Screening self-peptides for recognition by mouse alloreactive CD8+ T cells using direct ex vivo multimer staining.

Here, we present a protocol to identify immunogenic self-peptide/allogeneic major histocompatibility complex (MHC) epitopes. We describe the generation of enriched alloreactive CD8+ T cells by priming mice with a skin graft expressing the allogeneic MHC class I molecule of interest, followed by boosting with a liver-specific AAV vector encoding the heavy chain of that donor MHC allomorph. We then use a peptide-exchange approach to assemble a range of peptide-MHC (pMHC) multimers for measuring recognition of the various epitopes by these alloreactive T cells. For complete details on the use and execution of this protocol, please refer to Son et al. (2021).1.

The self-peptide repertoire plays a critical role in transplant tolerance induction.

While direct allorecognition underpins both solid organ allograft rejection and tolerance induction, the specific molecular targets of most directly alloreactive CD8+ T cells have not been defined. In this study, we used a combination of genetically engineered major histocompatibility complex class I (MHC I) constructs, mice with a hepatocyte-specific mutation in the class I antigen-presentation pathway, and immunopeptidomic analysis to provide definitive evidence for the contribution of the peptide cargo of allogeneic MHC I molecules to transplant tolerance induction. We established a systematic approach for the discovery of directly recognized pMHC epitopes and identified 17 strongly immunogenic H-2Kb-associated peptides recognized by CD8+ T cells from B10.BR (H-2k) mice, 13 of which were also recognized by BALB/c (H-2d) mice. As few as 5 different tetramers used together were able to identify a high proportion of alloreactive T cells within a polyclonal population, suggesting that there are immunodominant allogeneic MHC-peptide complexes that can account for a large component of the alloresponse.

Liver-Targeted Angiotensin Converting Enzyme 2 Therapy Inhibits Chronic Biliary Fibrosis in Multiple Drug-Resistant Gene 2-Knockout Mice.

There is a large unmet need for effective therapies for cholestatic disorders, including primary sclerosing cholangitis (PSC), a disease that commonly results in liver failure. Angiotensin (Ang) II of the renin Ang system (RAS) is a potent profibrotic peptide, and Ang converting enzyme 2 (ACE2) of the alternate RAS breaks down Ang II to antifibrotic peptide Ang-(1-7). In the present study, we investigated long-term effects of ACE2 delivered by an adeno-associated viral vector and short-term effects of Ang-(1-7) peptide in multiple drug-resistant gene 2-knockout (Mdr2-KO) mice. These mice develop progressive biliary fibrosis with pathologic features closely resembling those observed in PSC. A single intraperitoneal injection of ACE2 therapy markedly reduced liver injury (P < 0.05) and biliary fibrosis (P < 0.01) at both established (3-6 months of age) and advanced (7-9 months of age) disease compared to control vector-injected Mdr2-KO mice. This was accompanied by increased hepatic Ang-(1-7) levels (P < 0.05) with concomitant reduction in hepatic Ang II levels (P < 0.05) compared to controls. Moreover, Ang-(1-7) peptide infusion improved liver injury (P < 0.05) and biliary fibrosis (P < 0.0001) compared to saline-infused disease controls. The therapeutic effects of both ACE2 therapy and Ang-(1-7) infusion were associated with significant (P < 0.01) reduction in hepatic stellate cell (HSC) activation and collagen expression. While ACE2 therapy prevented the loss of epithelial characteristics of hepatocytes and/or cholangiocytes in vivo, Ang-(1-7) prevented transdifferentiation of human cholangiocytes (H69 cells) into the collagen-secreting myofibroblastic phenotype in vitro. We showed that an increased ratio of hepatic Ang-(1-7) to Ang II levels by ACE2 therapy results in the inhibition of HSC activation and biliary fibrosis. Conclusion: ACE2 therapy has the potential to treat patients with biliary diseases, such as PSC.

Serum Amyloid A Stimulates Vascular and Renal Dysfunction in Apolipoprotein E-Deficient Mice Fed a Normal Chow Diet.

Elevated serum amyloid A (SAA) levels may promote endothelial dysfunction, which is linked to cardiovascular and renal pathologies. We investigated the effect of SAA on vascular and renal function in apolipoprotein E-deficient (ApoE-/-) mice. Male ApoE-/- mice received vehicle (control), low-level lipopolysaccharide (LPS), or recombinant human SAA by i.p. injection every third day for 2 weeks. Heart, aorta and kidney were harvested between 3 days and 18 weeks after treatment. SAA administration increased vascular cell adhesion molecule (VCAM)-1 expression and circulating monocyte chemotactic protein (MCP)-1 and decreased aortic cyclic guanosine monophosphate (cGMP), consistent with SAA inhibiting nitric oxide bioactivity. In addition, binding of labeled leukocytes to excised aorta increased as monitored using an ex vivo leukocyte adhesion assay. Renal injury was evident 4 weeks after commencement of SAA treatment, manifesting as increased plasma urea, urinary protein, oxidized lipids, urinary kidney injury molecule (KIM)-1 and multiple cytokines and chemokines in kidney tissue, relative to controls. Phosphorylation of nuclear-factor-kappa-beta (NFκB-p-P65), tissue factor (TF), and macrophage recruitment increased in kidneys from ApoE-/- mice 4 weeks after SAA treatment, confirming that SAA elicited a pro-inflammatory and pro-thrombotic phenotype. These data indicate that SAA impairs endothelial and renal function in ApoE-/- mice in the absence of a high-fat diet.

Lipid and glucose metabolism in hepatocyte cell lines and primary mouse hepatocytes: a comprehensive resource for in vitro studies of hepatic metabolism.

The liver is a critical tissue for maintaining glucose, fatty acid, and cholesterol homeostasis. Primary hepatocytes represent the gold standard for studying the mechanisms controlling hepatic glucose, lipid, and cholesterol metabolism in vitro. However, access to primary hepatocytes can be limiting, and therefore, other immortalized hepatocyte models are commonly used. Here, we describe substrate metabolism of cultured AML12, IHH, and PH5CH8 cells, hepatocellular carcinoma-derived HepG2s, and primary mouse hepatocytes (PMH) to identify which of these cell lines most accurately phenocopy PMH basal and insulin-stimulated metabolism. Insulin-stimulated glucose metabolism in PH5CH8 cells, and to a lesser extent AML12 cells, responded most similarly to PMH. Notably, glucose incorporation in HepG2 cells were 14-fold greater than PMH. The differences in glucose metabolic activity were not explained by differential protein expression of key regulators of these pathways, for example glycogen synthase and glycogen content. In contrast, fatty acid metabolism in IHH cells was the closest to PMHs, yet insulin-responsive fatty acid metabolism in AML12 and HepG2 cells was most similar to PMH. Finally, incorporation of acetate into intracellular-free cholesterol was comparable for all cells to PMH; however, insulin-stimulated glucose conversion into lipids and the incorporation of acetate into intracellular cholesterol esters were strikingly different between PMHs and all tested cell lines. In general, AML12 cells most closely phenocopied PMH in vitro energy metabolism. However, the cell line most representative of PMHs differed depending on the mode of metabolism being investigated, and so careful consideration is needed in model selection.

Direct recognition of hepatocyte-expressed MHC class I alloantigens is required for tolerance induction.

Adeno-associated viral vector-mediated (AAV-mediated) expression of allogeneic major histocompatibility complex class I (MHC class I) in recipient liver induces donor-specific tolerance in mouse skin transplant models in which a class I allele (H-2Kb or H-2Kd) is mismatched between donor and recipient. Tolerance can be induced in mice primed by prior rejection of a donor-strain skin graft, as well as in naive recipients. Allogeneic MHC class I may be recognized by recipient T cells as an intact molecule (direct recognition) or may be processed and presented as an allogeneic peptide in the context of self-MHC (indirect recognition). The relative contributions of direct and indirect allorecognition to tolerance induction in this setting are unknown. Using hepatocyte-specific AAV vectors encoding WT allogeneic MHC class I molecules, or class I molecules containing a point mutation (D227K) that impedes direct recognition of intact allogeneic MHC class I by CD8+ T cells without hampering the presentation of processed peptides derived from allogeneic MHC class I, we show here that tolerance induction depends upon recognition of intact MHC class I. Indirect recognition alone yielded a modest prolongation of subsequent skin graft survival, attributable to the generation of CD4+ Tregs, but it was not sufficient to induce tolerance.

Blockade of HMGB1 Attenuates Diabetic Nephropathy in Mice.

Activation of TLR2 or TLR4 by endogenous ligands such as high mobility group box 1 (HMGB1) may mediate inflammation causing diabetic kidney injury. We determined whether blockade of HMGB1 signaling by: (1) supra-physiological production of endogenous secretory Receptor for Advanced Glycation End-products (esRAGE), a receptor for HMGB1; (2) administration of HMGB1 A Box, a specific competitive antagonist, would inhibit development of streptozotocin induced diabetic nephropathy (DN). Wild-type diabetic mice developed albuminuria, glomerular injuries, interstitial fibrosis and renal inflammation. Using an adeno-associated virus vector, systemic over-expression of esRAGE afforded significant protection from all parameters. No protection was achieved by a control vector which expressed human serum albumin. Administration of A Box was similarly protective against development of DN. To determine the mechanism(s) of protection, we found that whilst deficiency of TLR2, TLR4 or RAGE afforded partial protection from development of DN, over-expression of esRAGE provided additional protection in TLR2-/-, modest protection against podocyte damage only in TLR4-/- and no protection in RAGE-/- diabetic mice, suggesting the protection provided by esRAGE was primarily through interruption of RAGE and TLR4 pathways. We conclude that strategies to block the interaction between HMGB1 and its receptors may be effective in preventing the development of DN.

ACE2 Therapy Using Adeno-associated Viral Vector Inhibits Liver Fibrosis in Mice.

Angiotensin converting enzyme 2 (ACE2) which breaks down profibrotic peptide angiotensin II to antifibrotic peptide angiotensin-(1-7) is a potential therapeutic target in liver fibrosis. We therefore investigated the long-term therapeutic effect of recombinant ACE2 using a liver-specific adeno-associated viral genome 2 serotype 8 vector (rAAV2/8-ACE2) with a liver-specific promoter in three murine models of chronic liver disease, including carbon tetrachloride-induced toxic injury, bile duct ligation-induced cholestatic injury, and methionine- and choline-deficient diet-induced steatotic injury. A single injection of rAAV2/8-ACE2 was administered after liver disease has established. Hepatic fibrosis, gene and protein expression, and the mechanisms that rAAV2/8-ACE2 therapy associated reduction in liver fibrosis were analyzed. Compared with control group, rAAV2/8-ACE2 therapy produced rapid and sustained upregulation of hepatic ACE2, resulting in a profound reduction in fibrosis and profibrotic markers in all diseased models. These changes were accompanied by reduction in hepatic angiotensin II levels with concomitant increases in hepatic angiotensin-(1-7) levels, resulting in significant reductions of NADPH oxidase assembly, oxidative stress and ERK1/2 and p38 phosphorylation. Moreover, rAAV2/8-ACE2 therapy normalized increased intrahepatic vascular tone in fibrotic livers. We conclude that rAAV2/8-ACE2 is an effective liver-targeted, long-term therapy for liver fibrosis and its complications without producing unwanted systemic effects.

Serum amyloid A receptor blockade and incorporation into high-density lipoprotein modulates its pro-inflammatory and pro-thrombotic activities on vascular endothelial cells.

The acute phase protein serum amyloid A (SAA), a marker of inflammation, induces expression of pro-inflammatory and pro-thrombotic mediators including ICAM-1, VCAM-1, IL-6, IL-8, MCP-1 and tissue factor (TF) in both monocytes/macrophages and endothelial cells, and induces endothelial dysfunction-a precursor to atherosclerosis. In this study, we determined the effect of pharmacological inhibition of known SAA receptors on pro-inflammatory and pro-thrombotic activities of SAA in human carotid artery endothelial cells (HCtAEC). HCtAEC were pre-treated with inhibitors of formyl peptide receptor-like-1 (FPRL-1), WRW4; receptor for advanced glycation-endproducts (RAGE), (endogenous secretory RAGE; esRAGE) and toll-like receptors-2/4 (TLR2/4) (OxPapC), before stimulation by added SAA. Inhibitor activity was also compared to high-density lipoprotein (HDL), a known inhibitor of SAA-induced effects on endothelial cells. SAA significantly increased gene expression of TF, NFκB and TNF and protein levels of TF and VEGF in HCtAEC. These effects were inhibited to variable extents by WRW4, esRAGE and OxPapC either alone or in combination, suggesting involvement of endothelial cell SAA receptors in pro-atherogenic gene expression. In contrast, HDL consistently showed the greatest inhibitory action, and often abrogated SAA-mediated responses. Increasing HDL levels relative to circulating free SAA may prevent SAA-mediated endothelial dysfunction and ameliorate atherogenesis.

Safety, feasibility, and effect of remote ischemic conditioning in patients undergoing lung transplantation.

BACKGROUND: Primary graft dysfunction (PGD) remains a significant problem after lung transplantation. Data from animal and clinical studies suggest that remote ischemic conditioning (RIC) may reduce ischemia-reperfusion injury in solid organ transplantation. METHODS: A pilot randomized controlled trial of 60 patients undergoing bilateral sequential lung transplantation assessed the utility of RIC in attenuating PGD. Treated recipients underwent 3 cycles of lower limb ischemic conditioning before allograft reperfusion. The primary outcome measure was a comparison of the partial pressure of arterial oxygen/fraction of inspired oxygen ratio (P/F ratio) between treatment groups. RESULTS: No adverse effects of tourniquet application were observed. The mean lowest P/F ratio during the first 24 hours after transplantation was 271.3 mm Hg in the treatment arm vs 256.1 mm Hg in the control arm (p = 0.46). PGD grade and severity and the rate of acute rejection also showed a tendency to favor the treatment arm. Sub-group analysis demonstrated a significant benefit of treatment in patients with a primary diagnosis of restrictive lung disease, a group at high risk for the development of PGD. RIC was not accompanied by systemic release of high-molecular-weight group box 1. Levels of cytokines, high-molecular-weight group box 1, and endogenous secretory receptor for advanced glycation end products peaked within 2 hours after reperfusion and likely reflected donor organ quality rather than an effect of RIC. CONCLUSIONS: RIC did not significantly improve P/F ratios or PGD in this randomized controlled trial. However, encouraging results in this small study warrant a large multicenter trial of RIC in lung transplantation.

Optimized method for ureteric reconstruction in a mouse kidney transplant model.

BACKGROUND: Murine kidney transplantation is an important model for studies of transplantation immunobiology. The most challenging aspect of the difficult surgical procedure is the ureteric anastomosis. METHODS: Two different approaches to ureteric reconstruction are compared here. Method 1, Patch: this involves anastomosis of the donor ureter together with a patch of donor bladder to recipient bladder. Method 2, Implant: this utilizes a 5-0 suture to pull the ureter through the bladder wall. The ureter's peripheral tissue is then fixed to the bladder wall at the implant site with 10-0 micro-sutures. RESULTS: In animals transplanted with the patch method, the initial success rate, defined as survival up to the third post-operative day, was 79% (n = 62), whereas the initial success rate for the implant method was 86.1% (n = 101; P = 0.28). The death rate from unknown and/or unspecified causes in the initial period was 16.1% (10/62) for the patch method, and 8.9% (9/101) for the implant method (P = 0.21). The average donor/recipient operation time with the implant method was 14.8 ± 2.2/61.4 ± 4.7 min (76 min per transplant), whereas operation time with the patch method was 28.3 ± 2.4/77.8 ± 5.5 min (106 min per transplant; P < 0.001). The ureteric implant method resulted in a lower rate of urinary leak compared with the patch method (1.1% versus 10.2%; P = 0.02). CONCLUSIONS: The ureteric implant method for mouse kidney transplantation is a reliable approach with at least as high a success rate as the bladder patch method and with a shorter operation time.

Gene therapy for tolerance: high-level expression of donor major histocompatibility complex in the liver overcomes naive and memory alloresponses to skin grafts.

BACKGROUND: The liver has long been recognized as having tolerogenic properties. We investigated whether recombinant adenoassociated virus (rAAV)-mediated expression of donor major histocompatibility complex in recipient livers could induce tolerance to donor-strain grafts. METHODS: Naive B10.BR (H-2) or B10.BR recipients primed with a H-2K-expressing (K) skin graft were injected with rAAV-expressing H-2K (rAAV-K) to induce K expression on hepatocytes 7 days before challenge with a K skin graft. K-specific responses were measured by interferon (IFN)-γ ELISpot and flow cytometric assessment of directly H-2K reactive cells. Fully allogeneic grafts from C57BL/6 (H-2) donors were transplanted onto longstanding B10.BR recipients of K skin to test for linked epitope suppression. RESULTS: rAAV-K-treated B10.BR mice accepted K skin grafts with increased median survival time (MST) more than 169 days compared to uninoculated (MST=18.5 days) and rAAV-K-treated controls (MST=19 days). rAAV-K-treated B10.BR animals primed with K skin grafts also accepted secondary K skin grafts in the long term (MST>100 days) compared to accelerated rejection in primed, uninoculated mice (MST=12 days). Treatments did not induce liver pathology, assessed by serum alanine aminotransferase levels and histology. IFN-γ ELISpot analysis of splenocytes from rAAV-K-treated mice indicated reduced responses to donor K antigen, but protection was not extended to fully allogeneic C57BL/6 skin or heart grafts, even in recipients that had accepted K skin grafts in the long term. CONCLUSIONS: High-level expression of donor major histocompatibility complex in recipient livers promotes tolerance to skin allografts, even in animals primed to produce a memory response. This provides proof of concept for an approach using liver-targeted gene delivery for tolerance induction to donor antigen.

Analysis of human liver disease using a cluster of differentiation (CD) antibody microarray.

BACKGROUND: A CD antibody microarray has been previously developed allowing semi-quantitative identification of greater than 80 CD antigens on circulating leucocytes from peripheral blood samples. This assay, which uses a live cell-capture technique, enables an extensive leucocyte immunophenotype determination in a single analysis and to date this has been used successfully to characterise diseases including human leukaemias and HIV infection. AIMS: To determine CD antigen expression profiles for patients with various liver diseases and to look for preserved disease-specific signatures. METHODS: Three liver disease groups including hepatitis C (HCV) (n = 35), non-alcoholic steatohepatitis (NASH) (n = 21) and alcohol-related liver disease (n = 14) were compared with a normal group (n = 23). Hierarchal Clustering (HCL) and Principal Component Analysis (PCA) of the data revealed distinct binding patterns for patients with and without cirrhosis. RESULTS: Patients with cirrhosis and portal hypertension compared with those without cirrhosis had significantly reduced expression of several markers of T-cell function including CD45, CD8, CD28 and TCR α/ß. Disease prediction algorithms based on the expression data were able to discriminate cirrhotics from non-cirrhotics with 71% overall success, which improved to 77% when only patients with HCV were considered. CONCLUSIONS: These results demonstrate disease-specific consensus patterns of expression of CD antigens for patients with chronic liver disease, suggesting that the CD antibody array is a promising tool in the analysis of human liver disease, and with further refinement may have future research and clinical utility.

Reliable and reproducible murine models for commonly used abdominal plastic surgical flaps.

Animal models have been used for many years in surgical research to develop different surgical techniques, improve understanding of anatomy and physiology and hone surgical skills. The benefit of such models has been particularly important in developing relatively young specialties like plastic surgery and many plastic surgical techniques are designed and studied in animals long before they are used in humans. We describe techniques for raising several reliable and reproducible abdominal flaps in rodents, including transverse rectus abdominis myocutaneous flaps in rats and mice, superficial inferior epigastric artery flaps in rats and perforator flaps in rats. The intention of this paper is to act as a point of reference for any microvascular or plastic surgeon who is planning to perform abdominal plastic surgical flap research or further microvascular skills.

Toll-like receptor 4 engagement contributes to expression of NKG2D ligands by renal tubular epithelial cells.

BACKGROUND: Engagement of Toll-like receptor (TLR) 4 on intrinsic kidney cells is critical for the full development of renal ischaemia-reperfusion injury (IRI). Effects of TLR signalling in renal parenchymal cells include the production of cytokines, chemokines and other soluble mediators which contribute to local inflammation and leucocyte accumulation. Whether engagement of TLR4 on kidney cells results in additional pro-inflammatory modifications of the renal microenvironment remains to be determined. METHODS: Renal IRI was induced by clamping of the renal pedicles, and expression of NKG2D ligands in mice deficient in TLR4 or its adaptor molecule MyD88, or else pretreated with blocking antibodies against the endogenous TLR4 ligand HMGB1, was compared to that in wild-type mice. Cultures of isolated renal tubular epithelial cells (TECs) from WT, TLR4(-/-) and MyD88(-/-) mice were stimulated with the TLR4 ligand lipopolysaccharide (LPS), or mineral oil occlusion was used to simulate IRI in vitro, prior to determination of NKG2D ligand expression. Chimeric mice lacking TLR4 in either the bone marrow derived or the parenchymal compartment were also subjected to IRI. RESULTS: In this study, we demonstrate a substantial increase in the expression of the NKG2D ligands retinoic acid early inducible-1 (RAE-1), murine ULBP-like transcript 1 (MULT-1) and histocompatibility-60 (H-60) in mouse kidneys during renal IRI. Expression of NKG2D ligands was attenuated in mice deficient in either TLR4 or the adaptor molecule MyD88. Antibody blockade of HMGB1 reduced NKG2D ligand expression by a comparable extent to TLR4 deficiency and did not result in further reduction of NKG2D ligand expression in TLR4(-/-) mice. Isolated TECs from normal mice but not those with defects in the TLR4-MyD88 signalling pathway expressed RAE-1 and MULT-1 upon exposure to LPS and after being subjected to in vitro conditions resembling ischaemia-reperfusion. TLR4 competence in the parenchymal but not the bone marrow-derived compartment was required for RAE-1 up-regulation in mouse kidneys after ischaemia, while TLR4 signalling in both compartments contributed to the intrarenal expression of MULT-1 during IRI. CONCLUSION: Expression of the NKG2D ligands RAE-1 and MULT-1 on kidney cells in response to TLR4 engagement by HMGB1 represents another mechanism by which TLR4 signalling may participate in the pathogenesis of renal IRI.

Liver-directed gene expression using recombinant AAV 2/8 vectors--a tolerogenic strategy for gene delivery?

Vectors based on recombinant adeno-associated virus (AAV) 2/8 hold considerable promise for use in human gene therapy. These vectors are safe, and have minimal immunostimulatory properties. Their combination with efficient, liver-specific promoters allows high-level transgene expression in the hepatocytes of small and large animals. In small animal models, this high level of liver expression results in tolerance to the transgene products. Tolerance to transgene products may also be achievable using these vectors for human gene therapy, but the HLA diversity (and thus variability in T cell recognition of transgene products) and high frequency of prior natural exposure to AAV in human populations impose additional challenges that must be overcome in order for this strategy to succeed.

Donor IL-4-treatment induces alternatively activated liver macrophages and IDO-expressing NK cells and promotes rat liver allograft acceptance.

Most approaches to transplant tolerance involve treatment of the recipient to prevent rejection. This study investigates donor treatment with IL-4 for its effect on subsequent rat liver allograft survival. Rat orthotopic liver transplants were performed in rejecting (PVG donor to Lewis recipient) or spontaneously tolerant (PVG to DA) strain combinations. Donors were untreated or injected intraperitoneally with IL-4 (30,000U/day) for 5days. Tissue infiltrates and gene expression were examined by immunohistochemistry and real-time quantitative PCR. IL-4 induced a marked leukocyte infiltrate in donor livers prior to transplant. Macrophages comprised the major population, although B cells, T cells and natural killer (NK) cells also increased. IL-4-induced liver macrophages had an alternatively activated phenotype with increased expression of mannose receptor but not inducible nitric oxide synthase (NOS2). IL-4 also induced IDO and IFN-gamma expression by NK cells. Donor IL-4-treatment converted rejection to acceptance in the majority of Lewis recipients (median survival time >96days) and did not prevent acceptance in DA recipients. Acceptance in Lewis recipients was associated with increased donor cell migration to recipient spleens and increased splenic IL-2, IFN-gamma and IDO expression 24h after transplantation. Donor IL-4-treatment increased leukocytes in the donor liver including potentially immunosuppressive populations of alternatively activated macrophages and IDO-expressing NK cells. Donor treatment led to long-term acceptance of most livers in association with early immune activation in recipient lymphoid tissues.

NKG2D and its ligands.

NKG2D is an activating immunoreceptor, first recognized on NK cells but subsequently found on gammadelta T cells, CD8(+) alphabeta T cells and macrophages. In NK cells, inhibitory signals are generally dominate over activating signals. However, activating signals mediated through engagement of NKG2D by its ligands on target cells can bypass signals transmitted through inhibitory NK receptors, allowing NKG2D to function as a "master-switch" in determining the activation status of NK cells. NKG2D is important for T cell and NK cell-mediated immunity to viruses and tumours, and has roles in autoimmune disease, allogeneic transplantation, and xenotransplantation. Depending upon the situation, development of strategies to either block or to enhance the interactions between NKG2D and its ligands may have important implications for human health and disease.

Overexpression of indoleamine dioxygenase in rat liver allografts using a high-efficiency adeno-associated virus vector does not prevent acute rejection.

The aim of this study was to evaluate the ability of local overexpression of indoleamine dioxygenase (IDO) to abrogate rat liver transplant rejection by the use of an adeno-associated virus vector [recombinant adeno-associated virus 2/8 (rAAV2/8)] to deliver the transgene to the allograft prior to transplantation. A green fluorescent protein (GFP)-expressing vector [recombinant adeno-associated virus 2/8-liver-specific promoter 1-enhanced green fluorescent protein (rAAV2/8-LSP1-eGFP)] was used to examine the kinetics of expression and optimal dosing for transduction of Piebald Virol Glaxo (PVG) rat livers. A vector encoding the rat IDO gene (rAAV2/8-LSP1-rIDO) was constructed and tested by its ability to induce tryptophan catabolism and kynurenine production in vitro and in vivo. PVG donor rats were injected, via the portal vein, with rAAV2/8-LSP1-rIDO 2 weeks before transplantation into PVG strain isograft or Lewis (LEW) strain allograft recipients. With the enhanced GFP vector, 29.5% and 47.4% of hepatocytes were found to express GFP at 3 and 6 weeks after injection, respectively. In untransplanted PVG animals, the rAAV2/8-LSP1-rIDO vector induced, 3 weeks after administration, a 1.8-fold increase (P = 0.0161) in liver IDO activity, which was associated with a fall in serum tryptophan to 0.5 times the baseline level (P < 0.001). PVG recipients of PVG liver isografts pretreated with the IDO-expressing vector had a 45% lower level of serum tryptophan than recipients of isografts pretreated with the GFP-expressing vector (P = 0.03). LEW recipients of PVG liver allografts pretreated with the rat IDO vector had a median survival time of 12 days, whereas recipients of allografts pretreated with rAAV2/8-LSP1-eGFP had a median survival time of 13 days (P = 0.38). Both groups displayed similar histological features of acute cellular rejection. In conclusion, rAAV2/8 vectors produce highly efficient, though delayed, hepatocyte transduction in vivo and provide a useful gene delivery tool for transplantation models. However, gene delivery using IDO was unsuccessful in prolonging rat liver allograft survival.