BK virus nephropathy due to KOM-3 strain

Area of Science:

• Nephrology
• Virology
• Transplant Immunology

Background:

• BK polyomavirus infection is a significant complication following kidney transplantation, leading to interstitial nephritis.
• Diagnosis of BK virus nephropathy typically relies on histological, immunostaining, and ultrastructural analyses.

Observation:

• A kidney transplant recipient presented with BK virus nephropathy.
• Biopsy showed characteristic viral changes but yielded negative immunostaining for BK virus large T antigen (LTag).

Findings:

• The negative immunostain was attributed to a novel KOM-3 strain of BK polyomavirus with a 4-amino acid deletion in the LTag C-terminus.
• DNA sequencing confirmed 100% homology to the KOM-3 strain, explaining the lack of antibody binding to the targeted epitope.
• The patient experienced graft loss two months post-diagnosis.

Implications:

• Pathologists must consider potential immunostaining pitfalls for BK virus detection, especially with emerging strains.
• The diagnostic limitations highlight the need for molecular methods like PCR and sequencing in specific cases.
• Further research is needed to understand the incidence and prognostic significance of the KOM-3 strain in kidney transplant recipients.