Sustained in vivo signaling by long-lived IL-2 induces prolonged increases of regulatory T cells

Interleukin-12 decorated nanosized semiflexible Immunofilaments enable directed targeting and augmented IFNγ responses of natural killer cells

Immunotherapies are a powerful strategy to treat cancer by modulating the immune system to raise an anti-tumor immune response. A prime example of immunotherapies are cytokines - small immunomodulatory molecules that are widely used to stimulate immune cells. Undirected administration of cytokines, however, can cause severe side effects, preventing the use of potent cytokines, such as Interleukin (IL)-12, which induces IFNγ responses by cytotoxic effector lymphocytes, including NK cells. Biomaterials, like nanoparticles, can encapsulate IL-12 and accumulate at the tumor site to alleviate side effects. Yet, the released IL-12 might not be directly targeted to extracellular IL-12 receptors on the specific effector cells, thereby potentially compromising the cytokine's therapeutic efficacy. Here, we develop a polymer-based platform to target NK cells, which we call immunofilaments. Immunofilaments are nanosized linear polymers that present an anti-CD16 antibody and IL-12 effectively to NK cells and lead to synergistic NK cell activation as highlighted by an increase in TNFα and IFNγ production and upregulation of multiple activation markers, including CD25, CD69, and degranulation marker CD107a. NK cell proliferation is enhanced in the presence of both anti-CD16 antibody and IL-12 compared to giving IL-12 separately. Finally, we demonstrate that the IF platform is suitable for in vivo applications, as immunofilaments readily activate human NK cells upon administration to mice. STATEMENT OF SIGNIFICANCE: IL-12 is a potent cytokine that stimulates IFNγ responses in NK cells, which supports an anti-tumor immune response. Due to its high potency, the delivery of IL-12 needs to be highly controlled to prevent severe adverse side effects, which can be achieved by using biomaterials. This study shows that nanosized polymers termed Immunofilaments can be used to immobilize IL-12 and effectively target and activate NK cells by co-conjugation of anti-CD16 antibodies. This work is a prime example of careful engineering of innovative biomaterials to improve immunotherapy.

Low-dose Interleukin-2 Therapy: Fine-tuning Treg in Solid Organ Transplantation?

Regulatory T cells (Treg), a subset of CD4 + T cells, are potent regulators of immune reactions, which have been shown to be a promising therapeutic alternative to toxic immunosuppressive drugs. Data support the utility of Treg in managing immunopathologies, including solid organ transplant rejection, graft-versus-host disease, and autoimmune disorders. Notably, reports suggest that interleukin-2 (IL-2) is critical to survival of Treg, which constitutively express high levels of CD25, that is, the IL-2 receptor α-chain, and are exquisitely sensitive to IL-2, even at very low concentrations in contrast to effector T cells, which only upregulate IL-2 receptor α-chain on activation. This has led to the notion of using low doses of exogenous IL-2 therapeutically to modulate the immune system, specifically Treg numbers and function. Here, we summarize developments of clinical experience with low-dose IL-2 (LD-IL-2) as a therapeutic agent. So far, no clinical data are available to support the therapeutic use of LD-IL-2 therapy in the solid organ transplant setting. For the latter, fine-tuning by biotechnological approaches may be needed because of the narrow therapeutic window and off-target effects of LD-IL-2 therapy and so to realize the therapeutic potential of this molecule.

Interleukin-2 is required for NKp30-dependent NK cell cytotoxicity by preferentially regulating NKp30 expression

Natural killer (NK) cells are key effectors in cancer immunosurveillance, eliminating a broad spectrum of cancer cells without major histocompatibility complex (MHC) specificity and graft-versus-host diseases (GvHD) risk. The use of allogeneic NK cell therapies from healthy donors has demonstrated favorable clinical efficacies in treating diverse cancers, particularly hematologic malignancies, but it requires cytokines such as IL-2 to primarily support NK cell persistence and expansion. However, the role of IL-2 in the regulation of activating receptors and the function of NK cells expanded for clinical trials is poorly understood and needs clarification for the full engagement of NK cells in cancer immunotherapy. Here, we demonstrated that IL-2 deprivation significantly impaired the cytotoxicity of primary expanded NK cells by preferentially downregulating NKp30 but not NKp46 despite their common adaptor requirement for expression and function. Using NK92 and IL-2-producing NK92MI cells, we observed that NKp30-mediated cytotoxicity against myeloid leukemia cells such as K562 and THP-1 cells expressing B7-H6, a ligand for NKp30, was severely impaired by IL-2 deprivation. Furthermore, IL-2 deficiency-mediated NK cell dysfunction was overcome by the ectopic overexpression of an immunostimulatory NKp30 isoform such as NKp30a or NKp30b. In particular, NKp30a overexpression in NK92 cells improved the clearance of THP-1 cells in vivo without IL-2 supplementation. Collectively, our results highlight the distinct role of IL-2 in the regulation of NKp30 compared to that of NKp46 and suggest NKp30 upregulation, as shown here by ectopic overexpression, as a viable modality to harness NK cells in cancer immunotherapy, possibly in combination with IL-2 immunocytokines.

Rapamycin nanoparticles increase the therapeutic window of engineered interleukin-2 and drive expansion of antigen-specific regulatory T cells for protection against autoimmune disease

Interleukin-2 (IL-2) therapies targeting the high affinity IL-2 receptor expressed on regulatory T cells (Tregs) have shown promising therapeutic benefit in autoimmune diseases through nonselective expansion of pre-existing Treg populations, but are potentially limited by the inability to induce antigen-specific Tregs, as well as by dose-limiting activation of effector immune cells in settings of inflammation. We recently developed biodegradable nanoparticles encapsulating rapamycin, called ImmTOR, which induce selective immune tolerance to co-administered antigens but do not increase total Treg numbers. Here we demonstrate that the combination of ImmTOR and an engineered Treg-selective IL-2 variant (termed IL-2 mutein) increases the number and durability of total Tregs, as well as inducing a profound synergistic increase in antigen-specific Tregs when combined with a target antigen. We demonstrate that the combination of ImmTOR and an IL-2 mutein leads to durable inhibition of antibody responses to co-administered AAV gene therapy capsid, even at sub-optimal doses of ImmTOR, and provides protection in autoimmune models of type 1 diabetes and primary biliary cholangitis. Importantly, ImmTOR also increases the therapeutic window of engineered IL-2 molecules by mitigating effector immune cell expansion and preventing exacerbation of disease in a model of graft-versus-host-disease. At the same time, IL-2 mutein shows potential for dose-sparing of ImmTOR. Overall, these results establish that the combination of ImmTOR and an IL-2 mutein show synergistic benefit on both safety and efficacy to provide durable antigen-specific immune tolerance to mitigate drug immunogenicity and to treat autoimmune diseases.

Multivalent, asymmetric IL-2-Fc fusions show enhanced selectivity for regulatory T cells

The cytokine interleukin-2 (IL-2) has the potential to treat autoimmune disease but is limited by its modest specificity toward immunosuppressive regulatory T (Treg) cells. IL-2 receptors consist of combinations of α, β, and γ chains of variable affinity and cell specificity. Engineering IL-2 to treat autoimmunity has primarily focused on retaining binding to the relatively Treg-selective, high-affinity receptor while reducing binding to the less selective, low-affinity receptor. However, we found that refining the designs to focus on targeting the high-affinity receptor through avidity effects is key to optimizing Treg selectivity. We profiled the dynamics and dose dependency of signaling responses in primary human immune cells induced by engineered fusions composed of either wild-type IL-2 or mutant forms with altered affinity, valency, and fusion to the antibody Fc region for stability. Treg selectivity and signaling response variations were explained by a model of multivalent binding and dimer-enhanced avidity-a combined measure of the strength, number, and conformation of interaction sites-from which we designed tetravalent IL-2-Fc fusions that had greater Treg selectivity in culture than do current designs. Biasing avidity toward IL2Rα with an asymmetrical multivalent design consisting of one α/β chain-binding and one α chain-binding mutant further enhanced Treg selectivity. Comparative analysis revealed that IL2Rα was the optimal cell surface target for Treg selectivity, indicating that avidity for IL2Rα may be the optimal route to producing IL-2 variants that selectively target Tregs.

Unlocking the potential of Tregs: innovations in CAR technology

Regulatory T cells (Tregs) adoptive immunotherapy is emerging as a viable treatment option for both autoimmune and alloimmune diseases. However, numerous challenges remain, including limitations related to cell number, availability of target-specific cells, stability, purity, homing ability, and safety concerns. To address these challenges, cell engineering strategies have emerged as promising solutions. Indeed, it has become feasible to increase Treg numbers or enhance their stability through Foxp3 overexpression, post-translational modifications, or demethylation of the Treg-specific demethylated region (TSDR). Specificity can be engineered by the addition of chimeric antigen receptors (CARs), with new techniques designed to fine-tune specificity (tandem chimeric antigen receptors, universal chimeric antigen receptors, synNotch chimeric antigen receptors). The introduction of B-cell targeting antibody receptor (BAR) Tregs has paved the way for effective regulation of B cells and plasma cells. In addition, other constructs have emerged to enhance Tregs activation and function, such as optimized chimeric antigen receptors constructs and the use of armour proteins. Chimeric antigen receptor expression can also be better regulated to limit tonic signaling. Furthermore, various opportunities exist for enhancing the homing capabilities of CAR-Tregs to improve therapy outcomes. Many of these genetic modifications have already been explored for conventional CAR-T therapy but need to be further considered for CAR-Tregs therapies. This review highlights innovative CAR-engineering strategies that have the potential to precisely and efficiently manage immune responses in autoimmune diseases and improve transplant outcomes. As these strategies are further explored and optimized, CAR-Treg therapies may emerge as powerful tools for immune intervention.

Overcoming lung cancer immunotherapy resistance by combining nontoxic variants of IL-12 and IL-2

Engineered cytokine-based approaches for immunotherapy of cancer are poised to enter the clinic, with IL-12 being at the forefront. However, little is known about potential mechanisms of resistance to cytokine therapies. We found that orthotopic murine lung tumors were resistant to systemically delivered IL-12 fused to murine serum albumin (MSA, IL12-MSA) because of low IL-12 receptor (IL-12R) expression on tumor-reactive CD8+ T cells. IL2-MSA increased binding of IL12-MSA by tumor-reactive CD8+ T cells, and combined administration of IL12-MSA and IL2-MSA led to enhanced tumor-reactive CD8+ T cell effector differentiation, decreased numbers of tumor-infiltrating CD4+ regulatory T cells, and increased survival of lung tumor-bearing mice. Predictably, the combination of IL-2 and IL-12 at therapeutic doses led to significant dose-limiting toxicity. Administering IL-12 and IL-2 analogs with preferential binding to cells expressing Il12rb1 and CD25, respectively, led to a significant extension of survival in mice with lung tumors while abrogating dose-limiting toxicity. These findings suggest that IL-12 and IL-2 represent a rational approach to combination cytokine therapy whose dose-limiting toxicity can be overcome with engineered cytokine variants.

Reigniting hope in cancer treatment: the promise and pitfalls of IL-2 and IL-2R targeting strategies

Interleukin-2 (IL-2) and its receptor (IL-2R) are essential in orchestrating immune responses. Their function and expression in the tumor microenvironment make them attractive targets for immunotherapy, leading to the development of IL-2/IL-2R-targeted therapeutic strategies. However, the dynamic interplay between IL-2/IL-2R and various immune cells and their dual roles in promoting immune activation and tolerance presents a complex landscape for clinical exploitation. This review discusses the pivotal roles of IL-2 and IL-2R in tumorigenesis, shedding light on their potential as diagnostic and prognostic markers and their therapeutic manipulation in cancer. It underlines the necessity to balance the anti-tumor activity with regulatory T-cell expansion and evaluates strategies such as dose optimization and selective targeting for enhanced therapeutic effectiveness. The article explores recent advancements in the field, including developing genetically engineered IL-2 variants, combining IL-2/IL-2R-targeted therapies with other cancer treatments, and the potential benefits of a multidimensional approach integrating molecular profiling, immunological analyses, and clinical data. The review concludes that a deeper understanding of IL-2/IL-2R interactions within the tumor microenvironment is crucial for realizing the full potential of IL-2-based therapies, heralding the promise of improved outcomes for cancer patients.

CD25: A potential tumor therapeutic target

CD25 is the alpha-chain of the heterotrimer IL-2 receptor. CD25 is expressed on the surface of both immune and non-immune cells with different frequencies. For cancers, CD25 is expressed at high levels in many types of hematological malignancies, but at low levels in most solid tumors. CD25 is also highly expressed in activated circulating immune cells and regulatory T cells (Tregs). Infiltration of Tregs in the tumor microenvironment can lead to an imbalanced ratio of effector T cells (Teffs) and Tregs, which is associated with the progression of cancers. A rescued Teff/Treg cell ratio indicates an efficient anti-tumor response to immunotherapy. CD25 as a potential target for the depletion of Tregs is critical in developing new immunotherapeutic strategies. Few articles have summarized the relationships between CD25 and tumors, or the recent progress of drugs targeting CD25. In this paper, we will discuss the structures of IL-2 and IL-2R, the biological function of CD25 and its important role in tumor therapy. In addition, the latest research on drugs targeting CD25 has been summarized, providing guidance for future drug development.

Low-dose IL-2 reduces IL-21+ T cell frequency and induces anti-inflammatory gene expression in type 1 diabetes

Despite early clinical successes, the mechanisms of action of low-dose interleukin-2 (LD-IL-2) immunotherapy remain only partly understood. Here we examine the effects of interval administration of low-dose recombinant IL-2 (iLD-IL-2) in type 1 diabetes using high-resolution single-cell multiomics and flow cytometry on longitudinally-collected peripheral blood samples. Our results confirm that iLD-IL-2 selectively expands thymic-derived FOXP3+HELIOS+ regulatory T cells and CD56bright NK cells, and show that the treatment reduces the frequency of IL-21-producing CD4+ T cells and of two innate-like mucosal-associated invariant T and Vγ9Vδ2 CD8+ T cell subsets. The cellular changes induced by iLD-IL-2 associate with an anti-inflammatory gene expression signature, which remains detectable in all T and NK cell subsets analysed one month after treatment. These findings warrant investigations into the potential longer-term clinical benefits of iLD-IL-2 in immunotherapy.

Costimulation blockade in combination with IL-2 permits regulatory T cell sparing immunomodulation that inhibits autoimmunity

Blockade of CD28 costimulation with CTLA-4-Ig/Abatacept is used to dampen effector T cell responses in autoimmune and transplantation settings. However, a significant drawback of this approach is impaired regulatory T cell homeostasis that requires CD28 signaling. Therefore, strategies that restrict the effects of costimulation blockade to effector T cells would be advantageous. Here we probe the relative roles of CD28 and IL-2 in maintaining Treg. We find provision of IL-2 counteracts the regulatory T cell loss induced by costimulation blockade while minimally affecting the conventional T cell compartment. These data suggest that combining costimulation blockade with IL-2 treatment may selectively impair effector T cell responses while maintaining regulatory T cells. Using a mouse model of autoimmune diabetes, we show combined therapy supports regulatory T cell homeostasis and protects from disease. These findings are recapitulated in humanised mice using clinically relevant reagents and provide an exemplar for rational use of a second immunotherapy to offset known limitations of the first.

Biological impact of iberdomide in patients with active systemic lupus erythematosus

OBJECTIVES

Iberdomide is a high-affinity cereblon ligand that promotes proteasomal degradation of transcription factors Ikaros (IKZF1) and Aiolos (IKZF3). Pharmacodynamics and pharmacokinetics of oral iberdomide were evaluated in a phase 2b study of patients with active systemic lupus erythematosus (SLE).

METHODS

Adults with autoantibody-positive SLE were randomised to placebo (n=83) or once daily iberdomide 0.15 mg (n=42), 0.3 mg (n=82) or 0.45 mg (n=81). Pharmacodynamic changes in whole blood leucocytes were measured by flow cytometry, regulatory T cells (Tregs) by epigenetic assay, plasma cytokines by ultrasensitive cytokine assay and gene expression by Modular Immune Profiling.

RESULTS

Iberdomide exhibited linear pharmacokinetics and dose-dependently modulated leucocytes and cytokines. Compared with placebo at week 24, iberdomide 0.45 mg significantly (p<0.001) reduced B cells, including those expressing CD268 (TNFRSF13C) (-58.3%), and plasmacytoid dendritic cells (-73.9%), and increased Tregs (+104.9%) and interleukin 2 (IL-2) (+144.1%). Clinical efficacy was previously reported in patients with high IKZF3 expression and high type I interferon (IFN) signature at baseline and confirmed here in those with an especially high IFN signature. Iberdomide decreased the type I IFN gene signature only in patients with high expression at baseline (-81.5%; p<0.001) but decreased other gene signatures in all patients.

CONCLUSION

Iberdomide significantly reduced activity of type I IFN and B cell pathways, and increased IL-2 and Tregs, suggesting a selective rebalancing of immune abnormalities in SLE. Clinical efficacy corresponded to reduction of the type I IFN gene signature.

TRIAL REGISTRATION NUMBER

NCT03161483.

Selective activation and expansion of regulatory T cells using lipid encapsulated mRNA encoding a long-acting IL-2 mutein

Interleukin-2 (IL-2) is critical for regulatory T cell (Treg) function and homeostasis. At low doses, IL-2 can suppress immune pathologies by expanding Tregs that constitutively express the high affinity IL-2Rα subunit. However, even low dose IL-2, signaling through the IL2-Rβ/γ complex, may lead to the activation of proinflammatory, non-Treg T cells, so improving specificity toward Tregs may be desirable. Here we use messenger RNAs (mRNA) to encode a half-life-extended human IL-2 mutein (HSA-IL2m) with mutations promoting reliance on IL-2Rα. Our data show that IL-2 mutein subcutaneous delivery as lipid-encapsulated mRNA nanoparticles selectively activates and expands Tregs in mice and non-human primates, and also reduces disease severity in mouse models of acute graft versus host disease and experimental autoimmune encephalomyelitis. Single cell RNA-sequencing of mouse splenic CD4+ T cells identifies multiple Treg states with distinct response dynamics following IL-2 mutein treatment. Our results thus demonstrate the potential of mRNA-encoded HSA-IL2m immunotherapy to treat autoimmune diseases.

Nanoparticle delivery of recombinant IL-2 (BALLkine-2) achieves durable tumor control with less systemic adverse effects in cancer immunotherapy

Recent strategies in cancer immunotherapy based on interleukin-2 (IL-2) are generally focused on reducing regulatory T cell (Treg) development by modifying IL-2 receptor alpha (IL-2Rα) domain. However, the clinical utility of high-dose IL-2 treatment is mainly limited by severe systemic toxicity. We find that peritumorally injectable 'BALLkine-2', recombinant human IL-2 (rIL-2) loaded porous nanoparticle, dramatically reduces systemic side effects of rIL-2 by minimizing systemic IL-2 exposure. Notably, in cynomolgus monkeys, subcutaneous (SC)-injection of BALLkine-2 not only dramatically reduces systemic circulation of rIL-2 in the blood, but also increases half-life of IL-2 compared to IV- or SC-injection of free rIL-2. Peritumorally-injected BALLkine-2 enhances intratumoral lymphocyte infiltration without inducing Treg development and more effectively synergizes with PD-1 blockade than high-dose rIL-2 administration in B16F10 melanoma model. BALLkine-2 could be a highly potent therapeutic option due to higher anti-tumor efficacy with lower and fewer doses and reduced systemic toxicity compared to systemic rIL-2.

Pharmacokinetics and Pharmacodynamic Effects of Nemvaleukin Alfa, a Selective Agonist of the Intermediate-Affinity IL-2 Receptor, in Cynomolgus Monkeys

Nemvaleukin alfa (nemvaleukin, ALKS 4230) is a novel cytokine created by the fusion of circularly permuted interleukin-2 (IL-2) to the IL-2Rα subunit of the IL-2 receptor (IL-2R) complex that confers selectivity for the intermediate-affinity IL-2R expressed on CD8+ T cells and natural killer (NK) cells. The pharmacokinetics and selective pharmacodynamic properties of nemvaleukin have been demonstrated using in vitro and in vivo mouse models. The pharmacokinetic/pharmacodynamic effects of nemvaleukin on immune cell subtypes were evaluated in cynomolgus monkeys after intravenous and subcutaneous administration to inform dose selection and predict pharmacodynamic effects in humans. Male drug-naïve cynomolgus monkeys (N = 15) were administered either single-dose (0.3 mg/kg i.v.; 0.3 mg/kg or 1.0 mg/kg s.c.) or repeated doses (0.1 mg/kg i.v. on days 1-5 or 0.5 mg/kg s.c. on days 1 and 4) of nemvaleukin. Serial blood samples were collected for pharmacokinetic assessment, immunophenotyping by flow cytometry, and profiling of serum cytokines. Repeat-dose subcutaneous administration of nemvaleukin with less frequent dosing resulted in total systemic exposure and trough serum concentrations comparable to those seen with intravenous administration, with lower peak serum concentrations. Transient elevation of interferon-γ and IL-6 peaked at 2 and 8 hours after intravenous and subcutaneous administration, respectively. Selective expansion of immunoprotective central memory, effector memory, terminal effector CD8+ T cells, and CD56+ NK cells, and minimal expansion of immunosuppressive CD4+CD25+FoxP3+ regulatory T cells was observed after both intravenous and subcutaneous administration. These data support the ongoing clinical evaluation of intravenous and subcutaneous nemvaleukin. SIGNIFICANCE STATEMENT: Administration of the novel interleukin-2 receptor agonist nemvaleukin alfa to cynomolgus monkeys resulted in selective expansion of immune effector cells, including CD8+ T and natural killer cells with minimal effects on immunosuppressive CD4+ regulatory T cells, confirming the design of nemvaleukin and highlighting its potential as a cancer immunotherapy. Subcutaneous administration of nemvaleukin achieved systemic exposure and immunostimulatory effects similar to those observed after more frequent intravenous dosing and may represent a practical alternative in a clinical setting.

A reasoned approach to the treatment of autoimmune hepatitis

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease affecting all ages, characterised by elevated transaminase and immunoglobulin G levels, positive autoantibodies, interface hepatitis on histology and good response to immunosuppressive treatment. If untreated, it has a poor prognosis. The aim of this review is to analyse AIH therapeutic interventions with reference to our knowledge of the pathogenesis of AIH. Standard treatment, based on steroids and azathioprine, leads to disease remission in 80-90% of patients. Alternative first-line treatment with budesonide is effective in adults, but less so in the juvenile form of AIH; first-line treatment with ciclosporin does not provide convincing advantages compared to standard treatment. Second-line treatments are needed for patients not responding or intolerant to first-line standard management. Mycophenolate mofetil is the most widely used second-line drug, and has good efficacy particularly for patients intolerant to azathioprine, but is teratogenic. Only few and heterogeneous data on calcineurin inhibitors and m-TOR inhibitors are available. Biologicals, including anti-tumour necrosis factor- α and anti-CD20 monoclonal antibodies, have given ambivalent results and may have severe side-effects. Clinical trials with new therapeutic options aiming at targeting B lymphocytes and proinflammatory cytokines, or expanding regulatory T cells to restore tolerance are ongoing.

Clinical Safety and Efficacy of Locoregional Therapy Combined with Adoptive Transfer of Allogeneic γδ T Cells for Advanced Hepatocellular Carcinoma and Intrahepatic Cholangiocarcinoma

PURPOSE

To investigate the safety and efficacy of locoregional therapy plus adoptive transfer of allogeneic gamma delta (γδ) T cells for patients with hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC).

METHODS

Thirty patients with HCC and 29 patients with ICC were randomly assigned to receive locoregional therapy (HCC, Group A, n = 15; ICC, Group C, n = 15) or locoregional therapy plus γδ T cell therapy (HCC, Group B, n = 15; ICC, Group D, n = 14). Groups A and C only received locoregional ablation (cryoablation or irreversible electroporation), whereas Groups B and D received locoregional therapy followed by adoptive transfer of allogeneic γδ T cells. The primary endpoints were safety, distant progression-free survival (PFS), local PFS, and overall survival (OS).

RESULTS

The median distant PFS was significantly longer in the combined treatment groups than the locoregional treatment groups (HCC: 8 vs 4 months, P = .04; ICC: 8 vs 4 months, P = .021). There was no significant difference in local PFS between the 2 treatment modalities. HCC patients in the combined treatment group had a longer OS (median OS: 13 vs 8 months, P = .029). However, there was no significant difference in OS in ICC patients between the 2 treatment modalities (median OS: 9.5 vs 8 months, P = .546). All adverse events were manageable with no significant difference in incidence between groups.

CONCLUSIONS

The novel combination of locoregional ablation with adoptive transfer of allogeneic γδ cells was safe, with encouraging clinical efficacy against HCC and ICC.

Regulatory T Cell Therapy of Graft-versus-Host Disease: Advances and Challenges

Graft-versus-host disease (GVHD) is the leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Immunomodulation using regulatory T cells (Tregs) offers an exciting option to prevent and/or treat GVHD as these cells naturally function to maintain immune homeostasis, can induce tolerance following HSCT, and have a tissue reparative function. Studies to date have established a clinical safety profile for polyclonal Tregs. Functional enhancement through genetic engineering offers the possibility of improved potency, specificity, and persistence. In this review, we provide the most up to date preclinical and clinical data on Treg cell therapy with a particular focus on GVHD. We discuss the different Treg subtypes and highlight the pharmacological and genetic approaches under investigation to enhance the application of Tregs in allo-HSCT. Lastly, we discuss the remaining challenges for optimal clinical translation and provide insights as to future directions of the field.

Exploring the Pathogenic Role and Therapeutic Implications of Interleukin 2 in Autoimmune Hepatitis

Interleukin 2 is essential for the expansion of regulatory T cells, and low-dose recombinant interleukin 2 has improved the clinical manifestations of diverse autoimmune diseases in preliminary studies. The goals of this review are to describe the actions of interleukin 2 and its receptor, present preliminary experiences with low-dose interleukin 2 in the treatment of diverse autoimmune diseases, and evaluate its potential as a therapeutic intervention in autoimmune hepatitis. English abstracts were identified in PubMed by multiple search terms. Full-length articles were selected for review, and secondary and tertiary bibliographies were developed. Interleukin 2 is critical for the thymic selection, peripheral expansion, induction, and survival of regulatory T cells, and it is also a growth factor for activated T cells and natural killer cells. Interleukin 2 activates the signal transducer and activator of transcription 5 after binding with its trimeric receptor on regulatory T cells. Immune suppressor activity is increased; anti-inflammatory interleukin 10 is released; pro-inflammatory interferon-gamma is inhibited; and activation-induced apoptosis of CD8⁺ T cells is upregulated. Preliminary experiences with cyclic injections of low-dose recombinant interleukin 2 in diverse autoimmune diseases have demonstrated increased numbers of circulating regulatory T cells, preserved regulatory function, improved clinical manifestations, and excellent tolerance. Similar improvements have been recognized in one of two patients with refractory autoimmune hepatitis. In conclusion, interferon 2 has biological actions that favor the immune suppressor functions of regulatory T cells, and low-dose regimens in preliminary studies encourage its rigorous investigation in autoimmune hepatitis.

Regulatory T Cells-Related Genes Are under DNA Methylation Influence

Regulatory T cells (Tregs) exert a highly suppressive function in the immune system. Disturbances in their function predispose an individual to autoimmune dysregulation, with a predominance of the pro-inflammatory environment. Besides Foxp3, which is a master regulator of these cells, other genes (e.g., Il2ra, Ctla4, Tnfrsf18, Ikzf2, and Ikzf4) are also involved in Tregs development and function. Multidimensional Tregs suppression is determined by factors that are believed to be crucial in the action of Tregs-related genes. Among them, epigenetic changes, such as DNA methylation, tend to be widely studied over the past few years. DNA methylation acts as a repressive mark, leading to diminished gene expression. Given the role of increased CpG methylation upon Tregs imprinting and functional stability, alterations in the methylation pattern can cause an imbalance in the immune response. Due to the fact that epigenetic changes can be reversible, so-called epigenetic modifiers are broadly used in order to improve Tregs performance. In this review, we place emphasis on the role of DNA methylation of the genes that are key regulators of Tregs function. We also discuss disease settings that have an impact on the methylation status of Tregs and systematize the usefulness of epigenetic drugs as factors able to influence Tregs functions.

NKTR-358: A novel regulatory T-cell stimulator that selectively stimulates expansion and suppressive function of regulatory T cells for the treatment of autoimmune and inflammatory diseases

Impaired interleukin-2 (IL-2) production and regulatory T-cell dysfunction have been implicated as immunological mechanisms central to the pathogenesis of multiple autoimmune and inflammatory diseases. NKTR-358, a novel regulatory T-cell stimulator, is an investigational therapeutic that selectively restores regulatory T-cell homeostasis in these diseases. We investigated NKTR-358's selectivity for regulatory T-cells, receptor-binding properties, ex vivo and in vivo pharmacodynamics, ability to suppress conventional T-cell proliferation in mice and non-human primates, and functional activity in a murine model of systemic lupus erythematosus. In vitro, NKTR-358 demonstrated decreased affinity for IL-2Rα, IL-2Rβ, and IL-2Rαβ compared with recombinant human IL-2 (rhIL-2). A single dose of NKTR-358 in cynomolgus monkeys produced a greater than 15-fold increase in regulatory T-cells, and the increase lasted until day 14, while daily rhIL-2 administration for 5 days only elicited a 3-fold increase, which lasted until day 7. Repeated dosing of NKTR-358 over 6 months in cynomolgus monkeys elicited cyclical, robust increases in regulatory T-cells with no loss in drug activity over the course of treatment. Regulatory T-cells isolated from NKTR-358-treated mice displayed a sustained, higher suppression of conventional T-cell proliferation than regulatory T-cells isolated from vehicle-treated mice. NKTR-358 treatment in a mouse model (MRL/MpJ-Fas^lpr) of systemic lupus erythematosus for 12 weeks maintained elevated regulatory T-cells for the treatment duration and ameliorated disease progression. Together, these results suggest that NKTR-358 has the ability to elicit sustained and preferential proliferation and activation of regulatory T-cells without corresponding effects on conventional T-cells, with improved pharmacokinetics compared with rhIL-2.

•

NKTR-358 is a pegylated IL-2 designed to induce Treg activation and proliferation.

•

This preclinical study compared NKTR-358 vs recombinant IL-2 for effects on Tregs.

•

NKTR-358 induced a greater increase in Treg:CD8+ T cell ratio compared with rhIL-2.

Modeling cell-specific dynamics and regulation of the common gamma chain cytokines

The γ-chain receptor dimerizes with complexes of the cytokines interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21 and their corresponding "private" receptors. These cytokines have existing uses and future potential as immune therapies because of their ability to regulate the abundance and function of specific immune cell populations. Here, we build a binding reaction model for the ligand-receptor interactions of common γ-chain cytokines, which includes receptor trafficking dynamics, enabling quantitative predictions of cell-type-specific response to natural and engineered cytokines. We then show that tensor factorization is a powerful tool to visualize changes in the input-output behavior of the family across time, cell types, ligands, and concentrations. These results present a more accurate model of ligand response validated across a panel of immune cell types as well as a general approach for generating interpretable guidelines for manipulation of cell-type-specific targeting of engineered ligands.

Immunotherapeutic strategy based on anti-OX40L and low dose of IL-2 to prolong graft survival in sensitized mice by inducing the generation of CD4+ and CD8+ Tregs

Alloreactive memory cells play a critical role after a second transplant and are difficult to suppress. This study investigated the effect of an immunotherapeutic strategy that combines anti-OX40L, rapamycin (Rapa), and a low dose of IL-2 in a memory cell-based adoptive model. In this model, the median survival time (MST) of the grafts of the combined treatment group was significantly extended compared to that of the control group and other treatment groups. A similar effect was observed regarding a reduction in memory T cells (Tm) and inflammatory cytokines production. Also, the percentages of Foxp3⁺ regulatory T cells (Tregs) increased in our model. In addition, mounting evidence has shown CD8⁺CD122⁺ T cells are also Tregs. We found that the group of CD8⁺CD122⁺PD1⁺ T cells was markedly increased in the combined treatment group, especially in the graft. We further demonstrated that CD8⁺CD122⁺PD1⁺ T cells could suppress activated T cells. Our data suggest that anti-OX40L combined with Rapa and a low dose of IL-2 can suppress Tm, modulate CD4 and CD8 Tregs, and induce long-term heart allograft survival in sensitized mice.

Evolving Antibody Therapies for the Treatment of Type 1 Diabetes

Type 1 diabetes (T1D) is widely considered to be a T cell driven autoimmune disease resulting in reduced insulin production due to dysfunction/destruction of pancreatic β cells. Currently, there continues to be a need for immunotherapies that selectively reestablish persistent β cell-specific self-tolerance for the prevention and remission of T1D in the clinic. The utilization of monoclonal antibodies (mAb) is one strategy to target specific immune cell populations inducing autoimmune-driven pathology. Several mAb have proven to be clinically safe and exhibit varying degrees of efficacy in modulating autoimmunity, including T1D. Traditionally, mAb therapies have been used to deplete a targeted cell population regardless of antigenic specificity. However, this treatment strategy can prove detrimental resulting in the loss of acquired protective immunity. Nondepleting mAb have also been applied to modulate the function of immune effector cells. Recent studies have begun to define novel mechanisms associated with mAb-based immunotherapy that alter the function of targeted effector cell pools. These results suggest short course mAb therapies may have persistent effects for regaining and maintaining self-tolerance. Furthermore, the flexibility to manipulate mAb properties permits the development of novel strategies to target multiple antigens and/or deliver therapeutic drugs by a single mAb molecule. Here, we discuss current and potential future therapeutic mAb treatment strategies for T1D, and T cell-mediated autoimmunity.

Treg Therapies Revisited: Tolerance Beyond Deletion

Induction of immune tolerance is the Holy Grail in transplantation medicine and autoimmunity. Currently, patients are required to use immunosuppressive drugs for the rest of their lives, resulting in unwanted side effects and complication from global suppression of the immune response. It is well established that regulatory T cells (Tregs) are critical for the maintenance of immune tolerance towards self-antigens by several mechanisms of immune regulation, in parallel with intrathymic deletion of self-reactive T cells during ontogeny. Therefore, approaches for increasing Treg numbers or function in vivo could provide an all-purpose solution for tolerance induction. Currently, most state-of-the-art therapeutics for treating autoimmune diseases or preventing allograft rejection work either by general immunosuppression or blocking inflammatory reactions and are non-specific. Hence, these approaches cannot provide satisfactory long-term results, let alone a cure. However, in animal models the therapeutic potential of Treg expansion for inducing effective tolerance has now been demonstrated in various models of autoimmunity and allogeneic transplantation. Here, we focus on therapies for increasing the size of the Treg pool by expanding endogenous Treg numbers in vivo or by adoptive transfer of Tregs. In particular, we discuss IL-2 based approaches (low dose IL-2, IL-2 complexes) for inducing Treg expansion in vivo as well as cell-based approaches (polyclonal, antigen specific, or cell engineered) for adoptive Treg therapy. We also mention new questions arising from the first clinical studies on Treg therapy in the fields of transplantation and autoimmunity.

Persistent IL-2 Receptor Signaling by IL-2/CD25 Fusion Protein Controls Diabetes in NOD Mice by Multiple Mechanisms

Low-dose interleukin-2 (IL-2) represents a new therapeutic approach to regulate immune homeostasis to promote immune tolerance in patients with autoimmune diseases, including type 1 diabetes. We have developed a new IL-2-based biologic, an IL-2/CD25 fusion protein, with greatly improved pharmacokinetics and pharmacodynamics when compared with recombinant IL-2 to enhance this type of immunotherapy. In this study, we show that low-dose mouse IL-2/CD25 (mIL-2/CD25), but not an equivalent amount of IL-2, prevents the onset of diabetes in NOD mice and controls diabetes in hyperglycemic mice. mIL-2/CD25 acts not only to expand regulatory T cells (Tregs) but also to increase their activation and migration into lymphoid tissues and the pancreas. Lower incidence of diabetes is associated with increased serum levels of IL-10, a cytokine readily produced by activated Tregs. These effects likely act in concert to lower islet inflammation while increasing Tregs in the remaining inflamed islets. mIL-2/CD25 treatment is also associated with lower anti-insulin autoantibody levels in part by inhibition of T follicular helper cells. Thus, long-acting mIL-2/CD25 represents an improved IL-2 analog that persistently elevates Tregs to maintain a favorable Treg/effector T cell ratio that limits diabetes by expansion of activated Tregs that readily migrate into lymphoid tissues and the pancreas while inhibiting autoantibodies.

Cancer immunotherapy with γδ T cells: many paths ahead of us

γδ T cells play uniquely important roles in stress surveillance and immunity for infections and carcinogenesis. Human γδ T cells recognize and kill transformed cells independently of human leukocyte antigen (HLA) restriction, which is an essential feature of conventional αβ T cells. Vγ9Vδ2 γδ T cells, which prevail in the peripheral blood of healthy adults, are activated by microbial or endogenous tumor-derived pyrophosphates by a mechanism dependent on butyrophilin molecules. γδ T cells expressing other T cell receptor variable genes, notably Vδ1, are more abundant in mucosal tissue. In addition to the T cell receptor, γδ T cells usually express activating natural killer (NK) receptors, such as NKp30, NKp44, or NKG2D which binds to stress-inducible surface molecules that are absent on healthy cells but are frequently expressed on malignant cells. Therefore, γδ T cells are endowed with at least two independent recognition systems to sense tumor cells and to initiate anticancer effector mechanisms, including cytokine production and cytotoxicity. In view of their HLA-independent potent antitumor activity, there has been increasing interest in translating the unique potential of γδ T cells into innovative cellular cancer immunotherapies. Here, we discuss recent developments to enhance the efficacy of γδ T cell-based immunotherapy. This includes strategies for in vivo activation and tumor-targeting of γδ T cells, the optimization of in vitro expansion protocols, and the development of gene-modified γδ T cells. It is equally important to consider potential synergisms with other therapeutic strategies, notably checkpoint inhibitors, chemotherapy, or the (local) activation of innate immunity.

An IL-2 mutein engineered to promote expansion of regulatory T cells arrests ongoing autoimmunity in mice

Interleukin-2 (IL-2) controls the homeostasis and function of regulatory T (Treg) cells, and defects in the IL-2 pathway contribute to multiple autoimmune diseases. Although recombinant IL-2 therapy has been efficacious in certain inflammatory conditions, the capacity for IL-2 to also activate inflammatory effector responses highlights the need for IL-2-based therapeutics with improved Treg cell specificity. From a panel of rationally designed murine IL-2 variants, we identified IL-2 muteins with reduced potency and enhanced Treg cell selectivity due to increased dependence on the IL-2 receptor component CD25. As an Fc-fused homodimer, the optimal Fc.IL-2 mutein induced selective Treg cell enrichment and reduced agonism of effector cells across a wide dose range. Furthermore, despite being a weaker agonist, overall Treg cell growth was greater and more sustained due to reduced receptor-mediated clearance of the Fc.IL-2 mutein compared with Fc-fused wild-type IL-2. Preferential Treg cell enrichment was also observed in the presence of activated pathogenic T cells in the pancreas of nonobese diabetic (NOD) mice, despite a loss of Treg cell selectivity in an IL-2R proximal response. These properties facilitated potent and extended resolution of NOD diabetes with infrequent dosing schedules.

Effects of interleukin-2 in immunostimulation and immunosuppression

Distinctions in the nature and spatiotemporal expression of IL-2R subunits on conventional versus regulatory T cells are exploited to manipulate IL-2 immunomodulatory effects. Particularly, low-dose IL-2 and some recombinant derivatives are being evaluated to enhance/inhibit immune responses for therapeutic purposes.

Historically, interleukin-2 (IL-2) was first described as an immunostimulatory factor that supports the expansion of activated effector T cells. A layer of sophistication arose when regulatory CD4⁺ T lymphocytes (Tregs) were shown to require IL-2 for their development, homeostasis, and immunosuppressive functions. Fundamental distinctions in the nature and spatiotemporal expression patterns of IL-2 receptor subunits on naive/memory/effector T cells versus Tregs are now being exploited to manipulate the immunomodulatory effects of IL-2 for therapeutic purposes. Although high-dose IL-2 administration has yielded discrete clinical responses, low-dose IL-2 as well as innovative strategies based on IL-2 derivatives, including “muteins,” immunocomplexes, and immunocytokines, are being explored to therapeutically enhance or inhibit the immune response.

Defining the Threshold IL-2 Signal Required for Induction of Selective Treg Cell Responses Using Engineered IL-2 Muteins

Among all T and NK cell subsets, regulatory T (Treg) cells typically respond to the lowest concentrations of IL-2 due to elevated surface expression of the IL-2R alpha chain (IL2RA; CD25) and the high affinity IL-2 receptor (IL-2R) complex. This enhanced sensitivity forms the basis for low-dose (LD) IL-2 therapy for the treatment of inflammatory diseases, where efficacy correlates with increased Treg cell number and expression of functional markers. Despite strong preclinical support for this approach, moderate and variable clinical efficacy has raised concerns that adequate Treg selectivity still cannot be achieved with LD IL-2, and/or that doses are too low to stimulate effective Treg-mediated suppression within tissues. This has prompted development of IL-2 variants with greater Treg selectivity, achieved through attenuated affinity for the signaling chains of the IL-2R complex (IL2RB or CD122 and IL2RG or CD132) and, consequently, greater reliance on high CD25 levels for full receptor binding and signaling. While certain IL-2 variants have advanced to the clinic, it remains unknown if the full range of IL-2R signaling potency and Treg-selectivity observed with low concentrations of wildtype IL-2 can be sufficiently recapitulated with attenuated IL-2 muteins at high concentrations. Using a panel of engineered IL-2 muteins, we investigated how a range of IL-2R signaling intensity, benchmarked by the degree of STAT5 phosphorylation, relates to biologically relevant Treg cell responses such as proliferation, lineage and phenotypic marker expression, and suppressor function. Our results demonstrate that a surprisingly wide dynamic range of IL-2R signaling intensity leads to productive biological responses in Treg cells, with negligible STAT5 phosphorylation associating with nearly complete downstream effects such as Treg proliferation and suppressor activity. Furthermore, we show with both in vitro and humanized mouse in vivo systems that different biological responses in Treg cells require different minimal IL-2R signaling thresholds. Our findings suggest that more than minimal IL-2R signaling, beyond that capable of driving Treg cell proliferation, may be required to fully enhance Treg cell stability and suppressor function in vivo.

Low-dose IL-2 induces CD56bright NK regulation of T cells via NKp44 and NKp46

Low-dose interleukin (IL)-2 has shown clinical benefits in patients with autoimmune and inflammatory diseases. Both regulatory T cells (Tregs ) and natural killer (NK) cells are increased in response to low-dose IL-2 immunotherapy. The role of regulatory T cells in autoimmune diseases has been extensively studied; however, NK cells have not been as thoroughly explored. It has not been well reported whether the increase in NK cells is purely an epiphenomenon or carries actual benefits for patients with autoimmune diseases. We demonstrate that low-dose IL-2 expands the primary human CD56bright NK cells resulting in a contact-dependent cell cycle arrest of effector T cells (Teffs ) via retention of the cycle inhibitor p21. We further show that NK cells respond via IL-2R-β, which has been shown to be significant for immunity by regulating T cell expansion. Moreover, we demonstrate that blocking NK receptors NKp44 and NKp46 but not NKp30 could abrogate the regulation of proliferation associated with low-dose IL-2. The increase in NK cells was also accompanied by an increase in Treg cells, which is dependent on the presence of CD56bright NK cells. These results not only heighten the importance of NK cells in low-dose IL-2 therapy but also identify key human NK targets, which may provide further insights into the therapeutic mechanisms of low-dose IL-2 in autoimmunity.

[Immunotoxins and immunocytokines]

Cytokines and biological toxins represent two potent classes of biomolecules that have long been explored for their potential as therapeutics. Considerable side effects and poor pharmacokinetics frequently observed with both have limited their broad application. Recombinant protein engineering has allowed the construction of immunocytokines and immunotoxins that seek to exploit the advantageous properties of immunoglobulins to address these issues. Whole antibodies, antibody fragments, constant domains and derivatives have been fused genetically to a range of cytokines and toxins. This review considers the strategies that have been employed and the problems sought to be resolved in the clinical evaluation of this class of biotherapeutic.

Complex interactions between the microbiome and cancer immune therapy

Immuno-oncology has rapidly grown in the last thirty years, and immunotherapeutic agents are now approved to treat many disparate cancers. Immune checkpoint inhibitors (ICIs) are employed to augment cytotoxic anti-cancer activity by inhibiting negative regulatory elements of the immune system. Modulating the immune system to target neoplasms has improved survivability of numerous cancers in many individuals, but forecasting outcomes post therapy is difficult due to insufficient predictive biomarkers. Recently, the tumor and gastrointestinal microbiome and immune milieu have been investigated as predictors and influencers of cancer immune therapy. In this review, we discuss: (1) ways to measure the microbiome including relevant bioinformatic analyses, (2) recent developments in animal studies and human clinical trials utilizing gut microbial composition and function as biomarkers of cancer immune therapy response and toxicity, and (3) using prebiotics, probiotics, postbiotics, antibiotics, and fecal microbiota transplant (FMT) to modulate immune therapy. We discuss the respective benefits of 16S ribosomal RNA (rRNA) gene and shotgun metagenomic sequencing including important considerations in obtaining samples and in designing and interpreting human and animal microbiome studies. We then focus on studies discussing the differences in response to ICIs in relation to the microbiome and inflammatory mediators. ICIs cause colitis in up to 25% of individuals, and colitis is often refractory to common immunosuppressive medications. Researchers have measured microbiota composition prior to ICI therapy and correlated baseline microbiota composition with efficacy and colitis. Certain bacterial taxa that appear to enhance therapeutic benefit are also implicated in increased susceptibility to colitis, alluding to a delicate balance between pro-inflammatory tumor killing and anti-inflammatory protection from colitis. Pre-clinical and clinical models have trialed probiotic administration, e.g. Bifidobacterium spp. or FMT, to treat colitis when immune suppressive agents fail. We are excited about the future of modulating the microbiome to predict and influence cancer outcomes. Furthermore, novel therapies employed for other illnesses including bacteriophage and genetically-engineered microbes can be adapted in the future to promote increased advancements in cancer treatment and side effect management.

The promise of CD4+FoxP3+ regulatory T-cell manipulation in vivo: applications for allogeneic hematopoietic stem cell transplantation

CD4⁺FoxP3⁺ regulatory T cells (Tregs) are a non-redundant population critical for the maintenance of self-tolerance. Over the past decade, the use of these cells for therapeutic purposes in transplantation and autoimmune disease has emerged based on their capacity to inhibit immune activation. Basic science discoveries have led to identifying key receptors on Tregs that can regulate their proliferation and function. Notably, the understanding that IL-2 signaling is crucial for Treg homeostasis promoted the hypothesis that in vivo IL-2 treatment could provide a strategy to control the compartment. The use of low-dose IL-2 in vivo was shown to selectively expand Tregs versus other immune cells. Interestingly, a number of other Treg cell surface proteins, including CD28, CD45, IL-33R and TNFRSF members, have been identified which can also induce activation and proliferation of this population. Pre-clinical studies have exploited these observations to prevent and treat mice developing autoimmune diseases and graft-versus-host disease post-allogeneic hematopoietic stem cell transplantation. These findings support the development of translational strategies to expand Tregs in patients. Excitingly, the use of low-dose IL-2 for patients suffering from graft-versus-host disease and autoimmune disease has demonstrated increased Treg levels together with beneficial outcomes. To date, promising pre-clinical and clinical studies have directly targeted Tregs and clearly established the ability to increase their levels and augment their function in vivo. Here we review the evolving field of in vivo Treg manipulation and its application to allogeneic hematopoietic stem cell transplantation.

Ammonia induces Treg/Th1 imbalance with triggered NF-κB pathway leading to chicken respiratory inflammation response

Ammonia (NH₃) is a severe air pollutant and a component of haze (PM2.5). The respiratory tract is the first route of exogenous ammonia's entry into the human and animal body. Many studies have suggested that exposure to NH₃ is associated with a higher risk of respiratory tract tracheitis; however, the underlying mechanism remains unclear. In this study, chicken tracheas were used as a model to investigate toxic effects and genetic changes induced by NH₃ exposure, as evaluated by scanning electron microscopy (SEM) and bioinformatic analyses. The transcript analysis illustrated that NH₃ exposure caused immune disorders, which play key roles in regulating inflammatory responses from NH₃ exposure. Therefore, we carried out Real-time quantitative PCR (RT-PCR) and Western Blot analyses to detect the immune response genes; Treg/Th1, Th2 and Th17 secretions were found that led to inflammatory responses. Next, we also detected the NF-κB pathway and downstream genes, accompanied by cytochromes P450 (CYPs), antioxidative genes, and heat shock proteins (HSPs). Our results are consistent with transcriptome detection, indicating that ammonia has a negative effect on immune responses and causes inflammatory injury of the trachea. This study provided baseline information for exploration of the molecular mechanism of NH₃-PM2.5 induced respiratory diseases.

Targeting Tregs in Juvenile Idiopathic Arthritis and Juvenile Dermatomyositis-Insights From Other Diseases

Regulatory T cells (Tregs) are believed to be dysfunctional in autoimmunity. Juvenile idiopathic arthritis (JIA) and juvenile dermatomyositis (JDM) result from a loss of normal immune regulation in specific tissues such as joints or muscle and skin, respectively. Here, we discuss recent findings in regard to Treg biology in oligo-/polyarticular JIA and JDM, as well as what we can learn about Treg-related disease mechanism, treatment and biomarkers in JIA/JDM from studies of other diseases. We explore the potential use of Treg immunoregulatory markers and gene signatures as biomarkers for disease course and/or treatment success. Further, we discuss how Tregs are affected by several treatment strategies already employed in the therapy of JIA and JDM and by alternative immunotherapies such as anti-cytokine or co-receptor targeting. Finally, we review recent successes in using Tregs as a treatment target with low-dose IL-2 or cellular immunotherapy. Thus, this mini review will highlight our current understanding and identify open questions in regard to Treg biology, and how recent findings may advance biomarkers and new therapies for JIA and JDM.

A long-lived IL-2 mutein that selectively activates and expands regulatory T cells as a therapy for autoimmune disease

Susceptibility to multiple autoimmune diseases is associated with common gene polymorphisms influencing IL-2 signaling and T_reg function, making T_reg-specific expansion by IL-2 a compelling therapeutic approach to treatment. As an in vivo IL-2 half-life enhancer we used a non-targeted, effector-function-silent human IgG1 as a fusion protein. An IL-2 mutein (N88D) with reduced binding to the intermediate affinity IL-2Rβγ receptor was engineered with a stoichiometry of two IL-2N88D molecules per IgG, i.e. IgG-(IL-2N88D)₂. The reduced affinity of IgG-(IL-2N88D)₂ for the IL-2Rβγ receptor resulted in a T_reg-selective molecule in human whole blood pSTAT5 assays. Treatment of cynomolgus monkeys with single low doses of IgG-(IL-2N88D)₂ induced sustained preferential activation of T_regs accompanied by a corresponding 10–14-fold increase in CD4⁺ and CD8⁺ CD25⁺FOXP3⁺ T_regs; conditions that had no effect on CD4⁺ or CD8⁺ memory effector T cells. The expanded cynomolgus T_regs had demethylated FOXP3 and CTLA4 epigenetic signatures characteristic of functionally suppressive cells. Humanized mice had similar selective in vivo responses; IgG-(IL-2N88D)₂ increased T_regs while wild-type IgG-IL-2 increased NK cells in addition to T_regs. The expanded human T_regs had demethylated FOXP3 and CTLA4 signatures and were immunosuppressive. These results describe a next-generation immunotherapy using a long-lived and T_reg-selective IL-2 that activates and expands functional T_regsin vivo. Patients should benefit from restored immune homeostasis in a personalized fashion to the extent that their autoimmune disease condition dictates opening up the possibility for remissions and cures.

•

A human IL-2 molecule mutated to decrease binding to the intermediate affinity IL-2 receptor preferentially activates Tregs.

•

Two IL-2 muteins fused to human IgG1 allow for sustained, preferential expansion of Tregs in cynomolgus and humanized mice.

•

As compared to the wild type IL-2 fusion protein, humanized mice expand fewer NK cells in response to the mutein.

•

The dynamic range of Treg increase based on dose suggests the ability to individualize dosing for particular diseases.

IL-2/CD25: A Long-Acting Fusion Protein That Promotes Immune Tolerance by Selectively Targeting the IL-2 Receptor on Regulatory T Cells

Low-dose IL-2 represents an immunotherapy to selectively expand regulatory T cells (Tregs) to promote tolerance in patients with autoimmunity. In this article, we show that a fusion protein (FP) of mouse IL-2 and mouse IL-2Rα (CD25), joined by a noncleavable linker, has greater in vivo efficacy than rIL-2 at Treg expansion and control of autoimmunity. Biochemical and functional studies support a model in which IL-2 interacts with CD25 in the context of this FP in trans to form inactive head-to-tail dimers that slowly dissociate into an active monomer. In vitro, IL-2/CD25 has low sp. act. However, in vivo IL-2/CD25 is long lived to persistently and selectively stimulate Tregs. In female NOD mice, IL-2/CD25 administration increased Tregs within the pancreas and reduced the instance of spontaneous diabetes. Thus, IL-2/CD25 represents a distinct class of IL-2 FPs with the potential for clinical development for use in autoimmunity or other disorders of an overactive immune response.

Targeting Regulatory T Cells to Treat Patients With Systemic Lupus Erythematosus

Regulatory T cells (Tregs) are central in integration and maintenance of immune homeostasis. Since breakdown of self-tolerance is a major culprit in the pathogenesis of systemic lupus erythematosus (SLE), restoration of the immune tolerance through the manipulation of Tregs can be exploited to treat patients with SLE. New information has revealed that Tregs besides their role in suppressing the immune response are important in tissue protection and regeneration. Expansion of Tregs with low-dose IL-2 represents an approach to control the autoimmune response. Moreover, control of Treg metabolism can be exploited to restore or improve their function. Here, we summarize the function and diversity of Tregs and recent strategies to improve their function in patients with SLE.

Targeting IL-2: an unexpected effect in treating immunological diseases

Regulatory T cells (Treg) play a crucial role in maintaining immune homeostasis since Treg dysfunction in both animals and humans is associated with multi-organ autoimmune and inflammatory disease. While IL-2 is generally considered to promote T-cell proliferation and enhance effector T-cell function, recent studies have demonstrated that treatments that utilize low-dose IL-2 unexpectedly induce immune tolerance and promote Treg development resulting in the suppression of unwanted immune responses and eventually leading to treatment of some autoimmune disorders. In the present review, we discuss the biology of IL-2 and its signaling to help define the key role played by IL-2 in the development and function of Treg cells. We also summarize proof-of-concept clinical trials which have shown that low-dose IL-2 can control autoimmune diseases safely and effectively by specifically expanding and activating Treg. However, future studies will be needed to validate a better and safer dosing strategy for low-dose IL-2 treatments utilizing well-controlled clinical trials. More studies will also be needed to validate the appropriate dose of IL-2/anti-cytokine or IL-2/anti-IL-2 complex in the experimental animal models before moving to the clinic.

Scanning the Immunopathogenesis of Psoriasis

Psoriasis is a chronic inflammatory skin disease, the immunologic model of which has been profoundly revised following recent advances in the understanding of its pathophysiology. In the current model, a crosstalk between keratinocytes, neutrophils, mast cells, T cells, and dendritic cells is thought to create inflammatory and pro-proliferative circuits mediated by chemokines and cytokines. Various triggers, including recently identified autoantigens, Toll-like receptor agonists, chemerin, and thymic stromal lymphopoietin may activate the pathogenic cascade resulting in enhanced production of pro-inflammatory and proliferation-inducing mediators such as interleukin (IL)-17, tumor necrosis factor (TNF)-α, IL-23, IL-22, interferon (IFN)-α, and IFN-γ by immune cells. Among these key cytokines lie therapeutic targets for currently approved antipsoriatic therapies. This review aims to provide a comprehensive overview on the immune-mediated mechanisms characterizing the current pathogenic model of psoriasis.

Human naïve regulatory T-cells feature high steady-state turnover and are maintained by IL-7

Naïve FoxP3-expressing regulatory T-cells (Tregs) are essential to control immune responses via continuous replenishment of the activated-Treg pool with thymus-committed suppressor cells. The mechanisms underlying naïve-Treg maintenance throughout life in face of the age-associated thymic involution remain unclear. We found that in adults thymectomized early in infancy the naïve-Treg pool is remarkably well preserved, in contrast to conventional naïve CD4 T-cells. Naïve-Tregs featured high levels of cycling and pro-survival markers, even in healthy individuals, and contrasted with other circulating naïve/memory CD4 T-cell subsets in terms of their strong γc-cytokine-dependent signaling, particularly in response to IL-7. Accordingly, ex-vivo stimulation of naïve-Tregs with IL-7 induced robust cytokine-dependent signaling, Bcl-2 expression, and phosphatidylinositol 3-kinase (PI3K)-dependent proliferation, whilst preserving naïve phenotype and suppressive capacity. Altogether, our data strongly implicate IL-7 in the thymus-independent long-term survival of functional naïve-Tregs, and highlight the potential of targeting the IL-7 pathway to modulate Tregs in different clinical settings.

In Vitro Induction of Human Regulatory T Cells Using Conditions of Low Tryptophan Plus Kynurenines

Thymic regulatory T cells (tTregs) and induced regulatory T cells (iTregs) suppress murine acute graft-versus-host disease (GVHD). Previously, we demonstrated that the plasmacytoid dendritic cell indoleamine 2,3-dioxygenase (IDO) fosters the in vitro development of human iTregs via tryptophan depletion and kynurenine (Kyn) metabolites. We now show that stimulation of naïve CD4⁺ T cells in low tryptophan (low Trp) plus Kyn supports human iTreg generation. In vitro, low Trp + Kyn iTregs and tTregs potently suppress T effector cell proliferation equivalently but are phenotypically distinct. Compared with tTregs or T effector cells, bioenergetics profiling reveals that low Trp + Kyn iTregs have increased basal glycolysis and oxidative phosphorylation and use glutaminolysis as an energy source. Low Trp + Kyn iTreg viability was reliant on interleukin (IL)-2 in vitro. Although in vivo IL-2 administration increased low Trp + Kyn iTreg persistence on adoptive transfer into immunodeficient mice given peripheral blood mononuclear cells to induce GVHD, IL-2-supported iTregs did not improve recipient survival. We conclude that low Trp + Kyn create suppressive iTregs that have high metabolic needs that will need to be addressed before clinical translation.

Triplebody Mediates Increased Anti-Leukemic Reactivity of IL-2 Activated Donor Natural Killer (NK) Cells and Impairs Viability of Their CD33-Expressing NK Subset

Natural killer cells (NK) are essential for the elimination of resistant acute myeloid and acute lymphoblastic leukemia (AML and ALL) cells. NK cell-based immunotherapies have already successfully entered for clinical trials, but limitations due to immune escape mechanisms were identified. Therefore, we extended our established NK cell protocol by integration of the previously investigated powerful trispecific immunoligand ULBP2-aCD19-aCD33 [the so-called triplebodies (TBs)] to improve the anti-leukemic specificity of activated NK cells. IL-2-driven expansion led to strongly elevated natural killer group 2 member D (NKG2D) expressions on donor NK cells which promote the binding to ULBP2⁺ TBs. Similarly, CD33 expression on these NK cells could be detected. Dual-specific targeting and elimination were investigated against the B-cell precursor leukemia cell line BV-173 and patient blasts, which were positive for myeloid marker CD33 and B lymphoid marker CD19 exclusively presented on biphenotypic B/myeloid leukemia’s. Cytotoxicity assays demonstrated improved killing properties of NK cells pre-coated with TBs compared to untreated controls. Specific NKG2D blocking on those NK cells in response to TBs diminished this killing activity. On the contrary, the observed upregulation of surface CD33 on about 28.0% of the NK cells decreased their viability in response to TBs during cytotoxic interaction of effector and target cells. Similar side effects were also detected against CD33⁺ T- and CD19⁺ B-cells. Very preliminary proof of principle results showed promising effects using NK cells and TBs against primary leukemic cells. In summary, we demonstrated a promising strategy for redirecting primary human NK cells in response to TBs against leukemia, which may lead to a future progress in NK cell-based immunotherapies.

Capturing the systemic immune signature of a norovirus infection: an n-of-1 case study within a clinical trial

BACKGROUND

The infection of a participant with norovirus during the adaptive study of interleukin-2 dose on regulatory T cells in type 1 diabetes (DILT1D) allowed a detailed insight into the cellular and cytokine immune responses to this prevalent gastrointestinal pathogen.

METHODS

Serial blood, serum and peripheral blood mononuclear cell (PBMC) samples were collected pre-, and post-development of the infection. To differentiate between the immune response to norovirus and to control for the administration of a single dose of aldesleukin (recombinant interleukin-2, rIL-2) alone, samples from five non-infected participants administered similar doses were analysed in parallel.

RESULTS

Norovirus infection was self-limited and resolved within 24 hours, with the subsequent development of anti-norovirus antibodies. Serum pro- and anti-inflammatory cytokine levels, including IL-10, peaked during the symptomatic period of infection, coincident with increased frequencies of monocytes and neutrophils. At the same time, the frequency of regulatory CD4 ⁺ T cell (Treg), effector T cell (Teff) CD4 ⁺ and CD8 ⁺ subsets were dynamically reduced, rebounding to baseline levels or above at the next sampling point 24 hours later.  NK cells and NKT cells transiently increased CD69 expression and classical monocytes expressed increased levels of CD40, HLA-DR and SIGLEC-1, biomarkers of an interferon response. We also observed activation and mobilisation of Teffs, where increased frequencies of CD69 ⁺ and Ki-67 ⁺ effector memory Teffs were followed by the emergence of memory CD8 ⁺ Teff expressing the mucosal tissue homing markers CD103 and β7 integrin. Treg responses were coincident with the innate cell, Teff and cytokine response. Key Treg molecules FOXP3, CTLA-4, and CD25 were upregulated following infection, alongside an increase in frequency of Tregs with the capacity to home to tissues.

CONCLUSIONS

The results illustrate the innate, adaptive and counter-regulatory immune responses to norovirus infection. Low-dose IL-2 administration induces many of the Treg responses observed during infection.

CD11a/ICAM-1 blockade combined with IL-2 targeting therapy causes a paradoxical acceleration of type 1 diabetes

Enhancement of regulatory T-cell (Treg) function is the goal of many immunotherapies aimed at treating type 1 diabetes (T1D). The use of interleukin (IL)-2 is hindered by its effects on other populations such as effector T cells and NK cells. Combination therapies aimed at suppressing effector T cells while using IL-2 to expand Tregs could be beneficial and have been trialed in T1D patients. We have investigated a combination therapy using IL-2 and αCD11a blocking antibody to simultaneously expand Tregs and suppress the activation and migration of autoreactive T cells. When non-obese diabetic mice were treated with low-dose IL-2/anti-IL-2 complexes (IL-2c) and αCD11a, significant Treg expansion occurred in both the spleen and pancreas. Activation and IFNγ production by islet-specific T cells was robustly suppressed in the periphery following IL-2c/αCD11a treatment. Surprisingly, combination therapy accelerated diabetes onset compared with control treatments. Analysis of IL-2 responsive populations found that combination therapy increased the activation of CD8⁺ T cells and natural killer (NK) cells specifically within the pancreas despite concomitant Treg expansion. Blocking effector T-cell migration with the inhibitor FTY720 together with IL-2c treatment also resulted in intra-pancreatic expansion of effector cell populations. Thus, inhibiting effector T-cell migration into the islets unleashes islet-resident pathogenic effectors in the presence of low doses of exogenous IL-2.