CD4+ CD25+ T cells responding to serologically defined autoantigens suppress antitumor immune responses

Innate Immune Recognition and Suppression of Tumors

In this chapter, we first summarized the strong evidence that now supports the existence of an effective cancer immune surveillance process that prevents cancer development in both mice and humans. We then focused the remainder of the chapter on methods of tumor recognition that contribute to natural host immune suppression of tumors. In particular, NKG2D is a type II transmembrane-anchored glycoprotein expressed as a disulfide-linked homodimer on the surface of all mouse and human natural killer cells (NK cells). Stimulation of NK cell through NKG2D triggers cell-mediated cytotoxicity and in some cases induces production of cytokines. NKG2D binds to family of ligands with structural homology to major histocompatibility complex (MHC) class I, however, NKG2D ligands often display upregulated surface expression on stressed cells and are frequently overexpressed by tumors unlike conventional MHC class I molecules. Evidence clearly implicate that NKG2D recognition plays an important role in tumor immune surveillance.

Cancer Immunosurveillance and Immunoediting: The Roles of Immunity in Suppressing Tumor Development and Shaping Tumor Immunogenicity

Cellular transformation and tumor development result from an accumulation of mutational and epigenetic changes that alter normal cell growth and survival pathways. For the last 100 years, there has been a vigorous debate as to whether the unmanipulated immune system can detect and eliminate such altered host derived cells despite the fact that cancer cells frequently express either abnormal proteins or abnormal levels of normal cellular proteins that function as tumor antigens. In this review, we discuss the current state of this argument and point out some of the recent key experiments demonstrating that immunity not only protects the host from cancer development (i.e., provides a cancer immunosurveillance function) but also can promote tumor growth, sometimes by generating more aggressive tumors. The terminology "cancer immunoediting" has been used to describe this dual host protective and tumor promoting action of immunity, and herein we summarize the ever-increasing experimental and clinical data that support the validity of this concept.

Genes to vaccines for immunotherapy: how the molecular biology revolution has influenced cancer immunology

Recent advances in our understanding of the complex signaling pathways involved in immune system regulation, along with analyses of genetic differences between tumors and their normal cellular counterparts, have accelerated development of immune-based strategies for cancer treatment and prevention. More clinically relevant animal models have shown that successful immune-based strategies will require the integration of interventions that target specific tumor antigens with regulators of the antitumor immune response. Immunotherapy for cancer is at a critical crossroad, as therapeutics designed to target cancer-associated antigens and regulatory signaling molecules enter clinical trials. We outline here a paradigm for early-stage clinical development of immunotherapy combinations that use vaccines to drive tumor antigen-specific responses while simultaneously targeting immune regulatory pathways.

Dendritic Cells Pulsed with Total Tumor RNA for Activation NK-like T Cells Against Glioblastoma Multiforme

Dendritic cells (DCs) are potent antigen presenting cells and play critical role in T cell-mediated immunity. DCs have been shown to induce strong anti-tumor responses both in vitro and in vivo. Their efficacies in tumor therapy are being investigated in clinical trials. Previous evidence has shown that these DCs enhance the cytotoxicity of NK cells. We generated NK-like T cells (CD3(+)CD56(+)), a novel type of effector cells differentiated from normal lymphocyte, which is now being used for adoptive immunotherapy in clinical trials. This study aimed to elucidate the effects of NK-like T cells after co-culturing with DCs against tumor cells. The result revealed that tumor-derived RNA-pulsed DCs can enhance the immune responses of NK-like T cells against glioblastoma multiforme cell line but these effector cells did not appear to have the cytotoxic effect against normal cells (human umbilical vein endothelial cells (HUVEC) and fibroblasts) in vitro. This study may be beneficial for the development of new immunologic effector cells for using in adoptive immunotherapy for glioblastoma multiforme in the future.

The role of TCR specificity in naturally arising CD25+ CD4+ regulatory T cell biology

CD25+ CD4+ T cells (TR) are a naturally arising subset of regulatory T cells important for the preservation of self-tolerance and the prevention of autoimmunity. Although there is substantial data that TCR specificity is important for TR development and function, relatively little is known about the antigen specificity of naturally arising TR. Here, we will review the available evidence regarding naturally arising TR TCR specificity in the context of TR development, function, and homeostasis.

IFN-γ Controls the Generation/Activation of CD4+CD25+ Regulatory T Cells in Antitumor Immune Response

Immunization with serological identification of Ags by recombinant expression cloning (SEREX)-defined self-Ags leads to generation/activation of CD4+ CD25+ regulatory T cells with suppressive activities and enhanced expression of Foxp3. This is associated with increased susceptibility to pulmonary metastasis following challenge with syngeneic tumor cells and enhanced development of 3-methylcholanthrene-induced primary tumors. In contrast, coimmunization with the same SEREX-defined self-Ags mixed with a CTL epitope results in augmented CTL activity and heightened resistance to pulmonary metastasis, both of which depend on CD4+ Th cells. These active regulatory T cells and Th cells were derived from two distinct CD4+ T cell subsets, CD4+ CD25+ T cells and CD4+ CD25- T cells, respectively. In the present study, IFN-gamma was found to abrogate the generation/activation of CD4+ CD25+ regulatory T cells by immunization with SEREX-defined self-Ag. CD4+ CD25+ T cells from these IFN-gamma-treated mice failed to exhibit immunosuppressive activity as measured by 1) increased number of pulmonary metastasis, 2) enhanced development of 3-methylcholanthrene-induced primary tumors, 3) suppression of peptide-specific T cell proliferation, and 4) enhanced expression of Foxp3. The important role of IFN-gamma produced by CD8+ T cells was shown in experiments demonstrating that CD4+ CD25+ T cells cotransferred with CD8+ T cells from IFN-gamma(-/-) mice, but not from wild-type BALB/c mice, became immunosuppressive and enhanced pulmonary metastasis when recipient animals were subsequently immunized with a SEREX-defined self-Ag and a CTL epitope. These findings support the idea that IFN-gamma regulates the generation/activation of CD4+ CD25+ regulatory T cells.

Current concepts of tumor-infiltrating lymphocytes in human malignancies

Tumor-infiltrating lymphocytes (TILs) develop as manifestations of the recognition and defense against malignant cells by the host immune system. TILs were literally defined as "tumor-infiltrating lymphocytes", which a posteriori locate within the tumor tissues. Although such cells can be found, they fail to control the growth of tumor. Many have proposed diverse mechanisms for dysfunction of TILs with regard to the roles of immunosurveillance against cancer. However, only a few cancer types, e.g. melanoma, have seen the benefits brought by activating these cells for immunotherapy. Functional defects of TILs have been linked to abnormalities of signaling molecules; however, there is conflicting data. The death of TILs was attributed to expression of cancer-derived FasL, PD-1 and RCAS1, and cancer-induced activation-induced cell death (AICD). Confirmed by studies using TILs and animal models, the compromise of tumor-specific immune responses was thought to result from not only mechanisms of clonal anergy but also exhaustion and/or deletion. Furthermore, functional cytotoxic CD8(+) TILs might be rendered incompetent by cancer-induced up-regulation of inhibitory NK receptors or proximal signaling abnormalities. Additionally, immune privilege was partly attributed to recruitment of regulatory T cells to the tumor sites. The failure of IL-2 signaling, which stands at the center of T cell functionalities, had been linked to the enzymatic activity of cancer-derived matrix metalloproteinases (MMPs). Finally, the exploitation of IDO expression, an important enzyme in pregnancy-related immunosuppression, by cancer cells might play a role in tumor immunity. The disparity of cancer types, origin, developmental stages and individual genetic backgrounds likely account for differences, or even contradictions, which might be the reason why immunotherapy works only on a few cancer types. Delineating the mechanisms behind functional defects of TILs can help not only boost chances of the development of a successful cure but understand the not fully identified roles played by immune system in the face of malignancies.

Toward an understanding of NKT cell biology: progress and paradoxes

Natural killer T (NKT) cells constitute a conserved T cell sublineage with unique properties, including reactivity for a synthetic glycolipid presented by CD1d, expression of an invariant T cell antigen receptor (TCR) alpha chain, and unusual requirements for thymic selection. They rapidly produce many cytokines after stimulation and thus influence diverse immune responses and pathogenic processes. Because of intensive research effort, we have learned much about factors promoting the development and survival of NKT cells, regulation of their cytokine production, and the means by which they influence dendritic cells and other cell types. Despite this progress, knowledge of the natural antigen(s) they recognize and their physiologic role remain incomplete. The activation of NKT cells paradoxically can lead either to suppression or stimulation of immune responses, and we cannot predict which will occur. Despite this uncertainty, many investigators are hopeful that immune therapies can be developed based on NKT cell stimulation.

Accelerated chemically induced tumor development mediated by CD4+CD25+ regulatory T cells in wild-type hosts

We examined the role of CD4+CD25+ regulatory T cells in the development of 3-methylcholanthrene (MCA)-induced tumors. Immunization of wild-type BALB/c mice with a series of SEREX (serological identification of antigens by recombinant expression cloning)-defined broadly expressed self-antigens results in the development of highly active CD4+CD25+ regulatory T cells. Accelerated tumor development was observed in mice immunized with self-antigens and was abolished by antibody-mediated depletion of CD4+ T cells or CD25+ T cells. A similar acceleration of tumorigenesis was also observed in mice adoptively transferred 2 or 4 weeks after MCA injection with CD4+CD25+ T cells derived from mice immunized with DnaJ-like 2, one of these self-antigens. Experiments with Jalpha281-/- mice lacking invariant natural killer (iNK) T cells indicated that iNK T cells, known for their protective role in the development of MCA-induced tumors, were suppressed in immunized hosts. NK cells, also known to play a protective role in MCA induced-tumorigenesis, were also suppressed in mice immunized with serologically defined self-antigens in a CD4+CD25+ T cell-dependent manner. We propose that CD4+CD25+ regulatory T cells generated by immunization with these self-antigens enhance susceptibility to MCA induced-tumorigenesis by down-regulating iNK T and NK reactivity, and suggest that these observations provide direct evidence for the existence of cancer immunosurveillance in this system of chemical carcinogenesis.

Tumor-induced antibodies resemble the response to tissue damage

Tumor-associated antibodies are frequently detected in cancer patients. To ask whether the recognized antigens are rejection antigens, we screened a cDNA expression library of the mouse TS/A tumor with TS/A-immune serum and isolated 8 IgG-reactive clones, representing self-antigens that were expressed in normal tissues and other tumor lines. Three of the antigens had previously been identified in the human system by this cloning strategy. None of the antigens revealed to be a rejection antigen in normal mice demonstrated by an otherwise effective plasmid immunization. For one of the identified antigens, alpha-catenin, it is shown that the induction of IgG antibodies by protein immunization does not correlate with tumor rejection. For another antigen, vimentin, it is shown that vimentin-deficient but not vimentin-competent mice reject vimentin-expressing tumors indicating T -cell tolerance despite the fact that tumor cell immunization induces antivimentin IgG antibodies. Tissue damage induced by adenovirus infection induced an antibody response similar to tumor cell immunization, exemplified with 2 of the antigens. We conclude that the tumor-induced antibodies mirror tissue damage and that the antibody-inducing antigens can serve as rejection antigens if they are recognized as foreign.

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.

CD4+ CD25+ regulatory T cells control the induction of antigen-specific CD4+ helper T cell responses in cancer patients

A proportion of cancer patients naturally develop CD4+ T-helper type 1 (Th1) cell responses to NY-ESO-1 that correlate with anti-NY-ESO-1 serum antibodies. To address the role of T-cell regulation in the control of spontaneous tumor immunity, we analyzed NY-ESO-1-specific Th1 cell induction before or after depletion of CD4+CD25+ T cells in vitro. While Th1 cells were generated in the presence of CD25+ T cells in cancer patients seropositive for NY-ESO-1, seronegative cancer patients and healthy donors required CD25+ T-cell depletion for in vitro induction of NY-ESO-1-specific Th1 cells. In vitro, newly generated NY-ESO-1-specific Th1 cells were derived from naive precursors, whereas preexisting memory populations were detectable exclusively in patients with NY-ESO-1 antibody. Memory populations were less sensitive than naive populations to CD4+CD25+ regulatory T cells. We propose that CD4+CD25+ regulatory T cells are involved in the generation and regulation of NY-ESO-1-specific antitumor immunity.

Naturally arising Foxp3-expressing CD25+CD4+ regulatory T cells in immunological tolerance to self and non-self

Naturally arising CD25(+)CD4(+) regulatory T cells actively maintain immunological self-tolerance. Deficiency in or dysfunction of these cells can be a cause of autoimmune disease. A reduction in their number or function can also elicit tumor immunity, whereas their antigen-specific population expansion can establish transplantation tolerance. They are therefore a good target for designing ways to induce or abrogate immunological tolerance to self and non-self antigens.

Recognition of a New ARTC1 Peptide Ligand Uniquely Expressed in Tumor Cells by Antigen-Specific CD4+ Regulatory T Cells

CD4(+) regulatory T (Treg) cells play an important role in the maintenance of immunological self-tolerance by suppressing immune responses against autoimmune diseases and cancer. Yet very little is known about the natural antigenic ligands that preferentially activate CD4(+) Treg cells. Here we report the establishment of tumor-specific CD4(+) Treg cell clones from tumor-infiltrating lymphocytes (TILs) of cancer patients, and the identification of an Ag recognized by Treg cells (ARTC1) gene encoding a peptide ligand recognized by tumor-specific TIL164 CD4(+) Treg cells. The mutations in a gene encoding an ARTC1 in 164mel tumor cells resulted in the translation of a gene product containing the peptide ligand recognized by CD4(+) Treg cells. ARTC1 peptide-activated CD4(+) Treg cells suppress the physiological function (proliferation and IL-2 secretion) of melanoma-reactive T cells. Furthermore, 164mel tumor cells, but not tumor lysates pulsed on B cells, were capable of activating TIL164 CD4(+) Treg cells. These results suggest that tumor cells may uniquely present an array of peptide ligands that preferentially recruit and activate CD4(+) Treg cells in sites where tumor-specific self-peptide is expressed, leading to the induction of local and tumor-specific immune suppression.

Valpha14 NKT cell-mediated anti-tumor responses and their clinical application

A unique lymphocyte population, Valpha14 NKT cells, has recently been revealed to be a key player in the immune responses against tumors. Activation of Valpha14 NKT cells affects various cell types, particularly dendritic cells (DCs), NK cells, CD4 Th1 cells, and CD8 cytotoxic T cells in the innate and acquired immune systems, eventually resulting in the enhanced activation of NKT cell-mediated cellular cascade in the anti-tumor responses. The specific ligand, alpha-galactosylceramide (alpha-GalCer), effectively stimulates mouse and human NKT cells, making NKT cells an ideal target for the development of cancer immunotherapy. Clinical trials using alpha-GalCer have actually started in several centers in the world. In this review, we summarize the Valpha14 NKT cell-mediated cellular cascade in the anti-tumor response in mice and discuss potential clinical applications of alpha-GalCer-pulsed DC therapy.

Regulation of antitumour immunity by CD1d-restricted NKT cells

An understanding of the complex interactions occurring between tumours and the immune system is a prerequisite for the rational design of effective cancer immunotherapies. To date, attention has focused mainly on the role the adaptive immune system plays in controlling tumourigenesis, with conventional T cells, which recognize peptide antigens presented by classical MHC molecules, coming under close scrutiny. Accumulating reports now suggest that an additional T-cell subset, known as CD1d-restricted natural killer T (NKT) cells, also plays a pivotal role in modulating antitumour responses. Found in both humans and mice, CD1d-restricted NKT cells are a highly specialized cell type that, in contrast to conventional T cells, recognize lipid/glycolipid antigens presented by the non-classical MHC molecule CD1d. Several features of NKT cells, including their ability to rapidly produce large quantities of cytokines upon primary stimulation, make them ideal targets for developing anticancer immunotherapies. This intriguing cell type is the focus of this review.

Going both ways: immune regulation via CD1d-dependent NKT cells

NKT cells are a unique T lymphocyte sublineage that has been implicated in the regulation of immune responses associated with a broad range of diseases, including autoimmunity, infectious diseases, and cancer. In stark contrast to both conventional T lymphocytes and other types of Tregs, NKT cells are reactive to the nonclassical class I antigen-presenting molecule CD1d, and they recognize glycolipid antigens rather than peptides. Moreover, they can either up- or downregulate immune responses by promoting the secretion of Th1, Th2, or immune regulatory cytokines. This review will explore the diverse influences of these cells in various disease models, their ability to suppress or enhance immunity, and the potential for manipulating these cells as a novel form of immunotherapy.

Going both ways: immune regulation via CD1d-dependent NKT cells

NKT cells are a unique T lymphocyte sublineage that has been implicated in the regulation of immune responses associated with a broad range of diseases, including autoimmunity, infectious diseases, and cancer. In stark contrast to both conventional T lymphocytes and other types of Tregs, NKT cells are reactive to the nonclassical class I antigen-presenting molecule CD1d, and they recognize glycolipid antigens rather than peptides. Moreover, they can either up- or downregulate immune responses by promoting the secretion of Th1, Th2, or immune regulatory cytokines. This review will explore the diverse influences of these cells in various disease models, their ability to suppress or enhance immunity, and the potential for manipulating these cells as a novel form of immunotherapy.

Regulation of skin and islet allograft survival in mice treated with costimulation blockade is mediated by different CD4+ cell subsets and different mechanisms

BACKGROUND

Donor-specific transfusion (DST) and a brief course of anti-CD154 monoclonal antibody (mAb) induces permanent islet and prolonged skin allograft survival in mice. Induction of skin allograft survival requires the presence of CD4 cells and deletion of alloreactive CD8 cells. The specific roles of CD4 and CD4CD25 cells and the mechanism(s) by which they act are not fully understood.

METHODS

We used skin and islet allografts, a CD8 T cell receptor (TCR) transgenic model system, and in vivo depleting antibodies to analyze the role of CD4 cell subsets in regulating allograft survival in mice treated with DST and anti-CD154 mAb.

RESULTS

Deletion of CD4 or CD25 cells during costimulation blockade induced rapid rejection of skin but only minimally shortened islet allograft survival. Deletion of CD4 or CD25 cells had no effect upon survival of healed-in islet allografts, and CD25 cell deletion had no effect upon healed-in skin allograft survival. In the TCR transgenic model, DST plus anti-CD154 mAb treatment deleted alloreactive CD8 T cells, and anti-CD4 mAb treatment prevented that deletion. In contrast, injection of anti-CD25 mAb did not prevent alloreactive CD8 T cell deletion.

CONCLUSIONS

These data document that (1) both CD4CD25 and CD4CD25 cells are required for induction of skin allograft survival, (2) CD4CD25 T cells are not required for alloreactive CD8 T cell deletion, and (3) CD4CD25 regulatory cells are not critical for islet allograft tolerance. It appears that skin and islet transplantation tolerance are mediated by different CD4 cell subsets and different mechanisms.

Visualization of naturally occurring Foxp3+ regulatory T cells in normal and tumor-bearing mice

CD25+CD4+ regulatory T cells (Treg) play pivotal roles in the host response to tumors. However, their exact location in vivo is largely unknown. The forkhead/winged helix transcription factor, Foxp3, is specifically expressed in naturally occurring Treg (nTreg) and programs their development and function. In this study, we produced a rabbit polyclonal antibody (pAb), which can detect mouse Foxp3 protein in situ. Results using this pAb revealed that Foxp3+CD4+ nTreg cells occur in direct contact with CD11c+ dendritic cells (DCs), and Foxp3-CD4+ and CD8+T lymphocytes in the T cell regions of lymphoid tissues from normal and tumor-bearing mice. The numbers of Foxp3+CD4+ nTreg cells are significantly increased in draining, but not nondraining, lymph nodes (LNs) and spleen (SPL) of tumor-bearing mice. Furthermore, a small number of nTreg could be also found at the tumor site. These observations support the notion that the numbers of Foxp3+CD4+ nTreg are increased by tumors and may contribute to the immunosuppression observed in tumor-bearing hosts at secondary lymphoid organs and also possibly at the tumor site.

Identification of human tumor antigens and its implications for diagnosis and treatment of cancer

Human tumor antigens recognized by T cells have been identified by means of various molecular biological and immunological methods, including cDNA expression cloning with patients' T cells and antibodies, cDNA subtraction using RDA and PCR differential display, systematic gene analysis such as DNA sequencing, CGH, DNA chip/microarray and SAGE, in vitro T cell induction and immunization of HLA transgenic mice. The identification of human tumor antigens has led to a better understanding of the nature of tumor antigens, anti-tumor immune responses in patients before and after immunotherapy, and tumor escape mechanisms. The information obtained from these researches has enabled us to develop and improve immunotherapy by attempting to overcome the identified problems, including intrinsically low immunogenicity of tumor antigens and several escape mechanisms, such as regulatory T cell induction. The existence of immunogenic unique antigens derived from genetic alterations in tumor cells, and the varied immunogenicity of shared tumor antigens among patients due to differing expression in tumor cells and immunoreactivity of patients, indicates that individualized immunotherapy should ideally be performed. The identified antigens will also be useful for development of diagnostic methods and molecular targeting therapy for cancer.

The immunobiology of cancer immunosurveillance and immunoediting

The last fifteen years have seen a reemergence of interest in cancer immunosurveillance and a broadening of this concept into one termed cancer immunoediting. The latter, supported by strong experimental data derived from murine tumor models and provocative correlative data obtained by studying human cancer, holds that the immune system not only protects the host against development of primary nonviral cancers but also sculpts tumor immunogenicity. Cancer immunoediting is a process consisting of three phases: elimination (i.e., cancer immunosurveillance), equilibrium, and escape. Herein, we summarize the data supporting the existence of each of the three cancer immunoediting phases. The full understanding of the immunobiology of cancer immunosurveillance and immunoediting will hopefully stimulate development of more effective immunotherapeutic approaches to control and/or eliminate human cancers.

Naturally arising CD4+ regulatory t cells for immunologic self-tolerance and negative control of immune responses

Naturally occurring CD4+ regulatory T cells, the majority of which express CD25, are engaged in dominant control of self-reactive T cells, contributing to the maintenance of immunologic self-tolerance. Their depletion or functional alteration leads to the development of autoimmune disease in otherwise normal animals. The majority, if not all, of such CD25+CD4+ regulatory T cells are produced by the normal thymus as a functionally distinct and mature subpopulation of T cells. Their repertoire of antigen specificities is as broad as that of naive T cells, and they are capable of recognizing both self and nonself antigens, thus enabling them to control various immune responses. In addition to antigen recognition, signals through various accessory molecules and via cytokines control their activation, expansion, and survival, and tune their suppressive activity. Furthermore, the generation of CD25+CD4+ regulatory T cells in the immune system is at least in part developmentally and genetically controlled. Genetic defects that primarily affect their development or function can indeed be a primary cause of autoimmune and other inflammatory disorders in humans. Based on recent advances in our understanding of the cellular and molecular basis of this T cell-mediated immune regulation, this review discusses how naturally arising CD25+CD4+ regulatory T cells contribute to the maintenance of immunologic self-tolerance and negative control of various immune responses, and how they can be exploited to prevent and treat autoimmune disease, allergy, cancer, and chronic infection, or establish donor-specific transplantation tolerance.

Allergen-responsive CD4+CD25+ regulatory T cells in children who have outgrown cow's milk allergy

Cow's milk allergy in children is often of short duration, which makes this disorder an interesting clinical model for studies of tolerance to dietary antigens. Here, we studied T cell responses in 21 initially allergic children who, after a milk-free period of >2 mo, had cow's milk reintroduced to their diet. Children who outgrew their allergy (tolerant children) had higher frequencies of circulating CD4⁺CD25⁺ T cells and decreased in vitro proliferative responses to bovine β-lactoglobulin in peripheral blood mononuclear cells (PBMCs) compared with children who maintained clinically active allergy. No significant difference in proliferative activity stimulated by the polyclonal mitogen phytohemagglutinin was observed between the two groups. Depletion of CD25⁺ cells from PBMCs of tolerant children led to a fivefold increase in in vitro proliferation against β-lactoglobulin. This suggests that tolerance is associated with the appearance of circulating CD4⁺CD25⁺ regulatory T (Treg) cells that are capable of suppressing the effector T cells generated 1 wk after reintroduction of cow's milk. The suppressive function of the CD4⁺CD25⁺ Treg cells was shown to be partly cell contact dependent. Collectively, our study provides human data to suggest that mucosal induction of tolerance against dietary antigens is associated with the development of CD4⁺CD25⁺ Treg cells.

[Development of immunotherapy for cancer: lessons from melanoma research]

Identification of human melanoma antigens by various molecular biological and immunological techniques and evaluation of tumor reactive T cells in patients with the identified tumor antigen and HLA tetramer technology, not only provided us more profound understanding of anti-tumor immune responses in human, but also led to reveal basic problems in each step towards immunological tumor rejection, including systemic suppressive mechanisms such as regulatory T cell induction and local inhibitory environment in tumors. Based on these results obtained from the basic and clinical researches, various improvements have been applied for immunotherapy, including active immunization with modified antigenic peptides and recombinant virus, T cell adoptive transfer with lymphodepletive pretreatment, and administration of anti-CTLA-4 Ab, although further improvement is necessary. The translational research performed on melanoma, would facilitate development of immunotherapy for other cancers.