IL-7 promotes T cell proliferation through destabilization of p27Kip1

IL-7 promotes CD19-directed CAR-T cells proliferation through miRNA-98-5p by targeting CDKN1A

CAR-T targeting CD19 have achieved significant effects in the treatment of B-line leukemia and lymphoma. However, the treated patients frequently relapsed and could not achieve complete remission. Therefore, improving the proliferation and cytotoxicity of CAR-T cells, reducing exhaustion and enhancing infiltration capacity are still issues to be solved. The IL-7 has been shown to enhance the memory characteristics of CAR-T cells, but the specific mechanism has yet to be elaborated. miRNAs play an important role in T cell activity. However, whether miRNA is involved in the activation of CAR-T cells by IL-7 has not yet been reported. Our previous study had established the 3rd generation CAR-T cells. The present study further found that IL-7 significantly increased the proliferation of anti-CD19 CAR-T cells, the ratio of CD4 + CAR + cells and the S phase of cell cycle. In vivo study NAMALWA xenograft model showed that IL-7-stimulated CAR-T cells possessed stronger tumoricidal efficiency. Further we validated that IL-7 induced CAR-T cells had low expression of CDKN1A and high expression of miRNA-98-5p. Additionally, CDKN1A was associated with miRNA-98-5p. Our results, for the first time, suggested IL-7 could conspicuously enhance the proliferation of CAR-T cells through miRNA-98-5p targeting CDKN1A expression, which should be applied to CAR-T production.

The Therapeutic Values of IL-7/IL-7R and the Recombinant Derivatives in Glioma: A Narrative Review

Interleukin-7 (IL-7) is essential for maintaining the immune system's defense functions by regulating the development and homeostasis of lymphocytes. Findings have shown the high efficacy of IL-7/IL-7 receptor (IL-7R)-based immunotherapy on various malignancies, with confirmation in both animal models and humans. In recent years, the progression-free survival and overall survival of patients suffering from gliomas significantly increased by introducing C7R-expressing chimeric antigen receptor (CAR)-T cells and long-acting IL-7 agonists such as NT-I7 (rhIL-7-hyFc, Efineptakin alfa). However, the effect of IL-7-based immunotherapies on the resistance of tumor cells to chemotherapy (when used simultaneously with chemotherapy agents) is still ambiguous and requires further studies. This article first reviews the pathophysiological roles of IL-7/IL-7R in tumors, focusing on gliomas. Subsequently, it discusses the therapeutic values of IL-7/IL-7R and the recombinant derivatives in gliomas.

TSLP/dendritic cell axis promotes CD4+ T cell tolerance to the gut microbiome

Thymic stromal lymphopoietin (TSLP) overexpression is widely associated with atopy. However, TSLP is expressed in normal barrier organs, suggesting a homeostatic function. To determine the function of TSLP in barrier sites, we investigated the impact of endogenous TSLP signaling on the homeostatic expansion of CD4+ T cells in adult mice. Surprisingly, incoming CD4+ T cells induced lethal colitis in adult Rag1-knockout animals that lacked the TSLP receptor (Rag1KOTslprKO). Endogenous TSLP signaling was required for reduced CD4+ T cell proliferation, Treg differentiation, and homeostatic cytokine production. CD4+ T cell expansion in Rag1KOTslprKO mice was dependent on the gut microbiome. The lethal colitis was rescued by parabiosis between Rag1KOTslprKO and Rag1KO animals and wild-type dendritic cells (DCs) suppressed CD4+ T cell-induced colitis in Rag1KOTslprKO mice. A compromised T cell tolerance was noted in TslprKO adult colon, which was exacerbated by anti-PD-1 and anti-CTLA-4 therapy. These results reveal a critical peripheral tolerance axis between TSLP and DCs in the colon that blocks CD4+ T cell activation against the commensal gut microbiome.

IL-7: A promising adjuvant ensuring effective T cell responses and memory in combination with cancer vaccines?

Cancer vaccines exhibit specificity, effectiveness, and safety as an alternative immunotherapeutic strategy to struggle against malignant diseases, especially with the rapid development of mRNA cancer vaccines in recent years. However, how to maintain long-term immune memory after vaccination, especially T cells memory, to fulfill lasting surveillance against cancers, is still a challenging issue for researchers all over the world. IL-7 is critical for the development, maintenance, and proliferation of T lymphocytes, highlighting its potential role as an adjuvant in the development of cancer vaccines. Here, we summarized the IL-7/IL-7 receptor signaling in the development of T lymphocytes, the biological function of IL-7 in the maintenance and survival of T lymphocytes, the performance of IL-7 in pre-clinical and clinical trials of cancer vaccines, and the rationale to apply IL-7 as an adjuvant in cancer vaccine-based therapeutic strategy.

Lymphopenia and Mechanisms of T-Cell Regeneration

Chronic lymphopenia, in particular, T-lymphocyte deficiency, increases the risk of death from cancer, cardiovascular and respiratory diseases and serves as a risk factor for a severe course and poor outcome of infectious diseases such as COVID-19. The regeneration of T-lymphocytes is a complex multilevel process, many questions of which still remain unanswered. The present review considers two main pathways of increasing the T-cell number in lymphopenia: production in the thymus and homeostatic proliferation in the periphery. Literature data on the signals that regulate each pathway are summarized. Their contribution to the quantitative and qualitative restoration of the immune cell pool is analyzed. The features of CD4⁺ and CD8⁺ T-lymphocytes’ regeneration are considered.

Down-regulated ALKBH5 Expression Could Affect the Function of T Cells in Systemic Lupus Erythematosus Patients

BACKGROUND

N6-methyladenosine (m6A) modification is widespread in eukaryotic mRNA, regulated by m6A demethylase, AlkB homolog 5 (ALKBH5). However, the role of m6A in systemic lupus erythematosus (SLE) is still obscure. We explored ALKBH5 expression in SLE patients and its effects on T cells.

METHODS

100 SLE patients and 110 healthy controls were recruited to investigate the expression of ALKBH5 in peripheral blood mononuclear cells (PBMCs). An additional 32 SLE patients and 32 health controls were enrolled to explore the expression of ALKBH5 in T cells. Then we explored the function of ALKBH5 in T cells by lentivirus.

RESULTS

The expressions of ALKBH5 were downregulated in both PBMCs and T cells in SLE patients (all P<0.05). In PBMCs: ALKBH5 mRNA levels were associated with complement C4 level in plasma (P<0.05). In T cells: ALKBH5 mRNA levels were downregulated in SLE patients with low complement levels, high anti-dsDNA, anti-Sm, anti-RNP, and proteinuria compared with those without, respectively (all P<0.05); ALKBH5 mRNA levels were negatively related with SLE disease activity index score, erythrocyte sedimentation rate, and anti-dsDNA levels (all P<0.05), and positively correlated with complement C3 and C4 level (all P<0.05). Functionally, the overexpression of ALKBH5 promoted apoptosis and inhibited the proliferation of T cells (all P<0.05).

CONCLUSION

ALKBH5 expression is downregulated in SLE patients and could affect the apoptosis and proliferation of T cells, but the exact mechanism still needs to be further explored.

Diagnosis and Treatment of a Patient With Severe Combined Immunodeficiency Due to a Novel Homozygous Mutation in the IL-7Rα Chain

The interleukin-7 receptor (IL-7R) is expressed on lymphoid cells and plays an important role in the development, homeostasis, survival, and proliferation of T cells. Bi-allelic mutations in the IL-7Rα chain abolish T cell development and function resulting in severe combined immunodeficiency disease. In this manuscript, we investigate a 1 year-old patient born to consanguineous parents, who suffered from autoimmune hemolytic anemia since birth associated with recurrent severe infections. Flow cytometric analysis of the patient’s peripheral blood demonstrated elevated numbers of B and NK cells, decreased numbers of T cells, defective thymic output, a predominance of memory T cells, and absent T cell proliferation. Next Generation Sequencing identified a novel homozygous pathogenic mutation in IL7RA (c.379G>A) that resulted in aberrant IL7RA RNA splicing and absent IL-7Rα expression. The patient was successfully transplanted using her HLA-matched relative as donor. One year after transplant, the patient is clinically stable with normal reconstitution of donor T cells that express IL-7Rα, a significant increase in the percentages of recent thymic emigrant and peripheral T cells, normalization of naïve and memory T cells, and restoration of her T cell’s proliferative response. Therefore, using genetic and functional approaches, we identified a novel deleterious mutation in IL-7Rα that results in T^-B⁺NK⁺ phenotype, and report successful hematopoietic stem cell transplantation of the patient. This represents the first bedside-to-bench-and-back case entirely performed on a patient with severe combined immunodeficiency at the American University of Beirut Medical Center.

The Broad Immunomodulatory Effects of IL-7 and Its Application In Vaccines

Interleukin-7 (IL-7) is produced by stromal cells, keratinocytes, and epithelial cells in host tissues or tumors and exerts a wide range of immune effects mediated by the IL-7 receptor (IL-7R). IL-7 is primarily involved in regulating the development of B cells, T cells, natural killer cells, and dendritic cells via the JAK-STAT, PI3K-Akt, and MAPK pathways. This cytokine participates in the early generation of lymphocyte subsets and maintain the survival of all lymphocyte subsets; in particular, IL-7 is essential for orchestrating the rearrangement of immunoglobulin genes and T-cell receptor genes in precursor B and T cells, respectively. In addition, IL-7 can aid the activation of immune cells in anti-virus and anti-tumor immunity and plays important roles in the restoration of immune function. These biological functions of IL-7 make it an important molecular adjuvant to improve vaccine efficacy as it can promote and extend systemic immune responses against pathogens by prolonging lymphocyte survival, enhancing effector cell activity, and increasing antigen-specific memory cell production. This review focuses on the biological function and mechanism of IL-7 and summarizes its contribution towards improved vaccine efficacy. We hope to provide a thorough overview of this cytokine and provide strategies for the development of the future vaccines.

Comprehensive analysis of the immunomodulatory effects of rapamycin on human T cells in graft-versus-host disease prophylaxis

Graft-versus-host disease (GVHD) is a major cause of toxicity after allogeneic hematopoietic cell transplantation (allo-HCT). While rapamycin (RAPA) is commonly used in GVHD prophylaxis in combination with a calcineurin inhibitor (CNI), the understanding of its mechanism of action on human T cells is still incomplete. Here, we performed an extensive analysis of RAPA effects on human T cells in a humanized mouse model of GVHD, in ex-vivo T cell cultures and in patients given RAPA plus tacrolimus as GVHD prophylaxis after nonmyeloablative allo-HCT. We demonstrate that RAPA mitigates GVHD by decreasing T cell engraftment and differentiation, inhibiting CD8⁺ T cell activation and increasing the long-term IL-2 secretion, thereby supporting regulatory T cell (Treg) proliferation. In contrast, graft-versus-leukemia effects were not abrogated, as RAPA-treated T cells had increased resistance to apoptosis and retained their effector function and proliferative capacity upon re-stimulation. Importantly, we found that RAPA impact on Treg and CD8⁺ T cells was closely dependent upon IL-2 signaling and that therapeutic options interfering with IL-2, such as calcineurin inhibitors, antagonize the IL-2-dependent promotion of Treg mediated by RAPA. Our results suggest that RAPA immunological efficacy could be improved in combination with drugs having possible synergistic effects such as the hypomethylating agent 5-azacytidine.

Interleukin (IL)-7 Signaling in the Tumor Microenvironment

Interleukin (IL)-7 plays an important immunoregulatory role in different types of cells. Therefore, it attracts researcher's attention, but despite the fact, many aspects of its modulatory action, as well as other functionalities, are still poorly understood. The review summarizes current knowledge on the interleukin-7 and its signaling cascade in context of cancer development. Moreover, it provides a cancer-type focused description of the involvement of IL-7 in solid tumors, as well as hematological malignancies.The interleukin has been discovered as a growth factor crucial for the early lymphocyte development and supporting the growth of malignant cells in certain leukemias and lymphomas. Therefore, its targeting has been explored as a treatment modality in hematological malignancies, while the unique ability to expand lymphocyte populations selectively and without hyperinflammation has been used in experimental immunotherapies in patients with lymphopenia. Ever since the early research demonstrated a reduced growth of solid tumors in the presence of IL-7, the interleukin application in boosting up the anticancer immunity has been investigated. However, a growing body of evidence indicative of IL-7 upregulation in carcinomas, facilitating tumor growth and metastasis and aiding drug-resistance, is accumulating. It therefore becomes increasingly apparent that the response to the IL-7 stimulus strongly depends on cell type, their developmental stage, and microenvironmental context. The interleukin exerts its regulatory action mainly through phosphorylation events in JAK/STAT and PI3K/Akt pathways, while the significance of MAPK pathway seems to be limited to solid tumors. Given the unwavering interest in IL-7 application in immunotherapy, a better understanding of interleukin role, source in tumor microenvironment, and signaling pathways, as well as the identification of cells that are likely to respond should be a research priority.

IL-7/αIL-7 mAb M25 immunocomplexes expand CD8+ T cells but paradoxically abrogate the antitumor activity of CTLA-4 and PD-1 blockage

Supraphysiological levels of IL-7 induce increase counts of pre-B cells, naive T cells and memory phenotype CD8⁺ T cells. Immunocomplexes of IL-7 and αIL-7 mAb M25 (IL-7/M25) were described as IL-7 superagonist in vivo. Thus, treatment of mice with IL-7/M25 remarkably increases the size of the T cell pool. We decided to use IL-7/M25 in order to expand the T cell population prior to the administration of αCTLA-4 and αPD-1 mAbs in tumor-bearing mice and in turn boost the immunotherapy based on a combination of CTLA-4 and PD-1 blockage. We found that just four doses of IL-7/M25 increased the absolute numbers of splenocytes approximately fivefold and significantly shifted the CD4⁺:CD8⁺ T cell ratio in favor of CD8⁺ T cells. There was also a substantive increase in relative counts of memory phenotype CD8⁺ T cells (approximately threefold) within CD8⁺ T cells but a significant decrease (approximately 30%) in relative counts of Treg cells within CD4⁺ T cells. All these data suggest that IL-7/M25 offer a suitable approach to potentiate tumor immunotherapy through CTLA-4 and PD-1 blockage. Unexpectedly, IL-7/M25 significantly abrogated the antitumor activity of αCTLA-4 plus αPD-1 mAbs in the following mouse tumor models: MC-38 and CT26 colon carcinoma and B16F10 melanoma. This paradoxical effect of IL-7/M25 on the antitumor activity of CTLA-4 and PD-1 blockage was not mediated via either increased levels of IL-10 or TGF-β in the sera or increased counts of IL-10-producing B or T cells in the spleen of mice injected with IL-7/M25. Thus, our work shows that caution should be exercised when combining two immunotherapy approaches together.

IL-7 induces sCD127 release and mCD127 downregulation in human CD8+ T cells by distinct yet overlapping mechanisms, both of which are impaired in HIV infection

The IL‐7 receptor specific α chain, CD127, can be expressed both as a membrane‐associated (mCD127) and a soluble form (sCD127), however, the mechanisms involved in their regulation remain to be defined. We first demonstrated in primary human CD8⁺ T cells that IL‐7‐induced downregulation of mCD127 expression is dependent on JAK and PI3K signaling, whereas IL‐7‐induced sCD127 release is also mediated by STAT5. Following stimulation with IL‐7, expression of alternatively spliced variants of the CD127 gene, sCD127 mRNA, is reduced, but to a lesser degree than the full‐length gene. Evaluation of the role of proteases revealed that MMP‐9 was involved in sCD127 release, without affecting the expression of mCD127, suggesting it does not induce direct shedding from the cell surface. Since defects in the IL‐7/CD127 pathway occur in various diseases, including HIV, we evaluated CD8⁺ T cells derived from HAART‐treated HIV‐infected individuals and found that IL‐7‐induced (1) downregulation of mCD127, (2) release of sCD127, and (3) expression of the sCD127 mRNA were all impaired. Expression of mCD127 and sCD127 is, therefore, regulated by distinct, but overlapping, mechanisms and their impairment in HIV infection contributes to our understanding of the CD8⁺ T cell dysfunction that persists despite effective antiretroviral therapy.

Therapeutic targeting of the E3 ubiquitin ligase SKP2 in T-ALL

Timed degradation of the cyclin-dependent kinase inhibitor p27^Kip1 by the E3 ubiquitin ligase F-box protein SKP2 is critical for T-cell progression into cell cycle, coordinating proliferation and differentiation processes. SKP2 expression is regulated by mitogenic stimuli and by Notch signaling, a key pathway in T-cell development and in T-cell acute lymphoblastic leukemia (T-ALL); however, it is not known whether SKP2 plays a role in the development of T-ALL. Here, we determined that SKP2 function is relevant for T-ALL leukemogenesis, whereas is dispensable for T-cell development. Targeted inhibition of SKP2 by genetic deletion or pharmacological blockade markedly inhibited proliferation of human T-ALL cells in vitro and antagonized disease in vivo in murine and xenograft leukemia models, with little effect on normal tissues. We also demonstrate a novel feed forward feedback loop by which Notch and IL-7 signaling cooperatively converge on SKP2 induction and cell cycle activation. These studies show that the Notch/SKP2/p27^Kip1 pathway plays a unique role in T-ALL development and provide a proof-of-concept for the use of SKP2 as a new therapeutic target in T-cell acute lymphoblastic leukemia (T-ALL).

Cancer Conditioned Medium Modulates Functional and Phenotypic Properties of Human Decidua Parietalis Mesenchymal Stem/Stromal Cells

Background

Mesenchymal Stem/Stromal Cells (MSCs) from the decidua parietalis (DPMSCs) of human term placenta express several molecules with important biological and immunological properties. DPMSCs induce natural killer cell expression of inflammatory receptors and their cytotoxic activity against cancer cells. These properties make DPMSCs promising therapeutical agent for cancer. The successful development of MSCs as an anti-cancer therapeutic cells rely on their ability to function in a hostile inflammatory and oxidative stress cancer environment. Here, we studied the effects of conditioned medium obtained from the culture of breast cancer cells (CMMDA-231) on the functional and phenotypic properties of DPMSCs.

Methods

DPMSCs were cultured with CMMDA-231 and important functions of DPMSCs were measured. The effect of CMMDA-231 on DPMSC expression of several genes with different functions was also evaluated.

Results

DPMSCs were able to function in response to CMMDA-231, but with reduced proliferative and adhesive potentials. Preconditioning of DPMSCs with CMMDA-231 enhanced their adhesion while reducing their invasion. In addition, CMMDA-231 modulated DPMSC expression of many genes with various functional (i.e., proliferation, adhesion, and invasion) properties. DPMSCs also showed increased expression of genes with anti-cancer property.

Conclusion

These data show the ability of DPMSCs to survive and function in cancer environment. In addition, preconditioning of DPMSCs with CMMDA-231 enhanced their anti-cancer properties and thus demonstrating their potential as an anti-cancer therapeutic agent. However, future studies are essential to reveal the mechanism underlying the effects of MDA-231 on DPMSC functional activities and also to confirm the anti-cancer therapeutic potential of DPMSCs.

FoxO1 controls the expansion of pre-B cells by regulating the expression of interleukin 7 receptor α chain and its signal pathway

Forkhead box O1 (FoxO1) has a crucial role in the early B cell development. To understand the functional importance of FoxO1 gene in the early B cell expansion, we established a FoxO1 knockdown model using 70Z/3 pre-B cell line. The FoxO1 knockdown 70Z/3 cells (70Z/3-KD cells) showed the down-regulated expression of interleukin 7 receptor α chain (IL-7Rα). Moreover, the signaling via IL-7Rα was significantly attenuated in the 70Z/3-KD cells, and this alteration was fully rescued by re-expression of FoxO1 gene. Compared to the mock cells, loss of FoxO1 reduced the growth rates in the 70Z/3-KD cells, and was fully rescued by reintroduction of FoxO1 gene. The expansion of pre-B cells (CD45R⁺CD43^- fraction) was also reduced by the knockdown of FoxO1 gene. Indeed, FoxO1 induces accumulation in the p27-mediated G0/G1 phase arrest in 70Z/3 cells. FoxO1 bound to the Il7ra locus specifically and regulate the IL-7Rα transcription. In conclusion, FoxO1 regulates the expansion of pre-B cells by regulating the expression of IL-7Rα and its signal transduction.

IL-7-induced proliferation of peripheral Th17 cells is impaired in HAART-controlled HIV infection

OBJECTIVES

Th17 cells are key regulators of functional immunity in mucosal tissues, including the gut-associated lymphoid tissue (GALT), an important site of immune impairment in HIV infection. During HIV infection, Th17 cells are lost in large numbers from the GALT. Despite the recovery of peripheral CD4 T cells that accompanies suppression of viral replication with HAART, Th17 cells in GALT are not completely restored. IL-7 is essential for the survival and proliferation of T cells, but its signaling through its receptor IL-7Rα (CD127), is impaired in CD8 T cells and thymocytes during HIV infection. We set out to determine if decreased CD127 expression or impaired CD127 signaling may be the cause of Th17 impairment in HAART-controlled HIV infection.

DESIGN

Healthy and HIV donors on HAART were selected for this study of Th17 cell function in HIV.

METHODS

Peripheral CD4 T cells and Th17 cells were isolated using magnetic beads, then stimulated with IL-7. CD127 expression and the phosphorylation of signaling molecules was determined using flow cytometry. Proliferation was determined with a CFSE dilution assay.

RESULTS

CD127 was not decreased on Th17 cells from HAART-controlled HIV individuals, in fact, the percentage of Th17 cells that express CD127 was increased in treated HIV individuals. Furthermore, Th17 cells from HAART-controlled individuals, have normal IL-7-induced STAT5 and Bcl-2 responses, but vastly decreased proliferative responses.

CONCLUSION

This reduced IL-7 responsiveness may explain the lack of Th17 cell recovery and ongoing systemic immune activation that persists despite well treated HIV infection.

Chimeric switch receptor: switching for improved adoptive T-cell therapy against cancers

Adoptive T-lymphocyte transfer-based immunotherapy for cancers has seen huge leaps with both CARs and engineered TCRs. Despite this, issues relating to safety and efficacy persist. To address this, chimeric switch receptors have been created to reverse the outcomes of their original signaling pathways in order to confer immune cells with the ability to overcome the immunosuppressive tumor microenvironment and to allow them to have greater in vivo persistence. Activating switch receptors exploit the inhibitory molecules expressed by cancer cells to further stimulate the tumor antigen-specific T lymphocytes. On the other hand, inhibitory switch receptors inhibit the effects of tumor-reactive T lymphocytes on unintended targets. This paper reviews the switch receptors reported thus far, and lists out potential improvements and future works.

Inhibiting Janus Kinase 1 and BCL-2 to treat T cell acute lymphoblastic leukemia with IL7-Rα mutations

Acute lymphoblastic leukemia (ALL) is the most common cancer in children. Current chemotherapy is quite toxic in growing children and more directed therapeutics are being sought. The IL-7R pathway is a major driver of ALL and here we evaluate two drugs directed to that pathway using a model of T cell ALL. Mutant gain-of-function IL-7Rα was transduced into an IL-7-dependent murine thymocyte line conferring ligand-independent survival and growth. JAK1 is associated with IL-7Rα and mediates signaling from the mutant receptor. In vitro, treating the transformed cell line with the JAK1/2 inhibitor ruxolitinib inhibited ligand-independent signaling and induced cell death. Transfer of the transformed cell line into mice resulted in aggressive leukemia and untreated mice succumbed in about three weeks. Treatment with ruxolitinib incorporated into chow showed a potent therapeutic benefit with reduction in leukemic burden and extension of survival. BCL-2 is an anti-apoptotic downstream mediator of the IL-7R survival mechanism. Venetoclax, an inhibitor of BCL-2, showed activity against the transformed cell line in vitro and could be combined with ruxolitinib in vivo. These findings support the therapeutic potential of treating T-ALL by targeting the IL-7R pathway.

Spontaneous T Cell Proliferation: A Physiologic Process to Create and Maintain Homeostatic Balance and Diversity of the Immune System

Naive T lymphocytes undergo heterogeneous proliferative responses when introduced into lymphopenic hosts, referred to as “homeostatic proliferation” and “spontaneous proliferation.” Spontaneous proliferation is a unique process through which the immune system generates memory phenotype cells with increasing T cell receptors repertoire complexity. Here, the mechanisms that initiate and control spontaneous proliferation are discussed.

Interleukin-7 restores lymphocytes in septic shock: the IRIS-7 randomized clinical trial

BACKGROUND

A defining pathophysiologic feature of sepsis is profound apoptosis-induced death and depletion of CD4+ and CD8+ T cells. Interleukin-7 (IL-7) is an antiapoptotic common γ-chain cytokine that is essential for lymphocyte proliferation and survival. Clinical trials of IL-7 in over 390 oncologic and lymphopenic patients showed that IL-7 was safe, invariably increased CD4+ and CD8+ lymphocyte counts, and improved immunity.

METHODS

We conducted a prospective, randomized, double-blind, placebo-controlled trial of recombinant human IL-7 (CYT107) in patients with septic shock and severe lymphopenia. Twenty-seven patients at academic sites in France and the United States received CYT107 or placebo for 4 weeks. Primary aims were to determine the safety of CYT107 in sepsis and its ability to reverse lymphopenia.

RESULTS

CYT107 was well tolerated without evidence of inducing cytokine storm or worsening inflammation or organ dysfunction. CYT107 caused a 3- to 4-fold increase in absolute lymphocyte counts and in circulating CD4+ and CD8+ T cells that persisted for weeks after drug administration. CYT107 also increased T cell proliferation and activation.

CONCLUSIONS

This is the first trial of an immunoadjuvant therapy targeting defects in adaptive immunity in patients with sepsis. CYT107 reversed the marked loss of CD4+ and CD8+ immune effector cells, a hallmark of sepsis and a likely key mechanism in its morbidity and mortality. CYT107 represents a potential new way forward in the treatment of patients with sepsis by restoring adaptive immunity. Such immune-based therapy should be broadly protective against diverse pathogens including multidrug resistant bacteria that preferentially target patients with impaired immunity.

TRIAL REGISTRATION

Trials registered at clinicaltrials.gov: NCT02640807 and NCT02797431.

FUNDING

Revimmune, NIH National Institute of General Medical Sciences GM44118.

A new approach to the role of IL-7 and TGF-ß in the in vitro generation of thymus-derived CD4+CD25+Foxp3+ regulatory T cells

Thymus-derived regulatory T cells of CD4+CD25+Foxp3+ phenotype develop as a functional, mature population playing an essential role in self-tolerance and immune homeostasis, and exhibiting therapeutic potential to inhibit adverse immune response. Despite intensive research on thymus-derived Tregs, the knowledge about agents involved in their generation, survival, proliferation, and biological functions is still insufficient. In this research we have focused on the role of selected cytokines in previously developed in vitro model based on the application of anti-CD3 monoclonal antibodies. We have demonstrated an essential role of IL-7 and TGF-β in the generation of thymus-derived Tregs in the co-culture of thymocytes and JAWS II cells. In addition, in vitro generated Tregs exhibited their suppressive function similarly to Tregs sorted from freshly isolated thymus.

Autophagy regulates T lymphocyte proliferation through selective degradation of the cell-cycle inhibitor CDKN1B/p27Kip1

The highly conserved cellular degradation pathway, macroautophagy, regulates the homeostasis of organelles and promotes the survival of T lymphocytes. Previous results indicate that Atg3-, Atg5-, or Pik3c3/Vps34-deficient T cells cannot proliferate efficiently. Here we demonstrate that the proliferation of Atg7-deficient T cells is defective. By using an adoptive transfer and Listeria monocytogenes (LM) mouse infection model, we found that the primary immune response against LM is intrinsically impaired in autophagy-deficient CD8(+) T cells because the cell population cannot expand after infection. Autophagy-deficient T cells fail to enter into S-phase after TCR stimulation. The major negative regulator of the cell cycle in T lymphocytes, CDKN1B, is accumulated in autophagy-deficient naïve T cells and CDKN1B cannot be degraded after TCR stimulation. Furthermore, our results indicate that genetic deletion of one allele of CDKN1B in autophagy-deficient T cells restores proliferative capability and the cells can enter into S-phase after TCR stimulation. Finally, we found that natural CDKN1B forms polymers and is physiologically associated with the autophagy receptor protein SQSTM1/p62 (sequestosome 1). Collectively, autophagy is required for maintaining the expression level of CDKN1B in naïve T cells and selectively degrades CDKN1B after TCR stimulation.

Interleukin-7 Modulates Anti-Tumor CD8+ T Cell Responses via Its Action on Host Cells

The adoptive transfer of antigen-specific CD8+ T cells is a promising approach for the treatment of chronic viral and malignant diseases. In order to improve adoptive T cell therapy (ATT) of cancer, recent strategies aim at the antibody-based blockade of immunosuppressive signaling pathways in CD8+ T cells. Alternatively, adjuvant effects of immunostimulatory cytokines might be exploited to improve therapeutic CD8+ T cell responses. For example, Interleukin-7 (IL-7) is a potent growth, activation and survival factor for CD8+ T cells that can be used to improve virus- and tumor-specific CD8+ T cell responses. Although direct IL-7 effects on CD8+ T cells were studied extensively in numerous models, the contribution of IL-7 receptor-competent (IL-7R+) host cells remained unclear. In the current study we provide evidence that CD8+ T cell-mediated tumor rejection in response to recombinant IL-7 (rIL-7) therapy is strictly dependent on IL-7R+ host cells. On the contrary, CD8+ T cell expansion is independent of host IL-7R expression. If, however, rIL-7 therapy and peptide vaccination are combined, host IL-7R signaling is crucial for CD8+ T cell expansion. Unexpectedly, maximum CD8+ T cell expansion relies mainly on IL-7R signaling in non-hematopoietic host cells, similar to the massive accumulation of dendritic cells and granulocytes. In summary, we provide evidence that IL-7R+ host cells are major targets of rIL-7 that modulate therapeutic CD8+ T cell responses and the outcome of rIL-7-assisted ATT. This knowledge may have important implications for the design and optimization of clinical ATT protocols.

Targeting Homeostatic T Cell Proliferation to Control Beta-Cell Autoimmunity

Immunomodulation of the autoreactive T cell response is considered a major strategy to control beta-cell autoimmunity, both in the natural history of type 1 diabetes and in islet transplantation, which can be affected by autoimmunity recurrence. So far, these strategies have had modest results, prompting efforts to define novel cellular and molecular targets to control autoreactive T cell expansion and activation. Novel findings highlighted the important role of the homeostatic cytokine interleukin-7 in inducing proliferation and differentiation of autoreactive T cell clones that causes beta-cell autoimmunity. In this review, we discuss recent evidences and novel findings on the role of IL-7 mediated homeostatic T cell proliferation in the process of beta-cell destruction and evidences of how targeting IL-7 and its receptor could be an innovative and effective strategy to control beta-cell autoimmunity.

The BMP Pathway Participates in Human Naive CD4+ T Cell Activation and Homeostasis

Bone Morphogenetic Proteins (BMPs) form a group of secreted factors that belongs to the TGF-β superfamily. Among different roles in a number of immune cell types, BMPs are known to regulate T cell development within the thymus, although the role of BMP signaling in human mature T cells remains elusive. In this study, we demonstrate that canonical BMP signaling is necessary during two critical events that regulate the size and function of human naive CD4⁺ T cell population: activation and homeostasis. Upon stimulation via TCR, naive CD4⁺ T cells upregulate the expression of BMP ligands triggering canonical BMP signaling in CD25⁺ cells. Blockade of BMP signaling severely impairs CD4⁺ T cell proliferation after activation mainly through regulation of IL-2, since the addition of this cytokine recuperates normal T cell expansion after inhibition of BMP signaling. Similarly, activation of canonical BMP pathway is required for both the maintenance of cell survival and the homeostatic proliferation induced by IL-7, a key factor for T cell homeostasis. Moreover, upregulation of two critical receptors for T cell homeostasis, CXCR4 and CCR9, triggered by IL-7 is also abrogated in the absence of BMP signaling. Collectively, we describe important roles of the canonical BMP signaling in human naive CD4⁺ T cell activation and homeostasis that could be valuable for clinical application.

Interferon-α inhibits CD4 T cell responses to interleukin-7 and interleukin-2 and selectively interferes with Akt signaling

Persistent type I IFN production occurs during chronic viral infections, such as HIV disease. As type I IFNs have antiproliferative activity, it is possible that chronic exposure to these cytokines could adversely affect T cell homeostasis. We investigated the capacity of IFN-α to impair T cell proliferation induced by the homeostatic cytokine, IL-7, or another common γ-chain cytokine, IL-2, in cells from healthy human donors. We found that IL-7- or IL-2-induced proliferation of CD4(+) T cells was partially inhibited in the presence of IFN-α. The CD4(+) T cells that were exposed to IFN-α also displayed attenuated induction of IL-2 and CD40L following TCR stimulation. Analyses of signaling pathways indicated that IL-7 and IL-2 induced a delayed and sustained P-Akt signal that lasted for several days and was partially inhibited by IFN-α. In contrast, IL-7-induced P-STAT5 was not affected by IFN-α. Furthermore, IFN-α had no detectable effect on P-Akt that was induced by the chemokine SDF-1. Both inhibitors of P-Akt and P-STAT5 blocked IL-7-induced T cell proliferation, confirming that both signaling pathways are important for IL-7-induced T cell proliferation. These results demonstrate that IFN-α can selectively inhibit cytokine-induced P-Akt as a potential mechanism to disrupt homeostasis of T lymphocytes.

Adaptive immunity to murine skin commensals

The adaptive immune system provides critical defense against pathogenic bacteria. Commensal bacteria have begun to receive much attention in recent years, especially in the gut where there is growing evidence of complex interactions with the adaptive immune system. In the present study, we observed that commensal skin bacteria are recognized by major populations of T cells in skin-draining lymph nodes of mice. Recombination activating gene 1 (Rag1)(-/-) mice, which lack adaptive immune cells, contained living skin-derived bacteria and bacterial sequences, especially mycobacteria, in their skin-draining lymph nodes. T cells from skin-draining lymph nodes of normal mice were shown, in vitro, to specifically recognize bacteria of several species that were grown from Rag1(-/-) lymph nodes. T cells from skin-draining lymph nodes, transferred into Rag1(-/-) mice proliferated in skin-draining lymph nodes, expressed a restricted T-cell receptor spectrotype and produced cytokines. Transfer of T cells into Rag1(-/-) mice had the effect of reducing bacterial sequences in skin-draining lymph nodes and in skin itself. Antibacterial effects of transferred T cells were dependent on IFNγ and IL-17A. These studies suggest a previously unrecognized role for T cells in controlling skin commensal bacteria and provide a mechanism to account for cutaneous infections and mycobacterial infections in T-cell-deficient patients.

p27KIP1 is involved in ERK1/2-mediated MMP-9 expression via the activation of NF-κB binding in the IL-7-induced migration and invasion of 5637 cells

Interleukin-7 (IL-7) plays a pivotal role in the development and survival of lymphocytes, but its role in cancer cell responses remains unexplained. In this study, IL-7 treatment resulted in a significant induction in the wound-healing migration and Matrigel invasion of the 5637 bladder cancer cells, but it did not result in cell proliferation. In addition, IL-7 treatment strongly induced MMP-9 expression, and increased the binding activation of NF-κB and AP-1 motifs, the important transcription factors that regulate MMP-9 expression. Moreover, the treatment of 5637 cells with IL-7 stimulated the phosphorylation of ERK1/2. U0126, an ERK1/2-specific inhibitor, blocked IL-7-induced cell migration and invasion, and also suppressed the expression of MMP-9 in the presence of IL-7. Inhibition of the ERK1/2 function consistently reversed the binding activity of NF-κB without altering AP-1 activation in IL-7-stimulated cells. Among the cell cycle regulators examined, only the expression of the cell cycle inhibitor p27KIP1 was induced by IL-7. Moreover, the inhibition of p27KIP1 by small interfering RNA (siRNA) abolished the migration, invasion and phosphorylation of ERK1/2, the expression of MMP-9, and the binding activity of the NF-κB motif in IL-7-stimulated 5637 cells. These results demonstrated that the cell cycle inhibitor p27KIP1 is involved in ERK1/2-mediated MMP-9 expression via activation of the NF-κB binding motif, which leads to the migration and invasion of bladder cancer cells induced by IL-7. These novel results could help explain the migration and invasion of bladder tumor cells.

Protein kinase C signaling and cell cycle regulation

A link between T cell proliferation and the protein kinase C (PKC) family of serine/threonine kinases has been recognized for about 30 years. However, despite the wealth of information on PKC-mediated control of, T cell activation, understanding of the effects of PKCs on the cell cycle machinery in this cell type remains limited. Studies in other systems have revealed important cell cycle-specific effects of PKC signaling that can either positively or negatively impact proliferation. The outcome of PKC activation is highly context-dependent, with the precise cell cycle target(s) and overall effects determined by the specific isozyme involved, the timing of PKC activation, the cell type, and the signaling environment. Although PKCs can regulate all stages of the cell cycle, they appear to predominantly affect G0/G1 and G2. PKCs can modulate multiple cell cycle regulatory molecules, including cyclins, cyclin-dependent kinases (cdks), cdk inhibitors and cdc25 phosphatases; however, evidence points to Cip/Kip cdk inhibitors and D-type cyclins as key mediators of PKC-regulated cell cycle-specific effects. Several PKC isozymes can target Cip/Kip proteins to control G0/G1 → S and/or G2 → M transit, while effects on D-type cyclins regulate entry into and progression through G1. Analysis of PKC signaling in T cells has largely focused on its roles in T cell activation; thus, observed cell cycle effects are mainly positive. A prominent role is emerging for PKCθ, with non-redundant functions of other isozymes also described. Additional evidence points to PKCδ as a negative regulator of the cell cycle in these cells. As in other cell types, context-dependent effects of individual isozymes have been noted in T cells, and Cip/Kip cdk inhibitors and D-type cyclins appear to be major PKC targets. Future studies are anticipated to take advantage of the similarities between these various systems to enhance understanding of PKC-mediated cell cycle regulation in T cells.

Interleukin-7 receptor controls development and maturation of late stages of thymocyte subpopulations

Interleukin (IL)-7 is a cytokine essential for T lymphocyte development and homeostasis. However, little is known about the roles of IL-7 receptor α-chain (IL-7Rα) in late stages of T-cell development. To address this question, we established IL-7Rα-floxed mice and crossed them with CD4-Cre transgenic mice. Resultant IL-7R conditional knockout (IL-7RcKO) mice exhibited marked reduction in CD8 single positive (SP) T cells, regulatory T cells (Tregs), and natural killer T (NKT) cells in thymus. The proportion and proliferation of both mature CD4SP and CD8SP thymocytes were decreased without affecting Runx expression. In addition, expression of the glucocorticoid-induced TNF receptor was reduced in CD4SP and CD8SP thymocytes, and expression of CD5 was decreased in CD8SP thymocytes. IL-7RcKO mice also showed impaired Treg and NKT cell proliferation and inhibition of NKT cell maturation. Bcl-2 expression was reduced in CD4SP and CD8SP thymocytes but not in Tregs and NKT cells, and introduction of a Bcl-2 transgene rescued frequency and CD5 expression of CD8SP thymocytes. Furthermore, IL-7RcKO mice exhibited greatly increased numbers of B cells and, to a lesser extent, γδ T and dendritic cells in thymus. Overall, this study demonstrates that IL-7Rα differentially controls development and maturation of thymocyte subpopulations in late developmental stages and suggests that IL-7R expression on αβ T cells suppresses development of other cell lineages in thymus.

T-cell intrinsic and extrinsic mechanisms of p27Kip1 in the regulation of CD8 T-cell memory

CD8 T cells exhibit dynamic alterations in proliferation and apoptosis during various phases of the CD8 T cell response, but the mechanisms that regulate cellular proliferation from the standpoint of CD8 T cell memory are not well defined. The cyclin-dependent kinase inhibitor p27^Kip1 functions as a negative regulator of the cell cycle in various cell types including T cells and it has been implicated in regulating cellular processes including differentiation, transcription and migration. Here, we investigated whether p27^Kip1 regulates CD8 T cell memory by T cell-intrinsic or T cell-extrinsic mechanisms, by conditional ablation of p27^Kip1 in T cells or non-T cells. Studies of T cell responses to an acute viral infection show that p27^Kip1 negatively regulates the proliferation of CD8 T cells by T cell-intrinsic mechanisms. However, the enhanced proliferation of CD8 T cells induced by T cell-specific p27^Kip1 deficiency minimally affects the primary expansion or the magnitude of CD8 T cell memory. Unexpectedly, p27^Kip1 ablation in non-T cells markedly augmented the number of high quality memory CD8 T cells by enhancing the accumulation of memory precursor effector cells without increasing their proliferation. Further studies show that p27^Kip1 deficiency in immunizing DCs fail to enhance CD8 T cell memory. Nevertheless, we have delineated the T cell-intrinsic, anti-proliferative activities of p27^Kip1 in CD8 T cells from its role as a factor in non-T cells that restricts the development of CD8 T cell memory. These findings have implications in vaccine development and understanding the mechanisms that maintain T cell homeostasis.

Sequential administration of cytokine genes to enhance cellular immune responses and CD4 (+) T memory cells during DNA vaccination

Antigen specific memory T cells (Tm) have shown to be an important factor in protecting hosts against subsequent infection by previously encountered pathogens. During T-cell activation, several cytokines including IL-6, IL-7 and IL-15, play crucial roles in the development of T cells into memory T cells. With the aim of generating specific Tm, we examined a strategy of sequential administration of molecular adjuvants. In this strategy a DNA vaccine encoding the VP1 capsid protein of foot and mouth disease virus (designated pcD-VP1) was co-delivered to mice along with an IL-6 expressing plasmid (pVAX-IL-6) as an initial molecular adjuvant and boosted with either an IL-7 or IL-15 expressing plasmid, (pVAX-IL-7 or proVAX-IL-15) as the secondary adjuvant. During the pcD-VP1 immunization, we demonstrated that the groups primed with IL-6 and boosted with either IL-7 or IL-15 resulted in the enhancement of cellular and humoral immune responses, maturation of dendritic cells (DCs) and macrophages, and a higher frequency of CD4 (+) Tm (characterized by expressing CD44 (high) CD62L (low) markers, compared with the other groups). Thus, we took advantage of the different effects of cytokines on T cell development, not only to induce a higher level of immune responses after vaccination, but also to generate a higher ratio of CD4 (+) Tm in this sequential cytokine prime-boost study. This would then lead to the mounting of an effective long-term antigen specific immune response.

The major isoforms of Bim contribute to distinct biological activities that govern the processes of autophagy and apoptosis in interleukin-7 dependent lymphocytes

Bim is a BH3-only member of the Bcl-2 family that enables the death of T-cells. Partial rescue of cytokine-deprived T-cells occurs when Bim and the receptor for the T-cell growth factor, interleukin-7, are deleted, implicating Bim as a possible target of interleukin-7-mediated signaling. Alternative splicing yields three major isoforms: BimEL, BimL and BimS. To study the effect of Bim deficiency and define the function of the major isoforms, Bim-containing and Bim-deficient T-cells, dependent on interleukin-7 for growth, were used. Loss of total Bim in interleukin-7-deprived T-cells resulted in delayed apoptosis. However, loss of Bim also impeded the later degradative phase of autophagy. p62, an autophagy-adaptor protein which is normally degraded, accumulated in Bim deficient cells. To explain this, BimL was found to support acidification of lysosomes that later may associate with autophagic vesicles. Key findings showed that inhibition of lysosomal acidification accelerated death upon interleukin-7 withdrawal only in Bim-containing T-cells. intereukin-7 dependent T-cells lacking Bim were less sensitive to inhibition of lysosomal acidification. BimL co-immunoprecipitated with dynein and Lamp1-containing vesicles, indicating BimL could be an adaptor for dynein to facilitate loading of lysosomes. In Bim deficient T-cells, lysosome-tracking probes revealed vesicles of less acidic pH. Over-expression of BimL restored acidic vesicles in Bim deficient T-cells, while other isoforms, BimEL and BimS, promoted intrinsic cell death. These results reveal a novel role for BimL in lysosomal positioning that may be required for the formation of degradative autolysosomes.

Pituitary adenylate cyclase-activating peptide and vasoactive intestinal polypeptide bias Langerhans cell Ag presentation toward Th17 cells

Epidermal Langerhans cells (LCs) are dendritic APCs that play an important role in cutaneous immune responses. LCs are associated with epidermal nerves and the neuropeptides vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) inhibit LC Ag presentation for Th1-type immune responses. Here, we examined whether PACAP or VIP modulates LC Ag presentation for induction of IL-17A-producing CD4(+) T cells. Treatment with VIP or PACAP prior to in vitro LC Ag presentation to CD4(+) T cells enhanced IL-17A, IL-6, and IL-4 production, decreased interferon (IFN)-γ and interleukin (IL)-22 release, and increased RORγt and Gata3 mRNA expression while decreasing T-bet expression. The CD4(+) T-cell population was increased in IL-17A- and IL-4-expressing cells and decreased in IFN-γ-expressing cells. Addition of anti-IL-6 mAb blocked the enhanced IL-17A production seen with LC preexposure to VIP or PACAP. Intradermal administration of VIP or PACAP prior to application of a contact sensitizer at the injection site, followed by harvesting of draining lymph node CD4(+) T cells and stimulation with anti-CD3/anti-CD28 mAbs, enhanced IL-17A and IL-4 production but reduced production of IL-22 and IFN-γ. PACAP and VIP are endogenous mediators that likely regulate immunity and immune-mediated diseases within the skin.

Interleukin-7 influences FOXP3+CD4+ regulatory T cells peripheral homeostasis

Mechanisms governing peripheral CD4+ FOXP3+ regulatory T cells (Treg) survival and homeostasis are multiple suggesting tight and complex regulation of regulatory T cells homeostasis. Some specific factors, such as TGF-β, interleukin-2 (IL-2) and B7 costimulatory molecules have been identified as essentials for maintenance of the peripheral Treg compartment. Conversely, Treg dependency upon classical T cell homeostatic factors such as IL-7 is still unclear. In this work, we formally investigated the role of IL-7 in Treg homeostasis in vivo in murine models. We demonstrated that IL-7 availability regulated the size of peripheral Treg cell pool and thus paralleled the impact of IL-7 on conventional T cell pool. Moreover, we showed that IL-7 administration increased Treg cell numbers by inducing thymic-independent Treg peripheral expansion. Importantly the impact of IL-7 on Treg expansion was detected whether conventional T cells were present or absent as IL-7 directly participates to the peripheral expansion of Treg after adoptive transfer into lymphopenic hosts. Our results definitively identify IL-7 as a central factor contributing to Treg peripheral homeostasis, thus reassembling Treg to other T cell subsets in respect of their need for IL-7 for their peripheral maintenance.

Decreased interleukin 7 responsiveness of T lymphocytes in patients with idiopathic CD4 lymphopenia

BACKGROUND

Elevated serum interleukin 7 (IL-7) levels are observed in lymphopenic conditions, including idiopathic CD4 lymphopenia (ICL), which is characterized by CD4 lymphopenia in the absence of human immunodeficiency virus infection or other known immunodeficiency.

METHODS

To test whether defective IL-7 signaling could be an etiologic or contributing factor in ICL, peripheral blood mononuclear cells from patients with ICL (median CD4 T-cell count, 160 cells/μL) and healthy controls (median CD4 T-cell count, 582 cells/μL) were evaluated for expression of IL-7Rα chain (CD127) and intracellular phosphorylated STAT-5 (a marker of γc cytokine signaling) after cytokine stimulation. Gene expression was analyzed by real-time polymerase chain reaction following IL-7 stimulation.

RESULTS

The percentage of CD4+CD127+ T cells was lower in patients with ICL, compared with controls (P < .001). Lower levels of STAT-5 phosphorylation after IL-7 stimulation were observed in both CD4 and CD8 T cells from patients with ICL, compared with controls (P < .001 and P = .017, respectively), that inversely correlated in CD4 T cells with serum IL-7 levels (r = -0.734, P = .013). Destabilization of p27(kip1), a critical step for IL-7-induced T-cell cycling, was decreased in patients with ICL, compared with controls (P = .004), after IL-7 stimulation.

CONCLUSIONS

These data suggest that diminished responsiveness to IL-7 in CD4 and CD8 T cells during ICL may be contributing to the dysregulation of T-cell homeostasis.

The many roles of IL-7 in B cell development; mediator of survival, proliferation and differentiation

Interleukin-7 (IL-7) plays several important roles during B cell development including aiding in; the specification and commitment of cells to the B lineage, the proliferation and survival of B cell progenitors; and maturation during the pro-B to pre-B cell transition. Regulation and modulation of IL-7 receptor (IL-7R) signaling is critical during B lymphopoiesis, because excessive or deficient IL-7R signaling leads to abnormal or inhibited B cell development. IL-7 works together with E2A, EBF, Pax-5 and other transcription factors to regulate B cell commitment, while also functions to regulate Ig rearrangement by modulating FoxO protein activation and Rag enhancer activity. Suppressor of cytokine signaling (SOCS) proteins are inhibitors of cytokine activation and, in B cells, function to fine tune IL-7R signaling; ensuring that appropriate IL-7 signals are transmitted to allow for efficient B cell commitment and development.

JunD/AP-1-mediated gene expression promotes lymphocyte growth dependent on interleukin-7 signal transduction

Interleukin-7 (IL-7) is an essential cytokine for lymphocyte growth that has the potential for promoting immune reconstitution. This feature makes IL-7 an ideal candidate for therapeutic development. As with other cytokines, signaling through the IL-7 receptor induces the JAK/STAT pathway. However, the broad scope of IL-7 regulatory targets likely necessitates the use of other signaling components whose identities remain poorly defined. To this end, we used an IL-7 dependent T-cell line to examine how expression of the glycolytic enzyme, Hexokinase II (HXKII) was regulated by IL-7 in a STAT5-independent manner. Our studies revealed that IL-7 promoted the activity of JNK (Jun N-terminal Kinase), and that JNK, in turn, drove the expression of JunD, a component of the Activating Protein 1 (AP-1) transcription factors. Gel shifts showed that the AP-1 complex induced by IL-7 contained JunD but not c-Fos or c-Jun. Inhibition of JNK/JunD blocked glucose uptake and HXKII gene expression, indicating that this pathway was responsible for promoting HXKII expression. Because others had shown that JunD was a negative regulator of cell growth, we performed a bioinformatics analysis to uncover possible JunD-regulated gene targets. Our search revealed that JunD could control the expression of proteins involved in signal transduction, cell survival and metabolism. One of these growth promoters was the oncogene, Pim-1. Pim-1 is an IL-7-induced protein that was inhibited when the activities of JNK or JunD were blocked, showing that in IL-7 dependent T-cells JunD can promote positive signals transduced through Pim-1. This was confirmed when the IL-7-induced proliferation of CD8 T-cells was impaired upon JunD inhibition. These results show that engagement of the IL-7 receptor drives a signal that is more complex than the JAK/STAT pathway, activating JNK and JunD to induce rapid growth stimulation through the expression of metabolic and signaling factors like HXKII and Pim-1.

TSC1/2 signaling complex is essential for peripheral naïve CD8+ T cell survival and homeostasis in mice

The PI3K-Akt-mTOR pathway plays crucial roles in regulating both innate and adaptive immunity. However, the role of TSC1, a critical negative regulator of mTOR, in peripheral T cell homeostasis remains elusive. With T cell-specific Tsc1 conditional knockout (Tsc1 KO) mice, we found that peripheral naïve CD8⁺ T cells but not CD4⁺ T cells were severely reduced. Tsc1 KO naïve CD8⁺ T cells showed profound survival defect in an adoptive transfer model and in culture with either stimulation of IL-7 or IL-15, despite comparable CD122 and CD127 expression between control and KO CD8⁺ T cells. IL-7 stimulated phosphorylation of Akt(S473) was diminished in Tsc1 KO naïve CD8⁺T cells due to hyperactive mTOR-mediated feedback suppression on PI3K-AKT signaling. Furthermore, impaired Foxo1/Foxo3a phosphorylation and increased pro-apoptotic Bim expression in Tsc1 KO naïve CD8⁺T cells were observed upon stimulation of IL-7. Collectively, our study suggests that TSC1 plays an essential role in regulating peripheral naïve CD8⁺ T cell homeostasis, possible via an mTOR-Akt-FoxO-Bim signaling pathway.

IL-7Rα deficiency in p53null mice exacerbates thymocyte telomere erosion and lymphomagenesis

Interleukin-7 (IL-7) is an essential T-cell survival cytokine. IL-7 receptor (IL-7Rα) deficiency severely impairs T-cell development due to substantial apoptosis. We hypothesized that IL-7Rα(null)-induced apoptosis is partially contributed by an elevated p53 activity. To investigate the genetic association of IL-7/IL-7Rα signaling with the p53 pathway, we generated IL-7Rα(null)p53(null) (DKO) mice. DKO mice exhibited a marked reduction of apoptosis in developing T cells and an augmented thymic lymphomagenesis with telomere erosions and exacerbated chromosomal anomalies, including chromosome duplications, breaks, and translocations. In particular, Robertsonian translocations, in which telocentric chromosomes fuse at the centromeric region, and a complete loss of telomeres at the fusion site occurred frequently in DKO thymic lymphomas. Cellular and molecular investigations revealed that IL-7/IL-7Rα signaling withdrawal diminished the protein synthesis of protection of telomere 1 (POT1), a subunit of telomere protective complex shelterin, leading to telomere erosion and the activation of the p53 pathway. Blockade of IL-7/IL-7Rα signaling in IL-7-dependent p53(null) cells reduced POT1 expression and caused telomere and chromosome abnormalities similar to those observed in DKO lymphomas. This study underscores a novel function of IL-7/IL-7Rα during T-cell development in regulating telomere integrity via POT1 expression and provides new insights into cytokine-mediated survival signals and T-cell lymphomagenesis.

Memory CD4 T cells induce selective expression of IL-27 in CD8+ dendritic cells and regulate homeostatic naive T cell proliferation

Naive T cells undergo robust proliferation in lymphopenic conditions, whereas they remain quiescent in steady-state conditions. However, a mechanism by which naive T cells are kept from proliferating under steady-state conditions remains unclear. In this study, we report that memory CD4 T cells are able to limit naive T cell proliferation within lymphopenic hosts by modulating stimulatory functions of dendritic cells (DC). The inhibition was mediated by IL-27, which was primarily expressed in CD8(+) DC subsets as the result of memory CD4 T cell-DC interaction. IL-27 appeared to be the major mediator of inhibition, as naive T cells deficient in IL-27R were resistant to memory CD4 T cell-mediated inhibition. Finally, IL-27-mediated regulation of T cell proliferation was also observed in steady-state conditions as well as during Ag-mediated immune responses. We propose a new model for maintaining peripheral T cell homeostasis via memory CD4 T cells and CD8(+) DC-derived IL-27 in vivo.

A central role for mTOR kinase in homeostatic proliferation induced CD8+ T cell memory and tumor immunity

The cell-intrinsic mechanisms guiding naive CD8+ T cells for clonal expansion and memory generation via homeostatic proliferation (HP) are unclear. Here, we have shown that HP of naive CD8+ T cells requires IL-7-, but not IL-15-induced mTOR kinase activation. HP-induced mTOR enhances transcription factor T-bet for functional maturation and CD122 expression, which sensitizes for an IL-15-dependent memory transition by favoring transcription factor Eomesodermin over T-bet. Inhibition of mTOR blocks T-bet and CD122 expression but preserves memory in an IL-15-independent manner by promoting Eomesodermin expression. The ability of rapamycin to augment HP-induced memory was cell-intrinsic given that silencing mTOR in CD8+ T cells generated identical outcomes. Strikingly, HP-induced CD8+ T cell memory generated by IL-15-dependent or -independent mechanisms demonstrated identical tumor efficacy. These results indicate a central role for mTOR in HP-induced CD8+ T cell responses and demonstrate the importance for CD8+ memory in HP-induced tumor efficacy.

Roles of avian herpesvirus microRNAs in infection, latency, and oncogenesis

MicroRNAs have been reported for the avian herpesviruses Marek's disease virus 1 (MDV1; oncogenic), Marek's disease virus 2 (MDV2; non-oncogenic), herpesvirus of turkeys (HVT), and infectious laryngotracheitis virus (ILTV). No obvious phylogenetic relationships exist among the avian herpesvirus microRNAs, but the general genomic locations of microRNA clusters are conserved, with microRNAs being located in the repeat regions of the genomes. In some cases, microRNAs are antisense to open reading frames. Among MDV1 field isolates with different virulence properties, microRNAs are highly conserved, and variations that have been observed lie in putative promoter regions. One cluster of MDV1 microRNAs lies upstream of the meq gene, and this cluster is more highly expressed in tumors caused by an extremely virulent MDV1 isolate compared to tumors caused by a less virulent isolate. Several of the avian herpesvirus microRNAs are orthologs of microRNAs in other species. For example, mdv1-miR-M4 shares a seed sequence with gga-miR-155 (also shared with Kaposi sarcoma herpesvirus (KSHV) kshv-miR-K12), mdv2-miR-M21 shares a seed with miR-29b, and hvt-miR-H14 shares a seed sequence with miR-221. Functional analyses of avian herpesvirus microRNAs include a variety of in vitro assays to demonstrate potential function as well as the use of mutants that can exploit the ability to assess phenotypes experimentally in the natural host. This article is part of a Special Issue entitled:MicroRNA's in viral gene regulation.

Cdc25A-driven proliferation regulates CD62L levels and lymphocyte movement in response to interleukin-7

OBJECTIVE

Interleukin-7 (IL-7) is a multifunctional cytokine and a promising immunotherapeutic agent. However, because transient T-cell depletion is an immediate outcome of IL-7 administration at supraphysiological doses, we investigated the mechanism by which the IL-7 proliferative signal transduced through Cdc25A, a key activator of cyclin-dependent kinases, could modulate lymphocyte movement.

MATERIALS AND METHODS

Employing novel methods of manipulating Cdc25A gene expression, combined with in vitro and in vivo evaluation of IL-7 application, we assessed the expression of activation and homing markers and identified the mechanism by which IL-7 could induce T-cell expansion and alter lymphocyte motility.

RESULTS

Constitutively active Cdc25A drove T-cell proliferation independently of IL-7 and resulted in an activated phenotype (CD69(hi), CD44(hi)). Conversely, inhibition of Cdc25A resulted in decreased proliferation, reduced expression of activation markers, and upregulation of the lymph node homing molecule, CD62L, which promoted cell adhesion when engaged by ligand. We found that IL-7 prevented the nuclear translocation of the transcription factor, Foxo1, in a manner dependent on the activity of Cdc25A, resulting in decreased levels of CD62L. In vivo administration of IL-7 decreased lymph node cellularity, while treatment with IL-7, premixed with a neutralizing IL-7 antibody (M25), increased total lymph node cells--with more nuclear Foxo1 detected in cells from mice receiving IL-7 + M25.

CONCLUSIONS

These results are consistent with the model that IL-7 drives Cdc25A-mediated T-cell proliferation, which prevents the nuclear translocation of Foxo1, leading to reduced expression of CD62L and the migration of T cells into circulation.

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.

Absence of both IL-7 and IL-15 severely impairs the development of CD8 T cell response against Toxoplasma gondii

CD8⁺ T cells play an essential role in the protection against both acute as well as chronic Toxoplasma gondii infection. Although the role of IL-15 has been reported to be important for the development of long-term CD8⁺ T cell immunity against the pathogen, the simultaneous roles played by both IL-15 and related γ-chain family cytokine IL-7 in the generation of this response during acute phase of infection has not been described. We demonstrate that while lack of IL-7 or IL-15 alone has minimal impact on splenic CD8⁺ T cell maturation or effector function development during acute Toxoplasmosis, absence of both IL-7 and IL-15 only in the context of infection severely down-regulates the development of a potent CD8⁺ T cell response. This impairment is characterized by reduction in CD44 expression, IFN-γ production, proliferation and cytotoxicity. However, attenuated maturation and decreased effector functions in these mice are essentially downstream consequences of reduced number of antigen-specific CD8⁺ T cells. Interestingly, the absence of both cytokines did not impair initial CD8⁺ T cell generation but affected their survival and differentiation into memory phenotype IL-7Rα^hi cells. Significantly lack of both cytokines severely affected expression of Bcl-2, an anti-apoptotic protein, but minimally affected proliferation. The overarching role played by these cytokines in eliciting a potent CD8⁺ T cell immunity against T. gondii infection is further evidenced by poor survival and high parasite burden in anti IL-7 treated IL-15^−/− mice. These studies demonstrate that the two cytokines, IL-7 and IL-15, are exclusively important for the development of protective CD8⁺ T cell immune response against T. gondii. To the best of our knowledge this synergism between IL-7 and IL-15 in generating an optimal CD8⁺ T cell immunity against intracellular parasite or any other infectious disease model has not been previously reported.