Identification of a previously unknown antigen-specific regulatory T cell and its mechanism of suppression

Despite increasing evidence for the existence of antigen-specific regulatory T cells, the mechanisms underlying suppression remain unclear. In this study we have identified and cloned a novel subset of antigen-specific regulatory T cells and demonstrated that these T cells possess a unique combination of cell surface markers and array of cytokines. The regulatory T cells are able to inhibit the function of T cells carrying the same T-cell receptor specificity and prevent skin allograft rejection in an antigen-specific, dose-dependent manner. The regulatory T cells are able to acquire alloantigen from antigen-presenting cells, present the alloantigen to activated syngeneic CD8+ T cells and then send death signals to CD8+ T cells. These findings provide a novel mechanism of regulatory T-cell-mediated, antigen-specific suppression.

NK cells induce apoptosis in tubular epithelial cells and contribute to renal ischemia-reperfusion injury

Renal ischemia-reperfusion injury (IRI) can result in acute renal failure with mortality rates of 50% in severe cases. NK cells are important participants in early-stage innate immune responses. However, their role in renal tubular epithelial cell (TEC) injury in IRI is currently unknown. Our data indicate that NK cells can kill syngeneic TEC in vitro. Apoptotic death of TEC in vitro is associated with TEC expression of the NK cell ligand Rae-1, as well as NKG2D on NK cells. In vivo following IRI, there was increased expression of Rae-1 on TEC. FACS analyses of kidney cell preparations indicated a quantitative increase in NKG2D-bearing NK cells within the kidney following IRI. NK cell depletion in wild-type C57BL/6 mice was protective, while adoptive transfer of NK cells worsened injury in NK, T, and B cell-null Rag2(-/-)gamma(c)(-/-) mice with IRI. NK cell-mediated kidney injury was perforin (PFN)-dependent as PFN(-/-) NK cells had minimal capacity to kill TEC in vitro compared with NK cells from wild-type, FasL-deficient (gld), or IFN-gamma(-/-) mice. Taken together, these results demonstrate for the first time that NK cells can directly kill TEC and that NK cells contribute substantially to kidney IRI. NK cell killing may represent an important underrecognized mechanism of kidney injury in diverse forms of inflammation, including transplantation.

Double-negative T cells, activated by xenoantigen, lyse autologous B and T cells using a perforin/granzyme-dependent, Fas-Fas ligand-independent pathway

The ability to control the response of B cells is of particular interest in xenotransplantation as Ab-mediated hyperacute and acute xenograft rejection are major obstacles in achieving long-term graft survival. Regulatory T cells have been proven to play a very important role in the regulation of immune responses to self or non-self Ags. Previous studies have shown that TCRalphabeta+CD3+CD4-CD8- (double-negative (DN)) T cells possess an immune regulatory function, capable of controlling antidonor T cell responses in allo- and xenotransplantation through Fas-Fas ligand interaction. In this study, we investigated the possibility that xenoreactive DNT cells suppress B cells. We found that DNT cells generated from wild-type C57BL/6 mice expressed B220 and CD25 after rat Ag stimulation. These xenoreactive B220+CD25+ DNT cells lysed activated, but not naive, B and T cells. This killing, which took place through cell-cell contact, required participation of adhesion molecules. Our results indicate that Fas ligand, TGF-beta, TNF-alpha, and TCR-MHC recognition was not involved in DNT cell-mediated syngenic cell killing, but instead this killing was mediated by perforin and granzymes. The xenoreactive DNT cells expressed high levels of granzymes in comparison to allo- or xenoreactive CD8+ T cells. Adoptive transfer of DNT cells in combination with early immune suppression by immunosuppressive analog of 15-deoxyspergualin, LF15-0195, significantly prolonged rat heart graft survival to 62.1 +/- 13.9 days in mice recipients. In conclusion, this study suggests that xenoreactive DNT cells can control B and T cell responses in perforin/granzyme-dependent mechanisms. DNT cells may be valuable in controlling B and T cell responses in xenotransplantation.

Osteopontin expressed in tubular epithelial cells regulates NK cell-mediated kidney ischemia reperfusion injury

Renal ischemia reperfusion injury (IRI) occurs after reduced renal blood flow and is a major cause of acute injury in both native and transplanted kidneys. Studies have shown diverse cell types in both the innate and the adaptive immune systems participate in kidney IRI as dendritic cells, macrophages, neutrophils, B cells, CD4(+) NK(+) cells, and CD4(+) T cells all contribute to this form of injury. Recently, we have found that NK cells induce apoptosis in tubular epithelial cells (TECs) and also contribute to renal IRI. However, the mechanism of NK cell migration and activation during kidney IRI remains unknown. In this study, we have identified that kidney TECs express a high level of osteopontin (OPN) in vitro and in vivo. C57BL/6 OPN-deficient mice have reduced NK cell infiltration with less tissue damage compared with wild-type C57BL/6 mice after ischemia. OPN can directly activate NK cells to mediate TEC apoptotic death and can also regulate chemotaxis of NK cells to TECs. Taken together, our study's results indicate that OPN expression by TECs is an important factor in initial inflammatory responses that involves NK cells activity in kidney IRI. Inhibiting OPN expression at an early stage of IRI may be protective and preserve kidney function after transplantation.

Interaction of the E1A oncoprotein with Yak1p, a novel regulator of yeast pseudohyphal differentiation, and related mammalian kinases

The C-terminal portion of adenovirus E1A suppresses ras-induced metastasis and tumorigenicity in mammalian cells; however, little is known about the mechanisms by which this occurs. In the simple eukaryote Saccharomyces cerevisiae, Ras2p, the homolog of mammalian h-ras, regulates mitogen-activated protein kinase (MAPK) and cyclic AMP-dependent protein kinase A (cAMP/PKA) signaling pathways to control differentiation from the yeast form to the pseudohyphal form. When expressed in yeast, the C-terminal region of E1A induced pseudohyphal differentiation, and this was independent of both the MAPK and cAMP/PKA signaling pathways. Using the yeast two-hybrid system, we identified an interaction between the C-terminal region of E1A and Yak1p, a yeast dual-specificity serine/threonine protein kinase that functions as a negative regulator of growth. E1A also physically interacts with Dyrk1A and Dyrk1B, two mammalian homologs of Yak1p, and stimulates their kinase activity in vitro. We further demonstrate that Yak1p is required in yeast to mediate pseudohyphal differentiation induced by Ras2p-regulated signaling pathways. However, pseudohyphal differentiation induced by the C-terminal region of E1A is largely independent of Yak1p. These data suggest that mammalian Yak1p-related kinases may be targeted by the E1A oncogene to modulate cell growth.

Ly-6A is critical for the function of double negative regulatory T cells

We have recently demonstrated that CD3+CD4-CD8- double negative (DN) T cells can down-regulate allogeneic immune responses both in vitro and in vivo by killing activated syngeneic CD8+ T cells. The goal of this study was to identify molecules that are crucial for DN T cell-mediated suppression. We demonstrate that Ly-6A (Sca-1) is highly expressed on DN T cells. Incubation with IL-10 significantly reduced Ly-6A expression and the function of DN T cells. DN T cell-mediated killing was significantly reduced when Ly-6A was blocked.Ly-6A-deficient mice showed an accelerated allograft rejection when compared to wild-type controls. Furthermore we demonstrate that pretransplantation donor lymphocyte infusion (DLI) led to activation and proliferation of recipient DN T cells and prolongation of bm1-->B6 skin allograft survival. However, when the recipients were deficient in Ly-6A, the beneficial effect of DLI on allograft survival was abolished. Moreover, deficiency in Ly-6A did not affect the activation and proliferation of DN T cells. Rather, it impaired the ability of DN T cells to kill activated anti-donor CD8+ T cells. Taken together, our data indicate that Ly-6A plays a crucial role in DN T cell-mediated regulation in vitro and in vivo, perhaps by enhancing DN-CD8+ T cell signaling.

Natural Killer Cells Mediate Long-term Kidney Allograft Injury

BACKGROUND

Chronic allograft injury remains the leading cause of late kidney graft loss despite improvements in immunosuppressive drugs and a reduction in acute T cell-mediated rejection. We have recently demonstrated that natural killer (NK) cells are cytotoxic to tubular epithelial cells and contribute to acute kidney ischemia-reperfusion injury. The role of NK cells in kidney allograft rejection has not been studied.

METHODS

A "parent to F1" kidney transplant model was used to study NK cell-mediated transplant rejection.

RESULTS

The C57BL/6 kidneys were transplanted into fully nephrectomized CB6F1 (C57BL/6 x BALB/c) mice. Serum creatinine levels increased from baseline (18.8 ± 5.0 μmol/L to 37.2 ± 5.9 μmol/L, P < 0.001) at 60 days after transplantation. B6Rag-to-CB6F1Rag (B6RagxBALB/cRag) recipients, which lack T and B cells but retain NK cells, showed similar levels of kidney dysfunction 65 days after transplantation (creatinine, 33.8 ± 7.9 μmol/L vs 17.5 ± 5.1 μmol/L in nontransplant Rag mice, P < 0.05). Importantly, depletion of NK cells in Rag1 recipients inhibited kidney injury (24.6 ± 5.5 μmol/L, P < 0.05). Osteopontin, which can activate NK cells to mediate tubular epithelial cell death in vitro, was highly expressed in 60 days kidney grafts. Osteopontin null kidney grafts had reduced injury after transplantation into CB6F1 mice (17.7 ± 3.1 μmol/L, P < 0.001).

CONCLUSIONS

Collectively, these data demonstrate for the first time that independent of T and B cells, NK cells have a critical role in mediating long-term transplant kidney injury. Specific therapeutic strategies that target NK cells in addition to conventional immunosuppression may be required to attenuate chronic kidney transplant injury.

Natural killer cells play a critical role in cardiac allograft vasculopathy in an interleukin-6--dependent manner

BACKGROUND

Approximately 50% of cardiac transplants fail in the long term, and currently, there are no specific treatments to prevent chronic rejection. In the clinic, donor cardiac graft ischemia time is limited to within a few hours and correlates with delayed graft function and organ failure. It is still unknown how ischemic injury negatively influences allograft function over the long term despite advances in immunosuppression therapy.

METHODS

Allogeneic cardiac grafts were stored at 4 °C for 4 hr before being transplanted into T/B cell-deficient Rag(-/-) mice or T/B/natural killer (NK) cell-deficient γc(-/-)Rag(-/-) mice. Grafts were harvested 60 days after transplantation and indicators of chronic allograft vasculopathy (CAV) were quantified.

RESULTS

We have found that cold ischemia of cardiac grafts induces CAV after transplantation into Rag1(-/-) mice. Interestingly, cold ischemia-induced CAV posttransplantation was not seen in T/B/NK cell-deficient γc(-/-)Rag(-/-) mice. However, cardiac grafts in γc(-/-)Rag(-/-) mice that received an adoptive transfer of NK cells developed CAV, supporting the role of NK cells in CAV development. Analysis of various cytokines that contribute to NK cell function revealed high interleukin (IL)-6 expression in cardiac grafts with CAV. In addition, IL-6-deficient cardiac grafts did not develop CAV after transplantation into allogeneic Rag(-/-) mice.

CONCLUSION

These data demonstrate that cold ischemia and NK cells play critical roles in the development CAV. Natural killer cells and injured grafts may play a reciprocal role for CAV development in an IL-6-independent manner. Specific therapeutic strategies may be required to attenuate NK cell contribution to chronic cardiac rejection.

Adoptive transfer of DNT cells induces long-term cardiac allograft survival and augments recipient CD4(+)Foxp3(+) Treg cell accumulation

Regulatory T (Treg) cells play an important role in the regulation of immune responses but whether Treg will induce tolerance in transplant recipients in the clinic remains unknown. Our previous studies have shown that TCRαβ(+)CD3(+)CD4⁻CD8⁻NK1.1⁻ (double negative, DN) T cells suppress T cell responses and prolong allograft survival in a single locus MHC-mismatched mouse model. In this study, we investigated the role of DNT cells in a more robust, fully MHC-mismatched BALB/c to C57BL/6 transplantation model, which may be more clinically relevant. Adoptive transfer of DNT cells in combination with short-term rapamycin treatment (days 1-9) induced long-term heart allograft survival (101±31 vs. 39±13 days rapamycin alone, p<0.01). Furthermore adoptive transfer DNT cells augmented CD4+Foxp3+ Treg cells accumulation in transplant recipients while depletion of CD4(+) Treg cells by anti-CD25 inhibited the effect of DNT cells on long-term graft survival (48±12 days vs. 101±31 days, p<0.001). In conclusion, DNT cells combined with short-term immunosuppression can prolong allograft survival, which may be through the accumulation of CD4(+)Foxp3(+) Treg cells in the recipient. Our result suggests that allograft tolerance may require the co-existence of different type Treg cell phenotypes which are affected by current immunosuppression.

Immune responses to the hepatitis C virus NS4A protein are profoundly influenced by the combination of the viral genotype and the host major histocompatibility complex

The interaction between the host major histocompatibility complex (MHC) and the genotype of the hepatitis C virus (HCV) was analysed using synthetic full-length non-structural (NS) 4A proteins, residues 1658-1712, of genotypes 1b, 2b, 3a, 4a and 5a. Human and murine antibodies specific for the five NS4A genotypes analysed focused on residues 1688-1707. In immunized B10 H-2 congenic mice, the H-2d, H-2f and H-2s haplotypes were good responders to NS4A, irrespective of the viral genotype. In contrast, the H-2k haplotype was a low or non-responder to all NS4A genotypes, except for genotype 2b. Also, H-2f- and H-2s-restricted NS4A genotype 1b-specific T-cells focused on residues 1670-1679 and 1683-1692, respectively, whereas H-2k-restricted NS4A genotype 2b-specific T-cells focused on the carboxy terminus. Interestingly, H-2f-restricted genotype 1b-specific T-cells did not cross-react with T-cell site analogues of seven other genotypes, whereas the H-2s-restricted, genotype 1b-specific T-cells cross-reacted with genotypes 1a, 4a and 5a. Thus the combination of viral genotype and host MHC profoundly influences the ability to mount an HCV NS4A-specific immune response.

Use of RNA interference to minimize ischemia reperfusion injury

RNA interference (RNAi) is an endogenous mechanism of cellular RNA control through degradation of specific messenger RNA sequences. This process of gene silencing may be exploited by the use of small interfering RNA (siRNA) to mediate precise control of targeted cellular functions. The nature of transplantation leads invariably to tissue injury, as organs are damaged by the loss of blood supply and resultant ischemia associated with the procurement procedure. Upon reperfusion, an inflammatory program is activated, and subsequent injury results in delayed graft function and, potentially, organ failure. Many of the molecular components in ischemia-reperfusion injury (IRI) have been identified, but effective therapeutics are not currently available. Accumulating evidence supports a role for siRNA in controlling IRI, as siRNA is specific, relatively low in toxicity, and limited in duration of effect. The capacity of siRNA to control IRI-related transcription factors, cell death and apoptosis, complement factors, and oxidative stress molecules supports the concept that RNAi-based therapeutics represent a novel and promising strategy for the control of IRI. However, there are issues of RNAi strategies, including siRNA design, "off-target" effects, and delivery that merit consideration in approaching IRI with gene silencing. This review will provide an overview of current concepts in RNAi and the potential application to IRI in solid organ transplantation.

Characterization of a monoclonal antibody and its single-chain antibody fragment recognizing the nucleoside Triphosphatase/Helicase domain of the hepatitis C virus nonstructural 3 protein

We have produced a murine monoclonal antibody (MAb), ZX10, recognizing the NTPase/helicase domain of the hepatitis C virus (HCV) nonstructural 3 protein (NS3), from which we designed a single-chain variable fragment (ScFv). The ZX10 MAb recognized a discontinuous epitope of the NTPase/helicase domain, of which the linear sequence GEIPFYGKAIPL at residues 1371 to 1382 constitutes one part. cDNAs from variable regions coding for the heavy and light chains were cloned, sequenced, and assembled into the NS3-ScFv, which was inserted into procaryotic and eucaryotic expression vectors. Escherichia coli-expressed NS3-ScFv inhibited the binding of the ZX10 MAb to NS3, confirming a retained specificity. However, the ability to bind the peptide 1371-1382 had been lost. In vitro-translated NS3-ScFv and HCV NS3/NS4A were coprecipitated by antibodies to HCV NS4A, confirming the in vitro activity of the NS3 ScFv. Thus, we have designed a functional NS3 NTPase/helicase domain-specific ScFv which should be evaluated further with respect to disturbing enzymatic functions of the NS3 protein.

Intracellular pH Regulates TRAIL-Induced Apoptosis and Necroptosis in Endothelial Cells

During ischemia or inflammation of organs, intracellular pH can decrease if acid production exceeds buffering capacity. Thus, the microenvironment can expose parenchymal cells to a reduced extracellular pH which can alter pH-dependent intracellular functions. We have previously shown that while silencing caspase-8 in an in vivo ischemia reperfusion injury (IRI) model results in improved organ function and survival, removal of caspase-8 function in a donor organ can paradoxically result in enhanced receptor-interacting protein kinase 1/3- (RIPK1/3-) regulated necroptosis and accelerated graft loss following transplantation. In our current study, TRAIL- (TNF-related apoptosis-inducing ligand-) induced cell death in vitro at neutral pH and caspase-8 inhibition-enhanced RIPK1-dependent necroptotic death were confirmed. In contrast, both caspase-8 inhibition and RIPK1 inhibition attenuated cell death at a cell pH of 6.7. Cell death was attenuated with mixed lineage kinase domain-like (MLKL) silencing, indicating that MLKL membrane rupture, a distinctive feature of necroptosis, occurs regardless of pH. In summary, there is a distinct regulatory control of apoptosis and necroptosis in endothelial cells at different intracellular pH. These results highlight the complexity of modulating cell death and therapeutic strategies that may need to consider different consequences on cell death dependent on the model.

Preventing tissue injury using siRNA

RNA interference (RNAi) is a process through which double-stranded RNA induces the activation of endogenous cellular pathways of RNA degradation, resulting in selective and potent silencing of genes that have homology to the double strand. Much of the excitement surrounding small interfering RNA (siRNA)-mediated therapeutics arises from the fact that this approach overcomes many of the shortcomings previously experienced with alternative approaches to selective blocking that use antibodies, antisense oligonucleotides or pharmacological inhibitors. Induction of RNAi through administration of siRNA has been successfully applied to the treatment of hepatitis, viral infections, and cancer. Increased success in addressing issues of siRNA delivery and efficiency will permit this approach to evolve as a new paradigm in clinical therapeutics. In this chapter, we present applications of RNAi in tissue injury, and the possibilities of using this highly promising approach in the context of transplantation.