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

The physiological and pathological roles of RNA modifications in T cells

RNA molecules undergo dynamic chemical modifications in response to various external or cellular stimuli. Some of those modifications have been demonstrated to post-transcriptionally modulate the RNA transcription, localization, stability, translation, and degradation, ultimately tuning the fate decisions and function of mammalian cells, particularly T cells. As a crucial part of adaptive immunity, T cells play fundamental roles in defending against infections and tumor cells. Recent findings have illuminated the importance of RNA modifications in modulating T cell survival, proliferation, differentiation, and functional activities. Therefore, understanding the epi-transcriptomic control of T cell biology enables a potential avenue for manipulating T cell immunity. This review aims to elucidate the physiological and pathological roles of internal RNA modifications in T cell development, differentiation, and functionality drawn from current literature, with the goal of inspiring new insights for future investigations and providing novel prospects for T cell-based immunotherapy.

N6-methyladenosine regulators-related immune genes enable predict graft loss and discriminate T-cell mediate rejection in kidney transplantation biopsies for cause

Objective

The role of m6A modification in kidney transplant-associated immunity, especially in alloimmunity, still remains unknown. This study aims to explore the potential value of m6A-related immune genes in predicting graft loss and diagnosing T cell mediated rejection (TCMR), as well as the possible role they play in renal graft dysfunction.

Methods

Renal transplant-related cohorts and transcript expression data were obtained from the GEO database. First, we conducted correlation analysis in the discovery cohort to identify the m6A-related immune genes. Then, lasso regression and random forest were used respectively to build prediction models in the prognosis and diagnosis cohort, to predict graft loss and discriminate TCMR in dysfunctional renal grafts. Connectivity map (CMap) analysis was applied to identify potential therapeutic compounds for TCMR.

Results

The prognostic prediction model effectively predicts the prognosis and survival of renal grafts with clinical indications (P< 0.001) and applies to both rejection and non-rejection situations. The diagnostic prediction model discriminates TCMR in dysfunctional renal grafts with high accuracy (area under curve = 0.891). Meanwhile, the classifier score of the diagnostic model, as a continuity index, is positively correlated with the severity of main pathological injuries of TCMR. Furthermore, it is found that METTL3, FTO, WATP, and RBM15 are likely to play a pivotal part in the regulation of immune response in TCMR. By CMap analysis, several small molecular compounds are found to be able to reverse TCMR including fenoldopam, dextromethorphan, and so on.

Conclusions

Together, our findings explore the value of m6A-related immune genes in predicting the prognosis of renal grafts and diagnosis of TCMR.

The regulation and potential roles of m6A modifications in early embryonic development and immune tolerance at the maternal-fetal interface

The immune microenvironment at the maternal-fetal interface was determined by the crosstalk between the trophoblast and maternal-derived cells, which dynamically changed during the whole gestation. Trophoblasts act as innate immune cells and dialogue with maternal-derived cells to ensure early embryonic development, depending on the local immune microenvironment. Therefore, dysfunctions in trophoblasts and maternal decidual cells contribute to pregnancy complications, especially recurrent pregnancy loss in early pregnancy. Since many unknown regulatory factors still affect the complex immune status, exploring new potential aspects that could influence early pregnancy is essential. RNA methylation plays an important role in contributing to the transcriptional regulation of various cells. Sufficient studies have shown the crucial roles of N6-methyladenosine (m6A)- and m6A-associated- regulators in embryogenesis during implantation. They are also essential in regulating innate and adaptive immune cells and the immune response and shaping the local and systemic immune microenvironment. However, the function of m6A modifications at the maternal-fetal interface still lacks wide research. This review highlights the critical functions of m6A in early embryonic development, summarizes the reported research on m6A in regulating immune cells and tumor immune microenvironment, and identifies the potential value of m6A modifications in shaping trophoblasts, decidual immune cells, and the microenvironment at the maternal-fetal interface. The m6A modifications are more likely to contribute to embryogenesis, placentation and shape the immune microenvironment at the maternal-fetal interface. Uncovering these crucial regulatory mechanisms could provide novel therapeutic targets for RNA methylation in early pregnancy.

Partial STAT5 signaling is sufficient for CD4+ T cell priming but not memory formation

Signal transducer and activator of transcription 5 (STAT5) plays an important role in regulating gene expression in response to cytokines of the common (γc) chain family. In this capacity, STAT5 promotes CD8⁺ effector and memory T cell survival and regulatory T cell development. However, its function in conventional CD4⁺ T cells is less clear. In this study, the requirement of intact STAT5 signaling for CD4⁺ effector and memory T cell generation and maintenance was investigated by using DO11.10 TCR transgenic T cells that are genetically deficient in STAT5A or B, as well as by transducing DO11 T cells with a dominant-negative STAT5 to temporally block STAT5 function. We found that the presence of STAT5A or B alone was sufficient for primary CD4⁺ effector T cell generation, but not for establishing a long-lived memory cell population. Similarly, blocking STAT5 signaling during priming did not prevent initial T cell activation, but inhibited the generation of memory cells. Surprisingly, blocking STAT5 post-priming did not impact the long-term survival of CD4⁺ memory T cells in vivo. Mechanistically, intact STAT5B, but not STAT5A, was required for IL-7Rα re-expression in activated T cells, which is an important cytokine receptor for CD4⁺ memory generation. These data show that fully functional STAT5 is essential to deliver an early, non-redundant signal for memory programming during the primary CD4⁺ T cell response, while partial STAT5 signaling is sufficient for effector differentiation. Our results have implications for the precise use of STAT5 inhibitors to timely inhibit memory T cell responses.

Molecular characterization, expression pattern and evolution of nine suppressors of cytokine signaling (SOCS) gene in the swamp eel (Monopterus albus)

Suppressors of cytokine signaling (SOCS) family members have negative effects on cytokine signaling pathways involved in immunity, growth and development. Owing to their typical feature, they have been extensively studied in mammalians, but they have not offered systematic studies among teleosts. In the present study, nine SOCS family genes were identified in the swamp eel genome and analyzed regulation mechanisms of SOCS family members in swamp eels. The open reading frames of MaSOCS1a, MaSOCS1b, MaSOCS2, MaSOCS3a, MaSOCS3b, MaSOCS4, MaSOCS5, MaSOCS6 and MaSOCS7 were 663 bp, 603 bp, 717 bp, 618 bp, 645 bp, 1188 bp, 1488 bp, 1611 bp and 1998 bp and encoded 220, 238, 200, 205, 214, 395, 496, 536 and 655 amino acids, respectively. All SOCS proteins have no signal peptides. Multiple alignment revealed that MaSOCS family members possessed a typical conserved SOCS box and SH2 region. Phylogenetic analyses showed that all SOCS proteins were divided into two main clusters. Taken together with the similarity and identity of SOCS protein amino acids, these results indicated that MaSOCS family members shared conserved with other homologous genes, in which MaSOCS7 was more conserved. Further syntenic analysis confirmed the phylogenetic analysis results and annotation of SOCS protein, suggesting that MaSOCS5 shared a common ancestor gene with that of fish and humans. MaSOCS family members were constitutively expressed in a wide range of tissues with different levels. In particular, spleen and head kidneys play an important role in immune-related pathways. After Aeromonas veronii and polyinosinic-polycytidylic acid (poly I:C) challenge in the spleen and head kidney, MaSOCS family members exhibit different expression profiles. These expression patterns indicated that MaSOCS family members could make acute responses after pathogen invasion. Taken together, these results indicate that MaSOCS family members participate in the immune response against pathogens and offer a solid foundation for future studies of SOCS function.

Foxo1 and Foxp1 play opposing roles in regulating the differentiation and antitumor activity of TH9 cells programmed by IL-7

Tumor-specific CD4⁺ T helper 9 (T_H9) cells, so-called because of their production of the cytokine interleukin-9 (IL-9), are a powerful effector T cell subset for cancer immunotherapy. We found that pretreatment of naïve CD4⁺ T cells with IL-7 further enhanced their differentiation into T_H9 cells and augmented their antitumor activity. IL-7 markedly increased the abundance of the histone acetyltransferase p300 by activating the STAT5 and PI3K-AKT-mTOR signaling pathways and promoting the acetylation of histones at the Il9 promoter. As a result, the transcriptional regulator Foxo1 was dephosphorylated and translocated to the nucleus, bound to the Il9 promoter, and induced the production of IL-9 protein. In contrast, Foxp1, which bound to the Il9 promoter in naïve CD4⁺ T cells and inhibited Il9 expression, was outcompeted for binding to the Il9 promoter by Foxo1 and translocated to the cytoplasm. Furthermore, forced expression of Foxo1 or a deficiency in Foxp1 in CD4⁺ T cells markedly increased the production of IL-9, whereas a deficiency in Foxo1 inhibited the ability of IL-7 to enhance the differentiation and antitumor activity of T_H9 cells. Thus, we identified the roles of Foxo1 as a positive regulator and Foxp1 as a negative regulator of T_H9 cell differentiation and antitumor activity, which may provide potential targets for cancer immunotherapy.

Induced Pluripotent Stem Cell as a New Source for Cancer Immunotherapy

The immune system consists of cells, proteins, and other molecules that beside each other have a protective function for the host against foreign pathogens. One of the most essential features of the immune system is distinguishability between self- and non-self-cells. This function has an important role in limiting development and progression of cancer cells. In this case, the immune system can detect tumor cell as a foreign pathogen; so, it can be effective in elimination of tumors in their early phases of development. This ability of the immune system resulted in the development of a novel therapeutic field for cancer treatment using host immune components which is called cancer immunotherapy. The main purpose of cancer immunotherapy is stimulation of a strong immune response against the tumor cells that can result from expressing either the immune activator cytokines in the tumor area or gene-modified immune cells. Because of the problems of culturing and manipulating immune cells ex vivo, in recent years, embryonic stem cell (ESC) and induced pluripotent stem cell (iPSC) have been used as new sources for generation of modified immune stimulatory cells. In this paper, we reviewed some of the progressions in iPSC technology for cancer immunotherapy.

Melanoma Immunotherapy in Mice Using Genetically Engineered Pluripotent Stem Cells

Adoptive cell transfer (ACT) of antigen (Ag)-specific CD8(+) cytotoxic T lymphocytes (CTLs) is a highly promising treatment for a variety of diseases. Naive or central memory T-cell-derived effector CTLs are optimal populations for ACT-based immunotherapy because these cells have a high proliferative potential, are less prone to apoptosis than terminally differentiated cells, and have the higher ability to respond to homeostatic cytokines. However, such ACT with T-cell persistence is often not feasible due to difficulties in obtaining sufficient cells from patients. Here we present that in vitro differentiated HSCs of engineered PSCs can develop in vivo into tumor Ag-specific naive CTLs, which efficiently suppress melanoma growth. Mouse-induced PSCs (iPSCs) were retrovirally transduced with a construct encoding chicken ovalbumin (OVA)-specific T-cell receptors (TCRs) and survival-related proteins (i.e., BCL-xL and survivin). The gene-transduced iPSCs were cultured on the delta-like ligand 1-expressing OP9 (OP9-DL1) murine stromal cells in the presence of murine recombinant cytokines (rFlt3L and rIL-7) for a week. These iPSC-derived cells were then intravenously adoptively transferred into recipient mice, followed by intraperitoneal injection with an agonist α-Notch 2 antibody and cytokines (rFlt3L and rIL-7). Two weeks later, naive OVA-specific CD8(+) T cells were observed in the mouse peripheral lymphatic system, which were responsive to OVA-specific stimulation. Moreover, the mice were resistant to the challenge of B16-OVA melanoma induction. These results indicate that genetically modified stem cells may be used for ACT-based immunotherapy or serve as potential vaccines.

Effects of somatotrophic axis (GH/GHR) double transgenesis on structural and molecular aspects of the zebrafish immune system

The development of growth hormone (GH) transgenic fish has been shown to be a promising method to improve growth rates. However, the role of GH is not restricted only to processes involved in growth. Several others physiological processes, including immune function, are impaired due to GH imbalances. Given the importance of generating GH transgenic organisms for aquaculture purposes, it is necessary to develop strategies to reduce or compensate for the collateral effects of GH. We hypothesized that the generation of double transgenic fish that overexpress GH and growth hormone receptor (GHR) in the skeletal muscle could be a possible alternative to compensate for the deleterious effects of GH on the immune system. Specifically, we hypothesized that increased GHR amounts in the skeletal muscle would be able to reduce the level of circulating GH, attenuating the GH signaling on the immune cells while still increasing the growth rate. To test this hypothesis, we evaluated the size of the immune organs, T cell content in the thymus and head kidney, and expression of immune-related genes in double-transgenic fish. Contrary to our expectations, we found that the overexpression of GHR does not decrease the deleterious effect of GH excess on the size of the thymus and head kidney, and in the content of CD3(+) and CD4(+) cells in the thymus and head kidney. Unexpectedly, the control GHR transgenic group showed similar impairments in immune system parameters. These results indicate that GHR overexpression does not reverse the impairments caused by GH and, in addition, could reinforce the damage to the immune functions in GH transgenic zebrafish.

An atlas of mouse CD4(+) T cell transcriptomes

BACKGROUND

CD4(+) T cells are key regulators of the adaptive immune system and can be divided into T helper (Th) cells and regulatory T (Treg) cells. During an immune response Th cells mature from a naive state into one of several effector subtypes that exhibit distinct functions. The transcriptional mechanisms that underlie the specific functional identity of CD4(+) T cells are not fully understood.

RESULTS

To assist investigations into the transcriptional identity and regulatory processes of these cells we performed mRNA-sequencing on three murine T helper subtypes (Th1, Th2 and Th17) as well as on splenic Treg cells and induced Treg (iTreg) cells. Our integrated analysis of this dataset revealed the gene expression changes associated with these related but distinct cellular identities. Each cell subtype differentially expresses a wealth of 'subtype upregulated' genes, some of which are well known whilst others promise new insights into signalling processes and transcriptional regulation. We show that hundreds of genes are regulated purely by alternative splicing to extend our knowledge of the role of post-transcriptional regulation in cell differentiation.

CONCLUSIONS

This CD4(+) transcriptome atlas provides a valuable resource for the study of CD4(+) T cell populations. To facilitate its use by others, we have made the data available in an easily accessible online resource at www.th-express.org.

MicroRNA-155 is required for effector CD8+ T cell responses to virus infection and cancer

MicroRNAs (miRNAs) regulate the function of several immune cells, but their role in promoting CD8(+) T cell immunity remains unknown. Here we report that miRNA-155 is required for CD8(+) T cell responses to both virus and cancer. In the absence of miRNA-155, accumulation of effector CD8(+) T cells was severely reduced during acute and chronic viral infections and control of virus replication was impaired. Similarly, Mir155(-/-) CD8(+) T cells were ineffective at controlling tumor growth, whereas miRNA-155 overexpression enhanced the antitumor response. miRNA-155 deficiency resulted in accumulation of suppressor of cytokine signaling-1 (SOCS-1) causing defective cytokine signaling through STAT5. Consistently, enforced expression of SOCS-1 in CD8(+) T cells phenocopied the miRNA-155 deficiency, whereas SOCS-1 silencing augmented tumor destruction. These findings identify miRNA-155 and its target SOCS-1 as key regulators of effector CD8(+) T cells that can be modulated to potentiate immunotherapies for infectious diseases and cancer.

Disparate roles for STAT5 in primary and secondary CTL responses

IL-2 signals during the primary response to infection are essential in shaping CD8(+) T cell fate decisions. How CD8(+) T cells integrate IL-2 signals in the development of functional memory is not well understood. Because IL-2 induces potent activation of the STAT5 transcription factor, we tested the role of STAT5 in CD8(+) memory T cell differentiation and function using a model system in which STAT5 activity is inducibly abrogated upon CD8(+) T cell activation. We report that STAT5 activity is broadly important for the expansion and effector function of all effector CTL subsets. After pathogen clearance, STAT5 was required for the survival of effector phenotype memory CTLs during the contraction phase. However, despite its role in supporting full primary CD8(+) T cell expansion, and unlike IL-2, STAT5 activity is not required for the development of memory CD8(+) T cells capable of robust secondary expansion upon rechallenge. Our findings highlight differential requirements for survival signals between primary and secondary effector CTL, and demonstrate that IL-2-dependent programming of memory CD8(+) T cells capable of secondary expansion and secondary effector differentiation is largely STAT5 independent.

IL-7 signaling and CD127 receptor regulation in the control of T cell homeostasis

After their development in the thymus, mature T cells are maintained in the periphery by two sets of survival signals, namely TCR signals from contact with self-peptide/MHC ligands and the cytokine receptor signals from binding IL-7 and IL-15. These signals cooperate to maximize the utility of finite resources to support a diverse pool of mature T cells. It is becoming increasingly clear that multiple mechanisms exist to regulate expression of IL-7R at the transcriptional and post-translational levels. The interplay between TCR signals and IL-7R signals are also important in regulation of IL-7R expression. This review will focus on regulation of T cell homeostasis by IL-7R signaling, with an emphasis on the cross talk between signals from TCR and IL-7R.

Directed differentiation of induced pluripotent stem cells towards T lymphocytes

Adoptive cell transfer (ACT) of antigen-specific CD8(+) cytotoxic T lymphocytes (CTLs) is a promising treatment for a variety of malignancies (1). CTLs can recognize malignant cells by interacting tumor antigens with the T cell receptors (TCR), and release cytotoxins as well as cytokines to kill malignant cells. It is known that less-differentiated and central-memory-like (termed highly reactive) CTLs are the optimal population for ACT-based immunotherapy, because these CTLs have a high proliferative potential, are less prone to apoptosis than more differentiated cells and have a higher ability to respond to homeostatic cytokines (2-7). However, due to difficulties in obtaining a high number of such CTLs from patients, there is an urgent need to find a new approach to generate highly reactive Ag-specific CTLs for successful ACT-based therapies. TCR transduction of the self-renewable stem cells for immune reconstitution has a therapeutic potential for the treatment of diseases (8-10). However, the approach to obtain embryonic stem cells (ESCs) from patients is not feasible. Although the use of hematopoietic stem cells (HSCs) for therapeutic purposes has been widely applied in clinic (11-13), HSCs have reduced differentiation and proliferative capacities, and HSCs are difficult to expand in in vitro cell culture (14-16). Recent iPS cell technology and the development of an in vitro system for gene delivery are capable of generating iPS cells from patients without any surgical approach. In addition, like ESCs, iPS cells possess indefinite proliferative capacity in vitro, and have been shown to differentiate into hematopoietic cells. Thus, iPS cells have greater potential to be used in ACT-based immunotherapy compared to ESCs or HSCs. Here, we present methods for the generation of T lymphocytes from iPS cells in vitro, and in vivo programming of antigen-specific CTLs from iPS cells for promoting cancer immune surveillance. Stimulation in vitro with a Notch ligand drives T cell differentiation from iPS cells, and TCR gene transduction results in iPS cells differentiating into antigen-specific T cells in vivo, which prevents tumor growth. Thus, we demonstrate antigen-specific T cell differentiation from iPS cells. Our studies provide a potentially more efficient approach for generating antigen-specific CTLs for ACT-based therapies and facilitate the development of therapeutic strategies for diseases.

Interleukin-7 matures suppressive CD127(+) forkhead box P3 (FoxP3)(+) T cells into CD127(-) CD25(high) FoxP3(+) regulatory T cells

We have identified a novel interleukin (IL)-7-responsive T cell population [forkhead box P3 (FoxP3(+) ) CD4(+) CD25(+) CD127(+) ] that is comparably functionally suppressive to conventional FoxP3(+) CD4(+) CD25(+) regulatory T cells (T(regs) ). Although IL-2 is the most critical cytokine for thymic development of FoxP3(+) T(regs) , in the periphery other cytokines can be compensatory. CD25(+) CD127(+) T cells treated with IL-7 phenotypically 'matured' into the known 'classical' FoxP3(+) CD4(+) CD25(high) CD127(-) FoxP3(+) T(regs) . In freshly isolated splenocytes, the highest level of FoxP3 expression was found in CD127(+) CD25(+) T cells when compared with CD127(-) CD25(+) or CD127(+) CD25(-) cells. IL-7 treatment of CD4(+) CD25(+) T cells induced an increase in the accumulation of FoxP3 in the nucleus in vitro. IL-7-mediated CD25 cell surface up-regulation was accompanied by a concurrent down-regulation of CD127 in vitro. IL-7 treatment of the CD127(+) CD25(+) FoxP3(+) cells also resulted in up-regulation of cytotoxic T lymphocyte antigen 4 without any changes in CD45RA at the cell surface. Collectively, these data support emerging evidence that FoxP3(+) T cells expressing CD127 are comparably functionally suppressive to CD25(+) CD127(-) FoxP3(+) T cells. This IL-7-sensitive regulation of FoxP3(+) T(reg) phenotype could underlie one peripheral non-IL-2-dependent compensatory mechanism of T(reg) survival and functional activity, particularly for adaptive T(regs) in the control of autoimmunity or suppression of activated effector T cells.

STAT5 is critical to maintain effector CD8+ T cell responses

During an immune response, most effector T cells die, whereas some are maintained and become memory T cells. Factors controlling the survival of effector CD4(+) and CD8(+) T cells remain unclear. In this study, we assessed the role of IL-7, IL-15, and their common signal transducer, STAT5, in maintaining effector CD4(+) and CD8(+) T cell responses. Following viral infection, IL-15 was required to maintain a subpopulation of effector CD8(+) T cells expressing high levels of killer cell lectin-like receptor subfamily G, member 1 (KLRG1), and lower levels of CD127, whereas IL-7 and IL-15 acted together to maintain KLRG1(low)CD127(high) CD8(+) effector T cells. In contrast, effector CD4(+) T cell numbers were not affected by the individual or combined loss of IL-15 and IL-7. Both IL-7 and IL-15 drove phosphorylation of STAT5 within effector CD4(+) and CD8(+) T cells. When STAT5 was deleted during the course of infection, both KLRG1(high)CD127(low) and KLRG1(low)CD127(high) CD8(+) T cells were lost, although effector CD4(+) T cell populations were maintained. Furthermore, STAT5 was required to maintain expression of Bcl-2 in effector CD8(+), but not CD4(+), T cells. Finally, IL-7 and IL-15 required STAT5 to induce Bcl-2 expression and to maintain effector CD8(+) T cells. Together, these data demonstrate that IL-7 and IL-15 signaling converge on STAT5 to maintain effector CD8(+) T cell responses.

Increased CD4+ T cell levels during IL-7 administration of antiretroviral therapy-treated simian immunodeficiency virus-positive macaques are not dependent on strong proliferative responses

CD4(+) T cell depletion is a fundamental component of HIV infection and AIDS pathogenesis and is not always reversed following antiretroviral therapy (ART). In this study, the SIV-infected rhesus macaque model was used to assess recombinant simian IL-7 in its glycosylated form (rsIL-7gly) to enhance regeneration of CD4(+) T cells, particularly the crucial central memory compartment, after ART. We assessed the impact of rsIL-7gly administration as single injections and as a cluster of three doses. Irrespective of the dosing strategy used, the rsIL-7gly administration transiently increased proliferation of both central memory and naive cells, in both CD4(+) and CD8(+) subsets, without increasing SIV levels in the blood. Administration of rsIL-7gly at intervals of 4-6 wk maximized the proliferative response to therapy but resulted in only transient increases in peripheral blood T cell counts. Although more frequent rsIL-7gly "clustered" dosing (three times weekly with 2 wk of rest and then repeat) induced only an initial proliferative burst by CD4(+) T cells, this dosing strategy resulted in sustained increases in peripheral blood CD4(+) T cell counts. The clustered rsIL-7gly treatment regimen was shown to increase the half-life of a BrdU label among memory T cells in the blood when compared with that of macaques treated with ART alone, which is consistent with enhanced cell survival. These results indicate that dosing intervals have a major impact on the response to rsIL-7gly in SIV-positive ART-treated rhesus macaques and that optimum dosing strategies may be ones that induce CD4(+) T cell proliferation initially and provide increased CD4(+) T cell survival.

Assessment of CD8(+) T cell differentiation in Trypanosoma cruzi-infected children

We previously reported that the T cell compartment in chronically Trypanosoma cruzi-infected adult subjects display functional and phenotypic signs of immune senescence. This study aimed to investigate the differentiation and the senescent profile of the overall CD8(+) T cell compartment in T. cruzi-infected children at the early stage of the disease. We found a lower percentage of naive (CD27(+)CD28(+)CD45RA(+)) and early antigen-experienced (CD45RA(-)CD27(+)CD28(+)), and higher percentages of late differentiated antigen-experienced (CD45RA(-)CD27(-)CD28(-)) CD8(+) T cells in T. cruzi-infected children as compared with age-matched uninfected controls. The expression of the interleukin (IL)-7R is also decreased on naive and on antigen-experienced total CD8(+) T cells with various degrees of differentiation. Conversely, the expression of HLA-DR, caspase-3, and CD57 did not vary on the total CD8(+) T cell compartment. These findings suggest that the duration of the infection is relevant in the process of immune senescent that this parasite can induce.

A Flt3- and Ras-dependent pathway primes B cell development by inducing a state of IL-7 responsiveness

Ras plays an important role in B cell development. However, the stage at which Ras governs B cell development remains unclear. Moreover, the upstream receptors and downstream effectors of Ras that govern B cell differentiation remain undefined. Using mice that express a dominant-negative form of Ras, we demonstrate that Ras-mediated signaling plays a critical role in the development of common lymphoid progenitors. This developmental block parallels that found in flt3(-/-) mice, suggesting that Flt3 is an important upstream activator of Ras in early B cell progenitors. Ras inhibition impaired proliferation of common lymphoid progenitors and pre-pro-B cells but not pro-B cells. Rather, Ras promotes STAT5-dependent pro-B cell differentiation by enhancing IL-7Ralpha levels and suppressing socs2 and socs3 expression. Our results suggest a model in which Flt3/Ras-dependent signals play a critical role in B cell development by priming early B cell progenitors for subsequent STAT5-dependent B cell differentiation.

Crucial role of interleukin-7 in T helper type 17 survival and expansion in autoimmune disease

Interleukin-7 receptor (IL-7R) is genetically associated with susceptibility to multiple sclerosis. Here we describe that IL-7 is essential for survival and expansion of pathogenic T helper type 17 (T(H)17) cells in experimental autoimmune encephalomyelitis (EAE). IL-7 directly expanded effector T(H)17 cells in EAE and human T(H)17 cells from subjects with multiple sclerosis, whereas it was not required for T(H)17 differentiation. IL-7R antagonism rendered differentiated T(H)17 cells susceptible to apoptosis through the inhibition of Janus kinase-signal transducer and activator of transcription-5 (JAK-STAT5) pathway and altered expression of the prosurvival protein Bcl-2 and the proapoptotic protein Bax, leading to decreased severity of EAE. In contrast, T(H)1 and regulatory T (T(reg)) cells were less susceptible to or not affected by IL-7R antagonism in vivo. The selectivity was attributable to minimal expression of IL-7Ralpha in T(reg) cells and correlated with a high level of Socs1 (encoding suppressor of cytokine signaling-1) expression in T(H)1 cells. The study reveals a unique, previously undescribed role of IL-7-IL-7R in T(H)17 cell survival and expansion and has implications in the treatment of autoimmune disease.

Regulation of memory T cells by γc cytokines

T cells rely on a duality of TCR and gammac cytokine signals for development, activation and peripheral T cell homeostasis. Previous data had suggested that the requirements for CD4 and CD8 memory T cell regulation were qualitatively distinct, but emerging data has shown that the requirements for true antigen specific memory T cells are very similar between these two cell types. This review will focus on contributions made by members of the gammac cytokine family (IL-2, IL-4, IL-7, IL-15 and IL-21) to homeostasis of naïve, memory phenotype and antigen experienced memory T cells.

Suppressors of cytokine signaling (SOCS) in T cell differentiation, maturation, and function

Cytokines are key modulators of T cell biology, but their influence can be attenuated by suppressors of cytokine signaling (SOCS), a family of proteins consisting of eight members, SOCS1-7 and CIS. SOCS proteins regulate cytokine signals that control the polarization of CD4(+) T cells into Th1, Th2, Th17, and T regulatory cell lineages, the maturation of CD8(+) T cells from naïve to "stem-cell memory" (Tscm), central memory (Tcm), and effector memory (Tem) states, and the activation of these lymphocytes. Understanding how SOCS family members regulate T cell maturation, differentiation, and function might prove critical in improving adoptive immunotherapy for cancer and therapies aimed at treating autoimmune and infectious diseases.

Cooperation between molecular targets of costimulation in promoting T cell persistence and tumor regression

Costimulation regulates multiple cellular processes of T cells inducing proliferation, expansion, and survival. The molecular targets of costimulation might then be useful to augment T cell activities. Two defined targets of costimulatory signals in primary T cells are the anti-apoptotic bcl-2 family molecule Bcl-x(L), and survivin, an inhibitor of apoptosis family member that might regulate both cell division and survival. However, the relative importance of, and relationship between, these molecules in primary T cells is not clear. To understand whether they have overlapping or cooperative functions, we used retrovirus-mediated transduction to introduce Bcl-x(L) and survivin separately, or together linked by a 2A picornavirus self-cleaving peptide, into Ag-responding CD8(+) T cells. We found that CD8(+) effector T cells expressing both Bcl-x(L) and survivin strongly expanded at an early stage and had a long-term survival advantage over cells transduced with either molecule alone. In vivo, with response to tumor-expressed Ag following adoptive T cell transfer, Ag-reactive CD8(+) T cells expressing both Bcl-x(L) and survivin displayed greatly enhanced tumor protective activity compared with CD8(+) T cells expressing either molecule introduced separately. These results indicate that Bcl-x(L) and survivin can critically contribute in a cooperative, nonredundant manner to augment the accumulation and persistence of CD8(+) T cells following encounter with Ag. The data provide new insights into why costimulatory signals might need to be sustained over time and suggest a potential novel approach to augment cellular immunotherapy for cancer.

Interleukin-7 receptor signaling is deficient in CD4+ T cells from HIV-infected persons and is inversely associated with aging

Loss of interleukin-7 (IL-2) receptor expression has been described in T lymphocytes from persons with human immunodeficiency virus (HIV) infection, potentially contributing to perturbations in T cell homeostasis. We investigated IL-7 receptor signaling by measuring signal transducer and activator of transcription 5 (STAT5) phosphorylation in CD4+ T cell subsets from HIV-infected persons. We determined that CD45RA- memory cell subsets (both CD27+ and CD27-) displayed the most robust immediate responses to IL-7, whereas naive CD4+ T cells sustained the signal most efficiently. Memory CD4+ T cells with a terminal phenotype (CD45RA+CD27-) responded poorly to IL-7 stimulation. Defects in signaling were observed in cells from viremic HIV-infected persons and were especially pronounced in CD45RA-CD27- memory subset. Although CD127 expression was diminished for T cells from HIV-infected persons, it was not directly related to IL-7 receptor signaling function. Instead, age was inversely related to IL-7 signaling in cells from both HIV-infected viremic subjects and healthy control subjects. Thus, HIV infection results in impaired IL-7 responsiveness, especially in memory CD4+ T cells, and this defect is likely compounded by aging.

HIV infection-associated immune activation occurs by two distinct pathways that differentially affect CD4 and CD8 T cells

HIV infection is characterized by a brisk immune activation that plays an important role in the CD4 depletion and immune dysfunction of patients with AIDS. The mechanism underlying this activation is poorly understood. In the current study, we tested the hypothesis that this activation is the net product of two distinct pathways: the inflammatory response to HIV infection and the homeostatic response to CD4 T cell depletion. Using ex vivo BrdU incorporation of PBMCs from 284 patients with different stages of HIV infection, we found that CD4 proliferation was better predicted by the combination of CD4 depletion and HIV viral load (R(2) = 0.375, P < 0.001) than by either parameter alone (CD4 T cell counts, R(2) = 0.202, P < 0.001; HIV viremia, R(2) = 0.302, P < 0.001). Interestingly, CD8 T cell proliferation could be predicted by HIV RNA levels alone (R(2) = 0.334, P < 0.001) and this predictive value increased only slightly (R(2) = 0.346, P < 0.001) when CD4 T cell depletion was taken into account. Consistent with the hypothesis that CD4 T cell proliferation is driven by IL-7 as a homeostatic response to CD4 T cell depletion, levels of phosphorylated STAT-5 were found to be elevated in naive subsets of CD4 and CD8 T cells from patients with HIV infection and in the central memory subset of CD4 T cells. Taken together these data demonstrate that at least two different pathways lead to immune activation of T cells in patients with HIV infection and these pathways differentially influence CD4 and CD8 T cell subsets.

Use of Cre-adenovirus and CAR transgenic mice for efficient deletion of genes in post-thymic T cells

Conditional gene deletion using lineage-specific transgenic expression of Cre has been useful for defining the role of specific gene products in mice in vivo. However, this technology has had limitations for studies of peripheral T cell biology, since the T-lineage promoters commonly used are active early in thymic development. As such, T cell development can be altered by the resulting genetic alterations, thus limiting the interpretation of the data in post-thymic T cell studies. Thus, new strategies are needed to delete targeted genes directly in peripheral T lymphocytes. The availability of transgenic mice expressing the CAR in the T cell compartment enabled testing of Cre-mediated recombination using an adenoviral vector in naïve peripheral T cells in vitro, even without cellular activation. Using Rosa26R reporterxCAR transgenic mice, we describe conditions by which Cre-mediated deletion of targeted genes can be achieved with primary T cells in vitro. These cells can also be adoptively transferred into defined recipient mice for study in vivo. We use conditional PTEN-deficient mice as proof of concept to confirm the value of this technique for deleting a negative regulator of T cell activation. This technology should be broadly applicable for studies of T cell-specific gene deletion to gain understanding of function in the post-thymic T cell compartment.