High-affinity Interleukin-2 Receptor Research Articles

A first-in-human, multicenter, phase 1/2, open-label study of XTX202, a masked and tumor-selective recombinant human interleukin-2 (IL-2) protein, in patients with advanced solid tumors.

TPS2697 Background: High-dose interleukin-2 (IL-2) has been approved in metastatic renal cell carcinoma (RCC) and metastatic melanoma, and can result in durable complete responses, including cures. Its use has been limited by life-threatening treatment-related multisystem toxicities, consisting mainly of vascular leak syndrome. XTX202 is a masked, tumor-selective IL-2 that is designed to be pharmacologically inactive in non-tumor tissue when circulating systemically and unmasked by matrix metalloproteases (MMPs) found preferentially in the tumor microenvironment (TME). XTX202 is expected, therefore, to achieve a wider therapeutic index resulting in increased efficacy and lower toxicity compared to existing non-tumor selective IL-2 based-therapies. The IL-2 domain of the XTX202 molecule is modified to reduce binding to the high-affinity IL-2 receptor while maintaining binding to the intermediate-affinity IL-2 receptor, thereby decreasing activation of regulatory T-cells relative to wild-type IL-2, while still activating effector T cells. A masking domain is designed to pharmacologically inactivate IL-2 until it is activated by MMPs that are enriched in the TME. Cleavage at a protease cleavage site in the XTX202 linker by MMPs results in an active IL-2 moiety when the masking domain is released. XTX202 is designed with the goal of producing a localized anti-tumor immune response and limiting exposure of the active form of XTX202 in non-tumor tissue. Preclinically, XTX202 exhibited tumor-selective activity in mice without peripheral toxicities in non-human primates [O’Neil et al. ASCO 2021]. Methods: XTX202-01 trial (NCT05052268) is a first-in-human Phase 1/2 study to determine a recommended Phase 2 dose of XTX202 (Phase 1) and to evaluate the efficacy of XTX202 monotherapy in patients with metastatic RCC and unresectable or metastatic melanoma (Phase 2). Patients with advanced solid tumors are eligible for Phase 1 and will receive XTX202 monotherapy administered every 21 days in an accelerated and standard 3+3 dose escalation design. Phase 2 will consist of 2 parts: Part 2a will enroll patients with metastatic RCC who have received a prior tyrosine kinase inhibitor therapy and have been treated and progressed on an anti-PD-1 therapy. Part 2b will enroll patients with unresectable or metastatic melanoma who have received immune-checkpoint therapy with an anti-PD-1 therapy and an anti-CTLA-4 therapy to determine the efficacy of XTX202 monotherapy in this population. Enrollment to the study began in January 2022. Clinical trial information: NCT05052268.

AB0432 EFAVALEUKIN ALFA, A NOVEL IL-2 MUTEIN, SELECTIVELY EXPANDS REGULATORY T CELLS IN PATIENTS WITH SLE: FINAL RESULTS OF A PHASE 1B MULTIPLE ASCENDING DOSE STUDY

BackgroundDefects in regulatory T cell (Treg) number and function are associated with autoimmune diseases including SLE. Interleukin (IL)-2 is essential for the development and suppressive function of Treg, and therapies that exploit the ability of IL-2 to expand Treg have shown disease-modifying potential in SLE1. However, low-dose IL-2 has a short half-life and narrow selectivity for Treg over conventional CD4+ T cells (Tcon) and natural killer (NK) cells. Efavaleukin alfa is an IL-2 mutein Fc fusion protein; an introduced mutation decreases binding to IL-2Rβ and increases dependence on IL-2Rα (CD25). This preferential binding to the high-affinity IL-2R, constitutively expressed at high levels on Treg, leads to increased cell surface retention and sustained Treg signaling compared with recombinant IL-2. In healthy subjects, a single dose of efavaleukin alfa was well tolerated and led to robust and selective Treg expansion2.ObjectivesThis final analysis of a phase 1b, double-blind, placebo-controlled, multiple ascending dose study (NCT03451422) reports the safety, tolerability, pharmacokinetics (PK), and pharmacodynamic effects of efavaleukin alfa in patients with SLE.MethodsThe study included five ascending dose cohorts (cohort 1=lowest dose; cohort 5=highest dose). A total of 35 patients with SLE (age 24–71 years; 85.7% female; SLE diagnosed using SLICC or ACR criteria with ANA ≥1:80 and/or elevated anti-dsDNA antibodies) were randomized to receive efavaleukin alfa or placebo (5:2 ratio for cohorts 1–3; 3:1 ratio for cohorts 4–5) subcutaneously every 2 weeks (Q2W; cohorts 1, 2, 4, and 5) or every week (QW; cohort 3) in addition to standard of care therapy for a total of 12 weeks, with 6 weeks of follow-up. The primary endpoint was the incidence of treatment-emergent adverse events (TEAEs). Additional endpoints included serum PK of efavaleukin alfa and changes in numbers of Treg, CD4+ Tcon, CD8+ T cells, and NK cells in peripheral blood.ResultsThe most commonly reported TEAEs (occurring in ≥25% of efavaleukin alfa-treated subjects) included non-serious, mild or moderate (grade 1–2) injection site reactions. No grade 4 TEAEs or deaths occurred. Two serious AEs were reported in efavaleukin alfa-treated subjects: one event of syncope (grade 3) was observed in cohort 2 and was not considered related to treatment, and one case of eosinophilia (grade 2) was observed in cohort 5 and was considered related to treatment. Efavaleukin alfa PK was generally linear and dose-proportional, with a terminal half-life ranging from 18–30 hours. Peak Foxp3+ Treg expansion was observed at 8 days post-dose, and the magnitude of the peak was generally sustained after multiple QW or Q2W doses. The mean peak increases in Foxp3+ Treg were 14.8-, 17.4-, 5.7-, 2.4-, and 1.1-fold above baseline for efavaleukin alfa Q2W dosing cohorts 5, 4, 2, and 1 and placebo, respectively. At the final study assessment (42 days after the last dose), the mean Treg count was 1.3-fold above baseline (95% CI, 0.9–1.9). Treatment with efavaleukin alfa also expanded CD25bright Treg (peak 53.8-fold change) and CD31+ recent thymic emigrant (RTE), naïve, and memory Treg subsets. At the highest dose (cohort 5), low-level increases in numbers of CD4+ Tcon (peak 2.3-fold), CD8+ T cells (peak 2.1-fold), and NK cells (peak 2.9-fold) were observed.ConclusionMultiple ascending doses of efavaleukin alfa were safe and well tolerated and led to selective and prolonged Treg expansion in SLE patients. Results at the highest dose suggest a plateau in Treg expansion with low-level increases in other IL-2–responsive cells, although interpretation is limited due to small subject numbers. The highest tested dose may be outside the therapeutic window and thus will not be assessed in phase 2 clinical studies. These findings confirm and extend previous results in healthy subjects and support the ongoing phase 2b adaptive randomized controlled trial in patients with SLE.

Impaired activation of STAT5 upon IL-2 stimulation in Tregs and elevated sIL-2R in Sjögren’s syndrome

BackgroundInterleukin-2 (IL-2) and the high-affinity IL-2 receptor (IL-2R) are essential for the survival of regulatory T cells (Tregs) which are the main players in immune tolerance and prevention of autoimmune diseases. Sjögren’s syndrome (SS) is a chronic autoimmune disease predominantly affecting women and is characterised by sicca symptoms including oral and ocular dryness. The aim of this study was to investigate an association between IL-2R and Treg function in patients with SS of different severity defined by the salivary flow rate.MethodsIn a cross-sectional study, we determined plasma soluble IL-2R (sIL-2R) levels in women with SS (n=97) and healthy females (n=50) using ELISA. A subset of those (n=51) was screened for Treg function measured by the STAT5 signalling response to IL-2 using phospho-flow cytometry.ResultsWe found that elevated plasma levels of sIL-2R were positively associated with the severity of SS reflected by a pathologically low salivary flow. Phospho-flow analysis revealed that patients with SS have a significantly lower frequency of pSTAT5+ Tregs upon IL-2 stimulation compared with healthy individuals, while the frequency of Tregs and pSTAT5 in conventional T cells remained unchanged. In addition, we observed more pSTAT5+ Tregs at baseline in patients with SS, which is significantly associated with seropositivity and elevated sIL-2R.ConclusionsOur data indicates that Tregs have a weakened immunosuppressive function in patients with SS due to impaired IL-2/IL-2R signalling capacity. This could mediate lymphocytic infiltration into salivary glands inducing sicca symptoms. We believe that sIL-2R could act as a useful indicator for SS and disease severity.

Targeting the high-affinity IL-2R with high-dose mIL-2/CD25 induces effective antitumor responses

Abstract Much interest remains to harness the T cell activating properties of IL-2 to promote antitumor immunity. Current efforts largely utilize approaches directed toward the intermediate-affinity IL-2R to broadly stimulate memory-phenotypic CD8+ T and NK cells while minimizing off-target Tregs. However, this approach does not effectively engage tumor-reactive CD4+ and CD8+ T effector cells that express the high-affinity IL-2R. Recently, we developed a fusion protein where mouse IL-2 was linked to CD25 (mIL-2/CD25 or FP) with selectivity toward the high-affinity IL-2R. At a low dose, the FP is Treg-selective to limit autoimmunity, but at a high dose with a tumor vaccine it expands tumor-reactive T cells to develop antitumor immunity. Here, we assessed the efficacy of high-dose (HD) FP as a cancer monotherapy or with checkpoint blockade. HD FP supports antitumor responses in mice bearing CT26, MC38, or B16.F10 tumors. Although HD FP led to increases in Tregs in immune tissues, Tregs were at a lower frequency in the tumor microenvironment (TME), leading to a high CD8+ T cell:Treg ratio. Further, adding anti-PD-1 to HD FP treatment was more effective in controlling tumors in CT26-bearing mice. Surprisingly, at the doses tested, HD FP supported more robust antitumor responses in each model than IL-2/S4B6 anti-IL-2 complexes (IL2/IC), directed to the intermediate-affinity IL-2R. In the CT26 TME, the number of tumor antigen-specific CD8+ T cells trended upward with HD FP over IL2/IC. These studies indicate that targeting the high-affinity IL-2R on activated tumor-specific T cells with HD FP alone or with PD-1 blockade supports antitumor responses and suggests that this strategy may be more effective than targeting the intermediate-affinity IL-2R. Supported by Bristol Myers Squibb grant support

Early heterogeneity of IL2R□ expression influences the programming of exhausted CD8T cells during chronic infection

Abstract IL-2 signaling at the time of CD8 T cell activation is a critical factor dictating effector and memory CD8 T cell differentiation. However, how IL-2 signaling impacts exhausted CD8 T cell fate outcomes remains poorly defined. Here, we address the role of IL-2 signaling in regulating the differentiation of the stem-like and terminally exhausted CD8 T cells. Prolonged expression of the high affinity IL-2 receptor (IL-2Ra, CD25), and resultant increase in IL-2 signaling drives terminal differentiation of effector cells during acute infection. We hypothesized that curtailing this signal would prevent terminal differentiation and promote the formation of less exhausted stem-cell like TCF-1+CD8T cells in chronic antigenic setting. Our studies show that blocking IL-2 signals at the early phase of chronic infection significantly increased the proportions of TCF-1+CD8T cells. Similarly, knocking down Il2ra augmented the development of TCF-1+CD8T cells. The therapeutic success of PD-1/PD-L1 checkpoint blockade immunotherapy (CBI) relies primarily on stem-cell like cells for vigorous expansion and effector responses. Thus, we next investigated how FACS-purified CD25Hi and CD25Lo cells adoptively transferred into infection-matched chronically infected recipients respond to PD-1 CBI. In contrast to CD25Hi cells, CD25Lo cells underwent vigorous proliferation after PD-1 CBI and produced high amount of effector molecules (GzmB, TNF-α and IFN-γ). Collectively, these data highlight the role of IL-2 signaling in the regulation of CD8 T cell exhaustion, which may be therapeutically exploited to optimize treatments of chronic infections and cancers with immune checkpoint inhibitors. Supported by NIH R21AI154363 NIH R01AI32819

Interleukin-2 signaling engages de novo cholesterol biosynthesis in regulatory T cells

Abstract In the absence of IL-2R signaling, Treg homeostasis is severely disrupted. This is accompanied by a decrease in the expression of enzymes related to cholesterol biosynthesis, but the function of this pathway in Tregs is unknown. To investigate this, we selectively ablated Sterol Regulatory Binding Element Protein 2 by crossing Srebp2flox/flox mice to Foxp3cre mice (Srebp2cKO). Consistent with published studies, homozygous Srebp2cKO mice are outwardly normal. However, when Srebp2cKO Tregs are placed in competition with wild-type Tregs, they are found at a reduced frequency in the spleen, lymph nodes and gut mucosa. In this setting, Srebp2cKO Tregs have reduced Foxp3 expression, suggesting that their function and/or stability may be impacted by altered cholesterol biosynthesis. These defects persist in lymphoid and non-lymphoid tissues when Tregs in competition are treated with an IL-2R agonist. In addition, a marked reduction in effector Treg differentiation is associated with Srebp2cKO Tregs, as expression of CD39, CD73, CD103, Klrg1 and ICOS is reduced while Bcl-2 and CD62L are increased. In response to IL-2R signaling, Srebp2cKO Tregs do not optimally upregulate CD25, which suggests a function for cholesterol biosynthesis in supporting the high affinity IL-2R. These results are consistent with a model whereby IL-2R signaling coordinates Treg cholesterol biosynthesis, which contributes to effector Treg development and raises the possibility that cholesterol biosynthesis could be a target in the therapeutic manipulation of Tregs. Supported by grants from NIH (F30 AI157211-01A1, RO1 AI148675-01)

CXCR1 participates in bone cancer pain induced by Walker 256 breast cancer cells in female rats.

Bone cancer pain (BCP) is a clinically intractable mixed pain, involving inflammation and neuropathic pain, and its mechanisms remain unclear. CXC chemokine receptor 1 (CXCR1, IL-8RA) and 2 (CXCR2, IL-8RB) are high-affinity receptors for interleukin 8 (IL8). According to previous studies, CXCR2 plays a crucial role in BCP between astrocytes and neurons, while the role of CXCR1 remains unclear. The objective of this study was to investigate the role of CXCR1 in BCP. We found that CXCR1 expression increased in the spinal dorsal horn. Intrathecal injection of CXCR1 siRNA effectively attenuated mechanical allodynia and pain-related behaviors in rats. It was found that CXCR1 was predominantly co-localized with neurons. Intrathecal injection of CXCR1-siRNA reduced phosphorylated JAK2/STAT3 protein levels and the NLRP3 inflammasome (NLRP3, caspase1, and IL-1β) levels. Furthermore, in vitro cytological experiments confirmed this conclusion. The study results suggest that the spinal chemokine receptor CXCR1 activation mediates BCP through JAK2/STAT3 signaling pathway and NLRP3 inflammasome (NLRP3, caspase1, and IL-1β).

Efficacy and antitumor activity of a mutant type of interleukin 2

Interleukin-2 (IL-2) is an important cytokine in survival, expansion, function of CD8+ T cells and natural killer cells in immunotherapy of melanoma and renal cell carcinomas. Its severe toxicity following binding to its high affinity IL-2 receptor alpha (IL-2Rα) has restricted its application in cancer patients. In the present study, we investigated the antitumor efficacy and cytotoxicity of a mutated human IL-2 previously designed by selective amino acid substitutions, and its reduced affinity towards high-affinity IL-2Rα (CD25) was approved compared to the wild type IL-2 (wtIL-2). Furthermore, their ability to induce PBMC cell proliferation, and interferon-gamma secretion was compared. The mutant IL-2 also represented higher antitumor activity and more efficient cytotoxicity than wild type hIL-2. The developed mutant IL-2 can be an alternative tool in IL-2 associated immunotherapy of various cancers.

Human IL-2Rɑ subunit binding modulation of IL-2 through a decline in electrostatic interactions: A computational and experimental approach.

Although high-dose IL-2 has clear antitumor effects, severe side effects like severe toxicity and activation of Tregs by binding of IL-2 to high-affinity IL-2R, hypotension, and vascular leak syndrome limit its applications as a therapeutic antitumor agent. Here in this study, a rational computational approach was employed to develop and design novel triple-mutant IL-2 variants with the aim of improving IL-2-based immunotherapy. The affinity of the mutants towards IL-2Rα was further computed with the aid of molecular dynamic simulations and umbrella sampling techniques and the obtained results were compared to those of wild-type IL-2. In vitro experiments by flow cytometry showed that the anti-CD25 mAb was able to bind to PBMC cells even after mutant 2 preincubation, however, the binding strength of the mutant to α-subunit was less than of wtIL-2. Additionally, reduction of IL-2Rα subunit affinity did not significantly disturb IL-2/IL2Rβγc subunits interactions.

Quantitative contributions of TNF receptor superfamily members to CD8+ T-cell responses.

T‐cell responses to infections and cancers are regulated by co‐signalling receptors grouped into the binary categories of co‐stimulation or co‐inhibition. The co‐stimulation TNF receptor superfamily (TNFRSF) members 4‐1BB, CD27, GITR and OX40 have similar signalling mechanisms raising the question of whether they have similar impacts on T‐cell responses. Here, we screened for the quantitative impact of these TNFRSFs on primary human CD8+ T‐cell cytokine production. Although both 4‐1BB and CD27 increased production, only 4‐1BB was able to prolong the duration over which cytokine was produced, and both had only modest effects on antigen sensitivity. An operational model explained these different phenotypes using shared signalling based on the surface expression of 4‐1BB being regulated through signalling feedback. The model predicted and experiments confirmed that CD27 co‐stimulation increases 4‐1BB expression and subsequent 4‐1BB co‐stimulation. GITR and OX40 displayed only minor effects on their own but, like 4‐1BB, CD27 could enhance GITR expression and subsequent GITR co‐stimulation. Thus, different co‐stimulation receptors can have different quantitative effects allowing for synergy and fine‐tuning of T‐cell responses.

High-dose IL-2/CD25 fusion protein amplifies vaccine-induced CD4+ and CD8+ neoantigen-specific T cells to promote antitumor immunity

BackgroundImmunization with tumor neoantigens is a promising vaccine approach to promote antitumor immunity due to their high immunogenicity, lack of expression in normal tissue, and preferential induction of tumor neoantigen-specific...

Targeted Association and Intracellular Delivery of Nanocargoes into Primary T Lymphocytes via Interleukin-2 Receptor-Mediated Endocytosis.

Despite the tremendous progress in immunotherapy regimens using T cells, efforts to modulate the functions of T cells are still significantly hampered by the lack of reliable methods to deliver various cargoes into the T cells. This ongoing challenge originates from the intrinsic resistance of T cells in taking up exogenous materials. Here, we strategically aimed to hijack the natural endocytosis of Interleukin-2 (IL2) by the activated T cells for the targeted association and intracellular delivery of cargoes in varying sizes. First, we carefully characterized the fluctuations in the expression levels of IL2 receptor (IL2R) subunits (CD25, CD122, and CD132) during the murine primary T cell cultures over 12 days. We identified the highest fraction of T cells that would express the high-affinity trimeric IL2R on Day 3. By examining the association and uptake efficiencies of IL2 molecules that are biotinylated via either random lysine-targeting chemical reaction (using NHS-PEG4-Biotin) or site-specific enzymatic modification (using Avitag sequence), we demonstrated that the most efficient delivery of cargo can be achieved by C-terminal conjugation. Upon confirmation of successful delivery of a small model cargo, streptavidin, we employed superparamagnetic iron oxide nanoparticles (SPIONs) as bigger model cargoes having core diameters of 50, 100, and 200 nm. We examined the association and intracellular delivery of the IL2-conjugated nanocargoes using flow cytometry, confocal laser scanning microscopy, and transmission electron microscopy. While cargoes of all tested sizes were successfully associated with the IL2R-expressing T cells in comparable efficiencies, the uptake efficiencies were inversely proportional to the sizes of the cargoes. Nevertheless, our current definitive report confirms that nanocargoes with a practical maximum size limit around 100-200 nm can be intracellularly delivered into activated primary T cells using IL2R-mediated endocytosis, which opens a new horizon for engineering and manufacturing of various T cell immunotherapeutics.

Abstract 1725: Short-term administration of high dose mIL-2/CD25 fusion protein elicits CD8+ T cell-driven anti-tumor immunity and memory

Abstract Recombinant IL-2 (rIL-2) promotes the differentiation, proliferation, and survival of antigen-activated T cells and induces potent anti-tumor activity. High dose (HD) rIL-2 broadly targets T effector (Teff) and NK cells. However, rIL-2 cancer therapy requires long-term infusions of high doses due to its short half-life and is associated with severe toxicities which limit efficacy. To circumvent these limitations, our lab has developed and is testing a new IL-2-based biologic, mIL-2/CD25, which can be used at high doses to promote anti-tumor immunity. mIL-2/CD25 is a fusion protein (FP) composed of mouse IL-2 fused to the mouse CD25 extracellular domain via a non-cleavable glycine-serine linker with selectivity toward the high affinity IL-2R. This FP has a much longer half-life (16 hr) than rIL-2 (15 min). At a low dose, mIL-2/CD25 selectively expands Tregs, but at a HD, Teff cells are also engaged. These properties allow for HD FP to readily expand activated endogenous tumor-reactive Teff cells, but not memory-phenotypic CD8+ T cells and NK cells. In the current study, we tested the extent short-term HD FP therapy activated tumor-reactive Teff cells to elicit efficacious anti-tumor immunity responses despite Treg stimulation. HD FP prolonged survival in mice bearing B16.F10 melanoma, MC-38 colon adenocarcinoma, or CT26 colon carcinoma. In the CT26 model, a significant increase in both the number and the frequency of CD8+ T cells was detected in the tumor microenvironment (TME) of treated mice. FP-dependent Treg expansion was observed in secondary lymphoid tissues but not the TME. This therapeutic approach, therefore, led to a higher CD8+ Teff to Treg ratio specifically in the TME. After FP treatment, CD8+ T cells isolated from the TME expressed lower levels of TOX, PD-1, and LAG-3, suggesting that they were less exhausted. T cell depletion studies using anti-CD8 revealed that CD8+ T cells are the major driver of the FP-induced anti-tumor response. Rechallenge of animals that had previously cleared CT26 due to FP treatment led to successful tumor rejection, showing that the FP supported anti-tumor memory. These findings demonstrate that mIL-2/CD25 amplifies recently activated tumor-reactive CD8+ Teff cells to generate efficacious anti-tumor responses that limit Treg-dependent negative regulation in the TME and lead to anti-tumor memory. Citation Format: Kathryn LaPorte, Rosmely Hernandez, Thomas Malek. Short-term administration of high dose mIL-2/CD25 fusion protein elicits CD8+ T cell-driven anti-tumor immunity and memory [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1725.

Retargeting IL-2 Signaling to NKG2D-Expressing Tumor-Infiltrating Leukocytes Improves Adoptive Transfer Immunotherapy.

Ex vivo expansion followed by reinfusion of tumor-infiltrating leukocytes (TILs) has been used successfully for the treatment of multiple malignancies. Most protocols rely on the use of the cytokine IL-2 to expand TILs prior to reinfusion. In addition, TIL administration relies on systemic administration of IL-2 after reinfusion to support transferred cell survival. The use of IL-2, however, can be problematic because of its preferential expansion of regulatory T and myeloid cells as well as its systemic side effects. In this study, we describe the use of a novel IL-2 mutant retargeted to NKG2D rather than the high-affinity IL-2R for TIL-mediated immunotherapy in a murine model of malignant melanoma. We demonstrate that the NKG2D-retargeted IL-2 (called OMCPmutIL-2) preferentially expands TIL-resident CTLs, such as CD8+ T cells, NK cells, and γδT cells, whereas wild-type IL-2 provides a growth advantage for CD4+Foxp3+ T cells as well as myeloid cells. OMCPmutIL-2-expanded CTLs express higher levels of tumor-homing receptors, such as LFA-1, CD49a, and CXCR3, which correlate with TIL localization to the tumor bed after i.v. injection. Consistent with this, OMCPmutIL-2-expanded TILs provided superior tumor control compared with those expanded in wild-type IL-2. Our data demonstrate that adoptive transfer immunotherapy can be improved by rational retargeting of cytokine signaling to NKG2D-expressing CTLs rather than indiscriminate expansion of all TILs.

Individual Patient Dose-Escalated Low-Dose Interleukin-2 for Steroid-Refractory Chronic Graft-Vs.-Host Disease in Children and Adults: Safety, Efficacy and Immune Correlates

CD4+CD25+FoxP3+ regulatory T cells (Treg) are broadly suppressive and play a central role in the prevention of chronic graft-versus-host disease (cGVHD) after allogeneic hematopoietic cell transplantation (HCT). Daily subcutaneous (SC) low-dose interleukin-2 (IL-2) at a fixed dose of 1x106 IU/m2/day in adult patients with refractory cGVHD induces selective Treg expansion and leads to clinical responses in 50-60% of evaluable participants (NEJM 2011, Blood 2016). During daily fixed-dose IL-2 therapy, plasma IL-2 levels rose rapidly by week 1, but subsequently decreased over time. The lower IL-2 levels were associated with a decline in Treg proliferation despite daily IL-2 administration (Sci Transl Med 2013), possibly due to IL-2 sequestration via binding to constitutively-expressed high affinity IL-2 receptors on Treg. We reasoned that IL-2 dose escalation at the time of anticipated fall in plasma IL-2 levels would avoid tachyphylaxis and maximize IL-2 induced Treg numbers in vivo.We conducted a phase 1 trial of individual patient IL-2 dose escalation over 8 weeks in adult and pediatric patients with steroid-refractory cGVHD. Daily SC IL-2 was initiated at 0.67x106 and 0.33x106 IU/m2/day in the adult and pediatric cohorts, respectively. Each participant had dose escalations at weeks 2 and 4 to a maximum dose of 2x106 IU/m2/day in adults and 1x106 IU/m2/day in children. We studied 18 HCT recipients (10 adult: 100% HLA-matched, 100% PBSC grafts, 40% prior aGVHD; 8 pediatric: 87.5% HLA-matched, 87.5% BM grafts, 28.6% prior aGVHD). Median age was 57 years (range, 33-71) in the adult cohort and 12 years (range, 5-22) in the pediatric cohort. The median time from HCT and from cGVHD onset to start of IL-2 treatment was 3 years (range, 1-12.1) and 597 days (range, 234-4336) respectively. Participants had a median of 2 cGVHD organ sites (range, 1-5) and 3 prior cGVHD therapies (range, 1-4) at enrollment. The cohorts did not differ in terms of time since cGVHD onset and number of failed therapies prior to enrollment.Individually dose-escalated IL-2 was well tolerated in children with 1 participant requiring dose reduction for electrolyte imbalances. In the adult cohort, 1 participant withdrew due to cGVHD progression, 1 required dose reduction for injection site reactions and 2 were unevaluable (1 IL-2 hold >1 month, 1 non-compliance). Seven grade 3 AEs were reported for six participants (electrolyte imbalance, vomiting, infection, increased ALT and soft tissue neoplasm); none relapsed. At week 8, objective cGVHD responses (PR) were seen in 7 of 8 pediatric participants (88%), but in only 1 of 8 evaluable adult participants (13%). cGVHD response sites included skin (n=4), joint/fascia/muscle (n=1), lung (n=4), and GI tract (n=2). Eight pediatric and 4 adult participants with clinical benefit (PR or SD with minor response) continued extended duration IL-2 therapy up to 120 weeks.Plasma IL-2 levels were higher in adults at weeks 1 and 2, but immune responses were similar between the 2 cohorts. Dose escalated IL-2 induced a >10-fold increase in median Treg count/µL that peaked at week 6. There were no significant changes in CD4 Tcon, CD8 T cell or B cell count. NK cell count increased >5-fold by week 8. The median Treg:Tcon ratio increased 6-fold from a baseline of 0.05 (Q1-Q3, 0.024-0.114) to a week 5 peak of 0.312 (Q1-Q3, 0.203-0.37). Compared with fixed daily dosing of IL-2 (Blood 2016), the individually dose escalated IL-2 schedule had a slower initial rise in Treg number and Treg:Tcon ratio (Figure 1). This likely reflects the lower starting doses in this study. The maximum IL-2 dose in the adults was twice the previously defined MTD but did not improve Treg expansion. Despite lower IL-2 doses, pediatric patients had a superior clinical response and a trend toward a better immunologic response compared with the adults.We demonstrate for the first time that low-dose IL-2 is safe in children with advanced steroid-refractory cGVHD and results in a high clinical response rate. A maximum dose of 1x106 IU/m2/day was well tolerated by pediatric patients in the extended duration phase and durably maintained Treg numbers above baseline. Five pediatric patients that continued IL-2 therapy for >20 weeks have reduced or discontinued steroid therapy. In adults, intrapatient dose escalation above fixed-dose MTD was not clinically tolerated and did not result in greater Treg expansion or clinical improvement relative to fixed daily dosing. [Display omitted] DisclosuresNikiforow:Kite Therapeutics: Membership on an entity's Board of Directors or advisory committees. Armand:Sequenta/Adaptive: Research Funding; Affimed: Research Funding; Roche: Research Funding; Merck & Co., Inc.: Consultancy, Research Funding; Infinity: Consultancy; Genmab: Consultancy; Bristol-Myers Squibb: Consultancy, Research Funding; Otsuka: Research Funding; Pfizer: Consultancy, Research Funding; Tensha: Research Funding; Sigma Tau: Research Funding. Antin:Gentium SpA/Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Koreth:Prometheus Labs: Research Funding; Amgen, Inc: Consultancy.

Interleukin-2 PET imaging in patients with metastatic melanoma before and during immune checkpoint inhibitor therapy

PurposeImmune checkpoint inhibitors can induce a T cell–mediated anti-tumor immune response in patients with melanoma. Visualizing T cell activity using positron emission tomography (PET) might allow early insight into treatment efficacy. Activated tumor–infiltrating T cells express the high-affinity interleukin-2 receptor (IL-2R). Therefore, we performed a pilot study, using fluorine-18-labeled IL-2 ([18F]FB-IL2 PET), to evaluate whether a treatment-induced immune response can be detected.MethodsPatients with metastatic melanoma received ~ 200 MBq [18F]FB-IL2 intravenously, followed by a PET/CT scan before and during immune checkpoint inhibitor therapy. [18F]FB-IL2 uptake was measured as standardized uptake value in healthy tissues (SUVmean) and tumor lesions (SUVmax). Response to therapy was assessed using RECIST v1.1. Archival tumor tissues were used for immunohistochemical analyses of T cell infiltration.ResultsBaseline [18F]FB-IL2 PET scans were performed in 13 patients. SUVmean at baseline was highest in the kidneys (14.2, IQR: 11.6–18.0) and liver (10.6, IQR: 8.6–13.4). In lymphoid tissues, uptake was highest in spleen (10.9, IQR: 8.8–12.4) and bone marrow (2.5, IQR: 2.1–3.0). SUVmax in tumor lesions (n = 41) at baseline was 1.9 (IQR: 1.7–2.3). In 11 patients, serial imaging was performed, three at week 6, seven at week 2, and one at week 4. Median [18F]FB-IL2 tumor uptake decreased from 1.8 (IQR: 1.7–2.1) at baseline to 1.7 (IQR: 1.4–2.1) during treatment (p = 0.043). Changes in [18F]FB-IL2 tumor uptake did not correlate with response. IL-2R expression in four archival tumor tissues was low and did not correlate with baseline [18F]FB-IL2 uptake. No [18F]FB-IL2-related side effects occurred.ConclusionPET imaging of the IL-2R, using [18F]FB-IL2, is safe and feasible. In this small patient group, serial [18F]FB-IL2-PET imaging did not detect a treatment-related immune response.Trial registrationClinicaltrials.gov: NCT02922283; EudraCT: 2014-003387.20

T cell signaling and Treg dysfunction correlate to disease kinetics in IL-2R\u03b1-KO autoimmune mice

IL-2Rα, in part, comprises the high affinity receptor for IL-2, a cytokine important in immune proliferation, activation, and regulation. IL-2Rα deficient mice (IL-2Rα-KO) develop systemic autoimmune disease and die from severe anemia between 18 and 80 days of age. These mice develop kinetically distinct autoimmune progression, with approximately a quarter dying by 21 days of age and half dying after 30 days. This research aims to define immune parameters and cytokine signaling that distinguish cohorts of IL-2Rα-KO mice that develop early- versus late-stage autoimmune disease. To investigate these differences, we evaluated complete blood counts (CBC), antibody binding of RBCs, T cell numbers and activation, hematopoietic progenitor changes, and signaling kinetics, during autoimmune hemolytic anemia (AIHA) and bone marrow failure. We identified several alterations that, when combined, correlate to disease kinetics. Early onset disease correlates with anti-RBC antibodies, lower hematocrit, and reduced IL-7 signaling. CD8 regulatory T cells (Tregs) have enhanced apoptosis in early disease. Further, early and late end stage disease, while largely similar, had several differences suggesting distinct mechanisms drive autoimmune disease kinetics. Therefore, IL-2Rα-KO disease pathology rates, driven by T cell signaling, promote effector T cell activation and expansion and Treg dysfunction.

CD122-Selective IL2 Complexes Reduce Immunosuppression, Promote Treg Fragility, and Sensitize Tumor Response to PD-L1 Blockade.

The IL2 receptor (IL2R) is an attractive cancer immunotherapy target that controls immunosuppressive T regulatory cells (Treg) and antitumor T cells. Here we used IL2Rβ-selective IL2/anti-IL2 complexes (IL2c) to stimulate effector T cells preferentially in the orthotopic mouse ID8agg ovarian cancer model. Despite strong tumor rejection, IL2c unexpectedly lowered the tumor microenvironmental CD8+/Treg ratio. IL2c reduced tumor microenvironmental Treg suppression and induced a fragile Treg phenotype, helping explain improved efficacy despite numerically increased Tregs without affecting Treg in draining lymph nodes. IL2c also reduced Treg-mediated, high-affinity IL2R signaling needed for optimal Treg functions, a likely mechanism for reduced Treg suppression. Effector T-cell IL2R signaling was simultaneously improved, suggesting that IL2c inhibits Treg functions without hindering effector T cells, a limitation of most Treg depletion agents. Anti-PD-L1 antibody did not treat ID8agg, but adding IL2c generated complete tumor regressions and protective immune memory not achieved by either monotherapy. Similar anti-PD-L1 augmentation of IL2c and degradation of Treg functions were seen in subcutaneous B16 melanoma. Thus, IL2c is a multifunctional immunotherapy agent that stimulates immunity, reduces immunosuppression in a site-specific manner, and combines with other immunotherapies to treat distinct tumors in distinct anatomic compartments. SIGNIFICANCE: These findings present CD122-targeted IL2 complexes as an advancement in cancer immunotherapy, as they reduce Treg immunosuppression, improve anticancer immunity, and boost PD-L1 immune checkpoint blockade efficacy in distinct tumors and anatomic locations.

Sustained IL-2R signaling of limited duration by high-dose mIL-2/mCD25 fusion protein amplifies tumor-reactive CD8+ T cells to enhance antitumor immunity.

High-dose IL-2 induces cancer regression but its therapeutic use is limited due to high toxicities resulting from its broad cell targeting. In one strategy to overcome this limitation, IL-2 has been modified to selectively target the intermediate affinity IL-2R that broadly activates memory-phenotypic CD8+ T and NK cells, while minimizing Treg-associated tolerance. In this study, we modeled an alternative strategy to amplify tumor antigen-specific TCR transgenic CD8+ T cells through limited application of a long-acting IL-2 fusion protein, mIL-2/mCD25, which selectively targets the high-affinity IL-2R. Here, mice were vaccinated with a tumor antigen and high-dose mIL-2/mCD25 was applied to coincide with the induction of the high affinity IL-2R on tumor-specific T cells. A single high dose of mIL-2/mCD25, but not an equivalent amount of IL-2, amplified the frequency and function of tumor-reactive CD8+ T effector (Teff) and memory cells. These mIL-2/mCD25-dependent effects relied on distinctive requirements for TLR signals during priming of CD8+ tumor-specific T cells. The mIL-2/mCD25-amplified tumor-reactive effector and memory T cells supported long-lasting antitumor responses to B16-F10 melanoma. This regimen only transiently increased Tregs, yielding a favorable Teff-Treg ratio within the tumor microenvironment. Notably, mIL-2/mCD25 did not increase non-tumor-specific Teff or NK cells within tumors, further substantiating the specificity of mIL-2/mCD25 for tumor antigen-activated T cells. Thus, the selectivity and persistence of mIL-2/mCD25 in conjunction with a tumor vaccine supports antitumor immunity through a mechanism that is distinct from recombinant IL-2 or IL-2-based biologics that target the intermediate affinity IL-2R.

Abstract IA16: Role of PI3K signaling in T cell-mediated immune responses

Abstract A number of receptors are capable of activating the PI3K pathway in T cells, most prominently the T-cell receptor for antigen (TCR), the costimulatory receptor CD28, and the interleukin 2 receptor (IL-2R). PI3K signaling is critical for the initiation of effector T-cell responses, and activated multiple central downstream cascades including mTOR. Consistent with this, drugs that target mTOR, such as rapamycin, are effective inhibitors of T cell-mediated immune responses. Despite the important role of PI3K in T-cell activation, mTOR inhibition has been reported to “spare” regulatory T-cell (Treg) responses. This was of particular interest as Tregs, in contrast to all other T cells, constitutively express the high-affinity IL-2R, and thus should be poised for continual PI3K activation. Tregs, defined as cells that express the lineage-defining transcription factor Foxp3, are required for normal immune homeostasis. Foxp3-deficient mice (scurfy) and humans (patients with IPEX) are characterized by widespread and severe multiorgan autoimmunity and inflammation. As well, deletion of Tregs in adult mice leads to rapid and fulminant autoimmunity and death. In a series of studies conducted by members of my group over the past several years, as well as a variety of other laboratories, we have gained insight into the role of PI3K signals in Tregs, and a complex picture has emerged. We have observed that signals that elicit PI3K pathway activation in stimulated T cells, such as the cytokine IL-2, fail to do so in Tregs, despite the fact that Tregs express the IL-2R. Moreover, we have found that this is a selective “defect” in IL-2R signaling as the other major pathway linked to this receptor, STAT5, is intact. Specific loss of PI3K signaling in Tregs can be linked to expression of the lipid phosphatase PTEN. All T cells express PTEN in their resting state. However, while “conventional” T cells (i.e., non-Tregs) downregulate PTEN expression upon activation, Tregs uniquely do not. To test the importance of maintained PTEN expression in Tregs, we created mice with constitutive and with inducible deletion of PTEN specifically in Foxp3+ Tregs. These mice developed a dramatic phenotype of lupus-like autoimmunity, despite the presence of large numbers of Tregs, indeed more than in control mice. Moreover, we observed that loss of PTEN was followed by lineage instability, i.e., loss of Foxp3, and expression of proinflammatory cytokines such as IL-17 and IFNg. PI3K signals activate pathways important for T-cell metabolism, including c-myc, HIF-1a, and mTOR, and promote aerobic glycolysis. In contrast to most activated T cells, Tregs have been reported to be more reliant on fatty acid oxidation for their energy demands, and indeed loss of PTEN in Tregs dramatically augments aerobic glycolysis in these cells. However, most of the studies of Treg metabolism have focused on cells that were differentiated to become Tregs in vitro. In this system, naïve T cells are activated in the presence of the anti-inflammatory cytokine TGF-b, which induces them to express Foxp3. Such cells, “iTregs,” are easy to generate in large numbers and believed to be induced in vivo when antigen is encountered in noninflammatory settings in visceral organs and tissues. However, most T cells in lymphoid organs are thought to have originated in the thymus, are called tTregs, and are important for the prevention of immune responses to self-antigens. We have recently characterized the metabolism of these two Treg subsets. While, as reported, iTregs make minimal use of glycolysis, tTregs are in fact as glycolytic as effector T cells. We have further found that exposure of tTregs to TGF-b represses PI3K-mediated mTOR signaling, inhibits glucose transporter expression, and reprograms their metabolism to favor oxidative phosphorylation. Conversely, replicating the effects of inflammation via elevation of PI3K signaling has minimal effects on tTregs but dramatically enhances the glycolysis of normally oxidative iTregs, resulting in reduction of Foxp3 expression. Collectively, these findings suggest unique signaling and metabolic demands of Tregs and Treg subsets that may be leveraged in the design of therapeutics, both in vivo agents and adoptive cellular therapies. Citation Format: Laurence Turka. Role of PI3K signaling in T cell-mediated immune responses [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr IA16.