Risk of antibody-mediated rejection in kidney transplant recipients with anti-HLA-C donor-specific antibodies

Impact of Preformed Donor-Specific Anti-HLA-Cw and Anti-HLA-DP Antibodies on Acute Antibody-Mediated Rejection in Kidney Transplantation

Given the risk of rejection, the presence of preformed donor specific antibodies (DSA) contraindicates transplantation in most allocation systems. However, HLA-Cw and -DP DSA escape this censorship. We performed a multicentric observational study, in which the objective was to determinate risk factors of acute antibody-mediated rejection (aABMR) in recipients transplanted with preformed isolated Cw- or DP-DSA. Between 2010 and 2019, 183 patients were transplanted with a preformed isolated Cw- or DP-DSA (92 Cw-DSA; 91 DP-DSA). At 2 years, the incidence of aABMR was 12% in the Cw-DSA group, versus 28% in the DP-DSA group. Using multivariable Cox regression model, the presence of a preformed DP-DSA was associated with an increased risk of aABMR (HR = 2.32 [1.21-4.45 (p = 0.001)]) compared with Cw-DSA. We also observed a significant association between the DSA's MFI on the day of transplant and the risk of aABMR (HR = 1.09 [1.08-1.18], p = 0.032), whatever the DSA was. Interaction term analysis found an increased risk of aABMR in the DP-DSA group compared with Cw-DSA, but only for MFI below 3,000. These results may plead for taking these antibodies into account in the allocation algorithms, in the same way as other DSA.

Fc Receptor-Like Gene Expression in Renal Transplantation Patients

Background:

It has been well-documented that the Fc receptor-like (FCRL) molecule contributes to the pathogenesis of certain autoimmune disorders. FCRL molecules belong to the immunoglobulin superfamily produced by B cells. Also, these molecules induce activating or inhibitory signals of B cells. According to this information and also considering the critical role of immune reactions in organ transplantation, the following experiment was performed to analyze the gene expression level of FCRLs in peripheral blood mononuclear cells of kidney transplant recipients.

Materials and Methods:

Blood samples were obtained from 32 renal transplant patients on days 1, 3, and 7 post-transplantations. Patients were divided into two groups according to the presence or absence of rejection. Also, 24 age-matched healthy subjects were enrolled as control group. After total RNA extraction from peripheral blood mononuclear cells (PBMC) and cDNA synthesis, the gene expression levels of FCRL1, FCRL2, and FCRL4 in each group were measured by real-time polymerase chain reaction.

Results:

Our results showed that FCRL1 expression levels in kidney transplant patients were significantly less than healthy controls. The overall FCRL2 expression level was not significantly different between them. However, at days 1 and 7, following transplantation in the non-rejected group FCRL2 level was significantly higher than the control group. Comparing the FCRL4 gene expression levels of both groups with healthy controls showed a significant decrease in the third and seventh days post-transplantation.

Conclusion:

It can be concluded that mononuclear cells, mainly B cells, have an essential role to play in kidney transplantation.

Histologic Antibody-Mediated Kidney Allograft Rejection in the Absence of Donor Specific HLA Antibodies

Histologic antibody-mediated rejection (hAMR) is defined as a kidney allograft biopsy satisfying the first 2 Banff criteria for diagnosing antibody-mediated rejection (AMR): tissue injury and evidence of current/recent antibody interaction with the endothelium. In approximately one-half of such cases, circulating HLA donor specific antibodies (DSA) are not detectable by current methodology at the time of biopsy. Some studies indicated a better prognosis for HLA-DSA-negative cases of hAMR compared to those with detectable HLA-DSA, whereas others found equally poor survival compared to hAMR-negative cases. We reviewed the literature regarding the pathophysiology of HLA-DSA-negative hAMR. We find 3 nonmutually exclusive possibilities: 1) HLA-DSA are involved, but just not detected; 2) non-HLA DSA (allo- or autoantibodies) are pathogenically involved; and/or 3) antibody-independent NK cell activation is mediating the process through "missing self" or other activating mechanisms. These possibilities are discussed in detail. Recommendations regarding the approach to such patients are made. Clearly, more research is necessary regarding the measurement of non-HLA antibodies, recipient/donor NK cell genotyping, and the use of antibody reduction therapy or other immunosuppression in any subset of patients with HLA-DSA-negative hAMR.

Clinical relevance of donor-specific antibodies directed at HLA-C: A long road to acceptance

In solid organ transplantation (SOT), the clinical relevance of donor-specific antibodies (DSA) directed at anti-HLA-A, -B, -DR and -DQ antigens is largely recognized while it is still a matter of debate for DSA directed at HLA-C. In this review, we summarize the peculiarities of HLA-C among class I HLA antigens as well as their immunogenicity, which underlie the clinical relevance of HLA-C locus and anti-HLA-C DSA in SOT. Many factors, both intrinsic and extrinsic to the HLA-C gene and HLA-C protein, explain its lower expression in comparison with HLA-A and -B. This lower expression can explain the apparent lower immunogenicity of HLA-C leading to a lower prevalence and strength of anti-HLA-C antibodies. Nevertheless, HLA-C antigens are truly immunogenic and preformed anti-HLA-C DSA are clinically relevant. Indeed, anti-HLA-C DSA are able to bind donor cells and to activate the complement pathway both ex vivo and in vivo. In line with this, numerous clinical studies now show that preformed DSA directed at native HLA-C molecules induce poorer graft outcomes. We then plead for the inclusion of HLA-C in all transplant allocation systems and we propose a strategy to cope with anti-HLA-C DSA in SOT. Beyond SOT, anti-HLA-C antibodies generate a growing interest in the allo-HCT, transfusion and obstetrics fields, while new concepts such as the role of the "missing-self" in solid organ rejection places HLA-C as an inescapable actor in transplant tolerance.

Reassessment of the clinical impact of preformed donor-specific anti-HLA-Cw antibodies in kidney transplantation

Anti-denatured HLA-Cw antibodies are highly prevalent, whereas anti-native HLA-Cw antibodies seem to lead to random flow cytometry crossmatch results. We aimed to reassess crossmatch prediction for anti-HLA-Cw using 2 types of single antigen flow beads (classical beads and beads with diminished expression of denatured HLA), and to compare the pathogenicity of preformed anti-denatured and anti-native HLA-Cw antibodies in kidney transplantation. We performed 135 crossmatches with sera reacting against donor HLA-Cw (classical beads fluorescence ≥500); only 20.6% were positive. Forty-three (31.6%) were anti-denatured HLA antibodies (beads with diminished expression of denatured HLA fluorescence <300); all were crossmatch negative. The correlation between classical beads fluorescence and the crossmatch ratio was low (ρ = 0.178), and slightly higher with beads with diminished expression of denatured HLA (ρ = 0.289). We studied 52 kidney recipients with preformed anti-HLA-Cw donor-specific antibodies. Those with anti-native HLA antibodies experienced more acute and chronic antibody-mediated rejections (P = .006 and .03, respectively), and displayed a lower graft survival (P = .04). Patients with anti-native HLA-Cw antibodies more frequently had previous sensitizing events (P < .000001) or plausibility of their antibody profile according to known anti-native HLA-Cw eplets (P = .0001). Anti-native but not anti-denatured HLA-Cw antibodies are deleterious, which underscores the need for reagents with diminished expression of denatured HLA.

Characteristics and predictive value for graft fibrosis of the complement-binding capacity of donor-specific human leukocyte antigen antibodies after pediatric liver transplantation

BACKGROUND

Donor-specific HLA antibodies (DSAs) have detrimental effects on short- and long-term outcomes after organ transplantation. Despite evidence that the complement-binding capacity of DSAs has predictive power in kidney transplantation, its clinical impact during long-term follow-up after LT remains unclear. In this study, we assessed the complement-binding capacities of DSAs and their association with histological findings.

METHODS

In total, 72 patients who underwent pediatric LT at our institution between July 1991 and October 2013 were retrospectively reviewed. A subgroup analysis of histological findings was performed for 37 subjects who underwent liver graft biopsy. Patients were divided into two groups based on the degree of graft fibrosis, and clinical characteristics were assessed.

RESULTS

All anti-class I DSAs were C1q-negative. Anti-DR and anti-DQ DSAs were identified in 34% and 41% of patients, respectively; however, only three of 25 patients with anti-DR DSAs exhibited a positive C1q-binding assay, whereas, 25 of 29 anti-DQ DSAs showed C1q-binding capacity. MFI values for DSA were significantly higher for patients with C1q-binding capacity than for those without (P < .0001). Complement-binding anti-DR DSA was relatively rare in both groups. Regarding anti-DQ DSA, there were no differences between fibrosis and non-fibrosis groups, irrespective of complement-binding capacity.

CONCLUSIONS

The association between anti-DR DSA and liver fibrosis, which was supported in this cohort, was not strengthened but rather impaired when accounting for complement-binding capacity due to low positive detection. Further studies of the association between complement-binding anti-DQ DSA and histological findings in LT are needed.

Comprehensive RNA-Sequencing Analysis in Peripheral Blood Cells Reveals Differential Expression Signatures with Biomarker Potential for Idiopathic Membranous Nephropathy

To date, the clinical course of idiopathic membranous nephropathy (iMN) remains unclear and lacks direct and effective diagnostic methods. To better understand the host gene expression changes involved in the iMN process and identify the potential signatures for clinical diagnosis, we performed a whole genome-wide transcriptome profile of peripheral blood cells (PBC) from patients with iMN and healthy controls (HCs). A total of 188 differentially expressed genes (DEGs) were detected in patients with iMN versus HCs. Gene ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that these DEGs were mainly correlated with protein targeting, ion homeostasis GO terms, and ribosome and phagosome pathways. The top 10 differentially expressed protein-coding genes with >2-fold changes and high expression levels were validated using quantitative real-time PCR, and showed high consistency with the high-throughput sequencing results. HLA-C, S100A8, and FTH1 genes were selected for further validation and showed the most significant difference between the iMN and HC group, indicating that they could be used as potential clinical diagnostic biomarkers. Our results provide novel potential diagnostic signatures for iMN and have important implications for better understanding the pathogenesis of iMN.

Comparison of Single Antigen Bead-Based, Cell-Based, and Solid Phase-Based Crossmatch Methods

AIM

Antibody assessment during pretransplantation term is important to detect donor specific antibodies. These donor-specific antibodies are determined by various crossmatch methods (flow cytometric [FCXM], complement-dependent cytotoxic [CDCXM], and Luminex [LMXM]). Recently, single antigen bead (SAB) assays have been used for the assessment of hypersensitized patients. The aim of this study was to compare sensitivity and specificity of the 3 crossmatch methods in reference to the SAB method.

METHOD

In this study, 69 hypersensitized patients with high class I and/or class II panel reactive antibodies were tested using the flow cytometric SAB method. Serum samples were cross-matched by 3 crossmatch methods with the cells of a volunteer healthy individual, and the results were evaluated according to HLA and cross-reactive epitope groups (CREGs).

RESULTS

Sensitivity was found to be better with T FCXM (0.91) and class I LMXM (0.87). Specificity of peripheral blood lymphocyte CDCXM method (1.0) was found to be better than the other 2 methods (0.33 and 0.57, respectively). Sensitivity of class II LMXM (0.88) was found to be better than the others (0.42 for B CDCXM and 0.82 for B FCXM, respectively). The specificity of the B CDCXM, B FCXM, and class II LMXM was similar (0.44, 0.44, and 0.33, respectively). CREGs results were similar to HLA results.

CONCLUSION

Although CDCXM has high specificity for the detection of anti-HLA antibodies, it has low sensitivity. To increase sensitivity, FCXM or LMXM methods may be used with the CDCXM test. These results will be beneficial for laboratories and clinicians during graft survival and patient health assessment.

Post-transplant donor specific antibody is associated with poor kidney transplant outcomes only when combined with both T-cell-mediated rejection and non-adherence

Post-transplant donor specific antibody (DSA) is associated with poor renal allograft outcomes. However, variable timing of DSA assessment and inclusion of patients who undergo desensitization treatments have hindered our understanding of its consequences and limited its predictive value. Here we prospectively studied non-desensitized patients to determine factors associated with poor four-year outcomes in patients who developed post-transplant DSA. Using serial monitoring, 67 of 294 patients were found to develop DSA by one year. Compared to patients who do not develop DSA, those with DSA exhibit an increased incidence of both clinical and subclinical T-cell-mediated rejection (TCMR). The combination of TCMR plus DSA led to an almost three-fold increase in graft loss compared to either DSA or TCMR alone. Moreover, DSA was associated with higher Banff grade TCMR and chronic changes at one year. Antibody-mediated rejection was uncommon and always associated with TCMR. Amongst factors independently associated with DSA plus TCMR; non-adherence is potentially modifiable. Non-adherence, measured as intra-patient variability of calcineurin trough levels during the first post-transplant year, further risk-stratified patients with DSA plus TCMR such that about 75% of these patients had impending graft loss by four years, whereas adherent patients with DSA plus TCMR had outcomes comparable to other patient groups. Thus, early post-transplant DSA, especially in non-adherent patients, is associated with increased incidence of TCMR and represents a high-risk group of patients who might benefit from targeted therapeutic interventions.

Clinical significance of donor-specific anti-HLA-DR51/52/53 antibodies for antibody-mediated rejection in kidney transplant recipients

Background

The presence of donor-specific antibodies (DSAs) to human leukocyte antigen (HLA) increases the risk of antibody-mediated rejection (ABMR) after kidney transplantation (KT). However, the clinical relevance of anti-HLA-DR51/52/53 antibodies remains unclear because of their weak antigen expression. This study evaluated the association between anti-HLA-DR51/52/53 DSAs and ABMR.

Methods

We retrospectively reviewed the single-antigen-bead panel reactive antibody (single PRA) results of 130 patients tested between August 1, 2009 and March 6, 2015, based on clinical necessity after allograft KT. Single PRA analysis was performed using Luminex assay kits (Lifecodes LSA class I and II). We reviewed the clinical course and biopsy results of patients with anti-HLA-DR51/52/53 DSAs.

Results

Post-KT DSAs were identified in 89 of the 130 patients (68.5%), with 26 of 32 class I DSAs and 63 of 66 class II DSAs being immunodominant DSAs. Thirteen patients had anti-HLA-DR51/52/53 DSAs. Three patients with anti-HLA-DR51/52/53 immunodominant DSAs alone were diagnosed with biopsy-proven ABMR. One patient who developed anti-HLA-DR DSA 13 days after KT showed a rapid increase in anti-HLA-DR51 DSA and had biopsy-proven ABMR.

Conclusions

Although the expression of the HLA-DR51/52/53 antigen was weak, anti-HLA-DR51/52/53 DSAs might be correlated with biopsy-proven ABMR. Therefore, anti-HLA-DR51/52/53 DSAs must be evaluated as a cause of ABMR after transplantation.

Association of post-transplant donor-specific HLA antibody with liver graft fibrosis during long-term follow-up after pediatric liver transplantation

The aim of this study was to evaluate the significance of post-transplant DSA as a predictor of liver fibrosis during long-term follow-up after pediatric LT. We evaluated the histological findings in 18 LT recipients who underwent liver biopsy after DSA screening. Liver fibrosis was scored based on the METAVIR fibrosis staging. Patients were divided into 2 groups based on histological findings, and clinical characteristics among patients with liver fibrosis were assessed. Of 18 patients, 7 were included in the fibrosis group. No significant between-group differences were found regarding peritransplant characteristics, including age, sex, primary disease, ABO incompatibility, and immunosuppressive regimen. Episodes of acute rejection and non-adherence to immunosuppressive drugs were comparable between both groups. The MFI for anti-DR DSA and positive rate were significantly higher in the fibrosis group (1655 vs 216; P = .019, 86% vs 27%; P = .012, respectively). MFI for anti-DQ DSA was higher in the fibrosis group, but non-significantly (2052 vs 384; P = .46). Post-transplant anti-DR DSA is associated with graft fibrosis during long-term follow-up. This finding seems useful for the implementation of valid histological examinations of liver grafts for patients with higher MFI, especially for anti-DR DSA, after pediatric LT.

HLA Epitope Matching in Kidney Transplantation: An Overview for the General Nephrologist

Rapid changes in tissue-typing technology, including the widespread availability of highly specific molecular typing methods and solid-phase assays for the detection of allele-specific anti-HLA antibodies, make it increasingly challenging to remain up to date with developments in organ matching. Terms such as epitopes and eplets abound in the transplantation literature, but often it can be difficult to see what they might mean for the patient awaiting transplantation. In this review, we provide the historical context for current practice in tissue typing and explore the potential role of HLA epitopes in kidney transplantation. Despite impressive gains in preventing and managing T-cell-mediated rejection and the associated improvements in graft survival, the challenge of the humoral alloresponse remains largely unmet and is the major cause of late graft loss. Describing HLA antigens as a series of antibody targets, or epitopes, rather than based on broad seroreactivity patterns or precise amino acid sequences may provide a more practical and clinically relevant system to help avoid antibody-mediated rejection, reduce sensitization, and select the most appropriate organs in the setting of pre-existing alloantibodies. We explain the systems proposed to define HLA epitopes, summarize the evidence to date for their role in transplantation, and explore the potential benefits of incorporating HLA epitopes into clinical practice as this field continues to evolve toward everyday practice.

Clinically relevant interpretation of solid phase assays for HLA antibody

Purpose of review

Accurate and timely detection and characterization of human leukocyte antigen (HLA) antibodies are critical for pre-transplant and post-transplant immunological risk assessment. Solid phase immunoassays have provided increased sensitivity and specificity, but test interpretation is not always straightforward. This review will discuss the result interpretation considering technical limitations; assessment of relative antibody strength; and the integration of data for risk stratification from complementary testing and the patient's immunological history.

Recent findings

Laboratory and clinical studies have provided insight into causes of test failures – false positive reactions because of antibodies to denatured HLA antigens and false negative reactions resulting from test interference and/or loss of native epitopes. Test modifications permit detection of complement-binding antibodies and determination of the IgG subclasses. The high degree of specificity of single antigen solid phase immunoassays has revealed the complexity and clinical relevance of antibodies to HLA-C, HLA-DQ, and HLA-DP antigens. Determination of antibody specificity for HLA epitopes enables identification of incompatible antigens not included in test kits.

Summary

Detection and characterization of HLA antibodies with solid phase immunoassays has led to increased understanding of the role of those antibodies in graft rejection, improved treatment of antibody-mediated rejection, and increased opportunities for transplantation. However, realization of these benefits requires careful and accurate interpretation of test results.

Prospective Analyses of Circulating B Cell Subsets in ABO-Compatible and ABO-Incompatible Kidney Transplant Recipients

Immunosuppressive strategies applied in renal transplantation traditionally focus on T cell inhibition. B cells were mainly examined in the context of antibody-mediated rejection, whereas the impact of antibody-independent B cell functions has only recently entered the field of transplantation. Similar to T cells, distinct B cell subsets can enhance or inhibit immune responses. In this study, we prospectively analyzed the evolution of B cell subsets in the peripheral blood of AB0-compatible (n = 27) and AB0-incompatible (n = 10) renal transplant recipients. Activated B cells were transiently decreased and plasmablasts were permanently decreased in patients without signs of rejection throughout the first year. In patients with histologically confirmed renal allograft rejection, activated B cells and plasmablasts were significantly elevated on day 365. Rituximab treatment in AB0-incompatible patients resulted in long-lasting B cell depletion and in a naïve phenotype of repopulating B cells 1 year following transplantation. Acute allograft rejection was correlated with an increase of activated B cells and plasmablasts and with a significant reduction of regulatory B cell subsets. Our study demonstrates the remarkable effects of standard immunosuppression on circulating B cell subsets. Furthermore, the B cell compartment was significantly altered in rejecting patients. A specific targeting of deleterious B cell subsets could be of clinical benefit in renal transplantation.

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.

De-novo donor-specific anti-HLA antibodies 30 days after lung transplantation are associated with a worse outcome

BACKGROUND

The impact of de-novo donor-specific anti-HLA antibodies (DSA) on patient and graft survival after lung transplantation remains controversial. We analyzed DSA that developed at Day 7 and Month (M) 1, M3, M6 and M12 after lung transplantation and evaluated their impact on chronic lung allograft dysfunction (CLAD) development and survival.

METHODS

One hundred thirty-four patients who underwent lung transplantation at our institution between November 2007 and August 2013 were included in this study. During the first post-transplant year, 82 (61%) patients developed de novo DSA and 52 (39%) patients did not. Three mean fluorescence intensity (MFI) intervals were used to define scores of anti-HLA antibody positivity: score 4 if MFI was 500 to 1,000; score 6 if MFI was 1,000 to 3,000; and score 8 if MFI was ≥3,000. Patients' records were retrospectively reviewed.

RESULTS

DSA with MFI scores of ≥4 (hazard ratio [HR] 2.21, 95% confidence interval [CI] 1.08 to 4.54, p = 0.03), 6 (HR 2.63, 95% CI 1.27 to 5.20, p < 0.01) and 8 (HR 2.83, 95% CI 1.42 to 5.67, p < 0.01) at M1; female gender (HR 0.49, 95% CI 0.28 to 0.87, P = 0.01); and with post-operative extracorporeal membrane oxygenation (HR 0.09, 95% CI 0.01 to 0.28, p = 0.02) were significantly associated with CLAD. Multivariate analysis identified score 8 at M1 (HR 2.71, 95% CI 1.34 to 5.47, p < 0.01) as an independent risk factor for mortality. Overall, 1-, 3- and 5-year survival rates were 76%, 52% and 41% compared with 84%, 74% and 70% for patients with or without de-novo DSA at M1, respectively (p = 0.02).

CONCLUSION

Early de-novo DSA may significantly impact long-term outcomes after lung transplantation and should therefore prompt regular screening.

[New aspects of HLA compatibility in organ transplantation]

In organ transplantation, HLA compatibility between a donor and a recipient is currently assessed through the comparison of their HLA antigens and the sole count of incompatible HLA antigens. Similarly, antibodies were originally described as antigenic-specific. With solid phase assays detection of anti-HLA antibodies and crystallographic studies, it is now recognized that anti-HLA antibodies are not specific for antigens, but for epitopes, i.e. short polymorphic sequences of amino acids that are more often in positions accessible to allo-antibodies. These epitopes, due to the distribution of HLA molecules polymorphism, may be shared by different HLA antigens. This explains why an immunization towards a given HLA antigen can lead to synthesis of antibodies reactive towards other antigens sharing one or more epitopes. Similarly, structural comparison of the HLA molecules of a recipient and his donor defines the epitope load, i.e. the number of incompatible epitopes. This epitope load is correlated with the risk of developing antibodies specific for the donor after transplantation. New tools, such as the HLAMatchmaker software, allow to determine the epitopic load and to analyze the epitopic specificity of alloantibodies. These tools will possibly lead to rethink the method of graft allocation, or at least to take differently into account HLA compatibility in allocation algorythms.

Clinical relevance of circulating antibodies and B lymphocyte markers in allograft rejection

The main challenge in solid organ transplantation remains to tackle antibody-mediated rejection. Our understanding of the antibody-mediated response and the capacity to detect it has improved in the last decade. However, the sensitivity and specificity of the current clinical tools to monitor B cell activation are perfectible. New strategies, including the refinement in the characterization of HLA and non-HLA antibodies, as well as a better understanding of the circulating B cell phenotype will hopefully help to non-invasively identify patients at risk or undergoing antibody-mediated allograft damage. The current review discusses the current knowledge of the B cell biomarkers in solid organ transplantation, with a focus on circulating antibodies and peripheral B cells.

Allele and Haplotype Frequencies of Human Leukocyte Antigen-A, -B, -C, -DRB1, and -DQB1 From Sequence-Based DNA Typing Data in Koreans

Background

Data on allele frequencies (AFs) and haplotype frequencies (HFs) of HLA-C and -DQB1 are limited in Koreans. We investigated AFs and HFs of HLA-A, -B, -C, -DRB1, and -DQB1 in Koreans by high-resolution sequence-based typing (SBT).

Methods

Hematopoietic stem cells were obtained from 613 healthy, unrelated donors to analyze HLA-A, -B, -C, -DRB1, and -DQB1 genotypes by using AlleleSEQR HLA-A, -B, -C, -DRB1, and -DQB1 SBT kits (Abbott Molecular, USA), respectively. Alleles belonging to HLA-C*07:01/07:06 group were further discriminated by using PCR-sequence specific primer analysis. AFs and HFs were calculated by direct counting and maximum likelihood method, respectively.

Results

In all, 24 HLA-A, 46 HLA-B, 24 HLA-C, 29 HLA-DRB1, and 15 HLA-DQB1 alleles were identified. AFs and HFs of HLA-A, -B, and -DRB1 were similar to those reported previously. For the HLA-C locus, C*01:02 was the most common allele, followed by C*03:03, C*03:04, C*14:02, C*03:02, and C*07:02 (AF ≥7%). AFs of C*07:01 and C*07:06 were 0.16% and 3.18%, respectively. For the HLA-DQB1 locus, DQB1*03:01 was the most common allele, followed by DQB1*03:03, *03:02, *06:01, *05:01, *04:01, and *06:02 (AF ≥7%). AFs of DQB1*02:01 and DQB1*02:02 were 2.12% and 6.69%, respectively. HFs of A*33:03-C*07:06 and C*07:06-B*44:03 were 3.09% and 3.10%, respectively, while those of DRB1*07:01-DQB1*02:02 and DRB1*03:01-DQB1*02:01 were 6.61% and 2.04%, respectively.

Conclusions

This study reported AFs and HFs of HLA, including HLA-C and -DQB1, in Koreans by using high-resolution SBT. These data can be used to resolve ambiguous results of HLA typing for organ and hematopoietic stem cell transplantations.

7th International Immunoglobulin Conference: Transplantation

In transplantation, harnessing the immune system is essential for allograft survival and function. This session explores different aspects of the immune system during transplantation, including the effect of donor-specific anti-human leucocyte antigen (HLA) antibodies (DSAs), antibody-mediated rejection (AMR), B cell modulation and the role of immunoglobulin (Ig) therapy. It is well known that DSAs play a key role in the failure of allografts. Identifying and characterizing DSAs provides information that can aid in risk stratification of transplant recipients. The ability to bind complement provides additional information regarding the cytotoxic potential of these antibodies and can therefore potentially guide individualized treatment strategies. AMR presents as several phenotypes, which vary in severity. As such, potentially different treatment strategies are required, emphasizing the importance of accurate diagnosis. In patients with elevated anti-HLA antibodies, waiting times for a compatible organ are often prolonged. Desensitization protocols using intravenous immunoglobulin (IVIg), in combination with other therapies, have been developed to enhance the availability of compatible donors. Another important aspect of transplantation is the role of B cells. While B cells may be involved in AMR and forms of cellular rejection, there is evidence to suggest that regulatory B cells may also have a positive impact upon long-term graft survival. Hypogammaglobulinaemia (HGG) has been reported after solid organ transplantation and is associated with an increased risk of infections. Monitoring immunoglobulin G (IgG) levels post-transplantation may identify patients at risk for infections who could potentially benefit from pre-emptive treatment with IVIg.

Clinical impact of preformed donor-specific denatured class I HLA antibodies after kidney transplantation

Class I single-antigen flow beads (SAFB) carry native and denatured human leukocyte antigen (HLA) molecules. Using a cohort of 179 class I HLA-sensitized kidney recipients, we described incidence and clinical relevance of preformed denatured HLA donor-specific antibodies (DSA) using two different assays: an acid-treated SAFB assay (anti-dHLA DSA) and the iBeads assays (SAFB+/iBeads- DSA). Eighty-five class I DSA were found in 67 patients (median mean fluorescence intensity [MFI] of 1729 [range 520-13 882]). Anti-dHLA and SAFB+/iBeads- DSA represented 11% and 18% of class I DSA and were mainly low MFI DSA (500-1000 MFI). Concordance between these two assays was good (90%). None of the patients with only class I anti-dHLA DSA or only SAFB+/iBeads- DSA developed acute clinical antibody-mediated rejection in the first-year post-transplantation, and their five-yr death-censored graft survival was similar to that of patients without DSA. Moreover, all these patients displayed a negative current T-cell flow cytometry cross-match. Therefore, both anti-dHLA DSA and SAFB+/iBeads- DSA appear irrelevant, which could explain the good outcome observed in some patients with preformed class I DSA.