Epitope-specific immunotherapy induces immune deviation of proinflammatory T cells in rheumatoid arthritis

Definition of target antigens for naturally occurring CD4(+) CD25(+) regulatory T cells

The antigenic targets recognized by naturally occurring CD4⁺ CD25⁺ regulatory T cells (T reg cells) have been elusive. We have serologically defined a series of broadly expressed self-antigens derived from chemically induced mouse sarcomas by serological identification of antigens by recombinant expression cloning (SEREX). CD4⁺ CD25⁺ T cells from mice immunized with SEREX-defined self-antigens had strong suppressive activity on peptide-specific proliferation of CD4⁺ CD25⁻ T cells and CD8⁺ T cells. The suppressive effect was observed without in vitro T cell stimulation. Foxp3 expression in these CD4⁺ CD25⁺ T cells from immunized mice was 5–10 times greater than CD4⁺ CD25⁺ T cells derived from naive mice. The suppressive effect required cellular contact and was blocked by anti-glucocorticoid–induced tumor necrosis factor receptor family–related gene antibody. In vitro suppressive activity essentially disappeared 8 wk after the last immunization. However, it was regained by in vitro restimulation with cognate self-antigen protein but not with control protein. We propose that SEREX-defined self-antigens such as those used in this study represent self-antigens that elicit naturally occurring CD4⁺ CD25⁺ T reg cells.

Role of regulatory T cells in experimental arthritis and implications for clinical use

CD4+CD25+ T regulatory cells are avidly studied because they modulate immune responses. Their possible role in autoimmunity and more specifically in rheumatoid arthritis (RA) has been highlighted by a string of reports, one of which is in the last issue of Arthritis Research & Therapy. There are, however, key questions that have not yet been addressed before their use can be considered as a real therapeutic option. The first is the actual, in a clinical setting, efficacy of Treg to treat active chronic autoimmune diseases such as RA. The second is how we can practically deliver their therapeutic activity in patients. Once these points have been addressed we will have a new and potentially very effective 'magic bullet' for the treatment of chronic autoimmune diseases.

Antigen-based immunointervention in human autoimmune diseases

Antigen administration can ameliorate autoimmune disease via various mechanisms, including deletion of autoreactive cells, induction of regulatory T cells, and deviation to non-pathogenic or protective responses. All these mechanisms of immunointervention have been successfully used to prevent and sometimes treat experimental models of autoimmune diseases. Based on these results, expectations have been raised for exploiting similar strategies to inhibit pathogenic autoreactive T cells in human autoimmune diseases. Among them, mucosal administration of autoantigen is an attractive mode of immunointervention still awaiting demonstration of clinical efficacy in human autoimmune diseases. A further step in this direction is now provided by the clear-cut immune deviation observed following oral administration of a disease-related peptide to rheumatoid arthritis patients, leading to inhibition of Th1 while enhancing Th2 and possibly Foxp3-positive regulatory T cells.

De novo generation of antigen-specific CD4+CD25+ regulatory T cells from human CD4+CD25- cells

Antigen-specificity is a hallmark of adaptive T cell-mediated immune responses. CD4+CD25+FOXP3+ regulatory T cells (T(R)) also require activation through the T cell receptor for function. Although these cells require antigen-specific activation, they are generally able to suppress bystander T cell responses once activated. This raises the possibility that antigen-specific T(R) may be useful therapeutically by localizing generalized suppressive activity to tissues expressing select target antigens. Here, we demonstrate that T(R) specific for particular peptide-MHC complexes can be generated from human CD4+CD25- T cells in vitro and isolated by using HLA class II tetramers. Influenza hemagglutinin epitopes were used to generate hemagglutinin-specific T(R), which required cognate antigen for activation but which subsequently suppressed noncognate bystander T cell responses as well. These findings have implications for the generation of therapeutic regulatory T cells in disease, and also suggest an important mechanism by which T cells may be regulated at the site of inflammation.

T cell epitope immunotherapy induces a CD4+ T cell population with regulatory activity

BACKGROUND

Synthetic peptides, representing CD4(+) T cell epitopes, derived from the primary sequence of allergen molecules have been used to down-regulate allergic inflammation in sensitised individuals. Treatment of allergic diseases with peptides may offer substantial advantages over treatment with native allergen molecules because of the reduced potential for cross-linking IgE bound to the surface of mast cells and basophils.

METHODS AND FINDINGS

In this study we address the mechanism of action of peptide immunotherapy (PIT) in cat-allergic, asthmatic patients. Cell-division-tracking dyes, cell-mixing experiments, surface phenotyping, and cytokine measurements were used to investigate immunomodulation in peripheral blood mononuclear cells (PBMCs) after therapy. Proliferative responses of PBMCs to allergen extract were significantly reduced after PIT. This was associated with modified cytokine profiles generally characterised by an increase in interleukin-10 and a decrease in interleukin-5 production. CD4(+) cells isolated after PIT were able to actively suppress allergen-specific proliferative responses of pretreatment CD4(neg) PBMCs in co-culture experiments. PIT was associated with a significant increase in surface expression of CD5 on both CD4(+) and CD8(+) PBMCs.

CONCLUSION

This study provides evidence for the induction of a population of CD4(+) T cells with suppressor/regulatory activity following PIT. Furthermore, up-regulation of cell surface levels of CD5 may contribute to reduced reactivity to allergen.

Transforming growth factor-beta-induced regulatory T cells referee inflammatory and autoimmune diseases

Naturally occurring CD4+CD25+ regulatory T cells mediate immune suppression to limit immunopathogenesis associated with chronic inflammation, persistent infections and autoimmune diseases. Their mode of suppression is contact-dependent, antigen-nonspecific and involves a nonredundant contribution from the cytokine transforming growth factor (TGF)-beta. Not only can TGF-beta mediate cell-cell suppression between the regulatory T cells and CD4+CD25- or CD8+ T cells, but new evidence also reveals its role in the conversion of CD4+CD25- T cells, together with TCR antigen stimulation, into the regulatory phenotype. Elemental to this conversion process is induction of expression of the forkhead transcription factor, Foxp3. This context-dependent coercion of naive CD4+ T cells into a powerful subset of regulatory cells provides a window into potential manipulation of these cells to orchestrate therapeutic intervention in diseases characterized by inadequate suppression, as well as a promising means of controlling pathologic situations in which excessive suppression dominates.

Tregs and allergic disease

Allergic diseases such as asthma, rhinitis, and eczema are increasing in prevalence and affect up to 15% of populations in Westernized countries. The description of Tregs as T cells that prevent development of autoimmune disease led to considerable interest in whether these Tregs were also normally involved in prevention of sensitization to allergens and whether it might be possible to manipulate Tregs for the therapy of allergic disease. Current data suggest that Th2 responses to allergens are normally suppressed by both CD4+CD25+ Tregs and IL-10 Tregs. Furthermore, suppression by these subsets is decreased in allergic individuals. In animal models, Tregs could be induced by high- or low-dose inhaled antigen, and prior induction of such Tregs prevented subsequent development of allergen sensitization and airway inflammation in inhaled challenge models. For many years, allergen-injection immunotherapy has been used for the therapy of allergic disease, and this treatment may induce IL-10 Tregs, leading to both suppression of Th2 responses and a switch from IgE to IgG4 antibody production. Improvements in allergen immunotherapy, such as peptide therapy, and greater understanding of the biology of Tregs hold great promise for the treatment and prevention of allergic disease.

Emerging approaches for the therapy of autoimmune and chronic inflammatory disease

Progress in defining protein and gene signatures that characterize autoimmune-mediated inflammatory diseases has uncovered a large number of potential therapeutic targets. Preclinical data from rodent models can be generated rapidly, as can data from the genetic crosses of gene-deficient mice on autoimmune-susceptible backgrounds. But humans are not the same as mice, and however robust preclinical data might appear, therapeutic intervention in patients with autoimmune disease remains the definitive experiment. Several studies published in the past year have tested paradigms of autoimmune disease in clinical trials. Recent therapeutic approaches for targeting B-cell subsets and co-stimulatory pathways are described here in detail. It is our belief that the future of immunotherapy in the clinic will depend to some extent upon the availability of biomarkers for defining biological signatures of immune function in vivo.

The role of immune tolerance in preventing and treating arthritis

It has become increasingly clear that the innate and adaptive arms of the immune response cooperate in generating autoimmune damage in the pathogenesis of rheumatoid arthritis and juvenile idiopathic arthritis. Treatment targets the immunologic pathophysiology of the disease and is based on regaining immune tolerance. Recently introduced biological agents neutralize or simply block cytokines and their proinflammatory pathways, with favorable clinical outcome. However, major downsides are their lack of specificity and the need of continuous administration to be effective. Possibly, more can be gained from a specific approach. Indeed, recent findings suggest that targeting antigen-specific T cells can reinstate regulatory mechanisms and thus induce immune tolerization. This improved understanding has paved the way to novel immunotherapeutic approaches, some of which will be discussed here.

Tregs and allergic disease

Allergic diseases such as asthma, rhinitis, and eczema are increasing in prevalence and affect up to 15% of populations in Westernized countries. The description of Tregs as T cells that prevent development of autoimmune disease led to considerable interest in whether these Tregs were also normally involved in prevention of sensitization to allergens and whether it might be possible to manipulate Tregs for the therapy of allergic disease. Current data suggest that Th2 responses to allergens are normally suppressed by both CD4+CD25+ Tregs and IL-10 Tregs. Furthermore, suppression by these subsets is decreased in allergic individuals. In animal models, Tregs could be induced by high- or low-dose inhaled antigen, and prior induction of such Tregs prevented subsequent development of allergen sensitization and airway inflammation in inhaled challenge models. For many years, allergen-injection immunotherapy has been used for the therapy of allergic disease, and this treatment may induce IL-10 Tregs, leading to both suppression of Th2 responses and a switch from IgE to IgG4 antibody production. Improvements in allergen immunotherapy, such as peptide therapy, and greater understanding of the biology of Tregs hold great promise for the treatment and prevention of allergic disease.

Suppressor T cells in human diseases

Although central and peripheral tolerance are important for the regulation of human immune responses to self- and microbial antigens, an important role of suppressor CD4⁺ CD25⁺ T cells is suggested from the recent investigations of human autoimmune diseases and HIV. These new data provide increasing evidence that altered function of CD4⁺ CD25⁺ T cells may be an important factor in a wide range of human inflammatory and infectious diseases.

A spectrum of biophysical interaction modes between T cells and different antigen-presenting cells during priming in 3-D collagen and in vivo

For activation T cells engage antigen-presenting cells (APCs) in lymphatic tissues. The contact duration and kinetics (static versus dynamic) vary considerably in different model systems; however, it is unclear whether T cells, APCs, or the environment are responsible for the observed discrepancies. Using 3-D collagen matrices as structural scaffold, we directly compared the kinetics of T-cell engagement and activation by functionally major APC types, ie, dendritic cells (DCs) and resting or activated B cells. Resting B cells engaged T cells in long-lived (several hours), adhesive, and leukocyte function-associated antigen-1 (LFA-1)-dependent conjugates in 3-D collagen as well as in intact lymph nodes in vivo. DCs and preactivated B cells, however, supported predominantly dynamic, short-lived (minutes), and sequential contacts to T cells that were dependent on high cytoskeletal activity of the APCs but could not be inhibited by anti-LFA-1 treatment. Naive T cells were most strongly activated by DCs and activated B cells, whereas resting B cells were 100-fold less efficient to induce T-cell proliferation. Thus, in the same 3-D environment, naive T cells respond with a spectrum of different interaction modes dependent on the type and activation state of the APCs. Thereby, more dynamic interaction kinetics is positively correlated with higher T-cell priming efficiency.