BACKGROUND: Presensitized patients with circulating donor-specific antibodies (DSAs) before transplantation are at risk for antibody-mediated rejection (AMR). Peritransplant desensitization mitigates but does not eliminate the alloimmune response. We examined the possibility that subthreshold AMR activity undetected by histology could be operating in some early biopsies. METHODS: Transcriptome of kidney allograft biopsies performed within the first month in presensitized patients (DSA+) who had received desensitization and did not develop active/probable AMR by histology (R-) was compared with biopsies showing active/probable AMR (R+/DSA+). As negative controls, biopsies without rejection by histology in patients without DSA at transplantation were used (R-/DSA-). RNA sequencing from biopsies selected from the biobank was used in cohort 1 (n = 32) and microarray, including the molecular microscope (Molecular Microscope Diagnostic System [MMDx]) algorithm, in recent cohort 2 (n = 30). RESULTS: The transcriptome of R-/DSA+ was similar to R+/DSA+ as these groups differed in 14 transcripts only. Contrarily, large differences were found between both DSA+ groups and negative controls. Fast gene set enrichment analyses showed upregulation of the immune system in both DSA+ groups (gene ontology terms: adaptive immune response, humoral immune response, antigen receptor-mediated signaling, and B-cell receptor signaling or complement activation) when compared with negative controls. MMDx assessment in cohort 2 classified 50% of R-/DSA+ samples as AMR and found no differences in AMR molecular scores between R+ and R- DSA+ groups. In imlifidase desensitization, MMDx series showed a gradual increase in AMR scores over time. CONCLUSIONS: Presensitized kidney transplant recipients exhibited frequent molecular calls of AMR in biopsy-based transcript diagnostics despite desensitization therapy and negative histology.

• Publication type
• Journal Article MeSH

Antibody-mediated rejection (ABMR) is a major obstacle to the long-term success in kidney transplantation. Diagnosis of ABMR is determined according to the internationally recognized Banff criteria. However, a significant proportion of patients does not meet all the defined criteria, and the outcome of such cases remains poorly understood. The histology of ABMR frequently lacks sensitivity and specificity. More importantly, mixed forms of ABMR and T cell-mediated rejection as well as findings of nonspecific injury are common in clinical settings. Donor-specific anti-HLA antibodies (DSA) are detectable only in half of the ABMR cases by histology. Prognostic role of non-HLA antibodies against various endothelial proteins has been discussed. Antibody independent NK cell activation reflecting killer-cells' inhibitory receptor incompatibility is suggested in microvascular inflammation in DSA negative patients. Molecular assessment of ABMR has been prioritized to overcome high interobserver variability and improve diagnostics in mixed forms of rejections and in DSA negative cases. Finally, donor-derived cell-free DNA detected in a recipient's peripheral blood sample has been proposed as a noninvasive marker for diagnosis of graft rejection, and thus might serve as a liquid biopsy in the near future. Despite all achievements, diagnosing ABMR in kidney allografts remains to be a challenge in a significant number of cases.

• MeSH
• Allografts MeSH
• Isoantibodies MeSH
• Kidney pathology   MeSH
• Humans MeSH
• Graft Rejection diagnosis   MeSH
• Kidney Transplantation * adverse effects   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Isoantibodies MeSH