The fate of anti-HLA antibodies following liver transplantation.

Introduction: Liver transplant recipients may have pre-formed anti-HLA antibodies directed to mismatched HLA of the liver donor (donor specific antibodies, DSA) or not directed to the liver donor (non-donor specific, non-DSA). We observed the fate of these antibodies (DSA and non-DSA) at 12 months after transplant. Methods: Patients transplanted between 4/2015 and 12/2018 (N = 216) who had anti-HLA antibody measurements at both transplant and 12 months posttransplant (N = 124) and with DSAs at transplant (N = 31) were considered informative for a paired analysis of the natural history of DSA and non-DSA following liver transplantation. Results: Class I DSAs and non-DSAs decreased between transplant and 12 months; however, Class I DSAs essentially disappeared by 12 months while Class I non-DSAs did not. Anti-HLA Class II DSAs performed differently. While there was a significant drop in values between transplant and 12 months, these antibodies mostly persisted at a low level. Discussion: Our study demonstrated a significant difference in the kinetics of DSA compared to non-DSA following liver transplantation, most profoundly for anti-HLA Class I antibodies. Class I DSAs were mostly absent at 12 months while Class II DSAs persisted, although at lower levels. The mechanisms of reduction in anti-HLA antibodies following liver transplantation are not completely understood and were not pursued as a part of this study. This detailed analysis of Class I and Class II DSAs and non-DSAs represents and important study to explore the change in antibodies at one year from liver transplantation.

Concordance and discordance in anti-HLA antibody testing.

BACKGROUND: Correct identification of the specificity of antibodies directed against HLA using single antigen Luminex beads (SALB) is essential in current HLA laboratory practice for transplantation. The aim of this study was to investigate the magnitude of concordance and discordance among laboratories in testing for anti-HLA antibodies using SALB. METHOD: 35 sera were distributed by the ASHI Proficiency Testing Program to HLA laboratories worldwide. We analyzed 4335 test results submitted between April 2010 and April 2013 by participating laboratories. RESULTS: SALB was used by approximately 94% of the participating laboratories, yet concordant assignment of antibody specificity was imperfect. For each serum, the assignment of an average of 10 antibody specificities was discordant. Disagreement was observed for antibodies directed against common as well as uncommon antigens. The assignment of an average of 15 antibody specificities in each "positive" serum appeared to be influenced by vendor-dependent causes. Inter-vendor concordance was lower than intra-vendor concordance, indicating that vendor dependent factors may be a central cause for disagreement. CONCLUSIONS: Our study illustrates the prevalence of concordance and discordance, also affected by unpremeditated causes, in reporting SALB antibody results. Insufficient concordance and standardization in antibody testing may have practical implications for organ allocation and organ sharing programs.

HOXA13 Is essential for placental vascular patterning and labyrinth endothelial specification.

In eutherian mammals, embryonic growth and survival is dependent on the formation of the placenta, an organ that facilitates the efficient exchange of oxygen, nutrients, and metabolic waste between the maternal and fetal blood supplies. Key to the placenta's function is the formation of its vascular labyrinth, a series of finely branched vessels whose molecular ontogeny remains largely undefined. In this report, we demonstrate that HOXA13 plays an essential role in labyrinth vessel formation. In the absence of HOXA13 function, placental endothelial cell morphology is altered, causing a loss in vessel wall integrity, edema of the embryonic blood vessels, and mid-gestational lethality. Microarray analysis of wild-type and mutant placentas revealed significant changes in endothelial gene expression profiles. Notably, pro-vascular genes, including Tie2 and Foxf1, exhibited reduced expression in the mutant endothelia, which also exhibited elevated expression of genes normally expressed in lymphatic or sinusoidal endothelia. ChIP analysis of HOXA13-DNA complexes in the placenta confirmed that HOXA13 binds the Tie2 and Foxf1 promoters in vivo. In vitro, HOXA13 binds sequences present in the Tie2 and Foxf1 promoters with high affinity (K(d) = 27-42 nM) and HOXA13 can use these bound promoter regions to direct gene expression. Taken together, these findings demonstrate that HOXA13 directly regulates Tie2 and Foxf1 in the placental labyrinth endothelia, providing a functional explanation for the mid-gestational lethality exhibited by Hoxa13 mutant embryos as well as a novel transcriptional program necessary for the specification of the labyrinth vascular endothelia.

HOXA13 directly regulates EphA6 and EphA7 expression in the genital tubercle vascular endothelia.

Hypospadias, a common defect affecting the growth and closure of the external genitalia, is often accompanied by gross enlargements of the genital tubercle (GT) vasculature. Because Hoxa13 homozygous mutant mice also exhibit hypospadias and GT vessel expansion, we examined whether genes playing a role in angiogenesis exhibit reduced expression in the GT. From this analysis, reductions in EphA6 and EphA7 were detected. Characterization of EphA6 and EphA7 expression in the GT confirmed colocalization with HOXA13 in the GT vascular endothelia. Analysis of the EphA6 and EphA7 promoter regions revealed a series of highly conserved cis-regulatory elements bound by HOXA13 with high affinity. GT chromatin immunoprecipitation confirmed that HOXA13 binds these gene-regulatory elements in vivo. In vitro, HOXA13 activates gene expression through the EphA6 and EphA7 gene-regulatory elements. Together these findings indicate that HOXA13 directly regulates EphA6 and EphA7 in the developing GT and identifies the GT vascular endothelia as a novel site for HOXA13-dependent expression of EphA6 and EphA7.