Calcineurin Inhibitor Toxicity In Kidney Allograft Protocol Biopsies

1. Calcineurin Inhibitor Toxicity In Kidney Allograft Protocol Biopsies Neeraja Kambham M.D. Stanford University

2. Calcineurin Inhibitor Toxicity (CNIT) • CNI toxicity is a very important cause of chronic allograft nephropathy (CAN) • Later phase of CAN (i.e. > 1 year post txp) is likely due to CNIT, and it’s contribution progressively increases (Nankivell et al.) • Acute phase of CNI toxicity is reversible, but chronic phase is probably irreversible

3. CNI Toxicity • Functional • Structural: • Acute: tubulopathy (proximal tubules), endothelial injury (thrombotic microangiopathy) • Chronic: arteriolopathy, tubular atrophy, striped fibrosis, glomerulosclerosis

4. Calcineurin Inhibitor (CNI) Toxicity • Can it it be scored objectively? • Is it clinically useful? • Does it correlate with subsequent graft function? • Is it better than Banff Chronicity score?

5. Study Design • 50 consecutive pediatric renal transplant patients (November 1999- December 2004) • Patients on Steroid free immunosuppression protocol* • Immunosuppression: Extended Daclizumab induction; Tacrolimus and Mycophenolate mofetil maintenance • Biopsies: Protocol 3, 6, 12 and 24 months (P); also as indicated clinically (NP) (Sarwal MM et al: Transplantation. 76 (9): 2003)

6. (Sarwal MM et al: Transplantation. 76 (9): 2003)

7. Study Design… • 231 biopsies (P+NP) scored in a blinded fashion • 27 were inadequate (diagnosis rendered on 5) • CNI toxicity (CNIT) score in biopsies with histological evidence of CNI toxicity • Banff chronicity score (BChS): cg, ct, ci, cv • Modified Banff chronicity score (MBChS): gs, ct, ci, cv • Chronic Allograft Damage Index (CADI) • C4d Stains on paraffin embedded tissue

8. Diagnostic Categories • CNI Toxicity • Acute Rejection • graded by Banff criteria • Chronic Allograft Nephropathy • Unclear etiology of chronic damage • Any tubular atrophy or interstitial fibrosis > 5% • No Significant Abnormality • No tubular atrophy; interstitial fibrosis < 5% • Other: ATN, glomerulonephritis, reflux

9. Acute Rejection (n=29) • Non-protocol Biopsies: 21 (9 %) • Borderline: 13 • IA: 6 • IB: 2 • Protocol Biopsies: 8 (4.8 %)* • Borderline: 4 • IA: 3 • IB: 1 * Includes clinical & subclinical acute rejections

10. Features of CNI Toxicity • Tubular isometric vacuolization • Arteriolar medial/peripheral hyaline • Striped pattern of tubular atrophy and interstitial fibrosis * Ischemic collapse of glomeruli, Tubular dystrophic calcifications, juxtaglomerular apparatus hyperplasia

16. CNI Toxicity Scoring

17. Results (P+NP Biopsies) *C4d +ve in 1 of 189 biopsies (NP, AR IB)

18. Protocol Biopsies

19. Diagnostic features of CNIT (n=70) TV: tubular vacuoles; AH: arteriolar hyaline; SF: striped fibrosis

20. End points for graft function • CNIT, BChS, MBChS and CADI correlated with • Creatinine Clearance (by Schwartz method) • Hypertension: # of anti-HTN agents to normalize blood pressure • Proteinuria • CNIT score also correlated with Tacrolimus trough levels (ng/ml) and dosage (mg/kg)

21. Follow up • Mean follow up period: 25.7 months (range 24-44 months) • 2 patients died with functioning grafts • None had urine protein/creatinine ratio > 1 • Mean Creatinine Clearance at 24 months: 88.2 ml/min (range: 46-135) • Mean # anti-HTN agents: 0.27 (range 0-2)

22. Results • By Pearson parametric correlation (one side test) • CNI Toxicity Score at 3 months significantly correlates with 12 mo CrCl (p=0.021, r2=-0.54) and 24 mo CrCl (p=0.03, r2 =-0.58)

23. Results… • No correlation with hypertension, Tacrolimus dose or levels • CADI, BChS and MBChS did not correlate with outcome • CNIT and MBChS seem to correlate with each other* * gs, ct and ci are common parameters in both

24. Scoring of Protocol Biopsies

25. Parameters of CNIT Score Gs:glomerulosclerosis; ct:tubular atrophy; ci:interstitial fibrosis; ah:arteriolar hyaline; tv:tubular vacuolization

26. Can we create a CNIT scoring model ? • We reduced the # of parameters to create the model for CNIT score: = -0.16+1.05 gs+ 2.05 ct + 0.94 ah +1.03 tv (P<0.001; r2=-0.95) Gs: glomerulosclerosis; ct: tubular atrophy; ah: arteriolar hyaline; tv: tubular vacuolization

27. Testing the validity of the model • Identified 14 patients with CNI toxicity on 3 month protocol biopsy with at least 12 months follow up • Patients on steroid based (3) and steroid free (11) immunosuppression • 11 patients had 24 mo post- txp follow up

28. Validity.. • Mean CNIT score (calculated using model): 4.08 (range 1.97-9.28) • 3 month CNIT score correlated significantly • 12 mo CrCl (p= 0.02; r2 =-0.54) • 24 mo CrCl (p= 0.004; r2 =-0.75)

29. CNIT Score Correlation with 12 mo CrCl (p=0.02)

30. CNIT Score Correlation with 24 mo CrCl (p=0.004)

31. Scoring System • Is linear scoring of parameters better? • Image analysis may be helpful • Need to validate the data with more protocol biopsies (steroid free and steroid based regimens) • We are probably underestimating the incidence of CNI toxicity

32. Conclusions • CNIT score: helpful in objective grading • A diagnosis of CNIT requires aggressive monitoring of CNI therapy • Need to modify maintenance immunosuppression • Arteriolar hyaline: most important factor and likely irreversible cause of progressive loss of graft function

33. Acknowledgements • Minnie Sarwal M.D., Ph.D. • Suja Nagarajan, M.D. • Sheryl Shah • Li Li