Early Acute Microvascular Kidney Transplant Rejection in the Absence of Anti-HLA Antibodies Is Associated with Preformed IgG Antibodies against Diverse Glomerular Endothelial Cell Antigens.

BACKGROUND: Although anti-HLA antibodies (Abs) cause most antibody-mediated rejections of renal allografts, non-anti-HLA Abs have also been postulated to contribute. A better understanding of such Abs in rejection is needed. METHODS: We conducted a nationwide study to identify kidney transplant recipients without anti-HLA donor-specific Abs who experienced acute graft dysfunction within 3 months after transplantation and showed evidence of microvascular injury, called acute microvascular rejection (AMVR). We developed a crossmatch assay to assess serum reactivity to human microvascular endothelial cells, and used a combination of transcriptomic and proteomic approaches to identify non-HLA Abs. RESULTS: We identified a highly selected cohort of 38 patients with early acute AMVR. Biopsy specimens revealed intense microvascular inflammation and the presence of vasculitis (in 60.5%), interstitial hemorrhages (31.6%), or thrombotic microangiopathy (15.8%). Serum samples collected at the time of transplant showed that previously proposed anti-endothelial cell Abs-angiotensin type 1 receptor (AT1R), endothelin-1 type A and natural polyreactive Abs-did not increase significantly among patients with AMVR compared with a control group of stable kidney transplant recipients. However, 26% of the tested AMVR samples were positive for AT1R Abs when a threshold of 10 IU/ml was used. The crossmatch assay identified a common IgG response that was specifically directed against constitutively expressed antigens of microvascular glomerular cells in patients with AMVR. Transcriptomic and proteomic analyses identified new targets of non-HLA Abs, with little redundancy among individuals. CONCLUSIONS: Our findings indicate that preformed IgG Abs targeting non-HLA antigens expressed on glomerular endothelial cells are associated with early AMVR, and that in vitro cell-based assays are needed to improve risk assessments before transplant.

Isolated De Novo Antiendothelial Cell Antibodies and Kidney Transplant Rejection.

BACKGROUND: Studies analyzing the role of antiendothelial cell antibodies (AECAs) in large series of kidney transplant recipients are scarce, and HLA, MHC (major histocompatibility complex) class I-related chain A (MICA), and angiotensin II type 1 receptor have not been formally excluded as targets. STUDY DESIGN: Retrospective study of a cohort of kidney transplant recipients. SETTING & PARTICIPANTS: 324 kidney transplant recipients who were negative for anti-HLA, anti-MICA, and anti-angiotensin II type 1 receptor antibodies were tested for AECAs in pre- and posttransplantation serum samples. PREDICTORS: AECA-positive (preformed [pre+/post+] vs de novo [pre-/post+]) versus AECA-negative (pre-/post-) before or after transplantation. OUTCOMES: Patient mortality, transplant loss, and acute rejection events. RESULTS: 66 (20%) patients were AECA positive (39 [12%] preformed, 27 [8%] de novo) and 258 (80%) were AECA negative. During a follow-up of 10 years, 7 (18%) AECA pre+/post+ patients had rejections compared with 14 (52%) AECA pre-/post+ and 57 (22%) AECA pre-/post- recipients (OR, 3.80; P=0.001). AECA pre-/post+ status emerged as an independent risk factor for transplant rejection compared to the AECA pre-/post- group (OR, 5.17; P<0.001). However, AECA pre+/post+ and AECA pre-/post+ patients did not show higher risk for either patient death (ORs of 1.49 [P=0.7] and 1.06 [P=0.9], respectively) or transplant loss (ORs of 1.22 and 0.86, respectively; P for both = 0.8) compared to the AECA pre-/post- population. LIMITATIONS: Retrospective study. Posttransplantation sera were collected before or after rejection, entailing a nearly cross-sectional relationship between the exposure and outcome. Lack of identification of precise antigens for AECAs. CONCLUSIONS: De novo AECAs may be associated with rejection. These antibodies might serve as biomarkers of endothelium damage in kidney transplant recipients.

A prospective study evaluating the role of donor-specific anti-endothelial crossmatch (XM-ONE assay) in predicting living donor kidney transplant outcome.

Anti-endothelial cell antibodies (AECAs) may play a role in allograft rejection. We prospectively tested 150 consecutive living donor kidney transplant recipients, with transplants performed at Northwestern Memorial Hospital between January and December 2010, using the donor-specific endothelial (XM-ONE) crossmatch. 88/150 Patients received standard of care (SOC) immunosuppression and analyzed separately, in addition to the complete study cohort. Patients were followed for one year and XM-ONE results were analyzed in relation to occurrence of acute rejection, proteinuria, serum creatinine levels, and biopsy proven fibrosis. No correlation was found between XM-ONE results and protocol or "for-cause" biopsy proven acute rejection or vasculopathy at 12 months. When IgG+ and IgM+ results of the XM-ONE assay were combined, a correlation with proteinuria at 12 months was observed (p=0.047). Although IgG+XM-ONE results were associated with significantly higher creatinine at 6 months (p=0.018), significance was lost at 12 months. Conversely, patients with an IgM+XM-ONE crossmatch had significantly lower creatinine at 1 month (p=0.019), 3 months (p=0.0045), and 6 months (p=0.038) post-transplant, but lost statistical significance at 12 months (p=0.67) post-transplant. In summary, the presence of AECAs as determined by a positive XM-ONE result was not predictive of overall poorer graft outcome after one year in our center.