Impact of persistent and cleared preformed HLA DSA on kidney transplant outcomes

Preformed HLA donor-specific antibodies (DSA) only detected with Luminex have been associated with increased risk of antibody-mediated rejection (ABMR) and graft failure after kidney transplantation (KT). Their evolution after KT may modify this risk. We analyzed postransplant evolution of preformed DSA identified retrospectively and their impact on outcomes of 370 KT performed 2006–2014. Antibodies were monitored prospectively at 1-3-5?years after KT and if any dysfunction. Early acute ABMR was more frequent among patients with preformed DSA class-I or I?+?II than isolated class-II (29.4% vs 4.5%, p?=?0.02). One year post-KT, 20 of 34 patients with functioning KT had persistent DSA. Preformed DSA class-II persisted more frequently than class-I/I?+?II (66.7% vs 33.3%; p?=?0.031). The only risk factor independently associated with persistence was pretransplant MFI. Patients with de novo DSA had the highest risk of ABMR (HR 22.2 [CI 6.1–81.2]). Although recipients with persisting preformed DSA had significantly increased ABMR risk (HR 14.7 [CI 6.5–33.0]), those with cleared preformed DSA also had a higher risk than those without DSA (HR 7.01 [CI 2.2–21.8]).Preformed DSA are a very important risk factor for ABMR and graft loss. Patients who clear preformed DSA still show an increased risk of ABMR and graft loss after KT.     

Early acute antibody-mediated rejection of a negative flow crossmatch 3rd kidney transplant with exclusive disparity at HLA-DP

Donor-specific alloantibodies (DSA) to HLA-DP may cause antibody-mediated rejection (AMR), especially in re-transplants. We describe the immunization history of a patient who received 3 kidney transplants; the 3rd kidney was completely matched except at DPA1 and DPB1. Prior to the 3rd transplant, single antigen bead analysis (SAB) showed DSA reactivity against DPA1 shared by the 1st and 3rd donors, but B and T flow crossmatch (FXM) results were negative. Within 11 days the 3rd transplant underwent acute C4d+ AMR which coincided with the presence of complement (C1q)-binding IgG1 DSA against donor DPA1 and DPB1. Using HLAMatchmaker and SAB, we provide evidence that eplet (epitope) spreading on DPA1 and eplet sharing on differing DPB1 alleles of the 1st and 3rd transplants was associated with AMR. Since weak DSA to DPA1/DPB1 may induce acute AMR with negative FXM, donor DPA1/DPB1 high resolution typing should be considered in sensitized patients with DP-directed DSA.     

Correlations between donor-specific antibodies and non-adherence with chronic active antibody-mediated rejection phenotypes and their impact on kidney graft survival

Chronic-active antibody-mediated rejection (CAABMR) is associated with poor kidney graft survival and has no clear effective treatment. Forty-one cases of CAABMR were detected in indication graft biopsies and evaluated according to current Banff classification. We investigated the impact of concurrent donor-specific antibodies (DSA) and their characteristics, together with non-adherence regarding immunosuppression on CAABMR histopathological phenotypes and prognosis. Twenty-four (59%) patients had detectable DSA at biopsy, with 15 of them being considered non-adherent. Graft function at biopsy was similar in DSA (+) and (?) patients. DSA (+) patients had significantly higher tubulointerstitial inflammation (i and ti) and acute humoral (g+ptc+v+C4d) composite score than DSA (?). DSA (+)/non-adherent cases presented additionally with increased microvascular inflammation (ptc and v), besides having a distinctively lower ah score. C1q DSA strength was higher (P?=?.046) in non-adherent patients and correlated closely with C4d score (P?=?.002). Lower graft function and ah score, higher proteinuria and ci?+?ct score, and, separately per each model, DSA (+) (HR?=?2.446, P?=?.034), DSA (+)/non-adherent (HR?=?3.657, P?=?.005) and DSA (+)/C1q (+) (HR?=?4.831, P?=?.003) status were independent predictors of graft failure. CAABMR with concomitant DSA pose a higher risk of graft failure. Adherence should be evaluated, and histopathological phenotyping and DSA characterization may add critical information.     

Impact on mid-term kidney graft outcomes of pretransplant anti-HLA antibodies detected by solid-phase assays: Do donor-specific antibodies tell the whole story?

The detrimental impact of preformed anti-HLA donor-specific antibodies (DSA) is well defined, contrarily to non-donor-specific antibodies (NDSA). We sought to evaluate their clinical impact in a cohort of 724 kidney graft recipients in whom anti-HLA antibodies were thoroughly screened and identified in pre-transplant sera by solid-phase assays. NDSA or DSA were detected in 100 (13.8%) and 47 (6.5%) recipients respectively, while 577 (79.7%) were non-allosensitized (NaS). Incidence of antibody-mediated rejection at 1-year was 0.7%, 4.0% and 25.5% in NaS, NDSA and DSA patients, respectively (NaS vs. NDSA P = 0.004; NaS vs. DSA P < 0.001; NDSA vs. DSA P < 0.001). Graft survival was lowest in DSA (78.7%), followed by NDSA (88.0%) and NaS (93.8%) recipients (NaS vs. NDSA P = 0.015; NaS vs. DSA P < 0.001; NDSA vs. DSA P = 0.378). Multivariable competing risk analysis confirmed both NDSA (sHR = 2.19; P = 0.025) and DSA (sHR = 2.87; P = 0.012) as significant predictors of graft failure. The negative effect of NDSA and DSA on graft survival was significant in patients receiving no induction (P = 0.019) or an anti-IL-2 receptor antibody (P < 0.001), but not in those receiving anti-thymocyte globulin (P = 0.852). The recognition of the immunological risk associated with preformed DSA but also NDSA have important implications in patients’ risk stratification, and may impact clinical decisions at transplant.     

(F)Utility of the physical crossmatch for living donor evaluations in the age of the virtual crossmatch

Flow cytometric crossmatches (FCXM) are routinely performed to support living-donor renal transplantation. While long a laboratory mainstay, a physical crossmatch is costly, time consuming, and frequently poses interpretative conundrums with both false-positive and false- negative results. Given the increased utilization of the virtual crossmatch (vXM) in the deceased donor setting, our aim was to assess its utility in living donor evaluations. We reviewed 100 living donor FCXMs and retrospectively performed a vXM for each pair. Seventy-five (75) cases were concordant, (i.e., FCXM?/vXM? or FCXM+/vXM+) while 25 cases were discordant; Five were vXM+/FCXM? and 20 were FCXM+/vXM?. Since donor-specific antibodies (DSA) were not detected in the 20 FCXM+/vXM? cases, these were interpreted as false-positive, i.e., due to non-HLA antibodies. Importantly, none of these patients, when transplanted across a positive FCXM, experienced early antibody mediated rejection or subsequently developed HLA DSA. These data reveal that, for the vast majority of living donor evaluations, a vXM is an acceptable vetting procedure.     

Degree of HLA class II eplet mismatch load improves prediction of antibody-mediated rejection in living donor kidney transplantation

BackgroundHLA mismatching is a well known risk factor for worst outcomes in kidney transplantation.MethodsIn the present study, HLA antigen and eplet mismatches were determined in 151 living donor-recipient pairs transplanted between 2007 and 2014 and rejection episodes and graft survival were evaluated.ResultsWe found that high HLA-II eplet mismatch load (EpMM ≥ 13, versus low EpMM ≤ 5), was an independent predictor of AMR (adjusted HR = 14.839; P = 0.011), while HLA-II AgMM was not. We also showed that HLA-II EpMM load was a significant better predictor of AMR than AgMM (c-statistic = 0.064; P = 0.023). After discriminating HLA-II into HLA-DR and HLA-DQ loci we demonstrated that high versus low eplet mismatch load for HLA-DR (T3 ≥ 6 versus T = 0–1, p = 0.013) and HLA-DQ (T3 ≥ 7 versus T = 0–1, p = 0.009) are independent predictors for AMR.HLA-II EpMM increased discrimination performance of the classical HLA-II AgMM risk model (IDI, 0.061, 95%CI: 0.005–0.195) for AMR. Compared with AgMM, HLA-II eplet model adequately reclassified 13 of 17 patients (76.5%) with AMR and 92 of 134 patients (68.7%) without AMR (cfNRI, 0.785, 95%CI: 0.300–1.426).ConclusionsOur study evidences that eplet-based matching is a refinement of the classical HLA antigen mismatch analysis in LDKT and is a potential biomarker for personalized assessment of alloimmune risk.