An Integrated Model of Immunoregulation Mediated by Regulatory T Cell Subsets

ACAID as a potential therapeutic approach to modulate inflammation in neurodegenerative diseases

The progressive loss of neurons and inflammation characterizes neurodegenerative diseases. Although the etiology, progression and outcome of different neurodegenerative diseases are varied, they share chronic inflammation maintained largely by central nervous system (CNS)-derived antigens recognized by T cells. Inflammation can be beneficial by recruiting immune cells to kill pathogens or to clear cell debris resulting from the primary insult. However, chronic inflammation exacerbates and perpetuates tissue damage. An increasing number of therapies that attempt to modulate neuroinflammation have been developed. However, so far none has succeeded in decreasing the secondary damage associated with chronic inflammation. A potential strategy to modulate the immune system is related to the induction of tolerance to CNS antigens. In this line, it is our hypothesis that this could be accomplished by using anterior chamber associated immune deviation (ACAID) as a strategy. Thus, we review current knowledge regarding some neurodegenerative diseases and the associated immune response that causes inflammation. In addition, we discuss further our hypothesis of the possible usefulness of ACAID as a therapeutic strategy to ameliorate damage to the CNS.

Pancreatic cancer alters human CD4+ T lymphocyte function: a piece in the immune evasion puzzle

OBJECTIVES

To verify whether the dysregulation of CD4 T cells concurs in worsening the outcome of pancreatic cancer, we compared the effects of pancreatic cancer and other gastrointestinal cancer cell-conditioned media on the (1) proliferation, migration, and differentiation of CD4 T cells and (2) expansion of CD4 memory (CD45RO), naive (CD45RA), activated (CD69), and regulatory (CD25) subsets.

METHODS

After culture of CD4 T cells in control, pancreatic (BxPC3, Capan1, MiaPaCa2), or gastrointestinal cancer (AGS, HepG2, HT29) cell-conditioned media, we evaluated proliferation, migration, interferon γ (IFNγ) production, and CD45RA, CD45RO, CD69, and CD25 membrane expression in control and conditioned CD4 T cells.

RESULTS

Only pancreatic cancer-conditioned media (1) inhibited CD4 T-cell proliferation (P < 0.001) and migration under human stromal cell-derived factor-α chemotaxis (P < 0.001) and (2) induced CD4 T-cell IFNγ production (P < 0.05) and the expansion of the CD69-positive subset (P < 0.001) with respect to the control, with no changes being found in the CD45RA, CD45RO, and CD25 subsets.

CONCLUSIONS

The in vitro findings achieved in the present study demonstrate that pancreatic cancer cells inhibit CD4 T-cell proliferation and migration, induce IFNγ production, and favor a CD69 subset expansion, suggesting that CD4 T cells play an important role in pancreatic cancer immune evasion.

Immune amplification of murine CD8 suppressor T cells induced via an immune-privileged site: quantifying suppressor T cells functionally

Background

CD8⁺ suppressor T cells exert antigen-specific suppression of the expression of hypersensitivity by activated T cells. Therefore, CD8⁺ suppressor T cells serve a major regulatory role for the control of active immunity. Accordingly, the number and/or activity of CD8⁺ suppressor T cells should be influenced by an immune response to the antigen. To test this hypothesis we used an adoptive transfer assay that measures the suppression of the expression of delayed-type hypersensitivity (DTH) by CD8⁺ suppressor T cells to quantify the antigen-specific suppression of DTH by these suppressor T cells.

Methods

Suppressor T cells were induced in the spleens of mice by the injection of antigen into the anterior chamber of an eye. Following this injection, the mice were immunized by the same antigen injected into the anterior chamber. Spleen cells recovered from these mice (AC-SPL cells) were titrated in an adoptive transfer assay to determine the number of AC-SPL cells required to effect a 50% reduction of antigen-induced swelling (Sw50) in the footpad of immunized mice challenged by antigen.

Results

Suppression of the expression of DTH is proportional to the number of AC-SPL cells injected into the site challenged by antigen. The number of AC-SPL cells required for a 50% reduction in DTH-induced swelling is reduced by injecting a cell population enriched for CD8⁺ AC-SPL cells. Immunizing the mice receiving intracameral antigen to the same antigen decreases the RSw50 of AC-SPL cells required to inhibit the expression of DTH.

Conclusions

The results provide the first quantitative demonstration that the numbers of antigen-specific splenic CD8⁺ suppressor T cells are specifically amplified by antigen during an immune response.

Antigen-specific splenic CD4+ and CD8+ regulatory T cells generated via the eye, suppress experimental autoimmune encephalomyelitis either at the priming or at the effector phase

The injection of antigen into the ocular anterior chamber (AC) induces the generation of splenic CD4(+) and CD8(+) regulatory T (Treg) cells, specific for the antigen injected into the AC. These Treg cells inhibit the induction (CD4(+)) and also the expression (CD8(+)) of a delayed-type hypersensitivity response. The ability of AC-induced self-antigen-specific Treg cells in modulating autoimmunity is not well defined. Here we show that an injection of encephalitogenic myelin oligodendrocyte glycoprotein (MOG(35-55)) peptide into the anterior chamber of the eye (AC-MOG), before the induction of or during established experimental autoimmune encephalomyelitis (EAE) induced by MOG(35-55), suppresses the induction or progression of EAE, respectively. CD4(+) or CD8(+) splenic Treg cells induced by an injection of AC-MOG prevent EAE either at the inductive (priming) or at the progressive (effector) phase, respectively. This suppression of EAE by an AC-MOG injection or by intravenous transfer of splenic regulatory cells induced by an AC-MOG injection is specific for the antigen injected into the AC. Additionally, our data suggest that splenic CD8(+) Treg cells that suppress active EAE may use a transforming growth factor (TGF)-β-dependent suppression mechanism while the suppression of the induction of EAE by the AC-induced CD4(+) Treg cells is independent of TGF-β. Thus, we show for the first time that regulation of EAE at the priming or the chronic phase requires different phenotypes of Treg cells. Hence, it is important to consider the phenotype of Treg cells while designing effective cell-based therapies against autoimmune disorders.

Expression of immune modulator cytokines in human fulminant amoebic colitis

Human fulminant amoebic colitis (FAC) is characterized by ulceration and inflammation of the colon. The specific mixture of pro-inflammatory and anti-inflammatory cytokines may participate in either the host defense or in the pathogenesis of amoebic colitis. Therefore, we studied the expression of IL-8, IL-10, IL-4, TGF-beta and IFN-gamma in human FAC patients and controls through immunohistochemistry analysis. The number of cells expressing IL-8, IL-4 and IL-10 was significantly enhanced in all FAC samples compared to the control samples. However, the expression of TGF- beta in patients was low in the colonic mucosa and high in the lamina propria compared with the control. No expression of IFN-gamma was found in the controls or FAC samples. The production of IL-8 by intestinal epithelial cells may play a role in the pathogenesis of amoebic infection, because this cytokine attracts neutrophils, which lead to an inflammatory reaction that results in tissue damage. The predominant expression of the macrophage down-regulating cytokines, IL-4, IL-10 and TGF-beta, or the Th2-type immune response could inhibit a cell-mediated immune response, which in turn would facilitate parasite invasion in these tissues.

T cell sensitivity to TGF-beta is required for the effector function but not the generation of splenic CD8+ regulatory T cells induced via the injection of antigen into the anterior chamber

The introduction of antigen into the anterior chamber (AC) of the eye induces the production of antigen-specific splenic CD8⁺ regulatory T cells (AC-SPL cells) that suppress a delayed-type hypersensitivity (DTH) reaction in immunized mice. Because the generation of these regulatory T cells is also induced by exposure to transforming growth factor (TGF)-β and antigen or F4/80⁺ cells exposed to TGF-β and antigen in vitro, we investigated (i) whether these cells are produced in dominant negative receptor for transforming growth factor β receptor type II (dnTGFβRII) or Cbl-b^−/− mice whose T cells are resistant to TGF-β, (ii) whether DTH is suppressed by wild type (WT) CD8⁺ AC-SPL cells in Cbl-b^−/− and dnTGFβRII mice and (iii) the effect of antibodies to TGF-β on the suppression of DTH by CD8⁺ AC-SPL cells. DnTGFβRII immunized and Cbl-b^−/− mice produced splenic CD8⁺ regulatory cells after the intracameral injection of antigen and immunization. The suppression of a DTH reaction by CD8⁺ AC-SPL cells in WT mice was blocked by the local inclusion of antibodies to TGF-β when WT splenic CD8⁺ AC-SPL cells were injected into the DTH reaction site. Moreover, the DTH reaction in immunized dnTGFβRII and Cbl-b^−/− mice was not suppressed by the transfer of WT CD8⁺ AC-SPL cells to the site challenged with antigen. In aggregate, these observations suggest that T cell sensitivity to TGF-β is not an obligate requirement for the in vivo induction of CD8⁺ AC-SPL T cells but the suppression of an in vivo DTH reaction by CD8⁺ AC-SPL cells is dependent on TGF-β.

The suppression of hypersensitivity by ocular-induced CD8(+) T cells requires compatibility in the Qa-1 haplotype

The injection of antigen into the anterior chamber (AC, intracameral injection)2 of a murine eye induces the generation of splenic CD8⁺ regulatory T cells (AC-SPL cells) that effect the antigen-specific suppression of a Delayed-Type Hypersensitivity (DTH) reaction. Here we show (i) for the first time that the local antigen-specific suppression of DTH-induced swelling in immunized mice by either an intracameral injection of antigen or by the direct injection of CD8⁺ AC-SPL cells into an antigen-challenged site is associated with an absence of infiltrated mononuclear cells, (ii) the local antigen-specific suppression of the DTH reaction by CD8⁺ AC-SPL cells requires compatibility between the Qa-1 but not H2 antigen haplotype of the immunized recipient and the injected AC-SPL regulatory T cells, (iii) The suppression of the DTH reaction by CD8⁺ AC-SPL cells requires the expression of Qa-1 but not H2 antigens and is not due to bystander suppression.

Regulation of CD8+ regulatory T cells: Interruption of the NKG2A-Qa-1 interaction allows robust suppressive activity and resolution of autoimmune disease

Regulation of autoreactive CD4 T cells is essential to maintain self-tolerance and prevent autoimmune disease. Although CD8 T regulatory (Treg) cells that recognize self-peptides restricted by Qa-1 (HLA-E in humans) inhibit autoreactive CD4 cells and attenuate experimental autoimmune encephalomyelitis (EAE), the mechanism of this interaction is unclear. We generated Qa-1 mutant knock-in mice that impair Qa-1 binding to the T cell receptor (TCR) and CD94/NKG2A receptors. Analysis of these mice showed that TCR-dependent recognition of Qa-1-peptide complexes on target CD4 cells is essential for suppression by CD8 Treg cells. Further analysis revealed that genetic disruption of the Qa-1-CD94/NKG2A interaction unleashes robust CD8 Treg cell activity that completely abolishes development of EAE.

HLA-G expression defines a novel regulatory T-cell subset present in human peripheral blood and sites of inflammation

Regulatory T cells can inhibit harmful immunopathologic responses directed against self and foreign antigens and play a major role in controlling autoimmunity. Here we have identified and characterized a subpopulation of CD4 and CD8 T cells in human peripheral blood expressing the immune tolerizing molecule HLA-G. HLA-G-expressing T cells are hypoproliferative, are CD25- and FOXP3-negative, and exhibit potent suppressive properties that are partially mediated by HLA-G. HLA-G-positive (HLA-G(pos)) T cells are found at low percentages among CD4 and CD8 single-positive thymocytes, suggesting a thymic origin. The presence of HLA-G(pos) T cells at sites of inflammation such as inflamed skeletal muscle in myositis or the cerebrospinal fluid of patients with acute neuroinflammatory disorders suggests an important function in modulating parenchymal inflammatory responses in vivo.

The suppression of delayed-type hypersensitivity by CD8+ regulatory T cells requires interferon-gamma

CD8(+) regulatory (suppressor) T cells are induced by complex cellular pathways in the spleens of mice that have received an injection of antigen into the anterior chamber (AC) of an eye, an immune-privileged site. Although these CD8(+) regulatory T cells perform an antigen-specific regulatory function for an immune response to self and non-self antigens, the mechanisms of the activation or function of these regulatory cells are not clear. Here, we describe a novel mechanism for the activation of splenic CD8(+) regulatory T cells induced by injection of antigen into the AC. Immunization of mice with trinitrophenyl and bovine serum albumin (TNP-BSA) amplified AC-induced splenic CD8(+) regulatory T cells that suppressed the initiation of contact sensitivity when transferred to immunized, challenged mice. These CD8(+) regulatory T cells were produced independently of perforin, indicating that they are not canonical cytotoxic T cells. Fas ligand (FasL)-deficient CD8(+) regulatory T-cell function was rescued by inclusion of exogenous interferon-gamma (IFN-gamma), demonstrating that the expression of FasL by CD8(+) regulatory T cells was dispensable, but IFN-gamma was not. Ultimately, we demonstrated that the generation of these CD8(+) regulatory T cells occurred independently of IFN-gamma, but their suppressor function required IFN-gamma receptor stimulation.

Induction of partial immune tolerance to factor VIII through prior mucosal exposure to the factor VIII C2 domain

BACKGROUND

The development of anti-factor VIII (FVIII) neutralizing antibodies (inhibitors) is a significant obstacle to FVIII replacement therapy.

OBJECTIVE

As mucosal administration of an antigen may induce immune tolerance we have evaluated the efficacy of mucosal antigen exposure to achieve tolerance to FVIII.

METHODS

We investigated the effects of oral and nasal administration of the purified FVIII C2 domain (FVIII-C2) to FVIII-deficient BALB/c mice prior to FVIII protein challenge. Mice received oral or nasal doses of FVIII-C2, followed by a subcutaneous challenge of either FVIII-C2 or FVIII. The development of anti-FVIII inhibitors, cytokine production by splenocytes in vitro, and adoptive transfer assays were analyzed.

RESULTS AND CONCLUSIONS

Mucosal administration of FVIII-C2 decreases the titer of anti-FVIII-C2 inhibitors after FVIII-C2 challenge, and decreases the percentage of FVIII-C2 specific antibodies after challenge with full-length FVIII. Tolerance induction to FVIII-C2 is associated with increased IL-10 production by splenocytes in vitro, and can be adoptively transferred to naïve mice. This study is the first to demonstrate that tolerance to the FVIII-C2 domain can be induced via the mucosal route. Based on these results, the potential use of FVIII-specific mucosal tolerance induction as an immunotherapy treatment for anti-FVIII inhibitor development warrants further investigation.

Cellular and molecular mechanisms of regulation of autoantibody production in lupus

The hyperactive interaction between helper T cells and autoimmune B cells in individuals predisposed to systemic lupus erythematosus (SLE) can be interrupted by induction of regulatory and suppressor T cells. Using two strategies-high dose tolerance to an immunoglobulin-derived peptide, and minigene vaccination with DNA encoding T cell epitopes presented by MHC class I molecules-our group has induced at least three types of regulatory/suppressive T cells. They include CD8+ T cells that suppress helper T cells by cytokine secretion, CD8+ T suppressors that kill B cells making anti-DNA antibodies, and peptide-binding CD4+CD25+ regulatory T cells that suppress B cells by direct cell contact. Each of these lymphocyte subsets suppresses anti-DNA antibody production and delays the onset of nephritis in BWF1 lupus-prone mice. Patients with SLE have amino acid sequences similar to those from murine anti-DNA antibodies used in these studies, and at similar locations in the VH regions of anti-DNA immunoglobulins. Therefore, strategies described here might ultimately be useful in therapy of the human disease.

Therapeutic induction of regulatory, cytotoxic CD8+ T cells in multiple sclerosis

In the setting of autoimmunity, one of the goals of successful therapeutic immune modulation is the induction of peripheral tolerance, a large part of which is mediated by regulatory/suppressor T cells. In this report, we demonstrate a novel immunomodulatory mechanism by an FDA-approved, exogenous peptide-based therapy that incites an HLA class I-restricted, cytotoxic suppressor CD8+ T cell response. We have shown previously that treatment of multiple sclerosis (MS) with glatiramer acetate (GA; Copaxone) induces differential up-regulation of GA-reactive CD8+ T cell responses. We now show that these GA-induced CD8+ T cells are regulatory/suppressor in nature. Untreated patients show overall deficit in CD8+ T cell-mediated suppression, compared with healthy subjects. GA therapy significantly enhances this suppressive ability, which is mediated by cell contact-dependent mechanisms. CD8+ T cells from GA-treated patients and healthy subjects, but not those from untreated patients with MS, exhibit potent, HLA class I-restricted, GA-specific cytotoxicity. We further show that these GA-induced cytotoxic CD8+ T cells can directly kill CD4+ T cells in a GA-specific manner. Killing is enhanced by preactivation of target CD4+ T cells and may depend on presentation of GA through HLA-E. Thus, we demonstrate that GA therapy induces a suppressor/cytotoxic CD8+ T cell response, which is capable of modulating in vivo immune responses during ongoing therapy. These studies not only explain several prior observations relating to the mechanism of this drug but also provide important insights into the natural immune interplay underlying this human immune-mediated disease.

CD4+CD25+ regulatory T cells in HIV infection

The immune system faces the difficult task of discerning between foreign, potentially pathogen-derived antigens and self-antigens. Several mechanisms, including deletion of self-reactive T cells in the thymus, have been shown to contribute to the acceptance of self-antigens and the reciprocal reactivity to foreign antigens. Over the last decade it has become increasingly clear that CD4(+)CD25(+) T(Reg) cells are crucial for maintenance of T cell tolerance to self-antigens in the periphery, and to avoid development of autoimmune disorders. Recently, evidence has also emerged that demonstrates that CD4(+)CD25(+) T(Reg) cells can also suppress T cell responses to foreign pathogens, including viruses such as HIV. In this article we review the current knowledge and potential role of CD4(+)CD25(+) T(Reg) cells in HIV infection.

An affinity/avidity model of peripheral T cell regulation

We show in these studies that Qa-1-dependent CD8+ T cells are involved in the establishment and maintenance of peripheral self tolerance as well as facilitating affinity maturation of CD4+ T cells responding to foreign antigen. We provide experimental evidence that the strategy used by the Qa-1-dependent CD8+ T cells to accomplish both these tasks in vivo is to selectively downregulate T cell clones that respond to both self and foreign antigens with intermediate, not high or low, affinity/avidity. Thus, the immune system evolved to regulate peripheral immunity using a unified mechanism that efficiently and effectively permits the system to safeguard peripheral self tolerance yet promote the capacity to deal with foreign invaders.

Qa-1 restriction of CD8+ suppressor T cells

There is increasing evidence that the immune response can be inhibited by several T cell subsets, including NK T cells, CD25+CD4+ T cells, and a subpopulation of CD8+ T cells. Animal model studies of multiple sclerosis have suggested an important role for suppressor CD8+ T cells in protection against disease recurrence and exacerbation. The molecular lynchpin of CD8+ suppressive activity is the murine MHC molecule Qa-1, termed HLA-E in humans. Here we summarize findings from work on Qa-1 that have begun to delineate suppressor CD8+ T cells and their mechanisms of action in the context of self tolerance and autoimmune disease.

Suppression of autoimmune disease after vaccination with autoreactive T cells that express Qa-1 peptide complexes

The ability of autoreactive T cells to provoke autoimmune disease is well documented. The finding that immunization with attenuated autoreactive T cells (T cell vaccination, or TCV) can induce T cell-dependent inhibition of autoimmune responses has opened the possibility that regulatory T cells may be harnessed to inhibit autoimmune disease. Progress in the clinical application of TCV, however, has been slow, in part because the underlying mechanism has remained clouded in uncertainty. We have investigated the molecular basis of TCV-induced disease resistance in two murine models of autoimmunity: herpes simplex virus-1 (KOS strain)-induced herpes stromal keratitis and murine autoimmune diabetes in non-obese diabetic (NOD) mice. We find that the therapeutic effects of TCV depend on activation of suppressive CD8 cells that specifically recognize Qa-1-bound peptides expressed by autoreactive CD4 cells. We clarify the molecular interaction between Qa-1 and self peptides that generates biologically active ligands capable of both inducing suppressive CD8 cells and targeting them to autoreactive CD4 cells. These studies suggest that vaccination with peptide-pulsed cells bearing the human equivalent of murine Qa-1 (HLA-E) may represent a convenient and effective clinical approach to cellular therapy of autoimmune disease.