INTRAGRAFT GENE EXPRESSION IN POSITIVE CROSSMATCH KIDNEY
ALLOGRAFTS: ACCOMMODATION OR CHRONIC INJURY?
P. G. Dean, W. D. Park, L. D. Cornell, J. M. Gloor, M. D. Stegall
William J. von Liebig Transplant Center, Mayo Clinic, Rochester, Minnesota, USA
Objectives:
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 assess intragraft gene expression phenotypes in XM+ living donor kidney transplants.
Methods:
Whole genome microarray analysis (Affymetrix) and quantitative rt-PCR of 30 transcripts
related to endothelial cell activation were performed on RNA from protocol renal allograft
biopsies in 3 groups: 1) XM+TG+ biopsies both before (usually 4 months post-tx, n=16) and
after TG (1-2 yrs post-tx) was diagnosed (n=22); 2) XM+TG- biopsies (>2 years post-tx.; n=11);
3) paired negative crossmatch (XM-) kidney allograft biopsies without TG both early (<1yr posttx; n=10) and late (>1 yr post-tx; n=10).
Results:
XM+TG+ vs. XM-: 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 showed overrepresentation of inflammatory genes associated with
innate and adaptive immune responses. At the early time point, increased expression of multiple
endothelial cell activation genes (CD74; CDH5; PECAM-1; E-selectin; STAT-1; TBX21;
TNFAIP3 and von Willebrand factor) were identified in the XM+TG+ biopsies. At the late time
point, RT-PCR showed significantly increased expression of Bcl-xL; HO-1; tribbles-1; and
VEGF in XM- biopsies.
XM+ pre-TG+ vs. TG+: Whole-genome microarrays showed relatively few differentially
expressed genes (579 genes; 4%) when comparing paired early and late biopsies. By RT-PCR,
no endothelial cell activation genes were differentially expressed.
XM+TG+ vs. XM+TG-: Using RT-PCR, TNF-, TBX21, IFN-γ and E-selectin were
significantly altered between these groups at late time points. Whole-genome microarrays
showed significantly altered gene expression for 3,718 genes. However, only a small proportion
of these genes were identified in canonical pathway analyses of known transplant-related
pathways.
Conclusions:
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 genes altered in the XM+TG- vs. XM+TG+ comparisons may participate
in accommodation and these genes deserve further investigation. However, the bulk of gene
expression data suggests that all XM+ grafts are exposed to chronic injury.