1. Case 5 Helmut Hopfer Institute of Pathology, University Hospital Basel

6. Pathological diagnosis
transplant kidney (biopsy): diffuse acute interstitial cellular rejection

7. Clinical history 37 year old women Unknown basic disease
Deceased donor kidney transplantation 6 months prior to biopsy
3 HLA-mismatches, 2 donor-specific antibodies, negative B- and T-cell cross match → induction therapy with ATG-Fresenius and IVIG
Maintenance immunosuppression with tacrolimus, mycophenolalte mofetil (MMF), steroids

8. Clinical course *1 antibody-mediated rejection (3 weeks)
*2 polyomavirus nephro-pathy (12 weeks)

9. Differential diagnosis
PVN progression
PVN resolution
Concurrent interstitial cellular rejection
Combination

11. SV40 immunohistochemistry
No cytopathic effect
SV40 positive cells in cortex and medulla

12. PVN progression
stage: A B C

13. PVN resolution Blood Kidney time after transplantation PVN
resolving PVN
residual PVN
BK dynamics
increasing
decreasing
cleared
distinction ICR?
impossible
impossible?
rejection therapy? no
yes, if clinical
BK-specific
immunity
viruria
viremia
BK-induced tubular damage
BK-induced inflammation
anti-BK inflammation
and IEL

14. Diagnosis Resolving polyomavirus nephropathy
Schaub et al., Neph Dial Transplant 22: ,2007

15. Follow up

16. BK-specific immune response
BK-specific humoral
immune response
BK-specific cellular
immune response
after clearance
Schaub et al., Neph Dial Transplant 22: ,2007

17. Take-home messages
If you think of acute interstitial cellular rejection in the context of PVN, think: anti-BK acute interstitial nephritis (resolving PVN)
Clinicopathological correlation is key to correct biopsy interpretation