MOLECULAR DIAGNOSTICS AND GENOMICS

L.G. Hidalgo¹, P.M. Campbell², P. Halloran^3
1Laboratory Medicine And Pathology, University of Alberta, Edmonton/CANADA, ², University of Alberta, Edmonton/AB/CANADA, ³, University of Alberta, Edmonton/CANADA

Body: INTRODUCTION: Antibody mediated rejection (ABMR) is increasingly recognized as a major cause of late graft loss. The diagnosis of ABMR relies on the presence of donor specific antibody (DSA), C4d deposition, and certain histologic lesions. However, the histopathology of ABMR is often subtle and C4d is insensitive. We sought to identify the molecules associated with DSA to improve the definition of new diagnostic criteria of ABMR. METHODS: Microarray analyses were performed in 145 clinically indicated biopsies from 145 patients with HLA antibody testing performed at the time of biopsy. DSA-selective transcripts (DSASTs) were identified by comparing rejection-classified biopsies from DSA+ patients to those from DSA negative patients. DSAST expression was examined in microarrays from a panel of primary human cells including allostimulated CD4 and CD8 CTL, NK cells, B cells, macrophages, HUVECs, and renal epithelial cells. DSAST scores were calculated as the geometric mean of fold changes of a biopsy versus controls calculated across all transcripts within each transcript set. Paraffin sections were graded according to the Banff criteria. Diagnosis for C4d negative ABMR or C4d negative Mixed were based on finding microvascular lesions of inflammation (g, or ptc>0) or microvascular deterioration (cg>0) from a patient with detectable HLA antibody (PRA+) at the time of biopsy. RESULTS: DSASTs were expressed by endothelium, as expected from previous analyses but also by NK cells. In contrast, no DSASTs were selectively expressed in CD4 or CD8 CTL, B cells, macrophages, or renal epithelial cells. DSAST scores were calculated for each biopsy, split into quintiles, and diagnoses were examined within each quintile (Figure 1). The quintile with the highest DSAST expression contained 23/29 (79%) biopsies diagnosed as ABMR including C4d positive or C4d negative ABMR/Mixed. Of the six biopsies with high DSAST scores that did not meet the histologic criteria for ABMR or Mixed, four were from patients with de novo DSA suggesting a high probability of antibody-mediated damage. CONCLUSION: The results implicate NK cells in the mechanism of endothelial injury. The highest DSAST scores were selective for biopsies independently diagnosed as ABMR or Mixed underscoring the specificity of high DSASTs for ABMR. Our study demonstrates that a high biopsy DSAST score is associated with an increased risk of an ABMR diagnosis and can be a valuable addition to new diagnostic criteria of ABMR.

Disclosure: All authors have declared no conflicts of interest.