengths were analyzed according to the different sensitization events and gender.

RESULTS

In this study, HLA-Ab screening tests positive rates (L-PRA, FC-XM and CDC-XM) were significantly higher in patients with previous transplantation (73.91%, 86.95% and 56.52% p < 0.001), previous pregnancy (57.46%, 70.14% and 18.85% p < 0.001) or blood transfusion (27.33%, 35.55% and 7.33% p < 0.001) compared with patients without a sensitizing event (6.17%, 13.58% & 1.09). In this study, re-transplantation group showed significantly stronger antibody strength (DSA) than non sensitized group (class I & II MFI 11418.04, 17,837.78 vs class I & II MFI 2659, 3329; P < 0.001) and those with single sensitization events of transfusion (class I & II MFI 11418.04, 17,837.78 vs class I & II MFI 5598.82, 5436.12; P < 0.001) or pregnancy (class I & II MFI 11418, 17,837 vs class I & II MFI 8580.12, 7556.08; P < 0.001).

CONCLUSIONS

Pregnancy and blood transfused had high allo-immunization rate for class I HLA antigens. While re-transplantation patients had high allo-immunization rate for both the HLA classes (HLA- class I & HLA- class II). Re-transplantation group showed significantly stronger antibody strength, followed by pregnancy and then transfusion.

Comparative analysis of complement-dependent lymphocytotoxicity crossmatch and flow cytometry crossmatch results versus Luminex single-antigen bead-based donor-specific IgG class I antibody MFI values in live related renal transplant cases; a retrospective observation in 102 cases

The aim of this study was to compare the results of solid phase assay and cell-based assay, and explore the near-accurate DSA-MFI-cutoff value detected on solid phase assay above which the cell-based assay would show a positive result. In this retrospective study, 102 prospective renal transplant recipients were tested for the presence of donor-specific antibodies (DSAs) by cell-based assay (T-cell-CDC-AHG-XM and T-cell-IgG-FC-XM) and solid phase assay (class-I-IgG-L-SAB) with their corresponding donor. Among the 40 patients in the group first (L-SAB-DSA-MFI<1000), one case was positive in IgG-T-cell-FC-XM while T-cell-CDC-AHG-XM was negative in all the cases. In the second group having L-SAB-DSA-MFI values between 1000 and 3000, 19 cases were positive and the remaining 11 cases were negative in IgG-T-cell-FC-XM. T-cell-CDC-AHG-XM showed a negative reaction in all 30 cases. In the third group having L-SAB-DSA-MFI values between 3000 and 5000, IgG-T-cell-FC-XM was positive in 18 cases while, two were negative. T-cell-CDC-AHG-XM demonstrated a negative result in 14 cases while reaming six cases demonstrated a positive result. In the fourth group having L-SAB-DSA-MFI values >5000, all 12 cases showed a positive result in both IgG-T-cell FC-XM and T-cell-CDC-AHG-XM. Our results indicated that the L-SAB-DSA-MFI values >2215 were significantly (P < .001) correlated with positive IgG-T-cell-FC-XM while L-SAB-DSA-MFI values >4689 were significantly (P < .001) correlated with positive CDC-XM.

The clinical impact of donor-specific antibodies in heart transplantation

Donor-specific antibodies (DSA) are integral to the development of antibody-mediated rejection (AMR). Chronic AMR is associated with high mortality and an increased risk for cardiac allograft vasculopathy (CAV). Anti-donor HLA antibodies are present in 3-11% of patients at the time of heart transplantation (HTx), with de novo DSA (predominantly anti-HLA class II) developing post-transplant in 10-30% of patients. DSA are associated with lower graft and patient survival after HTx, with one study suggesting a three-fold increase in mortality in patients who develop de novo DSA (dnDSA). DSA against anti-HLA class II, notably DQ, are at particularly high risk for graft loss. Although detection of DSA is not a criterion for pathologic diagnosis of AMR, circulating DSA are found in almost all cases of AMR. MFI thresholds of ~5000 for DSA against class I antibodies, 2000 against class II antibodies, or an overall cut-off of 5-6000 for any DSA, have been suggested as being predictive for AMR. There is no firm consensus on pre-transplant strategies to treat HLA antibodies, or for the elimination of antibodies after diagnosis of AMR. Minimizing the risk of dnDSA is rational but data on risk factors in HTx are limited. The effect of different immunosuppressive regimens is largely unexplored in HTx, but studies in kidney transplantation emphasize the importance of adherence and maintaining adequate immunosuppression. One study has suggested a reduced risk for dnDSA with rabbit antithymocyte globulin induction. Management of DSA pre- and post-HTx varies but typically most centers rely on a plasmapheresis or immunoadsorption, with or without rituximab and/or intravenous immunoglobulin. Based on the literature and a multi-center survey, an algorithm for a suggested surveillance and therapeutic strategy is provided.

Antibody-mediated rejection in the cardiac allograft: diagnosis, treatment and future considerations

PURPOSE OF REVIEW

This review summarizes the latest publications dealing with antibody-mediated rejection (AMR) and defines areas of controversy and future steps that may improve the outcome for patients with this virulent form of rejection.

RECENT FINDINGS

Recent progress includes publication of standardized pathologic criteria for acute AMR by the International Society for Heart and Lung Transplantation (ISHLT) and guidelines for treatment of acute AMR by the American Heart Association, endorsed by ISHLT as well. Recently published review articles emphasize the important role of innate immune mechanisms, clarify the role of viral infection and provide insights into vascular biology and the role of innate effector populations, macrophages and dendritic cells.

SUMMARY

Strategies for future studies are discussed in the context of these new findings and similar efforts undertaken by renal and liver allograft investigators.

Significance of Anti-HLA Antibodies on Adult and Pediatric Heart Allograft Outcomes

As methods for human leukocyte antigens (HLA) antibody detection have evolved and newer solid phase assays are much more sensitive, the last 15 years has seen a renewed focus on the importance of HLA antibodies in solid organ transplant rejection. However, there is still much controversy regarding the clinical significance of antibody level as depicted by the mean fluorescence intensity of a patient’s neat serum. Emerging techniques, including those that identify antibody level and function, show promise for the detection of individuals at risk of allograft rejection, determination of the effectiveness of desensitization prior to transplant, and for monitoring treatment of rejection. Here, we review current publications regarding the relevance of donor-specific HLA antibodies (DSA) in adult and pediatric heart transplantation (HT) with graft survival, development of antibody-mediated rejection and cardiac allograft vasculopathy (CAV). The negative impact of DSA on patient and allograft survival is evident in adult and pediatric HT recipients. Many questions remain regarding the most appropriate frequency of assessment of pre- and posttransplant DSA as well as the phenotype of DSA memory vs. true de novo antibody using large multicenter adult and pediatric cohorts and state-of-the-art methodologies for DSA detection and characterization.

The XIIIth Banff Conference on Allograft Pathology: The Banff 2015 Heart Meeting Report: Improving Antibody-Mediated Rejection Diagnostics: Strengths, Unmet Needs, and Future Directions

The 13th Banff Conference on Allograft Pathology was held in Vancouver, British Columbia, Canada from October 5 to 10, 2015. The cardiac session was devoted to current diagnostic issues in heart transplantation with a focus on antibody-mediated rejection (AMR) and small vessel arteriopathy. Specific topics included the strengths and limitations of the current rejection grading system, the central role of microvascular injury in AMR and approaches to semiquantitative assessment of histopathologic and immunophenotypic indicators, the role of AMR in the development of cardiac allograft vasculopathy, the important role of serologic antibody detection in the management of transplant recipients, and the potential application of new molecular approaches to the elucidation of the pathophysiology of AMR and potential for improving the current diagnostic system. Herein we summarize the key points from the presentations, the comprehensive, open and wide-ranging multidisciplinary discussion that was generated, and considerations for future endeavors.

Detection of HLA Antibodies in Organ Transplant Recipients - Triumphs and Challenges of the Solid Phase Bead Assay

This review outlines the development of human leukocyte antigen (HLA) antibody detection assays and their use in organ transplantation in both antibody screening and crossmatching. The development of sensitive solid phase assays such as the enzyme-linked immunosorbent assay technique, and in particular the bead-based technology has revolutionized this field over the last 10-15 years. This revolution however has created a new paradigm in clinical decision making with respect to the detection of low level pretransplant HLA sensitization and its clinical relevance. The relative sensitivities of the assays used are discussed and the relevance of conflicting inter-assay results. Each assay has its advantages and disadvantages and these are discussed. Over the last decade, the bead-based assay utilizing the Luminex® fluorocytometer instrument has become established as the "gold standard" for HLA antibody testing. However, there are still unresolved issues surrounding this technique, such as the presence of denatured HLA molecules on the beads which reveal cryptic epitopes and the issue of appropriate fluorescence cut off values for positivity. The assay has been modified to detect complement binding (CB) in addition to non-complement binding (NCB) HLA antibodies although the clinical relevance of the CB and NCB IgG isotypes is not fully resolved. The increase sensitivity of the Luminex® bead assay over the complement-dependent cytotoxicity crossmatch has permitted the concept of the "virtual crossmatch" whereby the crossmatch is predicted to a high degree of accuracy based on the HLA antibody specificities detected by the solid phase assay. Dialog between clinicians and laboratory staff on an individual patient basis is essential for correct clinical decision making based on HLA antibody results obtained by the various techniques.

Concordance and discordance in anti-HLA antibody testing

BACKGROUND

Correct identification of the specificity of antibodies directed against HLA using single antigen Luminex beads (SALB) is essential in current HLA laboratory practice for transplantation. The aim of this study was to investigate the magnitude of concordance and discordance among laboratories in testing for anti-HLA antibodies using SALB.

METHOD

35 sera were distributed by the ASHI Proficiency Testing Program to HLA laboratories worldwide. We analyzed 4335 test results submitted between April 2010 and April 2013 by participating laboratories.

RESULTS

SALB was used by approximately 94% of the participating laboratories, yet concordant assignment of antibody specificity was imperfect. For each serum, the assignment of an average of 10 antibody specificities was discordant. Disagreement was observed for antibodies directed against common as well as uncommon antigens. The assignment of an average of 15 antibody specificities in each "positive" serum appeared to be influenced by vendor-dependent causes. Inter-vendor concordance was lower than intra-vendor concordance, indicating that vendor dependent factors may be a central cause for disagreement.

CONCLUSIONS

Our study illustrates the prevalence of concordance and discordance, also affected by unpremeditated causes, in reporting SALB antibody results. Insufficient concordance and standardization in antibody testing may have practical implications for organ allocation and organ sharing programs.