The common cytokine receptor gamma chain plays an essential role in regulating lymphoid homeostasis

Soluble factors from TLR4- or TCR-activated cells contribute to stability of the resting phenotype and increase the expression of CXCR4 of human memory CD4 T cells

It has been proposed that cytokines can induce activation of resting T cells in an antigen-independent manner. However, experimental conditions have included the use of fetal serum and nanogram concentrations of added cytokines. To evaluate the effect of cytokines and chemokines generated by activated immune cells on the phenotypic profile of human memory CD4 T cells, the cells were cultured in FBS-free conditions in the presence of IL-15 and 5% of hAB serum and incubated with conditioned medium (CM) obtained from PBMC activated through the TCR using anti-CD3/CD28/CD2 antibodies (TCR-CM) or through TLR4 using bacterial LPS (TLR4-CM). Cytokines and chemokines present in the CMs were evaluated by ProcartaPlex immunoassay. Cell viability, proliferation, and surface markers were determined by flow cytometry on day 2, 5, and 8 of culture. Cell viability was maintained by TLR4-CM plus IL-15 for 8 days but decreased in the presence of the TCR-CM plus IL-15. In combination with IL-15, the TLR4-CM, but not the TCR-CM, maintained the expression of CD3 and CD4 stable. Both conditions stabilized the expression of CD45RO and CCR5. Thus, the TLR4-CM better supported the viability and stability of the memory phenotype. None of the CMs induced proliferation or expression of activation markers; however, they induced an increased expression of CXCR4. This study indicates that resting memory CD4 T cells are not activated by, but may be sensitive to soluble factors produced by antigen or PAMP-stimulated cells, which may contribute to their homeostasis and favor the CXCR4 expression.

Protein Arginine Methyltransferase 5 in T Lymphocyte Biology

Protein arginine methyltransferase 5 (PRMT5) is the major methyltransferase (MT) catalyzing symmetric dimethylation (SDM). PRMT5 regulates developmental, homeostatic and disease processes in vertebrates and invertebrates, and a carcinogenic role has been observed in mammals. Recently, tools generated for PRMT5 loss of function have allowed researchers to demonstrate essential roles for PRMT5 in mouse and human lymphocyte biology. PRMT5 modulates CD4⁺ and CD8⁺ T cell development in the thymus, peripheral homeostasis, and differentiation into CD4⁺ helper T lymphocyte (Th)17 cell phenotypes. Here, we provide a timely review of the milestones leading to our current understanding of PRMT5 in T cell biology, discuss current tools to modify PRMT5 expression/activity, and highlight mechanistic pathways.

Specific Inhibition of Soluble γc Receptor Attenuates Collagen-Induced Arthritis by Modulating the Inflammatory T Cell Responses

IL-17 produced by Th17 cells has been implicated in the pathogenesis of rheumatoid arthritis (RA). It is important to prevent the differentiation of Th17 cells in RA. Homodimeric soluble γc (sγc) impairs IL-2 signaling and enhances Th17 differentiation. Thus, we aimed to block the functions of sγc by inhibiting the formation of homodimeric sγc. The homodimeric form of sγc was strikingly disturbed by sγc-binding DNA aptamer. Moreover, the aptamer effectively inhibited Th17 cell differentiation and restored IL-2 and IL-15 signaling impaired by sγc with evidences of increased survival of T cells. sγc was highly expressed in SF of RA patients and increased in established CIA mice. The therapeutic effect of PEG-aptamer was tested in CIA model and its treatment alleviated arthritis pathogenesis with impaired differentiation of pathogenic Th17, NKT1, and NKT17 cells in inflamed joint. Homodimeric sγc has pathogenic roles to exacerbate RA progression with differentiation of local Th17, NKT1, and NKT17 cells. Therefore, sγc is suggested as target of a therapeutic strategy for RA.

Fas/FasL signaling is critical for the survival of exhausted antigen-specific CD8+ T cells during tumor immune response

Antigen (Ag)-specific activated CD8⁺ T cells are critical for tumor elimination but become exhausted, and thus, dysfunctional during immune response against the tumor due to chronic antigen stimulation. The signaling of immune checkpoint receptors is known to be a critical component in this exhaustion; however, the fate of these exhausted CD8⁺ T cells remains unclear. Therefore, to elucidate this, we followed the fate of Ag-specific CD8⁺ T cells by directly visualizing them using MHC class I tetramers coupled with ovoalubumin_257-264 in C57BL/6 mice inoculated with EG.7. We found that the number of generated Ag-specific activated CD8⁺ T cells decreased via apoptosis during a prolonged tumor immune response. However, the number of Ag-specific CD8⁺ T cells was significantly higher in Fas ligand (FasL)-dysfunctional gld mice than in control mice, resulting in suppressed tumor growth. In contrast, the enforced expression of Bcl-2 failed to rescue apoptosis of the exhausted CD8⁺ T cells following EG.7 inoculation. These results suggest that Fas/FasL signaling is critical for the survival of exhausted CD8⁺ T cells during the tumor immune response.

IL-7 Induces an Epitope Masking of γc Protein in IL-7 Receptor Signaling Complex

IL-7 signaling via IL-7Rα and common γ-chain (γc) is necessary for the development and homeostasis of T cells. Although the delicate mechanism in which IL-7Rα downregulation allows the homeostasis of T cell with limited IL-7 has been well known, the exact mechanism behind the interaction between IL-7Rα and γc in the absence or presence of IL-7 remains unclear. Additionally, we are still uncertain as to how only IL-7Rα is separately downregulated by the binding of IL-7 from the IL-7Rα/γc complex. We demonstrate here that 4G3, TUGm2, and 3E12 epitope masking of γc protein are induced in the presence of IL-7, indicating that the epitope alteration is induced by IL-7 binding to the preassembled receptor core. Moreover, the epitope masking of γc protein is inversely correlated with the expression of IL-7Rα upon IL-7 binding, implying that the structural alteration of γc might be involved in the regulation of IL-7Rα expression. The conformational change in γc upon IL-7 binding may contribute not only to forming the functional IL-7 signaling complex but also to optimally regulating the expression of IL-7Rα.

Janus kinase inhibition for immunosuppression in solid organ transplantation: Is there a role in complex immunologic challenges?

Inhibition of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway for immunosuppression in solid organ transplantation is appealing due to its specificity for immune cell function, particularly for JAK3. This is due to its unique association with only the common gamma chain (γ_c). The γ_c is an appealing immunosuppression target in transplantation because of the critically important lymphokines that act at it, including IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. Tofacitinib was initially purported to selectively inhibit solely JAK3, but subsequent analyses have also demonstrated its activity at the other members of the JAK family. Clinical outcomes have validated tofacitinib's pan-JAK activity in kidney transplantation after demonstrating an increased risk of infection and malignancy as compared to CNI-based regimens. After these trials, tofacitinib investigation for use in transplantation has effectively ceased. However, a post-hoc analysis has shed new light on the monitoring of tofacitinib exposure in order to predict infection and oncologic events. With new methods to monitor tofacitinib exposure, clinicians may be able to effectively reduce toxicities while providing a high level of immunosuppression. The purpose of this review to identify when, and for whom, JAK inhibitors may provide benefit in solid organ transplantation.

Stromal-Derived Factor-1α and Interleukin-7 Treatment Improves Homeostatic Proliferation of Naïve CD4(+) T Cells after Allogeneic Stem Cell Transplantation

Graft-versus-host disease (GVHD) impairs immune reconstitution after allogeneic stem cell transplantation (allo-SCT) and effective therapies aimed at restoring T cell counts in GVHD patients have yet to be developed. During GVHD, CD4(+) T cell reconstitution is particularly affected and current models hold that GVHD insult to the peripheral lymphoid niche is responsible for this effect. Here, we show that naïve CD4(+) T cell homeostatic proliferation (HP) is lost during GVHD because of low systemic IL-7 and impaired dendritic cell (DC) regeneration. We assessed factors involved in DC differentiation and found that although fms-like tyrosine kinase 3 ligand (Flt3-L) levels were normal, stromal-derived factor-1α (SDF-1α) was diminished in the blood of GVHD mice. Unlike Flt3-L treatment, the administration of SDF-1α specifically increased CD8α(+) DC numbers and did not worsen GVHD. Importantly, CD4(+) T cell HP was enhanced only when IL-7 and SDF-1α or Flt3L were coadministered, confirming the crucial role of DCs and IL-7 in restoring CD4(+) T cell regeneration during GVHD. Altogether, our results indicate that CD8α(+) DCs are part of the peripheral niche that controls CD4(+) T cell HP and that their depletion, combined with low systemic IL-7, explains how GVHD constrains naïve CD4(+) T cell reconstitution after allo-SCT.

Protecting and rescuing the effectors: roles of differentiation and survival in the control of memory T cell development

Vaccines, arguably the single most important intervention in improving human health, have exploited the phenomenon of immunological memory. The elicitation of memory T cells is often an essential part of successful long-lived protective immunity. Our understanding of T cell memory has been greatly aided by the development of TCR Tg mice and MHC tetrameric staining reagents that have allowed the precise tracking of antigen-specific T cell responses. Indeed, following acute infection or immunization, naïve T cells undergo a massive expansion culminating in the generation of a robust effector T cell population. This peak effector response is relatively short-lived and, while most effector T cells die by apoptosis, some remain and develop into memory cells. Although the molecular mechanisms underlying this cell fate decision remain incompletely defined, substantial progress has been made, particularly with regards to CD8(+) T cells. For example, the effector CD8(+) T cells generated during a response are heterogeneous, consisting of cells with more or less potential to develop into full-fledged memory cells. Development of CD8(+) T cell memory is regulated by the transcriptional programs that control the differentiation and survival of effector T cells. While the type of antigenic stimulation and level of inflammation control effector CD8(+) T cell differentiation, availability of cytokines and their ability to control expression and function of Bcl-2 family members governs their survival. These distinct differentiation and survival programs may allow for finer therapeutic intervention to control both the quality and quantity of CD8(+) T cell memory. Effector to memory transition of CD4(+) T cells is less well characterized than CD8(+) T cells, emerging details will be discussed. This review will focus on the recent progress made in our understanding of the mechanisms underlying the development of T cell memory with an emphasis on factors controlling survival of effector T cells.

Antigen-Experienced CD4lo T Cells Are Linked to Deficient Contraction of the Immune Response in Autoimmune Diabetes

Following proper activation, naïve “CD4lo” T cells differentiate into effector T cells with enhanced expression of CD4 -“CD4hi” effectors. Autoimmune diabetes-prone NOD mice display a unique set of antigen-experienced “CD4lo” T cells that persist after primary stimulation. Here, we report that a population of such cells remained after secondary and tertiary TCR stimulation and produced cytokines upon antigenic challenge. However, when NOD blasts were induced in the presence of rIL-15, the number of antigen-experienced “CD4lo” T cells was significantly reduced. Clonal contraction, mediated in part by CD95-dependent activation-induced cell death (AICD), normally regulates the accumulation of “CD4hi” effectors. Interestingly, CD95 expression was dramatically reduced on the AICD-resistant NOD “CD4lo” T cells. Thus, while autoimmune disease has often been attributed to the engagement of robust autoimmunity, we suggest that the inability to effectively contract the immune response distinguishes benign autoimmunity from progressive autoimmune diseases that are characterized by chronic T cell-mediated inflammation.

Self-specific CD8+ T cells maintain a semi-naive state following lymphopenia-induced proliferation

Upon transfer into T cell-deficient hosts, naive CD8(+) T cells typically undergo lymphopenia-induced proliferation (LIP, also called homeostatic proliferation) and develop the phenotypic and functional characteristics of memory CD8(+) T cells. However, the capacity of T cells with self-peptide/MHC specificity to respond in this way has not been intensively studied. We examined pmel-1 TCR transgenic CD8(+) T cells that are specific for an epitope from gp100, a protein expressed by melanoma cells and normal melanocytes. Despite their self-specificity, naive pmel-1 cells were inefficient at LIP in typical lymphopenic hosts. In CD132 (common gamma-chain)-deficient hosts, pmel-1 CD8(+) T cells underwent extensive proliferation, but, surprisingly, the majority of these cells retained certain naive phenotypic traits (CD44(low), CD122(low)) rather than acquiring the expected central-memory phenotype. Following LIP, pmel-1 T cells acquired the capacity to control B16F10 tumor growth, but only in common gamma-chain-deficient host mice. Together, these data suggest that LIP does not always favor expansion of self-specific CD8 T cells and that sustained extensive lymphopenia is required for such cells to exhibit tumor control.

Tumor-shed PGE(2) impairs IL2Rgammac-signaling to inhibit CD4 T cell survival: regulation by theaflavins

Background

Many tumors are associated with decreased cellular immunity and elevated levels of prostaglandin E2 (PGE2), a known inhibitor of CD4+ T cell activation and inducer of type-2 cytokine bias. However, the role of this immunomodulator in the survival of T helper cells remained unclear. Since CD4+ T cells play critical roles in cell-mediated immunity, detail knowledge of the effect tumor-derived PGE2 might have on CD4+ T cell survival and the underlying mechanism may, therefore, help to overcome the overall immune deviation in cancer.

Methodology/Principal Findings

By culturing purified human peripheral CD4+ T cells or Jurkat cells with spent media of theaflavin- or celecoxib-pre-treated MCF-7 cells, we show that tumor-shed PGE2 severely impairs interleukin 2 receptor γc (IL2Rγc)-mediated survival signaling in CD4+ T cells. Indeed, tumor-shed PGE2 down-regulates IL2Rγc expression, reduces phosphorylation as well as activation of Janus kinase 3 (Jak-3)/signal transducer and activator of transcription 5 (Stat-5) and decreases Bcl-2/Bax ratio thereby leading to activation of intrinsic apoptotic pathway. Constitutively active Stat-5A (Stat-5A1*6) over-expression efficiently elevates Bcl-2 levels in CD4+ T cells and protects them from tumor-induced death while dominant-negative Stat-5A over-expression fails to do so, indicating the importance of Stat-5A-signaling in CD4+ T cell survival. Further support towards the involvement of PGE2 comes from the results that (a) purified synthetic PGE2 induces CD4+ T cell apoptosis, and (b) when knocked out by small interfering RNA, cyclooxygenase-2 (Cox-2)-defective tumor cells fail to initiate death. Interestingly, the entire phenomena could be reverted back by theaflavins that restore cytokine-dependent IL2Rγc/Jak-3/Stat-5A signaling in CD4+ T cells thereby protecting them from tumor-shed PGE2-induced apoptosis.

Conclusions/Significance

These data strongly suggest that tumor-shed PGE2 is an important factor leading to CD4+ T cell apoptosis during cancer and raise the possibility that theaflavins may have the potential as an effective immunorestorer in cancer-bearer.

Opposing effects of TGF-beta and IL-15 cytokines control the number of short-lived effector CD8+ T cells

An effective immune response against infectious agents involves massive expansion of CD8(+) T cells. Once the infection is cleared, the majority of these effector cells die through unknown mechanisms. How is expansion controlled to maximize pathogen clearance and minimize immunopathology? We found, after Listeria infection, plasma transforming growth factor beta (TGF-beta) titers increased concomitant with the expansion of effector CD8(+) T cells. Blocking TGF-beta signaling did not affect effector function of CD8(+) T cells. However, TGF-beta controlled effector cell number by lowering Bcl-2 amounts and selectively promoting the apoptosis of short-lived effector cells. TGF-beta-mediated apoptosis of this effector subpopulation occurred during clonal expansion and contraction, whereas interleukin-15 (IL-15) promoted their survival only during contraction. We demonstrate that the number of effector CD8(+) T cells is tightly controlled by multiple extrinsic signals throughout effector differentiation; this plasticity should be exploited during vaccine design and immunotherapy against tumors and autoimmune diseases.

New insights into the regulation of T cells by gamma(c) family cytokines

Common cytokine receptor gamma-chain (gamma(c)) family cytokines have crucial roles in the development, proliferation, survival and differentiation of multiple cell lineages of both the innate and adaptive immune systems. In this Review, we focus on our current understanding of the distinct and overlapping effects of interleukin-2 (IL-2), IL-7, IL-9, IL-15 and IL-21, as well as the IL-7-related cytokine thymic stromal lymphopoietin (TSLP), on the survival and proliferation of conventional alphabeta T cells, gammadelta T cells and regulatory T cells. This knowledge potentially allows for the therapeutic manipulation of immune responses for the treatment of cancer, autoimmunity, allergic diseases and immunodeficiency, as well as for vaccine development.

The Immune Privilege of the Eye: Human Retinal Pigment Epithelial Cells Selectively Modulate T-Cell ActivationIn Vitro

PURPOSE

To examine the effect of human retinal pigment epithelial (RPE) cells on phytohemagglutinin (PHA) activation of T cells.

METHODS

Resting peripheral blood lymphocytes (PBLs) were stimulated with PHA with or without the presence of gamma-irradiated RPE cells. Proliferation and the cell cycle profile were thereafter investigated by 3H-thymidine incorporation and flow cytometric analysis. In addition, the PBLs expression of CD69, major histocompatibility complex (MHC) class I and II, CD3, as well as the IL-2 receptor chains were evaluated by flow cytometry, and the content of IL-2 in cell culture supernatant was measured by ELISA.

RESULTS

Human RPE cells were found to suppress PHA-induced proliferation, cyclin A, IL-2R-alpha and -gamma, and CD71 expression and decrease the production of IL-2; but RPE cells do not inhibit the PHA-induced expression of early activation markers CD69, MHC class I and II, and of cyclin D of the PBLs.

CONCLUSIONS

These results are the first to indicate that RPE cells impede generation of activated T cells by interfering with the induction of high-affinity IL-2R-alphabetagamma, IL-2 production, and the expression of CD71 and cyclin A.

IL-15 protects antigen-specific CD8+ T cell contraction after Mycobacterium bovis bacillus Calmette-Guérin infection

We reported previously that IL-15 plays a critical role in protecting effector CD8(+) T cells from apoptosis during the contraction phase following acute infection with Listeria monocytogenes by inducing antiapoptotic molecules. In the present study, we examined the effects of in vivo administration of rIL-15 on contraction of CD8(+) T cells after chronic infection with Mycobacterium bovis BCG and on the efficacy of BCG vaccination against Mycobacterium tuberculosis infection. Antigen-specific CD8(+) T cells reached an expansion peak at approximately Day 21, followed by a contraction after inoculation with rBCG expressing OVA. In vivo administration of rIL-15 from Days 22 to 42 after BCG inoculation inhibited apoptosis of effector CD8(+) T cells by up-regulating their Bcl-2 expression, resulting in a significant increase of antigen-specific memory CD8(+) T cells producing IFN-gamma. However, the IL-15 treatment did not elicit improved efficacy of BCG vaccination against M. tuberculosis. These results suggest that IL-15 plays a critical role in protecting activated CD8(+) T cells from apoptosis during the contraction phase following BCG inoculation, although IL-15 administration alone at the contraction phase might not be sufficient to protect the efficient memory T cell responses against subsequent infection with M. tuberculosis.

Distinct and overlapping patterns of cytokine regulation of thymic and bone marrow-derived NK cell development

Although bone marrow (BM) represents the main site for postnatal NK cell development, recently a distinct thymic-dependent NK cell pathway was identified. These studies were designed to investigate the role of cytokines in regulation of thymic NK cells and to compare with established regulatory pathways of BM-dependent NK cell compartment. The common cytokine receptor gamma-chain (Il2rg) essential for IL-15-induced signaling, and FMS-like tyrosine kinase 3 (FLT3) receptor ligand (Flt3l) were previously identified as important regulatory pathways of the BM NK cell compartment based on lack of function studies in mice, however their complementary action remains unknown. By investigating mice double-deficient in Il2rg and Flt3l (Flt3l(-/-) Il2rg(-/-)), we demonstrate that FLT3L is important for IL2Rg-independent maintenance of both immature BM as well as peripheral NK cells. In contrast to IL-7, which is dispensable for BM but important for thymic NK cells, IL-15 has a direct and important role in both thymic and BM NK cell compartments. Although thymic NK cells were not affected in Flt3l(-/-) mice, Flt3l(-/-)Il2rg(-/-) mice lacked detectable thymic NK cells, suggesting that FLT3L is also important for IL-2Rg-independent maintenance of thymic NK cells. Thus, IL-2Rg cytokines and FLT3L play complementary roles and are indispensable for homeostasis of both BM and thymic dependent NK cell development, suggesting that the cytokine pathways crucial for these two distinct NK cell pathways are largely overlapping.

Endogenously produced IL-4 nonredundantly stimulates CD8+ T cell proliferation

T cell proliferation and survival are regulated by the cytokine receptor common gamma-chain-associated cytokines IL-2, IL-7, and IL-15, while IL-4, another gamma-chain-associated cytokine, is thought to primarily affect T cell quality rather than quantity. In contrast, our experiments reveal that endogenously produced IL-4 is a direct, nonredundant, and potent stimulator of CD8(+) T cell proliferation in Ag- and pathogen-induced CD8(+) T cell responses. These stimulatory effects of IL-4 are observed in both BALB/c and C57BL/6 mice and activate both naive and memory/activated phenotype CD8(+) T cells, although the former are stimulated less than are the latter. IL-4 effects are IL-7- and IL-15-independent, but MHC class I-dependent stimulation appears to be required for the mitogenic effect of IL-4 on naive phenotype CD8(+) T cells. Thus, endogenously produced IL-4 is an important regulator of quantitative as well as qualitative aspects of T cell immunity.

Use of humanized severe combined immunodeficient mice for human vaccine development

The severe combined immunodeficient (SCID) mouse has no adaptive immunity, lacking mature T and B cells in the peripheral blood or the lymphoid organs. It has been used extensively in biomedical research as a valuable translational model for xeno-engraftment of human tissues and cells. This review focuses on the engraftment of human peripheral blood cells and tissues in SCID mice, as well as in the newly established and more permissive SCID mice deficient in the IL-2 receptor gamma-chain. Human immune responses could be elicited and assessed in these humanized SCID mice upon vaccination or sensitization with allogeneic tissues. A translational model is proposed to attain preclinical data for testing human vaccines.

Post-transplant adoptive T-cell immunotherapy

Immune reconstitution following haematopoietic stem cell transplantation (SCT) is an often slow and incomplete process that leads to increased risk of infection and malignant disease. Immunization in SCT is frequently unsuccessful due to the prolonged lymphopenia, especially of CD4 T cells, seen following transplant. The transfusion of T cells, also called 'adoptive T-cell therapy', has the potential to enhance anti-tumour and overall immunity, and augment vaccine efficacy in the post-transplant setting. Recent advances in tissue culture, cellular immunology and tumour biology are guiding new approaches to adoptive T-cell therapy. This chapter will discuss the challenges that face the field before adoptive T-cell therapy can be translated into routine clinical practice.

Increased T-cell survival by structural bronchial cells derived from asthmatic subjects cultured in an engineered human mucosa

BACKGROUND

Interaction between lymphocytes and structural cells has been proposed as a key factor in regulating inflammation in asthma.

OBJECTIVE

This study was designed to investigate the effect of epithelial cells and fibroblasts on T-lymphocyte survival by using a 3-dimensional tissue-engineered model.

METHODS

Engineered human bronchial mucosal tissues were produced by using fibroblasts, epithelial cells, and autologous T cells from asthmatic and healthy donors. T-cell apoptosis and apoptotic marker expression by T cells were evaluated by using the terminal deoxynucleotidyl transferase biotinylated d-UTP nick end-labeling technique and immunofluorescence, respectively. Cytokines implicated in T-cell survival were measured by means of ELISA in culture supernatants.

RESULTS

We demonstrated histologically that we were able to generate a well-structured engineered bronchial mucosa by using epithelial cells, fibroblasts, and T cells cultured from healthy and asthmatic subjects. Structural cells from asthmatic subjects cultured in this model induced a significant decrease in the ability of T cells to undergo apoptosis represented by a decrease in DNA fragmentation and proapoptotic molecule expression (Bcl-2-associated X protein and Fas ligand). Structural cells from healthy control subjects have no effect. Among cytokines measured in the supernatants, only TGF-beta(1) was significantly increased in the model derived from cells of asthmatic subjects.

CONCLUSION

These results support the concept that bronchial structural cells might play a critical role in the regulation of inflammation in asthma by increasing the survival of T lymphocytes. The results also further validated the model as a tool for investigating the interaction between inflammatory and structural cells.

Long-term exposure to superantigen induces p27Kip1 and Bcl-2 expression in effector memory CD4+ T cells

The long-term exposure of mice to superantigen SEA using a mini-osmotic pump (SEA pump) induced a long-lasting expansion of Vbeta3+ CD4+ T cells with T helper (Th) 2 cell-type properties. Removal of the SEA pump 10 days after pump implantation did not significantly alter the level of Vbeta3+ CD4+ T cell expansion/maintenance. Furthermore, CFSE-labeled CD4+ T cells failed to divide when transferred to post-implantation day 15 mice. Thus, CD4+ T cells appeared to survive for at least 30 days in the absence of a sufficient amount of antigen to trigger cell division. STAT6 deficient mice, in which Th2 cell development is largely impaired, also exhibited a protracted cell expansion, similar to that observed in normal mice, suggesting that the Th2 cell property is dispensable for the maintenance of Vbeta3+ CD4+ T cell expansion. The expanded CD4+ T cells on post-implantation day 26 were arrested in the G0/G1 phase of the cell cycle and showed a lower level of cell division upon restimulation. The Cdk inhibitor p27(Kip1) was highly expressed, and Cdk2 was downregulated. Moreover, the CD4+ T cells were resistant to in vitro apoptosis induction in parallel with their level of Bcl-2 expression. Collectively, the Vbeta3+ CD4+ T cells appeared to develop into long-lived memory T cells with cell cycle arrest upon long-term exposure to SEA.

gamma(c) cytokines provide multiple homeostatic signals to naive CD4(+) T cells

Cytokines signaling through receptors sharing the common gamma chain (gamma(c)), including IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21, are critical for the generation and peripheral homeostasis of B, T and NK cells. To identify unique or redundant roles for gamma(c) cytokines in naive CD4(+) T cells, we compared monoclonal populations of CD4(+) T cells from TCR-Tg mice that were gamma(c) (+), gamma(c) (-), CD127(-/-) or CD122(-/-). We found that gamma(c) (-) naive CD4(+) T cells failed to accumulate in the peripheral lymphoid organs and the few remaining cells were characterized by small size, decreased expression of MHC class I and enhanced apoptosis. By over-expressing human Bcl-2, peripheral naive CD4(+) T cells that lack gamma(c) could be rescued. Bcl-2(+) gamma(c) (-) CD4(+) T cells demonstrated enhanced survival characteristics in vivo and in vitro, and could proliferate normally in vitro in response to antigen. Nevertheless, Bcl-2(+) gamma(c) (-) CD4(+) T cells remained small in size, and this phenotype was not corrected by enforced expression of an activated protein kinase B. We conclude that gamma(c) cytokines (primarily but not exclusively IL-7) provide Bcl-2-dependent as well as Bcl-2-independent signals to maintain the phenotype and homeostasis of the peripheral naive CD4(+) T cell pool.

Staying alive--naïve CD4(+) T cell homeostasis

The immune system must maintain a broad repertoire of naïve T cells in order to respond to the diverse range of pathogens that it will encounter over the course of a lifetime. Although it is known that contact with IL-7 is crucial for the survival of naïve T cells, the precise intracellular signals that mediate its effects remain obscure. An article in this issue of the European Journal of Immunology has found that IL-7 requires the coordinated action of multiple pathways to maintain naïve CD4(+) T cells.

Gamma c cytokines condition the progressive differentiation of CD4+ T cells

After their initial antigen encounter in the secondary lymphoid organs, activated T cells must receive additional signals in the peripheral tissues to fully differentiate. Here, we provide evidence that gamma(c) cytokines are critical during this process. Using the Marilyn (Ml) T cell antigen receptor (TCR) transgenic model, we show that male skin grafts are tolerated in the absence of gamma(c), but that Ml CD4(+) T cells proliferate normally in response to antigen, traffic to the graft site and recruit an inflammatory response [including natural killer (NK) cells, neutrophils, and macrophages] that is independent of T cell gamma(c) expression. Whereas wild-type T cells demonstrate a progressive differentiation phenotype from the spleen to the tissues, skin-infiltrating effector T cells (CD44(hi)CD62L(lo)) from gamma(c)(-) mice were phenotypically abnormal with reduced ICOS, NKG2D, granzyme B, and IFN-gamma expression. These defects could be mapped to deficiencies in IL-2 and, surprisingly, IL-15. These results define a late checkpoint in T cell differentiation in the tissues where gamma(c) cytokines, including IL-15, authenticate CD4(+) T cell effector functions.

Development of anti-PAX3 immune responses; a target for cancer immunotherapy

PAX3 is overexpressed in several human cancers and is absent from normal adult human tissues. It is known to have an oncogenic function in human malignancy, and is therefore a promising target for cancer immunotherapy. We screened the murine and human PAX3 amino acid sequences for peptides that bind common MHC class I types, and identified murine GVFINGRPL and human KLTEARVQV sequences. Mice immunised with either a selected PAX3 peptide, or with a PAX3 expressing DNA vector, developed specific anti-PAX3 immune responses that inhibited tumour growth. The intensity of the immune response was significantly enhanced by pulsing of the peptide onto dendritic cells. Anti-PAX3 T cell lines were established from splenocytes of immunised mice. Intravenous administration of anti-PAX3 T cells caused regression of established tumours indicating a promising clinical application for anti-PAX3 immunotherapy. The human peptide stimulated growth of similar T cell lines from peripheral blood of three out of three normal human blood donors. These showed specific cytotoxicity against a range of human PAX3+ and HLA-A2+ cancer cell lines. Moreover, an anti-PAX3 response was detected as a component of the anti-tumour immune response in a patient treated with lysate pulsed dendritic cell vaccination. The ability to generate strong and specific anti PAX3 immune responses from the T cell repertoire in both mice and humans, provides evidence for PAX3 as a promising target for immunotherapy of cancer.

Critical regulation of CD4+ T cell survival and autoimmunity by beta-arrestin 1

CD4+ T cells are important in adaptive immunity, but their dysregulation can cause autoimmunity. Here we demonstrate that the multifunctional adaptor protein beta-arrestin 1 positively regulated naive and activated CD4+ T cell survival. We found enhanced expression of the proto-oncogene Bcl2 through beta-arrestin 1-dependent regulation of acetylation of histone H4 at the Bcl2 promoter. Mice deficient in the gene encoding beta-arrestin 1 (Arrb1) were much more resistant to experimental autoimmune encephalomyelitis, whereas overexpression of Arrb1 increased susceptibility to this disease. CD4+ T cells from patients with multiple sclerosis had much higher Arrb1 expression, and 'knockdown' of Arrb1 by RNA-mediated interference in those cells increased apoptosis induced by cytokine withdrawal. Our data demonstrate that beta-arrestin 1 is critical for CD4+ T cell survival and is a factor in susceptibility to autoimmunity.

Principles of adoptive T cell cancer therapy

The transfusion of T cells, also called adoptive T cell therapy, is an effective treatment for viral infections and has induced regression of cancer in early-stage clinical trials. However, recent advances in cellular immunology and tumor biology are guiding new approaches to adoptive T cell therapy. For example, use of engineered T cells is being tested as a strategy to improve the functions of effector and memory T cells, and manipulation of the host to overcome immunotoxic effects in the tumor microenvironment has led to promising results in early-stage clinical trials. Challenges that face the field and must be addressed before adoptive T cell therapy can be translated into routine clinical practice are discussed.

Reduced CD4+ T-cell-specific gene expression in human type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) in humans is characterized by the T-cell-dependent destruction of the insulin producing pancreatic beta cells; however, the precise pathogenesis of the disease, especially the initiation of pathologic immune response, is still largely unknown. We hypothesized that the function of human CD4+ T cells is altered in T1DM and analyzed unstimulated human peripheral blood CD4+ T-cell gene expression. We used a novel three-way comparison of DNA microarray data of CD4+ T cells isolated from patients with new onset T1DM, patients with long-term Type 2 diabetes (T2DM), and from healthy control subjects in order to eliminate any possible influence of glucose homeostasis on our findings. We analyzed the T1DM specific gene-expression changes and their functional relevance to T1DM autoimmunity. Our genetic and functional data show that T1DM CD4+ T cells are down-regulated specifically affecting key immune functions and cell cycle. Histone deacetylase gene expression, a key regulator of epigenetic modification is also reduced. The CD4+ T cells showed impaired function, including an abnormal immune response, which may be a key element that leads to the breakdown of self-tolerance.

Human Resting CD4+ T Cells Are Constitutively Inhibited by TGFβ under Steady-State Conditions

Based on studies in knockout mice, several inhibitory factors such as TGFbeta, IL-10, or CTLA-4 have been implicated as gate keepers of adaptive immune responses. Lack of these inhibitory molecules leads to massive inflammatory responses mainly mediated by activated T cells. In humans, the integration of these inhibitory signals for keeping T cells at a resting state is less well understood. To elucidate this regulatory network, we assessed early genome-wide transcriptional changes during serum deprivation in human mature CD4(+) T cells. The most striking observation was a "TGFbeta loss signature" defined by down-regulation of many known TGFbeta target genes. Moreover, numerous novel TGFbeta target genes were identified that are under the suppressive control of TGFbeta. Expression of these genes was up-regulated once TGFbeta signaling was lost during serum deprivation and again suppressed upon TGFbeta reconstitution. Constitutive TGFbeta signaling was corroborated by demonstrating phosphorylated SMAD2/3 in resting human CD4(+) T cells in situ, which were dephosphorylated during serum deprivation and rephosphorylated by minute amounts of TGFbeta. Loss of TGFbeta signaling was particularly important for T cell proliferation induced by low-level TCR and costimulatory signals. We suggest TGFbeta to be the most prominent factor actively keeping human CD4(+) T cells at a resting state.

Expression of Tyk2 in dendritic cells is required for IL-12, IL-23, and IFN-gamma production and the induction of Th1 cell differentiation

It is well documented that dendritic cells (DCs), representative antigen-presenting cells, are important sources of Th1-promoting cytokines and are actively involved in the regulation of T-helper-cell differentiation. However, the intracellular event that regulates this process is still largely unknown. In this study, we examined the role of Tyk2, a JAK kinase that is involved in the signaling pathway under IL-12 and IL-23, in DC functions. While the differentiation and maturation of DCs was normal in Tyk2-deficient (Tyk2(-/-)) mice, IL-12-induced Stat4 phosphorylation was diminished in Tyk2(-/-) DCs. IL-12-induced IFN-gamma production was also significantly diminished in Tyk2(-/-) DCs to levels similar to those in Stat4(-/-) DCs. Interestingly, Tyk2(-/-) DCs were defective in IL-12 and IL-23 production upon stimulation with CpG ODN. Furthermore, Tyk2(-/-) DCs were impaired in their ability to induce Th1-cell differentiation but not Th2-cell differentiation. Taken together, these results indicate that the expression of Tyk2 in DCs is crucial for the production of Th1-promoting cytokines such as IL-12 and IFN-gamma from DCs and thereby for the induction of antigen-specific Th1-cell differentiation.

Tyk2 Signaling in Host Environment Plays an Important Role in Contraction of Antigen-Specific CD8+T Cells following a Microbial Infection

Tyrosine kinase 2 (Tyk2), a member of JAK signal transducer family contributes to the signals triggered by IL-12 for IFN-gamma production. To elucidate potential roles of Tyk2 in generation and maintenance of Ag-specific CD8+ T cells, we followed the fate of OVA-specific CD8+ T cells in Tyk2-deficient (-/-) mice after infection with recombinant Listeria monocytogenes expressing OVA (rLM-OVA). Results showed that the numbers of OVA(257-264)/K(b) tetramer-positive CD8+ T cells in Tyk2(-/-) mice were almost the same as those in Tyk2(+/+) mice at the expansion phase on day 7 but were significantly larger in Tyk2(-/-) mice than those in Tyk2(+/+) mice at the contraction phase on day 10 and at the memory phase on day 60 after infection. The intracellular expression level of active caspase-3 was significantly decreased in the OVA-specific CD8+ T cells of Tyk2(-/-) mice on day 7 compared with those of Tyk2(+/+) mice. Adaptive transfer experiments revealed that Tyk2 signaling in other factors rather than CD8+ T cells played a regulatory role in CD8+ T cell contraction following infection. Administration of exogenous IFN-gamma from day 6 to day 9 restored the CD8+ T cell contraction in Tyk2(-/-) mice after infection with rLM-OVA. These results suggest that Tyk2 signaling for IFN-gamma production in host environment plays an important role in contraction of effector CD8+ T cells following a microbial infection.

IL-7/STAT5 cytokine signaling pathway is essential but insufficient for maintenance of naive CD4 T cell survival in peripheral lymphoid organs

Constitutive expression of suppressors of cytokine signaling (SOCS)1 in T lineage in vivo attenuated cytokine signaling and resulted in a dramatic reduction in the number of naive CD44(low)CD62L(high) CD4 T cells in the spleen. After adoptive transfer of thymocytes from SOCS1 transgenic mice into normal recipients, naive CD4 T cells rapidly disappeared from the spleen within 1 wk. Likewise, T cell-specific deletion of STAT5a/b in vivo resulted in a similar phenotype characterized by loss of naive CD4 T cells. Thus, STAT5-mediated signaling is crucial for promoting naive T cell survival. However, forced expression of constitutively active STAT5 failed to rescue CD4 T cells in SOCS1 transgenic mice, implying that STAT5 activation is necessary but not sufficient for naive CD4 T cell survival. Although blockade of the IL-7R, a SOCS1 target, resulted in clear inhibition of naive T cell survival, the effect occurred 3 wk after anti-IL-7R Ab treatment, but not at earlier time points. These results suggest that IL-7-mediated STAT5 activation is essential for long-term survival of naive CD4 cells after export from thymus, and that another SOCS1-sensitive cytokine is critical for short-term naive T cell survival.

Both integrated and differential regulation of components of the IL-2/IL-2 receptor system

Interleukin-2 was discovered in 1976 as a T-cell growth factor. It was the first type I cytokine cloned and the first for which a receptor component was cloned. Its importance includes its multiple actions, therapeutic potential, and lessons for receptor biology, with three components differentially combining to form high, intermediate, and low-affinity receptors. IL-2Ralpha and IL-2Rbeta, respectively, are markers for double-negative thymocytes and regulatory T-cells versus memory cells. gamma(c), which is shared by six cytokines, is mutated in patients with X-linked severe-combined immunodeficiency. We now cover an under-reviewed area-the regulation of genes encoding IL-2 and IL-2R components, with an effort to integrate/explain this knowledge.

Increased level and longevity of protective immune responses induced by DNA vaccine expressing the HIV-1 Env glycoprotein when combined with IL-21 and IL-15 gene delivery

We investigated the ability of a plasmid-derived IL-21 delivered alone or in combination with the IL-15 gene to regulate immune responses to the HIV-1 envelope (Env) glycoprotein induced by DNA vaccination. Mice were injected with the gp140DeltaCFI(HXB2/89.6) vector expressing a modified Env glycoprotein with C-terminal mutations intended to mimic a fusion intermediate, in which the most divergent region encoding the variable V1, V2, and V3 domains of CXCR4-tropic HxB2 virus was replaced with the dual-tropic 89.6 viral strain. Using a recombinant vaccinia virus expressing 89.6 Env glycoprotein (vBD3) in a mouse challenge model, we observed that IL-21 plasmid produced sustained resistance to viral transmission when injected 5 days after DNA vaccination. Moreover, IL-21 in a synergistic manner with IL-15 expression vector augmented the vaccine-induced recall responses to the vBD3 challenge compared with those elicited by immunization in the presence of either cytokine alone. The synergistic combination of IL-21 and IL-15 plasmids promoted expansion of CD8+CD127+ memory T cell pools specific for a subdominant HLA-A2-restricted Env(121-129) epitope (KLTPLCVTL). Our results also show that coimmunization with IL-21 and IL-15 plasmid combination resulted in enhanced CD8+ T cell function that was partially independent of CD4+ T cell help in mediating protection against vBD3 challenge. Furthermore, the use of IL-21 and IL-15 genes was able to increase Ab-dependent cellular cytotoxicity and complement-dependent lysis of Env-expressing target cells through augmentation of Env-specific IgG Ab levels. These data indicate that the plasmid-delivered IL-21 and IL-15 can increase the magnitude of the response to DNA vaccines.

Identification of molecular markers for endometriosis in blood lymphocytes by using deoxyribonucleic acid microarrays

OBJECTIVE

To identify molecular biomarkers for endometriosis in peripheral blood lymphocytes by using DNA microarrays.

DESIGN

Case-control.

SETTING

Multicenter academic research programs.

PATIENT(S)

Premenopausal women with or without endometriosis, determined by obstetrics and gynecology specialists during surgery. Microarray analysis included six endometriosis patients and five controls; 15 endometriosis patients and 15 controls were analyzed by using real-time reverse-transcription polymerase chain reaction (RT-PCR). Patients with all disease stages were included.

INTERVENTION(S)

Peripheral blood samples were collected by venipuncture.

MAIN OUTCOME MEASURE(S)

The expression levels of mRNAs in blood lymphocytes from endometriosis patients and controls were compared with those of a standard total RNA. Gene expression data were validated by real-time RT-PCR analysis.

RESULT(S)

A gene selection program identified genes that were differentially expressed in samples from endometriosis patients. To validate the gene expression data, the nine most discriminatory genes were analyzed by real-time RT-PCR. Two of the nine genes identified, IL2RG and LOXL1, were shown to be significantly differentially expressed.

CONCLUSION(S)

This is the first report of genes that are differentially expressed in peripheral blood lymphocytes of patients with endometriosis, which may provide important clues regarding the pathogenesis of this disease. Moreover, they could be considered potential targets for noninvasive diagnostic assays for endometriosis and need to be validated in a larger population.

Self-limitation of Th1-mediated inflammation by IFN-gamma

IFN-gamma is an effector cytokine of cell-mediated immunity that plays an essential role in both innate and adaptive phases of an immune response. Interestingly, in several Th1-dependent autoimmune models, lack of IFN-gamma is associated with an acceleration of disease. To distinguish the influence of IFN-gamma on the polarization of naive precursors from the influence on effector cells, we used an adoptive transfer model of differentiated Ag-specific Th1 cells. In this study, IFN-gamma displayed a dual function in a Th1-dependent immune reaction. In the early phase, IFN-gamma accelerated the inflammation, whereas in the late phase it mediated the process of self-limitation. We demonstrated that IFN-gamma limits the number of Th1 effector cells after Ag challenge. Studies using IFN-gammaR-/- mice as recipients showed that IFN-gamma acts indirectly via host cells to regulate the pool size of Th1 cells. NO was a downstream effector molecule. Transfer experiments of Th1 cells into IFN-gamma-/- mice revealed that Th1 cells control both themselves and the corresponding inflammation by the release of IFN-gamma. Thus, the proinflammatory cytokine IFN-gamma can act as a negative feedback regulator to control Th1-mediated immune responses.

Interleukins and STAT signaling

Metazoan cells secrete small proteins termed cytokines that execute a variety of biological functions essential for the survival of organisms. Binding of cytokines that belong to the hematopoietin- or interferon-family, to their cognate receptors on the surface of target cells, induces receptor aggregation, which in turn sequentially triggers tyrosine-phosphorylation-dependent activation of receptor-associated Janus-family tyrosine kinases (JAKs), receptors, and signal transducers and activators of transcription (STATs). Phosphorylated STATs form dimers that migrate to the nucleus, bind to cognate enhancer elements and activate transcription of target genes. Each cytokine activates a specific set of genes to execute its biological functions with a certain degree of redundancy. Cytokine signals are, in general, transient in nature. Therefore, under normal physiological conditions, initiation and attenuation of cytokine signals are tightly controlled via multiple cellular and molecular mechanisms. Aberrant activation of cytokine signaling pathways is, however, found under a variety of patho-physiological conditions including cancer and immune diseases.

IL-15 Regulates CD8+T Cell Contraction during Primary Infection

During the course of acute infection with an intracellular pathogen, Ag-specific T cells proliferate in the expansion phase, and then most of the T cells die by apoptosis in the following contraction phase, but the few that survive become memory cells and persist for a long period of time. Although IL-15 is known to play an important role in long-term maintenance of memory CD8+ T cells, the potential roles of IL-15 in CD8+ T cell contraction are not known. Using an adoptive transfer system of OT-I cells expressing OVA257-264/Kb-specific TCR into control, IL-15 knockout (KO) and IL-15 transgenic (Tg) mice followed by challenge with recombinant Listeria monocytogenes expressing OVA, we found that the survival of CD44+CD62L-CD127- effector OT-I cells during the contraction phase is critically dependent on IL-15. In correlation with the expression level of Bcl-2 in OT-I cells, the number of OT-I cells was markedly reduced in IL-15 KO mice but remained at a high level in IL-15 Tg mice during the contraction phase, compared with control mice. In vivo administration of rIL-15 during the contraction phase in IL-15 KO mice inhibited the contraction of effector OT-I cells accompanied by up-regulation of Bcl-2 expression. Furthermore, enforced expression of Bcl-2 protected the majority of effector OT-I cells from death in IL-15 KO mice after infection. These results suggest that IL-15 plays a critical role in protecting effector CD8+ T cells from apoptosis during the contraction phase following a microbial infection via inducing antiapoptotic molecules.

Human T cells constitutively express IL-15 that promotes ex vivo T cell homeostatic proliferation through autocrine/juxtacrine loops

Homeostatic proliferation of T cells in vivo is responsible for the maintainance of the T cell pool, and IL-15 is a pivotal cytokine implicated in this process. Known cell sources providing physiologically active IL-15 are monocytes/macrophages, dendritic cells, and stromal cells. T lymphocyte expression of functionally active IL-15 and its possible role in T cell biology have not been investigated. In this study, we demonstrate that human T cells constitutively express IL-15 that acts through autocrine/juxtacrine loops to promote ex vivo homeostatic T cell proliferation.

Genes, pathways and checkpoints in lymphocyte development and homeostasis

A plethora of genes involved in murine B and T cell development have been identified, and developmental pathways within the primary lymphoid tissues have been well delineated. The generation of a functional, but non-self reacting lymphocyte repertoire results from the completion of several checkpoints during lymphocyte development and competition for survival factors in the periphery. Improved knowledge of these developmental checkpoints and homeostatic mechanisms is critical for understanding human immunodeficiency, leukaemia/lymphoma and autoimmunity, which are conditions where checkpoints and homeostasis are likely to be deregulated.

Stat5a is essential for the proliferation and survival of murine mast cells

The regulatory role of signal transducer and activator of transcription (Stat) 5a in the proliferation and survival of mast cells was determined using Stat5a-deficient (Stat5a(-/-)) mice. First, although the mast cells in Stat5a(-/-) mice were morphologically indistinguishable from those in wild-type (WT) mice, the number of peritoneal mast cells was significantly decreased in Stat5a(-/-) mice as compared with that in WT mice. Furthermore, the interleukin-3 (IL-3)-dependent development of bone marrow-derived mast cells (BMMCs) was markedly decreased in Stat5a(-/-) mice. Second, IL-3-induced but not stem cell factor (SCF)-induced proliferation of BMMCs was significantly diminished in Stat5a(-/-) mice as compared with that in WT mice. Moreover, survival rates of both peritoneal mast cells and BMMCs were significantly decreased with increased apoptotic cells in Stat5a(-/-) mice as compared with those in WT mice. Finally, mRNA of Bcl-x(L) was induced after IL-3 stimulation in WT BMMCs but not in Stat5a(-/-) BMMCs, which may account for the accelerated apoptosis in Stat5a(-/-) mast cells. These results indicate that Stat5a plays an important role in mast cell development, proliferation, and survival.

T cell homeostasis in tolerance and immunity

The size of the peripheral T cell pool is remarkably stable throughout life, reflecting precise regulation of cellular survival, proliferation, and apoptosis. Homeostatic proliferation refers to the process by which T cells spontaneously proliferate in a lymphopenic host. The critical signals driving this expansion are "space," contact with self-major histocompatibility complex (MHC)/peptide complexes, and cytokine stimulation. A number of studies have delineated an association between T cell lymphopenia, compensatory homeostatic expansion, and the development of diverse autoimmune syndromes. In the nonobese diabetic mouse model of type 1 diabetes, lymphopenia-induced homeostatic expansion fuels the generation of islet-specific T cells. Excess interleukin-21 facilitates T cell cycling but limited survival, resulting in recurrent stimulation of T cells specific for self-peptide/MHC complexes. Indeed, data from several experimental models of autoimmunity indicate that a full T cell compartment restrains homeostatic expansion of self-reactive cells that could otherwise dominate the repertoire. This review describes the mechanisms that govern T cell homeostatic expansion and outlines the evidence that lymphopenia presents a risk for development of autoimmune disease.

Colitis in mice lacking the common cytokine receptor gamma chain is mediated by IL-6-producing CD4+ T cells

BACKGROUND & AIMS

Mice that have a truncated mutation of the common cytokine receptor gamma chain (CR gamma -/Y) are known to spontaneously develop colitis. To identify the pathologic elements responsible for triggering this localized inflammatory disease, we elucidated and characterized aberrant T cells and their enteropathogenic cytokines in CR gamma -/Y mice with colitis.

METHODS

The histologic appearance, cell population, T-cell receptor V beta usage, and cytokine production of lamina propria lymphocytes were assessed. CR gamma -/Y mice were treated with anti-interleukin (IL)-6 receptor monoclonal antibody to evaluate its ability to control colitis, and splenic CD4 + T cells from the same mouse model were adoptively transferred into SCID mice to see if they spurred the appearance of colitis.

RESULTS

We found marked thickening of the large intestine, an increase in crypt depth, and infiltration of the colonic lamina propria and submucosa with mononuclear cells in the euthymic CR gamma -/Y mice, but not in the athymic CR gamma -/Y mice, starting at the age of 8 weeks. Colonic CD4 + T cells with high expressions of antiapoptotic Bcl-x and Bcl-2 were found to use selected subsets (V beta 14) of T-cell receptor and to exclusively produce IL-6. Treatment of CR gamma -/Y mice with anti-IL-6 receptor monoclonal antibody prevented the formation of colitis via the induction of apoptosis in IL-6-producing CD4 + T cells. Adoptive transfer of pathologic CD4 + T cells induced colitis in the recipient SCID mice.

CONCLUSIONS

Colonic IL-6-producing thymus-derived CD4 + T cells are responsible for the development of colitis in CR gamma -/Y mice.

Synergy of IL-21 and IL-15 in regulating CD8+ T cell expansion and function

Interleukin (IL)-21 is the most recently recognized of the cytokines that share the common cytokine receptor γ chain (γ_c), which is mutated in humans with X-linked severe combined immunodeficiency. We now report that IL-21 synergistically acts with IL-15 to potently promote the proliferation of both memory (CD44^high) and naive (CD44^low) phenotype CD8⁺ T cells and augment interferon-γ production in vitro. IL-21 also cooperated, albeit more weakly, with IL-7, but not with IL-2. Correspondingly, the expansion and cytotoxicity of CD8⁺ T cells were impaired in IL-21R^−/− mice. Moreover, in vivo administration of IL-21 in combination with IL-15 boosted antigen-specific CD8⁺ T cell numbers and resulted in a cooperative effect on tumor regression, with apparent cures of large, established B16 melanomas. Thus, our studies reveal that IL-21 potently regulates CD8⁺ T cell expansion and effector function, primarily in a synergistic context with IL-15.

A role for thymic stromal lymphopoietin in CD4(+) T cell development

Thymic stromal lymphopoietin (TSLP) signals via a receptor comprising the interleukin (IL)-7 receptor α chain and a distinctive subunit, TSLP receptor (TSLPR), which is most related to the common cytokine receptor γ chain, γ_c. We have generated TSLPR knockout (KO) mice and found that although these mice had normal lymphocyte numbers, γ_c/TSLPR double KO mice had a greater lymphoid defect than γ_c KO mice. This indicates that TSLP contributes to lymphoid development and accounts for some of the residual lymphoid development in γ_c KO mice and presumably in patients with X-linked severe combined immunodeficiency. Injection of TSLP into γ_c KO mice induced the expansion of T and B cells. Moreover, sublethally irradiated TSLPR KO mice showed weaker recovery of lymphocyte populations than wild-type (WT) littermates, even when neutralizing anti–IL-7 antibodies were injected. Interestingly, TSLP preferentially stimulated the proliferation and survival of CD4⁺ single positive thymocytes and peripheral T cells in vitro. Additionally, CD4⁺ T cells from TSLPR KO mice expanded less efficiently than WT CD4⁺ T cells in irradiated hosts, and TSLP preferentially expanded CD4⁺ T cells both in vitro and in vivo. Thus, as compared with other known cytokines, TSLP is distinctive in exhibiting a lineage preference for the expansion and survival of CD4⁺ T cells.

Control of T cell viability

The factors affecting T cell viability vary depending on the type and status of the T cell involved. Naive T cells die via a Bcl-2/Bim dependent route. Their deaths are prevented in animals by IL-7 and contact with MHC. Activated T cells die in many different ways. Among these is a pathway involving signals that come from outside the T cell and affect it via surface receptors such as Fas. Activated T cells also die through a pathway driven by signals generated within the T cell itself, a cell autonomous route. This pathway involves members of the Bcl-2 family, in particular Bcl-2, Bcl-xl, Bim, and probably Bak. The viability of CD8+ and CD4+ memory T cells is controlled in different ways. CD8+ memory T cells are maintained by IL-15 and IL-7. The control of CD4+ memory T cells is more mysterious, with roles reported for IL-7 and/or contact via the TCR.

Thymopoiesis and T cell development in common gamma chain-deficient dogs

Our laboratory has identified an X-linked severe combined immunodeficiency (XSCID) in dogs that is the result of mutations in the common gamma chain (gammac) subunit of the interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21 receptors. Canine XSCID, unlike genetically engineered gammac-deficient mice, has a clinical and immunologic phenotype virtually identical to human XSCID, suggesting species-specific differences exist in the role of the gammac and its associated cytokines in mice in comparison to their role in humans and dogs. This review compares and contrasts thymopoiesis and postnatal T cell development in gammac-deficient (XSCID) dogs raised in a conventional environment, with gammac-deficient dogs raised in a gnotobiotic environment. Therapy to accelerate T cell regeneration following hematopoietic stem cell transplantation or gene therapy is also discussed.