Pre‐existing donor‐specific antibodies are detrimental to kidney allograft only when persistent after transplantation

Donor‐specific antibodies (DSA) increase the risk of allograft rejection and graft failure. They may be present before transplant or develop de novo after transplantation. Here, we studied the evolution of preformed DSA and their impact on graft outcome in kidney transplant recipients. Using the Luminex Single Antigen assay, we analyzed the sera on the day of transplantation of 239 patients who received a kidney transplant. Thirty‐seven patients (15.5%) had pre‐existing DSA detected the day of transplantation. After 5 years, the pre‐existing DSA disappeared in 22 patients whereas they persisted in 12. Variables associated with DSA persistence were age <50 years (P = 0.009), a history of previous transplantation (P = 0.039), the presence of class II DSA (P = 0.009), an MFI of preformed DSA >3500 (P < 0.001), and the presence of two or more DSA (P < 0.001). DSA persistence was associated with a higher risk of graft loss and antibody‐mediated rejection. Previously undetected preformed DSA are deleterious to graft survival only when they persist after transplantation.     

Donor‐specific HLA antibody‐mediated complement activation is a significant indicator of antibody‐mediated rejection and poor long‐term graft outcome during lung transplantation: a single center cohort study

Complement‐mediated allograft injury, elicited by donor‐specific HLA antibodies (DSA ), is a defining pathophysiological characteristic of allograft damage. We aimed to study DSA ‐induced complement activation as a diagnostic marker of antibody‐mediated rejection (AMR ) and a risk stratification tool for graft loss in the context of lung transplantation (LT ). We identified 38 DSA ‐positive patients whose serum samples were submitted for C3d deposition testing via the C3d assay. Among these 38 patients, 15 had AMR (DSA^{P os}AMR^{P os}). Results were reported for each patient as the C3d ratio for each DSA , the immunodominant DSA , and the C3d ratio for all DSA present in a sample (C3d ratio_SUM ). DSA^{P os}AMR^{P os} patients had higher C3d ratio_SUM values (58.66 (?1.32 to 118.6) vs. 1.52 (0.30 to 2.74), P  = 0.0016) and increased immunodominant C3d ratios (41.87 (1.72 to 82.02) vs. 0.69 (0.21 to 1.19), P  = 0.001) when compared with DSA^{P os}AMR^{N eg} patients. Specificity and calculated positive predictive value of the immunodominant C3d ratio and BCM sum tests for AMR diagnosis were both 100% (CI  = 17.4–100) in this cohort. Worst graft survival was associated with both immunodominant C3d ratio ≥4 or C3d ratio_SUM ≥10 or BCM sum >7000, suggesting that the antibody composition and/or strength are the principal determinants of an HLA DSA 's capacity to activate complement.     

Determining donor‐specific antibody C1q‐binding ability improves the prediction of antibody‐mediated rejection in human leucocyte antigen‐incompatible kidney transplantation

Detrimental impact of preformed donor‐specific antibodies (DSAs) against human leucocyte antigens on outcomes after kidney transplantation are well documented, however, the value of their capacity to bind complement for predicting antibody‐mediated rejection (AMR) and graft survival still needs to be confirmed. We aimed to study DSA characteristics (strength and C1q binding) that might distinguish harmful DSA from clinically irrelevant ones. We retrospectively studied 60 kidney‐transplanted patients with preformed DSA detected by single antigen bead (SAB) assays (IgG and C1q kits), from a cohort of 517 kidney graft recipients (124 with detectable anti‐HLA antibodies). Patients were divided into DSA strength (MFI < vs. ≥ 15 000) and C1q‐binding ability. AMR frequency was high (30%) and it increased with DSA strength (P = 0.002) and C1q+ DSA (P < 0.001). The performance of DSA C1q‐binding ability as a predictor of AMR was better than DSA strength (diagnostic odds ratio 16.3 vs. 6.4, respectively). Furthermore, a multivariable logistic regression showed that C1q+ DSA was a risk factor for AMR (OR = 16.80, P = 0.001), while high MFI DSAs were not. Graft survival was lower in high MFI C1q+ DSA in comparison with patients with C1q? high or low MFI DSA (at 6 years, 38%, 83% and 80%, respectively; P = 0.001). Both DSA strength and C1q‐binding ability assessment seem valuable for improving pretransplant risk assessment. Since DSA C1q‐binding ability was a better predictor of AMR and correlated with graft survival, C1q‐SAB may be a particularly useful tool.     

Dynamics of anti‐human leukocyte antigen antibodies after renal transplantation and their impact on graft outcome

The purpose of this study was to sequentially monitor anti‐HLA antibodies and correlate the results with antibody‐mediated rejection (AMR), graft survival (GS), and graft function (GF). We collected sera from 111 kidney transplant recipients on transplant days 0, 7, 14, 30, 60, 90, 180, and 360 and analyzed PRA levels by ELISA. DSAs were analyzed by single‐antigen beads in rejecting kidneys. At pre‐transplant, 79.3% of the patients were non‐sensitized (PRA = 0%) and 20.7% were sensitized (PRA > 1%). After transplant, patients were grouped by PRA profile: no anti‐HLA antibodies pre‐ or post‐transplant (group HLApre?/post?; n = 80); de novo anti‐HLA antibodies post‐transplant (group HLApre?/post+; n = 8); sensitized pre‐transplant/increased PRA post‐transplant (group HLApre+/post↑; n = 9); and sensitized pre‐transplant/decreased PRA post‐transplant (group HLApre+/post↓; n = 14). De novo anti‐HLA antibodies were detected at 7–180 d. In sensitized patients, PRA levels changed within the first 30 d post‐transplant. Incidence of AMR was higher in HLApre?/post+ and HLApre+/post↑ than in HLApre?/post?, and HLApre+/post↓ (p < 0.001) groups. One‐yr death‐censored GS was 36% in group HLApre+/post↑, compared with 98%, 88% and 100% in groups HLApre?/post?, HLApre?/post+, and HLApre+/post↓, respectively (p < 0.001). Excluding first‐year graft losses, GF and GS were similar among the groups. In conclusion, post‐transplant antibody monitoring can identify recipients at higher risk of AMR.     

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.     

Outcome of the risk‐stratified desensitization protocol in donor‐specific antibody‐positive living kidney transplant recipients: a retrospective study

Acceptable outcomes of donor‐specific antibody (DSA)‐positive living kidney transplantation (LKT) have recently been reported. However, LKT in crossmatch (XM)‐positive patients remains at high‐risk and requires an optimal desensitization protocol. We report our intermediate‐term outcomes of XM‐positive LKT vs. XM‐negative LKT in patients who underwent LKT between January 2012 and June 2015 in our institution. The rate of acute antibody‐mediated rejection (ABMR) within 90 days postoperation, graft function, and patient, and graft survival rates at 4 years were investigated. Patients were divided into three groups: XM?DSA? (n = 229), XM?DSA+ (n = 36), and XM + DSA+ (n = 15). The XM + DSA+ group patients underwent desensitization with high‐dose intravenous immunoglobulin, plasmapheresis, and rituximab. The rates of ABMR within 90 days in the XM?DSA?, XM?DSA+, and XM + DSA+ groups were 1.3%, 9.4%, and 60.0%, respectively (P < 0.001). There were no significant differences in the graft function throughout the observational period, the 4‐year patient or graft survival rates among three groups. This study showed that intermediate‐term outcomes of XM‐positive LKT were comparable to XM‐negative LKT. However, our current desensitization protocol cannot avert ABMR within 90 days, and XM positivity is still a significant risk factor for ABMR. Further refinement of the current desensitization regimen is required.     

Poor graft outcome in recipients with de novo donor-specific anti-HLA antibodies after living related kidney transplantation

Antibody-mediated rejection (AMR) is now widely recognized as a major problem in organ transplantation. This study was conducted to investigate the relationship between newly developing anti-HLA antibodies post-transplantation (de novo Abs) and the outcome of living related kidney transplantation (LRKT). The subjects included 87 patients who had received living donor kidney allografts at our institution. Panel reactive Ab assay (Flow-PRA) and graft biopsies were performed in all the recipients before and 6 months after the LRKT. The incidence of AMR, the donor specificity and time of appearance of the de novo Abs were retrospectively studied. Among the 87 LRKT recipients, 47 (54%) showed negative/negative (N/N) results, 15 (17%) showed positive/positive (P/P) results, 12 (14%) showed positive/negative results (P/N), and 13 (15%) showed negative/positive (N/P) results (de novo Abs) in the pre-/post-transplant Flow-PRA analysis. Among the 13 cases with de novo Abs, 5 (38%) had donor-specific Abs (DSA) and the remaining 8 (62%) had nondonor-specific Abs, as determined by LAB single antigen analysis. Eighty percent of the recipients with DSA showed evidence of AMR in the graft biopsies. The 5-year graft survival rate of the recipients with de novo Abs (N/P) was 69%, as compared with 96% in the N/N, 88% in the P/N and 93% in the P/P recipient groups (P = 0.009). LRKT recipients developing de novo Abs, especially those with DSA, showed a much higher incidence of AMR and a worse prognosis. Cautious monitoring for the appearance of anti-HLA Abs should be adopted after transplantation, even in patients without anti-HLA Abs prior to the transplantation.     

Difference in outcomes after antibody‐mediated rejection between abo‐incompatible and positive cross‐match transplantations

Graft survival seems to be worse in positive cross‐match (HLAi) than in ABO‐incompatible (ABOi) transplantation. However, it is not entirely clear why these differences exist. Sixty‐nine ABOi, 27 HLAi and 10 combined ABOi+HLAi patients were included in this retrospective study, to determine whether the frequency, severity and the outcome of active antibody‐mediated rejection (AMR) were different. Five‐year death‐censored graft survival was better in ABOi than in HLAi and ABOi+HLAi patients (99%, 69% and 64%, respectively, P = 0.0002). Features of AMR were found in 38%, 95% and 100% of ABOi, HLAi and ABOi+HLAi patients that had a biopsy, respectively (P = 0.0001 and P = 0.001). After active AMR, a declining eGFR and graft loss were observed more frequently in HLAi and HLAi+ABOi than in ABOi patients. The poorer prognosis after AMR in HLAi and ABOi+HLAi transplantations was not explained by a higher severity of histological lesions or by a less aggressive treatment. In conclusion, ABOi transplantation offers better results than HLAi transplantation, partly because AMR occurs less frequently but also because outcome after AMR is distinctly better. HLAi and combined ABOi+HLAi transplantations appear to have the same outcome, suggesting there is no synergistic effect between anti‐A/B and anti‐HLA antibodies.     

The possible critical role of T‐cell help in DSA‐mediated graft loss

In this review, we discuss a possible central role of T‐cell help in severe forms of graft damage mediated by donor‐specific HLA antibodies (DSA). Some kidney transplant recipients with pretransplant DSA show a high graft failure rate, whereas in other patients DSA do not harm the transplanted kidney and in most cases, disappear shortly after transplantation. Analyzing 80 desensitized highly immunized kidney transplant recipients and another multicenter cohort of 385 patients with pretransplant HLA antibodies, we reported recently that an ongoing T‐cell help from an activated immune system, as measured by an increased level of soluble CD30 in serum, might be necessary for the DSA to exert a deleterious effect. Patients positive for both pretransplant DSA and sCD30 appear to require special measures, such as the elimination of DSA from the circulation, potent immunosuppression, good HLA‐matching, and intense post‐transplant monitoring, whereas exclusion of DSA‐positive patients from transplantation in the absence of high sCD30 may not be justified in all cases, even if the pretransplant DSA are strong and complement‐activating.     

Kidney Intragraft Donor‐Specific Antibodies as Determinant of Antibody‐Mediated Lesions and Poor Graft Outcome

Allograft pathology, antibody–tissue interaction as demonstrated by C4d deposition and serological evidence of donor‐specific antibodies (DSA) are the cardinal diagnostic features of antibody‐mediated lesions (AML) in kidney transplantation. However, discrepancy between histological and serological findings is common, and more reliable diagnostic tools are called for. Here, we asked whether the in situ detection of DSA could serve as marker for AML. To that end, we applied the anti‐HLA single antigen flow bead assay to eluates from 51 needle core graft biopsies performed for cause. Intragraft antibody profiles were correlated to serum DSA (sDSA), histological data and transplant outcome. The prevalence and the mean number of intragraft DSA (gDSA) were lower than that of sDSA (15/51 gDSA+ vs. 37/51 sDSA+ patients; 1.64 gDSA vs. 2.24 sDSA per patient). DSA were detected in all anti‐HLA antibody‐positive biopsies (15/15). The presence of gDSA was significantly associated with (1) microcirculation lesions taken individually (g, cg) and analyzed in functional clusters (ptc + g + cg > 0, cg + mm > 0), (2) C4d positivity and (3) a worse short‐term transplant outcome (p = 0.05). These associations were not found for patients presenting only sDSA. Taken together, these results indicate that gDSA is a severity marker of antibody‐mediated pathogenic process.     

ABO incompatible living donor kidney transplantation in Korea: highly uniform protocols and good medium‐term outcome

The organ shortage is as serious in Korea as in other parts of the world. As about one‐third of the potential living donors are ABO incompatible (ABOi), transplantation across the blood group barrier can help overcome this shortage. One hundred and twenty‐five ABOi kidney transplantations (KTs) were performed between 2007 and 2010 in Korea. We collected the perioperative and follow‐up data for 118 of these patients until September 2011. The preconditioning and immunosuppressive protocols were almost identical across the different transplant centers, with rituximab but no splenectomy; pre‐transplant plasmapheresis (PP) with target anti‐A/B titer 8 or 16 on transplant day, on‐demand, rather than routine, post‐transplant PP, and tacrolimus‐based immunosuppressants. The number of patients and participating centers showed a rapid increase over time, and in 2010, ABOi KT (n = 79) comprised 10% of all the living donor KTs in Korea. The mean follow‐up period was 21 months (range, 1–56 months). Sixteen (14%) patients developed acute rejection, and three of these had antibody‐mediated rejection (AMR). Two‐yr patient and graft survival were 99.2% and 97.5%, respectively. No graft was lost due to AMR. ABOi KT is rapidly expanding in Korea with excellent medium‐term outcome and will help mitigate the organ shortage.     

Early findings of prospective anti‐HLA donor specific antibodies monitoring study in pancreas transplantation: Indiana University Health Experience

The significance of donor‐specific antibodies (DSA) is not well known in the setting of pancreas transplantation. Since December 2009, we prospectively followed pancreas transplant patients with single‐antigen‐luminex‐bead testing at one, two, three, six, and then every six months for the first two yr. Thirty‐five of the 92 patients that underwent pancreas transplantation (13 pancreas‐alone [PTA], 20 with a kidney [SPK], and two after a kidney [PAK]) agreed to participate in study. Median age at transplant was 45 yr and follow‐up was 23 months. Majority were Caucasian (n = 33) and male (n = 18). Rabbit anti‐thymocyte globulin induction was used. Median HLA‐mismatch was 4.2 ± 1.1. Eight patients (7SPK, 1PAK) developed post‐transplant DSA at median follow‐up of 76 d (26–119), 1 SPK had pre‐formed DSA. Seven patients had both class I and class II DSA, one with class I and one with class II only. Mean peak class I DSA‐MFI was 3529 (±1456); class II DSA‐MFI was 5734 (±3204) whereas cumulative DSA MFI (CI + CII) was 9264 (±4233). No difference was observed in the patient and donor demographics among patients with and without DSA. One patient in non‐DSA group developed acute cellular rejection of pancreas. From our data it appears that post‐transplant DSA in pancreas allograft recipients may not impact the early‐pancreatic allograft outcomes. The utility of prospective DSA monitoring in pancreatic transplant patients needs further evaluation and long‐term follow‐up.     

Preformed donor‐specific antibodies do not affect the 1‐year allograft survival in living donor liver transplantation

The effect of preformed donor‐specific antibodies (DSAs) on liver transplantation (LT) remains unclear, especially in the field of living donor LT (LDLT). Herein, we evaluated the prevalence of preformed DSAs and their effect on graft outcome in LDLT in the first year following surgery. Using the Luminex^® Single Antigen assay, we analyzed the preoperative sera of 61 adult LDLT recipients between 2014 and 2015. Clinical outcomes and pathologic findings including complement component 4d (C4d) expression in the first year after LT were retrospectively reviewed. Regardless of the class of DSA, DSAs with mean fluorescence intensity (MFI) ≥1000 were defined as positive and preformed DSA with MFI ≥5000 was defined as strongly positive. Fifteen patients (24.6%) had preformed DSAs, and 8 patients (13.1%) showed strongly positive preformed DSAs. Among 15 DSA positive patients, 2 (13.3%) showed persistent DSAs after LDLT. No de novo DSAs were noted in patients without preformed DSAs. Preformed DSAs were not related to graft dysfunction, laboratory values, or C4d expression or other pathologic findings in the first year of LDLT. In conclusion, preformed DSAs persisted during follow‐up in 13.3% of cases and did not have adverse effect on histologic or clinical outcomes in the first year of LDLT.     

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

The aim of this study was to evaluate the utility of donor-specific antibodies (DSA) and flow cytometry crossmatch (FCCM) as tools for predicting antibody-mediated rejection (AMR) in desensitized kidney recipients. Sera from 44 patients with DSA at the time of transplant were reviewed. Strength of DSA was determined by single antigen Luminex bead assay and expressed as mean fluorescence intensity (MFI). T- and B-cell FCCM results were expressed as mean channel shift (MCS). AMR was diagnosed by C4d deposition on biopsy. Incidence of early AMR was 31%. Significant differences in the number of DSAs (p = 0.0002), cumulative median MFI in DSA class I (p = 0.0004), and total (class I + class II) DSA (p < 0.0001) were found in patients with and without AMR. No significant difference was seen in MCS of T and B FCCM (p = 0.095 and p = 0.307, respectively). The three-yr graft survival in desensitized patients with DSA having total MFI < 9500 was 100% compared to 76% with those having total MFI > 9500 (p = 0.022). Desensitized kidney transplant recipients having higher levels of class I and total DSA MFI are at high risk for AMR and poor graft survival. Recipient DSA MFI appears to be a more reliable predictor of AMR than MCS of FCCM.     

Postoperative rebound of antiblood type antibodies and antibody‐mediated rejection after ABO‐incompatible living‐related kidney transplantation

The purpose of this study is to examine whether postoperative antiblood type antibody rebound is attributed to kidney allograft rejection in ABO blood type‐incompatible (ABO‐I) living‐related kidney transplantation (KTx). A total of 191 ABO‐I recipients who received ABO‐I living‐related KTx between 2001 and 2013 were divided into two groups: Group 1 consisted of low rebound [(≦1:32), N = 170] and Group 2 consisted of high rebound [(≧1:64), N = 21], according to the levels of the rebounded antiblood type antibodies within 1 year after transplantation. No prophylactic treatment for rejection was administered for elevated antiblood type antibodies, regardless of the levels of the rebounded antibodies. Within 1 year after transplantation, T‐cell‐mediated rejection was observed in 13 of 170 recipients (13/170, 8%) in Group 1 and in 2 of 21 recipients (2/21, 10%) in Group 2 (Groups 1 vs. 2, P = 0.432). Antibody‐mediated rejection was observed in 15 of 170 recipients (15/170, 9%) and 2 of 21 recipients (2/21, 10%) in Groups 1 and 2, respectively (P = 0.898). In this study, we found no correlation between the postoperative antiblood type antibody rebound and the incidence of acute rejection. We concluded that no treatment is necessary for rebounded antiblood type antibodies.     

Subclinical inflammation phenotypes and long‐term outcomes after pediatric kidney transplantation

The implementation of surveillance biopsies in pediatric kidney transplantation remains controversial. Surveillance biopsies detect subclinical injury prior to clinical dysfunction, which could allow for early interventions that prolong allograft survival. We conducted a single‐center retrospective cohort study of 120 consecutive pediatric kidney recipients, of whom 103 had surveillance biopsies ≤6 months posttransplant. We tested the hypothesis that subclinical inflammation (borderline or T cell–mediated rejection without clinical dysfunction) is associated with a 5‐year composite endpoint of acute rejection and allograft failure. Overall, 36% of subjects had subclinical inflammation, which was associated with increased hazard for the composite endpoint (adjusted hazard ratio 2.89 [1.27, 6.57]; P < .01). Subjects with treated vs untreated subclinical borderline rejection had a lower incidence of the composite endpoint (41% vs 67%; P < .001). Subclinical vascular injury (subclinical inflammation with Banff arteritis score > 0) had a 78% incidence of the composite endpoint vs 11% in subjects with no major surveillance abnormalities (P < .001). In summary, we showed that subclinical inflammation phenotypes were prevalent in pediatric kidney recipients without clinical dysfunction and were associated with increased acute rejection and allograft failure. Once prospectively validated, our data would support implementation of surveillance biopsies as standard of care in pediatric kidney transplantation.