The transCampus Metabolic Training Programme Explores the Link of SARS-CoV-2 Virus to Metabolic Disease

Currently, we are experiencing a true pandemic of a communicable disease by the virus SARS-CoV-2 holding the whole world firmly in its grasp. Amazingly and unfortunately, this virus uses a metabolic and endocrine pathway via ACE2 to enter our cells causing damage and disease. Our international research training programme funded by the German Research Foundation has a clear mission to train the best students wherever they may come from to learn to tackle the enormous challenges of diabetes and its complications for our society. A modern training programme in diabetes and metabolism does not only involve a thorough understanding of classical physiology, biology and clinical diabetology but has to bring together an interdisciplinary team. With the arrival of the coronavirus pandemic, this prestigious and unique metabolic training programme is facing new challenges but also new opportunities. The consortium of the training programme has recognized early on the need for a guidance and for practical recommendations to cope with the COVID-19 pandemic for the community of patients with metabolic disease, obesity and diabetes. This involves the optimal management from surgical obesity programmes to medications and insulin replacement. We also established a global registry analyzing the dimension and role of metabolic disease including new onset diabetes potentially triggered by the virus. We have involved experts of infectious disease and virology to our faculty with this metabolic training programme to offer the full breadth and scope of expertise needed to meet these scientific challenges. We have all learned that this pandemic does not respect or heed any national borders and that we have to work together as a global community. We believe that this transCampus metabolic training programme provides a prime example how an international team of established experts in the field of metabolism can work together with students from all over the world to address a new pandemic.

Galectin-1 is required for the regulatory function of B cells

Galectin-1 (Gal-1) is required for the development of B cells in the bone marrow (BM), however very little is known about the contribution of Gal-1 to the development of B cell regulatory function. Here, we report an important role for Gal-1 in the induction of B cells regulatory function. Mice deficient of Gal-1 (Gal-1^−/−) showed significant loss of Transitional-2 (T2) B cells, previously reported to include IL-10⁺ regulatory B cells. Gal-1^−/− B cells stimulated in vitro via CD40 molecules have impaired IL-10 and Tim-1 expression, the latter reported to be required for IL-10 production in regulatory B cells, and increased TNF-α expression compared to wild type (WT) B cells. Unlike their WT counterparts, T2 and T1 Gal-1^−/− B cells did not suppress TNF-α expression by CD4⁺ T cells activated in vitro with allogenic DCs (allo-DCs), nor were they suppressive in vivo, being unable to delay MHC-class I mismatched skin allograft rejection following adoptive transfer. Moreover, T cells stimulated with allo-DCs show an increase in their survival when co-cultured with Gal-1^−/− T2 and MZ B cells compared to WT T2 and MZ B cells. Collectively, these data suggest that Gal-1 contributes to the induction of B cells regulatory function.

Constitutive expression of the anti-apoptotic Bcl-2 family member A1 in murine endothelial cells leads to transplant tolerance

Anti-apoptotic genes, including those of the Bcl-2 family, have been shown to have dual functionality inasmuch as they inhibit cell death but also regulate inflammation. Several anti-apoptotic molecules have been associated with endothelial cell (EC) survival following transplantation; however, their exact role has yet to be elucidated in respect to controlling inflammation. In this study we created mice expressing murine A1 (Bfl-1), a Bcl-2 family member, under the control of the human intercellular adhesion molecule 2 (ICAM-2) promoter. Constitutive expression of A1 in murine vascular ECs conferred protection from cell death induced by the proinflammatory cytokine tumour necrosis factor (TNF)-α. Importantly, in a mouse model of heart allograft transplantation, expression of A1 in vascular endothelium increased survival in the absence of CD8⁺ T cells. Better graft outcome in mice receiving an A1 transgenic heart correlated with a reduced immune infiltration, which may be related to increased EC survival and reduced expression of adhesion molecules on ECs. In conclusion, constitutive expression of the anti-apoptotic molecule Bfl1 (A1) in murine vascular ECs leads to prolonged allograft survival due to modifying inflammation.

Humanized Mice as Preclinical Models in Transplantation

Animal models have been instrumental in our understanding of the mechanisms of rejection and the testing of novel treatment options in the context of transplantation. We have now entered an exciting era with research on humanized mice driving advances in translational studies and in our understanding of the function of human cells in response to pathogens and cancer as well as the recognition of human allogeneic tissues in vivo. In this chapter we provide a historical overview of humanized mouse models of transplantation to date, outlining the distinct strains and share our experiences in the study of human transplantation immunology.

Promoting transplantation tolerance; adoptive regulatory T cell therapy

Transplantation is a successful treatment for end-stage organ failure. Despite improvements in short-term outcome, long-term survival remains suboptimal because of the morbidity and mortality associated with long-term use of immunosuppression. There is, therefore, a pressing need to devise protocols that induce tolerance in order to minimize or completely withdraw immunosuppression in transplant recipients. In this review we will discuss how regulatory T cells (T(regs)) came to be recognized as an attractive way to promote transplantation tolerance. We will summarize the preclinical data, supporting the importance of these cells in the induction and maintenance of immune tolerance and that provide the rationale for the isolation and expansion of these cells for cellular therapy. We will also describe the data from the first clinical trials, using T(regs) to inhibit graft-versus-host disease (GVHD) after haematopoietic stem cell transplantation and will address both the challenges and opportunities in human T(reg) cell therapy.

The potency of allospecific Tregs cells appears to correlate with T cell receptor functional avidity

CD4(+) CD25(+) regulatory T cells (T(reg) cells) are an attractive adoptive cell therapy in mediating transplantation tolerance. T-cell receptor (TcR) activation is critical for T(reg) function, suggesting that the TcR avidity of T(reg) cells used in therapy may affect the therapeutic outcome. To address this, we compared the regulatory capacity of T(reg) lines expressing TcRs derived from two TcR transgenic mice shown to have the same specificity but different functional avidities. T(reg) lines generated from CD4(+)CD25(+) T cells from C57BL/6 mice were transduced with one of either of these TcRs. The antigen specificity of the transduced T(reg) lines was confirmed in vitro. T(reg) lines expressing the TcR with higher functional avidity showed stronger suppressive capacity in a linked suppression model in vitro. Furthermore, the same T(reg) lines demonstrated a stronger proliferation in vivo following antigen exposure. Pretreatment of recipient BL/6 mice with these T(reg) cells, together with anti-CD8 antibody and Rapamycin therapies, prolonged survival of BALB/c skins, as compared with mice that received T(reg) lines with lower TcR avidity. Taken together, these data suggest that the TcR functional avidity may be important for T(reg) function. It highlights the fact that strategies to select T(reg) with higher functional avidity might be beneficial for immunotherapy in transplantation.

Increased frequencies of CD4(+)CD25(high) T(regs) correlate with disease relapse after allogeneic stem cell transplantation for chronic myeloid leukemia

The therapeutic efficacy of allogeneic hemopoietic stem cell transplantation (SCT) for chronic myeloid leukemia (CML) largely relies on the graft-versus-leukemia (GvL) effect exerted by donor T cells. CD4(+)CD25(high) regulatory T cells (T(regs)) have been shown to downregulate antitumor responses but their role on GvL has not been evaluated. We performed a cross-sectional study in which we enumerated and characterized CD4(+)CD25(high) T(regs) in the peripheral blood of CML patients undergoing allogeneic SCT. We documented higher frequencies of T(regs) in patients after transplant as compared to normal controls and newly diagnosed patients. The increment was particularly evident in patients who had received their SCT 18 months before. In vitro functional studies demonstrated that the T(regs) purified from SCT patients exhibited a more potent suppressive activity than T(regs) isolated from healthy volunteers. Patients in whom T(regs) numbers were higher than controls more than 18 months after SCT showed evidence of disease relapse. Although the increment in T(regs) might have an advantageous effect on graft rejection in the early phase post-transplant, our data suggest that T(regs) exert an inhibitory effect on GvL.

Aspirin-treated human DCs up-regulate ILT-3 and induce hyporesponsiveness and regulatory activity in responder T cells

Mature dendritic cells (mDCs) are potent antigen presenting cells, but immature DCs (iDCs) have been shown to have reduced antigen stimulatory capacity. Different strategies have been investigated to augment the tolerogenic capacity of dendritic cells (DCs). We demonstrate that in aspirin-treated human DCs, there is reduced expression of CD1a, HLA-DR and CD86, up-regulation of ILT-3 expression and marginal increases in PDL-1. Aspirin-treated DCs are partially resistant to phenotypic changes following maturational stimuli, such as lipopolysaccharide (LPS) or TNFalpha, IL-1alpha and PGE2. Aspirin-treated DCs demonstrate normal endocytic function, but have a reduced ability to stimulate allogeneic T cells, which is comparable to iDCs. Furthermore, they induce hyporesponsiveness and regulatory activity in responder naïve and memory T cells; for naïve T cells this is achieved more quickly and efficiently than with iDCs. We investigated the mechanism of this regulatory activity and found that both cell-cell contact and inhibitory cytokine activity are involved, although no one cytokine predominates in importance. Blocking ILT-3 or IL-12 does not diminish the capacity of these DCs to induce regulation or Foxp3 expression on the regulatory T cells. Results demonstrate that aspirin-treated DCs display tolerogenic potential, which is of interest in their therapeutic potential in reducing chronic allograft rejection.

Location of major histocompatibility complex class II molecules in rafts on dendritic cells enhances the efficiency of T-cell activation and proliferation

The existence of major histocompatibility complex (MHC) class II molecules in lipid rafts has been described in dendritic cells (DC); however, the importance of rafts in T-cell activation has not been clarified. In this study, the distribution of the lipid raft components (CD59 and GM1 ganglioside) in human monocyte-derived DC was investigated. DC had an even distribution of these components at the cell surface. In addition, raft-associated GM1 ganglioside colocalized with cross-linked MHC class II. This implies coaggregation of raft components with these MHC molecules, which may be important in the interaction between T cells and antigen-presenting cells. In studies carried out to investigate the effect of the DC : T-cell interaction on raft distribution, we found a clustering of the lipid raft component CD59 on DC at the synaptic interface, with associated activation of the interacting T cell. In an antigen-specific response between DC and CD4+ T-cell clones, disruption of lipid rafts resulted in inhibition of both CD59 clustering and T-cell activation. This was most pronounced when limiting amounts of cognate peptide were used. Together, these data demonstrate the association of MHC class II with lipid rafts during DC : T-cell interaction and suggest an important role for DC lipid rafts in T-cell activation.

A randomized, double-blind trial of basiliximab immunoprophylaxis plus triple therapy in kidney transplant recipients

BACKGROUND

A double-blind, placebo-controlled, randomized study was performed to assess whether immunoprophylaxis with basiliximab (Simulect) could reduce the incidence of acute rejection in kidney transplant recipients treated with cyclosporine (Neoral), steroids, and azathioprine.

METHODS

Three hundred forty patients received either placebo or basiliximab at a dose of 20 mg, given intravenously on days 0 and 4. All patients received cyclosporine, steroids, and azathioprine. The primary endpoint was the incidence of acute rejection at 6 months. Secondary endpoints included the safety and tolerability of basiliximab and placebo, 1-year patient and graft survival, and significant medical events up to 12 months.

RESULTS

During the first 6 months posttransplantation, acute rejection occurred in 20.8% of patients given basiliximab versus 34.9% of patients administered placebo (P=0.005). Similarly, there was a reduction in biopsy-proven acute rejection at 6 months in the patients receiving basiliximab (P=0.023). One-year patient survival was 97.6% with basiliximab and 97.1% with placebo, graft survival was 91.5% versus 88.4%, respectively (NS). The adverse-events profile of patients treated with basiliximab was indistinguishable from that of patients treated with placebo. The number of patients with infections was similar (65.5% for basiliximab vs. 65.7% for placebo), including cytomegalovirus infections (17.3% vs. 14.5%, P=0.245). Nine neoplasms (three in the basiliximab group, six in the placebo arm) were recorded up to 1 year from transplantation.

CONCLUSIONS

Basiliximab in combination with cyclosporine, steroids, and azathioprine triple therapy was highly effective in reducing the incidence of acute renal allograft rejection without increasing the incidence of infections and other side effects.

T-cell anergy and peripheral T-cell tolerance

The discovery that T-cell recognition of antigen can have distinct outcomes has advanced understanding of peripheral T-cell tolerance, and opened up new possibilities in immunotherapy. Anergy is one such outcome, and results from partial T-cell activation. This can arise either due to subtle alteration of the antigen, leading to a lower-affinity cognate interaction, or due to a lack of adequate co-stimulation. The signalling defects in anergic T cells are partially defined, and suggest that T-cell receptor (TCR) proximal, as well as downstream defects negatively regulate the anergic T cell's ability to be activated. Most importantly, the use of TCR-transgenic mice has provided compelling evidence that anergy is an in vivo phenomenon, and not merely an in vitro artefact. These findings raise the question as to whether anergic T cells have any biological function. Studies in rodents and in man suggest that anergic T cells acquire regulatory properties; the regulatory effects of anergic T cells require cell to cell contact, and appear to be mediated by inhibition of antigen-presenting cell immunogenicity. Close similarities exist between anergic T cells, and the recently defined CD4+ CD25+ population of spontaneously arising regulatory cells that serve to inhibit autoimmunity in mice. Taken together, these findings suggest that a spectrum of regulatory T cells exists. At one end of the spectrum are cells, such as anergic and CD4+ CD25+ T cells, which regulate via cell-to-cell contact. At the other end of the spectrum are cells which secrete antiinflammatory cytokines such as interleukin 10 and transforming growth factor-beta. The challenge is to devise strategies that reliably induce T-cell anergy in vivo, as a means of inhibiting immunity to allo- and autoantigens.

Beryllium binding to HLA-DP molecule carrying the marker of susceptibility to berylliosis glutamate beta 69

Berylliosis is a chronic granulomatous disorder caused by inhalation of Be dusts that is driven by the accumulation of Be-specific CD4+ Th1-cells at disease sites. Susceptibility to berylliosis has been associated with the supratypic variant of HLA-DP gene coding for glutamate at position beta69 (HLA-DPbetaGlu69). The aim of this study was to test the hypothesis that the HLA-DPbetaGlu69 residue plays a role in the interaction with Be. To this end, soluble HLA-DP2 molecule (carrying betaGlu69) and its mutated form carrying lysine at position beta69 (HLA-DP2Lys69) were produced in Drosophila melanogaster and then used in a Be binding assays. BeSO4 (1-1000 microM) was used to compete for the binding of the biotinilated invariant chain-derived peptide CLIP (50 microM). BeSO4 was capable of compete out biotin-CLIP binding from the HLA-DP2 (IC50%: 4.5 microM of BeSO4 at pH 5.0 and 5.5 microM of BeSO4 at pH 7.5), but not from the HLA-DP2Lys69 molecule (IC50%: 480 microM of BeSO4 at pH 5.0 and 220 microM of BeSO4 at pH 7.5). Moreover, the binding of NFLD.M60, a MoAb recognizing an epitope in the HLA-DP peptide binding region, to the HLA-DP2, but not to the HLA-DP2Lys69 soluble molecules was inhibited BeSO4. NFLD.M60 binding to HLA-DP2, but not to HLA-DP2Lys69 stably transfected murine cells was also inhibited by Be both at pH 5.0 and at pH 7.5. The data indicate a direct interaction of Be with the HLA-DPGlu69 molecule, in the absence of antigen processing.

HLA-DP allele-specific T cell responses to beryllium account for DP-associated susceptibility to chronic beryllium disease

Occupational exposure to small molecules, such as metals, is frequently associated with hypersensitivity reactions. Chronic beryllium (Be) disease (CBD) is a multisystem granulomatous disease that primarily affects the lung, and occurs in approximately 3% of individuals exposed to this element. Immunogenetic studies have demonstrated a strong association between CBD and possession of alleles of HLA-DP containing glutamic acid (Glu) at position 69 in the HLA-DP beta-chain. T cell clones were raised from three patients with CBD in whom exposure occurred 10 and 30 years previously. Of 25 Be-specific clones that were obtained, all were restricted by HLA-DP alleles with Glu at DP beta69. Furthermore, the proliferative responses of the clones were absolutely dependent upon DP beta Glu(69) in that a single amino acid substitution at this position abolished the response. As befits a disease whose pathogenesis involves a delayed type hypersensitivity response, the large majority of Be-specific clones secreted IFN-gamma (Th1) and little or no IL-4 (Th2) cytokines. This study provides insights into the molecular basis of DP2-associated susceptibility to CBD.

Amino acid substitutions in the putative MHC class II "dimer of dimers" interface inhibit CD4+ T cell activation

Activation of T lymphocytes is dependent on multiple ligand-receptor interactions. The possibility that TCR dimerization contributes to T cell triggering was raised by the crystallographic analysis of MHC class II molecules. The MHC class II molecules associated as double dimers, and in such a way that two TCR (and two CD4 molecules) could bind simultaneously. Several subsequent studies have lent support to this concept, although the role of TCR cross-linking in T cell activation remains unclear. Using DRA cDNAs modified to encode two different C-terminal tags, no evidence of constitutive double dimer formation was obtained following immunoprecipitation and Western blotting from cells transiently transfected with wild-type DRB and tagged DRA constructs, together with invariant chain and HLA-DM. To determine whether MHC class II molecules contribute actively to TCR-dependent dimerization and consequent T cell activation, panels of HLA-DR1beta and H2-E(k) cDNAs were generated with mutations in the sequences encoding the interface regions of the MHC class II double dimer. Stable DAP.3 transfectants expressing these cDNAs were generated and characterized biochemically and functionally. Substitutions in either interface region I or III did not affect T cell activation, whereas combinations of amino acid substitutions in both regions led to substantial inhibition of proliferation or IL-2 secretion by human and murine T cells. Because the amino acid-substituted molecules were serologically indistinguishable from wild type, bound antigenic peptide with equal efficiency, and induced Ag-dependent CD25 expression indicating TCR recognition, the reduced ability of the mutants to induce full T cell activation is most likely the result of impaired double dimer formation. These data suggest that MHC class II molecules, due to their structural properties, actively contribute to TCR cross-linking.

[Alloreactive helper T cell responses in kidney transplant patients]

OBJECTIVE

To study allo-specific immune responses of CD4+ helper T lymphocytes (Th) in patients with long-term and well-functioning renal grafts.

METHODS

Peripheral blood mononuclear cells (PBMC) were collected from 16 patients with long-term (3-15 years) and well-functioning live-related renal grafts. Donor-specific Th precursor (Th-p) frequencies in the PBMC were determined by limiting dilution analysis(LDA).

RESULTS

Eight out of the 16 patients showed donor-specific hyporesponsiveness. Donor-specific Th-p from the other 8 patients was susceptible to anti-CD4 inhibition.

CONCLUSION

Some of the patients carrying long-term and well-functioning renal grafts had become immunologic tolerant to donor cells. Donor-specific Th-p from patients who did not show donor-specific hyporesponsiveness were of low avidity type.

CD152 ligation by CD80 on T cells is required for the induction of unresponsiveness by costimulation-deficient antigen presentation

Two apparently contradictory observations have been made concerning peripheral T cell tolerance; costimulation-deficient Ag presentation leads to unresponsiveness, and CTLA4 (CD152) ligation is required for unresponsiveness to be induced. This issue was addressed using a CD80- CD86low B cell line to present Ag to DO.11.10 naive CD4+ T cells. Proliferation was substantially enhanced by anti-CD80 or anti-CD152, but was inhibited by anti-CD86. Furthermore, anti-CD80 partially, and anti-CD152 totally protected cloned DO.11.10 T cells from the induction of unresponsiveness following culture with peptide and Chinese hamster ovary H2-Ad+ CD80- CD86- cells. Fab of anti-CD80 caused similar enhancement, and coimmobilized anti-CD80 failed to costimulate the anti-CD3 response of purified T cells, indicating that direct signaling by anti-CD80 was not responsible for these effects. The possibility that anti-CD80 liberated CD28 molecules that were sequestered by the T cell-expressed CD80, enabling them to coaggregate with TCR:CD3 complexes was excluded by finding that anti-CD80 and anti-CD152 individually caused maximal enhancement, rather than having additive effects. These data suggest that T cell-expressed CD80 has a regulatory function and plays a key role in the induction of unresponsiveness due to costimulation-deficient Ag presentation by the ligation of CD152 on neighboring, or even the same, T cell.

Anergic T cells inhibit the antigen-presenting function of dendritic cells

The phenomena of infectious tolerance and linked-suppression are well established, but the mechanisms involved are incompletely defined. Anergic T cells can inhibit responsive T cells in vitro and prolong skin allograft survival in vivo. In this study the mechanisms underlying these events were explored. Allospecific mouse T cell clones rendered unresponsive in vitro inhibited proliferation by responsive T cells specific for the same alloantigens. The inhibition required the presence of APC, in that the response to coimmobilized anti-CD3 and anti-CD28 Abs was not inhibited. Coculture of anergic T cells with bone marrow-derived dendritic cells (DC) led to profound inhibition of the ability of the DC to stimulate T cells with the same or a different specificity. After coculture with anergic T cells expression of MHC class II, CD80 and CD86 by DC were down-regulated. These effects did not appear to be due to a soluble factor in that inhibition was not seen in Transwell experiments, and was not reversed by addition of neutralizing anti-IL-4, anti-IL-10, and anti-TGF-beta Abs. Taken together, these data suggest that anergic T cells function as suppressor cells by inhibiting Ag presentation by DC via a cell contact-dependent mechanism.

Critical role of costimulation in the activation of naive antigen-specific TCR transgenic CD8+ T cells in vitro

The influence of costimulation on the activation of naive CD8+ T cells and thymocytes was studied in vitro using H-Y-specific TCR-transgenic mice and H-Y antigenic peptide. Using a variety of physiological APC types, the activation of naive CD8+ T cells depended strictly on costimulation, which could not be substituted by high epitope density. T cell activation is known to be regulated by the interactions between CD86/CD80 and CD28/CD152, although it remains unclear whether the B7 isoforms have distinct roles. Addition of soluble anti-CD86 Ab led to profound inhibition of T cell reactivity, further confirming the importance of costimulation in naive CD8+ T cell activation. Finally, TCR engagement in the absence of costimulation had no effect on the subsequent reactivity of peripheral naive transgenic CD8+ T cells, but induced nonresponsiveness in mature CD8+ transgenic thymocytes. Collectively, these results demonstrate the importance of costimulation for naive CD8+ T cell activation, suggest that CD80 and CD86 can mediate opposing effects, possibly due to differential interaction with CD152 and CD28, and indicate differences in the sensitivity of immature vs mature CD8+ T cells to the induction of nonresponsiveness following costimulation-deficient Ag presentation.

Anergic T cells act as suppressor cells in vitro and in vivo

The potential suppressive effects of allospecific anergic T cells were investigated both in vitro and in vivo. Allospecific T cells were rendered unresponsive in vitro using immobilized anti-CD3 mAb. These anergic T cells profoundly inhibited proliferation of responsive T cells in an antigen-specific manner. The observed inhibition did not appear to be due to the release of inhibitory cytokines in that secretion of IL-2, IFN-gamma, IL-4, IL-10 and TGF-beta was greatly reduced following the induction of anergy, and neutralizing mAb specific for IL-4, IL-10 and TGF-beta failed to reverse the inhibition. Furthermore, the suppression mediated by anergic T cells required cell to cell contact. In vivo, adoptive transfer of anergic T cells into recipients of allogeneic skin grafts led to prolonged skin graft survival. Consistent with the lack of inhibitory cytokine production by the anergic cells, prolongation of skin allograft rejection was not influenced by the simultaneous administration of a neutralizing anti-IL-4 antibody. These results indicate that anergic T cells can function as antigen-specific suppressor cells both in vitro and in vivo.

T:T antigen presentation by activated murine CD8+ T cells induces anergy and apoptosis

Using an IL-2-secreting, noncytolytic, H-Y-specific, CD8+ T cell clone, the functional consequences of Ag presentation by T cells to T cells were investigated. Incubation of the T cells with H-Y-soluble peptide led to nonresponsiveness to Ag rechallenge. This was due to the simultaneous induction of apoptosis, involving approximately 40% of the T cells, and of anergy in the surviving cells. These effects were strictly dependent upon bidirectional T:T presentation, in that exposure of C6 cells to peptide-pulsed T cells from the same clone induced proliferation but not apoptosis or anergy. The inhibitory effects of T:T presentation were not due to a lack of costimulation, since the T cells expressed levels of CD80 and CD86 higher than those detected on cultured dendritic cells and equipped them to function as efficient APCs for primary CD8+ T cell responses. Following incubation with soluble peptide, CD80 expression increased, and high levels of CTLA-4 (CD152) expression were induced. Although addition of anti-CTLA-4 Ab augmented proliferation in response to soluble peptide, no protection from apoptosis or anergy was observed. Neither Fas nor TNF-alpha was expressed/produced by the C6 cells, and coligation of MHC class I molecules and TCR failed to reproduce the effects of T:T presentation. Taken together, these data suggest that T:T Ag presentation induces anergy and apoptosis in murine CD8+ T cells and may reflect the regulatory consequences of T:T interactions in the course of clonal expansion in vivo.

Detection of CD40 on human thyroid follicular cells: analysis of expression and function

Thyroid follicular cells (TFC) are a common target of autoimmune attack, but the role they play in inciting and maintaining this attack is unclear. TFC express cytokines, adhesion molecules, and class I and II major histocompatibility complex molecules, but without additional signals that costimulate T cells, they may down-regulate, rather than stimulate, T cell function. In this report, we have investigated whether TFC can express the CD40 molecule, which plays a crucial role in the reciprocal two-way communication between T and B cells. We have shown by immunohistochemistry and flow cytometry that CD40 is expressed by TFC in vivo and in vitro in both autoimmune and nonautoimmune glands. CD40 expression was up-regulated by interleukin-1alpha and interferon-gamma, but not by TSH. Although there was no significant effect of CD40 ligation on cAMP synthesis or [3H]thymidine incorporation, there was a significant increase in interleukin-6 release by TFC. Thus, although TFC do not express members of the B7 family of T cell costimulators, they do express CD40, indicating the possibility of mutually stimulatory T cell-TFC interaction. This has important implications, both for TFC synthesis of immunological mediators and for the biasing of T cell behavior toward a T helper 2-type phenotype.

Interferon-gamma-treated renal tubular epithelial cells induce allospecific tolerance

Following organ transplantation, tissue parenchymal cells commonly express major histocompatibility complex (MHC) class II molecules as a result of local cytokine release, and thus acquire the capacity to present donor MHC alloantigens to alloreactive CD4+ T cells. The consequences of such a presentation are likely to be relevant in the induction of tolerance to the transplanted tissues, and this has been reported in animal models of transplantation and in humans. In this study, the consequences of antigen presentation by interferon-gamma (IFN-gamma)-treated human renal tubular epithelial cells (RTEC) to resting and activated CD4+ T cells were investigated. Allogeneic RTEC were unable to stimulate proliferation by peripheral blood CD45 RA+ or RO+ CD4+ T cells from three HLA-mismatched responders. The response to RTEC was partially reconstituted by the addition of murine L cell transfectants expressing human B7.1 (DAP.3-B7), suggesting that the failure of RTEC to stimulate a primary alloresponse was due, at least in part, to a lack of costimulation. T cell clones dependent on B7-mediated co-stimulation also did not respond to peptide presented by RTEC. Most importantly, this lack of reactivity was accompanied by the induction of nonresponsiveness. Incubation with allogeneic, DR-expressing RTEC induced allospecific hyporesponsiveness in both CD45RA+ and RO+ cells. Similarly, overnight incubation with antigen-pulsed RTEC induced nonresponsiveness in the B7-dependent T cell clones. These results suggest that MHC class II expression on RTEC may contribute to the induction of an allospecific nonresponsiveness following organ transplantation.

Mechanisms of peripheral T-cell tolerance

It is becoming increasingly clear that the control of self-reactivity involves peripheral mechanisms that supplement thymic negative selection. It is now generally accepted that T-cell activation depends upon both T-cell receptor engagement and the delivery of B7-mediated costimulation by specialized antigen presenting cells (APC). In contrast, failure to deliver B7-mediated costimulation can result in the induction of antigen-specific non-responsiveness. In physiological terms, costimulation-deficient antigen presentation is the prerogative of those cells that do not express B7 molecules, even during inflammatory conditions, such as tissue parenchymal cells. The consequences of such costimulation-deficient antigen presentation are illustrated by the allospecific tolerance that is observed in animal models of transplantation following the depletion of bone marrow-derived APC from an allograft. In this paper the possible role of antigen presentation by tissue parenchymal cells in the induction and maintenance of peripheral tolerance is discussed, with particular attention to the important contribution that the liver may make to these events.

Anergic T cells effect linked suppression

Although the phenomenon of T cell-mediated suppression is well established, particularly in experimental models of transplantation, the mechanisms involved in this form of immunoregulation remain controversial. We have recently demonstrated, using an in vitro system, that anergic T cells can act as suppressor cells by competing for the membrane of the antigen-presenting cell (APC) and for locally produced interleukin-2. In the experiments described here we have explored the ability of anergic T cells to effect linked suppression in antigen-specific and allospecific responses. We observed that anergic antigen-specific CD4+ T cells can inhibit T cells restricted by a different major histocompatibility complex (MHC) class II molecule provided that both restriction elements are expressed by the same APC. In addition, anergic allospecific clones could also effect linked suppression since they could regulate not only T cells specific for the same alloantigen but also responder T cells with direct allospecificity for a second allogeneic MHC molecule or with indirect, self MHC-restricted allospecificity for a processed MHC class I alloantigen. Furthermore, the regulatory effect of the anergic T cells was dependent on cell contact, was not dependent upon irradiation, and was maintained during in vitro culture. These data demonstrate that linked suppression can be effected by anergic T cells in vitro. In the clinical context this raises the possibility that induction of tolerance to a single alloantigen could serve to regulate the immune response to an allograft carrying several MHC and minor antigen differences.

Measurement of cytotoxic T lymphocyte precursor frequencies reveals cryptic HLA class I mismatches in the context of unrelated donor bone marrow transplantation

BACKGROUND

In this large, two-center study, 260 cytotoxic T lymphocyte precursor (CTLp) frequency assays, performed to assess patient-donor compatibility, were analyzed in relation to the degree of HLA matching.

METHODS

While the tissue-typing techniques used at the Royal Postgraduate Medical School (RPMS) and Anthony Nolan Bone Marrow Trust (ANBMT) differ, the results of the analyses on the two sites are analogous, with high CTLp frequencies (>1:100,000) in 42% and 41% of recipient-donor pairs, respectively.

RESULTS

Recipient-donor combinations with class I mismatches and class II identity were associated with high CTLp frequencies (collectively 83% vs. 17% low CTLp). This correlation was not as strong in pairs where class II mismatches were demonstrated (61% high vs. 39% low). Despite using different matching procedures, the RPMS and ANBMT both show that 32% of the "perfectly" matched pairs (i.e., where no mismatch was detected by any of the techniques used here) had high frequencies of recipient-specific CTLp.

CONCLUSIONS

The failure of conventional methods to identify such a level of histoincompatibilities indicates that the CTLp assay has an important role in the selection of unrelated donors for bone marrow transplantation.

In the absence of the invariant chain, HLA-DR molecules display a distinct array of peptides which is influenced by the presence or absence of HLA-DM

The independent influences of invariant chain (Ii) and HLA-DM molecules on the array of naturally processed peptides displayed by HLA-DR molecules were studied using transfected cell lines. The absence of Ii led to an altered set of HLA-DR-bound peptides as judged by the discriminating responses of alloreactive T cell clones. While most T cell clones raised against DR+Ii+DM+ peripheral blood mononuclear cells (PBMC) failed to respond to DR+Ii-DM- cells, T cell clones raised against DR+Ii-DM- transfectants were not stimulated by DR+Ii+DM+ cells. Furthermore, coexpression of HLA-DM with HLA-DR1 in the absence of Ii augmented responses of anti-PBMC T cell clones but inhibited allorecognition by T cell clones raised against DR+Ii-DM- transfectants. The conformational integrity of the class II molecules, as judged by serology, suggests that the patterns of reactivity of the T cell clones reflect specificity for different alloantigen-bound peptides. Hence, discordant regulation of expression of major histocompatibility complex class II, Ii, and HLA-DM molecules in vivo may lead to the display of novel self-peptides and possible interruption of self-tolerance.

Allele-specific variation in the degeneracy of major histocompatibility complex (MHC) restriction

The role of peptides in determining immune responses for both allorecognition and antigen-specific recognition has been clearly documented. The importance of different regions of the major histocompatibility complex (MHC) class II molecule in contributing to recognition has been demonstrated by studies involving site-directed mutagenesis and exon shuffling. These studies have indicated that the N-terminal region of the MHC class II molecule has a role to play in contributing to the T-cell receptor (TCR)-MHC-peptide interaction. Variation in the importance of different regions of the MHC class II molecule may be dependent on different aspects of this interaction, such as restriction specificity and affinity of the responding T-cell clone, and the nature of the bound peptide. We demonstrate here that the degree of T-cell degeneracy may be allele dependent. Thus, a series of exon-shuffled molecules were generated by shuffling the first and second variable region of a particular DR beta 1 molecule with the third variable region of a different DR beta 1 molecule. A panel of transfectants, which expressed these hybrid molecules, was then generated and used as antigen-presenting cells (APCs). A panel of peptide-specific T-cell clones was generated using the native HLA-DR molecules as the restricting elements. For the majority of restricting alleles, HLA-DRB5*0101, HLA-DRB1*1101, and HLA-DRB1*0701, all three variable regions were required for recognition. The exception to this observation was HLA-DRB1*0401, which was degenerate. Such degeneracy may facilitate the breakdown of self-tolerance through the cross-reactive recognition of other alleles in DR4/DR"x" heterozygotes. Such an observation as this may contribute to our understanding of the etiopathology of rheumatoid arthritis, an autoimmune disease strongly associated with HLA-DRB1*0401.

Clinical xenotransplantation of solid organs

A possible solution to the chronic shortage of allografts is xenotransplantation, the use of tissue from an animal donor. Most experts believe that the pig will provide the most suitable solid organs for use in human beings. Although porcine organs are rapidly rejected by a process called hyperacute rejection (HAR), there is hope that several novel therapeutic strategies, already tested in animal models, will overcome this hurdle in patients. Successful clinical trials of these strategies, expected within the next few years, may herald the era of clinical xenotransplantation. However, there is increasing evidence that other barriers, both immune and non-immune, might exist to limit the survival of xenografts beyond the HAR phase. New strategies to overcome these barriers will be needed if long-term xenograft survival equivalent to, or better than, that of allografts is ever to be achieved.

Antigen presentation by interferon-gamma-treated thyroid follicular cells inhibits interleukin-2 (IL-2) and supports IL-4 production by B7-dependent human T cells

The consequence of recognition of antigen on antigen-presenting cells that are induced to express major histocompatibility complex (MHC) class II molecules following an inflammatory process is still not clear. In this study, we have investigated the outcome of antigen presentation by epithelial cells and we have used as a model thyroid follicular cells (TFC) that are known to express MHC class II molecules in autoimmune thyroid diseases and acquire the capacity to present autoantigens to T cells infiltrating the thyroid gland. The result show that MHC class II-expressing TFC were unable to stimulate a primary T cell alloresponse, using CD4+ T cells from three HLA-mismatched responders. Phenotypic analysis showed that TFC, after incubation with interferon-gamma, do not express the costimulatory molecules B7-1 (CD80) and -2 (CD86). Addition of murine DAP.3 cells expressing human B7-1 (DAP.3-B7) to cultures containing peripheral blood CD4+ T cells and DR1-expressing TFC led to a proliferative response, suggesting that the failure of TFC to stimulate a primary alloresponse was due to a lack of co-stimulation. Similarly, HLA-DR-restricted, influenza-specific T cell clones dependent on B7 for co-stimulation did not respond to peptide presented by TFC; again the lack of response could be overcome by co-culture of TFC with DAP.3-B7. Furthermore, recognition of antigen on TFC inhibited interleukin-2 (IL-2) production in the B7-dependent T cells. In contrast, in T helper type 0 (Th0) T cells, IL-4 release was not affected by TFC presentation. In addition, antigen presentation by TFC favored IL-4 production relative to IL-2 production by B7-independent Th0 clones. These results suggest that antigen presentation by MHC class II+ TFC may induce tolerance in autoreactive Th1 cells but may simultaneously favors a Th2 response in uncommitted T cells, and thereby support autoantibody production.

The TAP complex influences allorecognition of class II MHC molecules

The influence of the TAP complex on T-cell allorecognition of MHC class II molecules was examined using human B-cell lines that have mutations in the TAP 1 or 2 genes. The TAP mutations led to the loss of allorecognition for two of 28 anti- HLA-DR T-cell clones. Restoration of TAP expression by transfection of a TAP 2 cDNA clone led to recovery of the alloresponse for both clones. These results could be explained in two ways. First, TAP dependence could reflect specificity for a peptide derived from an MHC class I molecule that is less efficiently generated by the endocytic pathway in the TAP-deficient stimulator cells owing to reduction in surface class I expression. The proliferative responses of these clones to the TAP-deficient stimulator cells was not restored by rescue of cell-surface expression of class I molecules by low temperature culture or by the addition of class I-binding peptides. These data therefore favor the alternative explanation that class II loading by some peptides is TAP dependent. Circumstances that lead to the amplification of this minority pathway of endogenous presentation by class II MHC molecules may have the potential to interrupt self-tolerance.

Antigen presentation by T cells inhibits IL-2 production and induces IL-4 release due to altered cognate signals

Conflicting results of the effects of Ag presentation by MHC class II-expressing T cells have been described. In some studies class II-expressing T cells have been shown to act as effective APCs, while others have reported that the recognition of Ag on the surface of another T cell inactivates IL-2 production. In this study we have investigated the mechanisms involved in Ag presentation by T cells. The results obtained suggest that 1) lack of costimulation is not responsible for the inhibitory effects of T cell Ag presentation on IL-2 production; the provision of costimulation by immobilized anti-CD28 Ab or by the addition of accessory cells failed to reverse the effects of T cell Ag presentation, but restored the response to immobilized anti-CD3; 2) T cell Ag presentation induced a minimal increase in intracellular Ca2+ compared with that induced by antigen-pulsed B cells; this difference in the calcium response is not explained by quantitative differences in ligand density between B cells and T cells; and 3) despite the weak calcium signal, T cell presentation supported IL-4 release in the absence of IL-2 production. Taken together these data suggest that T cell Ag presentation leads to altered TCR/CD3-transduced signals, which biases the T cell towards a Th2 phenotype.

Antigen presentation by T cells inhibits IL-2 production and induces IL-4 release due to altered cognate signals

Conflicting results of the effects of Ag presentation by MHC class II-expressing T cells have been described. In some studies class II-expressing T cells have been shown to act as effective APCs, while others have reported that the recognition of Ag on the surface of another T cell inactivates IL-2 production. In this study we have investigated the mechanisms involved in Ag presentation by T cells. The results obtained suggest that 1) lack of costimulation is not responsible for the inhibitory effects of T cell Ag presentation on IL-2 production; the provision of costimulation by immobilized anti-CD28 Ab or by the addition of accessory cells failed to reverse the effects of T cell Ag presentation, but restored the response to immobilized anti-CD3; 2) T cell Ag presentation induced a minimal increase in intracellular Ca2+ compared with that induced by antigen-pulsed B cells; this difference in the calcium response is not explained by quantitative differences in ligand density between B cells and T cells; and 3) despite the weak calcium signal, T cell presentation supported IL-4 release in the absence of IL-2 production. Taken together these data suggest that T cell Ag presentation leads to altered TCR/CD3-transduced signals, which biases the T cell towards a Th2 phenotype.

Ligation of either CD2 or CD28 rescues CD4+ T cells from HIV-gp120-induced apoptosis

Temporal or quantitative imbalance in signals delivered to T cells via T cell antigen receptor (TCR), the CD4 co-receptor, and accessory molecules can lead to anergy, apoptosis, or both. This has been observed following ligation of CD4 by HIV gp120 prior to TCR occupancy. The ability of molecules such as CD2 and CD28, interacting with their ligands LFA-3 and B7, to provide signals that protect T cells from the induction of anergy, has been reported. Here, we demonstrate that ligation of CD2 and CD28 in conjunction with TCR occupancy rescue T cells that have been programmed for apoptotic death by prior CD4 ligation to gp120. This appears to be the result of augmented interleukin-2 and interleukin-4 release by the T cells following these molecular interactions. In conclusion, our results suggest that an impairment of antigen-presenting accessory cell functions could favor gp120-mediated apoptosis in HIV-uninfected cells.

The primary alloresponse of human CD4+ T cells is dependent on B7 (CD80), augmented by CD58, but relatively uninfluenced by CD54 expression

Conflicting data have been reported regarding the relative abilities of B7, ICAM-1 and LFA-3 to provide co-stimulation for the induction of a primary T cell alloproliferative response. A series of naturally HLA-DR-expressing cell lines and panels of human and murine transfectants expressing DR alloantigens in conjunction with combinations of mouse or human B7.1, human LFA-3 and human ICAM-1 were used to analyse the contributions of these molecules to primary alloproliferative responses by adult and cord blood CD4+ T cells. The results demonstrated that B7 expression is required, and may be sufficient for the induction of a primary alloresponse. The allostimulation observed in response to DR-expressing murine DAP.3 cells, that constitutively express B7.1, was inhibited by the presence of the murine cytolytic T lymphocyte-associated antigen 4-human Fc gamma 11 fusion protein, suggesting that mouse B7.1 provides sufficient costimulation for a primary human alloproliferative response. Expression of supranormal levels of human B7.1 on the allostimulator cells led to a reduction in the proliferative response, suggesting that an optimal level of B7 exists which, if exceeded, leads to inhibition. Co-expression of LFA-3 with B7.1 by the allostimulator cells caused a marked increase in the proliferative response. Expression of ICAM-1a had relatively little effect. No differences were seen in the co-stimulatory requirements of naive cord blood versus CD45RO adult T cells. There results highlight the key molecular interactions that govern immunogenicity with relevance to inhibiting unwanted immune response to transplanted tissues and provoking anti-tumour immunity.