#6395 tubuloreticular inclusions: a new prognostic biomarker in kidney transplantation

Abstract Background and Aims Tubuloreticular inclusions (TRIs) seen on electron microscopy (EM) are classically associated with lupus nephritis (LN) and systemic viral infections in native biopsies. Traditionally a marker for enhanced type I interferon expression, little is known about their significance post-transplant. We aimed to look at a large cohort of transplant biopsies showing TRIs to investigate associations and outcomes. Method A retrospective analysis was performed on two prospective databases; an in-centre transplant registry and a histopathology database holding data on all kidney biopsies performed at our centre. All patients biopsied since 2015, who had EM examination were included. Where patients had more than one biopsy showing a TRI the earliest one was included. Demographic, clinical and transplant data was collected from the laboratory records. Results 2283 kidney transplant biopsies were performed between January 2015 and November 2022; 1898 (83.1%) had EM performed. Of 1898 with EM, 176 (10.8%) had evidence of TRIs. Of 176 patients, 34% were female, the median age was 52.2 (38.9-59.4) years, 32% had underlying glomerulonephritis as their cause of ESKD, 65% were deceased donors and 75% were of non-white ethnicity. TRIs were associated with serological evidence of autoimmunity (16%), viral infections (26%) and donor specific antibodies (28%), with no association found in 41%. Rejection occurred in 49%, including 31% of patients with no recognised association with TRIs. Allograft outcomes were poor, with all-cause allograft survival and death-censored allograft survival of 66% and 60%, after a follow up of 1.9 +/− 1.8 years post index biopsy. A comparison with a matched control group is planned Conclusion In extension to previous work, we show that TRIs appear to be associated with alloimmunity. In this regard they may be a useful biomarker especially in cases where the diagnosis is unclear or biopsy findings are ‘subthreshold’. Irrespective of aetiology, TRIs are associated with poor outcomes and warrant further consideration.