Specificity,strength, and evolution of pretransplant donor‐specific HLA antibodies determine outcome after kidney transplantation

In this cohort study (N = 924), we investigated the evolution and clinical significance of pretransplant donor‐specific HLA antibodies (preDSA), detected in the single‐antigen beads assay but complement‐dependent cytotoxicity crossmatch‐negative. Donor specificity of the preDSA (N = 107) was determined by high‐resolution genotyping of donor‐recipient pairs. We found that in 52% of the patients with preDSA, preDSA spontaneously resolved within the first 3 months posttransplant. PreDSA that persisted posttransplant had higher pretransplant median fluorescence intensity values and more specificity against DQ. Patients with both resolved and persistent DSA had a high incidence of histological picture of antibody‐mediated rejection (ABMR_h; 54% and 59% respectively). Patients with preDSA that persisted posttransplant had worse 10‐year graft survival compared to resolved DSA and preDSA‐negative patients. Compared to cases without preDSA, Cox modeling revealed an increased risk of graft failure only in the patients with persistent DSA, in the presence (hazard ratio [HR] = 8.3) but also in the absence (HR = 4.3) of ABMR_h. In contrast, no increased risk of graft failure was seen in patients with resolved DSA. We conclude that persistence of preDSA posttransplant has a negative impact on graft survival, beyond ABMR_h. Even in the absence of antibody‐targeting therapy, low median fluorescence intensity DSA and non‐DQ preDSA often disappear early posttransplantation and are not deleterious for graft outcome.     

Value of monitoring circulating donor‐reactive memory B cells to characterize antibody‐mediated rejection after kidney transplantation

Antibody‐mediated rejection (ABMR) is defined by specific histopathological lesions and evidence of circulating donor‐specific antibodies (DSA). Although DSA are not always detectable, monitoring donor‐reactive memory B cells (mBC) could identify patients at risk of developing ABMR. Peripheral donor‐reactive mBC using a novel HLA B cell ELISpot assay, serum DSA, and numbers of different B cell subsets were assessed in 175 consecutive kidney transplants undergoing either for‐cause or 6‐ and 24‐month surveillance biopsies for their association with main histological lesions of ABMR and impact on allograft outcome. In 85 incident for‐cause biopsies, high frequencies of donor‐reactive mBC were detected in all 16 (100%) acute ABMR/DSA+ and most chronic ABMR, with or without DSA (24/30[80%] and 21/29[72.4%], respectively). In a longitudinal cohort of 90 nonsensitized patients, a progressively higher expansion of donor‐reactive mBC than de novo DSA was observed at 6 and 24 months (8.8% vs 7.7% and 15.5% vs 11.1%, respectively) and accurately identified patients with ongoing subclinical ABMR (area under the curve = 0.917 and area under the curve = 0.809, respectively). An unsupervised hierarchical cluster analysis revealed a strong association between donor‐reactive mBC with main fundamental allograft lesions associated with ABMR and conferred a significant deleterious impact on graft outcome. Monitoring donor‐reactive mBC may be useful to further characterize humoral rejection after kidney transplantation.     

Markers of graft microvascular endothelial injury may identify harmful donor‐specific anti‐HLA antibodies and predict kidney allograft loss

Graft microvasculature is a major target of donor‐specific antibodies (DSA) and endothelial damage is direct evidence of antibody‐mediated rejection (ABMR). Using immunohistochemistry, we analyzed the expression of three microvascular endothelial activation markers (fascin, vimentin, and hsp47), suggestive of endothelial‐to‐mesenchymal transition (EndMT) in 351 graft biopsies from 248 kidney recipients, with concomitant screening of circulating antihuman leukocyte antigen (HLA) DSA at the time of the biopsy. The factors associated with EndMT marker expression were DSA and the presence of microvascular inflammation (MI). EndMT expressing grafts had significantly more allograft loss compared to EndMT negative grafts (P < .0001). The expression of EndMT markers positively correlated with anti‐HLA DSA class II mean fluorescence intensity (MFI) levels and especially identified DQ and DR antibodies as being more closely associated with microvascular injury. Moreover, only DSA linked to positive EndMT score affected allograft survival, regardless of DSA MFI levels or presence of C4d deposition. Thus, EndMT markers could represent a clinically relevant tool for early identification of ongoing endothelial injury, harmful DSA, and patients at high risk for allograft failure.     

Donor Specificity but Not Broadness of Sensitization Is Associated With Antibody‐Mediated Rejection and Graft Loss in Renal Allograft Recipients

Panel‐reactive antibodies are widely regarded as an important immunological risk factor for rejection and graft loss. The broadness of sensitization against HLA is most appropriately measured by the “calculated population‐reactive antibodies” (cPRA) value. In this study, we investigated whether cPRA represent an immunological risk in times of sensitive and accurate determination of pretransplantation donor‐specific HLA antibodies (DSA). Five hundred twenty‐seven consecutive transplantations were divided into four groups: cPRA 0% (n = 250), cPRA 1–50% (n = 129), cPRA 51–100% (n = 43), and DSA (n = 105). Patients without DSA were considered as normal risk and received standard immunosuppression without T cell–depleting induction. Patients with DSA received an enhanced induction therapy and maintenance immunosuppression. Surveillance biopsies were performed at 3 and 6 months. Median follow‐up was 5.7 years. Among the three cPRA groups, there were no differences regarding the 1‐year incidence of ABMR (p = 0.16) and TCMR (p = 0.75). The 5‐year allograft survival rates were similar and around 87% (p = 0.28). The estimated glomerular filtration rate at last follow‐up was 50–53 mL/min (p = 0.45). On multivariable Cox proportional hazard analysis, the strongest independent predictor for ABMR and (death‐censored) graft survival was pretransplantation DSA. cPRA were not predictive for ABMR, TCMR, or (death‐censored) graft survival. We conclude that with current DSA assignment, the broadness of sensitization measured by cPRA does not imply an immunological risk.     

Profiling non‐HLA antibody responses in antibody‐mediated rejection following heart transplantation

Antibody‐mediated rejection (AMR) driven by the development of donor‐specific antibodies (DSA) directed against mismatched donor human leukocyte antigen (HLA) is a major risk factor for graft loss in cardiac transplantation. Recently, the relevance of non‐HLA antibodies has become more prominent as AMR can be diagnosed in the absence of circulating DSA. Here, we assessed a single‐center cohort of 64 orthotopic heart transplant recipients transplanted between 1994 and 2014. Serum collected from patients with ≥ pAMR1 (n = 43) and non‐AMR (n = 21) were tested for reactivity against a panel of 44 non‐HLA autoantigens. The AMR group had a significantly greater percentage of patients with elevated reactivity to autoantigens compared to non‐AMR (P = .002) and healthy controls (n = 94, P < .0001). DSA‐positive AMR patients exhibited greater reactivity to autoantigens compared to DSA‐negative (P < .0001) and AMR patients with DSA and PRA > 10% were identified as the subgroup with significantly elevated responses. Reactivity to 4 antigens, vimentin, beta‐tubulin, lamin A/C, and apolipoprotein L2, was significantly different between AMR and non‐AMR patients. Moreover, increased reactivity to these antigens was associated with graft failure. These results suggest that antibodies to non‐HLA are associated with DSA‐positive AMR although their specific role in mediating allograft injury is not yet understood.     

A Probabilistic Approach to Histologic Diagnosis of Antibody‐Mediated Rejection in Kidney Transplant Biopsies

Histologic diagnosis of antibody‐mediated rejection (ABMR) in kidney transplant biopsies uses lesion score cutoffs such as 0 versus >0 rather than actual scores and requires donor‐specific antibody (DSA); however, cutoffs lose information, and DSA is not always reliable. Using microarray‐derived molecular ABMR scores as a histology‐independent estimate of ABMR in 703 biopsies, we reassessed criteria for ABMR to determine relative importance of various lesions, the utility of equations using actual scores rather than cutoffs, and the potential for diagnosing ABMR when DSA is unknown or negative. We confirmed that the important features for ABMR diagnosis were peritubular capillaritis (ptc), glomerulitis (g), glomerular double contours, DSA and C4d staining, but we questioned some features: arterial fibrosis, vasculitis, acute tubular injury, and sum of ptc+g scores. Regression equations using lesion scores predicted molecular ABMR more accurately than score cutoffs (area under the curve 0.85–0.86 vs. 0.75). DSA positivity improved accuracy, but regression equations predicted ABMR with moderate accuracy when DSA was unknown. Some biopsies without detectable DSA had high probability of ABMR by regression, although most had HLA antibody. We concluded that regression equations using lesion scores plus DSA maximized diagnostic accuracy and can estimate probable ABMR when DSA is unknown or undetectable.     

Shared alloimmune responses against blood and transplant donors result in adverse clinical outcomes following blood transfusion post–renal transplantation

De novo HLA donor‐specific antibodies (DSA) following transplantation are associated with alloimmune injury and allograft failure. Blood transfusions are allogeneic, and when given posttransplant (PTBT) they may independently increase the risk of HLA antibody development. This study aims to analyze the development of HLA transfusion‐specific antibodies (TSA) to blood donors of transfusions given posttransplant and examine the impact on clinical outcomes. A total of 244 blood donors of transfusions received by 86 transplant patients (46 who developed a DSA post transfusion and 40 who remained DSA negative) were HLA typed. De novo TSA developed against 150/244 (61.5%) blood donors. In 70/150 (46.7%) cases the TSA was of shared HLA antibody specificity with a DSA response in the recipient (DSA+ = TSA+). This occurred when there was a greater overall HLA match between the blood and transplant donor. DSA+ = TSA+ patients had increased risk of allograft failure (P = .0025) and AMR (P = .02) compared with the DSA+ ≠ TSA+ patients. To conclude, PTBT may elicit de novo HLA antibodies. Enhanced HLA matching between the blood and transplant donor is more likely to result in a DSA and TSA of shared antibody specificities. Transfusion avoidance or the use of HLA matched or selected blood may reduce this risk and improve outcomes.     

Comparison of C4d Detection on Erythrocytes and PTC‐C4d to Histological Signs of Antibody‐Mediated Rejection in Kidney Transplantation

C4d on erythrocytes (EC4d), C4d peritubular capillary deposition (PTC‐C4d) staining and histology were compared in a cross‐sectional cohort of 146 renal allograft biopsies (132 patients). EC4d levels paralleled PTC‐C4d staining, but were more predictive of peritubular capillaritis (PTC). Donor‐specific antibodies (DSA), PTC‐C4d, EC4d and PTC were analyzed in an independent longitudinal follow‐up cohort (96 biopsies, 76 patients). Seventy‐six samples were PTC and EC4d concordant, 11 positive and 65 negative, 7 PTC‐EC4d+ and 13 PTC+EC4d?. EC4d levels were related to DSA occurrence. With ABMR defined by PTC and DSA, all apparently discordant patients, EC4d negative, were correctly reassigned comparing EC4d level curves with rejection kinetics, with positive EC4d samples predating biopsy or late biopsies compared with ABMR flare‐ups. All EC4d‐positive patients without PTC or DSA had permanent high EC4d levels unrelated to rejection. EC4d was more abundant in PTC‐positive (mean = 108.5%± 3.4; n = 50) than PTC‐negative samples (mean = 88.1%± 1.3; n= 96; p < 0.0001). Sensitivity, specificity, positive predictive value and negative predictive value of PTC‐C4d and EC4d for PTC were, respectively, 75%, 79%; 64%, 76% (p < 0.05); 28%, 46% (p < 0.05) and 93%, 94%. Values were similar for DSA. A noninvasive blood test, EC4d, and particularly longitudinally monitoring EC4d levels, may increase surrogate ABMR testing options.     

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.     

Impact of pretransplant donor‐specific antibodies on kidney allograft recipients with negative flow cytometry cross‐matches

The Luminex test can detect low levels of donor‐specific antibody (DSA) that cannot be detected by flow‐cytometric cross‐matching (FCXM) in kidney transplantation (KT). This study evaluated the impact of DSA on clinical outcomes in KT recipients negative on FCXM. Of 575 consecutive patients who underwent living donor KT between January 2013 and July 2016, 494 (85.9%) were DSA‐negative and 81 (14.1%) were DSA‐positive. Although rates of acute cellular rejection (ACR) at 1 year were similar in the 2 groups (P = .54), the incidence of antibody‐mediated rejection (ABMR) was significantly higher in the DSA‐positive group (P < .01). There was no statistically significant association between rejection‐free graft survival (RFGS) rates and pretransplant class I DSA. However, evaluation of pretransplant class II DSA showed that RFGS rates were significantly lower in patients with mean fluorescence intensity (MFI) >3000 than in patients with DSA‐negative (P < .01). On multivariate analyses, class II DSA MFI ≥5000 was a significant risk factor for acute rejection (hazard ratio, 7.48; P < .01). These findings suggested that pretransplant DSA alone did not affect graft survival in KT recipients without desensitization. However, class II DSA MFI >5000 was an independent predictor of acute rejection in DSA‐positive patients.     

Development and outcomes of de novo donor‐specific antibodies in low,moderate, and high immunological risk kidney transplant recipients

De novo donor‐specific antibodies (dnDSA) play an important role in antibody‐mediated rejection (ABMR) and graft failure, yet their development in kidney transplant recipients (KTx) of higher immunological risk has not been characterized. We prospectively determined the incidence of dnDSA at 3 and 12 months posttransplant and assessed their associations with outcomes in recipients stratified by low, moderate, and high immunological risk. Adult KTx were screened for DSA pretransplant, months 3 and 12 posttransplant, and when clinically indicated. Outcomes included incidence of dnDSA, death‐censored graft survival (DCGS), and ABMR. Of 371 recipients, 154 (42%) were transplanted across a pretransplant DSA that became undetectable by 12 months posttransplant in 78% of cases. dnDSA were detected in 16% (95% confidence interval [CI]: 12‐20%) by 3 months and 23% (95% CI: 18‐29%) by 12 months posttransplant. Incidence at 12 months was higher in the moderate (30%) and high‐risk groups (29%) compared to the low‐risk group (16%). dnDSA were associated with an increased risk of ABMR (hazard ratio [HR] 2.2; 95% CI: 1.1‐4.4; P = .04) but were not an independent risk factor for DCGS. In conclusion, dnDSA were more frequent in transplant recipients of higher immune risk and associated with an increased risk of ABMR.     

Chronic‐active antibody‐mediated rejection with or without donor‐specific antibodies has similar histomorphology and clinical outcome – a retrospective study

Chronic‐active antibody‐mediated rejection (c‐aABMR) is defined as histological evidence of chronic endothelial injury (cg), also known as transplant glomerulopathy, and either microvascular inflammation (MVI) or positivity for C4d. Importantly, the presence of donor‐specific antibodies (DSA) is currently still mandatory for the diagnosis of c‐aABMR. This retrospective study of 41 c‐aABMR patients investigates whether cases suspicious for c‐aABMR (DSA negative, n = 24) differ from cases of c‐aABMR (DSA positive, n = 17) with respect to renal histology, allograft function and long‐term graft survival. All included patients had progressive loss of allograft function and were diagnosed by for cause biopsy and scored according to the Banff ’15 criteria. In all DSApos cases, DSA were de novo and the majority was directed against HLA‐II being mostly anti‐HLA‐DQ antibodies. There were no statistically significant differences in clinical characteristics, decline in allograft function and renal allograft survival in cases with or without DSAs. All cases showed chronic histomorphological damage and inflammation, irrespective of the presence of DSA. Renal histology and clinical outcome of patients suspicious for c‐aABMR (DSAneg) do not significantly differ from patients with a diagnosis of c‐aABMR (DSApos). We believe that our study adds to the ongoing debate regarding the need for DSAs to be present for the diagnosis of c‐aABMR.     

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.     

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.     

Alloantibody Responses After Renal Transplant Failure Can Be Better Predicted by Donor–Recipient HLA Amino Acid Sequence and Physicochemical Disparities Than Conventional HLA Matching

We have assessed whether HLA immunogenicity as defined by differences in donor–recipient HLA amino‐acid sequence (amino‐acid mismatch score, AMS; and eplet mismatch score, EpMS) and physicochemical properties (electrostatic mismatch score, EMS) enables prediction of allosensitization to HLA, and also prediction of the risk of an individual donor–recipient HLA mismatch to induce donor‐specific antibody (DSA). HLA antibody screening was undertaken using single‐antigen beads in 131 kidney transplant recipients returning to the transplant waiting list following first graft failure. The effect of AMS, EpMS, and EMS on the development of allosensitization (calculated reaction frequency [cRF]) and DSA was determined. Multivariate analyses, adjusting for time on the waiting list, maintenance on immunosuppression after transplant failure, and graft nephrectomy, showed that AMS (odds ratio [OR]: 1.44 per 10 units, 95% CI: 1.02–2.10, p = 0.04) and EMS (OR: 1.27 per 10 units, 95% CI: 1.02–1.62, p = 0.04) were independently associated with the risk of developing sensitization to HLA (cRF > 15%). AMS, EpMS, and EMS were independently associated with the development of HLA‐DR and HLA‐DQ DSA, but only EMS correlated with the risk of HLA‐A and ‐B DSA development. Differences in donor–recipient HLA amino‐acid sequence and physicochemical properties enable better assessment of the risk of HLA‐specific sensitization than conventional HLA matching.     

Belatacept‐based immunosuppression: A calcineurin inhibitor‐sparing regimen in heart transplant recipients

Belatacept (BTC) is indicated for prophylaxis of graft rejection in adults receiving a renal transplant (Tx). This retrospective observational study (three centers) included all heart transplant recipients receiving BTC between January 2014 and October 2018. Forty EBV+ patients mean GFR 35 ± 20 mL/min/m² were identified, among whom belatacept was initiated during the first 3 months after transplantation in 12 patients, and later in 28 patients. Several patients were multiorgan transplant recipients. Study outcomes were GFR, safety, and changes in immunosuppressive therapy. The main reason for switching to BTC was to preserve renal function, resulting in discontinuation of CNI and changes in immunosuppressive therapy in 76% of cases. At study closeout, 24/40 patients were still on BTC therapy. GFR was improved (+59%, P = .0002*) within 1 month, particularly in the early group. More episodes of rejection were observed among “late” patients (1 death). Sixteen treatment discontinuations were recorded: GFR recovery (n = 4), DSA no longer detectable (n = 1), compliance issues (n = 3), poor venous access (n = 2), multiple infections (n = 1), 1 death (fungal lung infection), and treatment failure (n = 4). Median follow‐up was 24 months. Four patients developed de novo DSA (MFI<1500). BTC is an effective alternative immunosuppressive for postoperative transient kidney failure, stabilizing delayed renal function, with acceptable safety profile under careful monitoring.     

Antibody‐mediated rejection in pediatric small bowel transplantation: Capillaritis is a major determinant of C4d positivity in intestinal transplant biopsies

The diagnostic criteria for antibody‐mediated rejection (ABMR) after small bowel transplantation (SBT) are not clearly defined, although the presence of donor‐specific antibodies (DSAs) has been reported to be deleterious for graft survival. We aimed to determine the incidence and prognostic value of DSAs and C4d in pediatric SBT and to identify the histopathologic features associated with C4d positivity. We studied all intestinal biopsies (IBx) obtained in the first year posttransplantation (N = 345) in a prospective cohort of 23 children. DSAs and their capacity to fix C1q were identified by using Luminex technology. Eighteen patients (78%) had DSAs, and 9 had the capacity to fix C1q. Seventy‐eight IBx (22.6%) were C4d positive. The independent determinants of C4d positivity were capillaritis grades 2 and 3 (odds ratio [OR] 4.02, P = .047 and OR 5.17, P = .003, respectively), mucosal erosion/ulceration (OR 2.8, P = .019), lamina propria inflammation grades 1 and 2/3 (OR 1.95, P = .043 and OR 3.1, P = .016, respectively), and chorion edema (OR 2.16, P = .028). Complement‐fixing DSAs and repeated C4d‐positive IBx were associated with poor outcome (P = .021 and P = .001, respectively). Our results support that capillaritis should be considered as a feature of ABMR in SBT and identify C1q‐fixing DSAs and repeated C4d positivity as potential markers of poor outcome.     

Modeling graft loss in patients with donor‐specific antibody at baseline using the Birmingham‐Mayo (BirMay) predictor: Implications for clinical trials

Predicting which renal allografts will fail and the likely cause of failure is important in clinical trial design to either enrich patient populations to be or as surrogate efficacy endpoints for trials aimed at improving long‐term graft survival. This study tests our previous Birmingham‐Mayo model (termed the BirMay Predictor) developed in a low‐risk kidney transplant population in order to predict the outcome of patients with donor specific alloantibody (DSA) at the time of transplantation and identify new factors to improve graft loss prediction in DSA+ patients. We wanted define ways to enrich the population for future therapeutic intervention trials. The discovery set included 147 patients from Mayo Cohort and the validation set included 111 patients from the Paris Cohort—all of whom had DSA at the time of transplantation. The BirMay predictor performed well predicting 5‐year outcome well in DSA+ patients (Mayo C statistic = 0.784 and Paris C statistic = 0.860). Developing a new model did not improve on this performance. A high negative predictive value of greater than 90% in both cohorts excluded allografts not destined to fail within 5 years. We conclude that graft‐survival models including histology predict graft loss well, both in DSA+ cohorts as well as DSA‐ patients.     

Identifying Subphenotypes of Antibody‐Mediated Rejection in Kidney Transplants

The key lesions in antibody‐mediated kidney transplant rejection (ABMR) are microcirculation inflammation (peritubular capillaritis and/or glomerulitis lesions, abbreviated “pg”) and glomerular double contours (cg lesions). We used these features to explore subphenotypes in 164 indication biopsies with ABMR‐related diagnoses: 137 ABMR (109 pure and 28 mixed with T cell–mediated rejection [TCMR]) and 27 transplant glomerulopathy (TG), identified from prospective multicenter studies. The lesions indicated three ABMR subphenotypes: pgABMR, cgABMR, and pgcgABMR. Principal component analysis confirmed these subphenotypes and showed that TG can be reclassified as pgcgABMR (n = 17) or cgABMR (n = 10). ABMR‐related biopsies included 45 pgABMR, 90 pgcgABMR, and 25 cgABMR, with four unclassifiable. Dominating all time intervals was the subphenotype pgcgABMR. The pgABMR subphenotype presented earliest (median <2 years), frequently mixed with TCMR, and was most associated with nonadherence. The cgABMR subphenotype presented late (median 9 years). Subphenotypes differed in their molecular changes, with pgABMR having the most histologic–molecular discrepancies (i.e. potential errors). Donor‐specific antibody (DSA) was not identified in 29% of pgcgABMR and 46% of cgABMR, but failure rates and molecular findings were similar to cases where DSA was known to be positive. Thus, ABMR presents distinct subphenotypes, early pg‐dominant, late cg‐dominant, and combined pgcg phenotype, differing in time, molecular features, accompanying TCMR, HLA antibody, and probability of nonadherence.