Reappraisal of HLA antibody analysis and crossmatching in kidney transplantation

Sensitive HLA antibody testing and the risk of antibody-mediated rejection and graft failure

Solid phase detection and identification of HLA antibodies in kidney transplantation currently relies on single antigen bead (Luminex®) assays, which is more sensitive than the previously used enzyme-linked immunosorbent assays (ELISA). To evaluate the impact of more sensitive HLA testing on antibody-mediated rejection (AMR) occurrence and allograft survival, we analysed 1818 renal allograft recipients transplanted between March 2004 and May 2021. In 2008, solid phase testing switched from ELISA to Luminex. We included 393 (21.6%) transplantations before and 1425 (78.4%) transplantations after transition from ELISA- to Luminex-based testing. For this study, bio-banked ELISA era samples were tested retrospectively with Luminex. Significantly less pretransplant DSA were found in patients transplanted with pre-existing HLA antibodies in the Luminex (109/387) versus the ELISA period (43/90) (28% vs. 48%, p < 0.01). Throughout histological follow-up, 169 of 1818 (9.3%) patients developed AMR. After implementing Luminex-based testing, the rate of AMR significantly decreased (p = 0.003). However, incidence of graft failure did not significantly differ between both eras. In conclusion, less patients with pretransplant DSA were transplanted since the implementation of Luminex HLA testing. Transition from ELISA- to Luminex-based HLA testing was associated with a significant decrease in AMR occurrence post-transplantation. Since the decline of AMR did not translate into improved graft survival, Luminex-based testing has the added value of preventing low-risk AMR cases. Therefore, Luminex' high sensitivity must be balanced against waiting time for a suitable organ.

Non-invasive molecular biomarkers for monitoring solid organ transplantation: A comprehensive overview

Solid organ transplantation is a life-saving intervention for individuals with end-stage organ failure. Despite the effectiveness of immunosuppressive therapy, the risk of graft rejection persists in all viable transplants between individuals. The risk of rejection may vary depending on the degree of compatibility between the donor and recipient for both human leucocyte antigen (HLA) and non-HLA gene-encoded products. Monitoring the status of the allograft is a critical aspect of post-transplant management, with invasive biopsies being the standard of care for detecting rejection. Non-invasive biomarkers are increasingly being recognized as valuable tools for aiding in the detection of graft rejection, monitoring graft status and evaluating the efficacy of immunosuppressive therapy. Here, we focus on the importance of molecular biomarkers in solid organ transplantation and their potential role in clinical practice. Conventional molecular biomarkers used in transplantation include HLA typing, detection of anti-HLA antibodies, killer cell immunoglobulin-like receptor genotypes, and anti-MHC class 1-related chain A antibodies, which are important for assessing the compatibility of the donor and recipient. Emerging molecular biomarkers include the detection of donor-derived cell-free DNA, microRNAs (regulation of gene expression), exosomes (small vesicles secreted by cells), and kidney solid organ response test, in the recipient's blood for early signs of rejection. This review highlights the strengths and limitations of these molecular biomarkers and their potential role in improving transplant outcomes.

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.

Significance of Luminex-based single antigen class II bead assay and its mean fluorescence intensity in renal transplant cases; a retrospective observation in 97 cases

The objective of this study was to determine the mean fluorescence intensity (MFI) values of class II Luminex single antigen bead (L-SAB) assay and compare these MFI values with cell-based complement-dependent cytotoxicity crossmatch with anti-human globulin (CDC-AHG-XM) and IgG-B-cell flow cytometry crossmatch (FC-XM) results and explore the near-accurate MFI-cutoff values of positive cell-based crossmatch results. This retrospective study was an analysis in 97 renal transplant recipients, who were tested for the presence of DSA by CDC-AHG-XM and IgG-B-cell-FC-XM methods with their corresponding donor as well as for anti-human leukocyte antigen (HLA) antibody detection using a sensitive L-SAB assay. In the group having DSA MFI values <1000, none of the patients showed positivity for FC-XM and CDC-AHG-XM; in the group having MFI values between 1000 and 3000, 35.48% showed positivity for FC-XM but none by the CDC-AHG-XM method. However, in the group having MFI values >3000, 83.33% of cases were positive for FC-XM. Further, in those groups with MFI values between 3000 and 6000, 38.09% were positive for CDC-AHG-XM, while 86.66% showed positivity in the group with MFI >6000. Our results indicated that Luminex-DSA MFI value >1995 (P < .0001) significantly correlated with IgG-B-cell-FC-XM positivity while Luminex-DSA MFI value of >4247 (P < .0006) was significantly correlated with positive CDC-AHG-XM. MFI cutoff of 1995 exhibited a diagnostic sensitivity of 97.56% and specificity of 89.29% for predicting positive IgG B-cell FC-XM and MFI cutoff of 4247 exhibited a diagnostic sensitivity of 90.48% and specificity of 97.37% for predicting positive CDC-AHG-XM. However, a cutoff MFI of >5000 and >7000 for SAB assay had a sensitivity and specificity of 100% in detecting a positive IgG B-cell FC-XM and CDC-AHG-XM, respectively.

Outcome after Desensitization in HLA or ABO-Incompatible Kidney Transplant Recipients: A Single Center Experience

BACKGROUND

The shortage of deceased donors led to an increase of living donor kidney (LDK) transplantations performed in the presence of donor-specific antibodies (DSA) or ABO incompatibility (ABOi) using various desensitization protocols.

METHODS

We herein analyzed 26 ABOi and 8 Luminex positive DSA patients who were successfully desensitized by anti-CD20, antigen-specific immunoadsorption and/or plasmapheresis to receive an LDK transplant. Twenty LDK recipients with non-donor-specific HLA-antibodies (low risk) and 32 without anti-HLA antibodies (no risk) served as control groups.

RESULTS

1-year graft survival rate and renal function was similar in all 4 groups (creatinine: 1.63 ± 0.5 vs 1.78 ± 0.6 vs 1.64 ± 0.5 vs 1.6 ± 0.3 mg/dl in ABOi, DSA, low risk and no risk group). The incidence of acute T-cell mediated rejections did not differ between the 4 groups (15% vs 12, 5% vs 15% vs 22% in ABOi, DSA, low risk and no risk), while antibody-mediated rejections were only found in the DSA (25%) and ABOi (7.5%) groups. Incidence of BK nephropathy (BKVN) was significantly more frequent after desensitization as compared to controls (5/34 vs 0/52, p = 0.03).

CONCLUSION

We demonstrate favorable short-term allograft outcome in LDK transplant recipients after desensitization. However, the desensitization was associated with an increased risk of BKVN.

Characteristics of Circulating Donor Human Leukocyte Antigen-specific Immunoglobulin G Antibodies Predictive of Acute Antibody-mediated Rejection and Kidney Allograft Failure

BACKGROUND

Characteristics of pretransplant antibodies directed at donor human leukocyte antigen (HLA) donor-specific antibodies (DSA) associated with adverse outcomes in kidney transplant recipients are being elucidated but uncertainties exist.

METHODS

We prospectively screened pretransplant sera from 543 kidney recipients using single antigen bead assays and identified 154 patients with and 389 without DSA. We investigated the association of DSA features to acute rejection and graft failure.

RESULTS

One-year acute rejection incidence was higher in DSA-positive group (P < 0.001), primarily due to antibody-mediated rejection (AMR, 13% vs. 1.8%, P < 0.001) and not T cell-mediated rejection (ACR, 5% vs.6%, P = 0.65). The sum of mean fluorescence intensity of DSA (DSA MFI-Sum) of 6,000 or higher (OR, 18; 95% CI, 7.0-47; P < 0.001) and the presence of DSA against both HLA class I and II (OR, 39; 95% CI, 14-106; P < 0.0001) predicted 1-year AMR, independent of other covariates. Calculated panel reactive antibody and a positive flow cytometry cross-match result were associated with AMR by bivariate analysis but neither was an independent predictor in a multivariable regression analysis that included DSA-MFI-Sum or HLA DSA class. In multivariable Cox proportional hazards models, the covariate-adjusted hazard ratio for graft failure was 2.03 (95%CI, 1.05-3.92; P = 0.04) for DSA MFI-Sum of 6,000 or higher and 2.23 (95% CI, 1.04-4.80; P = 0.04) for class I and II DSA. Prediction of graft failure was not independent of AMR.

CONCLUSION

Our study suggests that DSA MFI-Sum and HLA class of DSA are characteristics predictive of AMR and graft failure. The elevated risk of graft failure in those with the identified features of DSA is attributable to increased risk of AMR.

Impact of sensitivity of human leucocyte antigen antibody detection by Luminex technology on graft loss at 1 year

Background

The clinical relevance of the detection of human leucocyte antigen (HLA) antibodies in sera of renal transplant recipients by highly sensitive methods such as Luminex alone is uncertain and a matter of debate. The choice of output thresholds affects antibody detection and thus organ allocation, yet there are no internationally agreed threshold levels. This study aims at evaluating our current practice of using an MFI threshold of 1000 in antibody detection.

Methods

We carried out a case–control study by looking at 761 renal transplant recipients at one unit between 2000 and 2010. Of these, there were 93 cases of graft loss within 1 year and stored serum samples of 40 cases were available for testing. Controls were selected (graft function >2 years) and individually matched according to age, sex, number of transplants and date of transplant. All 40 cases and 40 controls had negative crossmatch by complement-dependent cytotoxicity (CDC) at the time of transplant, and pre-transplant sera were re-analysed for the presence of detectable HLA and donor-specific antibodies (DSAs) using Luminex screen and single-antigen beads and MFI threshold values of 1000, 2000 and 4000.

Results

In nearly 48% of cases with graft loss within a year, HLA antibodies were detectable by Luminex when using a 1000 MFI threshold. This was 25% greater than in controls (P = 0.017). There was also a 15% increase in detected DSAs; however, statistical significance depends on the inclusion or exclusion of one specific case. Using MFI thresholds of 2000 and 4000, no DSAs were found in any long-term surviving grafts.

Conclusions

Selection of appropriate MFI cut-off values influences the detection of DSAs and, thus, organ allocation. Using a threshold of 1000 led to the detection of DSAs in 5% of long-term graft survivors in our population and should be considered too sensitive. Using a detection threshold of 2000 is sufficiently sensitive and leads to clinically relevant detection of DSA.

Histocompatibility testing for organ transplantation purposes in Albania: a single center experience

BACKGROUND

Histocompatibility testing (HT) which includes donor-recipient human leukocyte antigen (HLA) matching, cross-match testing (XMT) and anti-HLA antibody searching are crucial examinations in solid organ transplantation aiming to avoid the hyperacute graft rejection and also to predict the immunological outcome of the graft.

AIMS

The aim of this study was to analyse the tissue typing data collected at the Laboratory of Immunology and Histocompatibility of the University Hospital Center of Tirana, Albania, in order to define those actions that should be taken for improvements in the situation of kidney transplantation in Albania.

STUDY DESIGN

Descriptive study.

METHODS

The donor/recipient cross-match testing was performed through a standard complement-dependent cytotoxicity (CDC) assay using separated donor T and B cells that were tested in parallel with the recipient serum sample. All recipient sera were screened for anti-Class I and anti-Class II HLA antibodies using a bead based Luminex anti-HLA antibody screening test. In the case of detected positivity, an allele-specific anti-HLA antibody determination was conducted with the respective Luminex anti-Class I and Class II HLA antibody determination kits.

RESULTS

A total of 174 recipients and 202 donors were typed for the purpose of living donor kidney transplantation at our laboratory between January 2006 and December 2012. The mean age and female gender proportion of patients were 34.9 years and 34.5%, respectively, and 48.0 years and 65.3% for the donors, respectively. Here, 25.9% of the patients reported a positive complement-dependent cytotoxicity cross-match test and/or a positive anti-HLA antibody testing result. Eighteen patients that were negative for the complement-dependent cytotoxicity cross-match test were positive for anti-HLA antibodies.

CONCLUSION

The predominant causes of end-stage renal disease (ESRD) in our patient population are chronic pyelonephritis and glomerulonephritis. The female gender is significantly more frequent among donors, which emphasises the need for more gender equity as far as the altruistic willingness for organ donation is concerned. The significant number of patients with Luminex anti-HLA antibody positivity combined with complement-dependent cytotoxicity cross-match negative results underlines the necessity of using additional methods like cell-based flow cytometry or bead-based Luminex anti-HLA antibody assays for the detection of anti-donor-specific antibodies. We also suggest that the number of kidney transplantations in Albania needs to be increased significantly by expanding it with paired exchange living donation and also by implementing an efficient deceased donor kidney transplantation program.

Influence of test technique on sensitization status of patients on the kidney transplant waiting list

The exquisitely sensitive single antigen bead (SAB) technique was shown to detect human leukocyte antigen (HLA) antibodies in sera of healthy male blood donors. Such false reactions can have an impact on critical decisions, especially with respect to the determination of unacceptable HLA-antigen mismatches in patients awaiting a kidney transplant. We tested pretransplant sera of 534 patients on the kidney waiting list using complement-dependent cytotoxicity (CDC), enzyme-linked immunosorbent assay (ELISA) and SAB in parallel. Evidence of HLA antibodies was obtained in 5% of patients using CDC, 14% using ELISA, and 81% using SAB. Among patients without history of an immunizing event, 77% showed evidence of HLA antibodies in SAB. In contrast 98% of these patients were negative in ELISA and CDC. In patients without an immunizing event, SAB-detected antibodies reacted not always weakly but with mean fluorescence intensity (MFI) values as high as 14 440. High-MFI-value antibodies were found in some of these patients with HLA specificities that are rather common in general population, consideration of which would lead to unjustified exclusion of potential kidney donors. False SAB reactions can be unveiled by testing with additional antibody assays. Denial of donor kidneys to recipients based on HLA-antibody specificities detected exclusively in the SAB assay is not advisable.

Algorithms for the determination of unacceptable HLA antigen mismatches in kidney transplant recipients

One of the major tasks of human leukocyte antigen (HLA) laboratories is the pretransplant determination of unacceptable HLA antigen mismatches (UAM) in organ transplant recipients. HLA antigen specificities are determined against which the patient has circulating alloantibodies that are expected to harm the transplanted organ. Using the information on UAM, negative crossmatch (XM) prediction or 'virtual XM' is possible when a potential donor's complete HLA typing is available. Before the introduction of solid-phase antibody detection assays, UAM were determined using the complement-dependent cytotoxicity methodology. After the introduction of the single antigen bead technique, however, various UAM determination algorithms have emerged. In this report, six different laboratories worldwide present how they determine UAM in their collective of kidney transplant recipients in the pretransplant phase and proceed thereafter to transplantation.

Multivariate analysis of antibody induction therapy and their associated outcomes in live donor kidney transplantation in the recent era

The majority of kidney transplant recipients in the United States receive antibody induction, but its impact on outcomes in living donor transplant is not well-described. We used Organ Procurement and Transplant Network/United Network for Organ Sharing (OPTN/UNOS) data as of November 2009 to compare acute rejection (AR) and graft survival among all primary adult living donor kidney recipients of no antibody induction, antithymocyte globulin (ATG) and interleukin-2 receptor antagonists (IL-2RA) in an earlier era (1998-2002; n=21,919) and a later era (2003-2008, n=26,837). The incidence of AR in the overall cohort decreased from 18.5% in 1998 to 8% in 2008. From 1998 to 2002, antibody induction was associated with a decreased risk of acute rejection at six months (RR 0.67, 95% CI 0.62-0.72) and one yr (RR 0.71, 0.65-0.76), while in the recent era, induction was not associated with acute rejection at six months (RR 0.97, 0.88-1.07) or one yr (RR 1.01, 0.91-1.10). There was no difference in graft survival over five yr with antibody induction in either era. Although antibody induction was associated with a decreased risk of AR from 1998 to 2002, it was not associated with a decreased risk of acute rejection from 2003 to 2008, nor was it associated with a difference in graft survival in either era.

[Comparative evaluation of ELISA and Luminex panel reactive antibody assays for HLA alloantibody screening]

BACKGROUND

For the detection of HLA antibodies, solid-phase tests using purified HLA antigens are increasingly used. In this study, we analyzed the panel reactive antibody (PRA) test results using ELISA and Luminex methods, and the results were compared with those of crossmatch test.

METHODS

A total of 111 sera including 90 sera from kidney transplanted patients were tested. ELISA-PRA was performed using Lambda Antigen Tray Class I and II Mixed kits (One Lambda Inc., USA) and additional test was performed to identify HLA specificities. Luminex-PRA tests were performed using LABScreen Mixed kits (One Lambda Inc., USA) and LIFECODES LifeScreen Deluxe kits (Tepnel Co., USA).

RESULTS

The positive rates of PRA were higher in Tepnel (P=0.006) and One Lambda Luminex (P<0.001) methods than ELISA, without significant difference between two Luminex methods (P=0.087). The overall concordance rate among the three PRA tests was 62.2% (69/111). The positive and negative predictive values of PRA tests for the flow cytometric crossmatch were 33.3-45.7% and 85.7-89.5%, respectively. Of the two Luminex methods, One Lambda showed higher positive rate than Tepnel for the detection of class I antibodies. The sensitivity of pretransplant PRA for the detection of posttransplant acute rejection episodes was higher in Luminex (P=0.007 for Tepnel, P=0.003 for One lambda) than ELISA method.

CONCLUSIONS

Different methods used to detect HLA antibodies showed discrepant results. As the Luminex method was more sensitive than ELISA for the detection of HLA antibodies, it can be used as a routine test in the transplantation laboratory.