De Novo Donor-Specific Human Leukocyte Antigen Antibody Screening in Kidney Transplant Recipients After the First Year Posttransplantation: A Medical Decision Analysis

The Clinical Utility of Post-Transplant Monitoring of Donor-Specific Antibodies in Stable Renal Transplant Recipients: A Consensus Report With Guideline Statements for Clinical Practice

Solid phase immunoassays improved the detection and determination of the antigen-specificity of donor-specific antibodies (DSA) to human leukocyte antigens (HLA). The widespread use of SPI in kidney transplantation also introduced new clinical dilemmas, such as whether patients should be monitored for DSA pre- or post-transplantation. Pretransplant screening through SPI has become standard practice and DSA are readily determined in case of suspected rejection. However, DSA monitoring in recipients with stable graft function has not been universally established as standard of care. This may be related to uncertainty regarding the clinical utility of DSA monitoring as a screening tool. This consensus report aims to appraise the clinical utility of DSA monitoring in recipients without overt signs of graft dysfunction, using the Wilson & Junger criteria for assessing the validity of a screening practice. To assess the evidence on DSA monitoring, the European Society for Organ Transplantation (ESOT) convened a dedicated workgroup, comprised of experts in transplantation nephrology and immunology, to review relevant literature. Guidelines and statements were developed during a consensus conference by Delphi methodology that took place in person in November 2022 in Prague. The findings and recommendations of the workgroup on subclinical DSA monitoring are presented in this article.

On the clinical relevance of using complete high-resolution HLA typing for an accurate interpretation of posttransplant immune-mediated graft outcomes

Complete and high-resolution (HR) HLA typing improves the accurate assessment of donor–recipient compatibility and pre-transplant donor-specific antibodies (DSA). However, the value of this information to identify de novo immune-mediated graft events and its impact on outcomes has not been assessed. In 241 donor/recipient kidney transplant pairs, DNA samples were re-evaluated for six-locus (A/B/C/DRB1/DQB1+A1/DPB1) HR HLA typing. De novo anti-HLA antibodies were assessed using solid-phase assays, and dnDSA were classified either (1) as per current clinical practice according to three-locus (A/B/DRB1) low-resolution (LR) typing, estimating donor HLA-C/DQ typing with frequency tables, or (2) according to complete six-locus HR typing. The impact on graft outcomes was compared between groups. According to LR HLA typing, 36 (15%) patients developed dnDSA (LR_dnDSA+). Twenty-nine out of 36 (80%) were confirmed to have dnDSA by HR typing (LR_dnDSA+/HR_dnDSA+), whereas 7 (20%) did not (LR_dnDSA+/HR_dnDSA−). Out of 49 LR_dnDSA specificities, 34 (69%) were confirmed by HR typing whereas 15 (31%) LR specificities were not confirmed. LR_dnDSA+/HR_dnDSA+ patients were at higher risk of ABMR as compared to dnDSA− and LR_dnDSA+/HR_dnDSA− (logRank < 0.001), and higher risk of death-censored graft loss (logRank = 0.001). Both LR_dnDSA+ (HR: 3.51, 95% CI = 1.25–9.85) and LR_dnDSA+/HR_dnDSA+ (HR: 4.09, 95% CI = 1.45–11.54), but not LR_dnDSA+/HR_dnDSA− independently predicted graft loss. The implementation of HR HLA typing improves the characterization of biologically relevant de novo anti-HLA DSA and discriminates patients with poorer graft outcomes.

The natural history of de novo donor-specific HLA antibodies after kidney transplantation

Background

De novo donor-specific HLA antibodies (dnDSA) are key factors in the diagnosis of antibody-mediated rejection (ABMR) and related to graft loss.

Methods

This retrospective study was designed to evaluate the natural course of dnDSA in graft function and kidney allograft survival and to assess the impact of mean fluorescence intensity (MFI) evolution as detected by annual Luminex^® screening. All 400 kidney transplant recipients with 731 dnDSA against the last graft (01/03/2000-31/05/2021) were included.

Results

During 8.3 years of follow-up, ABMR occurred in 24.8% and graft loss in 33.3% of the cases, especially in patients with class I and II dnDSA, and those with multiple dnDSA. We observed frequent changes in MFI with 5-year allograft survivals post-dnDSA of 74.0% in patients with MFI reduction ≥ 50%, 62.4% with fluctuating MFI (MFI reduction ≥ 50% and doubling), and 52.7% with doubling MFI (log-rank p < 0.001). Interestingly, dnDSA in 168 (24.3%) cases became negative at some point during follow-up, and 38/400 (9.5%) patients became stable negative, which was associated with better graft survival. Multivariable analysis revealed the importance of MFI evolution and rejection, while class and number of dnDSA were not contributors in this model.

Conclusion

In summary, we provide an in-depth analysis of the natural course of dnDSA after kidney transplantation, first evidence for the impact of MFI evolution on graft outcomes, and describe a relevant number of patients with a stable disappearance of dnDSA, related to better allograft survival.

The Role of Donor Sex in Females Undergoing Repeat Kidney Transplant: Does Prior Donor Sex Matter?

Female recipients of male donor kidneys are at increased risk for graft failure because of the HY antigen effect. However, whether prior transplant with a male donor impacts subsequent transplant outcomes is unknown. Therefore, the purpose of this study was to determine whether prior male-current male donor sex is associated with an increased risk of graft failure in female recipients.

Methods

We performed a cohort study of adult female recipients undergoing a second kidney transplant (2000-2017), identified using the Scientific Registry of Transplant Recipients. Using multivariable Cox models, we analyzed the risk of death-censored graft loss (DCGL) if the second transplant was from a male versus female kidney donor, conditional on donor sex at the time of the first transplant. In a secondary analysis, we stratified results by recipient age (>50 or ≤50 y) at the time of retransplant.

Results

Of 5594 repeat kidney transplants, 1397 (25.0%) developed DCGL. Overall, there was no association between first and second donor sex pairing and DCGL. A prior and current female donor (FD₁FD₂) posed a higher risk for DCGL in recipients aged >50 y at second transplant (hazard ratio,≤0.67, confidence interval 0.46-0.98, for all other donor combinations), but posed a lower risk if aged ≤50 y at retransplant (hazard ratio, ≥1.37, confidence interval 1.04-1.80, for all other donor combinations).

Conclusions

Overall, past-current donor sex pairing was not associated with DCGL in female recipients undergoing second kidney transplant; however, the risk with a past and current female donor was increased in older, and decreased in younger, female recipients at retransplant.

The Clinical Impact of Anti-HLA Donor Specific Antibody Detection Through First Year Screening on Stable Kidney Transplant Recipients

Anti-HLA Donor Specific Antibody (DSA) detection post kidney transplant has been associated with adverse outcomes, though the impact of early DSA screening on stable patients remain unclear. We analyzed impact of DSA detection through screening in 1st year stable patients (n = 736) on subsequent estimated glomerular filtration rate (eGFR), death censored graft survival (DCGS), and graft failure (graft loss including return to dialysis or re-transplant, patient death, or eGFR < 20 ml/min at last follow up). Patients were grouped using 1st year screening into DSA+ (Class I, II; n = 131) or DSA- (n = 605). DSA+ group were more DR mismatched (p = 0.02), more sensitized (cPRA ≥90%, p = 0.002), less Caucasian (p = 0.04), and had less pre-emptive (p = 0.04) and more deceased donor transplants (p = 0.03). DSA+ patients had similar eGFR (54.8 vs. 53.8 ml/min/1.73 m², p = 0.56), DCGS (91% vs. 94%, p = 0.30), and graft failure free survival (76% vs. 82%, p = 0.11). DSA timing and type did not impact survival. Among those with a protocol biopsy (n = 515), DSA detected on 1st year screening was a predictor for graft failure on multivariate analysis (1.91, 95% CI 1.03-3.55, p = 0.04). Overall, early DSA detection in stable patients was an independent risk factor for graft failure, though only among those who underwent a protocol biopsy.

Screening strategy for de novo donor-specific HLA antibodies beyond the first year after kidney transplantation: Personalized or "one size fits all"?

Screening for de novo donor-specific HLA antibodies (DSAs) after kidney transplantation is widely recommended. The aim of this single-center, cross-sectional study was to investigate the frequency of therapeutic interventions triggered by de novo DSA screening. We included 464 patients screened for de novo DSA at annual visits after a median of 5 years post-transplant (range 1 to 19 years). Overall, de novo DSAs were detected in 55/464 patients (11.9%) with a stepwise increase of the prevalence from 4.9% at 1 year post-transplant to 18.9% at >10 years post-transplant. Subsequent allograft biopsies were performed in 24/55 patients (44%). The main reasons to omit biopsies were good/stable allograft function and anticipated lack of clinical consequences (eg, relevant comorbidities). Rejection processes were detected in 16/24 biopsies (67%). Therapeutic interventions were made in 18/464 screened patients (3.9%) with a significantly higher rate in the youngest quartile of patients (≤48 years; 7.9%) compared to the middle 50% (49-67 years; 3%) and the oldest quartile (≥68 years; 1.7%) (P = .03). Our study suggests that the frequency of therapeutic interventions triggered by de novo DSA screening after kidney transplantation is overall low, but significantly higher in younger patients, arguing for a personalized, age-adapted de novo DSA screening strategy.

Association of immunosuppressive agents and cytomegalovirus infection with de novo donor-specific antibody development within 1 year after renal transplantation

The association between immunosuppressive therapy or cytomegalovirus (CMV) infection and detection of de novo donor-specific antibody (dnDSA) at 1 year after transplantation was evaluated. The impact of dnDSA positivity at 1 year after transplantation on long-term death-censored renal graft survival was also evaluated. One hundred and sixty adults receiving living renal allografts were studied. Inclusion criteria were renal graft survival for at least 1 year and a standard regimen of immunosuppressive therapy with tacrolimus, mycophenolate mofetil (MMF), steroids, and basiliximab. DSA were measured retrospectively by the Luminex assay. The coefficient of variation (CV) was calculated and receiver operating characteristic (ROC) analysis was employed to clarify the association of tacrolimus with development of dnDSA. Seven of the 160 patients (4.4%) were positive for dnDSA. The intra-patient minimum trough level of tacrolimus (cutoff value: 3.2 ng/mL) was associated with development of dnDSA. Discontinuation of MMF and treatment of CMV infection were more frequent in patients with dnDSA than in those without dnDSA. In multivariate analysis, a low trough level of tacrolimus, discontinuation of MMF, and treatment of CMV infection within 1 year after transplantation were independently associated with detection of dnDSA at 1 year. In patients with or without dnDSA at 1 year, the 10-year allograft survival rate was 51.4 versus 87.9%, respectively (P = 0.002). A lower tacrolimus trough level, discontinuation of MMF, and treatment of CMV infection were associated with dnDSA positivity. Further investigation is needed to determine whether a new immunosuppressive regimen that avoids these factors can reduce dnDSA positivity.

Impact of persistent preformed and de novo donor-specific antibodies detected at 1 year after kidney transplantation on long-term graft survival in Japan: a retrospective study

BACKGROUND

We evaluated the impact of persistent preformed donor-specific antibody (DSA) and de novo DSA (dnDSA) detected at 1 year posttransplantation on long-term death-censored graft survival.

METHODS

One hundred and sixty adult patients who received living kidney allograft with pretransplant-negative T-cell complement-dependent cytotoxicity crossmatch (CDCXM), and without periodic screening for DSA, were eligible for this study. All enrolled patients were retrospectively tested for DSA using the Luminex assay. The presence of DSA was analyzed in stored serum samples collected at 1 year posttransplantation. If the recipients had DSA, it was analyzed in the pretransplant serum sample. The detection of DSA solely in the 1 year posttransplant sample was defined as dnDSA, and DSA detection in both pretransplant and 1 year posttransplant samples was defined as persistent preformed DSA.

RESULTS

DSAs were identified in 14 (8.8%) of the 160 patients. Seven patients had persistent preformed DSA, 6 had dnDSA, and 1 had both persistent preformed and dnDSA at 1 year posttransplantation. Death-censored allograft survival rates of patients with DSA versus those without DSA at 7 and 11 years were 77.9 vs. 97.8% and 60.6 vs. 89.2%, respectively. The graft survival rate was lower in patients with persistent preformed DSA and/or dnDSA. Each case of preformed DSA and dnDSA was associated with long-term graft survival.

CONCLUSION

The presence of persistent preformed DSA or dnDSA at 1 year posttransplantation may be a predictor of long-term graft survival. Further study is needed to evaluate whether periodic screening for DSA improves long-term graft survival.

Biomarkers and Pharmacogenomics in Kidney Transplantation

This review is focused on present and future biomarkers, along with pharmacogenomics used in clinical practice for kidney transplantation. It aims to highlight biomarkers that could potentially be used to improve kidney transplant early and long-term graft survival, but also potentially patient co-morbidity. Future directions for improving outcomes are discussed, which include immune tolerance and personalising immunosuppression regimens.

Utility of protocol kidney biopsies for de novo donor-specific antibodies

There is limited information about the role of protocol kidney biopsies for de novo donor-specific antibodies (dnDSA) in kidney transplant recipients, especially in those with stable graft function. We initiated a routine posttransplant DSA monitoring and surveillance biopsy program for dnDSA since 2014. We identified 45 kidney transplant recipients with dnDSA detected between January 2014 and February 2017 who underwent kidney biopsy within 60 days of detection of dnDSA. Twenty-nine (64%) had stable graft function and 16 (36%) had impaired graft function at the time of dnDSA detection. Even in the group with stable graft function, we found a high rate of rejection (53%) on biopsy. Eighty-eight percent of patients with impaired graft function had rejection. Those patients with impaired graft function had significantly lower estimated glomerular filtration rate at 12 months postbiopsy and at last follow-up. Those with impaired graft function had more graft failures; however, this result was not statistically significant. The high rate of asymptomatic rejection, and the fact that outcomes in asymptomatic patients are poor, is in support of the utility of surveillance biopsies in patients with dnDSA.

Ibrutinib suppresses alloantibody responses in a mouse model of allosensitization

BACKGROUND

Ibrutinib is a Bruton's tyrosine Kinase (BTK) antagonist that inhibits B cell receptor (BCR) signaling. Complete BTK deficiency is associated with absence of B-cells. Ibrutinb is currently approved by FDA for treatment of B-cell malignancies, including Waldenström macroglobulinaemia. We recently carried out studies to determine if ibrutinib could modify alloantibody responses.

MATERIALS AND METHODS

A mouse model of allogenic sensitization using a C57BL/6 mouse as the recipient of a skin allograft from an HLA-A2 transgenic mouse was utilized to examine the effects of ibrutinib on alloantibody responses and B cell effector functions. Donor-specific antibody (DSA) levels were measured in a flow-cytometric antibody binding assay. Splenic T and B cell subsets and plasma cells were analyzed in flow cytometry.

RESULTS

Control mice developed peak levels of DSA IgM at day 14 PTx while the ibrutinib treated mice had significantly lower levels of DSA IgM (p=0.0047). Control mice developed HLA.A2-specific IgG antibodies at day 14 (230±60 MFI) and reached peak levels at day 21 (426±61 MFI). In contrast, mice in the treatment group had low levels of HLA.A2-specific IgG at day 14 (109±59 MFI, p=0.004) and day 21 (241±86 MFI, p=0.003). FACS analysis found a reduction of B220⁺ or CD19⁺ B cell population (p<0.05). In addition, ibrutinib attenuated recall DSA IgG responses to re-sensitization (p<0.05) and reduced CD38⁺CD138⁺ plasma cells (p<0.05) in the spleens.

CONCLUSIONS

Ibrutinib is effective in suppressing alloantibody responses through blocking BTK-mediated BCR signaling, leading to reduction of B cells and short-lived plasma cells in the spleens. Use of ibrutinib may provide benefits to HLA-sensitized transplant patients for alloantibody suppression.

Changing Paradigms in the Management of Rejection in Kidney Transplantation: Evolving From Protocol-Based Care to the Era of P4 Medicine

PURPOSE OF REVIEW

P4 medicine denotes an evolving field of medicine encompassing predictive, preventive, personalized, and participatory medicine. Using the example of kidney allograft rejection because of donor-recipient incompatibility in human leukocyte antigens, this review outlines P4 medicine's relevance to the various stages of the kidney transplant cycle.

SOURCES OF INFORMATION

A search for English articles was conducted in Medline via OvidSP (up to August 18, 2016) using a combination of subject headings (MeSH) and free text in titles, abstracts, and author keywords for the concepts kidney transplantation and P4 medicine. The electronic database search was expanded further on particular subject headings.

FINDINGS

Available histocompatibility methods exemplify current applications of the predictive and preventive domains of P4 medicine in kidney transplant recipients' care. Pharmacogenomics are discussed as means to facilitate personalized immunosuppression regimens and promotion of active patient participation as a means to improve adherence.

LIMITATIONS

For simplicity, this review focuses on rejection. P4 medicine, however, should more broadly address health concerns in kidney transplant recipients, including competing outcomes such as infections, malignancies, and cardiovascular disease. This review highlights how biomarkers to evaluate these competing outcomes warrant validation and standardization prior to their incorporation into clinical practice.

IMPLICATIONS

Consideration of all 4 domains of the P4 medicine framework when caring for and/or studying kidney transplant recipients has the potential of increasing therapeutic efficiency, minimizing adverse effects, decreasing health care costs, and maximizing wellness. Technologies to gauge immune competency, immunosuppression requirements, and early/reversible immune-mediated injuries are required to optimize kidney transplant care.