New research conducted by the Paris Translational Research Center for Organ Transplantation team could help clinicians determine which patients will have a disease that usually occurs after a kidney transplant and which are at high risk of transplant failure. The results are published today in the prestigious Journal of the American Society of Nephrology (JASN).

Transplant glomerulopathy was first described and characterized 50 years ago. It is a disease associated with the loss of a kidney transplant and common after a transplant. It affects the functional units (i. e. glomeruli) of the transplanted kidney. There is currently no treatment for this heterogeneous disease.

Abstract
Halloran PF, Potena L, Van Huyen JD, Bruneval P, Leone O, Kim DH, Jouven X, Reeve J, Loupy A.

The emergence of molecular systems offers opportunities for improving the assessment of rejection in heart transplant biopsy specimens. The present study developed a microarray-based system for assessing heart transplant endomyocardial biopsy (EMB) specimens.
We analyzed 331 protocol or for-cause EMB specimens from 221 subjects in 3 centers (Edmonton, Bologna, and Paris). Unsupervised principal component analysis (PCA) and archetype analysis used rejection-associated transcripts (RATs) shown in kidney transplants to be associated with antibody-mediated rejection (ABMR) or T cell-mediated rejection (TCMR), or both. To compare EMB specimens to kidney biopsy specimens, rejection status in both was simplified to TCMR, ABMR, or no rejection.
The pattern of RAT expression was similar in EMB and kidney specimens, permitting use of RATs to assign scores and group ("cluster") membership to each EMB, independent of histology. Three clusters emerged in EMB specimens, similar to kidney specimens: TCMR, ABMR, and no rejection. This permitted each EMB specimen to be given 3 scores and assigned to 1 cluster by its highest score. There was significant agreement between molecular phenotype-archetype scores or clusters-and both histologic diagnoses and donor-specific antibody. Area under curve estimates for predicting histologic TCMR, ABMR, and no rejection by molecular assessment were lower in EMB specimens than in kidney specimens, reflecting more uncertainty in EMB specimens, particularly in histologic diagnosis of TCMR.
Rejection-associated transcripts can be used to estimate the probability of TCMR and ABMR in heart transplant specimens, providing a new dimension to improve the accuracy of diagnoses and an independent system for recalibrating the histology guidelines.

1/ MOLECULAR CORRELATES OF ENDOTHELIAL MTOR ACTIVATION IN HEART TRANSPLANT RECIPIENTS
Session: “ Basic and translational immunology” (17:45 to 18:45)
Location: Room 118 + 119 – 18:29 

M Racapé, A Loupy, J Reeve, J Venner , R Guillemain, L Hidalgo, C Lefaucher, X Jouven, P Bruneval, J Duaong Van Huyen, P Halloran 
Background
The detection of phosphorylated effectors of the mTOR pathway such as phosphorylated-S6RP in endothelial cells by immunohistochemistry (IHC) has been associated with Antibody-Mediated allograft Rejection (AMR). The aim of this study was to evaluate the molecular phenotype related to the endothelial detection of pS6RP in heart transplant recipients.
Methods
This case-control study included 41 heart transplant patients from four French referral centers with biopsy proven antibody-mediated rejection (pAMR+) and a matched control group of 30 patients without rejection (pAMR0) based on the updated ISHLT classification. From these patients, 94 endomyocardial biopsies (EMB) had adequate material for microarray analysis and endothelial expression analysis of pS6RP by IHC. We also determined the allograft gene expression profile using the ABMR molecular score in addition to pathogenesis-based transcripts reflecting endothelial activation (DSAST and ENDAT), macrophage burden (QCMAT), gamma-interferon response (GRIT) and NK-cell burden (NKB) (http://atagc.med.ualberta.ca).
Results
Among the 94 EMBs included in the main analyses, 50 were pAMR+ (53.2%) and 44 (46.8%) were pAMR0 normal EMBs. Endothelial expression of pS6RP was observed in 27/50 (54%) of pAMR+ biopsies and 12 out of 44 normal biopsies (27.3%, Fischer's exact: p=0.012). As compared with biopsies without pS6RP labeling, biopsies with pS6RP staining showed increased expression of DSAST (Mann-Whitney: p<0.0001), ENDAT (p=0.0009), QCMAT (p=0.0046), NKB (p=0.0001), GRIT (p=0.0008) and increased ABMR molecular score reflecting AMR injury (p=0.0001).
Conclusion
Endothelial activation of mTOR pathway is associated with AMR and increased expression in transcripts reflecting endothelial activation, macrophage burden, microcirculation and NK burden. Our results suggest the importance of the mTOR pathway activation in AMR injury and the potential interest of using mTOR inhibitors in this setting.

Authors
M. Racapé, A. Loupy, J. Reeve, J. Venner, R. Guillemain, L. Hidalgo, C. Lefaucheur, X. Jouven, P. Bruneval, J. Duong Van Huyen, P. Halloran. 

Abstract

• Purpose: The detection of phosphorylated effectors of the mTOR pathway in endothelial cells by immunohistochemistry (IHC) has been associated with allograft rejection. The aim of this study was to evaluate in heart transplant recipients the molecular phenotype related to the endothelial detection of the phosphorylated effectors of the mTOR pathway, pS6RP.
• Methods: This case-control study included 41 heart transplant patients from four French referral centers with biopsy proven antibody-mediated rejection (pAMR+) and a matched control group of 32 patients without rejection (pAMR0) based on the updated ISHLT classification. From these patients, 93 endomyocardial biopsies (EMB) had adequate material for microarray analysis and IHC. We studied in all EMB the endothelial expression of pS6RP by IHC. We also determined the allograft gene expression profile using the ABMR molecular score in addition to pathogenesis-based transcripts reflecting endothelial activation (DSAST and ENDAT), macrophage burden (QCMAT), gamma-interferon response (GRIT) and NK-cell burden (NKB) (http://atagc.med.ualberta.ca).
• Results: Among the 93 EMBs included in main analyses, 49 were pAMR+ (52.7%) and 44 (47.3%) were pAMR0 normal EMBs. Endothelial expression of pS6RP was observed in 27/49 (55.1%) of pAMR+ biopsies and 12 out of 44 normal biopsies (27.3%, Fischer's exact: p=0.011). As compared with biopsies without endothelial pS6RP labeling, biopsies with positive endothelial pS6RP staining showed increased expression in DSAST (Mann-Whitney: p<0.0001), ENDAT (p=0.0008), QCMAT (p=0.0052), NKB (p=0.0001) and increased ABMR molecular score reflecting interferon-effects, microcirculation stress and NK burden (p=0.0001).
• Conclusion: Endothelial activation of mTOR pathway is associated with antibody-mediated allograft rejection and increased expression in transcripts reflecting endothelial activation, macrophage burden, microcirculation and NK burden. Our results suggest the importance of the mTOR pathway activation in antibody-mediated heart allograft injury and the potential interest of using mTOR inhibitors in this setting.