Naive CD8+ T cells differentiate into protective memory-like cells after IL-2 anti IL-2 complex treatment in vivo

Impact of patient characteristics on innate immune responses and inflammasome activation in ex vivo human lung tissues infected with influenza A virus

Background

Influenza A virus (IAV) infection poses a persistent global health challenge, necessitating a nuanced grasp of host immune responses for optimal interventions. While the interplay between aging, immunosenescence, and IAV is recognized as key in severe lower respiratory tract infections, the role of specific patient attributes in shaping innate immune reactions and inflammasome activity during IAV infection remains under-investigated. In this study, we utilized an ex vivo infection model of human lung tissues with H3N2 IAV to discern relationships among patient demographics, IAV nucleoprotein (NP) expression, toll-like receptor (TLR) profiles, PD-1/PD-L1 markers, and cytokine production.

Methods

Our cohort consisted of thirty adult patients who underwent video-assisted thoracoscopic surgery during 2018-2019. Post-surgical lung tissues were exposed to H3N2 IAV for ex vivo infections, and the ensuing immune responses were profiled using flow cytometry.

Results

We observed pronounced IAV activity within lung cells, as indicated by marked NP upregulation in both epithelial cells (P = 0.022) and macrophages (P = 0.003) in the IAV-exposed group relative to controls. Notably, interleukin-2 levels correlated with variations in TLR1 expression on epithelial cells and PD-L1 markers on macrophages. Age emerged as a modulating factor, dampening innate immune reactions, as evidenced by reduced interleukin-2 and interferon-γ concentrations (both adjusted P < 0.05). Intriguingly, a subset of participants with pronounced tumor necrosis factor-alpha post-mock infection (Cluster 1) showed attenuated cytokine responses in contrast to their counterparts in Cluster 2 and Cluster 3 (all adjusted P < 0.05). Individuals in Cluster 2, characterized by a low post-mock infection NP expression in macrophages, exhibited reduced variations in both NP and TLR1-3 expressions on these cells and a decreased variation in interleukin-2 secretion in comparison to their Cluster 3 counterparts, who were identified by their elevated NP macrophage expression (all adjusted P < 0.05).

Conclusion

Our work elucidates the multifaceted interplay of patient factors, innate immunity, and inflammasome responses in lung tissues subjected to ex vivo H3N2 IAV exposure, reflecting real-world lower respiratory tract infections. While these findings provide a foundation for tailored therapeutic strategies, supplementary studies are requisite for thorough validation and refinement.

Advancing Biologic Therapy for Refractory Autoimmune Hepatitis

Biologic agents may satisfy an unmet clinical need for treatment of refractory autoimmune hepatitis. The goals of this review are to present the types and results of biologic therapy for refractory autoimmune hepatitis, indicate opportunities to improve and expand biologic treatment, and encourage comparative clinical trials. English abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and secondary and tertiary bibliographies were developed. Rituximab (monoclonal antibodies against CD20 on B cells), infliximab (monoclonal antibodies against tumor necrosis factor-alpha), low-dose recombinant interleukin 2 (regulatory T cell promoter), and belimumab (monoclonal antibodies against B cell activating factor) have induced laboratory improvement in small cohorts with refractory autoimmune hepatitis. Ianalumab (monoclonal antibodies against the receptor for B cell activating factor) is in clinical trial. These agents target critical pathogenic pathways, but they may also have serious side effects. Blockade of the B cell activating factor or its receptors may disrupt pivotal B and T cell responses, and recombinant interleukin 2 complexed with certain interleukin 2 antibodies may selectively expand the regulatory T cell population. A proliferation-inducing ligand that enhances T cell proliferation and survival is an unevaluated, potentially pivotal, therapeutic target. Fully human antibodies, expanded target options, improved targeting precision, more effective delivery systems, and biosimilar agents promise to improve efficacy, safety, and accessibility. In conclusion, biologic agents target key pathogenic pathways in autoimmune hepatitis, and early experiences in refractory disease encourage clarification of the preferred target, rigorous clinical trial, and comparative evaluations.

Adrenergic signaling controls early transcriptional programs during CD8+ T cell responses to viral infection

Norepinephrine is a key sympathetic neurotransmitter, which acts to suppress CD8 + T cell cytokine secretion and lytic activity by signaling through the β2-adrenergic receptor (ADRB2). Although ADRB2 signaling is considered generally immunosuppressive, its role in regulating the differentiation of effector T cells in response to infection has not been investigated. Using an adoptive transfer approach, we compared the expansion and differentiation of wild type (WT) to Adrb2-/- CD8 + T cells throughout the primary response to vesicular stomatitis virus (VSV) infection in vivo. We measured the dynamic changes in transcriptome profiles of antigen-specific CD8 + T cells as they responded to VSV. Within the first 7 days of infection, WT cells out-paced the expansion of Adrb2-/- cells, which correlated with reduced expression of IL-2 and the IL-2Rα in the absence of ADRB2. RNASeq analysis identified over 300 differentially expressed genes that were both temporally regulated following infection and selectively regulated in WT vs Adrb2-/- cells. These genes contributed to major transcriptional pathways including cytokine receptor activation, signaling in cancer, immune deficiency, and neurotransmitter pathways. By parsing genes within groups that were either induced or repressed over time in response to infection, we identified three main branches of genes that were differentially regulated by the ADRB2. These gene sets were predicted to be regulated by specific transcription factors involved in effector T cell development, such as Tbx21 and Eomes. Collectively, these data demonstrate a significant role for ADRB2 signaling in regulating key transcriptional pathways during CD8 + T cells responses to infection that may dramatically impact their functional capabilities and downstream memory cell development.

The immunomodulatory activity of lenvatinib prompts the survival of patients with advanced hepatocellular carcinoma

BACKGROUND

Lenvatinib is a novel multiple receptor tyrosine kinase inhibitor used for hepatocellular carcinoma (HCC) treatment. Although its main function is to suppress VEGFR and FGFR pathway, its immunomodulatory activity in HCC is not elucidated. Thus, this study aimed to investigate the immunomodulatory capability of lenvatinib in HCC.

MATERIAL AND METHODS

Totally 47 patients with HCC were enrolled in this study, and the immune cells and serum cytokine profiles before initiation of treatment and after 1 and 3 months were measured. The immune checkpoint receptors on the immune cells were also evaluated. Kaplan-Meier survival estimate and log rank tests were used to assess the prognostic value.

RESULT

The frequency of T helper (Th) cells and T regulatory (Treg) cells reduced after lenvatinib treatment, while cytotoxic T lymphocyte (CTL) cells increased significantly. The cytokine profiles showed IL-2, IL-5, IFN-γ increased; other cytokines including IL-6, IL-10, TNF- α and TNF- β decreased with lenvatinib therapy. Furthermore, the PD-1 and TIM-3 expressed on CTL had greatly decreased; the expression of TIM-3 and CTLA-4 was reduced on Treg cells as well. Besides, the new index CTL/Treg ratio was created, and low ratio was associated with the unfavorable outcome of HCC patients.

CONCLUSION

Our results confirmed that lenvatinib is capable of improving patients' immune status, saving the effector cells from exhaustion status and inhibiting the number and function of immunosuppressive cells. The novel index CTL/Treg ratio qualifies as a predictor for the outcome of patients with lenvatinib therapy.

Generation of Tumor-activated T cells using electroporation

Expansion of cytotoxic T lymphocytes (CTLs) is a crucial step in almost all cancer immunotherapeutic methods. Current techniques for expansion of tumor-reactive CTLs present major limitations. This study introduces a novel method to effectively produce and expand tumor-activated CTLs using high-voltage pulsed electric fields. We hypothesize that utilizing high-voltage pulsed electric fields may be an ideal method to activate and expand CTLs due to their non-thermal celldeath mechanism. Tumor cells were subjected to high-frequency irreversible electroporation (HFIRE) with various electric field magnitudes (1250, 2500 V/cm) and pulse widths (1, 5, and 10 µs), or irreversible electroporation (IRE) at 1250 V/cm. The treated tumor cells were subsequently cocultured with CD4+ and CD8+ T cells along with antigen-presenting cells. We show that tumor-activated CTLs can be produced and expanded when exposed to treated tumor cells. Our results suggest that CTLs are more effectively expanded when pulsed with HFIRE conditions that induce significant cell death (longer pulse widths and higher voltages). Activated CD8+ T cells demonstrate cytotoxicity to untreated tumor cells suggesting effector function of the activated CTLs. The activated CTLs produced with our technique could be used for clinical applications with the goal of targeting and eliminating the tumor.

Characterization and ex vivo expansion of rare in situ cytokine secreting T cell populations from tumor tissue and blood of oral squamous cell carcinoma patients

Rare subpopulations of tumor antigen-reactive memory T cells, which actively secrete type-1 effector cytokines, particularly TNF-α in situ, possess anti-tumor activity and prognostic relevance. These cells are relevant for cancer immunotherapy; however, their low frequencies make them difficult to study and novel protocols for their culture and expansion ex vivo are needed. Here, we studied the presence of T cells secreting type-1 cytokines (Cy⁺T cells) in the blood and tumors of 24 patients with oral squamous cell carcinomas (OSCC) and explored possibilities for their isolation and expansion. More than 90% of OSCC patients contained enriched numbers Cy⁺T cells in the blood and tumors compared to healthy donors in which these were hardly detectable. The majority of TNF-α⁺T cells were CD4⁺ T helper cells while IFN-γ⁺TIL were predominantly CD8⁺. Cy⁺T helper cells in the blood were early-differentiated memory T cells while Cy⁺TIL and Cy⁺CD8⁺T cells showed advanced-differentiated memory T cell phenotypes. We explored different conditions for their in vitro culture and found that Cy⁺T cells can be efficiently expanded in vitro to similar levels as Cy^-T cells and after expansion maintained their TNF-α secreting capacity. However, for optimal expansion they required specific culture conditions to support the maintenance of stem-like and central memory T cell phenotype. In conclusion, we show that Cy⁺T cells are enriched in OSCC patients and report a novel cell culture protocol optimized to specifically expand and functionally maintain these cells for further functional characterization or for their exploitation in immunotherapy of OSCC.

Manipulating the TCR signaling network for cellular immunotherapy: Challenges & opportunities

T cells can help confer protective immunity by eliminating infections and tumors or drive immunopathology by damaging host cells. Both outcomes require a series of steps from the activation of naïve T cells to their clonal expansion, differentiation and migration to tissue sites. In addition to specific recognition of the antigen via the T cell receptor (TCR), multiple accessory signals from costimulatory molecules, cytokines and metabolites also influence each step along the progression of the T cell response. Current efforts to modify effector T cell function in many clinical contexts focus on the latter - which encompass antigen-independent and broad, contextual regulators. Not surprisingly, such approaches are often accompanied by adverse events, as they also affect T cells not relevant to the specific treatment. In contrast, fine tuning T cell responses by precisely targeting antigen-specific TCR signals has the potential to radically alter therapeutic strategies in a focused manner. Development of such approaches, however, requires a better understanding of functioning of the TCR and the biochemical signaling network coupled to it. In this article, we review some of the recent advances which highlight important roles of TCR signals throughout the activation and differentiation of T cells during an immune response. We discuss how, an appreciation of specific signaling modalities and variant ligands that influence the function of the TCR has the potential to influence design principles for the next generation of pharmacologic and cellular therapies, especially in the context of tumor immunotherapies involving adoptive cell transfers.

CD25-Targeted IL-2 Signals Promote Improved Outcomes of Influenza Infection and Boost Memory CD4 T Cell Formation

IL-2 is a pleotropic cytokine with potent pro- and anti-inflammatory effects. These divergent impacts can be directed in vivo by forming complexes of IL-2 and anti-IL-2 mAbs (IL-2C) to target IL-2 to distinct subsets of cells based on their expression of subunits of the IL-2R. In this study, we show that treatment of mice with a prototypical anti-inflammatory IL-2C, JES6-1-IL-2C, best known to induce CD25⁺ regulatory CD4 T cell expansion, surprisingly causes robust induction of a suite of inflammatory factors. However, treating mice infected with influenza A virus with this IL-2C reduces lung immunopathology. We compare the spectrum of inflammatory proteins upregulated by pro- and anti-inflammatory IL-2C treatment and uncover a pattern of expression that reveals potentially beneficial versus detrimental aspects of the influenza-associated cytokine storm. Moreover, we show that anti-inflammatory IL-2C can deliver survival signals to CD4 T cells responding to influenza A virus that improve their memory fitness, indicating a novel application of IL-2 to boost pathogen-specific T cell memory while simultaneously reducing immunopathology.

JAK/STAT Cytokine Signaling at the Crossroad of NK Cell Development and Maturation

Natural Killer (NK) cells are cytotoxic lymphocytes of the innate immune system and play a critical role in anti-viral and anti-tumor responses. NK cells develop in the bone marrow from hematopoietic stem cells (HSCs) that differentiate through common lymphoid progenitors (CLPs) to NK lineage-restricted progenitors (NKPs). The orchestrated action of multiple cytokines is crucial for NK cell development and maturation. Many of these cytokines such as IL-2, IL-7, IL-12, IL-15, IL-21, IL-27, and interferons (IFNs) signal via the Janus Kinase / Signal Transducer and Activator of Transcription (JAK/STAT) pathway. We here review the current knowledge about these cytokines and the downstream signaling involved in the development and maturation of conventional NK cells and their close relatives, innate lymphoid cells type 1 (ILC1). We further discuss the role of suppressor of cytokine signaling (SOCS) proteins in NK cells and highlight their potential for therapeutic application.

Dynamics and genomic landscape of CD8+ T cells undergoing hepatic priming

The responses of CD8⁺ T cells to hepatotropic viruses such as hepatitis B range from dysfunction to differentiation into effector cells, but the mechanisms that underlie these distinct outcomes remain poorly understood. Here we show that priming by Kupffer cells, which are not natural targets of hepatitis B, leads to differentiation of CD8⁺ T cells into effector cells that form dense, extravascular clusters of immotile cells scattered throughout the liver. By contrast, priming by hepatocytes, which are natural targets of hepatitis B, leads to local activation and proliferation of CD8⁺ T cells but not to differentiation into effector cells; these cells form loose, intravascular clusters of motile cells that coalesce around portal tracts. Transcriptomic and chromatin accessibility analyses reveal unique features of these dysfunctional CD8⁺ T cells, with limited overlap with those of exhausted or tolerant T cells; accordingly, CD8⁺ T cells primed by hepatocytes cannot be rescued by treatment with anti-PD-L1, but instead respond to IL-2. These findings suggest immunotherapeutic strategies against chronic hepatitis B infection.

From immune checkpoints to vaccines: The past, present and future of cancer immunotherapy

Cancer is a worldwide medical problem with significant repercussions on individual patients and societies as a whole. In order to alter the outcomes of this deadly disease the treatment of cancer over the centuries has undergone a unique evolution. However, utilizing the best treatment modalities and achieving cures or long-term durable responses have been inconsistent and limited, that is until recently. Contemporary research has highlighted a fundamental gap in our understanding of how we approach treating cancer, by revealing the intricate relationship between the immune system and tumors. In this atmosphere, the growth of immunotherapy has not only forever changed our understanding of cancer biology, but the manner by which we treat patients. It's paradigm shifting success has led to the approval of over 10 different immunotherapeutic agents, including checkpoint inhibitors, vaccine-based therapies, oncolytic viruses and T cell directed therapies for nearly 20 different indications across countless tumor types. Despite the breakthroughs that have occurred in the field of immunotherapy, it has not been the panacea for all cancers. With a deeper understanding of the immune system we have been able to peer into tumor immune escape and therapy resistance. Simultaneously this understanding has paved the way for the investigation and development of novel immune system altering agents and combinatorial therapies. In this chapter we review the immune system and its intricate relationship with cancer, the evolution of immunotherapy, its current landscape, and future directions in the context of resistance mechanisms and the challenges faced by immunotherapy against cancer.

Cross-Talk Between Antigen Presenting Cells and T Cells Impacts Intestinal Homeostasis, Bacterial Infections, and Tumorigenesis

Innate immunity is maintained in part by antigen presenting cells (APCs) including dendritic cells, macrophages, and B cells. APCs interact with T cells to link innate and adaptive immune responses. By displaying bacterial and tumorigenic antigens on their surface via major histocompatibility complexes, APCs can directly influence the differentiation of T cells. Likewise, T cell activation, differentiation, and effector functions are modulated by APCs utilizing multiple mechanisms. The objective of this review is to describe how APCs interact with and influence the activation of T cells to maintain innate immunity during exposure to microbial infection and malignant cells. How bacteria and cancer cells take advantage of some of these interactions for their own benefit will also be discussed. While this review will cover a broad range of topics, a general focus will be held around pathogens, cancers, and interactions that typically occur within the gastrointestinal tract.

Combination treatment with hypofractionated radiotherapy plus IL-2/anti-IL-2 complexes and its theranostic evaluation

Background

Immunogenic radiotherapy (RT) can act synergistically with immune checkpoint blockers (ICBs). However, alternatives are needed for non-responding patients and those with pre-existing or ICB-induced autoimmune symptoms. Combination of RT with IL-2 could be an alternative. But IL-2 has a short half-life, and, by binding to its high-affinity receptor, it strongly stimulates immunosuppressive CD4+ Tregs and seems to promote potentially life-threatening vascular leakage. IL-2/anti-IL-2 complexes (IL-2c), which bind to the low-affinity receptor, have been reported to circumvent these disadvantages but they have not yet been thoroughly tested in conjunction with radiotherapy.

Methods

We evaluated, in three mouse models, the antitumoral effects induced by hypofractionated RT (hRT) plus IL-2c. We also used non-invasive imaging with a newly developed PET tracer based on therapeutically active IL-2c and a PD-L1 PET tracer for the theranostic evaluation of the treatment and its side effects.

Results

Treatment of mice bearing established B16 melanomas with hRT + IL-2c was superior to hRT + uncomplexed IL-2 or hRT alone; IL-2c alone was not effective. hRT + IL-2c was also synergistic in mice bearing C51 colon carcinomas or 4T1 mammary carcinomas. The better antitumor response correlated with increased tumor-specific CD8+ T cells and NK cells, but not CD4+ Tregs, in the irradiated tumor and in lymphoid organs. With the new PET tracer, we visualized the whole-body distribution of IL-2c and the bound receptors in naïve mice and tumor-bearing mice. Surprisingly, the tumor uptake was non-specific and only moderate. This prompted experiments demonstrating that specific IL-2c binding in the tumor is limited by IL-2 secreted by tumor-resident effector cells and that extratumorally expanded T and NK cells can infiltrate the irradiated tumor, which suggests that systemic immune activation considerably contributed to the reduction of tumor growth. Lastly, we show that a side effect of IL-2c treatment – a quite dramatic non-specific expansion of CD8+ T and NK cells – is only transient, and we visualized the associated splenomegaly as well as side effects on liver and lung by contrast-enhanced CT and PD-L1 PET.

Conclusions

Our results show that the combination of immunogenic RT with IL-2c that are directed towards the low-affinity IL-2 receptor can be synergistic and more effective than the combination with uncomplexed IL-2. In addition, our theranostic evaluation provided insights into the mechanism of action and the side effects of IL-2c treatment.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0537-9) contains supplementary material, which is available to authorized users.

Spontaneous Proliferation of CD4+ T Cells in RAG-Deficient Hosts Promotes Antigen-Independent but IL-2-Dependent Strong Proliferative Response of Naïve CD8+ T Cells

The fast and intense proliferative responses have been well documented for naïve T cells adoptively transferred into chronic lymphopenic hosts. This response known as spontaneous proliferation (SP), unlike antigen-independent lymphopenia-induced proliferation (LIP), is driven in a manner dependent on antigens derived from commensal microbiota. However, the precise nature of the SP response and its impact on homeostasis and function for T cells rapidly responding under this lymphopenic condition are still unclear. Here we demonstrate that, when naïve T cells were adoptively transferred into specific pathogen-free (SPF) but not germ-free (GF) RAG^-/- hosts, the SP response of these cells substantially affects the intensity and tempo of the responding T cells undergoing LIP. Therefore, the resulting response of these cells in SPF RAG^-/- hosts was faster and stronger than the typical LIP response observed in irradiated B6 hosts. Although the intensity and tempo of such augmented LIP in SPF RAG^-/- hosts were analogous to those of antigen-dependent SP, the former was independent of antigenic stimulation but most importantly, dependent on IL-2. Similar observations were also apparent in other acute lymphopenic settings where antigen-dependent T cell activation can strongly occur and induce sufficient levels of IL-2 production. Consequently, the resulting T cells undergoing IL-2-driven strong proliferative responses showed the ability to differentiate into functional effector and memory cells that can control infectious pathogens. These findings therefore reveal previously unappreciated role of IL-2 in driving the intense form of T cell proliferative responses in chronic lymphopenic hosts.

Prospects of IL-2 in Cancer Immunotherapy

IL-2 is a powerful immune growth factor and it plays important role in sustaining T cell response. The potential of IL-2 in expanding T cells without loss of functionality has led to its early use in cancer immunotherapy. IL-2 has been reported to induce complete and durable regressions in cancer patients but immune related adverse effects have been reported (irAE). The present review discusses the prospects of IL-2 in immunotherapy for cancer.

Antigen-Induced but Not Innate Memory CD8 T Cells Express NKG2D and Are Recruited to the Lung Parenchyma upon Viral Infection

The pool of memory-phenotype CD8 T cells is composed of Ag-induced (AI) and cytokine-induced innate (IN) cells. IN cells have been described as having properties similar to those of AI memory cells. However, we found that pathogen-induced AI memory cells can be distinguished in mice from naturally generated IN memory cells by surface expression of NKG2D. Using this marker, we described the increased functionalities of AI and IN memory CD8 T cells compared with naive cells, as shown by comprehensive analysis of cytokine secretion and gene expression. However, AI differed from IN memory CD8 T cells by their capacity to migrate to the lung parenchyma upon inflammation or infection, a process dependent on their expression of ITGA1/CD49a and ITGA4/CD49d integrins.

Telomerase activity and telomere on stem progeny senescence

The end of linear chromosomes is formed of a special nucleoprotein heterochromatin structure with repetitive TTAGGG sequences called telomere. Telomere length is regulated by a special enzyme called telomerase, a specific DNA polymerase that adds new telomeric sequences to the chromosome ends. Telomerase consists of two parts; the central protein part and the accessory part which is a RNA component transported by the central part. Regulation of telomere length by this enzyme is a multi-stage process. Telomere length elongation is strongly influenced by the level of telomerase and has a strong correlation with the activity of telomerase enzyme. Human Telomerase Reverse Transcriptase (hTERT) gene expression plays an important role in maintaining telomere length and high proliferative property of cells. Except a low activity of telomerase enzyme in hematopoietic and few types of stem cells, most of somatic cells didn't showed telomerase activity. Moreover, cytokines are secretory proteins that control many aspects of hematopoiesis, especially immune responses and inflammation. Also, the induction of hTERT gene expression by cytokines is organized through the PI3K/AKT and NF/kB signaling pathways. In this review we have tried to talk about effects of immune cell cytokines on telomerase expression/telomere length and the induction of telomerase expression by cytokines.

Effects of herbal medicine Sijunzi decoction on rabbits after relieving intestinal obstruction

Intestinal obstruction leads to blockage of the movement of intestinal contents. After relieving the obstruction, patients might still suffer with compromised immune function and nutritional deficiency. This study aimed to evaluate the effects of Sijunzi decoction on restoring the immune function and nutritional status after relieving the obstruction. Experimental rabbits (2.5±0.2 kg) were randomly divided into normal control group, 2-day intestinal obstruction group, 2-day natural recovery group, 4-day natural recovery group, 2-day treated group, and 4-day treated group. Sijunzi decoction was given twice a day to the treated groups. The concentration of markers was analyzed to evaluate the immune function and nutritional status. The concentration of interleukin-2, immunoglobulins and complement components of the treated groups were significantly higher than the natural recovery group (P<0.05). The levels of CD4⁺ and CD4⁺/CD8⁺ increased then decreased in the treated groups. The levels of tumor necrosis factor-α and CD8⁺ were significantly lower than the natural recovery group. The level of total protein in the treated groups also increased then decreased after relieving the obstruction. The levels of albumin, prealbumin and insulin-like growth factor-1 were significantly higher in the treated groups than in the natural recovery group (P<0.05). Transferrin level in the treated groups was significantly higher than the obstruction group (P<0.05). Sijunzi decoction can lessen the inflammatory response and improve the nutrition absorption after relieving the obstruction.

IRF4 Modulates CD8+ T Cell Sensitivity to IL-2 Family Cytokines

IFN regulatory factor 4 (IRF4) is a key transcription factor that promotes effector CD8+ T cell differentiation and expansion. The roles of IRF4 in regulating the CD8+ T cell response to cytokines have not been explored. In this article, we show that IL-2 and IL-15 signaling and STAT5 activation regulate IRF4 expression in CD8+ T cells. Gene-expression profile analysis has also revealed that IRF4 is required for expression of the receptors of IL-2 family cytokines CD122 and CD127. We found that IRF4 binds directly to CD122 and CD127 gene loci, indicating that it may directly promote CD122 and CD127 gene transcription. As a consequence, IRF4-deficient CD8+ T cells show diminished sensitivity to IL-2, IL-15, and IL-7 treatment in vitro. Furthermore, we found that IRF4-deficient CD8+ T cells had lower expression of CD122 and CD127 in vivo during influenza virus infection. These data suggest that IRF4 regulates the sensitivity of CD8+ T cells to IL-2 family cytokines, which correlates with the diminished effector and memory CD8+ T cell responses in IRF4-deficient CD8+ T cells.

Modulation of let-7 miRNAs controls the differentiation of effector CD8 T cells

The differentiation of naive CD8 T cells into effector cytotoxic T lymphocytes upon antigen stimulation is necessary for successful antiviral, and antitumor immune responses. Here, using a mouse model, we describe a dual role for the let-7 microRNAs in the regulation of CD8 T cell responses, where maintenance of the naive phenotype in CD8 T cells requires high levels of let-7 expression, while generation of cytotoxic T lymphocytes depends upon T cell receptor-mediated let-7 downregulation. Decrease of let-7 expression in activated T cells enhances clonal expansion and the acquisition of effector function through derepression of the let-7 targets, including Myc and Eomesodermin. Ultimately, we have identified a novel let-7-mediated mechanism, which acts as a molecular brake controlling the magnitude of CD8 T cell responses.

DOI:http://dx.doi.org/10.7554/eLife.26398.001

Early Subretinal Allograft Rejection Is Characterized by Innate Immune Activity

Successful subretinal transplantation is limited by considerable early graft loss despite pharmacological suppression of adaptive immunity. We postulated that early innate immune activity is a dominant factor in determining graft survival and chose a nonimmunosuppressed mouse model of retinal pigment epithelial (RPE) cell transplantation to explore this. Expression of almost all measured cytokines by DH01 RPE cells increased significantly following graft preparation, and the neutrophil chemoattractant KC/GRO/CINC was most significantly increased. Subretinal allografts of DH01 cells (C57BL/10 origin) into healthy, nonimmunosuppressed C57BL/6 murine eyes were harvested and fixed at 1, 3, 7, and 28 days postoperatively and subsequently cryosectioned and stained. Graft cells were detected using SV40 large T antigen (SV40T) immunolabeling and apoptosis/necrosis by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). Sections were also immunolabeled for macrophage (CD11b and F4/80), neutrophil (Gr1 Ly-6G), and T-lymphocyte (CD3-ɛ) infiltration. Images captured with an Olympus FV1000 confocal microscope were analyzed using the Imaris software. The proportion of the subretinal bolus comprising graft cells (SV40T+) was significantly (p < 0.001) reduced between postoperative day (POD) 3 (90 ± 4%) and POD 7 (20 ± 7%). CD11b+, F4/80+, and Gr1 Ly-6G+ cells increased significantly (p < 0.05) from POD 1 and predominated over SV40T+ cells by POD 7. Colabeling confocal microscopic analysis demonstrated graft engulfment by neutrophils and macrophages at POD 7, and reconstruction of z-stacked confocal images confirmed SV40T inside Gr1 Ly-6G+ cells. Expression of CD3-ɛ was low and did not differ significantly between time points. By POD 28, no graft cells were detectable and few inflammatory cells remained. These studies reveal, for the first time, a critical role for innate immune mechanisms early in subretinal graft rejection. The future success of subretinal transplantation will require more emphasis on techniques to limit innate immune-mediated graft loss, rather than focusing exclusively on suppression of the adaptive immune response.

Manipulation of Regulatory Cells' Responses to Treatments for Chronic Hepatitis B Virus Infection

BACKGROUND

Identification of effective treatments in hepatitis B virus (HBV) infection remains a controversial topic. Although the currently approved drugs for HBV control the disease's progression and also limit associated outcomes, these drugs may not fully eradicate HBV infection. In addition to better managing patients with chronic hepatitis B (CHB) infection, the induction of seroclearance by these drugs has been a commonly discussed topic in recent years.

OBJECTIVES

In this study, we focused on treating CHB infection via the manipulation of T cells' responses to identify possible approaches to cure CHB.

MATERIALS AND METHODS

All studies relevant to the role of cellular and humoral responses in HBV infection (especially regulatory cells) were investigated via a systematic search of different databases, including PubMed, Scopus, and Google Scholar. Considering extracted data and also our unpublished data regarding the association between regulatory cytokines and CHB, we introduced a novel approach for the induction of seroclearance.

RESULTS

Considering the increased levels of regulatory cytokines and also regulatory T cells (Tregs) during CHB, it seems that these cells are deeply involved in CHB infection. The inhibition of regulatory T cells may reverse the dysfunction of effector T cells in patients with CHB infection. In order to inhibit Tregs' responses, different types of approaches could be employed to restore the impaired function of effector T cells. The blockade of IL-10, IL-35, CTLA-4, PD-1, and TIM-3 were discussed throughout this study. Regardless of the efficacy of these methods, CHB patients may experience serious liver injuries due to the cytotoxic action of CD8+ T cells. Antiviral therapy and a decrease in HBV DNA to undetectable levels could also significantly reduce the risk of the hepatitis B flare.

CONCLUSIONS

The inhibition of Tregs is a novel therapeutic approach to cure chronically HBV infected patients. However, further studies are needed to investigate the safety and efficacy of this approach.

Changes in Gab2 phosphorylation and interaction partners in response to interleukin (IL)-2 stimulation in T-lymphocytes

Interleukin-2 (IL-2) stimulation results in T-cell growth as a consequence of activation of highly sophisticated and fine-tuned signaling pathways. Despite lacking intrinsic enzymatic activity, scaffold proteins such as Gab2, play a pivotal role in IL-2-triggered signal transduction integrating, diversifying and amplifying the signal by serving as a platform for the assembly of effectors proteins. Traditionally, Gab2-mediated protein recruitment was believed to solely depend on cytokine-induced phosphotyrosine moieties. At present, phosphorylation on serine/threonine residues is also emerging as a key mediator of Gab2-dependent signal regulation. Despite its relevance, IL-2-triggered regulation on Gab2 phosphorylation is yet poorly understood. Combining antibody- and TiO2-based enrichment of the scaffold protein with SILAC quantitative mass spectrometry we disclose the prominent regulation IL-2 exerts on Gab2 serine/threonine phosphorylation by showing that at least 18 serines and 1 threonine, including previously non-reported ones, become phosphorylated in response to cytokine stimulation. Additionally, we decipher the interactome of the docking protein in resting and cytokine-treated T-lymphocytes and besides well-known Gab2 interactors we discover three novel cytokine-inducible Gab2-binding proteins. Thus, our data provide novel insights and a wealth of candidates for future studies that will shed light into the role of Gab2 in IL-2-initiated signal transduction.

IL-2/anti-IL-2 mAb immunocomplexes: A renascence of IL-2 in cancer immunotherapy?

The in vivo biological activity of IL-2 can be dramatically increased by complexing with anti-IL-2 mAb. Moreover, IL-2/anti-IL-2 mAb immunocomplexes selectively stimulate different subsets of immune cells, depending on the clone of anti-IL-2 mAb that is used. Thus, IL-2/S4B6 mAb complexes strongly stimulate CD122^high populations, namely NK and memory CD8⁺ T cells. They also intermediately stimulate T_reg cells. Conversely, IL-2/JES6.1 mAb immunocomplexes have no stimulatory activity for CD122^high populations. However, they potently and highly selectively stimulate CD25⁺ cells (i.e., T_reg and activated T cells). IL-2/S4B6 mAb immunocomplexes have also been shown to possess antitumor activity in various mouse tumor models.

Low-affinity TCR engagement drives IL-2-dependent post-thymic maintenance of naive CD4+ T cells in aged humans

Insight into the maintenance of naive T cells is essential to understand defective immune responses in the context of aging and other immune compromised states. In humans, naive CD4+ T cells, in contrast to CD8+ T cells, are remarkably well retained with aging. Here, we show that low-affinity TCR engagement is the main driving force behind the emergence and accumulation of naive-like CD4+ T cells with enhanced sensitivity to IL-2 in aged humans. In vitro, we show that these CD45RA(+) CD25(dim) CD4(+) T cells can develop from conventional naive CD25(-) CD4+ T cells upon CD3 cross-linking alone, in the absence of costimulation, rather than via stimulation by the homeostatic cytokines IL-2, IL-7, or IL-15. In vivo, TCR engagement likely occurs in secondary lymphoid organs as these cells were detected in lymph nodes and spleen where they showed signs of recent activation. CD45RA(+) CD25(dim) CD4+ T cells expressed a broad TCRVβ repertoire and could readily differentiate into functional T helper cells. Strikingly, no expansion of CD45RA(+) CD25(dim) CD8+ T cells was detected with aging, thereby implying that maintenance of naive CD4+ T cells is uniquely regulated. Our data provide novel insight into the homeostasis of naive T cells and may guide the development of therapies to preserve or restore immunity in the elderly.

An Excess of the Proinflammatory Cytokines IFN-γ and IL-12 Impairs the Development of the Memory CD8+ T Cell Response to Chlamydia trachomatis

The obligate intracellular bacterium Chlamydia trachomatis is the most common cause of bacterial sexually transmitted disease in the United States and the leading cause of preventable blindness worldwide. Transfer of cultured Chlamydia-specific CD8(+) T cells or vaccination with recombinant virus expressing an MHC I-restricted Chlamydia Ag confers protection, yet surprisingly a protective CD8(+) T cell response is not stimulated following natural infection. In this study, we demonstrate that the presence of excess IL-12 and IFN-γ contributes to poor memory CD8(+) T cell development during C. trachomatis infection of mice. IL-12 is required for CD8(+) T cell expansion but drives effector CD8(+) T cells into a short-lived fate, whereas IFN-γ signaling impairs the development of effector memory cells. We show that transient blockade of IL-12 and IFN-γ during priming promotes the development of memory precursor effector CD8(+) T cells and increases the number of memory T cells that participate in the recall protection against subsequent infection. Overall, this study identifies key factors shaping memory development of Chlamydia-specific CD8(+) T cells that will inform future vaccine development against this and other pathogens.

mTOR Complex Signaling through the SEMA4A-Plexin B2 Axis Is Required for Optimal Activation and Differentiation of CD8+ T Cells

Mammalian target of rapamycin (mTOR) plays crucial roles in activation and differentiation of diverse types of immune cells. Although several lines of evidence have demonstrated the importance of mTOR-mediated signals in CD4(+) T cell responses, the involvement of mTOR in CD8(+) T cell responses is not fully understood. In this study, we show that a class IV semaphorin, SEMA4A, regulates CD8(+) T cell activation and differentiation through activation of mTOR complex (mTORC) 1. SEMA4A(-/-) CD8(+) T cells exhibited impairments in production of IFN-γ and TNF-α and induction of the effector molecules granzyme B, perforin, and FAS-L. Upon infection with OVA-expressing Listeria monocytogenes, pathogen-specific effector CD8(+) T cell responses were significantly impaired in SEMA4A(-/-) mice. Furthermore, SEMA4A(-/-) CD8(+) T cells exhibited reduced mTORC1 activity and elevated mTORC2 activity, suggesting that SEMA4A is required for optimal activation of mTORC1 in CD8(+) T cells. IFN-γ production and mTORC1 activity in SEMA4A(-/-) CD8(+) T cells were restored by administration of recombinant Sema4A protein. In addition, we show that plexin B2 is a functional receptor of SEMA4A in CD8(+) T cells. Collectively, these results not only demonstrate the role of SEMA4A in CD8(+) T cells, but also reveal a novel link between a semaphorin and mTOR signaling.

KDEL receptor 1 regulates T-cell homeostasis via PP1 that is a key phosphatase for ISR

KDEL receptors are responsible for retrotransporting endoplasmic reticulum (ER) chaperones from the Golgi complex to the ER. Here we describe a role for KDEL receptor 1 (KDELR1) that involves the regulation of integrated stress responses (ISR) in T cells. Designing and using an N-ethyl-N-nitrosourea (ENU)-mutant mouse line, T-Red (naïve T-cell reduced), we show that a point mutation in KDELR1 is responsible for the reduction in the number of naïve T cells in this model owing to an increase in ISR. Mechanistic analysis shows that KDELR1 directly regulates protein phosphatase 1 (PP1), a key phosphatase for ISR in naïve T cells. T-Red KDELR1 does not associate with PP1, resulting in reduced phosphatase activity against eIF2α and subsequent expression of stress responsive genes including the proapoptotic factor Bim. These results demonstrate that KDELR1 regulates naïve T-cell homeostasis by controlling ISR.

KDEL receptors are known to be involved in retrotransporting chaperones to the endoplasmic reticulum from the Golgi complex. Here the authors unravel a role of KDEL receptor 1 in regulating integrated stress responses in naïve T cells through its association with protein phosphatase 1.

Eos Is Redundant for Regulatory T Cell Function but Plays an Important Role in IL-2 and Th17 Production by CD4+ Conventional T Cells

Eos belongs to the Ikaros family of transcription factors. It was reported to be a regulatory T cell (Treg) signature gene, to play a critical role in Treg suppressor functions, and to maintain Treg stability. We used mice with a global deficiency in Eos to re-examine the role of Eos expression in both Tregs and conventional T cells (Tconvs). Tregs from Eos-deficient (Eos(-/-)) mice developed normally, displayed a normal Treg phenotype, and exhibited normal suppressor function in vitro. Eos(-/-) Tregs were as effective as Tregs from wild-type (WT) mice in suppressing inflammation in a model of inflammatory bowel disease. Bone marrow (BM) from Eos(-/-) mice was as effective as that from WT mice in controlling T cell activation when used to reconstitute immunodeficient mice in the presence of scurfy fetal liver cells. Surprisingly, Eos was expressed in activated Tconvs and was required for IL-2 production, CD25 expression, and proliferation in vitro by CD4(+) Tconvs. Eos(-/-) mice developed more severe experimental autoimmune encephalomyelitis than WT mice, displayed increased numbers of effector T cells in the periphery and CNS, and amplified IL-17 production. In conclusion, our studies are not consistent with a role for Eos in Treg development and function but demonstrate that Eos plays an important role in the activation and differentiation of Tconvs.

CD8+ T Cell Fate and Function Influenced by Antigen-Specific Virus-Like Nanoparticles Co-Expressing Membrane Tethered IL-2

A variety of adjuvants fostering humoral immunity are known as of today. However, there is a lack of adjuvants or adjuvant strategies, which directly target T cellular effector functions and memory. We here determined whether systemically toxic cytokines such as IL-2 can be restricted to the site of antigen presentation and used as ‘natural adjuvants’. Therefore, we devised antigen-presenting virus-like nanoparticles (VNP) co-expressing IL-2 attached to different membrane-anchors and assessed their potency to modulate CD8⁺ T cell responses in vitro and in vivo. Efficient targeting of IL-2 to lipid rafts and ultimately VNP was achieved by fusing IL-2 at its C-terminus to a minimal glycosylphosphatidylinositol (GPI)-anchor acceptor sequence. To identify optimal membrane-anchor dimensions we inserted one (1Ig), two (2Ig) or four (4Ig) immunoglobulin(Ig)-like domains of CD16b between IL-2 and the minimal GPI-anchor acceptor sequence of CD16b (GPI). We found that the 2IgGPI version was superior to all other evaluated IL-2 variants (IL-2v) in terms of its i) degree of targeting to lipid rafts and to the VNP surface, ii) biological activity, iii) co-stimulation of cognate T cells in the absence of bystander activation and iv) potency to induce differentiation and acquisition of CD8⁺ T cell effector functions in vitro and in vivo. In contrast, the GPI version rather favored memory precursor cell formation. These results exemplify novel beneficial features of membrane-bound IL-2, which in addition to its mere T cell stimulatory capacity include the induction of differential effector and memory functions in CD8⁺ T lymphocytes.

Tuning IL-2 signaling by ADP-ribosylation of CD25

Control of immunologic tolerance and homeostasis rely on Foxp3⁺CD4⁺CD25⁺ regulatory T cells (Tregs) that constitutively express the high affinity receptor for Interleukin-2, CD25. Tregs proliferate in response to injections of IL-2/anti-IL-2 antibody complexes or low doses of IL-2. However, little is known about endogenous mechanisms that regulate the sensitivity of CD25 to signaling by IL-2. Here we demonstrate that CD25 is ADP-ribosylated at Arg35 in the IL-2 binding site by ecto-ADP-ribosyltransferase ARTC2.2, a toxin-related GPI-anchored ecto-enzyme. ADP-ribosylation inhibits binding of IL-2 by CD25, IL-2- induced phosphorylation of STAT5, and IL-2-dependent cell proliferation. Our study elucidates an as-yet-unrecognized mechanism to tune IL-2 signaling. This newly found mechanism might thwart Tregs at sites of inflammation and thereby permit a more potent response of activated effector T cells.

Innate memory T cells

Memory T cells are usually considered to be a feature of a successful immune response against a foreign antigen, and such cells can mediate potent immunity. However, in mice, alternative pathways have been described, through which naïve T cells can acquire the characteristics and functions of memory T cells without encountering specific foreign antigen or the typical signals required for conventional T cell differentiation. Such cells reflect a response to the internal rather the external environment, and hence such cells are called innate memory T cells. In this review, we describe how innate memory subsets were identified, the signals that induce their generation and their functional properties and potential role in the normal immune response. The existence of innate memory T cells in mice raises questions about whether parallel populations exist in humans, and we discuss the evidence for such populations during human T cell development and differentiation.

Challenges and developing solutions for increasing the benefits of IL-2 treatment in tumor therapy

Interleukin-2 (IL-2) is a cytokine with pleiotropic effects on the immune system. Systemic IL-2 treatment has produced durable responses in melanoma and renal cancer patients, but unfortunately this is effective only in a fraction of patients. Moreover, IL-2 treatment also engenders serious side effects, which limit its clinical utility. It is now appreciated that IL-2 not only stimulates NK and effector T cells but also has a critical role in the generation and maintenance of regulatory T cells, which act to dampen immune responses. Thus, successful immunotherapy of cancers using IL-2 has to address two fundamentally important issues: (1) how to limit side effects yet be active where it is needed, and (2) how to preferentially activate effector T cells while limiting the stimulation of Tregs. Strategies are now being developed to address these critical obstacles that may lead to a renaissance of IL-2 therapy.

Antigen-specific activation and cytokine-facilitated expansion of naive, human CD8+ T cells

Antigen-specific priming of human, naive T cells has been difficult to assess. Owing to the low initial frequency in the naive cell pool of specific T cell precursors, such an analysis has been obscured by the requirements for repeated stimulations and prolonged culture time. In this protocol, we describe how to evaluate antigen-specific priming of CD8(+) cells 10 d after a single specific stimulation. The assay provides reference conditions, which result in the expansion of a substantial population of antigen-specific T cells from the naive repertoire. Various conditions and modifications during the priming process (e.g., testing new cytokines, co-stimulators and so on) can now be directly compared with the reference conditions. Factors relevant to achieving effective priming include the dendritic cell preparation, the T cell preparation, the cell ratio at the time of priming, the serum source used for the experiment and the timing of addition and concentration of the cytokines used for expansion. This protocol is relevant for human immunology, vaccine biology and drug development.

Increasing the biological activity of IL-2 and IL-15 through complexing with anti-IL-2 mAbs and IL-15Rα-Fc chimera

IL-2 and IL-15 are structurally relative cytokines that share two receptor subunits, CD132 (γ(c) chain) and CD122 (β chain). However, the expression pattern and physiological role of IL-2 and IL-15 private receptor α chains CD25 and IL-15Rα, respectively, are strikingly different. CD25, together with CD122 and CD132, forms a trimeric high affinity IL-2 receptor that is expressed and functions on cells acquiring an IL-2 signal. Conversely, IL-15Rα is expressed and binds IL-15 with high affinity per se already in the endoplasmic reticulum of the IL-15 producing cells and it presents IL-15 to cells expressing CD122/CD132 dimeric receptor in trans. Thus, while IL-2 is secreted almost exclusively by activated T cells and acts as a free molecule, IL-15 is expressed mostly by myeloid cells and works as a cell surface-associated cytokine. Interestingly, the in vivo biological activity of IL-2 can be dramatically increased through complexing with certain anti-IL-2 mAbs; such IL-2/anti-IL-2 mAbs immunocomplexes selectively stimulate the proliferation of a distinct population of immune cells, depending on the clone of the anti-IL-2 mAb used. IL-2/S4B6 mAb immunocomplexes are highly stimulatory for CD122(high) populations (memory CD8(+) T and NK cells) and intermediately also for CD25(high) populations (Treg and activated T cells), while IL-2/JES6-1 mAb immunocomplexes enormously expand only CD25(high) cells. Although IL-2 immunocomplexes are much more potent than IL-2 in vivo, they show comparable to slightly lower activity in vitro. The in vivo biological activity of IL-15 can be dramatically increased through complexing with recombinant IL-15Rα-Fc chimera; however, IL-15/IL-15Rα-Fc complexes are significantly more potent than IL-15 both in vivo and in vitro. In this review we summarize and discuss the features and biological relevance of IL-2/anti-IL-2 mAbs and IL-15/IL-15Rα-Fc complexes, and try to foreshadow their potential in immunological research and immunotherapy.

Vaccination issues in patients with chronic kidney disease

Infections are an important cause of morbidity and mortality among patients at all stages of chronic kidney disease. Prevention through vaccination remains the best strategy to minimize the adverse consequences associated with these infectious diseases in this, and all, populations. Unfortunately, patients with chronic kidney disease demonstrate inadequacies of specific immune-cell function that are required for generating a protective vaccine response. Nevertheless, early vaccination of this high-risk population has demonstrated good clinical outcomes during progression to late-stage disease. We review the available evidence linking immune impairment in adult patients with late-stage chronic kidney disease to diminished vaccine responses. We highlight the importance of early vaccination in disease with high risk for development of CKD and novel vaccine approaches in development that may help to address improvement in protective boosting of immunity during late-stage disease.

Mathematical Models of the Impact of IL2 Modulation Therapies on T Cell Dynamics

Several reports in the literature have drawn a complex picture of the effect of treatments aiming to modulate IL2 activity in vivo. They seem to promote either immunity or tolerance, probably depending on the specific context, dose, and timing of their application. Such complexity might derive from the pleiotropic role of IL2 in T cell dynamics. To theoretically address the latter possibility, our group has developed several mathematical models for Helper, Regulatory, and Memory T cell population dynamics, which account for most well-known facts concerning their relationship with IL2. We have simulated the effect of several types of therapies, including the injection of: IL2; antibodies anti-IL2; IL2/anti-IL2 immune-complexes; and mutant variants of IL2. We studied the qualitative and quantitative conditions of dose and timing for these treatments which allow them to potentiate either immunity or tolerance. Our results provide reasonable explanations for the existent pre-clinical and clinical data, predict some novel treatments, and further provide interesting practical guidelines to optimize the future application of these types of treatments.

Human IL2RA null mutation mediates immunodeficiency with lymphoproliferation and autoimmunity

Cell-surface CD25 expression is critical for maintaining immune function and homeostasis. As in few reported cases, CD25 deficiency manifests with severe autoimmune enteritis and viral infections. To dissect the underlying immunological mechanisms driving these symptoms, we analyzed the regulatory and effector T cell functions in a CD25 deficient patient harboring a novel IL2RA mutation. Pronounced lymphoproliferation, mainly of the CD8⁺ T cells, was detected together with an increase in T cell activation markers and elevated serum cytokines. However, Ag-specific responses were impaired in vivo and in vitro. Activated CD8⁺STAT5⁺ T cells with lytic potential infiltrated the skin, even though FOXP3⁺ Tregs were present and maintained a higher capacity to respond to IL-2 compared to other T-cell subsets. Thus, the complex pathogenesis of CD25 deficiency provides invaluable insight into the role of IL2/IL-2RA-dependent regulation in autoimmunity and inflammatory diseases.

The T-cell response to HIV

HIV is a disease in which the original clinical observations of severe opportunistic infections gave the first clues regarding the underlying pathology, namely that HIV is essentially an infection of the immune system. HIV infects and deletes CD4(+) T cells that normally coordinate the adaptive T- and B-cell response to defend against intracellular pathogens. The immune defect is immediate and profound: At the time of acute infection with an AIDS virus, typically more than half of the gut-associated CD4(+) T cells are depleted, leaving a damaged immune system to contend with a life-long infection.

Transient enhanced IL-2R signaling early during priming rapidly amplifies development of functional CD8+ T effector-memory cells

Much is known concerning the cellular and molecular basis for CD8(+) T memory immune responses. Nevertheless, conditions that selectively support memory generation have remained elusive. In this study, we show that an immunization regimen that delivers TCR signals through a defined antigenic peptide, inflammatory signals through LPS, and growth and differentiation signals through the IL-2R initially favors Ag-specific CD8(+) T cells to develop rapidly and substantially into T effector-memory cells by TCR transgenic OVA-specific OT-I CD8(+) T cells. Amplified CD8(+) T memory development depends upon a critical frequency of Ag-specific T cells and direct responsiveness to IL-2. A homologous prime-boost immunization protocol with transiently enhanced IL-2R signaling in normal mice led to persistent polyclonal Ag-specific CD8(+) T cells that supported protective immunity to Listeria monocytogenes. These results identify a general approach for amplified T memory development that may be useful to optimize vaccines aimed at generating robust cell-mediated immunity.

Innate IFN-γ is essential for programmed death ligand-1-mediated T cell stimulation following Listeria monocytogenes infection

Although best characterized for sustaining T cell exhaustion during persistent viral infection, programmed death ligand-1 (PDL-1) also stimulates the expansion of protective T cells after infection with intracellular bacterial pathogens. Therefore, establishing the molecular signals that control whether PDL-1 stimulates immune suppression or activation is important as immune modulation therapies based on manipulating PDL-1 are being developed. In this study, the requirement for PDL-1 blockade initiated before infection with the intracellular bacterium Listeria monocytogenes in reducing pathogen-specific T cell expansion is demonstrated. In turn, the role of proinflammatory cytokines triggered early after L. monocytogenes infection in controlling PDL-1-mediated T cell stimulation was investigated using mice with targeted defects in specific cytokines or cytokine receptors. These experiments illustrate an essential role for IL-12 or type I IFNs in PDL-1-mediated expansion of pathogen-specific CD8(+) T cells. Unexpectedly, direct stimulation by neither IL-12 nor type I IFNs on pathogen-specific CD8(+) cells was essential for PDL-1-mediated expansion. Instead, the absence of early innate IFN-γ production in mice with combined defects in both IL-12 and type I IFNR negated the impacts of PDL-1 blockade. In turn, IFN-γ ablation using neutralizing Abs or in mice with targeted defects in IFN-γR each eliminated the PDL-1-mediated stimulatory impacts on pathogen-specific T cell expansion. Thus, innate IFN-γ is essential for PDL-1-mediated T cell stimulation.

Differential effect of CD69 targeting on bystander and antigen-specific T cell proliferation

In spite of an initially proposed role as a costimulatory molecule for CD69, in vivo studies showed it as a regulator of immune responses and lymphocyte egress. We found constitutive CD69 expression by T cell subsets and pDC. We examined a possible effect of CD69 on T cell proliferation using transfer models and in vitro assays. In mice locally expressing or receiving antigen, anti-CD692.2 treatment did not affect the proliferation of antigen-specific transgenic T cells in ADLN, although we observed the presence of proliferated T cells in non-ADLN and spleen. This was not affected by FTY720 treatment and thus, not contributed by increased egress of proliferated lymphocytes from ADLN. In the absence of antigen, anti-CD69 2.2 treatment induced bystander proliferation of transferred memory phenotype T cells. This proliferation was mediated by IL-2, as it was inhibited by anti-IL-2 or anti-CD25 antibodies in vitro and by anti-CD25 antibodies in vivo. It was also dependent on CD69 expression by donor T cells and recipient cells. CD69 targeting on T cells enhanced IL-2-mediated proliferation and CD25 expression. However, it did not lead to increased early IL-2 production by T cells. No T cell subset was found to be specifically required in the recipient. Instead, CD69 targeting on pDC induced their expression of IL-2 and CD25, and pDC depletion showed that this subset was involved in the proliferation induction. These results indicate that CD69 targeting induces bystander T cell proliferation through pDC IL-2 production and T cell sensitization to IL-2 without affecting antigen-driven T cell proliferation.

Dual anti-OX40/IL-2 therapy augments tumor immunotherapy via IL-2R-mediated regulation of OX40 expression

The provision of T cell co-stimulation via members of the TNFR super-family, including OX40 (CD134) and 4-1BB (CD137), provides critical signals that promote T cell survival and differentiation. Recent studies have demonstrated that ligation of OX40 can augment T cell-mediated anti-tumor immunity in pre-clinical models and more importantly, OX40 agonists are under clinical development for cancer immunotherapy. OX40 is of particular interest as a therapeutic target as it is not expressed on naïve T cells but rather, is transiently up-regulated following TCR stimulation. Although TCR engagement is necessary for inducing OX40 expression, the downstream signals that regulate OX40 itself remain unclear. In this study, we demonstrate that OX40 expression is regulated through a TCR and common gamma chain cytokine-dependent signaling cascade that requires JAK3-mediated activation of the downstream transcription factors STAT3 and STAT5. Furthermore, combined treatment with an agonist anti-OX40 mAb and IL-2 augmented tumor immunotherapy against multiple tumor types. Dual therapy was also able to restore the function of anergic tumor-reactive CD8 T cells in mice with long-term well-established (>5 wks) tumors, leading to increased survival of the tumor-bearing hosts. Together, these data reveal the ability of TCR/common gamma chain cytokine signaling to regulate OX40 expression and demonstrate a novel means of augmenting cancer immunotherapy by providing dual anti-OX40/common gamma chain cytokine-directed therapy.

Antigen-specific versus antigen-nonspecific immunotherapeutic approaches for human melanoma: the need for integration for optimal efficacy?

Due to its immunogenecity and evidence of immune responses resulting in tumor regression, metastatic melanoma has been the target for numerous immunotherapeutic approaches. Unfortunately, based on the clinical outcomes, even the successful induction of tumor-specific responses does not correlate with efficacy. Immunotherapies can be divided into antigen-specific approaches, which seek to induce T cells specific to one or several known tumor associated antigens (TAA), or with antigen-nonspecific approaches, which generally activate T cells to become nonspecifically lytic effectors. Here the authors critically review the different immunotherapeutic approaches in melanoma.

Modeling the role of IL2 in the interplay between CD4+ helper and regulatory T cells: studying the impact of IL2 modulation therapies

Several reports in the literature have drawn a complex picture of the effect of treatments aiming to modulate IL2 activity in vivo. They seem to promote indistinctly immunity or tolerance, probably depending on the specific context, dose and timing of their application. Such complexity might derives from the dual role of IL2 on T-cell dynamics. To theoretically address the latter possibility, we develop a mathematical model for helper, regulatory and memory T-cells dynamics, which account for most well-known facts relative to their relationship with IL2. We simulate the effect of three types of therapies: IL2 injections, IL2 depletion using anti-IL2 antibodies and IL2/anti-IL2 immune complexes injection. We focus in the qualitative and quantitative conditions of dose and timing for these treatments which allow them to potentate either immunity or tolerance. Our results provide reasonable explanations for the existent pre-clinical and clinical data and further provide interesting practical guidelines to optimize the future application of these types of treatments. Particularly, our results predict that: (i) Immune complexes IL2/anti-IL2 mAbs, using mAbs which block the interaction of IL2 and CD25 (the alpha chain of IL2 receptor), is the best option to potentate immunity alone or in combination with vaccines. These complexes are optimal when a 1:2 molar ratio of mAb:IL2 is used and the mAbs have the largest possible affinity; (ii) Immune complexes IL2/anti-IL2 mAbs, using mAbs which block the interaction of IL2 and CD122 (the beta chain of IL2 receptor), are the best option to reinforce preexistent natural tolerance, for instance to prevent allograft rejection. These complexes are optimal when a 1:2 molar ratio of mAb:IL2 is used and the mAbs have intermediate affinities; (iii) mAbs anti-IL2 can be successfully used alone to treat an ongoing autoimmune disorder, promoting the re-induction of tolerance. The best strategy in this therapy is to start treatment with an initially high dose of the mAbs (one capable to induce some immune suppression) and then scales down slowly the dose of mAb in subsequent applications.

Peptide-loaded Langerhans cells, despite increased IL15 secretion and T-cell activation in vitro, elicit antitumor T-cell responses comparable to peptide-loaded monocyte-derived dendritic cells in vivo

PURPOSE

We compared the efficacy of human Langerhans cells (LC) as tumor immunogens in vivo with monocyte-derived dendritic cells (moDC) and investigated how interleukin 15 (IL15) supports optimal DC-stimulated antitumor immunity.

EXPERIMENTAL DESIGN

American Joint Committee on Cancer stage III/IV melanoma patients participated in this first clinical trial comparing melanoma peptide-pulsed LC with moDC vaccines (NCT00700167, www.ClinicalTrials.gov). Correlative studies evaluated mechanisms mediating IL15 support of DC-stimulated antitumor immunity.

RESULTS

Both DC vaccines were safe and immunogenic for melanoma antigens. LC-based vaccines stimulated significantly greater tyrosinase-HLA-A*0201 tetramer reactivity than the moDC-based vaccines. The two DC subtypes were otherwise statistically comparable, in contrast to extensive prior data in vitro showing LC superiority. LCs synthesize much more IL15 than moDCs and stimulate significantly more antigen-specific lymphocytes with a cytolytic IFN-γ profile even without exogenous IL15. When supplemented by low-dose IL15, instead of IL2, moDCs stimulate 5 to 6 logs more tumor antigen-specific effector memory T cells (T(EMRA)) over 3 to 4 weeks in vitro. IL2 and IL15 can be synergistic in moDC stimulation of cytolytic T cells. IL15 promotes T-cell expression of the antiapoptotic bcl-2 and inhibits candidate regulatory T-cell (Treg) expansion after DC stimulation, countering two effects of IL2 that do not foster tumor immunity.

CONCLUSIONS

MoDC-based vaccines will require exogenous IL15 to achieve clinical efficacy. Alternatively, LCs can couple the endogenous production of IL15 with potent T-cell stimulatory activity. Optimization of full-length tumor antigen expression for processing into multiple immunogenic peptides for presentation by both class I and II MHC therefore merits emphasis to support more effective antitumor immunity stimulated by LCs.

Induction and function of virus-specific CD4+ T cell responses

CD4+ T cells - often referred to as T-helper cells - play a central role in immune defense and pathogenesis. Virus infections and vaccines stimulate and expand populations of antigen-specific CD4+ T cells in mice and in man. These virus-specific CD4+ T cells are extremely important in antiviral protection: deficiencies in CD4+ T cells are associated with virus reactivation, generalized susceptibility to opportunistic infections, and poor vaccine efficacy. As described below, CD4+ T cells influence effector and memory CD8+ T cell responses, humoral immunity, and the antimicrobial activity of macrophages and are involved in recruiting cells to sites of infection. This review summarizes a few key points about the dynamics of the CD4+ T cell response to virus infection, the positive role of pro-inflammatory cytokines in the differentiation of virus-specific CD4+ T cells, and new areas of investigation to improve vaccines against virus infection.

Single dose of anti-CTLA-4 enhances CD8+ T-cell memory formation, function, and maintenance

CTLA-4, an Ig superfamily molecule with homology to CD28, is one of the most potent negative regulators of T-cell responses. In vivo blockade of CTLA-4 exacerbates autoimmunity, enhances tumor-specific T-cell responses, and may inhibit the induction of T-cell anergy. Clinical trials of CTLA-4-blocking antibodies to augment T-cell responses to malignant melanoma are at an advanced stage; however, little is known about the effects of CTLA-4 blockade on memory CD8(+) T-cell responses and the formation and maintenance of long-term CD8(+) T-cell memory. In our studies, we show that during in vivo memory CD8(+) T-cell responses to Listeria monocytogenes infection, CTLA-4 blockade enhances bacterial clearance and increases memory CD8(+) T-cell expansion. This is followed by an accumulation of memory cells that are capable of producing the effector cytokines IFN-γ and TNF-α. We also demonstrate that in a vaccination setting, blocking CTLA-4 during CD8(+) T-cell priming leads to increased expansion and maintenance of antigen-specific memory CD8(+) T cells without adversely affecting the overall T-cell repertoire. This leads to an increase in memory cell effector function and improved protective immunity against further bacterial challenges. These results indicate that transient blockade of CTLA-4 enhances memory CD8(+) T-cell responses and support the possible use of CTLA-4-blocking antibodies during vaccination to augment memory formation and maintenance.

CD4+ natural regulatory T cells prevent experimental cerebral malaria via CTLA-4 when expanded in vivo

Studies in malaria patients indicate that higher frequencies of peripheral blood CD4(+) Foxp3(+) CD25(+) regulatory T (Treg) cells correlate with increased blood parasitemia. This observation implies that Treg cells impair pathogen clearance and thus may be detrimental to the host during infection. In C57BL/6 mice infected with Plasmodium berghei ANKA, depletion of Foxp3(+) cells did not improve parasite control or disease outcome. In contrast, elevating frequencies of natural Treg cells in vivo using IL-2/anti-IL-2 complexes resulted in complete protection against severe disease. This protection was entirely dependent upon Foxp3(+) cells and resulted in lower parasite biomass, impaired antigen-specific CD4(+) T and CD8(+) T cell responses that would normally promote parasite tissue sequestration in this model, and reduced recruitment of conventional T cells to the brain. Furthermore, Foxp3(+) cell-mediated protection was dependent upon CTLA-4 but not IL-10. These data show that T cell-mediated parasite tissue sequestration can be reduced by regulatory T cells in a mouse model of malaria, thereby limiting malaria-induced immune pathology.