Spectrum of Clinical Presentations, Imaging Findings, and HLA Types in Immune Checkpoint Inhibitor-Induced Hypophysitis

Context

Hypophysitis is a known immune-related adverse event (irAE) of immune checkpoint inhibitors (CPIs), commonly associated with CTLA-4 inhibitors and less often with PD-1/PD-L1 inhibitors.

Objective

We aimed to determine clinical, imaging, and HLA characteristics of CPI-induced hypophysitis (CPI-hypophysitis).

Methods

We examined the clinical and biochemical characteristics, magnetic resonance imaging (MRI) of the pituitary, and association with HLA type in patients with CPI-hypophysitis.

Results

Forty-nine patients were identified. Mean age was 61.3 years, 61.2% were men, 81.6% were Caucasian, 38.8% had melanoma, and 44.5% received PD-1/PD-L1 inhibitor monotherapy while the remainder received CTLA-4 inhibitor monotherapy or CTLA-4/PD-1 inhibitor combination therapy. A comparison of CTLA-4 inhibitor exposure vs PD-1/PD-L1 inhibitor monotherapy revealed faster time to CPI-hypophysitis (median 84 vs 185 days, P < .01) and abnormal pituitary appearance on MRI (odds ratio 7.00, P = .03). We observed effect modification by sex in the association between CPI type and time to CPI-hypophysitis. In particular, anti-CTLA-4 exposed men had a shorter time to onset than women. MRI changes of the pituitary were most common at the time of hypophysitis diagnosis (55.6% enlarged, 37.0% normal, 7.4% empty or partially empty) but persisted in follow-up (23.8% enlarged, 57.1% normal, 19.1% empty or partially empty). HLA typing was done on 55 subjects; HLA type DQ0602 was over-represented in CPI-hypophysitis relative to the Caucasian American population (39.4% vs 21.5%, P = 0.01) and CPI population.

Conclusion

The association of CPI-hypophysitis with HLA DQ0602 suggests a genetic risk for its development. The clinical phenotype of hypophysitis appears heterogenous, with differences in timing of onset, changes in thyroid function tests, MRI changes, and possibly sex related to CPI type. These factors may play an important role in our mechanistic understanding of CPI-hypophysitis.

Accelerating the development of innovative cellular therapy products for the treatment of cancer

The field of cell therapy is rapidly emerging as a priority area for oncology research and drug development. Currently, two chimeric antigen receptor T-cell therapies are approved by the US Food and Drug Administration and other agencies worldwide for two types of hematologic cancers. To facilitate the development of these therapies for patients with life-threatening cancers with limited or no therapeutic options, science- and risk-based approaches will be critical to mitigating and balancing any potential risk associated with either early clinical research or more flexible manufacturing paradigms. Friends of Cancer Research and the Parker Institute for Cancer Immunotherapy convened an expert group of stakeholders to develop specific strategies and proposals for regulatory opportunities to accelerate the development of cell therapies as promising new therapeutics. This meeting took place in Washington, DC on May 17, 2019. As academia and industry expand research efforts and cellular product development pipelines, this report summarizes opportunities to accelerate entry into the clinic for exploratory studies and optimization of cell products through manufacturing improvements for these promising new therapies.

IL-6 overexpression triggers inflammation through its only relevant receptor IL-6R

IL-6 is a pleiotropic cytokine that regulates development and function of variety immune cells. Here we used a novel mouse strain in which IL-6 can be overexpressed in a Cre-dependent manner and show that mice with CD11c-Cre mediated IL-6 overexpression succumb from systemic inflammation. High levels of IL-6 perturbed B and T cell development in primary lymphoid organs, bone marrow and thymus. Interestingly, IL-6-triggered inflammation promoted expansion of both Th17 and Treg cells, two cell types known for their reciprocal developmental requirements. However, the most dramatic increase was noted for myeloid cells, mostly neutrophils, which invaded spleen, thymus and blood of mice with IL-6 overexpression. Observed systemic inflammation ultimately led to mice mortality within 11 weeks of age. Mechanistically, IL-6 mediates its biological functions strictly through binding to IL-6R alpha chain followed by recruitment of the signal transducer gp130. Previously, an alternative pathway was suggested in which IL-6 can utilize CD5 to signal via gp130. However, when IL-6R was deleted in mice with IL-6 overexpression these mice were completely protected from IL-6- triggered pathology and fully phenocopied IL-6R deficient mice. In fact, IL-6R deficiency prevented downstream activation of STAT3 in response to IL-6. Together, our data suggest that IL-6R is the only biological relevant receptor for IL-6 in mice.

Relationship between liver metastases and PD-1 blockade in melanoma

3072

Background: WhilePD-1 blockade is effective in melanoma, durable responses remain elusive. We have previously reported that liver metastasis is associated with reduced response rates and that the fraction of CTLA4 hi/PD-1 hi CD8+ cells (“activated-exhausted” or T-ex cells) within the TIL is predictive of response to PD-1 blockade. Here, we explore the biology behind liver metastasis in human melanoma and in animal models. Methods: Patients with metastatic melanoma with or without liver metastasis were biopsied pre- PD-1 treatment and immune infiltrates were analyzed by FACS. The CD8 fraction was gated on CTLA4 and PD-1. C57BL/6 mice were implanted with a “primary” subcutaneous tumor and a “metastatic” tumor in the liver or the lungs (control), and given systemic PD-1 blockade therapy. Results: Patients with melanoma and liver metastasis (n = 25) had 15.2% T-ex cells while those without liver metastasis (n = 76) had 26.5 % T-ex cells, p = 0.0092. A T-ex fraction < 20% was significantly associated with lack of PD-1 response, p < 0.005. In C57BL/6 mice implanted with a B16 tumor (subQ & liver) treated with PD-1 antibody, 0/35 mice achieved subQ tumor rejection while in the SubQ only mice 9/30 mice (30%) rejected their tumors. The mean tumor size of mice with Sub Q+liver metastasis was 139.2 mm2 vs subQ only mice 23.4 mm2 at d 14, p = 0.002. Mice with liver metastasis showed a T-ex fraction 31.9% vs 67.3%without liver met, p = 0.0003. In contrast, in mice made lung metastatic, the subQ tumor rejection rate was 7/20 (35%), with T-ex infiltrate at 57.9%. The implantation of liver metastases from an unrelated MC38 tumor does not protect the subQ tumor from immune rejection. Conclusions: The presence of liver metastases is associated with reduced response to PD-1 blockade and reduced T-ex infiltrate in patients with stage IV melanoma. Mechanistic studies using a mouse model of syngeneic organ site specific metastasis confirms that the liver metastasis results in reduced antigen specific T cell at distant sites, resulting in reduced response. Site of metastasis may determine immune responsiveness in both mouse models and in humans with melanoma.

Unveiling the specificity of islet-antigen specific regulatory T cells in T1D patient using single cell deep-sequencing

CD4+CD25hiCD127loFoxp3+ T Regulatory cells (Tregs) are critical in controlling autoreactive T cells. The deficiency of functional Tregs is associated with Type 1 diabetes (T1D) and many other autoimmune diseases. In addition, antigen-specific Tregs suppresses more efficiently compared to polyclonal Tregs in mouse models. Thus, identifying the antigen specificity of Tregs, especially at the site of inflammation, is critical to improve our understanding of Treg deficiencies in T1D and may lead to clinically applicable advances. However, the Treg TCRs recognizing self-antigens in autoimmune diseases are less clarified due to the rare frequency and the anergic status of Treg in vitro. In this study, by the combination of sub-culturing, polyclonal stimulation and antigen stimulation, we can identify islet-antigen specific Tregs from both PBMC and pancreatic draining lymph node of T1D patients using antigen-driven Treg proliferation assay we developed in our lab. The majority of islet antigen-specific Tregs is CD45RO+Tregs compared to the CD45RA+ counterpart. Importantly, we confirmed the enrichment and identified the specificity of the islet antigen-specific Tregs using single cell deep-sequencing. In the future, we will further characterize the uncovered Treg TCR and the phenotype of the identified islet antigen-specific Tregs via comparison between healthy and T1D subjects.

Regulatory T cells in prevention of islet-graft rejection in humanized mice (P2230)

Regulatory T cells (Tregs) are potent suppressor of adverse immune reaction and have shown lot of promise in the preclinical studies for the treatment of autoimmune diseases and organ transplantation. In the current study we tested if ex vivo expanded human Tregs can be used to enhance the engraftment of human islets. To test this we developed a humanized mice model by injecting immune deficient NSG mice with human PBMCs or by injecting fetal-liver derived human CD34+ stem cells. Mice were transplanted with purified human islets or human embryonic stem cells (hESC)-derived islets and followed for graft function by measuring serum levels of human c-peptide. We demonstrate that hESC-derived islet graft or purified human islets were rejected by allogeneic PBMCs, which could be prevented by co-stimulation blockade using CTLA-4Ig and anti-CD40L antibodies. Adoptive transfer of ex vivo expanded human Tregs also rescued the rejection albeit not completely. We are currently generating Ag (islet Ag or allo-Ag)-specific Tregs to test their efficacy in preventing islet graft rejection in a mouse expressing human HLA (DR 0401). Our results indicate that ex vivo expanded Tregs can prevent islet graft rejection by allogeneic PBMCs and that humanized mouse could be an excellent model to test the safety and preclinical efficacy of different Treg population.

Production of an NKT cell stimulatory glycosphingolipid by a prominent member of the human gut microbiota (55.22)

While the human gut microbiota are suspected to produce diffusible small molecules that modulate host signaling pathways, few of these molecules have been identified. Species of Bacteroides and their relatives, which often comprise &gt;50% of the gut community, are unusual among bacteria in that their membrane is rich in sphingolipids, a class of signaling molecules that play a key role in modulating the host immune response. Although known for more than three decades, the full repertoire of Bacteroides sphingolipids has not been defined or linked to immune modulatory activity. We report that Bacteroides fragilis produces the glycosphingolipid α-galactosylceramide (α-GalCerBf), which is structurally related to a sponge-derived glycosphingolipid (α-GalCer, KRN7000) that is the prototypical agonist of CD1d-restricted natural killer T (NKT) cells. We demonstrate that α-GalCerBf binds to CD1d and stimulates the production of cytokines by both mouse and human NKT cells. In vivo, we show that α-GalCerBf stimulates NKT cells to induce the activation markers CD25 and CD69, secrete IFN-γ in a CD1d-dependent manner and can prevent cyclophosphamide-induced diabetes. These data suggest that NKT cells directly sense an endogenous antigen produced by a prominent human gut symbiont, uncovering a new mechanism by which the gut microbiota modulate a subset of immune cells relevant to pathogen response and autoimmune disease.

Anti-CD3 mAb therapy promotes tolerance by selectively depleting pathogenic cells while preserving regulatory T cells (107.12)

Monoclonal anti-CD3 antibodies have been used clinically for two decades to reverse steroid-resistant acute graft rejection. In autoimmune diabetes, short course treatment with FcR non-binding anti-CD3 mAb in mice with recent onset of diabetes induces long-term disease remission. Induction of tolerogenic regulatory T cells (Tregs) has been implicated to be one of the mechanisms of action by FcR non-binding (FNB) anti-CD3 mAb in these settings. In this study, we examined the effect of FNB anti-CD3 mAb treatment on the homeostasis of CD4+CD25+Foxp3+ Treg cells in vivo. Anti-CD3 mAb treatment induced a transient systemic rise in the percentage but not absolute number of Tregs due to selective deletion of CD4+CD25- naïve and effector T cells. T cell depletion induced by FNB anti-CD3 mAb was independent of pro-apoptotic proteins Fas or Bim and was caspase 3 independent. Tregs were not preferentially expanded and we found no evidence of convertion of conventional T cells into Tregs suggesting that Tregs are resistant to anti-CD3-induced cell death. Interestingly, we found increased Helios expression on Tregs further showing that adaptive Tregs are not induced by anti-CD3 treatment. Taken together, our results suggest that FNB anti-CD3 mAb therapy selectively induce death of potentially pathogenic CD25- T cells and stabilized, although did not induce, Tregs, thus promoting tolerance by restoring the balance between pathogenic T cells and regulatory T cells.

Auto-reactive exTreg cells are generated during the initiation of autoimmune inflammation. (115.23)

The onset of autoimmunity is associated with a reduced frequency of Foxp3+ T regulatory (Treg) cells, or reduced Foxp3 expression. We have observed that Tregs can lose Foxp3 under homeostatic conditions to form exTreg cells, and that islet-specific exTreg cells induced autoimmune type 1 diabetes (T1D). ExTreg generation in the islets correlates with low IL-2Rα (CD25) expression, and IL-2 complexes directed at Treg cells can rescue T1D. Unstable Foxp3 expression may weaken the ability of the Treg compartment to suppress effectors, and, exTregs can themselves be pathogenic. In this study, we used class II tetramers conjugated with myelin oligodendrocyte peptide 38-49 (MOG38-49) to analyze the myelin-reactive potentially pathogenic CD4+ conventional effector T cells and Treg cells during experimental autoimmune encephalomyelitis (EAE). We observed exTreg generation from Tregs enriched for MOG38-49-specificity, and this correlated with EAE progression. CD25 expression was high on Tregs and exTregs in the inflamed central nervous system, so low CD25 cannot explain Foxp3 instability in this setting. This is the first description of auto-reactive Treg cells within a normal T cell repertoire losing Foxp3 expression during the onset of autoimmunity. It supports the hypothesis that Tregs are enriched for self-reactivity, and that unstable Tregs are associated with progressive autoimmune disease.

Phenotypic and functional characterization of adaptive regulatory T cells using a novel TCR-transgenic mouse model of EAE (152.29)

A defect in functions of Foxp3+ CD4 T helper cells called regulatory T cells (Tregs) play Tregs results in the onset of autoimmune diseases, however the basis for these Treg defects and specific roles of nTregs and aTregs and their relative contributions in autoimmunity remain unknown. We have developed a novel mouse model (1B3) that allows for the direct study of the aTreg population, with a defined TCR specificity and autoreactive potential. 1B3 mouse when bred to RAG2-/- background developed spontaneous EAE by 2-3 weeks of age. 1B3.RAG-/- mice had significant number of Foxp3+ cells in periphery but there was a complete lack of Treg generation in the thymus. aTregs isolated from 1B3.RAG-/-exhibited CpG demethylation in TSDR and showed suppressive activity in vitro. Microarray analysis demonstrated that compared to nTregs, aTregs displayed significantly lower levels of surface markers PD-1, Nrp-1 and previously described transcription factor Helios. PD-1 and Nrp-1 allowed us to separate Foxp3+ Tregs into Helios+/hi nTregs and Helios-/lo aTregs in WT NOD or B6 mice. This is the first report describing phenotypic markers to distinguish aTregs from nTregs. aTregs were less effective in controlling effector T cells and exhibited unstable Foxp3 expression in vivo. Thus nTregs are critical in maintaining tolerance while aTregs are generated in periphery to control local inflammatory response but may not provide long lasting protection due to less stable Foxp3 expression.

Interleukin-7 promotes autoimmune disease by enabling memory T cells to escape PD-1-mediated tolerance (164.21)

An important challenge in the therapy of immune-mediated inflammatory diseases is to control established disease, largely because autoreactive memory T lymphocytes are difficult to suppress or eliminate. Memory T cells depend on interleukin-7 (IL-7) for their generation and maintenance and genomic studies have associated the cytokine’s receptor, IL-7Rα, with increased risk for autoimmune diseases such as type 1 diabetes. Here we show that IL-7Rα blockade reverses hyperglycemia in the non-obese diabetic (NOD) mouse model of type 1 diabetes. Diabetogenic memory T cells deprived of IL-7 signals remained present in the lymphoid organs but expressed the inhibitory molecule Programmed Death 1 (PD-1), which is critical for preventing autoimmunity. Blocking the interaction of PD-1 with its ligand, PD-L1, in cured mice rapidly induced hyperglycemia, demonstrating that this mechanism inhibited memory responses to pancreatic islets after IL-7Rα blockade. Conversely, IL-7 suppressed PD-1 expression after T cell activation, indicating that IL-7 contributes to the pathogenesis of autoimmune diabetes by keeping memory T cells in a functionally competent, tolerance-resistant state. Our data uncover a novel link between IL-7 and the PD-1/PD-L1 tolerance pathway and identify IL-7Rα blockade as a potential therapeutic approach to induce PD-1-mediated inhibition of pathogenic memory T cells in established T cell-dependent inflammatory diseases.

The miR-17-92 cluster is essential for regulatory T cell function in vivo (168.14)

microRNAs (miRNAs) are posttranscriptional regulators of the proteome. We have identified CD28-responsive miRNAs in human CD4+ T cells. Among others, the miR-17-92 cluster was of particular interest because abnormal miR-17 levels have been reported in peripheral blood mononuclear cells from patients with multiple sclerosis. When activated with low CD28-costimulation the miR-17-92 cluster was necessary to drive maximal proliferation in conventional mouse CD4+ T cells (Tconv) in vitro. However, the miR-17-92 cluster was largely dispensable for total T cell numbers in secondary lymphoid tissues and for antigen-response in vivo. Since FoxP3+ regulatory T cells (Treg) are strongly co-stimulation dependent we deleted the miR-17-92 cluster specifically in Treg. Preliminary data suggest that as for Tconv the miR-17-92 cluster was dispensable for Treg numbers and function under homeostatic conditions, even in aging mice. By contrast, mice with miR-17-92-deficient Treg develop much more severe experimental autoimmune encephalitis than control mice. Preliminary results suggest that miR-17-92-deficient Treg numbers are significantly reduced in the spinal cord while antigen-specific effector cells are present in normal numbers. We are currently investigating how miR-17-92 mediates this crucial function. Our results demonstrate that miRNAs are critical for optimal T cell co-stimulation via CD28. The miR-17-92 cluster is essential for Treg function under inflammatory conditions in vivo.

Transcriptional profile of CD28 costimulation and Dec1 relevance in T-cell activation (113.14)

Antigen recognition by the T cell receptor and costimulatory signal through CD28 receptor are required for a complete T-cell activation. CD28 ligation regulates a wide range of biochemical processes that drive T-cell proliferation, prevent apoptosis and enhance IL-2 production. However, the direct effect of CD28 signaling on the global gene transcription after T-cell activation remains controversial. We described the transcriptional profile of CD28 costimulation employing microarray analysis of human naïve CD4+ T cells. Although we demonstrated that CD28-dependent signaling had quantitative effects on gene expression during the first stages of activation, strong qualitative changes on transcription were observed by 24 hours after activation. Among the genes directly induced by CD28 costimulation we identified the transcription factor Dec1. We described the critical role of Dec1 for the transcriptional response to CD28 costimulation in both Jurkat T cells and primary mouse CD4+ T cells. Importantly, we showed that the effects of Dec1 deficiency impact specifically on CD28 costimulation-dependent gene expression. Further, we proved that Dec1 is necessary to induce experimental autoimmune encephalitis in mice after MOG peptide immunization. This observation validates the in vivo importance of Dec1 for immune system function in a CD28-dependent disease.

IL-2 reverses established type 1 diabetes in NOD mice by a local effect on pancreatic regulatory T cells

Regulatory T cells (T reg cells) play a major role in controlling the pathogenic autoimmune process in type 1 diabetes (T1D). Interleukin 2 (IL-2), a cytokine which promotes T reg cell survival and function, may thus have therapeutic efficacy in T1D. We show that 5 d of low-dose IL-2 administration starting at the time of T1D onset can reverse established disease in NOD (nonobese diabetic) mice, with long-lasting effects. Low-dose IL-2 increases the number of T reg cells in the pancreas and induces expression of T reg cell–associated proteins including Foxp3, CD25, CTLA-4, ICOS (inducible T cell costimulator), and GITR (glucocorticoid-induced TNF receptor) in these cells. Treatment also suppresses interferon γ production by pancreas-infiltrating T cells. Transcriptome analyses show that low-dose IL-2 exerts much greater influence on gene expression of T reg cells than effector T cells (T eff cells), suggesting that nonspecific activation of pathogenic T eff cells is less likely. We provide the first preclinical data showing that low-dose IL-2 can reverse established T1D, suggesting that this treatment merits evaluation in patients with T1D.

The Type 1 Diabetes PhysioLab Platform: a validated physiologically based mathematical model of pathogenesis in the non-obese diabetic mouse

Type 1 diabetes is an autoimmune disease whose clinical onset signifies a lifelong requirement for insulin therapy and increased risk of medical complications. To increase the efficiency and confidence with which drug candidates advance to human type 1 diabetes clinical trials, we have generated and validated a mathematical model of type 1 diabetes pathophysiology in a well-characterized animal model of spontaneous type 1 diabetes, the non-obese diabetic (NOD) mouse. The model is based on an extensive survey of the public literature and input from an independent scientific advisory board. It reproduces key disease features including activation and expansion of autoreactive lymphocytes in the pancreatic lymph nodes (PLNs), islet infiltration and beta cell loss leading to hyperglycaemia. The model uses ordinary differential and algebraic equations to represent the pancreas and PLN as well as dynamic interactions of multiple cell types (e.g. dendritic cells, macrophages, CD4+ T lymphocytes, CD8+ T lymphocytes, regulatory T cells, beta cells). The simulated features of untreated pathogenesis and disease outcomes for multiple interventions compare favourably with published experimental data. Thus, a mathematical model reproducing type 1 diabetes pathophysiology in the NOD mouse, validated based on accurate reproduction of results from multiple published interventions, is available for in silico hypothesis testing. Predictive biosimulation research evaluating therapeutic strategies and underlying biological mechanisms is intended to deprioritize hypotheses that impact disease outcome weakly and focus experimental research on hypotheses likely to provide insight into the disease and its treatment.

Immunoregulatory pathways controlling progression of autoimmunity in NOD mice

The activation, expansion, and survival of regulatory T cells (Tregs) as well as the expression of their suppressive capacities result from distinct signaling pathways involving various membrane receptors and cytokines. Multiple studies have shown that thymus-derived naturally occurring Tregs constitutively express the forkhead/winged helix transcription factor FoxP3 in addition to high levels of CD25, the negative co-stimulatory molecule CTLA-4, and the glucocorticoid-induced TNF receptor-related protein GITR. At variance, adaptive or induced Tregs acquire these phenotypic markers as they differentiate in the periphery, following adequate stimulation in the appropriate environment, together with their capacity to produce immunomodulatory cytokines (mainly, IL-4, IL-10 and TGF-beta) and to display regulatory capacities. However, none of these molecules but FoxP3 are restricted to Tregs since they may also be expressed and upregulated on activated effector T cells. This explains why different hypotheses were proposed to interpret interesting reports showing that in vivo abrogation of CTLA-4 signaling using neutralizing CTLA-4 antibodies triggers different autoimmune or immune-mediated manifestations. Thus, an effect on pathogenic T cell effectors and/or Tregs has been proposed. Here we present and discuss recent results we obtained in the nonobese diabetic (NOD) mouse model of spontaneous autoimmune diabetes, arguing for a key role of CTLA-4 in the functional activity of Tregs. Moreover, data are presented that simultaneous blockade of CTLA4 and TGF-beta further impairs immunoregulatory circuits that control disease progression.

Targeting CD22 reprograms B-cells and reverses autoimmune diabetes

OBJECTIVES

To investigate a B-cell-depleting strategy to reverse diabetes in naïve NOD mice.

RESEARCH DESIGN AND METHODS

We targeted the CD22 receptor on B-cells of naïve NOD mice to deplete and reprogram B-cells to effectively reverse autoimmune diabetes.

RESULTS

Anti-CD22/cal monoclonal antibody (mAb) therapy resulted in early and prolonged B-cell depletion and delayed disease in pre-diabetic mice. Importantly, when new-onset hyperglycemic mice were treated with the anti-CD22/cal mAb, 100% of B-cell-depleted mice became normoglycemic by 2 days, and 70% of them maintained a state of long-term normoglycemia. Early therapy after onset of hyperglycemia and complete B-cell depletion are essential for optimal efficacy. Treated mice showed an increase in percentage of regulatory T-cells in islets and pancreatic lymph nodes and a diminished immune response to islet peptides in vitro. Transcriptome analysis of reemerging B-cells showed significant changes of a set of proinflammatory genes. Functionally, reemerging B-cells failed to present autoantigen and prevented diabetes when cotransferred with autoreactive CD4(+) T-cells into NOD.SCID hosts.

CONCLUSIONS

Targeting CD22 depletes and reprograms B-cells and reverses autoimmune diabetes, thereby providing a blueprint for development of novel therapies to cure autoimmune diabetes.

Clinical application of regulatory T cells for treatment of type 1 diabetes and transplantation

Immune regulation is a complex process that depends on the maintenance of self tolerance while retaining robust immune responses against microbes. The emergence of Treg as a central mechanism for immune regulation has generated a new paradigm where Treg-resistant memory T cells and/or "defective" Treg lead to a breakdown in tolerance resulting in immune pathology. In this perspective, we highlight the opportunities and challenges in the field of Treg therapy.

New reagents on the horizon for immune tolerance

Recent advances in immunology and a growing arsenal of new drugs are bringing the focus of tolerance research from animal models into the clinical setting. The conceptual framework for therapeutic tolerance induction has shifted from a "sledgehammer" approach that relies solely on cellular depletion and cytokine targeting, to a strategy directed toward restoring a functional balance across the immune system, namely the different populations of naive cells, effector and memory cells, and regulatory cells. Unlocking the key to tolerance induction in the future will likely depend on our ability to harness the functions of T regulatory cells. Also, dendritic cells are strategically positioned at the interface between innate and adaptive immunity and may be subject to deliberate medical intervention in a way that can control a chronic inflammatory response. Many reagents with tolerance-inducing potential are currently undergoing clinical testing in transplantation, autoimmune diseases, and allergic diseases, and even more that are on the horizon promise to offer enormous benefits to human health.

International trial of the Edmonton protocol for islet transplantation

BACKGROUND

Islet transplantation offers the potential to improve glycemic control in a subgroup of patients with type 1 diabetes mellitus who are disabled by refractory hypoglycemia. We conducted an international, multicenter trial to explore the feasibility and reproducibility of islet transplantation with the use of a single common protocol (the Edmonton protocol).

METHODS

We enrolled 36 subjects with type 1 diabetes mellitus, who underwent islet transplantation at nine international sites. Islets were prepared from pancreases of deceased donors and were transplanted within 2 hours after purification, without culture. The primary end point was defined as insulin independence with adequate glycemic control 1 year after the final transplantation.

RESULTS

Of the 36 subjects, 16 (44%) met the primary end point, 10 (28%) had partial function, and 10 (28%) had complete graft loss 1 year after the final transplantation. A total of 21 subjects (58%) attained insulin independence with good glycemic control at any point throughout the trial. Of these subjects, 16 (76%) required insulin again at 2 years; 5 of the 16 subjects who reached the primary end point (31%) remained insulin-independent at 2 years.

CONCLUSIONS

Islet transplantation with the use of the Edmonton protocol can successfully restore long-term endogenous insulin production and glycemic stability in subjects with type 1 diabetes mellitus and unstable control, but insulin independence is usually not sustainable. Persistent islet function even without insulin independence provides both protection from severe hypoglycemia and improved levels of glycated hemoglobin. (ClinicalTrials.gov number, NCT00014911 [ClinicalTrials.gov].).

Insulin secretion in type 1 diabetes

Type 1 diabetes, a chronic autoimmune disease, causes destruction of insulin-producing beta-cells over a period of years. Although many markers of the autoimmune process have been described, none can convincingly predict the rate of disease progression. Moreover, there is relatively little information about changes in insulin secretion in individuals with type 1 diabetes over time. Previous studies document C-peptide at a limited number of time points, often after a nonphysiologic stimulus, and under non-steady-state conditions. Such methods do not provide qualitative information and may not reflect physiologic responses. We have studied qualitative and quantitative insulin secretion to a 4-h mixed meal in 41 patients with newly diagnosed type 1 diabetes and followed the course of this response for 24 months in 20 patients. Newly diagnosed diabetic patients had an average total insulin secretion in response to a mixed meal that was 52% of that in nondiabetic control subjects, considerably higher than has been described previously. In diabetic patients there was a decline of beta-cell function at an average rate of 756 +/- 132 pmol/month to a final value of 28 +/- 8.4% of initial levels after 2 years. There was a significant correlation between the total insulin secretory response and control of glucose, measured by HbA(1c) (P = 0.003). Two persistent patterns of insulin response were seen depending on the peak insulin response following the oral meal. Patients with an early insulin response (i.e., within the first 45 min after ingestion) to a mixed meal, which was also seen in 37 of 38 nondiabetic control subjects, had a significantly accelerated loss of insulin secretion, as compared with those in whom the insulin response occurred after this time (P < 0.05), and significantly greater insulin secretory responses at 18 and 24 months (P < 0.02). These results, which are the first qualitative studies of insulin secretion in type 1 diabetes, indicate that the physiologic metabolic response is greater at diagnosis than has previously been appreciated, and that the qualitative insulin secretory response is an important determinant of the rate of metabolic decompensation from autoimmune destruction.

The immune tolerance network and rheumatic disease: immune tolerance comes to the clinic

The development of effective, new, biologically based therapies for RA has created real excitement and justifiable optimism in recent years among rheumatologists and among patients with rheumatic diseases. Recent advances in our understanding of the mechanisms of immune activation and immune tolerance provide further cause for optimism. Against this background, the establishment of the ITN is an important step. However, significant hurdles remain to be cleared. First, despite dramatic scientific progress, restoration of immune tolerance in the face of an established autoimmune response is still an elusive goal, even in the laboratory. Not only does the ITN face this fundamental scientific challenge, but it also faces daunting practical and political challenges. For example, can the ITN influence the research agenda of the pharmaceutical and biotechnology industries? This question and other important questions will only be answered as the ITN matures. Autoimmune disease, although individually uncommon, affects more than 2% of Americans. The rheumatologist is especially aware of the devastating potential of autoimmune diseases. If the ITN succeeds in linking basic research into the mechanisms of autoimmunity with clinical trials of promising new therapies, it can be expected to play a critical role in advancing the practice of clinical rheumatology.

Effect of immune deficiency on lipoproteins and atherosclerosis in male apolipoprotein E-deficient mice

To determine whether T cells and B cells influence lipid metabolism and atherosclerosis, we crossed apolipoprotein E-deficient (apoE degrees ) mice with recombination activating gene 2-deficient (RAG2 degrees ) mice. Total plasma cholesterol levels were approximately 20% higher in male apoE degrees mice compared with the apoE degrees RAG2 degrees mice at 8 weeks of age, and plasma triglyceride levels were 2.5-fold higher in the apoE degrees mice even when plasma cholesterol levels were similar. Male mice with plasma cholesterol levels between 400 and 600 mg/dL at 8 weeks of age were euthanized at 27 and 40 weeks of age. The aortic root lesion area in the apoE degrees RAG2 degrees mice, compared with that in the immune-competent apoE degrees mice, was 81% and 57% smaller at 27 and 40 weeks of age, respectively. In contrast, there was no difference in the size of the brachiocephalic trunk lesions. Similar results were obtained with mice euthanized at 40 weeks of age that had 8-week cholesterol levels between 300 and 399 mg/dL. In apoE degrees RAG2 degrees mice, aortic root atherosclerosis was more profoundly suppressed at lower cholesterol levels. Thus, T and B cells and their products differentially influence the development of atherosclerosis at different sites. We also demonstrate a profound effect of the immune system on plasma lipid homeostasis.

CD2 and CD3 receptor-mediated tolerance: constraints on T cell activation

BACKGROUND

Antigen specific allograft tolerance is induced in mice by anti-CD2 plus anti-CD3epsilon monoclonal antibody (mAb) treatment. Because anti-CD2 mAb inhibits several aspects of anti-CD3epsilon driven T cell activation, we investigated what components of T cell activation are required or may be dispensed with for tolerance induction. Anti-CD3epsilon-mediated T cell activation depends on FcgammaR interactions.

METHODS

To assess the role of FcgammaR-mediated T cell activation in tolerance induction, FcgammaR binding IgG or non-binding IgG3 anti-CD3epsilon mAbs were examined.

RESULTS

These mAbs, administered in conjunction with anti-CD2, were equally effective in inducing tolerance. Moreover, in vivo administration of a blocking mAb directed against the FcgammaR, or the use of allograft recipients deficient in FcgammaR, had no effect on tolerance induction. Blocking IL-2 using mAb directed against IL-2 or IL-2R also did not prevent the induction of tolerance. These results suggest that complete T cell activation was not required for tolerance induction. However, substitution of a partially activating mAb, directed against the T cell receptor (TCR) beta subunit for anti-CD3epsilon, failed to synergize with anti-CD2 mAb to induce tolerance. The anti-TCRbeta mAb and anti-CD3epsilon mAb were found to differentially down modulate expression of TCR/CD3 complex subunits. In particular, anti-CD3epsilon caused transient down modulation of the TCRbeta receptor subunit and the TCRzeta signaling module, and this pattern was enhanced and prolonged by anti-CD2. Anti-TCRbeta caused persistent TCRzeta modulation but no TCRbeta modulation, and anti-CD2 did not influence this pattern.

CONCLUSIONS

These results suggest that, although full T cell activation is not required for the induction of tolerance by anti-CD2 plus anti-CD3epsilon mAb, a signal transduction pathway that is associated with TCRbeta and TCRzeta expression, and, specifically, is perturbed by mAb binding of the CD3epsilon epitope, is critical.

Enhanced induction of antitumor T-cell responses by cytotoxic T lymphocyte-associated molecule-4 blockade: the effect is manifested only at the restricted tumor-bearing stages

Cytotoxic T lymphocyte-associated molecule-4 (CTLA-4), a second counterreceptor for the B7 family of costimulatory molecules, functions as a negative regulator of T-cell activation. Here, we investigated whether the blockade of the CTLA-4 function leads to enhancement of antitumor T-cell responses at various stages of tumor growth. Unfractionated spleen cells taken from CSAIM fibrosarcoma-bearing mice 1-2 weeks after CSA1M cell implantation (early tumor-bearing mice) contained tumor-primed T cells that produced interleukin 2 and IFN-gamma through collaboration with antigen-presenting cell-binding tumor antigens when cultured in vitro. However, this initial lymphokine-producing capacity decreased at later stages of tumor growth (7-10 weeks after tumor cell implantation). Anti-CTLA-4 monoclonal antibody (mAb) was added to whole-spleen cell cultures from early or late tumor-bearing mice. Spleen cells from early tumor-bearing mice exhibited enhanced production of interleukin 2 and IFN-gamma upon in vitro culture in the presence of anti-CTLA-4 mAb. However, addition of anti-CTLA-4 mAb to whole-spleen cell cultures from late tumor-bearing mice failed to display such an enhancement. Consistent with these in vitro results, the in vivo antitumor effect of anti-CTLA-4 administration was observed in a tumor-bearing stage-restricted manner; in vivo administration of anti-CTLA-4 (1 mg/mouse, three times at 1-week intervals) into early tumor-bearing mice resulted in regression of growing tumors, whereas the same treatment did not affect tumor growth when performed for late tumor-bearing mice. Similar anti-CTLA-4 effect was observed in another tumor (OV-HM ovarian carcinoma) model. These in vitro and in vivo results indicate that CTLA-4 blockade in tumor-bearing individuals enhances the capacity to generate antitumor T-cell responses, but the expression of such an enhancing effect is restricted to early stages of tumor growth.

Regulation of CTLA-4 expression during T cell activation

T cell activation requires at least two distinct signals, including signaling via the Ag-specific TCR and a costimulatory pathway. The best characterized costimulatory pathway involves the CD28 molecule, which is expressed constitutively on T cells and binds the family of B7 counter-receptors on APCs. Inhibition of this costimulatory pathway prevents T cell activation and can lead to long-term T cell unresponsiveness or anergy. In contrast, CTLA4, which is homologous to CD28, has been shown to be a negative regulator of T cell activation. The CTLA4 molecule is not expressed on resting T cells, but is induced after the initial steps of T cell activation. To address the regulation of CTLA4 expression, we have analyzed CTLA4 at the level of cell surface expression, mRNA, rate of transcription, and rate of decay of message. Nuclear runoff results show an increase in the rate of transcription following T cell activation. Our analyses of non-T cells, including B cells, mastocytoma, and fibroblasts, by Northern blot analysis detect only T cell expression of CTLA4. Reporter gene analysis indicates that 335 bp of upstream CTLA4 sequence are sufficient to control inducibility. We have identified important regulatory regions that control inducible and cell-specific CTLA4 expression. These results also suggest that both positive and negative response elements modulate the transcriptional regulation of CTLA4 gene expression. Understanding the regulation of CTLA4 should provide insight into the regulation of T cell activation at the molecular level.

Regulation of CTLA-4 expression during T cell activation

T cell activation requires at least two distinct signals, including signaling via the Ag-specific TCR and a costimulatory pathway. The best characterized costimulatory pathway involves the CD28 molecule, which is expressed constitutively on T cells and binds the family of B7 counter-receptors on APCs. Inhibition of this costimulatory pathway prevents T cell activation and can lead to long-term T cell unresponsiveness or anergy. In contrast, CTLA4, which is homologous to CD28, has been shown to be a negative regulator of T cell activation. The CTLA4 molecule is not expressed on resting T cells, but is induced after the initial steps of T cell activation. To address the regulation of CTLA4 expression, we have analyzed CTLA4 at the level of cell surface expression, mRNA, rate of transcription, and rate of decay of message. Nuclear runoff results show an increase in the rate of transcription following T cell activation. Our analyses of non-T cells, including B cells, mastocytoma, and fibroblasts, by Northern blot analysis detect only T cell expression of CTLA4. Reporter gene analysis indicates that 335 bp of upstream CTLA4 sequence are sufficient to control inducibility. We have identified important regulatory regions that control inducible and cell-specific CTLA4 expression. These results also suggest that both positive and negative response elements modulate the transcriptional regulation of CTLA4 gene expression. Understanding the regulation of CTLA4 should provide insight into the regulation of T cell activation at the molecular level.

T-cell receptor gamma delta diversity and specificity of intestinal intraepithelial lymphocytes: analysis of IEL-derived hybridomas

The phenotype, T-cell antigen receptor (TCR) usage and specificity of intestinal intraepithelial lymphocytes (IEL), and hybridomas derived from IEL have been examined. In young conventionally reared mice, approximately 50% of the IEL express TCR alpha beta and 50% express TCR gamma delta, although there is considerable variation between individuals. Here we demonstrate that T-cell hybridomas can be prepared from freshly isolated BALB/c mouse IEL. The expressed TCR of these hybridomas reflects the TCR isotype distribution of the IEL population. Analysis of the gamma delta TCR expressed by the hybridomas demonstrates that IEL express a greater number of TCR V gene segments than has been reported for gamma delta T cells in several other epithelial sites. At least five types of gamma delta TCRs are expressed by a panel of BALB/c IEL hybridomas, although use of the gamma delta TCR V gene repertoire clearly is not random. Some TCR gamma delta cells and gamma delta hybridomas have been reported to recognize purified protein derivative (PPD); however, none of the IEL hybridomas secreted IL-2 in response to PPD. These data suggest that most TCR gamma delta IEL are not likely to be PPD reactive.

In vitro and in vivo activation of murine gamma/delta T cells induces the expression of IgA, IgM, and IgG Fc receptors

The present studies examined resting and activated murine gamma/delta T lymphocytes, in vitro and in vivo, for surface expression of FcR. Polyclonal gamma/delta TCR+ lymphocytes selectively grown from the spleen and intestine of normal mice did not express FcR when the cells were in a resting state, but when cells were activated with anti-CD3 antibody virtually all of the splenic gamma/delta lymphocytes and a large subpopulation of the intestinal gamma/delta lymphocytes expressed IgA and IgM FcR. This was confirmed by using transgenic mice. Resting gamma/delta TCR+ lymphocytes from the spleen, thymus, lymph node, and blood of gamma/delta TCR transgenic mice did not express FcR for any of the five major classes of Ig H chains. Activation of the gamma/delta TCR+ cells via the CD3/TCR complex induced high levels of IgM and IgA FcR and low levels of IgG FcR. Finally, in hepatic granulomas of schistosome-infected mice, activated gamma/delta TCR+ cells are present and express high levels of IgA and IgM FcR and low levels of IgG FcR. These investigations establish that transition of gamma/delta TCR+ lymphocytes from a resting to an activated state (triggered via the T3Ti TCR complex) is accompanied by the induction of surface membrane receptors specific for Ig H chain isotypes. The activation-linked expression of FcR on gamma/delta TCR+ lymphocytes provides potential mechanisms for coupling the functional activities of gamma/delta T lymphocytes with immune mechanisms that involve Ig molecules, such as antibody-dependent cellular cytotoxicity.

In vitro and in vivo activation of murine gamma/delta T cells induces the expression of IgA, IgM, and IgG Fc receptors

The present studies examined resting and activated murine gamma/delta T lymphocytes, in vitro and in vivo, for surface expression of FcR. Polyclonal gamma/delta TCR+ lymphocytes selectively grown from the spleen and intestine of normal mice did not express FcR when the cells were in a resting state, but when cells were activated with anti-CD3 antibody virtually all of the splenic gamma/delta lymphocytes and a large subpopulation of the intestinal gamma/delta lymphocytes expressed IgA and IgM FcR. This was confirmed by using transgenic mice. Resting gamma/delta TCR+ lymphocytes from the spleen, thymus, lymph node, and blood of gamma/delta TCR transgenic mice did not express FcR for any of the five major classes of Ig H chains. Activation of the gamma/delta TCR+ cells via the CD3/TCR complex induced high levels of IgM and IgA FcR and low levels of IgG FcR. Finally, in hepatic granulomas of schistosome-infected mice, activated gamma/delta TCR+ cells are present and express high levels of IgA and IgM FcR and low levels of IgG FcR. These investigations establish that transition of gamma/delta TCR+ lymphocytes from a resting to an activated state (triggered via the T3Ti TCR complex) is accompanied by the induction of surface membrane receptors specific for Ig H chain isotypes. The activation-linked expression of FcR on gamma/delta TCR+ lymphocytes provides potential mechanisms for coupling the functional activities of gamma/delta T lymphocytes with immune mechanisms that involve Ig molecules, such as antibody-dependent cellular cytotoxicity.

Inter-mouse strain differences in the in vivo anti-CD3 induced cytokine release

Triggering of the CD3 molecule by in vivo injection of the hamster anti-murine CD3 monoclonal antibody 145-2C11 in adult BALB/c mice leads to massive although transient T cell activation. High levels of tumour necrosis factor (TNF), interferon-gamma (IFN-gamma), IL-2, IL-3 and IL-6 are released into the circulation 1 to 8 h after a single 10 micrograms 145-2C11 i.v. injection. This release induces an impressive self-limited physical reaction associating hypothermia, hypomotility (as assessed by actimetry), diarrhoea, piloerection and even death when high doses (a single dose of greater than 100 micrograms/mouse injection) are administered. In vivo injection of 145-2C11 to other selected mouse strains, namely NZW, CBA/J and C3H/HeJ, induced both different cytokine release patterns and sickness. 145-2C11 induced significant release of TNF and IL-2 in all four strains. At variance, IFN-gamma was only detected in BALB/c mice sera which, in terms of physical reaction (hypothermia and hypomotility) were the most affected. Higher and long-lasting circulating IL-3/GM-CSF levels were present in CBA/J sera, correlating with a later recovery. These results underline heterogeneity in the in vivo cell activation pattern among different mouse strains, when triggering T lymphocytes via the CD3/Ti molecule as compared to exclusive targeting of monocyte/macrophages by means of lipopolysaccharide.

Cascade modulation by anti-tumor necrosis factor monoclonal antibody of interferon-gamma, interleukin 3 and interleukin 6 release after triggering of the CD3/T cell receptor activation pathway

In addition to being potent immunosuppressants, anti-CD3 monoclonal antibodies (mAb) are powerful mitogens in both humans and mice. The first antibody injection consistently induced an initial monocyte-dependent T cell activation with subsequent release of both monocyte- and T cell-derived cytokines [mainly tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma), interleukin (IL) 2, IL 3 and IL 6) into the circulation. This cytokine release is associated with a self-limiting, often severe, acute physical reaction in both patients and mice. We report here that a single injection of anti-TNF mAb prior to anti-CD3 administration not only neutralizes the biological activity of TNF but also strongly affects the release of other cytokines, with notably an up-regulation of IFN-gamma release and a down-regulation of IL 3 and IL 6 release. Conversely, pretreatment with anti-IFN-gamma mAb increases IL 3 and IL 6 production but does not affect TNF levels. Taken together, these data point to a pivotal role of IFN-gamma in the anti-CD3-induced cytokine cascade and reveal new regulatory pathways between TNF and IFN-gamma. With regard to the clinical implications of these findings, as anti-TNF mAb prevents anti-CD3-induced sickness in mice, whereas anti-IFN-gamma does not, such a therapeutic approach might be of value in OKT3-treated patients.

Reduction of morbidity and cytokine release in anti-CD3 MoAb-treated mice by corticosteroids

In keeping with the in vitro mitogenic properties of anti-CD3 MoAbs, the first injections of anti-CD3 are invariably responsible for an in vivo cellular activation. This activation induces a massive cytokine release in the circulation (TNF, IFN gamma, IL-2, IL-6, and IL-3). Paralleling this release, a severe clinical reaction occurs in OKT3-treated patients and in 145 2C11-treated mice. Corticosteroids both in vitro and in vivo inhibit the production of several cytokines involved in the anti-CD3 reaction. A single 1 mg hydrocortisone dose was administered to 145 2C11-treated mice according to different kinetics schedules. When given 1 hr prior to the anti-CD3 MoAb, hydrocortisone exerted a beneficial effect on the mouse physical reaction. Hypothermia was totally abrogated at the 4-hr time point. Diarrhea decreased by 50%. Hypomotility improved although not significantly. This improvement correlated with a major modification in the anti-CD3 pattern of cytokine release. At the 90-min blood withdrawal time point cytokine serum levels showed a 100% decrease for IFN gamma, an 88% decrease for IL-6, and 85% decrease for IL-2, and a 75% decrease for TNF. At 4 hr IL-2 serum levels were diminished by 65%; IL-6, IL-3, and IFN gamma serum levels were comparable to controls; and, interestingly, TNF was still detected, whereas it has already disappeared when 145 2C11 was administered alone. Importantly, when given more than 1 hr prior to anti-CD3 injection, corticosteroids were ineffective. To conclude, high doses of corticosteroids must be given with a precise kinetics--i.e. 1 hr prior to anti-CD3 MoAb--to achieve their maximal beneficial effect in the prevention of the anti-CD3 reaction.

Cytokine-related syndrome following injection of anti-CD3 monoclonal antibody: further evidence for transient in vivo T cell activation

In vivo injection of the hamster anti-murine CD3 monoclonal antibody 145 2C11 into BALB/c mice induces a massive systemic release of several cytokines. Very high circulating levels of tumor necrosis factor are detected both by enzyme-linked immunosorbent assay and L-929 bioassay 90 min following a single injection of 10 micrograms/mouse 145 2C11. Peak circulating levels of exclusively T cell-derived products such as interferon-gamma, interleukin 2 and interleukin 3 are also detected 90 min to 8 h post-injection. Importantly, this cytokine release is transient since none of these cytokines are still present 12 to 24 h post-injection. In parallel to cytokine release, 145 2C11-treated mice (10 micrograms/mouse) exhibit somnolence, hypomotility (quantified by actimetry), hypothermia, diarrhea and piloerection. At this dosage, the physical reaction is not lethal and reverses in all mice by 48 h post-injection. Severe but again reversible anatomopathological changes are also observed: massive cellular depletion, necrosis and edema of lymphoid organs, leakage syndrome and inflammatory cell infiltrates of the lung, cell vacuolization, necrosis and vascular congestion of the liver. All these data are similar to the clinical and immunological manifestations of the OKT3-induced reaction in patients and, thus, provide an invaluable experimental tool to study its mechanisms and explore its prevention.

Structure and expression of class I MHC genes in the miniature swine

The genome of the miniature swine, unlike other species, contains a relatively small class I MHC gene family, consisting of only seven members. This provides an excellent system in which to identify and characterize the regulatory mechanisms which operate to both coordinately and differentially regulate the expression of a multi-gene family. The structure of class I SLA genes, like other class I genes, consists of eight exons encoding a leader sequence, three extracytoplasmic domains, a transmembrane domain and intracytoplasmic domains. Despite the common structure, two sub-families of class I genes can be distinguished within the SLA family. One, containing the closely related PD1 and PD14 genes, encodes the classical transplantation antigens. Another contains the highly divergent PD6; the functions of the products of this subfamily, if any, are not known. The class I SLA genes share some common regulatory mechanisms, as evidenced by the fact that all three genes analyzed are transcribed in mouse L cells. Furthermore, interferon treatment of transfected mouse L cells enhances expression of all three genes. Both PD1 and PD6 are transcribed in vivo, where the highest levels of expression are observed in lymphoid tissues. Superimposed on the common patterns of class I gene expression are distinct ones, as evidenced by the findings that PD1 is preferentially expressed in B cells, whereas PD6 is preferentially expressed in T cells. These differences may reflect the extensive divergence of the 5' flanking sequences of these genes. Future studies will be aimed at elucidating the precise molecular interactions and mechanisms which give rise to the observed differential expression.