The strength of donor-specific antibody is a more reliable predictor of antibody-mediated rejection than flow cytometry crossmatch analysis in desensitized kidney recipients

Impact of Low-Level Donor-Specific Anti-HLA Antibody on Posttransplant Clinical Outcomes in Kidney Transplant Recipients

Background

The clinical significance of low-level donor-specific anti-HLA antibody (low-DSA) remains controversial. We investigated the impact of low-DSA on posttransplant clinical outcomes in kidney transplant (KT) recipients.

Methods

We retrospectively reviewed 1,027 KT recipients, namely, 629 living donor KT (LDKT) recipients and 398 deceased donor KT (DDKT) recipients, in Seoul St. Mary's Hospital (Seoul, Korea) between 2010 and 2018. Low-DSA was defined as a positive anti-HLA-DSA result in the Luminex single antigen assay (LABScreen single antigen HLA class I - combi and class II - group 1 kits; One Lambda, Canoga Park, CA, USA) but a negative result in a crossmatch test. We compared the incidence of biopsy-proven allograft rejection (BPAR), changes in allograft function, allograft survival, patient survival, and posttransplant infections between subgroups according to pretransplant low-DSA.

Results

The incidence of overall BPAR and T cell-mediated rejection did not differ between the subgroups. However, antibody-mediated rejection (ABMR) developed more frequently in patients with low-DSA than in those without low-DSA in the total cohort and the LDKT and DDKT subgroups. In multivariate analysis, low-DSA was identified as a risk factor for ABMR development. Its impact was more pronounced in DDKT (odds ratio [OR]: 9.60, 95% confidence interval [CI]: 1.79-51.56) than in LDKT (OR: 3.76, 95% CI: 0.99-14.26) recipients. There were no significant differences in other outcomes according to pretransplant low-DSA.

Conclusions

Pretransplant low-DSA has a significant impact on the development of ABMR, and more so in DDKT recipients than in LDKT recipients, but not on long-term outcomes.

EDTA Treatment for Overcoming the Prozone Effect and for Predicting C1q Binding in HLA Antibody Testing

The Luminex-based single antigen bead (SAB) assay is widely used to detect HLA antibody in transplant recipients. However, one limitation of the SAB assay is the prozone effect, which occurs mostly as a result of complement interference. We investigated the efficacy of EDTA treatment for overcoming the prozone effect and predicting C1q binding of HLA antibody. We subjected 27 non-treated (naïve) and EDTA-treated serum samples from highly sensitized patients to IgG-SAB assays, and we confirmed the prozone effect in 53% and 31% of class I and class II antibody tests, respectively, after EDTA treatment. When we conducted additional assays after dithiothreitol treatment and serum dilution, EDTA was the most efficacious in eliminating the prozone effect. Reducing the prozone effect by EDTA treatment strengthened the correlation between IgG mean fluorescence intensity (MFI) and C1q MFI values (ρ=0.825) as compared with the naïve sera (ρ=0.068). Although C1q positivity was dependent on the concentration of HLA antibody in EDTA-treated sera, the correlations varied individually. Overall, our results confirmed the efficacy of EDTA treatment for overcoming the prozone effect. EDTA treatment showed a positive effect on the correlation between IgG MFI and C1q MFI values.

Predicting Humoral Alloimmunity from Differences in Donor and Recipient HLA Surface Electrostatic Potential

In transplantation, development of humoral alloimmunity against donor HLA is a major cause of organ transplant failure, but our ability to assess the immunological risk associated with a potential donor–recipient HLA combination is limited. We hypothesized that the capacity of donor HLA to induce a specific alloantibody response depends on their structural and physicochemical dissimilarity compared with recipient HLA. To test this hypothesis, we first developed a novel computational scoring system that enables quantitative assessment of surface electrostatic potential differences between donor and recipient HLA molecules at the tertiary structure level [three-dimensional electrostatic mismatch score (EMS-3D)]. We then examined humoral alloimmune responses in healthy females subjected to a standardized injection of donor lymphocytes from their male partner. This analysis showed a strong association between the EMS-3D of donor HLA and donor-specific alloantibody development; this relationship was strongest for HLA-DQ alloantigens. In the clinical transplantation setting, the immunogenic potential of HLA-DRB1 and -DQ mismatches expressed on donor kidneys, as assessed by their EMS-3D, was an independent predictor of development of donor-specific alloantibody after graft failure. Collectively, these findings demonstrate the translational potential of our approach to improve immunological risk assessment and to decrease the burden of humoral alloimmunity in organ transplantation.

Soluble CD30, Acute Rejection, and Graft Survival: Pre- and 6-Month Post-Transplant Determinations-When Is the Best Time to Measure?

BACKGROUND

Pretransplantation soluble CD30 (sCD30) has been shown to be a good predictor of acute rejection (AR) and graft loss. This study aimed to evaluate the effectiveness of sCD30 measured pretransplant and up to 6 months after transplantation as a predictor of AR, graft loss, and survival at 5 years post-transplantation. Subjects were patients receiving living donor renal transplants at Bonsucesso Federal Hospital (Rio de Janeiro) in 2006 and between August 2010 and May 2011.

METHODS

sCD30 was analyzed in samples collected pretransplantation and 7, 14, and 21, 28 days and 3, 4, 5, and 6 months post-transplantation from 73 kidney recipients.

RESULTS

Patients in the AR group did not present a positive correlation with the sCD30 levels pretransplant (P = .54); in the post-transplant period, the 7- to 14-day samples showed patients with AR had higher levels of this biomarker (P = .036). The graft survival in 5 years of follow-up was not different between groups.

CONCLUSIONS

The best time to predict AR using sCD30 is the 7- to 14-day sample; however, identifying and following the decrease of this biomarker from pre- to post-transplant seems to be better than just 1 measurement. The sCD30 post-transplant is another tool that may be used in monitoring patients after renal transplantation.

Successful Renal Transplantation between Identical Twins with Very Brief Immunosuppression

Renal transplantation between monozygous identical twins provides an opportunity to utilize minimal immunosuppression to maintain stable allograft function, thereby alleviating the toxicities of immunosuppressive therapy. Despite monozygosity, there is a possibility of discordant protein presentation in identical twins that could trigger alloimmune response and lead to graft injury. Therefore, the optimal immunosuppression regimen in this patient population is unknown, and the safety of immunosuppression withdrawal remains controversial. Herein, we describe two patients who underwent successful renal transplantation from monozygotic identical twin donors. Monozygosity was determined using short tandem repeat (STR) analysis. All immunosuppression was successfully discontinued at 2 days and 3 weeks, respectively, after transplantation. Both patients are alive with functioning renal grafts at 1 year and 5 years after transplant, respectively. These two cases suggest that immunosuppression can be withdrawn safely and rapidly in select monozygous identical twin renal transplant recipients.

Characteristics of Donor-Specific Antibodies Associated With Antibody-Mediated Rejection in Lung Transplantation

Although donor-specific anti-human leukocyte antigen (HLA) antibodies (DSAs) are frequently found in recipients after lung transplantation (LT), the characteristics of DSA which influence antibody-mediated rejection (AMR) in LT are not fully defined. We retrospectively analyzed 206 consecutive LT patients of our center (2010–2013). DSAs were detected by using luminex single antigen beads assay and mean fluorescence intensity was assessed. Within the study population, 105 patients had positive DSA. Patients with and without AMR (AMR^Pos, n = 22, and AMR^Neg, n = 83, respectively) were compared. AMR^Pos patients had significantly greater frequencies of anti-HLA DQ DSA (DQ DSA) than AMR^Neg patients (95 vs 58%, respectively, p < 0.0001). Compared to AMR^Neg patients, AMR^Pos patients had higher DQ DSA sum MFI [7,332 (2,067–10,213) vs 681 (0–1,887), p < 0.0001]. DQ DSA when associated with AMR, had more frequent graft loss and chronic lung allograft dysfunction (CLAD). These data suggest (i) that DSA characteristics clearly differ between AMR^Pos and AMR^Neg patients and (ii) the deleterious impact of DQ DSA on clinical outcome.

Impact of preformed donor-specific antibodies against HLA class I on kidney graft outcomes: Comparative analysis of exclusively anti-Cw vs anti-A and/or -B antibodies

AIM

To analyze the clinical impact of preformed antiHLA-Cw vs antiHLA-A and/or -B donor-specific antibodies (DSA) in kidney transplantation.

METHODS

Retrospective study, comparing 12 patients transplanted with DSA exclusively antiHLA-Cw with 23 patients with preformed DSA antiHLA-A and/or B.

RESULTS

One year after transplantation there were no differences in terms of acute rejection between the two groups (3 and 6 cases, respectively in the DSA-Cw and the DSA-A-B groups; P = 1). At one year, eGFR was not significantly different between groups (median 59 mL/min in DSA-Cw group, compared to median 51 mL/min in DSA-A-B group, P = 0.192). Moreover, kidney graft survival was similar between groups at 5-years (100% in DSA-Cw group vs 91% in DSA-A-B group, P = 0.528). The sole independent predictor of antibody mediated rejection (AMR) incidence was DSA strength (HR = 1.07 per 1000 increase in MFI, P = 0.034). AMR was associated with shortened graft survival at 5-years, with 75% and 100% grafts surviving in patients with or without AMR, respectively (Log-rank P = 0.005).

CONCLUSION

Our data indicate that DSA-Cw are associated with an identical risk of AMR and impact on graft function in comparison with “classical” class I DSA.

Antibody-Dependent NK Cell Activation Is Associated with Late Kidney Allograft Dysfunction and the Complement-Independent Alloreactive Potential of Donor-Specific Antibodies

Although kidney transplantation remains the best treatment for end-stage renal failure, it is limited by chronic humoral aggression of the graft vasculature by donor-specific antibodies (DSAs). The complement-independent mechanisms that lead to the antibody-mediated rejection (ABMR) of kidney allografts remain poorly understood. Increasing lines of evidence have revealed the relevance of natural killer (NK) cells as innate immune effectors of antibody-dependent cellular cytotoxicity (ADCC), but few studies have investigated their alloreactive potential in the context of solid organ transplantation. Our study aimed to investigate the potential contribution of the antibody-dependent alloreactive function of NK cells to kidney graft dysfunction. We first conducted an observational study to investigate whether the cytotoxic function of NK cells is associated with chronic allograft dysfunction. The NK-Cellular Humoral Activation Test (NK-CHAT) was designed to evaluate the recipient and antibody-dependent reactivity of NK cells against allogeneic target cells. The release of CD107a/Lamp1⁺ cytotoxic granules, resulting from the recognition of rituximab-coated B cells by NK cells, was analyzed in 148 kidney transplant recipients (KTRs, mean graft duration: 6.2 years). Enhanced ADCC responsiveness was associated with reduced graft function and identified as an independent risk factor predicting a decline in the estimated glomerular filtration rate over a 1-year period (hazard ratio: 2.83). In a second approach, we used the NK-CHAT to reveal the cytotoxic potential of circulating alloantibodies in vitro. The level of CD16 engagement resulting from the in vitro recognition of serum-coated allogeneic B cells or splenic cells was further identified as a specific marker of DSA-induced ADCC. The NK-CHAT scoring of sera obtained from 40 patients at the time of transplant biopsy was associated with ABMR diagnosis. Our findings indicate that despite the administration of immunosuppressive treatments, robust ADCC responsiveness can be maintained in some KTRs. Because it evaluates both the Fab recognition of alloantigens and Fc-driven NK cell activation, the NK-CHAT represents a potentially valuable tool for the non-invasive and individualized evaluation of humoral risk during transplantation.

The relative benefits and costs of solid phase bead technology to detect preformed donor specific antihuman leukocyte antigen antibodies in determining suitability for kidney transplantation

BACKGROUND

Screening for donor-specific anti-HLA antibodies (DSA) using bead-based multiplex assays to determine transplant suitability is standard practice in many countries. We compared the health benefits and costs of screening preformed DSA using bead-based assay as an add-on test to complement-dependent cytotoxicity (CDC) crossmatch with CDC crossmatch alone, and determined the optimal threshold to determine transplant suitability.

METHODS

Three probabilistic Markov models were developed to compare bead-based assay with CDC and CDC alone. The model assumed a hypothetical cohort of 10,000 patients who received only a single kidney transplant and terminated when all patients were deceased.

RESULTS

Assuming transplantation was permitted for recipients with no DSA or with a DSA mean fluorescence intensity (MFI) value of 500 or less, screening by bead-based assay and CDC saved 6.5 grafts and U.S. $1,192,303 per 100 transplants compared with CDC alone. If the thresholds were increased to an MFI of 2000 or less and 5000 or less, an extra 6.4 and 6.1 grafts would be saved, with cost savings of U.S. $867,203 and U.S. $830,664 per 100 transplants compared with CDC alone. The total number of kidney transplants performed would have increased by 8 and 9, respectively, but at the expense of an extra 0.1 and 0.4 graft lost per 100 transplants after 5 years.

CONCLUSIONS

Screening using bead-based assay is cost-saving and improves graft outcomes. The greatest benefits and cost-savings are achieved if transplantation occurs at a threshold of MFI of 500 or less or in those without preformed DSA. Increasing the threshold to an MFI of 2000 or less may provide an acceptable balance for improving transplant eligibility without compromising longer-term outcomes.

Analysis of preformed donor-specific anti-HLA antibodies characteristics for prediction of antibody-mediated rejection in kidney transplantation

BACKGROUND

The relevance of preformed donor specific antibodies (DSA) detected by Luminex assays, with a negative complement-dependent cytotoxicity (CDC) crossmatch, remains unsettled in kidney transplantation (KT). We aimed to analyze the impact of preformed DSA characteristics on kidney graft outcomes.

METHODS

In 462 patients that received a kidney graft in our unit, between 2007 and 2012, pre-transplant sera were analyzed by Luminex screening assay to determine the presence of anti-human leukocyte antigen (HLA) antibodies and single-antigen bead assay [positive if mean fluorescence intensity (MFI) ≥ 1000] to assign anti-HLA specificities.

RESULTS

Anti-HLA antibodies were present in 95 patients (20.6%), but only 40 (8.7%) had DSA. Antibody-mediated rejection (AMR) at 1-year was higher in patients with DSA (35.0%) than in those without them (0.9%) (P < 0.001). Only DSA with a MFI of >3000 were significantly associated with AMR occurrence. Receiver operator curves revealed that a MFI of >4900 in the highest DSA bead had a high sensitivity (85.7%) and that the sum of all DSA beads MFI > 11,000 had a high specificity (92.3%) for AMR prediction. Anti-thymocyte globulin versus basiliximab induction was more frequent in DSA+ AMR- (65.4%) versus DSA+ AMR+ (34.6%) patients (P = 0.072). Five-year censored graft survival was lower in DSA+ than in DSA- patients (respectively, 84.8% versus 94.9%, P = 0.006), although survival was only reduced in DSA+ AMR+ (68.8%) versus DSA+ AMR- (96.0%) patients (P = 0.038).

CONCLUSIONS

Preformed DSA is associated with kidney graft loss, in relation with AMR occurrence. DSA strength may be used to improve immunological risk stratification of sensitized patients and their clinical management.

Methodological aspects of anti-human leukocyte antigen antibody analysis in solid organ transplantation

Donor human leukocyte antigen (HLA)-specific antibodies (DSA) play an important role in solid organ transplantation. Preexisting IgG isotype DSA are considered a risk factor for antibody mediated rejection, graft failure or graft loss. The post-transplant development of DSA depends on multiple factors including immunogenicity of mismatched antigens, HLA class II typing of the recipient, cytokine gene polymorphisms, and cellular immunoregulatory mechanisms. De novo developed antibodies require special attention because not all DSA have equal clinical significance. Therefore, it is important for transplant clinicians and transplant immunologists to accurately characterize DSA. In this review, the contemporary immunological techniques for detection and characterization of anti-HLA antibodies and their pitfalls are described.

Impact of flow cytometry crossmatch B-cell positivity on living renal transplantation

BACKGROUND

Various studies have reported poorer graft survival among individuals displaying T-cell-positive flow cytometry crossmatches (FCXM). Good outcomes have been observed in immunologically high-risk patients with the use of rituximab, plasmapheresis, and γ-globulin. Because the relevance of FCXM B-cell-positivity (BCXM (+)) alone remains controversial, we examined its impact on living donor renal transplantations.

PATIENTS AND METHODS

We retrospectively studied 146 adult renal transplantation recipients from April 2007 to June 2012, dividing the patients into BCXM (+) (n = 31) versus BCXM (-) recipients (n = 115). We examined patient and graft survivals as well as rejection rates at 0 to 3, 3 to 12, and 12 to 24 months. We also determined the incidence of infectious diseases. We performed stepwise multivariate regression to identify risk factors contributing rejection episodes.

RESULTS

One-year patient and graft survivals were 100% in both groups. The BCXM (-) group have a 16.8% rejection probability whereas the BCXM (+) group, 33.2% (P = .201). There were no significantly differences in the incidence of infectious diseases. Only the rate of a sensitizing history was an independent risk factor for a rejection episode.

CONCLUSION

BCXM (+) showed only a tendency but not a significant impact on rejection episodes compared with BCXM (-); short-term graft survivals were similar.

Algorithm to manage highly sensitized kidney transplant recipients in Poland

OBJECTIVE

Programs for immunized transplant recipients are essential to achieve graft survivals comparable to those of non-immunized recipients. The threshold in Poland is a PRA by the complement-dependent cytotoxicity (CDC) method greater than 50%, which includes approximately 3.8% of the patients. At the same time the United Network for Organ Sharing there recipients represent approximately 16% of the waiting list in the United Network for Organ Sharing (UNOS). The underestimation of the immunized group in Poland may be due to differences in laboratory techniques to assess alloantibodies.

MATERIALS AND METHODS

This study investigated 55 potential recipients with a PRA by CDC>50%. We used the following algorithm to assess their immunization: Luminex screening test for an HLA antibody; specificity assessed with Luminex Single Antigen, vPRA (evaluation of immunization of the patient); and analysis of acceptable HLA incompatibilities (HLAMatchmaker).

RESULTS

All recipients were positive class I anti-HLA antibodies and 94.5% were positive for class II. For the groups of subjects with PRA-CDC from 50% to 79% versus those greater than 80%, the average values of PRA-CDC were 62.2% and 89.5%, respectively. The virtual PRA results for these groups were 95.7% and 97.2%, respectively. In addition, anti-HLA-Cw, anti-DQ and anti-DP antibodies were detected in 77%, 84%, and 51% of recipients, respectively. Immunized recipients reported to the next transplant were characterized by the antibodies against mismatch only in 68%. For all potential recipients, additional acceptable non-compliance was determined with HLAMatchmaker: 152 specificity for locus A and 252 for locus B.

CONCLUSIONS

Evaluation of immunization status of recipient candidates should be routinely performed using tests to assess class and specificity as well as level of alloantibodies to enable determination of a safe potential donor. As a routine test, PRA-CDC underestimates the number of highly immunized patients. Exclusion from the list of patients with repeated non-compliance is a simplification, which reduces their chance for transplantation.

Steroid-resistant acute allograft rejection in renal transplantation

Steroid-resistant rejection after pediatric renal transplantation forms a rare but severe complication with a guarded prognosis particularly if this occurs late after transplantation. There is a paucity of data on how to manage these challenging rejection episodes, particularly in the pediatric literature. Mohan Shenoy et al. published a case series of 15 patients who were treated with anti-thymocyte globulin for steroid-resistant acute allograft rejection over a 15-year period in a single center in this issue of Pediatric Nephrology. While the results for the early rejection group were encouraging, the results in the eight patients with late rejection episodes after transplantation were unfavorable and afflicted with a high incidence of side-effects. Important diagnostic tools such as C4d staining of the renal transplant biopsy and the measurement of donor-specific antibodies were underutilized. The editorial reviews the importance of the differentiation between humoral and cellular rejection and the challenges of treating late antibody-mediated acute rejection in these patients. A multi-center approach is required to establish a registry of these events and ideally prospective randomized interventions should be designed to provide some evidence base for the management of this challenging complication after pediatric renal transplantation.