Computerized histomorphometric assessment of protocol renal transplant biopsy specimens for surrogate markers of chronic rejection.

BACKGROUND

Chronic transplant rejection has emerged as the commonest cause of long-term renal allograft failure, and early identification of those grafts at risk could allow the targeting of specific therapies aimed at delaying this process. This study explores the usefulness of quantitative immunohistochemistry in defining biopsy-based surrogate markers of allograft damage.

METHODS

A consecutive series of 52 renal transplant recipients immunosuppressed with cyclosporine were studied. Needle core transplant biopsies were performed at 1, 3, and 6 months postoperatively. Immunostaining for collagen III, and smooth muscle actin, tenascin, and infiltrating leukocytes was performed using an indirect immunoperoxidase technique. The interstitial area stained (%) was measured using a semiautomatic image analysis system. The results were related to glomerular filtration rates (GFR) measured at 6, 12, and 24 months after transplantation using rank correlation coefficients.

RESULTS

The area fraction of immunostained collagen III correlated with 6-month GFR (r=-0.42, P=0.005) and was predictive of 12-month GFR (r=-0.32, P=0.03). An area fraction of immunostained collagen III of >40% at 6 months was associated with a significantly lower GFR at 24 months, compared with a percentage area of < or =40% (31+/-4 versus 45+/-4 ml/min/1.73 m2, P=0.01). Furthermore, a collagen III of >40% at 6 months identified patients who were at risk of progressive deterioration in graft function.

CONCLUSIONS

Grafts with poorer long-term function can be predicted using 6-month protocol biopsy specimens immunostained for collagen III. This should prove to be a useful ad interim surrogate marker of allograft damage in studies addressing the effects of new immunosuppressive agents on the development of chronic rejection.