Background: Tubulointerstitial damage (TID) is a key feature of chronic kidney transplant failure; however, the associated gene expression changes are poorly defined.
Methods: This pilot study used RNA from 59 protocol kidney transplant biopsies at implantation, 1, 3, and 12 months (n=18 patients), processed into cDNA and hybridized to 8K human cDNA microarrays. Gene expression was correlated with graft histology categorized by the Banff schema.
Results: Gene and pathway expression were differentially activated according to the time after transplantation. Immune pathway activity peaked at 1 month, fibrotic expression at 3 months, wound healing-remodelling and cell proliferation-repair processes were activated between 3 and 12 months, whereas macrophage-related gene expression occurred late by 12 months. Forty percent of genes and 50% pathways initially activated persisted to 3 months. Biopsies with TID displayed 262 differentially expressed genes (P<0.001, B>2 compared with implantation), dominated by upregulated fibrogenic and immune-related genes reflecting unique immune (10% to 15% of genes) and fibrotic (15% vs. 4% in normal) pathway activation. Profibrotic genes were expressed before interstitial fibrosis was observed by sequential microscopic analysis. Kidneys progressing to TID by 3 months demonstrated 30 unique genes (B>1, P<0.05) versus nonprogressors with 95 genes (B>1, P<0.009). Fourteen of these progressor genes also occurred in the top decile from an independent validation set.
Conclusions: Allografts display predictable immune and fibrotic gene expression profiles, with patterns of expression gradually varying by time after transplantation. The pathology reflects differential activation of intrinsic pathways. Gene expression predated histologic damage, suggesting its possible use in early diagnostic testing.