DSA in solid organ transplantation: is it a matter of specificity, amount, or functional characteristics?

Impact of low-level pretransplant donor-specific antibodies detected by the Luminex platform on acute rejection and long-term graft survival

BACKGROUND

The Luminex platform, where beads are coated with single human leukocyte antigens (HLA), detects HLA antibodies with higher sensitivity and specificity compared to complement-dependent cytotoxicity (CDC) assay and flow cross-match (FCXM). The clinical significance of donor-specific antibodies (DSAs) detected by this method is still under investigation.

AIM

To report the impact of low-level pretransplant DSAs detected by the Luminex platform on the rates of acute rejection (AR), allograft function, and long-term graft survival.

METHODS

This retrospective study was conducted at the Immunology Department of Sindh Institute of Urology and Transplantation, Karachi, Pakistan between January 2013 and December 2022. During this period 2714 patients were transplanted. Out of these patients 78 (2.9%) patients had low-level DSAs detected by the Luminex flow beads method and were negative by CDC and FCXM with their donors. All recipients received ABO-compatible live-related kidney transplants. All patients had a minimum follow-up of 1 year. Graft rejection rates, graft function, and patient and graft survival were analyzed. The estimated glomerular filtration rate was calculated by the full CKD-EPI formula.

RESULTS

The mean age of all recipients was 29.57 ± 10.11 years and 34.53 ± 9.09 years for the donors. In 48 (61.5%) patients, the cause of end-stage kidney disease was unknown. DSA against HLA class I was detected in 36 (46.1%) patients, class II in 35 (44.8%) patients, and both class I and II in 7 (8.9%) patients. AR episodes were encountered in 8 (10.3%) cases. Seven (87.5%) had T cell mediated rejection (type IA) and one acute antibody-mediated rejection. Antibody status was re-evaluated at the time of biopsy-proven ARs. Five (62.5%) patients lost their DSAs, while three (37.5%) had persistent DSAs. The mean estimated glomerular filtration rate at 1 year was 80.56 ± 27.48 mL/min/1.73 m² and at the last follow-up 73.41 ± 28.80 mL/min/1.73 m². The 1-year and 10-year patient and graft survival rates were 99% and 79% and 95% and 75%, respectively. During the follow-up period, 10 (12.8%) patients died, 8 patients had a functioning graft, and 2 patients had failed grafts. Eight patients died due to cardiopulmonary arrest, and two died due to sepsis with failed grafts.

CONCLUSION

Patients with pretransplant low-level DSAs on Luminex without CDC and FCXM reactivity had good allograft outcomes at 1 year and 10 years as long as they are induced with biological agents and given potent maintenance immunosuppressants.

Outcome-based Risk Assessment of Non-HLA Antibodies in Heart Transplantation: A Systematic Review

BACKGROUND

Current monitoring after heart transplantation (HT) employs repeated invasive endomyocardial biopsies (EMB). Although positive EMB confirms rejection, EMB fails to predict impending, subclinical, or EMB-negative rejection events. While non-human leukocyte antigen (non-HLA) antibodies have emerged as important risk factors for antibody-mediated rejection after HT, their use in clinical risk stratification has been limited. A systematic review of the role of non-HLA antibodies in rejection pathologies has the potential to guide efforts to overcome deficiencies of EMB in rejection monitoring.

METHODS

Databases were searched to include studies on non-HLA antibodies in HT recipients. Data collected included the number of patients, type of rejection, non-HLA antigen studied, association of non-HLA antibodies with rejection, and evidence for synergistic interaction between non-HLA antibodies and donor-specific anti-human leukocyte antigen antibody (HLA-DSA) responses.

RESULTS

A total of 56 studies met the inclusion criteria. Strength of evidence for each non-HLA antibody was evaluated based on the number of articles and patients in support versus against their role in mediating rejection. Importantly, despite previous intense focus on the role of anti-major histocompatibility complex class I chain-related gene A (MICA) and anti-angiotensin II type I receptor antibodies (AT1R) in HT rejection, evidence for their involvement was equivocal. Conversely, the strength of evidence for other non-HLA antibodies supports that differing rejection pathologies are driven by differing non-HLA antibodies.

CONCLUSIONS

This systematic review underscores the importance of identifying peri-HT non-HLA antibodies. Current evidence supports the role of non-HLA antibodies in all forms of HT rejection. Further investigations are required to define the mechanisms of action of non-HLA antibodies in HT rejection.

Recurrent IgA Nephropathy or Subclinical Chronic Humoral Rejection With Predominance of Plasma Cells: A Case Report

Both antibody-mediated rejection and recurrence of kidney disease are major causes of allograft loss. A possible strategy to address the former is donor-specific antibody (DSA) monitoring. In this patient with IgA nephropathy, DSA detection triggered biopsy 10 years after transplant despite preserved graft function and normal urinary examination. Biopsy showed mild glomerulitis, mild capillaritis, and transplant glomerulopathy with no C4d peritubular capillary staining, along with IgA-dominant mesangial immunofluorescence staining. Interstitial inflammation had a notable predominance of plasma cells, a finding that has been variably attributed to rejection and worse prognosis. Immunosuppression was optimized with the working diagnosis of recurrent IgA nephropathy and/or chronic active humoral rejection with predominance of plasma cells, with favorable response at follow-up. This case illustrates the conflicting role of DSA monitoring and allograft biopsy to optimize immunosuppression management. Despite imperfect correlation with each other and clinical outcomes, they are key to tailor therapy. In the future, characterization of the role of plasma cell infiltrates in rejection might further enable prognosis and treatment individualization.

Lowering maintenance immune suppression in elderly kidney transplant recipients; connecting the immunological and clinical dots

The management of long-term immune suppressive medication in kidney transplant recipients is a poorly explored field in the area of transplant medicine. In particular, older recipients are at an increased risk for side effects and have an exponentially increased risk of infection-related death. In contrast, an aged immune system decreases the risk of acute T-cell-mediated rejection in older recipients. Recent advances in alloimmunity research have shown a rapid and substantial decline in polyfunctional, high-risk CD4⁺ T cells post-transplantation. This lowers the direct alloreactivity responsible for T-cell-mediated rejection, also known as donor-specific hyporesponsiveness. Chronic antibody-mediated rejection (c-aABMR) is the most frequent cause of kidney graft loss in the long term. However, in older adults, c-aABMR as a cause of graft loss is outnumbered by death with a functioning graft. In addition, DSA development and a diagnosis of c-aABMR plateau ~10 years after transplantation, resulting in a very low risk for rejection thereafter. The intensity of immune suppression regimes could likely be reduced accordingly, but trials in this area are scarce. Tacrolimus monotherapy for 1 year after transplantation seems feasible in older kidney transplant recipients with standard immunological risk, showing the expected benefits of fewer infections and better vaccination responses.