Workshop report: a website for the antibody-defined HLA epitope registry

http://epregistry.ufpi.br

The concept that HLA antibodies are specific for epitopes rather than HLA antigens is important not only for the determination of mismatch acceptability for sensitized patients but also for a better understanding of the antibody response to an HLA mismatch. Numerous publications describe epitope-specific antibodies, but there is no standardized information about the repertoire of clinically relevant HLA epitopes. Under auspices of the 16th IHIW, we have developed a website-based registry of antibody-verified HLA epitopes. Epitope notations are based on HLA molecular modelling of amino acid residues in polymorphic sequence positions. Informative epitope-specific antibodies had been induced by a transplant, transfusion or pregnancy and were monoclonal antibodies or eluates of sera absorbed with single HLA alleles. Antibody reactivity was determined in binding assays with single-allele panels. Antibody producer/immunizer HLA types enhanced the characterization of specific epitopes. The Registry also includes epitopes described in original research publications. Based on the extent of antibody reactivity information, we assigned epitope status as confirmed (well documented) or provisional (more data are needed). At present, the Registry has 69 HLA-ABC, 53 DRB1/3/4/5, 17 DQ, 8 DP and 22 MICA antibody-verified epitopes and will be updated on a quarterly basis. Laboratories worldwide continue to submit data about previously unreported antibody-specific epitopes. For each epitope, the website shows its amino acid composition and HLA alleles that share the epitope. Links show antibody reactivity patterns, sensitization information and references. Other links show molecular modelling of corresponding structural epitopes and polymorphic residue information for epitope-carrying alleles. The website will also have a link to epitope frequency information in different populations. Search functions will list mismatched epitopes on mismatched alleles for selected HLA types. The HLA Epitope Registry will become a valuable resource for researchers interested in HLA compatibility at the epitope level and investigating antibody responses to HLA mismatches (read more)

Chronic GVHD is associated with inferior relapse risk irrespective of stem cell source among patients receiving transplantation from unrelated donors

Chronic GVHD (cGVHD) has been associated with reduced risk of relapse after allo-SCT for onco-hematological disease due to a graft-vs-malignancy effect. Here we retrospectively analyzed a series of 802 adult patients transplanted from unrelated donors and found that cGVHD was associated with significantly lower relapse and that the limited form was associated with a survival advantage: hazard ratio for OS=0.63 (0.46–0.87); P=0.004; this was due to combination of relapse reduction and similar non-relapse mortality with respect to patients without cGVHD. Importantly, the graft-vs-malignancy effect observed here did not differ when PBSC or BM were used as stem cell source, thus suggesting that the protective effect of limited cGVHD is similar after PBSC- or BM-based transplantation. These findings could have practical implications and suggest no qualitative difference between cGVHD occurring after transplantation performed with different stem cell sources (read more)

Is it time to revisit our current hematopoietic progenitor cell quantification methods in the clinic?

In the clinical practice of hematopoietic SCT, the minimum numbers of cells required for a successful engraftment are defined on the basis of their CD45 and CD34 expression profiles. However, the quantity of earlier progenitors or CD34-positive cells at different differentiation stages within stem cell grafts is not generally taken into consideration. During the last decade, various teams have quantified the number of cells expressing various combinations of CD34, CD38, CD133, CD90 co-expression and/or aldehyde dehydrogenase functional capacity using flow cytometry. Some of these studies resulted in the greater appreciation that combinations of these Ags were associated with varied myeloid, erythroid and platelet engraftment rates whereas others showed that the relative absence or presence of these markers could define cells responsible for either short- or long-term engraftment. These findings were also extended to differences between progenitor cell populations found within BM vs peripheral or cord-blood grafts. Cells harvested from donors are also generally frozen and stored; thawed cells have variable levels of viability and functional capacity based on the time tested post thaw, which also can be assessed by flow cytometry. Finally, flow cytometry has the potential for analysis of cells carrying a mesenchymal stem cell phenotype, which may be quiescent within some of the stem cell products. This review will address the need for stem cell subpopulation quantification and summarize existing published data to identify some Ags and functional characteristics that can be applicable to daily clinical practice (read more).

Pretransplantation Soluble CD30 Level As a Predictor of Acute Rejection in Kidney Transplantation: A Meta-Analysis

Background: The question of whether high pretransplantation soluble CD30 (sCD30) level can be a predictor of kidney transplant acute rejection (AR) is under debate. Herein, we performed a meta-analysis on the predictive efficacy of sCD30 for AR in renal transplantation.
Methods: PubMed (1966–2012), EMBASE (1988–2012), and Web of Science (1986–2012) databases were searched for studies concerning the predictive efficacy of sCD30 for AR after kidney transplantation. After a careful review of eligible studies, sensitivity, specificity, and other measures of the accuracy of sCD30 were pooled. A summary receiver operating characteristic curve was used to represent the overall test performance.
Results: Twelve studies enrolling 2507 patients met the inclusion criteria. The pooled estimates for pretransplantation sCD30 in prediction of allograft rejection risk were poor, with a sensitivity of 0.70 (95% confidence interval (CI), 0.66–0.74), a specificity of 0.48 (95% CI, 0.46–0.50), a positive likelihood ratio of 1.35 (95% CI, 1.20–1.53), a negative likelihood ratio of 0.68 (95% CI, 0.55–0.84), and a diagnostic odds ratio of 2.07 (95% CI, 1.54–2.80). The area under curve of the summary receiver operating characteristic curve was 0.60, indicating poor overall accuracy of the serum sCD30 level in the prediction of patients at risk for AR.
Conclusions: The results of the meta-analysis show that the accuracy of pretransplantation sCD30 for predicting posttransplantation AR was poor. Prospective studies are needed to clarify the usefulness of this test for identifying risks of AR in transplant recipients (read more)

Non-HLA Antibodies Targeting Vascular Receptors Enhance Alloimmune Response and Microvasculopathy After Heart Transplantation

Background: Non–human leukocyte antigen antibodies (Abs) targeting vascular receptors are implicated in the pathogenesis of renal allograft vascular rejection and in progressive vasculopathy in patients with systemic sclerosis.
Methods: We prospectively tested in 30 heart transplant recipients the impact of Abs directed against endothelin-1 type A (ETAR) and angiotensin II type 1 receptors (AT1R, cell-enzyme–linked immunosorbent assay) at time of transplantation and during the first posttransplantation year on cellular and Ab-mediated rejection (immunohistochemistry, C3d, and immunoglobulins) and microvasculopathy in endomyocardial biopsy.
Results: Cellular rejection, Ab-mediated rejection, and microvasculopathy was found in 40% and 13%, 57% and 18%, and 37% and 40% of biopsies at 1 month and 1 year posttransplantation, respectively. Maximum levels of AT1R and ETAR Abs were higher in patients with cellular (16.5±2.6 vs. 9.4±1.3; P=0.021 and 16.5±2.5 vs. 9.9±1.9; P=0.041) and Ab-mediated rejection (19.0±2.6 vs. 10.0±1.3; P=0.004 and 19.4±2.7 vs. 9.0±1.7; P=0.002), as compared with patients who had no rejection. Patients with elevated AT1R Abs (53% [16/30]) or ETAR Abs (50% [15/30]; pretransplantation prognostic rejection cutoff >16.5 U/L) presented more often with microvasculopathy (both, 67% vs. 23%; P=0.048) than patients without.
Conclusions: Elevated levels of AT1R and ETAR Abs are associated with cellular and Ab-mediated rejection and early onset of microvasculopathy and should be routinely monitored after heart transplantation (read more).

No Evidence for Recipient-Derived Hepatocytes in Serial Biopsies of Sex-Mismatched Liver Transplants

Background: Bone marrow–derived hematopoietic stem cells (BM-HSCs) have been shown to act as source for hepatic regeneration in rodent models; however, their ability to participate in human liver regeneration remains controversial. The aim of this study was to investigate the origin of hepatocytes in sex-mismatched cases of orthotopic liver transplantation in longitudinally performed liver biopsies.
Methods: Paraffin-embedded liver biopsy samples of 14 patients after sex-mismatched (female-to-male) liver transplantation were investigated. Biopsies were taken at multiple time points and subjected to histologic examination. Immunohistochemical staining with a hepatocyte-specific antibody and fluorescent in situ hybridization for visualization of Y chromosomes were performed to analyze the presence of recipient-derived hepatocytes.
Results: We analyzed 30 liver biopsy samples ranging from 1 week to more than 3 years after transplantation. There was no evidence for recipient-derived hepatocytes in liver transplants at any time point. We were able to detect recipient-specific chromosomal status in inflammatory cells within the liver but not within hepatocytes. Results were independent of liver injury at the time of biopsy, caused by hepatitis C recurrence or rejection episodes.
Conclusions: Our results show no evidence for involvement of BM-HSCs in liver regeneration after orthotopic liver transplantation. We think that recipient BM-HSC–derived hepatocyte repopulation is a very rare event at best and is not of clinical relevance (read more)

Cold ischemic time is critical in outcomes of expanded criteria donor renal transplantation

The outcomes of expanded criteria donor (ECD) kidneys have been reported to be inferior compared with standard criteria donor (SCD) kidneys. However, the graft survival rate of ECD is not so inferior to SCD in Korea. The purposes of this study were to compare the outcomes of ECD kidneys with SCD kidneys and identify the influencing factors. We retrospectively studied 143 deceased donor transplants from August 2006 to June 2010. The patients were divided into SCD (n = 117) and ECD (n = 26) by UNOS criteria. The one- and three-yr graft survival rates of SCD and ECD (99.1% and 94.4% vs. 100% and 92.9%, respectively, p = 0.15) were not significantly different between groups. The mean cold ischemic time (CIT) was 3.8 ± 2.2 h. When compared the outcome of ECD kidneys with data reported by Organ Procurement and Transplantation Network and the Scientific Registry of Transplant Recipients (OPTN/SRTR) (one- and three-yr graft survival rate: 86.7% and 73.2%), the graft survival rate of our center was superior. In OPTN/SRTR data, transplant with CIT shorter than 11 h was only 20%. The outcomes of ECD grafts are outstanding and comparable with SCD grafts in our center, and the only distinguishing factor is markedly short CIT. Finishing the allocation before organ recovery and immediate operations after recovery could shorten the CIT (read more)