An engineered IL-2 partial agonist promotes CD8+ T cell stemness and anti-tumor efficacy

Adoptive cell transfer of antigen specific T cells represents a major advance in cancer immunotherapy, with robust clinical outcomes in a subset of patients. To achieve effective responses, both the number of transferred T cells and their cell differentiation state are critical determinants. T cells can be expanded with T cell receptor (TCR)-mediated stimulation and IL-2 but this can also lead to T cell differentiation into effector T cells, resulting in diminished therapeutic efficacy, whereas maintenance of a more stem-like prior to adoptive transfer is beneficial. Here, we show that an engineered IL-2 partial agonist generated on the super-IL-2 background promoted T-cell expansion without driving terminal differentiation. The partial agonist exhibited altered signaling and mediated distinctive downstream transcriptional, epigenetic, and metabolic programs. Moreover, it sustained expression of transcription factor TCF-1 (T cell transcription factor 1) and promoted mitochondrial fitness, facilitating the maintenance of a stem cell-like state. Accordingly, TCR transgenic and CAR-modified CD8+ T cells expanded with this engineered molecule displayed robust anti-tumor activity in vivo in established models of melanoma and acute lymphoblastic leukemia. Thus, tempering cytokine signaling with the IL-2 partial agonist provides a strategy for enhancing therapeutic efficacy by limiting exhaustion while preserving stemness. Moreover, our findings demonstrate the distinctive power of generation cytokine partial agonists with distinctive activities.

Transcription factor p73 regulates Th1 differentiation

Inter-individual differences in T helper (Th) cell responses affect susceptibility to infectious, allergic and autoimmune diseases. To identify factors contributing to these response differences, here we analyze in vitro differentiated Th1 cells from 16 inbred mouse strains. Haplotype-based computational genetic analysis indicates that the p53 family protein, p73, affects Th1 differentiation. In cells differentiated under Th1 conditions in vitro, p73 negatively regulates IFNγ production. p73 binds within, or upstream of, and modulates the expression of Th1 differentiation-related genes such as Ifng and Il12rb2. Furthermore, in mouse experimental autoimmune encephalitis, p73-deficient mice have increased IFNγ production and less disease severity, whereas in an adoptive transfer model of inflammatory bowel disease, transfer of p73-deficient naïve CD4⁺ T cells increases Th1 responses and augments disease severity. Our results thus identify p73 as a negative regulator of the Th1 immune response, suggesting that p73 dysregulation may contribute to susceptibility to autoimmune disease.

Heterogeneous helper T (Th) cell responses contribute to differential susceptibility to immunological disorders. Here the authors perform haplotype-based computational screens of 16 inbred mouse strains to identify a transcription factor, p73, as an important negative regulator of Th1 differentiation, with p73 deficient mice manifesting alterations in two inflammatory disease models.

Proliferating Transitory T Cells with an Effector-like Transcriptional Signature Emerge from PD-1+ Stem-like CD8+ T Cells during Chronic Infection

T cell dysfunction is a characteristic feature of chronic viral infection and cancer. Recent studies in chronic lymphocytic choriomeningitis virus (LCMV) infection have defined a PD-1+ Tcf-1+ CD8+ T cell subset capable of self-renewal and differentiation into more terminally differentiated cells that downregulate Tcf-1 and express additional inhibitory molecules such as Tim3. Here, we demonstrated that expression of the glycoprotein CD101 divides this terminally differentiated population into two subsets. Stem-like Tcf-1+ CD8+ T cells initially differentiated into a transitory population of CD101-Tim3+ cells that later converted into CD101+ Tim3+ cells. Recently generated CD101-Tim3+ cells proliferated in vivo, contributed to viral control, and were marked by an effector-like transcriptional signature including expression of the chemokine receptor CX3CR1, pro-inflammatory cytokines, and granzyme B. PD-1 pathway blockade increased the numbers of CD101-Tim3+ CD8+ T cells, suggesting that these newly generated transitional cells play a critical role in PD-1-based immunotherapy.

The γc Family of Cytokines: Basic Biology to Therapeutic Ramifications

The common cytokine receptor γ chain, γ_c, is a component of the receptors for interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21. Mutation of the gene encoding γ_c results in X-linked severe combined immunodeficiency in humans, and γ_c family cytokines collectively regulate development, proliferation, survival, and differentiation of immune cells. Here, we review the basic biology of these cytokines, highlighting mechanisms of signaling and gene regulation that have provided insights for immunodeficiency, autoimmunity, allergic diseases, and cancer. Moreover, we discuss how studies of this family stimulated the development of JAK3 inhibitors and present an overview of current strategies targeting these pathways in the clinic, including novel antibodies, antagonists, and partial agonists. The diverse roles of these cytokines on a range of immune cells have important therapeutic implications.

Biology and regulation of IL-2: from molecular mechanisms to human therapy

IL-2 was first identified as a growth factor capable of driving the expansion of activated human T cell populations. In the more than 40 years since its discovery, a tremendous amount has been learned regarding the mechanisms that regulate the expression of both IL-2 and its cell surface receptor, its mechanisms of signalling and its range of biological actions. More recently, the mechanisms by which IL-2 regulates CD4⁺ T cell differentiation and function have been elucidated. IL-2 also regulates the effector and memory responses of CD8⁺ T cells, and the loss of IL-2 or responsiveness to IL-2 at least in part explains the exhausted phenotype that occurs during chronic viral infections and in tumour responses. These basic mechanistic studies have led to the therapeutic ability to manipulate the action of IL-2 on regulatory T (T_reg) cells for the treatment of autoimmune disease and on CD8⁺ T cells for immunotherapy of cancer. IL-2 can have either positive or deleterious effects, and we discuss here recent ideas and approaches for manipulating the actions and overall net effects of IL-2 in disease settings, including cancer.

IL-10 signaling in dendritic cells controls IL-1β-mediated IFNγ secretion by human CD4+ T cells: relevance to inflammatory bowel disease

Uncontrolled interferon γ (IFNγ)-mediated T-cell responses to commensal microbiota are a driver of inflammatory bowel disease (IBD). Interleukin-10 (IL-10) is crucial for controlling these T-cell responses, but the precise mechanism of inhibition remains unclear. A better understanding of how IL-10 exerts its suppressive function may allow identification of individuals with suboptimal IL-10 function among the heterogeneous population of IBD patients. Using cells from patients with an IL10RA deficiency or STAT3 mutations, we demonstrate that IL-10 signaling in monocyte-derived dendritic cells (moDCs), but not T cells, is essential for controlling IFNγ-secreting CD4⁺ T cells. Deficiency in IL-10 signaling dramatically increased IL-1β release by moDCs. IL-1β boosted IFNγ secretion by CD4⁺ T cells either directly or indirectly by stimulating moDCs to secrete IL-12. As predicted a signature of IL-10 dysfunction was observed in a subgroup of pediatric IBD patients having higher IL-1β expression in activated immune cells and macroscopically affected intestinal tissue. In agreement, reduced IL10RA expression was detected in peripheral blood mononuclear cells and a subgroup of pediatric IBD patients exhibited diminished IL-10 responsiveness. Our data unveil an important mechanism by which IL-10 controls IFNγ-secreting CD4⁺ T cells in humans and identifies IL-1β as a potential classifier for a subgroup of IBD patients.

Epigenetic signature of PD-1+ TCF1+ CD8 T cells that act as resource cells during chronic viral infection and respond to PD-1 blockade

We have recently defined a novel population of PD-1 (programmed cell death 1)+ TCF1 (T cell factor 1)+ virus-specific CD8 T cells that function as resource cells during chronic LCMV infection and provide the proliferative burst seen after PD-1 blockade. Such CD8 T cells have been found in other chronic infections and also in cancer in mice and humans. These CD8 T cells exhibit stem-like properties undergoing self-renewal and also differentiating into the terminally exhausted CD8 T cells. Here we compared the epigenetic signature of stem-like CD8 T cells with exhausted CD8 T cells. ATAC-seq analysis showed that stem-like CD8 T cells had a unique signature implicating activity of HMG (TCF) and RHD (NF-κB) transcription factor family members in contrast to higher accessibility to ETS and RUNX motifs in exhausted CD8 T cells. In addition, regulatory regions of the transcription factors Tcf7 and Id3 were more accessible in stem-like cells whereas Prdm1 and Id2 were more accessible in exhausted CD8 T cells. We also compared the epigenetic signatures of the 2 CD8 T cell subsets from chronically infected mice with effector and memory CD8 T cells generated after an acute LCMV infection. Both CD8 T cell subsets generated during chronic infection were strikingly different from CD8 T cell subsets from acute infection. Interestingly, the stem-like CD8 T cell subset from chronic infection, despite sharing key functional properties with memory CD8 T cells, had a very distinct epigenetic program. These results show that the chronic stem-like CD8 T cell program represents a specific adaptation of the T cell response to persistent antigenic stimulation.

STAT5b dimers and tetramers are critical for Mast Cell Function

Signal transducers and activators of transcription (STATs) are latent transcription factors vital for lymphoid, myeloid, and erythroid cell development, survival, proliferation, and function. Activated STATs form dimers that translocate to the nucleus and bind high affinity STAT DNA motifs to modulate gene expression. We previously found that Stat5b is required for IgE-mediated mast cell cytokine production in vitro. In this study, we found that STAT5b KO mice demonstrate decreased sensitivity to IgE-mediated passive systemic anaphylaxis (PSA) and reduced cytokine production in vivo. This is not due to differences in mast cell numbers or distribution. Interestingly, STAT5b KO mice exhibit elevated levels of serum IgE that could diminish PSA by preventing binding of antigen-specific IgE. Increased serum IgE is not tied to changes in B cell number or their ability to produce IgE in vitro. In addition to dimers, activated STAT proteins can also form tetramers through an oligomerization process once dimers bind to tandem low-affinity STAT DNA motifs. Similar to STAT5bKO, in vitro IgE-mediated cytokine production is decreased in Stat5a-Stat5b double knock-in (DKI) mice in which STAT5 proteins can form dimers but not tetramers. In vivo, DKI mice exhibit decreased PSA sensitivity, with no difference in mast cell numbers or distribution, and a modest increase in serum IgE. Collectively, these data illuminate the unique and specific roles of STAT5 dimers and tetramers in mast cell function and allergic disease.

PU.1 and IRF8 regulate the transcriptional landscapes differently in naïve and activated B cells

The Ets family member PU.1 and the IRF family member IRF8 play crucial roles in regulating hematopoietic cell development including B cells. Both factors are constitutively expressed at high levels in B cells and control plasma cell differentiation. IRF8 and PU.1 function either together as a heterodimer or by pairing with other factors to bind target DNA sequences. Several consensus binding sequences for IRF8 and PU.1 have been identified, including the canonical interferon stimulated response element (ISRE) sequence motif (GAAANNGAAA), the Ets-IRF composite element (EICE) (GGAANNGAAA) and the IRF-Ets composite sequence (IECS) (GAAANN[N]GGAA). Although the target genes of IRF8 and PU.1 have been studied previously by chromatin immunoprecipitation (ChIP), the nature and the importance of the motifs engaging both PU.1 and IRF8 in B cells have not been determined. In this study, we performed ChIP-seq using sort-purified naïve follicular B cells from C57BL/6 mice that were either not stimulated or stimulated with anti-IgM plus anti-CD40, which mimic signals for germinal center B cell differentiation. We also integrated our ChIP-seq data with RNA-seq data from B cells deficient for both IRF8 and PU.1, and found that IRF8 and PU.1 regulate gene expression by preferentially binding to the EICE motifs of target genes known to maintain follicular B cell identity, localization, and survival. In contrast, in activated B cells, the binding landscape of IRF8/PU.1 in target genes shifts to IRF8-dominant ISRE motifs, possibly due to elevated expression of IRF8. These results provide new insights into our understanding of the molecular mechanisms underlying the transcriptional control of late stage B cell development.

Critical role of STAT5 tetramerization in the pathogenesis of experimental autoimmune encephalomyelitis, a murine model of multiple sclerosis

Multiple sclerosis (MS) is an immune mediated disease that predominantly impacts the central nervous system (CNS). Current MS treatments have demonstrated the ability to reduce the rate of MS relapses; however, they are not effective at preventing disease progression. Elucidating the pathways that govern the pathogenesis of MS may identify molecular mediators, which can act as novel therapeutic targets to treat MS progression. STAT5 is a transcription factor critical for the generation, activation, and function of different immune cell types. Upon activation, STAT5 can form dimers or tetramers, which have distinct functions. Using a Stat5a-Stat5b double knock-in N-domain mutant mouse strain (DKI mice), in which STAT5 dimers are functional, but STAT5 tetramers cannot be formed, we demonstrated that DKI mice developed less severe experimental autoimmune encephalomyelitis (EAE), a model of MS, compared to WT littermates. Moreover, a portion of DKI mice did not develop EAE symptoms. Flow cytometric analysis of peripheral blood revealed that during the early phase of EAE, WT and DKI mice exhibited similar levels of immune cell expansion in the periphery. However, at the peak of EAE, DKI mice had fewer immune cells in the CNS. This suggests that STAT5 tetramers promote immune cell egress to the CNS or/and immune cell expansion within the CNS. In addition, multiplex protein assays established that the expression of a pro-inflammatory cytokine and several chemokines, including IL-1α, CCL3, CCL17, and CCL22, are reduced in DKI mice compared to WT mice, which may account for the reduced disease severity observed in DKI mice. Taken together, the data suggest that STAT5 tetramers plays a multifaceted role in promoting inflammation resulting in EAE.

Fine-Tuning Cytokine Signals

Cytokines are secreted or otherwise released polypeptide factors that exert autocrine and/or paracrine actions, with most cytokines acting in the immune and/or hematopoietic system. They are typically pleiotropic, controlling development, cell growth, survival, and/or differentiation. Correspondingly, cytokines are clinically important, and augmenting or attenuating cytokine signals can have deleterious or therapeutic effects. Besides physiological fine-tuning of cytokine signals, altering the nature or potency of the signal can be important in pathophysiological responses and can also provide novel therapeutic approaches. Here, we give an overview of cytokines, their signaling and actions, and the physiological mechanisms and pharmacologic strategies to fine-tune their actions. In particular, the differential utilization of STAT proteins by a single cytokine or by different cytokines and STAT dimerization versus tetramerization are physiological mechanisms of fine-tuning, whereas anticytokine and anticytokine receptor antibodies and cytokines with altered activities, including cytokine superagonists, partial agonists, and antagonists, represent new ways of fine-tuning cytokine signals.

IL-21/type I interferon interplay regulates neutrophil-dependent innate immune responses to Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major hospital- and community-acquired pathogen, but the mechanisms underlying host-defense to MRSA remain poorly understood. Here, we investigated the role of IL-21 in this process. When administered intra-tracheally into wild-type mice, IL-21 induced granzymes and augmented clearance of pulmonary MRSA but not when neutrophils were depleted or a granzyme B inhibitor was added. Correspondingly, IL-21 induced MRSA killing by human peripheral blood neutrophils. Unexpectedly, however, basal MRSA clearance was also enhanced when IL-21 signaling was blocked, both in Il21r KO mice and in wild-type mice injected with IL-21R-Fc fusion-protein. This correlated with increased type I interferon and an IFN-related gene signature, and indeed anti-IFNAR1 treatment diminished MRSA clearance in these animals. Moreover, we found that IFNβ induced granzyme B and promoted MRSA clearance in a granzyme B-dependent fashion. These results reveal an interplay between IL-21 and type I IFN in the innate immune response to MRSA.

A recessive form of hyper-IgE syndrome by disruption of ZNF341-dependent STAT3 transcription and activity

Heterozygosity for human signal transducer and activator of transcription 3 (STAT3) dominant-negative (DN) mutations underlies an autosomal dominant form of hyper-immunoglobulin E syndrome (HIES). We describe patients with an autosomal recessive form of HIES due to loss-of-function mutations of a previously uncharacterized gene, ZNF341 ZNF341 is a transcription factor that resides in the nucleus, where it binds a specific DNA motif present in various genes, including the STAT3 promoter. The patients' cells have low basal levels of STAT3 mRNA and protein. The autoinduction of STAT3 production, activation, and function by STAT3-activating cytokines is strongly impaired. Like patients with STAT3 DN mutations, ZNF341-deficient patients lack T helper 17 (T_H17) cells, have an excess of T_H2 cells, and have low memory B cells due to the tight dependence of STAT3 activity on ZNF341 in lymphocytes. Their milder extra-hematopoietic manifestations and stronger inflammatory responses reflect the lower ZNF341 dependence of STAT3 activity in other cell types. Human ZNF341 is essential for the STAT3 transcription-dependent autoinduction and sustained activity of STAT3.

Homeostatic Control of Sebaceous Glands by Innate Lymphoid Cells Regulates Commensal Bacteria Equilibrium

Immune cells and epithelium form sophisticated barrier systems in symbiotic relationships with microbiota. Evidence suggests that immune cells can sense microbes through intact barriers, but regulation of microbial commensalism remain largely unexplored. Here, we uncovered spatial compartmentalization of skin-resident innate lymphoid cells (ILCs) and modulation of sebaceous glands by a subset of RORγt⁺ ILCs residing within hair follicles in close proximity to sebaceous glands. Their persistence in skin required IL-7 and thymic stromal lymphopoietin, and localization was dependent on the chemokine receptor CCR6. ILC subsets expressed TNF receptor ligands, which limited sebocyte growth by repressing Notch signaling pathway. Consequently, loss of ILCs resulted in sebaceous hyperplasia with increased production of antimicrobial lipids and restricted commensalism of Gram-positive bacterial communities. Thus, epithelia-derived signals maintain skin-resident ILCs that regulate microbial commensalism through sebaceous gland-mediated tuning of the barrier surface, highlighting an immune-epithelia circuitry that facilitates host-microbe symbiosis.

Chromatin Accessibility and Interactions in the Transcriptional Regulation of T Cells

During T cell differentiation and activation, specific stimuli, and a network of transcription factors (TFs) are involved in orchestrating chromatin accessibility, establishing enhancer-promoter interactions, and regulating gene expression. Over the past few years, there have been new insights into how chromatin interactions coordinate differentiation during T cell development and how regulatory elements are programmed to allow T cells to differentially respond to distinct stimuli. In this review, we discuss recent advances related to the roles of TFs in establishing the regulatory chromatin landscapes that orchestrate T cell development and differentiation. In particular, we focus on the role of TFs (e.g., TCF-1, BCL11B, PU.1, STAT3, STAT5, AP-1, and IRF4) in mediating chromatin accessibility and interactions and in regulating gene expression in T cells, including gene expression that is dependent on IL-2 and IL-21. Furthermore, we discuss the state of knowledge on enhancer-promoter interactions and how autoimmune disease risk variants can be linked to molecular functions of putative target genes.

The Common Cytokine Receptor γ Chain Family of Cytokines

Interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21 form a family of cytokines based on their sharing the common cytokine receptor γ chain (γc), which was originally discovered as the third receptor component of the IL-2 receptor, IL-2Rγ. The IL2RG gene is located on the X chromosome and is mutated in humans with X-linked severe combined immunodeficiency (XSCID). The breadth of the defects in XSCID could not be explained solely by defects in IL-2 signaling, and it is now clear that γc is a shared receptor component of the six cytokines noted above, making XSCID a disease of defective cytokine signaling. Janus kinase (JAK)3 associates with γc, and JAK3-deficient SCID phenocopies XSCID, findings that served to stimulate the development of JAK3 inhibitors as immunosuppressants. γc family cytokines collectively control broad aspects of lymphocyte development, growth, differentiation, and survival, and these cytokines are clinically important, related to allergic and autoimmune diseases and cancer as well as immunodeficiency. In this review, we discuss the actions of these cytokines, their critical biological roles and signaling pathways, focusing mainly on JAK/STAT (signal transducers and activators of transcription) signaling, and how this information is now being used in clinical therapeutic efforts.

Act1 is a negative regulator in T and B cells via direct inhibition of STAT3

Although Act1 (adaptor for IL-17 receptors) is necessary for IL-17-mediated inflammatory responses, Act1- (but not Il17ra-, Il17rc-, or Il17rb-) deficient mice develop spontaneous SLE- and Sjögren's-like diseases. Here, we show that Act1 functions as a negative regulator in T and B cells via direct inhibition of STAT3. Mass spectrometry analysis detected an Act1-STAT3 complex, deficiency of Act1 (but not Il17ra-, Il17rc-, or Il17rb) results in hyper IL-23- and IL-21-induced STAT3 activation in T and B cells, respectively. IL-23R deletion or blockade of IL-21 ameliorates SLE- and Sjögren's-like diseases in Act1-/- mice. Act1 deficiency results in hyperactivated follicular Th17 cells with elevated IL-21 expression, which promotes T-B cell interaction for B cell expansion and antibody production. Moreover, anti-IL-21 ameliorates the SLE- and Sjögren's-like diseases in Act1-deficient mice. Thus, IL-21 blocking antibody might be an effective therapy for treating SLE- and Sjögren's-like syndrome in patients containing Act1 mutation.

Balance of IL-21 and type I IFN in the granzyme-dependent innate immune response to Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) infection is a major complication of viral respiratory infections and immunodeficient states. Here, we investigated the role of interleukin-21 (IL-21) in host response to pulmonary MRSA infection and unexpectedly found that IL-21 acts directly on neutrophils and can promote MRSA clearance. When administered intra-tracheally into wild-type mice, IL-21 potently induced granzymes and augmented host defense, and IL-21-induced killing of MRSA was also observed with peripheral blood neutrophils from healthy donors but not from patients with autosomal dominant hyper-IgE (Jobs) syndrome. Unexpectedly, however, loss of IL-21 signaling, as occurs in Il21r KO mice or WT mice treated with an IL-21R-Fc fusion protein or mice expressing a mutant STAT3 transgene, also resulted in enhanced clearance of MRSA, and this was associated with enhanced expression of interferon-dependent genes. Moreover, IFNb induced granzyme B expression by neutrophils, and a granzyme B inhibitor blocked IFNb-induced MRSA clearance. These results reveal a balance and an interplay between IL-21 and type-I IFN signaling in the granzyme-dependent neutrophil response to MRSA, indicating that manipulating IL-21 signaling may be a strategy for controlling pulmonary bacterial infections.

All-Trans Retinoic Acid Enhances Antibody Production by Inducing the Expression of Thymic Stromal Lymphopoietin Protein

Many classical vaccines contain whole pathogens and, thus, may occasionally induce adverse effects, such as inflammation. Vaccines containing purified rAgs resolved this problem, but, owing to their low antigenicity, they require adjuvants. Recently, the use of several cytokines, including thymic stromal lymphopoietin (TSLP), has been proposed for this purpose. However, it is difficult to use cytokines as vaccine adjuvants in clinical practice. In this study, we examined the effects of all-trans retinoic acid (atRA) on TSLP production and Ag-induced Ab production. Application of atRA onto the ear lobes of mice selectively induced TSLP production without inducing apparent inflammation. The effects appeared to be regulated via retinoic acid receptors γ and α. Treatment with atRA was observed to enhance OVA-induced specific Ab production; however, this effect was completely absent in TSLP receptor–knockout mice. An enhancement in Ab production was also observed when recombinant hemagglutinin was used as the Ag. In conclusion, atRA was an effective adjuvant through induction of TSLP production. Therefore, we propose that TSLP-inducing low m.w. compounds, such as atRA, may serve as effective adjuvants for next-generation vaccines.

TSLP signaling in CD4+ T cells programs a pathogenic T helper 2 cell state

Pathogenic T helper 2 (T_H2) cells, which produce increased amounts of the cytokines interleukin-5 (IL-5) and IL-13, promote allergic disorders, including asthma. Thymic stromal lymphopoietin (TSLP), a cytokine secreted by epithelial and innate immune cells, stimulates such pathogenic T_H2 cell responses. We found that TSLP signaling in mouse CD4⁺ T cells initiated transcriptional changes associated with T_H2 cell programming. IL-4 signaling amplified and stabilized the genomic response of T cells to TSLP, which increased the frequency of T cells producing IL-4, IL-5, and IL-13. Furthermore, the TSLP- and IL-4-programmed T_H2 cells had a pathogenic phenotype, producing greater amounts of IL-5 and IL-13 and other proinflammatory cytokines than did T_H2 cells stimulated with IL-4 alone. TSLP-mediated T_H2 cell induction involved distinct molecular pathways, including activation of the transcription factor STAT5 through the kinase JAK2 and repression of the transcription factor BCL6. Mice that received wild-type CD4⁺ T cells had exacerbated pathogenic T_H2 cell responses upon exposure to house dust mites compared to mice that received TSLP receptor-deficient CD4⁺ T cells. Transient TSLP signaling stably programmed pathogenic potential in memory T_H2 cells. In human CD4⁺ T cells, TSLP and IL-4 promoted the generation of T_H2 cells that produced greater amounts of IL-5 and IL-13. Compared to healthy controls, asthmatic children showed enhancement of such T cell responses in peripheral blood. Our data support a sequential cytokine model for pathogenic T_H2 cell differentiation and provide a mechanistic basis for the therapeutic targeting of TSLP signaling in human allergic diseases.

Biology of IL-2 and its therapeutic modulation: Mechanisms and strategies

Cytokines signal through specific cell surface receptors to broadly regulate immune development, differentiation, proliferation, and survival, thereby influencing cellular fate and function. Accordingly, cytokines are potential therapeutic targets for modulation of immune responses. Indeed, over the last several decades, an increasing number of cytokine-based clinical trials have been performed, collectively using either recombinant forms of cytokines or blocking agents that modulate the actions of cytokines. The pleiotropic actions of cytokines, including their abilities to mediate both inflammatory and protective immune responses, indicate that using or targeting cytokines can have desired but also potentially undesirable effects. Here, we focus on the immunomodulatory cytokine, IL-2. We review the underlying basic science related to IL-2 and its biologic actions, discuss the current state of IL-2-based immunotherapy, and focus on emerging concepts of modulating the activities of this cytokine, including the generation of novel partial cytokine agonists as new potential therapeutics.

Critical functions for STAT5 tetramers in the maturation and survival of natural killer cells

Interleukin-15 (IL-15) is essential for the development and maintenance of natural killer (NK) cells. IL-15 activates STAT5 proteins, which can form dimers or tetramers. We previously found that NK cell numbers are decreased in Stat5a-Stat5b tetramer-deficient double knockin (DKI) mice, but the mechanism was not investigated. Here we show that STAT5 dimers are sufficient for NK cell development, whereas STAT5 tetramers mediate NK cell maturation and the expression of maturation-associated genes. Unlike the defective proliferation of Stat5 DKI CD8⁺ T cells, Stat5 DKI NK cells have normal proliferation to IL-15 but are susceptible to death upon cytokine withdrawal, with lower Bcl2 and increased active caspases. These findings underscore the importance of STAT5 tetramers in maintaining NK cell homoeostasis. Moreover, defective STAT5 tetramer formation could represent a cause of NK cell immunodeficiency, and interrupting STAT5 tetramer formation might serve to control NK leukaemia.

The γ c family of cytokines: fine-tuning signals from IL-2 and IL-21 in the regulation of the immune response

Interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15, and IL-21 form a family of cytokines based on the sharing of a receptor component, the common cytokine receptor γ chain, γ _c, which is encoded by the gene mutated in humans with X-linked severe combined immunodeficiency (XSCID). Together, these cytokines play critical roles in lymphoid development, differentiation, growth, and survival as well as mediating effector function. Here, we provide an overview of the main actions of members of this cytokine family but then primarily focus on IL-2 and IL-21, discussing their dynamic interplay and contributions to a fine-tuned immune response. Moreover, we discuss the therapeutic utility of modulating their actions, particularly for autoimmunity and cancer.

Transient expression of ZBTB32 in anti-viral CD8+ T cells limits the magnitude of the effector response and the generation of memory

Virus infections induce CD8⁺ T cell responses comprised of a large population of terminal effector cells and a smaller subset of long-lived memory cells. The transcription factors regulating the relative expansion versus the long-term survival potential of anti-viral CD8⁺ T cells are not completely understood. We identified ZBTB32 as a transcription factor that is transiently expressed in effector CD8⁺ T cells. After acute virus infection, CD8⁺ T cells deficient in ZBTB32 showed enhanced virus-specific CD8⁺ T cell responses, and generated increased numbers of virus-specific memory cells; in contrast, persistent expression of ZBTB32 suppressed memory cell formation. The dysregulation of CD8⁺ T cell responses in the absence of ZBTB32 was catastrophic, as Zbtb32^-/- mice succumbed to a systemic viral infection and showed evidence of severe lung pathology. We found that ZBTB32 and Blimp-1 were co-expressed following CD8⁺ T cell activation, bound to each other, and cooperatively regulated Blimp-1 target genes Eomes and Cd27. These findings demonstrate that ZBTB32 is a key transcription factor in CD8⁺ effector T cells that is required for the balanced regulation of effector versus memory responses to infection.

CD8⁺ T lymphocytes are essential for immune protection against viruses. In response to an infection, these cells are activated, proliferate, and generate antiviral effector cells that eradicate the infection. Following this, the majority of these effector cells die, leaving a small subset of long-lived virus-specific memory T cells. Our study identifies a transcription factor, ZBTB32, that is required for the regulation of CD8⁺ T cell responses. In its absence, antiviral CD8⁺ T cell numbers increase to abnormally high levels, and generate an overabundance of memory T cells. When this dysregulated response occurs following infection with a virus that cannot be rapidly eliminated by the immune system, the infected animals die from immune-mediated tissue damage, indicating the importance of this pathway.

Microbiota-dependent IL-21 signaling regulates intestinal immune cell homeostasis and immunopathology to infection

Despite studies indicating a role for IL-21 in intestinal inflammation, how it precisely affects intestinal homeostasis and immunity to infection is not yet clear. In this study, we report a potent effect of commensal microbiota on the phenotypic manifestations of IL-21 receptor deficiency. IL-21 is expressed highly by CD4 T cells of Peyer’s patches (PPs) and small intestine lamina propria (LP) and strongly induced by co-housing with SFB-positive mice. Mice deficient in IL-21 receptor exhibit reduced numbers of GC B cells, B cell expression of AID, and IgA+ B cell populations in PPs, consistent with the known roles for IL-21 in B cell function. Consequently, IL-21R KO mice show a significant reduction in IgA+ plasmablasts and plasma cells in the small intestine LP. Interestingly, microbiota-dependent increases in RORgt+ T cells and Treg cells are observed in the small intestine of IL21-R KO mice. Neither the Th1 nor RORgt+ ILC populations are altered in the KO mice intestine compared to WT mice. Demonstrating a critical role of IL-21 signaling in immunopathology during Citrobacter rodentium infection, IL-21 receptor deficiency leads to strikingly reduced tissue pathology without affecting bacterial clearance. This reduced immunopathology likely results from dampened production of IFNg, IL-12, and IL-1b that promote severe immunopathology/lethality. Taken together, we demonstrate the regional and pleotropic effects of IL-21 signaling that fine-tunes intestinal mucosal immunity in a microbiota-dependent manner, which has significant implication for anti-IL-21 therapy to treat inflammatory bowel disease.