The effect of Perforin and Granzyme B expression profile of cytotoxic T lymphocytes to graft rejection and graft prognosis in renal allograft biopsies

Renal transplantation is the most effective treatment method that improves the survival of patients with end-stage renal disease. Despite significant advances in immunosuppression and transplant management, acute/active and chronic rejection still remain the primary causes of allograft loss. Identifying biomarkers that can predict acute rejection and chronic allograft dysfunction is crucial for improving graft survival. Recent studies investigating the pathogenesis of rejection have highlighted the roles of Perforin (PRF) and GranzymeB (GrB), key determinants of cytotoxic effector cell function. These essential protease-function molecules are thought to have a role in both acute rejection and chronic allograft dysfunction in solid organ transplantation. In our study, we aimed to investigate the relationship between immunohistochemical expression profiles of PRF and GrB in renal allograft biopsies and graft rejection mechanisms and also graft prognosis. Fifty-two renal allograft biopsies from 36 recipients, reported between January 2022 and September 2025 at the Ankara University Medical School of Pathology Department, were reviewed. Clinical and serological data were obtained from the Ankara University Nephrology Department. Histopathological examination of the biopsies revealed Banff lesions, and diagnostic groups were established according to the updated Banff 2024 rejection diagnostic criteria. Immunohistochemical examination included CD8, PRF, and GrB antibodies. For each immune marker; staining scores were achieved in glomerular (g-score), tubular (t-score), interstitial (i-score), and vascular (v-score) compartments of the renal tissue. These scores were compared with Banff lesion scores, diagnostic groups, and clinical data. Twenty-six of the allograft biopsies were diagnosed with acute cellular rejection; 4 with chronic active cellular rejection; 8 with acute humoral rejection; and 3 with chronic active humoral rejection. Eleven biopsies were evaluated as having suspected acute humoral rejection; 14 as having borderline changes; 3 as having immunocomplex glomerulonephritis, 1 as having BK nephropathy and 8 as having no signs of rejection. Among immunohistochemical markers, GrB v-score was determined to be higher in the presence of severe interstitial inflammation (≥ci2), severe tubular atrophy (≥ct2), severe interstitial fibrosis (≥ci2), severe i-IFTA (≥i-IFTA2) and severe total inflammation (≥ti2) (p>0.05). High GrB activity in the arteries was found to be associated with chronic parenchymal damage findings. When 'acute rejection (cellular/humoral)' and 'no signs of rejection' groups were compared in terms of IHC staining scores; PRF g-score (p=0.038) and PRF i-score (p=0.021) were higher in the acute rejection group. Immunohistochemical analysis of PRF and GrB expression in allograft renal biopsies based on renal tissue compartments revealed valuable findings. Increased PRF expression in the glomerular and interstitial compartments was found to be associated with acute rejection. Increased GrB expression in the interstitial and vascular compartments was associated with signs of chronic parenchymal damage. By these findings we may suggest that PRF indicates acute rejection, while GrB indicates chronic graft dysfunction. It appears that PRF and GrB have different clinical significance.