Antibody-mediated chronic rejection (AMCR) is the leading cause of kidney graft loss. On average, more than 50% of patients resume dialysis within two years of diagnosis. The prevalence of AMCR reported in the literature varies, reaching up to 30%. The causes of chronic humoral rejection are not yet fully understood; however, its mechanism is based on donor-specific antibodies (DSAs), which may appear in the patient's serum and play a critical role. It remains unclear whether different inflammatory stimuli and/or inadequate immunosuppression induce their formation.
AMCR-related damage develops insidiously and often progresses rapidly to end-stage renal failure, with the onset of nephrotic-range proteinuria. For several years, it has been possible to detect and monitor DSAs in patient serum using the Luminex technique (LSAB: Luminex single antigen beads), which offers extremely high sensitivity and specificity.
De novo DSAs (dnDSAs) have been reported in 12-19% of kidney transplant recipients, and in 63% of cases their presence is associated with histological features of chronic rejection, high levels of proteinuria, and a rapid decline in glomerular filtration rate (GFR). It has been estimated that the reduction in GFR is four times greater in patients with dnDSAs than in age-matched transplant recipients without dnDSAs. Some authors report that even low dnDSA levels (MFI \< 1000) are predictive of poor outcomes. The unfavorable prognosis associated with dnDSAs appears to depend on their ability to fix complement (C1q, C4d, and C3d), which confers increased cytotoxicity.
The diagnostic criteria for AMCR, revised at the 2013 Banff meeting, are threefold: (i) morphological evidence of chronic rejection in tissue, (ii) evidence of antibody interaction with the vascular endothelium, and (iii) serum positivity for DSAs.
Currently, there is no effective therapy for chronic humoral rejection, and there is broad consensus within the scientific community that prevention-through optimal organ allocation and adequate immunosuppressive regimens-remains the only viable strategy. Most published studies describe small patient cohorts treated with steroids and/or rituximab (RTX), high-dose intravenous immunoglobulin (IVIG), plasmapheresis (PHP), and/or bortezomib (BTZ) in addition to standard therapy. None of these treatments has demonstrated proven efficacy, while an increased risk of infection has been consistently reported.
Extracorporeal photoapheresis (ECP) is currently used for the treatment of cutaneous lymphoma, graft-versus-host disease (GVHD), and chronic lung transplant rejection. Several studies have shown preservation of transplanted organ function. ECP is well tolerated, has no significant side effects, and has recently been included in treatment guidelines for GVHD refractory to other therapies. Clinical trials are currently underway to evaluate its efficacy in chronic pulmonary rejection (bronchiolitis obliterans syndrome, BOS), liver transplantation, and chronic GVHD.
In kidney transplantation, ECP has been reported in cases of acute antibody-mediated rejection, recurrent acute rejection, refractory acute rejection, and steroid-resistant acute rejection, both as adjunctive prophylaxis to standard immunosuppression and as therapy in patients diagnosed with chronic rejection. In our experience, ECP treatment administered to 11 kidney transplant recipients with biopsy-proven AMCR and stage 2-3 chronic kidney disease resulted in stabilization of estimated GFR and proteinuria over a three-year follow-up period. Concurrently, DSA levels were reduced and completely eliminated in 73% of patients. Furthermore, we demonstrated that the therapeutic efficacy of ECP was mediated by an increase in regulatory T cells (Treg) and a decrease in Th17 cells.
In lung transplantation, long-term graft survival is also significantly affected by the development of chronic rejection, known as chronic lung allograft dysfunction (CLAD). CLAD is defined as a persistent decline in lung function-particularly a reduction in FEV1 of at least 20% compared with post-transplant baseline-in the absence of other identifiable causes. Chronic rejection was previously identified exclusively with bronchiolitis obliterans syndrome (BOS), an irreversible obstructive defect. More recent studies have described an additional phenotype, restrictive allograft syndrome (RAS). Although no universally accepted definition of RAS exists, emerging evidence suggests that BOS and RAS differ in pathological features, pathogenesis, clinical course, and natural history.
At present, no randomized controlled trials have evaluated ECP in lung transplantation, and, as in kidney transplantation, the mechanisms underlying its effects in chronic lung rejection remain unclear. Two small studies have suggested a role for ECP in the expansion of peripheral regulatory T-cell clones, while a more recent study indicates that ECP may modulate B cells and DSA production. Finally, there are currently no data supporting the early identification of so-called "responders" to ECP therapy.
Therefore, based on current knowledge, despite the increasingly widespread use of this treatment in various clinical settings, the mechanisms underlying the efficacy of ECP are not yet fully understood, particularly in the field of transplantation
