Donor-specific HLA Antibodies Research Articles

HLA antibody affinity determination: From HLA-specific monoclonal antibodies to donor HLA specific antibodies (DSA) in patient serum.

Organs transplanted across donor-specific HLA antibodies (DSA) are associated with a variety of clinical outcomes, including a high risk of acute kidney graft rejection. Unfortunately, the currently available assays to determine DSA characteristics are insufficient to clearly discriminate between potentially harmless and harmful DSA. To further explore the hazard potential of DSA, their concentration and binding strength to their natural target, using soluble HLA, may be informative. There are currently a number of biophysical technologies available that allow the assessment of antibody binding strength. However, these methods require prior knowledge of antibody concentrations. Our objective within this study was to develop a novel approach that combines the determination of DSA-affinity as well as DSA-concentration for patient sample evaluation within one assay. We initially tested the reproducibility of previously reported affinities of human HLA-specific monoclonal antibodies and assessed the technology-specific precision of the obtained results on multiple platforms, including surface plasmon resonance (SPR), bio-layer interferometry (BLI), Luminex (single antigen beads; SAB), and flow-induced dispersion analysis (FIDA). While the first three (solid-phase) technologies revealed comparable high binding-strengths, suggesting measurement of avidity, the latter (in-solution) approach revealed slightly lower binding-strengths, presumably indicating measurement of affinity. We believe that our newly developed in-solution FIDA-assay is particularly suitable to provide useful clinical information by not just measuring DSA-affinities in patient serum samples but simultaneously delivering a particular DSA-concentration. Here, we investigated DSA from 20 pre-transplant patients, all of whom showed negative CDC-crossmatch results with donor cells and SAB signals ranging between 571 and 14899 mean fluorescence intensity (MFI). DSA-concentrations were found in the range between 11.2 and 1223 nM (median 81.1 nM), and their measured affinities fall between 0.055 and 24.7 nM (median 5.34 nM; 449-fold difference). In 13 of 20 sera (65%), DSA accounted for more than 0.1% of total serum antibodies, and 4/20 sera (20%) revealed a proportion of DSA even higher than 1%. To conclude, this study strengthens the presumption that pre-transplant patient DSA consists of various concentrations and different net affinities. Validation of these results in a larger patient cohort with clinical outcomes will be essential in a further step to assess the clinical relevance of DSA-concentration and DSA-affinity.

Luminex Crossmatch in Kidney Transplantation.

The introduction of the Luminex Crossmatch assay (LumXm) which uses Luminex bead technology, consists of extracting the donor's Human Leukocyte Antigen (HLA) molecules from their lymphocytes, and binding them to fluorescent beads that are put in contact with recipient's serum. HLA donor-specific antibodies (DSA) are detected using a fluorescent conjugate. The goal of our study is to determine the benefits of using LumXm in a renal transplantation algorithm. We tested 78 recipients' sera using the LumXm, and the results were compared with the Luminex single antigen bead assay (SAB) for all sera, as well as the Flow Cytometry Crossmatch (FCXM) for 46 sera. We compared our results with those of SAB using 3 cutoffs, the first being the manufacturer's criteria where sensitivity and specificity were at 62.5% and 91.3% respectively for HLA class 1, and 88.5% and 50.0% respectively for HLA class 2. When using the third cutoff criteria ( ≥2 Adjusted values + MFI (Mean fluorescence intensity) >500 + Neg MFI < 500), the sensitivity increased to 69.0% for HLA class 1 and decreased to 84.0% for HLA class 2, while the specificity increased for HLA class 1 and 2. When comparing with FCXM, the 3 assays agreed in 55.8% of results for class 1 and 2 alike. However, major discrepancies were found for two groups in HLA class 1 and one in HLA class 2. The LumXm when used with other techniques to overcome its' weak points, can provide an interesting insight into the patient's HLA-DSA profile.

Local administration of mesenchymal stromal cells is safe and modulates the immune compartment in ulcerative proctitis.

Due to their immunoregulatory and tissue regenerative features, mesenchymal stromal cells (MSCs) are a promising novel tool for the management of ulcerative proctitis (UP). Here we report on a phase IIa clinical study to evaluate the impact of local MSC therapy in UP. Thirteen refractory UP patients, with endoscopic Mayo score (EMS) 2 or 3, were included. Seven patients received 20-40 x 106 allogeneic MSCs (cohort 1), while six patients received 40-80 x 106 MSCs (cohort 2). Adverse events (AEs) were assessed at baseline and week 2, 6, 12, and 24. Clinical, endoscopic, and biochemical parameters were assessed at baseline, week 2 and 6. Furthermore, we evaluated the engraftment of MSCs, presence of donor-specific human leukocyte antigen (HLA) antibodies (DSAs), and we determined the impact of MSC therapy on the local immune compartment. No serious AEs were observed. The clinical Mayo score was significantly improved at week 2 and 6, and the EMS was significantly improved at week 6, compared to baseline. At week 6, donor MSCs were still detectable in rectum biopsies of 4/9 patients and DSAs against both HLA-class I and -class II were found. Mass cytometry showed a reduction of activated CD8+ T cells and CD16+ monocytes and an enrichment in mononuclear phagocytes and natural killer cells in biopsies after local MSC therapy. Local administration of allogeneic MSCs is safe, tolerable, and feasible for treatment of refractory UP and shows encouraging signs of clinical efficacy and modulation of local immune responses. This sets the stage for larger clinical trials. clinicaltrialsregister.eu, EudraCT: 2017-003524-75, Dutch Trial register: NTR7205. ECCO grant 2020.

Association Between Severe SARS-CoV-2 Infection and De Novo HLA Donor Specific Antibody Production in Lung Transplant Recipients: Single-center study

The COVID-19 pandemic has led to significant morbidity and mortality in lung transplant recipients (LTR). Respiratory viral infections may be associated with de-novo HLA donor-specific antibody (DSA) production and impact lung transplant outcome. Since one of the immunomodulation strategies post-SARS-CoV-2 infection in LTR include decreasing or holding anti-metabolites, concerns have been raised for higher incidence of de-novo DSA production in LTR. We performed a retrospective chart review of 80 consecutive LTR diagnosed with COVID-19 to investigate this concern. COVID-19 disease severity was divided into 3 groups: mild, moderate, and severe. Mild disease was defined as patients with COVID-19 diagnosis who were stable enough to be treated as out-patients. Moderate disease was defined as patients who required admission to the hospital and were on less than 10 liters of oxygen at rest. Severe disease was identified as patients who required hospitalization and were on more than 10 liters of oxygen with or without mechanical ventilation or extra corporal membrane oxygenation (ECMO). Groups were compared using the Kruskal-Wallis test. A total of 23, 47, and 10 LTR were diagnosed with mild, moderate, and severe COVID-19 respectively. De-novo HLA DSAwere detected in 0/23 (0%), 3/47 (6.3%), and 4/10 (40%) LTR with mild, moderate, and severe COVID-19 respectively (p = 0.0007) within 6 months post-COVID-19 diagnosis. Severe COVID-19 may be associated with increased risk of de novo HLA DSA production resulting in allograft dysfunction.

Case Report: Suspected Hyperacute Rejection During Living Kidney Transplantation

We report a case of suspected hyperacute rejection during living kidney transplantation. A 61-year-old man underwent kidney transplantation in November 2019. Before the transplantation, immunologic tests revealed the presence of anti-HLA antibodies but not donor-specific HLA antibodies. The patient was intravenously administered 500 mg of methylprednisolone (MP) and basiliximab before perioperative blood flow reperfusion. After blood flow restoration, the transplanted kidney turned bright red and then blue. Hyperacute rejection was suspected. After the intravenous administration of 500 mg of MP and 30 g of intravenous immunoglobulin, the transplanted kidney gradually changed from blue to bright red. The initial postoperative urine output was good. On the 22nd day after the renal transplantation, the patient was discharged with a serum creatinine level of 2.38 mg/dL, and the function of the transplanted kidney gradually improved. In this study, non-HLA antibodies may have been a cause of the hyperacute rejection, which was managed with additional perioperative therapies.

New insights into maladaptive vascular responses to donor specific HLA antibodies in organ transplantation.

Transplant vasculopathy (TV) causes thickening of donor blood vessels in transplanted organs, and is a significant cause of graft loss and mortality in allograft recipients. It is known that patients with repeated acute rejection and/or donor specific antibodies are predisposed to TV. Nevertheless, the exact molecular mechanisms by which alloimmune injury culminates in this disease have not been fully delineated. As a result of this incomplete knowledge, there is currently a lack of effective therapies for this disease. The immediate intracellular signaling and the acute effects elicited by anti-donor HLA antibodies are well-described and continuing to be revealed in deeper detail. Further, advances in rejection diagnostics, including intragraft gene expression, provide clues to the inflammatory changes within allografts. However, mechanisms linking these events with long-term outcomes, particularly the maladaptive vascular remodeling seen in transplant vasculopathy, are still being delineated. New evidence demonstrates alterations in non-coding RNA profiles and the occurrence of endothelial to mesenchymal transition (EndMT) during acute antibody-mediated graft injury. EndMT is also readily apparent in numerous settings of non-transplant intimal hyperplasia, and lessons can be learned from advances in those fields. This review will provide an update on these recent developments and remaining questions in our understanding of HLA antibody-induced vascular damage, framed within a broader consideration of manifestations and implications across transplanted organ types.

The Influence of Antibodies against Angiotensin II Type-1 Receptor on the Outcome of Kidney Transplantation: A Single-Center Retrospective Study.

Allo- and autoimmune mechanisms are involved in kidney allograft rejection and loss. This study investigates the impact of anti-angiotensin II type-1 receptor antibodies (anti-AT1RAbs) detected alone or in association with HLA donor-specific antibodies (HLA-DSAs) on the outcome of kidney transplantation (KTx). Anti-AT1RAbs and HLA-DSAs were detected in 71 kidney transplant (KT) recipients who developed biopsy-proven acute or chronic active T-cell rejection (TCMR) (n = 51) or antibody-mediated rejection (ABMR) (n = 20), forming the rejection group (RG). The control group (CG) included 71 KTx recipients with comparable characteristics without rejection. All patients had been transplanted with negative T/B flow crossmatch (T/BFCXM). The median follow-up period was 3.7 years. Antibodies were determined pre- and periodically post-KTx by Luminex method for HLA-DSAs and enzyme-linked immunosorbent assay for anti-AT1RAbs. Before KTx, twenty-three (32.4%) patients in the RG, sixteen with TCMR and seven with ABMR, were found anti-AT1Rabs-positive (≥10 U/mL) versus eleven (15.5%) patients in the CG (p = 0.031). Simultaneous detection of preformed anti-AT1RAbs and HLA-DSAs was found in five patients of the RG versus two of the CG (p = 0.355). At the time of transplant biopsy, fifteen (21.1%) patients, four with ABMR and eleven with TCMR, were positive for anti-AT1RAbs. Anti-AT1RAbs and HLA-DSAs were detected simultaneously in 7/15 (46.7%) cases, three with ABMR and four with TCMR. During the follow-up, thirteen (18.3%) patients in the RG, eight with ABMR and five with TCMR, lost their graft compared to one patient (1.4%) in the CG (p = 0.001). Six out of thirteen (46.2%) RG patients who lost the graft were found positive for anti-AT1RAbs pretransplant. Patient survival with functioning graft did not differ significantly between anti-AT1Rabs-positive and negative KT recipients (log-rank p = 0.88). Simultaneous detection of anti-ATR1Abs and HLA-DSAs did not have a significant influence on patient survival with functioning graft (log-rank p = 0.96). Graft function at the end of the follow-up was better, but not significantly, in anti-AT1Rabs-negative patients, with serum creatinine 1.48 [1.20-1.98] mg/dL and eGFR (CKD-EPI) 48.5 [33.5-59.0] mL/min/1.73 m2, compared to anti-AT1Rabs-positive ones who had serum creatinine 1.65 [1.24-2.02] mg/dL (p = 0.394) and eGFR (CKD-EPI) 47.0 [34.8-60.3] mL/min/1.73 m2 (p = 0.966). Anti-AT1RAbs detection pretransplant characterizes KT recipients at increased risk of cellular or antibody-mediated rejection. Furthermore, anti-AT1RAbs, detected alone or simultaneously with HLA-DSAs, appear to be associated with impaired graft function, but their role in graft survival has not been documented in this study. Screening for these antibodies appears to complement pretransplant immunological risk assessment.

Predictive value of molecular matching tools for the development of donor specific HLA-antibodies in patients undergoing lung transplantation.

Molecular matching is a new approach for virtual histocompatibility testing in organ transplantation. The aim of our study was to analyze whether the risk for de novo donor-specific HLA antibodies (dnDSA) after lung transplantation (LTX) can be predicted by molecular matching algorithms (MMA) and their combination. In this retrospective study we included 183 patients undergoing LTX at our center from 2012-2020. We monitored dnDSA development for 1 year. Eplet mismatches (epMM) using HLAMatchmaker were calculated and highly immunogenic eplets based on their ElliPro scores were identified. PIRCHE-II scores were calculated using PIRCHE-II algorithm (5- and 11-loci). We compared epMM and PIRCHE-II scores between patients with and without dnDSA using t-test and used ROC-curves to determine optimal cut-off values to categorize patients into four groups. We used logistic regression with AIC to compare the predictive value of PIRCHE-II, epMM, and their combination. In total 28.4% of patients developed dnDSA (n = 52), 12.5% class I dnDSA (n = 23), 24.6% class II dnDSA (n = 45), and 8.7% both class II and II dnDSA (n = 16). Mean epMMs (p-value = 0.005), mean highly immunogenic epMMs (p-value = 0.003), and PIRCHE-II (11-loci) (p = 0.01) were higher in patients with compared to without class II dnDSA. Patients with highly immunogenic epMMs above 30.5 and PIRCHE-II 11-loci above 560.0 were more likely to develop dnDSA (31.1% vs. 14.8%, p-value = 0.03). The logistic regression model including the grouping variable showed the best predictive value. MMA can support clinicians to identify patients at higher or lower risk for developing class II dnDSA and might be helpful tools for immunological risk assessment in LTX patients.

Molecular HLA mismatching for prediction of primary humoral alloimmunity and graft function deterioration in paediatric kidney transplantation.

Rejection remains the main cause of allograft failure in paediatric kidney transplantation and is driven by donor-recipient HLA mismatching. Modern computational algorithms enable assessment of HLA mismatch immunogenicity at the molecular level (molecular-mismatch, molMM). Whilst molMM has been shown to correlate with alloimmune outcomes, evidence demonstrating improved prediction performance against traditional antigen mismatching (antMM) is lacking. We analysed 177 patients from the CERTAIN registry (median follow-up 4.5 years). molMM scores included Amino-Acid-Mismatch-Score (AAMS), Electrostatic-Mismatch-Score (EMS3D) and netMHCIIpan (netMHC1k: peptide binding affinity ≤1000 nM; netMHC: binding affinity ≤500 nM plus rank <2%). We stratified patients into high/low-risk groups based on risk models of DSA development. Donor-specific HLA antibodies (DSA) predominantly targeted the highest scoring molMM donor antigen within each HLA locus. MolMM scores offered superior discrimination versus antMM in predicting de novo DSA for all HLA loci; the EMS3D algorithm had particularly consistent performance (area under the receiver operating characteristic curve (AUC) >0.7 for all HLA loci vs. 0.52-0.70 for antMM). ABMR (but not TCMR) was associated with HLA-DQ molMM scores (AAMS, EMS3D and netMHC). Patients with high-risk HLA-DQ molMM had increased risk of graft function deterioration (50% reduction in baseline eGFR (eGFR50), adjusted HR: 3.5, 95% CI 1.6-8.2 high vs. low EMS3D). Multivariable modelling of the eGFR50 outcome using EMS3D HLA-DQ stratification showed better discrimination (AUC EMS3D vs. antMM at 2 years: 0.81 vs. 0.77, at 4.5 years: 0.72 vs. 0.64) and stratified more patients into the low-risk group, compared to traditional antMM. Molecular mismatching was superior to antigen mismatching in predicting humoral alloimmunity. Molecular HLA-DQ mismatching appears to be a significant prognostic factor for graft function deterioration in paediatric kidney transplantation.

Estimation of Sensitization Status in Renal Transplant Recipients by Assessing Indirect Pathway CD4 + T Cell Response to Donor Cell-pulsed Dendritic Cell.

Generation of donor-specific human leukocyte antigen antibody (DSA) via indirect allorecognition is detrimental to long-term survival of transplant organs. The detection of such immune responses would make it possible to define patients with high risk of sensitization. In this study, we established a novel method for evaluating indirect allorecognition to assess sensitization in kidney transplant recipients. Recipient CD14 + monocytes were mixed with donor peripheral blood mononuclear cells; cultured in the presence of IL-4, GM-CSF, IL-1β, and TNFα; and used as pulsed dendritic cells (DCs). Cell proliferation and cytokine production were evaluated by carboxyfluorescein diacetate succinimidyl ester-based T cell proliferation assay and Enzyme-Linked ImmunoSpot assay, respectively. CD4 + T cell proliferation was strongly observed in following coculture with allogeneic antigen-pulsed DC leading to interferon-γ and IL-21 production. About 1% of CD4 + T cells exhibited Tfh-like phenotype (PD-1 high CXCR5 + ICOS + CD40L + ). Recipient DC pulsed with donor peripheral blood mononuclear cells was cocultured with recipient CD45RA+CD4+ and CD45RA-CD4+ (generally defined as naive and memory in humans, respectively) T cells. Irrespective of preformed or de novo DSA status, CD45RA + CD4 + T cells constantly produced IL-21. In contrast, IL-21-produced CD45RA - CD4 + T cells were significantly higher in preformed DSA-positive patients than those in negative patients (80.8 ± 51.2 versus 14.8 ± 20.4, P < 0.001). In de novo DSA-positive patients, IL-21-produced CD45RA - CD4 + T cells were significantly increased after transplantation compared with before transplantation (9.23 ± 9.08 versus 43.9 ± 29.1, P < 0.001). Assessment of indirect pathway CD4 + T cell response could provide new insights into the underlying mechanism of de novo DSA production, leading to the development of effective strategies against antibody-mediated rejection.

Propensity score-matched analysis of long-term outcomes for living kidney donation in alternative complement pathway diseases: a pilot study.

Atypical hemolytic syndrome (aHUS) and C3 glomerulopathy (C3G) are complement-mediated rare diseases with excessive activation of the alternative pathway. Data to guide the evaluation of living-donor candidates for aHUS and C3G are very limited. The outcomes of living donors to recipients with aHUS and C3G (Complementdisease-living donor group) were compared with a control group to improve our understanding of the clinical course and outcomes of living donation in this context. Complementdisease-living donor group [n = 28; aHUS(53.6%), C3G(46.4%)] and propensity score-matched control-living donor group (n = 28) were retrospectively identified from 4 centers (2003-2021) and followed for major cardiac events (MACE), de novo hypertension, thrombotic microangiopathy (TMA), cancer, death, estimated glomerular filtration rate (eGFR) and proteinuria after donation. None of the donors for recipients with complement-related kidney diseases experienced MACE or TMA whereas two donors in the control group developed MACE (7.1%) after 8 (IQR, 2.6-12.8) years (p = 0.15). New-onset hypertension was similar between complementdisease and control donor groups (21.4% vs 25%, respectively, p = 0.75). There were no differences between study groups regarding last eGFR and proteinuria levels (p = 0.11 and p = 0.70, respectively). One related donor for a recipient with complement-related kidney disease developed gastric cancer and another related donor developed a brain tumor and died in the 4th year after donation (2, 7.1% vs none, p = 0.15).No recipienthad donor-specific human leukocyte antigen antibodies at the time of transplantation. Median follow-up period of transplant recipients was 5years (IQR, 3-7). Eleven (39.3%) recipients [aHUS (n = 3) and C3G (n = 8)] lost their allografts during the follow-up period. Causes of allograft loss were chronic antibody-mediated rejection in 6 recipientsand recurrence of C3G in 5. Last serum creatinine and last eGFR of the remaining patients on follow up were 1.03 ± 038mg/dL and 73.2 ± 19.9m/min/1.73 m2 for aHUS patients and 1.30 ± 0.23mg/dL and 56.4 ± 5.5m/min/1.73 m2 for C3G patients. The present study highlights the importance and complexity of living related-donor kidney transplant for patients with complement-related kidney disorders and motivates the need for further research to determine the optimal risk-assessment for living donor candidates to recipients with aHUS and C3G.

Donor specific antibodies association with survival and adverse events after heart transplantation: A single center retrospective study between 2006 and 2021.

Newly detected donor HLA-specific antibodies (DSA) are historically known to be associated with reduced survival in heart transplant patients. Our objective is to clarify the modern incidence of DSA and determine its relationship with survival and MACE. This retrospective study included all patients undergoing orthotopic heart transplantation at Harefield Hospital, London between January 1, 2006 and May 31, 2021. We identified patients who developed DSA at any point post heart transplantation and its effect on survival and MACE (defined as rejection, coronary event, stroke, and arrhythmia. In total of 232 patients were included with a median follow up time of 4.7years post heart transplantation. 23.7% of patients included developed DSA post heart transplantation. There was a significantly increased risk of death in patients developing DSA versus not (sub distribution hazard ratio [SHR] 1.83, 95% confidence interval 1.03-3.24, p=.04). At the time of detection of DSA, 38.2% of the cohort had rejection necessitating treatment. A MACE event had occurred in 48.1% by 2years and 53.7% by 3years in the DSA cohort. There was a significantly increased risk of MACE in patients developing DSA versus not (SHR 2.48 [1.58-3.89, p<.0001]). This study showed an increased risk of death and MACE in patients developing DSA post heart transplantation. Further research is required into the optimal management of these patients.

Successful combined auxiliary partial liver and intestinal transplantation in two highly sensitized, cross-match positive patients.

Sensitization to human leukocyte antigen (HLA) creates an immunological barrier to intestinal transplantation (ITx). Current desensitization therapies are limited and ineffective in the most highly sensitized patients. A co-transplanted whole liver transplant can protect a kidney, heart, or intestinal allograft from antibody-mediated injury. Whether an auxiliary partial liver allograft provides effective protection for highly sensitized intestinal transplant recipients is unknown. Two patients with strong HLA donor-specific antibody at high titer against their deceased donors underwent combined auxiliary partial liver and ITx across a positive cross-match. The left lateral lobes from the combined-graft recipients and the right liver lobes from the deceased donors were transplanted as a domino procedure to other four patients. Two combined-graft recipients have had an uneventful postoperative course without major complications at a 12- and 24-month follow-up, respectively. Intestinal graft function has been excellent with no evidence of humoral or cellular rejection. While a positive cross-match turned negative, titers of donor-specific HLA antibodies gradually declined over time after transplant. The left liver lobes procured from the combined-graft recipients were successfully transplanted into two pediatric patients (age 1.9, 2.4years) and the right lobes from two deceased donors were successfully transplanted into two adult patients. All transplant procedures went well, without post-operative complications related to the splitting technique. Our results indicate that an auxiliary liver transplant can effectively protect a co-transplanted intestinal allograft against rejection and suggest that this combined procedure may serve as a useful therapeutic adjunct for a highly sensitized intestinal transplant candidate.

Microvascular inflammation in the absence of human leukocyte antigen-donor-specific antibody and C4d: An orphan category in Banff classification with cytotoxic T and natural killer cell infiltration

Isolated microvascular inflammation (iMVI) without HLA donor-specific antibodies or C4d deposition in peritubular capillaries remains an enigmatic phenotype that cannot be categorized as antibody-mediated rejection (ABMR) in recent Banff classifications. We included 221 kidney transplant recipients with biopsies with ABMR (n = 73), iMVI (n = 32), and normal (n = 116) diagnoses. We compared peripheral blood leukocyte distribution by flow cytometry and inflammatory infiltrates in kidney transplant biopsies among groups. Flow cytometry showed fewer lymphocytes and total, CD4+, and CD8+ peripheral T cells in iMVI compared with ABMR and normal cases. ABMR and iMVI had fewer total natural Killer (NK) cells but more NKG2A+ NK cells. Immunohistochemistry indicated that ABMR and iMVI had greater CD3+ and CD68+ glomerular infiltration than normal biopsies, whereas CD8+ and TIA1+ cells showed only increased iMVI, suggesting they are cytotoxic T cells. Peritubular capillaries displayed more CD3+, CD56+, TIA1+, and CD68+ cells in both ABMR and iMVI. In contrast, iMVI had less plasma cell infiltration in peritubular capillaries and interstitial aggregates than ABMR. iMVI displayed decreased circulating T and NK cells mirrored by T cell and NK cell infiltration in the renal allograft, similar to ABMR. However, the lesser plasma cell infiltration in iMVI may suggest an antibody-independent underlying stimulus.

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

BackgroundThe 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). MethodsIn 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. ResultsT-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. ConclusionsOur 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.

HLA diversity in ethnic populations can affect detection of donor-specific antibodies by single antigen beads.

In solid-organ transplantation, human leukocyte antigen (HLA) donor-specific antibodies (DSA) are strongly associated with graft rejection, graft loss, and patient death. The predominant tests used for detecting HLA DSA before and after solid-organ transplantation are HLA single antigen bead (SAB) assays. However, SAB assays may not detect antibodies directed against HLA epitopes that are not represented in the SAB. The prevalence and potential impact of unrepresented HLA epitopes are expected to vary by ethnicity, but have not been thoroughly investigated. To address this knowledge gap, HLA allele frequencies from seven ethnic populations were compared with HLA proteins present in SAB products from two manufacturers to determine unrepresented HLA proteins. Allele frequencies were obtained from the Common, Intermediate, and Well Documented HLA catalog v3.0, and frequencies of unrepresented HLA types were calculated. Next-generation sequencing was used to determine HLA types of 60 deceased solid-organ donors, and results were used to determine if their HLA-A, -B, -C, and -DRB1 proteins were not present in SAB reagents from two vendors. Unrepresented HLA proteins were compared with the most similar protein in SAB assays from either vendor and then visualized using modeling software to assess potential HLA epitopes. For the seven ethnic populations, 0.5% to 11.8% of each population had HLA proteins not included in SAB assays from one vendor. Non-European populations had greater numbers of unrepresented alleles. Among the deceased donors, 26.7% (16/60) had at least one unrepresented HLA-A, -B, -C, or -DRB1 protein. Structural modeling demonstrated that a subset of these had potential HLA epitopes that are solvent accessible amino acid mismatches and are likely to be accessible to B cell receptors. In conclusion, SAB assays cannot completely rule out the presence of HLA DSA. HLA epitopes not represented in those assays vary by ethnicity and should not be overlooked, especially in non-European populations. Allele-level HLA typing can help determine the potential for HLA antibodies that could evade detection.

Clinical recommendations for posttransplant assessment of anti–HLA (Human Leukocyte Antigen) donor-specific antibodies: A Sensitization in Transplantation: Assessment of Risk consensus document

Although anti–HLA (Human Leukocyte Antigen) donor-specific antibodies (DSAs) are commonly measured in clinical practice and their relationship with transplant outcome is well established, clinical recommendations for anti-HLA antibody assessment are sparse. Supported by a careful and critical review of the current literature performed by the Sensitization in Transplantation: Assessment of Risk 2022 working group, this consensus report provides clinical practice recommendations in kidney, heart, lung, and liver transplantation based on expert assessment of quality and strength of evidence. The recommendations address 3 major clinical problems in transplantation and include guidance regarding posttransplant DSA assessment and application to diagnostics, prognostics, and therapeutics: (1) the clinical implications of positive posttransplant DSA detection according to DSA status (ie, preformed or de novo), (2) the relevance of posttransplant DSA assessment for precision diagnosis of antibody-mediated rejection and for treatment management, and (3) the relevance of posttransplant DSA for allograft prognosis and risk stratification. This consensus report also highlights gaps in current knowledge and provides directions for clinical investigations and trials in the future that will further refine the clinical utility of posttransplant DSA assessment, leading to improved transplant management and patient care.

Basiliximab is associated with a lower incidence of De novo donor-specific HLA antibodies in kidney transplant recipients: A single-center experience

PurposeInduction immunosuppression has improved the long-term outcomes after kidney transplant. This study explores the association of different induction immunosuppression medications (Basiliximab vs. Alemtuzumab vs. rabbit Antithymocyte Globulin) used at the time of kidney transplant with the development of de novo donor-specific HLA antibodies (DSA) in the first 12 months post-transplant period. MethodsA total of 390 consecutive kidney transplant recipients (KTR), between 2016 and 2018, were included in the analysis. A 104 (26.6%) received Basiliximab, 186 (47.6%) received Alemtuzumab, and 100 (25.6%) received rabbit Antithymocyte Globulin (rATG) for induction. All recipients had a negative flow cytometry crossmatch before transplant. Serum samples at 4- and 12-months post-transplant were assessed for the presence of de novo HLA DSA. kidney allograft function was compared among the three groups with calculated Creatinine Clearance on 24 h urine collection. ResultsDe novo HLA DSA were detected in total of 81 (20.8%) patients within 12 months post-transplant. De novo HLA DSA were detected in 12/104 (11.5%), 43/186 (23.11%), and 26/100 (26%) KTR that received Basiliximab, Alemtuzumab, and rATG respectively (p = 0.006). KTR that received Basiliximab were significantly older, and the last follow-up creatinine clearance was significantly lower at 42 ml/min compared to KTR that received Alemtuzumab or rATG (p = 0.006). ConclusionInduction immunosuppression utilizing Basiliximab is associated with significant reduction in development of de novo DSA within the first 12-months post kidney transplant but had lower creatinine clearance with long-term follow up.

HLA antigen and HLA eplet mismatches - important factors for developing donor-specific antibodies after kidney transplantation

Kidney donor-recipient mismatches (MM) in human leukocyte antigen (HLA) system can have the impact on graft survival as de novo formation of donor-specific HLA antibodies (DSA) post-transplant can increase the risk of acute and chronic rejections. Eplets, the smallest functional units of epitopes, are in recent years also being considered in recipient-donor matching. We have retrospectively analysed the relationship between MM at HLA-A, -B, -DRB1 and -DQB1 loci and the development of DSA in 47 kidney transplant recipients that were negative for the presence of HLA antibodies pre-transplant. A total of 19 patients (40%) developed DSA (DSA+) post-transplant, revealing sensitization to HLA class II MM antigens as the most prevalent (84% of DSA+ patients). MM at all HLA loci contributed to the development of HLA locus-specific antibodies, with the prevalence of HLA-DQ sensitization, as 41% of recipients with HLA-DQ MM developed DSA. HLAMatchmaker analysis for HLA-DR/DQ total eplet MM showed statistically significant difference between DSA- (N=33) and DSA+ recipients (N=14) for a total number of eplet MM (300 in DSA- vs 248 in DSA+; P=0.0004). These results emphasize the importance of HLA Class II matching in kidney transplantation.

Study about the immunological investigations done before Kidney transplant in Basrah during (2012-2017)

Kidney transplant considered as alternative treatment in end-stage renal disease. Human leukocyte antigens an important role in graft rejection, donor specific HLA antibodies that measured by panel reactive antibody, lead to increased sensitization. Cytomegalovirus, Epstein-Barr virus, Hepatitis-B, and -C viruses have an association with poor outcome of the transplant. Aim of the study the immunological investigations done before the transplant. The study have carried out in College of Medicine by analyzing the data records for 36 patients undergo kidney transplant in Al-Sadder Teaching Hospital, 5 patients excluded for incomplete data. Data recorded during (2012-2017). HLA matching between recipients and donors including HLA-A, -B, -DR and -DRB1. Presence of PRAs, Hepatitis B virus surface antigen, Hepatitis C virus antibody, Cytomegalovirus IgM and IgG, Epstein-Barr virus IgM and IgG screened in recipients. Out of 31 recipients, 83.9% of were males and 16.1% females. 77.4% of donors and recipients were relatives and 22.6% were not relatives. 22.6% of donors and 25.8% of recipients tested for HLA and only 57.14% showed partially matching within some HLA classes. 9.7% of recipients have PRA. No recipient showed positive results for the presence of HBV sAg and HCV Ab. 6.5% of recipients have CMV IgM, 67.7% have CMV IgG, 9.7% showed positive results for the presence of EBV IgM and 6.5% have EBV IgG. In a conclusion, recipients and donors showed partially matched HLA classes, not all recipients and donors tested for HLA matching. Some recipients have PRA, high percentage of recipients has CMV IgG, and some of them have CMV IgM antibodies. All these factors might effects on the fate of transplant. HLA-DQ have to be tested and screening for the presence of PRA, viral Ag or Abs specific to these viruses in both recipients and donors is recommended.