Calcineurin Inhibitor Toxicity In Kidney Allograft Protocol

BiopsiesNeeraja Kambham M.D.

Stanford University

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

CNI Toxicity

• Functional• Structural:

– Acute: tubulopathy (proximal tubules), endothelial injury (thrombotic microangiopathy)

– Chronic: arteriolopathy, tubular atrophy, striped fibrosis, glomerulosclerosis

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?

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)

Variable mean / % RangeRecipient age at transplant (years) 11.8 0.8-21.8Recipients <5 years age at transplant 24%Recipient sex male 64%Donor age (years) 34.3 18.6-50.6Living donor 90%Etiology of ESRD Glomerulonephritis 36% Dysplasia/reflux nephropathy 36% Obstructive uropathy 14% Others 14%Recipient race C/H/A/AA/O 52/18/14/6/10%Mean HLA match Living related donor 2.8 Cadaver donor 1.6PRA 0%

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

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

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

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

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

CNI Toxicity ScoringHistological feature Criteria

Score

% Glomerulosclerosis 0; 1-25%, 26-50%; >50% 0-3

Mesangial matrix expansion 0; 1-25%, 26-50%; >50% 0-3

Isometric tubular vacuolization

0; 1-25%, 26-50%; >50% 0-3

Tubular atrophy 0; 1-25%, 26-50%; >50% 0-3

Interstitial fibrosis 0-5%; 6-25%, 26-50%; >50% 0-3

Arteriolar hyaline

0; mild-moderate (1 arteriole); moderate-severe (1-2

arteriole); severe (many arterioles)

0-3

Total score 18

Results (P+NP Biopsies)

Diagnosis N (%)CNI toxicity 77 (37%)

CNIT + AR 8 (4%)

Acute Rejection (AR) 21 (10%)

Chronic allograft nephropathy 75 (36%)

No significant abnormality 16 (7%)

Other (ATN, GN, reflux etc) 12 (6%)

Total (P+NP) 209

*C4d +ve in 1 of 189 biopsies (NP, AR IB)

Protocol Biopsies

Diagnosis 3 mo 6 mo 12 mo 24 mo N (%)

CNI toxicity 17 18 18 14 67 (41%)

CNIT + AR 1 1 0 1 3 (1.8%)

Acute Rejection 0 2 3 0 5 (3%)

CAN 17 13 13 10 53 (32%)

NSA 7 2 1 2 12 (7%)

Other + inadequate

4 8 7 5 24 (15%)

Total 46 44 42 32 164

0

5

10

15

20

25

30

35

40

TV AH SF 2 or more

Diagnostic features

TV

AH

SF

2 or more

Diagnostic features of CNIT (n=70)

TV: tubular vacuoles; AH: arteriolar hyaline; SF: striped fibrosis

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)

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)

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)

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

0

1

2

3

4

5

6

3 mo 6 mo 12 mo 24 mo

Time Post Transplantation

Me

an

Sc

ore CNIT

BChS

MBChS

CADI

Scoring of Protocol Biopsies

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

gs ct ci ah tv

CNIT score parameters

Me

an

Sc

ore 3 mo

6 mo

12 mo

24 mo

Parameters of CNIT Score

Gs:glomerulosclerosis; ct:tubular atrophy; ci:interstitial fibrosis; ah:arteriolar hyaline; tv:tubular vacuolization

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

Gs: glomerulosclerosis; ct: tubular atrophy; ah: arteriolar hyaline; tv: tubular vacuolization

(P<0.001; r2=-0.95)

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

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)

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

y = -10.97x + 156.69R2 = 0.2957

0

20

40

60

80

100

120

140

160

180

200

0 2 4 6 8 10

CNIT Score

Cre

atin

ine

Cle

aran

ce (

cc/m

in)

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

y = -11.194x + 150.37R2 = 0.5556

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10

CNIT Score

Cre

atin

ine

Cle

aran

ce (

cc/m

in)

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

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

Minnie Sarwal M.D., Ph.D.– Suja Nagarajan, M.D.– Sheryl Shah– Li Li

Acknowledgements