In Press, 1995, Transplantation Proceedings copyright by Appleton and Lange.

Protocol Core Biopsy as Intermediate Efficacy End-Point in Chronic Kidney Allograft Rejection

Serdar Yilmaz*, Eero Taskinen, Pekka Häyry

Helena Isoniemi Transplantation Laboratory, PO Box 21 (Haartmaninkatu 3), FIN-00014 University of Helsinki, Finland and *Division Transplantation, Department of Surgery, Ohio State University, Columbus, OH

Telefax of corresponding author: +358-0-2411 227

Life table statistics to demonstrate the impact of a new drug regimen on chronic allograft failure, require 5-10 years to reach significance even with a large number of patients. This time period is definitely marginal, if not too long, to develop a new molecule for a drug. Therefore, there is significant interest to generate new end-points, intermediate efficacy end-points, which would signify later chronic rejection of the transplant. Until now, no such end-points have been available.

Chronic rejection is both a clinical and histopathological diagnosis. In two recent consensus conferences, the first one in Kiruna, Sweden [1] and the next one in Palo Alto, CA [2], chronic renal allograft rejection has been defined as progressively declining transplant function three months after the transplantation or later, with compatible biopsy histology. This emphasizes the role of biopsies in the diagnosis of chronic rejection.

 

Histopathology and differential diagnosis

The first histological presentation of chronic rejection in a kidney transplant, derives from David Hume and his associates in 1955 [3] and by Porter et al. in 1963 and 1967 [4, 5]. Their description is so complete that only minor additions have been made since then.

In the study of Kasiske et al. [6] the histopathological findings most closely associated with chronic deteriorated graft function, were interstitial fibrosis, glomerular mesangial expansion and sclerosis, basement membrane reduplication, arterial intimal occlusion and tubular atrophy. The sum score of these six parameters was expressed as a single numerical figure, the so-called "chronic rejection score". Kasiske et al also found that this score correlated with the duration of subsequent survival (r=-0.65, p<0.001).

In Helsinki [7, 8] we investigated the histopathological alterations in 89 consecutive first cadaveric renal transplant recipients, where prospective protocol core biopsies were performed at two years after transplantation. We quantitated 31 separate histological variables from these biopsies, by scoring them blindly from zero (no changes) to three (severe changes), and correlated the biopsy histology to renal transplant function at the time of the biopsy. Six histological alterations which significantly correlated, were interstitial Iymphocytic inflammation and fibrosis, glomerular mesangial matrix increase and sclerosis, vascular intimal proliferation and tubular dilatation and atrophy. These alterations in human biopsies, with the exception of tubular changes, were virtually identical with those observed in a rat renal allograft study in the same laboratory, when long-term changes in the allografts were compared to syngeneic transplants [9]. On the basis of these two studies the "chronic allograft damage index" (CADI) was formed consisting of the sum score of the following six histological changes characteristic to chronic rejection, i.e., interstitial inflammation and fibrosis, glomerular sclerosis and mesangial matrix increase, vascular intimal proliferation and tubular atrophy.

The differentiation of chronic CyA nephrotoxicity from chronic rejection leading to renal scaring, remains one of the major problems in renal allograft biopsy interpretation. Hyaline arteriolar thickening appears to be the only specific finding that distinguishes CyA nephrotoxicity from other entities [10, 11]. Proliferative arteriopathy of interlobular or arcuate arteries are not the feature of CyA toxicity [12]. As rule of thumb, vascular changes in chronic rejection occur in arteries, whereas CyA nephrotoxicity mainly affects arterioli [10]. Isometric vacuolization, tubular calcification, giant mitochondria and focal or striped form of interstitial fibrosis that were considered useful diagnostic indicators in CyA nephrotoxicity in the past, are of little value today when specifying CyA nephrotoxicity [11].

 

Histological changes of chronic allograft rejection occur also in renal allografts with normal function

The histological features characteristic to chronic rejection in the Helsinki protocol core biopsy study, were also observed in transplants with entirely normal function at the time of the biopsy. Needless to say, these alterations were mostly mild and correlated in inverse fashion to the intensity of immunosuppression [7]. This observation was later confirmed by the Uppsala group [13]: in 99 protocol core biopsies performed at 6 months after the transplantation, minor histological changes compatible with chronic rejection were frequently observed also in transplants with entirely normal function.

 

Predictive value of early histological changes of chronic rejection for long-term clinical outcome of the allograft

An intriguing question, considering possible intermediate efficacy end-points for chronic rejection, is whether these incipient histological changes in renal allografts are self-limiting or predictive to subsequent chronic rejection.

In order to answer this question, the Helsinki group correlated the CADI index at 2 years to transplant function during the subsequent years of follow-up. The correlation coefficient (r-value) between CADI index at 2 years and graft function at 6 years post transplantation was 0.717 and was highly significant (p=0.0001) (24, 25) [14]. Furthermore, the CADI index at 2 years, reliably (p=0.001) predicted the patients who will proceed to clinical chronic rejection later [14].

This observation [Figure 1], suggesting a high predictive value of protocol core biopsy and quantitative histopathology to subsequent chronic rejection, has already been confirmed by the Uppsala group [13]. In their study they performed 99 protocol core biopsies at 6 months after transplantation and quantitated the chronic allograft damage score (CGD score) from vascular intimal hyperplasia, glomerular mesangial changes, focal Iymphocytic infiltration, focal and diffuse interstitial fibrosis and tubular atrophy, by scoring each individual variable from zero to three as in Helsinki. There was a strong association between CGD score at 6 months, and risk of graft loss up to 2 and 3 years following transplantation: patients with a biopsy CGD score <6 had a higher graft loss rate at 2 years than those with a score of <6 (p=0.037). In addition, higher serum creatinine (p=0.003) and lower glomerular filtration rate (p=0.01) were observed in patients with high CGD score compared to patients with a low score [13].

 

Recommendations

Even now, protocol core needle biopsy is a seldom-used instrument in the monitoring of organ allografts. The emotional dangers related to the procedure are difficult to overcome. Most of these dangers are, however, linked with earlier experience employing less sophisticated methods such as the True-Cut biopsy. The new Uppsala-designed spring-loaded biopsy device [15] has largely overcome these complications.

In Helsinki and Uppsala more than 2000 renal allograft biopsies with this device, using a 0.8 mm OD needle for renal transplants have been done. So far the complications have been negative. The results are similar from other centres employing the spring-loaded device for biopsy histology (unpublished).

On the other hand, balanced to risk, the protocol core biopsy should gain a wider use. If substantiated by other centres outside Scandinavia that chronic rejection may be accurately identified already at 0.5-2 years post transplantation, this would facilitate meaningful trials for chronic rejection with early intermediate efficacy end points. Not only the industry, but by far most importantly transplant patients would benefit from this approach.

 

REFERENCES

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  11. Solez K, Racusen LC, Marcussen N, et al. Kidney Int 1993;43:1058-67.

     

  12. Sommer BG, Innes JT, Whitehurst RM, et al. Am J Surg 1985;149:756-64.

     

  13. Dimeny E, Wahlberg J, Larsson E, Fellström, B. Clin .Transplantation 1995; 9: 79

     

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  15. Wahlberg J, Andersson T, Bush C, et al. Transpl Proc 1988;20:419-20.

     


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