IL-2 induction of Blimp-1 is a key in vivo signal for CD8+ short-lived effector T cell differentiation

Stat5 opposes the transcription factor Tox and rewires exhausted CD8+ T cells toward durable effector-like states during chronic antigen exposure

Rewiring exhausted CD8+ T (Tex) cells toward functional states remains a therapeutic challenge. Tex cells are epigenetically programmed by the transcription factor Tox. However, epigenetic remodeling occurs as Tex cells transition from progenitor (Texprog) to intermediate (Texint) and terminal (Texterm) subsets, suggesting development flexibility. We examined epigenetic transitions between Tex cell subsets and revealed a reciprocally antagonistic circuit between Stat5a and Tox. Stat5 directed Texint cell formation and re-instigated partial effector biology during this Texprog-to-Texint cell transition. Constitutive Stat5a activity antagonized Tox and rewired CD8+ T cells from exhaustion to a durable effector and/or natural killer (NK)-like state with superior anti-tumor potential. Temporal induction of Stat5 activity in Tex cells using an orthogonal IL-2:IL2Rβ-pair fostered Texint cell accumulation, particularly upon PD-L1 blockade. Re-engaging Stat5 also partially reprogrammed the epigenetic landscape of exhaustion and restored polyfunctionality. These data highlight therapeutic opportunities of manipulating the IL-2-Stat5 axis to rewire Tex cells toward more durably protective states.

Engineering IL-2 for immunotherapy of autoimmunity and cancer

Preclinical studies of the T cell growth factor activity of IL-2 resulted in this cytokine becoming the first immunotherapy to be approved nearly 30 years ago by the US Food and Drug Administration for the treatment of cancer. Since then, we have learnt the important role of IL-2 in regulating tolerance through regulatory T cells (Treg cells) besides promoting immunity through its action on effector T cells and memory T cells. Another pivotal event in the history of IL-2 research was solving the crystal structure of IL-2 bound to its tripartite receptor, which spurred the development of cell type-selective engineered IL-2 products. These new IL-2 analogues target Treg cells to counteract the dysregulated immune system in the context of autoimmunity and inflammatory disorders or target effector T cells, memory T cells and natural killer cells to enhance their antitumour responses. IL-2 biologics have proven to be effective in preclinical studies and clinical assessment of some is now underway. These studies will soon reveal whether engineered IL-2 biologics are truly capable of harnessing the IL-2-IL-2 receptor pathway as effective monotherapies or combination therapies for autoimmunity and cancer.

Transcriptional Control of Cell Fate Determination in Antigen-Experienced CD8 T Cells

Robust immunity to intracellular infections is mediated by antigen-specific naive CD8 T cells that become activated and differentiate into phenotypically and functionally diverse subsets of effector cells, some of which terminally differentiate and others that give rise to memory cells that provide long-lived protection. This developmental system is an outstanding model with which to elucidate how regulation of chromatin structure and transcriptional control establish gene expression programs that govern cell fate determination, insights from which are likely to be useful for informing the design of immunotherapeutic approaches to engineer durable immunity to infections and tumors. A unifying framework that describes how naive CD8 T cells develop into memory cells is still outstanding. We propose a model that incorporates a common early linear path followed by divergent paths that slowly lose capacity to interconvert and discuss classical and contemporary observations that support these notions, focusing on insights from transcriptional control and chromatin regulation.

The Role of T Cell Receptor Signaling in the Development of Type 1 Diabetes

T cell receptor (TCR) signaling influences multiple aspects of CD4⁺ and CD8⁺ T cell immunobiology including thymic development, peripheral homeostasis, effector subset differentiation/function, and memory formation. Additional T cell signaling cues triggered by co-stimulatory molecules and cytokines also affect TCR signaling duration, as well as accessory pathways that further shape a T cell response. Type 1 diabetes (T1D) is a T cell-driven autoimmune disease targeting the insulin producing β cells in the pancreas. Evidence indicates that dysregulated TCR signaling events in T1D impact the efficacy of central and peripheral tolerance-inducing mechanisms. In this review, we will discuss how the strength and nature of TCR signaling events influence the development of self-reactive T cells and drive the progression of T1D through effects on T cell gene expression, lineage commitment, and maintenance of pathogenic anti-self T cell effector function.

Blockade of Kv1.3 potassium channel inhibits CD8+ T cell-mediated neuroinflammation via PD-1/Blimp-1 signaling

Kv1.3 potassium channel is considered as a target for the treatment of autoimmune diseases such as multiple sclerosis (MS), since Kv1.3 blockade suppresses memory T cell activation including cytotoxic CD8⁺ T cells. However, the underlying signaling pathway related to autoimmune CD8⁺ T cell inhibition by Kv1.3 channel in neuroinflammatory diseases remains unclear. We found that ImK, a selective Kv1.3 blocker, reduced auto-reactive CD8⁺ T cell infiltration in the spinal cords of experimental autoimmune encephalomyelitis (EAE) rats, an animal model of MS. ImK suppressed transcriptional factor Blimp-1 expression and reduced the cytotoxicity of CD8⁺ T cells on neuronal cells. Furthermore, ImK upregulated co-inhibitory molecule PD-1 to inhibit B lymphocyte-induced maturation protein (Blimp-1) in an IL-2 independent way. In addition, PD-1 inhibitor impaired the suppression of ImK on CD8⁺ T cells and accelerated EAE progression. Our study demonstrated a novel regulatory mechanism of Kv1.3 blockade on modulating CD8⁺ T cell differentiation through PD-1/Blimp-1 signaling. This work expands the understanding of Kv1.3 channel for modulating neuroinflammation.

Early programming of CD8+ T cell response by the orphan nuclear receptor NR4A3

Enhancing long-term persistence while simultaneously potentiating the effector response of CD8⁺ T cells has been a long-standing goal in immunology to produce better vaccines and adoptive cell therapy products. NR4A3 is a transcription factor of the orphan nuclear receptor family. While it is rapidly and transiently expressed following T cell activation, its role in the early stages of T cell response is unknown. We show that NR4A3-deficient murine CD8⁺ T cells differentiate preferentially into memory precursor and central memory cells, but also produce more cytokines. This is explained by an early influence of NR4A3 deficiency on the memory transcriptional program and on accessibility of chromatin regions with motifs for bZIP transcription factors, which impacts the transcription of Fos/Jun target genes. Our results reveal a unique and early role for NR4A3 in programming CD8⁺ T cell differentiation and function. Manipulating NR4A3 activity may represent a promising strategy to improve vaccination and T cell therapy.

GCNT1-Mediated O-Glycosylation of the Sialomucin CD43 Is a Sensitive Indicator of Notch Signaling in Activated T Cells

Notch signaling is emerging as a critical regulator of T cell activation and function. However, there is no reliable cell surface indicator of Notch signaling across activated T cell subsets. In this study, we show that Notch signals induce upregulated expression of the Gcnt1 glycosyltransferase gene in T cells mediating graft-versus-host disease after allogeneic bone marrow transplantation in mice. To determine if Gcnt1-mediated O-glycosylation could be used as a Notch signaling reporter, we quantified the core-2 O-glycoform of CD43 in multiple T cell subsets during graft-versus-host disease. Pharmacological blockade of Delta-like Notch ligands abrogated core-2 O-glycosylation in a dose-dependent manner after allogeneic bone marrow transplantation, both in donor-derived CD4⁺ and CD8⁺ effector T cells and in Foxp3⁺ regulatory T cells. CD43 core-2 O-glycosylation depended on cell-intrinsic canonical Notch signals and identified CD4⁺ and CD8⁺ T cells with high cytokine-producing ability. Gcnt1-deficient T cells still drove lethal alloreactivity, showing that core-2 O-glycosylation predicted, but did not cause, Notch-dependent T cell pathogenicity. Using core-2 O-glycosylation as a marker of Notch signaling, we identified Ccl19-Cre⁺ fibroblastic stromal cells as critical sources of Delta-like ligands in graft-versus-host responses irrespective of conditioning intensity. Core-2 O-glycosylation also reported Notch signaling in CD8⁺ T cell responses to dendritic cell immunization, Listeria infection, and viral infection. Thus, we uncovered a role for Notch in controlling core-2 O-glycosylation and identified a cell surface marker to quantify Notch signals in multiple immunological contexts. Our findings will help refine our understanding of the regulation, cellular source, and timing of Notch signals in T cell immunity.

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.

The Notch signaling pathway controls CD8+ T cell differentiation independently of the classical effector HES1

During CD8⁺ T cell response, Notch signaling controls short-lived-effector-cell (SLEC) generation, but the exact mechanisms by which it does so remains unclear. The Notch signaling pathway can act as a key regulator of Akt signaling via direct transcriptional induction of Hes1, which will then repress the transcription of Pten, an inhibitor of Akt signaling. As both Notch and Akt signaling can promote effector CD8⁺ T cell differentiation, we asked whether Notch signaling influences SLEC differentiation via the HES1-PTEN axis. Here, we demonstrate that HES1 deficiency in murine CD8⁺ T cells did not impact SLEC differentiation. Moreover, we show that Pten transcriptional repression in effector CD8⁺ T cells is not mediated by Notch signaling although Akt activation requires Notch signaling. Therefore, HES1 is not an effector of Notch signaling during CD8⁺ T cell response.

Regulation of Effector and Memory CD8 T Cell Differentiation by IL-2-A Balancing Act

Interleukin-2 (IL-2) regulates key aspects of CD8 T cell biology–signaling through distinct pathways IL-2 triggers critical metabolic and transcriptional changes that lead to a spectrum of physiological outcomes such as cell survival, proliferation, and effector differentiation. In addition to driving effector differentiation, IL-2 signals are also critical for formation of long-lived CD8 T cell memory. This review discusses a model of rheostatic control of CD8 T cell effector and memory differentiation by IL-2, wherein the timing, duration, dose, and source of IL-2 signals are considered in fine-tuning the balance of key transcriptional regulators of cell fate.

The PDL1-inducible GTPase Arl4d controls T effector function by limiting IL-2 production

Interleukin-2 (IL-2) is a key regulator of adaptive immune responses but its regulation is incompletely understood. We previously found that PDL1-dependent signals were pivotal for liver sinusoidal endothelial cell-mediated priming of CD8 T cells, which have a strongly reduced capacity to produce IL-2. Here, we show that the expression of the ARF-like GTPase Arl4d is PD-L1-dependently induced in such LSEC-primed T cells, and is associated with reduced IL-2 secretion and Akt phosphorylation. Conversely, Arl4d-deficient T cells overproduced IL-2 upon stimulation. Arl4d-deficiency in CD8 T cells also enhanced their expansion and effector function during viral infection in vivo. Consistent with their increased IL-2 production, Arl4d-deficient T cells showed enhanced development into KLRG1⁺CD127⁻ short-lived effector cells (SLEC), which is dependent on IL-2 availability. Thus, our data reveal a PD-L1-dependent regulatory circuitry that involves the induction of Arl4d for limiting IL-2 production in T cells.

Immunological Approaches Towards Cancer and Inflammation: A Cross Talk

The inflammation is the protective response of the body against various harmful stimuli; however, the aberrant and inappropriate activation tends to become harmful. The acute inflammatory response tends to resolved once the offending agent is subside but this acute response becomes chronic in nature when the body is unable to successfully neutralized the noxious stimuli. This chronic inflammatory microenvironment is associated with the release of various pro-inflammatory and oncogenic mediators such as nitric oxide (NO), cytokines [IL-1β, IL-2, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α)], growth factor, and chemokines. These mediators make the inflammatory microenvironment more vulnerable toward tumorigenesis. The pro-inflammatory mediators released during the chronic inflammation tends to induce several molecular signaling cascades such as nuclear factor kappa B, MAPKinase, nuclear factor erythroid 2-related factor 2, phosphoinositide-3-kinase, Janus kinases/STAT, Wnt/B-catenin, and cyclic AMP response element binding protein. The immune system and its components have a pleiotropic effect on inflammation and cancer progression. Immune components such as T cells, natural killer cells, macrophages, and neutrophils either inhibit or enhance tumor initiation depending on the type of tumor and immune cells involved. Tumor-associated macrophages and tumor-associated neutrophils are pro-tumorigenic cells highly prevalent in inflammation-mediated tumors. Similarly, presence of T regulatory (Treg) cells in an inflammatory and tumor setting suppresses the immune system, thus paving the way for oncogenesis. However, Treg cells also inhibit autoimmune inflammation. By contrast, cytotoxic T cells and T helper cells confer antitumor immunity and are associated with better prognosis in patients with cancer. Cytotoxic T cells inflict a direct cytotoxic effect on cells expressing oncogenic markers. Currently, several anti-inflammatory and antitumor therapies are under trials in which these immune cells are exploited. Adoptive cell transfer composed of tumor-infiltrating lymphocytes has been tried for the treatment of tumors after their ex vivo expansion. Mediators released by cells in a tumorigenic and inflammatory microenvironment cross talk with nearby cells, either promoting or inhibiting inflammation and cancer. Recently, several cytokine-based therapies are either being developed or are under trial to treat such types of manifestations. Monoclonal antibodies directed against TNF-α, VEGF, and IL-6 has shown promising results to ameliorate inflammation and cancer, while direct administration of IL-2 has been shown to cause tumor regression.

miR-29a-3p/T-bet Regulatory Circuit Is Altered in T Cells of Patients With Hashimoto's Thyroiditis

OBJECTIVE

Hashimoto's thyroiditis (HT) is a common autoimmune thyroid disorder that frequently evolves from asymptomatic, T-cell mediated chronic inflammation toward overt hypothyroidism. Previously, we have demonstrated a role for T-bet, a T helper 1/CD8⁺ T cell transcription factor (TF), and FoxP3, a regulatory T cell TF, in disease progression and severity, but the basis behind their altered mRNA expression remains unknown. In this study, we aimed to leverage the role for microRNAs, representing negative transcriptional regulators, across the spectrum of HT clinical presentations using the same, well-characterized RNA sample cohort.

METHOD

Ten hypothyroid, untreated patients (hypoHT), 10 hypothyroid cases rendered euthyroid by l-thyroxine therapy (substHT), 11 spontaneously euthyroid HT subjects (euHT), and 10 healthy controls (ctrl) were probed for three candidate immunoregulatory miRNA (miR-9-5p, miR-29a-3p, and miR-210-3p) using quantitative real-time PCR measurements. Data were normalized to U6snRNA and fold difference in expression calculated by the efficiency corrected 2^-ΔΔCt model.

RESULTS

Compared to healthy controls, peripheral blood (PB) T cells of HT patients exhibited significantly diminished miR-29a-3p expression levels [median expression levels (IQR), HT vs CTRL, 0.62 (0.44-1.01) vs 1.373 (0.63-2.7), P = 0.046], and a similar, but not significant decline in miR-210-3p abundance [HT vs CTRL, 0.64 (0.39-1.31) vs 1.2 (0.5-2.56), P = 0.24, Wilcoxon test]. A significant inverse correlation was observed between the two differentially expressed transcripts, T-bet mRNA and miR-29a-3p. Moreover, altered miR-29a-3p/T-bet expression in T cells of untreated HT patients was related to low serum FT4, high serum thyrotropin, and decreased thyroid volumes. Of note, miR-210-3p expression was positively correlated to HIF1α, and inversely to FoxP3 mRNA levels, but no evidence of differential expression for any of these miRNA-mRNA pairs was observed. Finally, miR-9-5p expression levels were no different in HT vs control comparisons, or related to clinicopathological features.

CONCLUSION

T cell miR-29a-3p is downregulated in HT patients and associated with clinical and biochemical parameters of progressive thyroid injury, plausibly subsequent to altered control of T-bet expression in PB T cells. As such miR-29a-3p/T-bet axis should be further explored as a biomarker or as a plausible target for therapeutic interventions in HT.

New insights into Blimp-1 in T lymphocytes: a divergent regulator of cell destiny and effector function

B lymphocyte-induced maturation protein-1 (Blimp-1) serves as a master regulator of the development and function of antibody-producing B cells. Given that its function in T lymphocytes has been identified within the past decade, we review recent findings with emphasis on its role in coordinated control of gene expression during the development, differentiation, and function of T cells. Expression of Blimp-1 is mainly confined to activated T cells and is essential for the production of interleukin (IL)-10 by a subset of forkhead box (Fox)p3⁺ regulatory T cells with an effector phenotype. Blimp-1 is also required to induce cell elimination in the thymus and critically modulates peripheral T cell activation and proliferation. In addition, Blimp-1 promotes T helper (Th) 2 lineage commitment and limits Th1, Th17 and follicular helper T cell differentiation. Furthermore, Blimp-1 coordinates with other transcription factors to regulate expression of IL-2, IL-21 and IL-10 in effector T lymphocytes. In CD8⁺ T cells, Blimp-1 expression is distinct in heterogeneous populations at the stages of clonal expansion, differentiation, contraction and memory formation when they encounter antigens. Moreover, Blimp-1 plays a fundamental role in coordinating cytokine receptor signaling networks and transcriptional programs to regulate diverse aspects of the formation and function of effector and memory CD8⁺ T cells and their exhaustion. Blimp-1 also functions as a gatekeeper of T cell activation and suppression to prevent or dampen autoimmune disease, antiviral responses and antitumor immunity. In this review, we discuss the emerging roles of Blimp-1 in the complex regulation of gene networks that regulate the destiny and effector function of T cells and provide a Blimp-1-dominated transcriptional framework for T lymphocyte homeostasis.

Evaluation of Attenuated Tumor Antigens and the Implications for Peptide-Based Cancer Vaccine Development

INTRODUCTION: Peptide vaccines offer anti-tumor efficacy with very low toxicity. However, repeat stimulation with an immunogenic peptide leads to activation induced cell death (AICD), decreasing efficacy. We engineered variants of an immunogenic peptide (E39) and tested their ability to induce a robust, sustainable immune response.

METHODS: Multiple variants of E39 were created by exchanging 1 or 2 amino acids. We tested the PBMC proliferation, cytokine production and cytolytic activity induced by each variant peptide. RESULTS: Repeated stimulation with E39 likely led to in vitro AICD, while stimulation with E39' led to T-cell proliferation with less evidence of AICD, modest cytokine production and high CTL activity. CONCLUSIONS: E39' appears to be the optimal variant of E39 for inducing effective long-term immunity.

VEGF Requires the Receptor NRP-1 To Inhibit Lipopolysaccharide-Dependent Dendritic Cell Maturation

To stimulate a productive T cell response, dendritic cells (DC) must undergo maturation characterized by heightened cell surface expression of MHC and costimulatory molecules as well as cytokine production. Conversely, the inhibition of DC maturation is a central mechanism of immune tolerance. The control of the DC maturation process relies on the integration of several cellular stimulatory or inhibitory signals. The soluble factors and their receptors controlling this central aspect of DC biology are incompletely characterized. We show that murine bone marrow-derived DC (BMDC) maturation induced by LPS, as opposed to polyinosinic:polycytidylic acid or cytosine-phosphate-guanine, is robustly inhibited by vascular endothelial growth factor (VEGF), a previously identified immunosuppressive cytokine. Using BMDC from wild type and conditional knockout mice, we show that neuropilin-1 (NRP-1), a known receptor of VEGF, is necessary to suppress LPS-dependent BMDC maturation. The absence of NRP-1 had no ostensible effects on the biology of BMDC in the absence of VEGF. However, NRP-1-deficient BMDC remained completely insensitive to the VEGF-dependent inhibition of BMDC maturation in culture. In the presence of VEGF, NRP-1 directly interacted with the LPS receptor TLR4 and suppressed downstream signaling through ERK and NF-κβ, resulting in a sharp inhibition of MHC class II and costimulatory molecules (CD40, CD86) expression as well as proinflammatory cytokine production. Consequently, we identify NRP-1 as a target to optimize DC maturation within environments that are rich in VEGF, such as tumors.

De novo DNA methylation by DNA methyltransferase 3a controls early effector CD8+ T-cell fate decisions following activation

DNMT3a is a de novo DNA methyltransferase expressed robustly after T-cell activation that regulates plasticity of CD4(+) T-cell cytokine expression. Here we show that DNMT3a is critical for directing early CD8(+) T-cell effector and memory fate decisions. Whereas effector function of DNMT3a knockout T cells is normal, they develop more memory precursor and fewer terminal effector cells in a T-cell intrinsic manner compared with wild-type animals. Rather than increasing plasticity of differentiated effector CD8(+) T cells, loss of DNMT3a biases differentiation of early effector cells into memory precursor cells. This is attributed in part to ineffective repression of Tcf1 expression in knockout T cells, as DNMT3a localizes to the Tcf7 promoter and catalyzes its de novo methylation in early effector WT CD8(+) T cells. These data identify DNMT3a as a crucial regulator of CD8(+) early effector cell differentiation and effector versus memory fate decisions.

A molecular threshold for effector CD8(+) T cell differentiation controlled by transcription factors Blimp-1 and T-bet

T cell responses are guided by cytokines that induce transcriptional regulators, which ultimately control differentiation of effector and memory T cells. However, it is unknown how the activities of these molecular regulators are coordinated and integrated during the differentiation process. Using genetic approaches and transcriptional profiling of antigen-specific CD8(+) T cells, we reveal a common program of effector differentiation that is regulated by IL-2 and IL-12 signaling and the combined activities of the transcriptional regulators Blimp-1 and T-bet. The loss of both T-bet and Blimp-1 leads to abrogated cytotoxic function and ectopic IL-17 production in CD8(+) T cells. Overall, our data reveal two major overlapping pathways of effector differentiation governed by the availability of Blimp-1 and T-bet and suggest a model for cytokine-induced transcriptional changes that combine, quantitatively and qualitatively, to promote robust effector CD8(+) T cell differentiation.

IL-21 Is Important for Induction of KLRG1+ Effector CD8 T Cells during Acute Intracellular Infection

Microsporidia, a latent opportunistic infection associated with mild inflammation, is characterized by a strong CD8 T cell response, which has been shown to be CD4 T cell dependent. In this manuscript, we demonstrate that CD4 help is provided via IL-21 production, a common γ-chain cytokine closely related to IL-2. The peak of IL-21 expression, observed during the acute infection, is associated with an elevated IL-21(+) CD4 T subset, and these cells bear a phenotypic resemblance to T follicular helper cells. We observed that, during per-oral microsporidial infection, IL-21 was critical for the generation of an optimal effector CD8 T cell immunity. Sharply decreased effector KLRG1(+) CD8 response was observed in IL-21R knockout mice, and although these cells exhibited reduced functional properties, they retained the ability to proliferate. The role of IL-21 in the generation of CD8 effectors was cell intrinsic, as stronger defects were observed in the IL-21-deficient compartment from the bone marrow chimeric mice (IL-21R knockout/wild-type). These findings are different from those reported for viral infections in which IL-21 has been primarily associated with the generation and maintenance of CD8 memory response. To the best of our knowledge, this report demonstrates a critical role for IL-21 in the generation of a primary effector CD8 T cell response to an infectious disease model.

The Notch signaling pathway controls short-lived effector CD8+ T cell differentiation but is dispensable for memory generation

Following an infection, naive CD8(+) T cells expand and differentiate into two main populations of effectors: short-lived effector cells (SLECs) and memory precursor effector cells (MPECs). There is limited understanding of the molecular mechanism and cellular processes governing this cell fate. Notch is a key regulator of cell fate decision relevant in many immunological pathways. In this study, we add to the role of Notch in cell fate decision and demonstrate that the Notch signaling pathway controls the MPEC/SLEC differentiation choice following both Listeria infection and dendritic cell immunization of mice. Although fewer SLECs were generated, Notch deficiency did not alter the rate of memory CD8(+) T cell generation. Moreover, we reveal that the Notch signaling pathway plays a context-dependent role for optimal cytokine production by effector CD8(+) T cells. Together, our results unravel critical functions for the Notch signaling pathway during effector CD8(+) T cell differentiation.

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.

CD4(+) T-cell dependence of primary CD8(+) T-cell response against vaccinia virus depends upon route of infection and viral dose

CD4(+) T-cell help (CD4 help) plays a pivotal role in CD8(+) T-cell responses against viral infections. However, the role in primary CD8(+) T-cell responses remains controversial. We evaluated the effects of infection route and viral dose on primary CD8(+) T-cell responses to vaccinia virus (VACV) in MHC class II(-/-) mice. CD4 help deficiency diminished the generation of VACV-specific CD8(+) T cells after intraperitoneal (i.p.) but not after intranasal (i.n.) infection. A large viral dose could not restore normal expansion of VACV-specific CD8(+) T cells in i.p. infected MHC II(-/-) mice. In contrast, dependence on CD4 help was observed in i.n. infected MHC II(-/-) mice when a small viral dose was used. These data suggested that primary CD8(+) T-cell responses are less dependent on CD4 help in i.n. infection compared to i.p. infection. Activated CD8(+) T cells produced more IFN-γ, TNF-α and granzyme B in i.n. infected mice than those in i.p. infected mice, regardless of CD4 help. IL-2 signaling via CD25 was not necessary to drive expansion of VACV-specific CD8(+) T cells in i.n. infection, but it was crucial in i.p. infection. VACV-specific CD8(+) T cells underwent increased apoptosis in the absence of CD4 help, but proliferated normally and had cytotoxic potential, regardless of infection route. Our results indicate that route of infection and viral dose are two determinants for CD4 help dependence, and intranasal infection induces more potent effector CD8(+) T cells than i.p. infection.