Intragraft Gene Expression in Positive Crossmatch Kidney Allografts: Accommodation or Chronic Injury?

Mark Stegall¹, Walter Park¹, Lynn Cornell², James Gloor³, Patrick Dean¹.

Departments of ¹Surgery, ²Pathology, and ³Nephrology and Internal Medicine, Mayo Clinic and Foundation, Rochester, MN, USA.

Protocol biopsies in kidney transplants with high levels of DSA (positive crossmatch, XM+) may develop features attributed to chronic injury [transplant glomerulopathy (TG) or endothelial cell activation] or have relatively normal histology, termed accommodation.The goal of this study was to assess intragraft gene expression phenotypes in XM+ living donor kidney transplants.

Methods: Whole genome microarray analysis and quantitative RT-PCR of 30 transcripts previously associated with TG and endothelial cell activation were performed on RNA from protocol renal allograft biopsies in 3 groups: 1) XM+TG+ biopsies both before (≤1 yr post-txp, n=16) and after TG (≥1 yr post-txp) was diagnosed (TG+, n=22); 2) XM+TG- biopsies (≥2 yr post-txp; n=11); 3) negative crossmatch (XM-) kidney transplants without TG (paired early [≤1 yr] and late [≥1 yr] biopsies; n=10).

Results: XM+ vs XM- biopsies (Groups 1 vs 3): Significantly altered expression was seen for 2,447 genes (18%) and 3,200 genes (24%) at early and late time points, respectively.Canonical pathway analyses of differentially expressed genes identified many inflammatory genes associated with innate and adaptive immune responses.At the late time point (≥1 yr), RT-PCR showed significantly altered expression of Bcl-xL; HO-1; tribbles-1; and VEGF.At the early time point (≤1 yr), altered expression of multiple endothelial cell activation genes were identified (CDH5; PECAM-1; E-selectin; von Willebrand factor, etc.).

XM+ pre-TG+ vs TG+ (Group 1): Whole-genome microarrays showed relatively few differentially expressed genes (579 genes; 4%).By RT-PCR no endothelial cell activation genes were differentially expressed.

XM+ ≤1 yr vs ≥2 yr biopsies without TG (Groups 1 vs 2): Using RT-PCR, only IFNg and SELE were significantly altered.

Conclusion: The presence of pre-transplant DSA results in a gene expression profile characterized by genes associated with inflammation and cellular infiltration when compared to XM- biopsies.The development TG was not associated with altered expression in selected endothelial cell activation genes.The few genes altered in the XM+TG- comparisons may represent true accommodation.However, the bulk of gene expression data suggests that all XM+ grafts are exposed to chronic injury.