We conducted this study in compliance with the principles of the Declaration of Helsinki. The study protocol was reviewed by the Institutional Review Board of Keimyung University Dongsan Medical Center, and they approved this study (IRB No. 2018-12-033). The Institutional Review Board waived the requirement for informed consent because the patients’ data were used retrospectively for research, except for important personal information, which the individual was identified by, and was explained to all the donors’ families and all recipients before kidney transplant (KT). Therefore, this study did not contain any identifiable personal information, except for the clinical process and outcome as a retrospective medical record study.

We retrospectively analyzed 35 kidney transplant recipients (KTRs) diagnosed with CABMR between 2010 and 2018. We excluded KTRs with positive crossmatching prior to KT, ABO-incompatible KT, and those whose data were insufficient. We divided the study population into two groups as follows: 14 KTRs without and 21 KTRs with dnDSA. We defined KTRs without dnDSA as KTRs with undetectable donor-specific anti-HLA antibodies and KTRs with dnDSA as KTRs with detectable donor-specific anti-HLA antibodies. We investigated the baseline characteristics of the study population, pathologic findings at the time of diagnosis of CABMR, change in allograft function before the diagnosis, and at 1, 3, 6, and 12 months after the diagnosis, the amount of proteinuria at the time of diagnosis, response to treatment for CABMR, and allograft survival rate based on the presence of dnDSA.

We used basiliximab (20 mg on days 0 and 4, Simulect; Novartis, Basel, Switzerland) for KTRs with low immunologic risk and anti-thymocyte globulin (thymoglobulin; Sanofi Genzyme, Cambridge, MA, USA; 1.5 mg/kg on day 0 and 1.0 mg/kg on days 1 through 3) for KTRs with high immunologic risk as immunosuppressants for induction treatment. We used cyclosporine (3 mg/kg, twice a day; Sandimmun; Novartis) or tacrolimus (0.05 mg/kg, twice a day, Prograf; Astellas Pharma Inc., Toyama, Japan), prednisolone (30 mg, once a day), and mycophenolate mofetil (750 or 1,000 mg, twice a day, CellCept; Hoffmann-La Roche Inc., Nutley, NJ, USA) as immunosuppressants for maintenance therapy. The treatment protocol for CABMR was as follows: high-dose intravenous immunoglobulin (IVIG; 2 g/kg) after a single dose of rituximab (375 mg/m²) infusion, and treatment with (2–3 sessions) or without plasmapheresis according to the pathologic findings, allograft function, and willingness to undergo the therapy.

We investigated the age of donors and recipients at the time of CABMR diagnosis, sex of the donors and recipients, KT type, frequency of KT, dialysis type prior to KT, dialysis vintage, causes of end-stage renal disease, the number of HLA mismatches, immunosuppressants for induction and maintenance treatment, previous biopsy-proven acute rejection (BPAR), the amount of proteinuria at the time of diagnosis of CABMR, panel reactive antibody (PRA) class I or II >50%, positive DSA class I or II, mean fluorescence index (MFI) value, and pathologic findings. Allograft protocol biopsies were performed at 12 months after KT, and indication biopsies were performed at the time of allograft dysfunction or if the KTR had persistent proteinuria. All BPARs were the result of an indication biopsy in this study. Allograft biopsies were analyzed using the Banff 2017 classification, which defined CABMR as follows: (1) morphologic evidence of chronic tissue injury, (2) evidence of current/recent antibody interaction with the vascular endothelium, and (3) serologic evidence of DSAs to the HLA or other antigens [1]. Allograft function was measured as the estimated glomerular filtration rate (eGFR) based on the modification of diet in the renal disease (MDRD) formula before the diagnosis of CABMR, at the time of diagnosis of CABMR, and at 1, 3, 6, and 12 months after diagnosis or treatment. Proteinuria was measured using the spot urine protein-creatinine ratio. We examined PRA screening and identification (class I and class II) before KT and annually after KT to evaluate KTRs with high immunological risks. We defined KTRs with PRA >50% as high-risk immunological patients. DSA was analyzed with a Luminex Single Antigen assay, using LABscreen Single Antigen HLA class I and class II (One Lambda, Canoga Park, CA, USA) according to the manufacturer’s manual prior to KT and at 1, 3, 6, and 12 months and annually after KT or at the time of diagnosis and monthly after the diagnosis or treatment of CABMR. We defined DSA that existed before KT as preformed DSA, and when DSA occurred newly during the follow-up period after KT without preformed DSA or was different from preformed DSA was defined as dnDSA.

Continuous variables were analyzed using the Mann–Whitney U-test, and categorical variables were analyzed by the chi-square or Fisher’s exact test. Graft and patient survival rates were evaluated using the Kaplan-Meier analysis with the log-rank test. Univariate and multivariate analyses with Cox regression analysis were performed to investigate the risk factors for allograft failure. P-values <0.05. were considered statistically significant. Statistical analysis was performed using SPSS ver. 18 (SPSS Inc., Chicago, IL, USA).

The mean age of KTRs at the time of diagnosis of CABMR was 50±13 years, and 24 patients (68.6%) were male. Living donor KT occurred in 24 patients (68.6%), and 30 patients (85.7%) were the first KT recipients. All patients underwent hemodialysis before KT, and 21 patients (77.1%) had chronic glomerulonephritis as the primary renal disease. The main immunosuppressants used were tacrolimus (30, 85.7%) and cyclosporine (5, 14.3%). Eight patients (22.9%) experienced BPAR prior to the diagnosis of CABMR. Median proteinuria at the time of diagnosis of CABMR was 1.1 g (interquartile range [IQR], 0.3–2.8 g). The time from KT to the development of dnDSA was 91.6±77.4 months. The time until the diagnosis of CABMR after transplantation was 74.9 months (IQR, 42.8–142.6 months).

The mean follow-up duration was 129.0±72.7 months. There were no significant differences in the mean age of donors and recipients, the proportion of sex distribution, KT type, Kidney Donor Profile Index score, KT number, duration of dialysis, dialysis type before KT, causes of end-stage renal disease, the number of HLA mismatches, induction and maintenance immunosuppressants, the rate of PRA >50%, and preformed DSA positivity, and the rate of previous BPAR between the dnDSA (–) and dnDSA (+) groups. There was one case (7.1%) of T-cell mediated rejection (TCMR) in the undetectable dnDSA group and one case (4.8%) of TCMR in the detectable dnDSA group. There were no significant differences in the coexistence of TCMR between the two groups. The time from KT until the diagnosis of CABMR showed no significant difference between the two groups (Table 1).

Pathologic findings showed that acute changes such as glomerulitis, peritubular capillaritis, microvascular inflammation, arteritis, and tubulitis were more severe in the dnDSA (+) group than in the dnDSA (–) group; however, there was no significant difference between the two groups. Chronic changes such as transplant glomerulopathy, arterial intimal fibrosis, and interstitial fibrosis/tubular atrophy were also not significantly different between the two groups. The proportion of C4d positivity was not significantly different between the two groups (Table 2).

There was no significant difference in the allograft function at 12 months after the diagnosis of CABMR and the difference in the amount of proteinuria at diagnosis between the dnDSA (–) and dnDSA (+) groups. The use of rituximab and IVIG treatment was higher in the dnDSA (+) group than in the dnDSA (–) group (Table 2).

Nine patients (25.7%) developed graft failure, including 5 (35.7%) patients in the dnDSA (–) group and 4 (19.0%) in the dnDSA (+) group. The causes of graft failure were as follows: chronic rejection, 4 (28.6%) and 3 (7.1%); infection, 1 (7.1%) and 1 (4.8%) in the dnDSA (–) and dnDSA (+) groups, respectively. In the Kaplan-Meier analysis, there was no significant difference in the death-censored overall graft survival rate (Fig. 1A) and death-censored graft survival rate after the diagnosis of CABMR (Fig. 1B) between the dnDSA (–) and dnDSA (+) groups. In the subgroup analysis, the death-censored graft survival rate was lower in the high-proteinuria group than in the low-proteinuria group in both the dnDSA (–) and dnDSA (+) groups (Fig. 2). However, there was no significant difference in the death-censored graft survival rate between the two groups, regardless of the treatment administered (Fig. 3). On multivariate Cox regression analysis, deceased donor kidney transplantation and eGFR at 12 months after the diagnosis of CABMR were the risk factors associated with graft failure in KT after adjusting for the significant variables in the univariate analysis (hazard ratio, 57.013; 95% confidence interval, 1.698–1,914.123, P=0.024; hazard ratio, 0.850; 95% confidence interval, 0.738–0.980, P=0.025) (Table 3).

Five patients (14.3%) died, including one (7.1%) patient in the dnDSA (–) group and 4 (19.0%) in the dnDSA (+) group. The causes of death were as follows: infection, 1 (7.1%) and 3 (14.3%); alveolar hemorrhage, 0 and 1 (4.8%) in the dnDSA (–) and dnDSA (+) groups, respectively. In the Kaplan-Meier analysis, patient survival rates showed no significant differences between the dnDSA (–) and dnDSA (+) groups (Table 3).