Does tubulitis without interstitial inflammation represent borderline acute T cell mediated rejection?

Area of Science:

• Nephrology
• Transplant Immunology
• Pathology

Background:

• Isolated tubulitis (ISO-T), defined as tubulitis without interstitial inflammation (Banff i0), is controversially categorized within the Banff borderline criteria for acute T cell mediated rejection (TCMR).
• Understanding the clinical significance of ISO-T is crucial for accurate diagnosis and patient management in kidney transplantation.

Purpose of the Study:

• To determine the clinical significance of isolated tubulitis (ISO-T) in kidney transplant recipients.
• To evaluate the association of ISO-T with clinical predictors, histological findings, and long-term graft outcomes.
• To propose reclassification of ISO-T regarding Banff criteria for TCMR.

Main Methods:

• Retrospective observational study of 2055 kidney transplant biopsies from 775 recipients.
• Analysis of clinical predictors, histological features, and graft survival in patients with and without ISO-T.
• Multivariable analysis to identify independent predictors of tubulitis.

Main Results:

• Isolated tubulitis (ISO-T) was present in 19.1% of biopsies, predominantly mild (i0t1).
• Clinical predictors included HLA mismatch, prior rejection, and BKVAN; histological associations included interstitial fibrosis/tubular atrophy (IF/TA) and SV40T.
• Graft survival for ISO-T was high (98.8% at 1 year, 92.7% at 5 years), with frequent improvement in allograft function.

Conclusions:

• Isolated tubulitis (ISO-T) does not represent borderline TCMR and should be removed from this category.
• Reinstating i1 as the diagnostic threshold for TCMR is recommended.
• ISO-T has a generally benign prognosis and does not significantly impact long-term graft survival.