Molecular Diagnosis of kidney allograft rejection using the BHOT gene panel-based HistoMx System in Chinese population: a validation study

Background: Molecular diagnostics have been increasingly incorporated into kidney allograft pathology to complement conventional histologic evaluation. The Banff Human Organ Transplant (B-HOT) gene panel–based molecular diagnostic system has been developed and validated primarily in European and North American cohorts, but its applicability in Chinese kidney transplant recipients remains unclear.
Methods: We retrospectively analyzed 84 kidney allograft biopsies performed at a large Chinese transplant center between 2015 and 2025. Histologic diagnoses were established according to the Banff 2019 classification and reassessed using the Banff 2022 criteria. RNA was extracted from formalin-fixed, paraffin-embedded biopsy tissue and profiled using the NanoString nCounter platform with the B-HOT gene panel. ABMR- and TCMR-associated molecular probabilities were calculated using established models. Concordance between molecular and histopathologic diagnoses was evaluated, and discrepant cases were further analyzed, including independent third-party histopathologic re-evaluation when tissue was available.
Results: Overall concordance between molecular and histopathologic diagnoses was high. Molecular–histologic discordance was observed in 27.4% (23/84) of biopsies and varied across diagnostic categories, occurring in 11.4% of ABMR, 23.8% of TCMR, and 50.0% of non-rejection biopsies. Discordant cases were predominantly observed in diagnostically challenging biopsies, such as those with borderline lesions, advanced chronic tissue injury, or concurrent pathological processes including BK virus infection or ischemia–reperfusion injury. Upon reassessment using the Banff 2022 criteria, 25 biopsies were identified as exhibiting donor-specific antibody–negative and C4d-negative microvascular inflammation, among which 48% demonstrated ABMR-associated molecular signatures, indicating marked biological heterogeneity. Independent third-party histopathologic re-evaluation of a subset of discordant cases revealed substantial interobserver variability.

Conclusions: In a Chinese kidney transplant population, the B-HOT gene panel–based molecular diagnostic system provides biologically meaningful complementary information to conventional histopathology, particularly in diagnostically ambiguous scenarios. These findings support the applicability of molecular diagnostics across populations and underscore the value of integrating molecular and histopathologic assessment within the contemporary Banff diagnostic framework.