Identification of risk epitope mismatches associated with de novo donor-specific HLA antibody development in cardiothoracic transplantation.

The development of de novo donor-specific HLA antibodies (dnDSA) after transplantation is associated with graft failure, mortality, and cost. There is no effective therapeutic intervention to prevent dnDSA or ameliorate associated injury. The aims of this study were to identify specific HLA factors associated with dnDSA development and to propose primary prevention strategies that could reduce the incidence of dnDSA without prohibitively limiting access to transplant. The investigation cohort included heart transplant recipients from 2008 to 2015 (n = 265). HLA typing was performed and HLA antibody testing was undertaken before and after transplantation. HLAMatchmaker analysis was performed for persistent dnDSA to identify potentially more immunogenic eplet differences. Validation was performed in recipients of lung transplants from 2008 to 2013 (n = 433). The majority of recipients with dnDSA had antibodies to identical eplet positions on DQ2 and DQ7. A high-risk epitope mismatch (found in DQA1*05 +  DQB1*02/DQB1*03:01(7)) was associated with a 4.2- and 4.9-fold increased risk of dnDSA in heart and lung recipients respectively. HLA electrostatic potential modeling provided a plausible explanation for this observed immunogenicity. A theoretical allocation algorithm avoiding high-risk epitope mismatches was generated and predicted to reduce dnDSA by up to 72% without additional testing, eplet analysis, or cost.

Vascular endothelial growth factor plays a major role in development of experimental obliterative bronchiolitis.

Obliterative bronchiolitis (OB) is the major limitation for long-term survival of lung allograft recipients. The exact molecular and cellular mechanisms contributing to obliterative lesion formation are unknown. Pathological characteristics of OB are epithelial damage, peribronchial inflammation, and increasing obliteration of bronchioli. Vascular endothelial growth factor (VEGF) is an angiogenic growth factor that exerts proinflammatory effects by increasing endothelial permeability and inducing expression of endothelial adhesion molecules. We investigated the role of VEGF in the development of OB in rat tracheal allografts and the role of VEGF receptors (VEGFR)-1 and -2 in the development of OB in mouse tracheal allografts. In nontreated allografts, with increasing loss of epithelium and airway occlusion, VEGF messenger RNA (mRNA) and protein expression vanished in the epithelium and increased in smooth muscle cells and mononuclear inflammatory cells compared with syngeneic grafts. Intragraft VEGF overexpression by adenoviral transfer of a mouse VEGF164 gene led to a decrease in epithelial necrosis but increased luminal occlusion by >50% compared with AdLacZ-treated rat tracheal allografts. When compared with the control immunoglobulin (Ig)G group, simultaneous treatment with antibodies against VEGFR-1 and -2 significantly lowered the degree of luminal occlusion of mouse tracheal allografts.

Prevention of cytomegalovirus infection-enhanced experimental obliterative bronchiolitis by antiviral prophylaxis or immunosuppression in rat tracheal allografts.

In this study, the prevention of rat cytomegalovirus (RCMV) infection-enhanced experimental obliterative bronchiolitis in rat tracheal allografts was investigated. RCMV infection markedly enhanced cell proliferation and histological changes of obliterative bronchiolitis, a form of chronic rejection after lung transplantation. These alterations were linked to increased interleukin (IL)-2 and tumor necrosis factor-alpha (TNF-alpha) immunoreactivity, and reduction of IL-10 expression. In recipient rats with acute RCMV infection, prophylaxis with either ganciclovir (DHPG) or hyperimmune serum (HIS) totally prevented RCMV infection-enhanced tracheal occlusion. DHPG treatment initiated during acute RCMV infection also reduced lesion development but markedly less than DHPG prophylaxis. Treatment of acute RCMV infection with HIS alone or in combination with DHPG had no significant effect on tracheal occlusion. Inhibition of the transcription of cytokines by high doses of cyclosporine A significantly reduced RCMV infection-enhanced tracheal obliteration. In rats with chronic RCMV infection, obliterative alterations were prevented by DHPG prophylaxis initiated at the time of transplantation. Prophylaxis either with DHPG or HIS did not affect the amount of infectious RCMV recovered from host salivary glands, nor were there differences seen in RCMV major immediate early DNA expression in tracheal allografts between different antiviral drug regimens. Immunohistochemical analysis of allografts revealed that inhibition of tracheal occlusion by antiviral prophylaxis was associated with a reduction in the number of ED1(+) macrophages and cells staining for Th1 cytokines and TNF-alpha, while immune modulation by cyclosporine A up-regulated IL-10 production. In conclusion, the results of the present study suggest that the CMV infection-enhanced chronic rejection develops independently of viral load but requires both immune activation and simultaneous CMV gene expression beyond immediate early genes.

Cytomegalovirus infection and cardiac allograft vasculopathy.

There is a wealth of clinical and experimental evidence indicating the interaction of cytomegalovirus (CMV) infection and rejection in cardiac and other solid organ allografts. A plausible explanation for this association comes from data showing that therapy with biologicals, sepsis, and rejection, all lead to the release of TNF-alpha which, upon binding to its receptor, activates NF-kB. TNF-alpha is also able to stimulate the activity of the CMV-IE enhancer/promoter region. CMV infection of several cell lines leads to NF-kB activation. NF-kB binding sites are present in regulatory regions of various cellular and viral genes, including the IE enhancer region of CMV. In a reciprocal situation, CMV infection, most likely via gamma-interferon, leads to upregulation of MHC antigens in the transplant and, thereby, to increased transplant immunogenicity. Thus, a vicious circle is induced. We have investigated in detail the pathobiology of CMV and allograft vasculopathy (chronic rejection) in experimental animals, using aortic and cardiac allografts as well as a trachea model. The results may be summarized as follows: Infection of the recipient with rat CMV results in an early inflammatory response in the aortic and cardiac allograft vascular adventitia and intima (endothelialitis) and in the airway wall of tracheal allografts. This early inflammatory response leads to enhanced intimal thickness in aortic and cardiac allografts and enhanced luminal occlusion of tracheal allografts. Timewise, this coincides with early activation of intragraft inflammatory leukocytes and increased mRNA of various growth factors and cytokines. When the recipients receive gancyclovir, the enhanced intimal response in aortic and cardiac allografts and luminal occlusion in tracheal allografts is entirely abolished. Gancyclovir treatment dramatically reduces the inflammatory response in the allograft, and thereby growth factor synthesis in response to injury. However, gancyclovir does not prevent the expression of IE antigen of CMV, suggested to inactivate tumor suppressor protein p53 predisposing smooth muscle cells to increased growth. Taken together, the effect of CMV infection on cardiac allograft dysfunction is bidirectional and biphasic. The bidirectional nature emerges from the observations that acute CMV infection may accelerate acute rejection, and, on the other hand, acute alloimmune response-associated cytokine response may activate latent CMV infection. The biphasic effect of CMV on allograft dysfunction refers to its early and late detrimental effects, i.e. during the time of acute and chronic rejection. These two effects of CMV on allograft dysfunction emphasize the need for precise diagnosis of CMV infection in transplant recipients and pre-emptive or prophylactic anti-viral therapy. The benefits of this strategy may not be evident during the early post-transplant period, but 5-10 years after transplantation they manifest as better graft survival.

Synthesis of Hexp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O) (CH2)7 CH3 probes for exploration of the substrate specificity of glycosyltransferases: Part II, Hex = 3-O-methyl-beta-D-Gal, 3-deoxy-beta-D-Gal, 3-deoxy-3-fluoro-beta-D-Gal, 3-amino-3-deoxy-beta-D-Gal, beta-D-Gul, alpha-L-Alt, or beta-L-Gal.

Seven analogues of the trisaccharide beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O)(CH 2)7CH3 have been synthesized as potential substrates for glycosyltransferases involved in the chain-termination of N-acetyllactosamine-type N-glycans. These compounds include: 3-O-methyl-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp -(1-->O) (CH2)7CH3, 3-deoxy-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1 -->O) (CH2)7CH3, 3-deoxy-3-fluoro-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-M anp- (1-->O)(CH2)7Ch3, 3-amino-3-deoxy-beta-D-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Ma np- (1-->O)(CH2)7CH3, beta-D-Gulp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-- >O)(CH2)7CH3, beta-L-Galp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1-->O)(CH 2)7CH3, and alpha-L-Altp-(1-->4)-beta-D-GlcpNAc-(1-->2)-alpha-D-Manp-(1- ->O) (CH2)7CH3. All trisaccharides were obtained by condensation of suitably modified glycosyl donors based on imidates or thioglycosides with the same disaccharide acceptor, octyl 3,4,6-tri-O-benzyl-2-O-(3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D- glucopyranosyl)-alpha-D-mannopyranoside, followed by deprotection.

Exploring the substrate specificities of alpha-2,6- and alpha-2,3-sialyltransferases using synthetic acceptor analogues.

The acceptor specificities of rat liver Gal(beta 1-4)GlcNAc alpha-2,6-sialyltransferase, recombinant full-length human liver Gal(beta 1-4)GlcNAc alpha-2,6-sialyltransferase, and a soluble form of recombinant rat liver Gal(beta 1-3/4)GlcNAc alpha-2,3-sialyltransferase were studied with a panel of analogues of the trisaccharide Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-O)(CH2)7CH3. These analogues contain structural variants of D-galactose, modified at either C3, C4 or C5 by deoxygenation, fluorination, O-methylation, epimerization, or by the introduction of an amino group. In addition, the enantiomer of D-galactose is included. The alpha-2,6-sialyltransferases tolerated most of the modifications at the galactose residue to some extent, whereas the alpha-2,3-sialyltransferase displayed a narrower specificity. Molecular dynamics simulations were performed in order to correlate enzymatic activity to three-dimensional structure. Ineffective acceptors for rat liver alpha-2,6-sialyltransferase were shown to be inhibitory towards the enzyme; likewise, the alpha-2,3-sialyltransferase was found to be inhibited by all non-substrates. Modified sialyloligosaccharides were obtained on a milligram scale by incubation of effective acceptors with one of each of the three enzymes, and characterized by 500-MHz 1H-NMR spectroscopy.