Receptor occupancy and blocking of STAT5 signaling by an anti-IL-7 receptor α antibody in cynomolgus monkeys

The IL-7R antagonist lusvertikimab reduces leukemic burden in xenograft ALL via antibody-dependent cellular phagocytosis

ABSTRACT

Acute lymphoblastic leukemia (ALL) arises from the uncontrolled proliferation of B-cell precursors (BCP-ALL) or T cells (T-ALL). Current treatment protocols obtain high cure rates in children but are based on toxic polychemotherapy. Novel therapies are urgently needed, especially in relapsed/refractory (R/R) disease, high-risk (HR) leukemias and T-ALL, in which immunotherapy approaches remain scarce. Although the interleukin-7 receptor (IL-7R) plays a pivotal role in ALL development, no IL-7R-targeting immunotherapy has yet reached clinical application in ALL. The IL-7Rα chain (CD127)-targeting IgG4 antibody lusvertikimab (LUSV; formerly OSE-127) is a full antagonist of the IL-7R pathway, showing a good safety profile in healthy volunteers. Here, we show that ∼85% of ALL cases express surface CD127. We demonstrate significant in vivo efficacy of LUSV immunotherapy in a heterogeneous cohort of BCP- and T-ALL patient-derived xenografts (PDX) in minimal residual disease (MRD) and overt leukemia models, including R/R and HR leukemias. Importantly, LUSV was particularly effective when combined with polychemotherapy in a phase 2-like PDX study with CD127high samples leading to MRD-negativity in >50% of mice treated with combination therapy. Mechanistically, LUSV targeted ALL cells via a dual mode of action comprising direct IL-7R antagonistic activity and induction of macrophage-mediated antibody-dependent cellular phagocytosis (ADCP). LUSV-mediated in vitro ADCP levels significantly correlated with CD127 expression levels and the reduction of leukemia burden upon treatment of PDX animals in vivo. Altogether, through its dual mode of action and good safety profile, LUSV may represent a novel immunotherapy option for any CD127+ ALL, particularly in combination with standard-of-care polychemotherapy.

A Bispecific Modeling Framework Enables the Prediction of Efficacy, Toxicity, and Optimal Molecular Design of Bispecific Antibodies Targeting MerTK

Inhibiting MerTK on macrophages is a promising therapeutic strategy for augmenting anti-tumor immunity. However, blocking MerTK on retinal pigment epithelial cells (RPEs) results in retinal toxicity. Bispecific antibodies (bsAbs) containing an anti-MerTK therapeutic and anti-PD-L1 targeting arm were developed to reduce drug binding to MerTK on RPEs, since PD-L1 is overexpressed on macrophages but not RPEs. In this study, we present a modeling framework using in vitro receptor occupancy (RO) and pharmacokinetics (PK) data to predict efficacy, toxicity, and therapeutic index (TI) of anti-MerTK bsAbs. We first used simulations and in vitro RO data of anti-MerTK monospecific antibody (msAb) to estimate the required MerTK RO for in vivo efficacy and toxicity. Using these estimated RO thresholds, we employed our model to predict the efficacious and toxic doses for anti-MerTK bsAbs with varying affinities for MerTK. Our model predicted the highest TI for the anti-MerTK/PD-L1 bsAb with an attenuated MerTK binding arm, which was consistent with in vivo efficacy and toxicity observations. Subsequently, we used the model, in combination with sensitivity analysis and parameter scans, to suggest an optimal molecular design of anti-MerTK bsAb with the highest predicted TI in humans. Our prediction revealed that this optimized anti-MerTK bsAb should contain a MerTK therapeutic arm with relatively low affinity, along with a high affinity targeting arm that can bind to a low abundance target with slow turnover rate. Overall, these results demonstrated that our modeling framework can guide the rational design of bsAbs.

Flow cytometry and receptor occupancy in immune-oncology

Introduction: Immunotherapies are focused on strategies that alter immune responses, using antibodies that binds to receptors on different immune cell subsets and either activate or suppress their functions depending on the immune response being targeted. Hence, the necessity of developing assays that assess the functional and biological effect of a therapeutic on its target. When incorporated into high-parameter flow cytometry panels, receptor occupancy assay can simultaneously evaluate receptor expression and drug occupancy on defined cell subsets, which can provide information related to functional effects, and safety.Areas covered: This review focuses on the importance of developing, optimizing, and validating a robust Receptor Occupancy Assay (ROA) to improve dose selection, pharmacology monitoring and safety mainly in clinical settings.Expert opinion: The designing of an ROA can be challenging and can lead to exaggerated pharmacology if not accurately developed, optimized, and validated. However, improvements in our understanding of epitopes, binding, affinities, and pharmacological effects may lead to improved antibody drug targeting and receptor evaluation.

Development of a long-term, IL7 dependent cell death rescue assay in CD4+ T-cells

Interfering with signalling pathways by targeting cell surface proteins has become an important strategy in the development of novel therapeutic agents. Notably, interfering with cytokine signalling revolutionised the treatment of chronic diseases. Cytokines can induce a range of effects that are not always accounted for in assays detecting cytokine binding to cell surface receptors and/or proximal signalling interference. Hence, robust assays are needed to characterise the activity of potential drug candidates targeting such effects. We chose interleukin-7 (IL7) as a cytokine model due to its long-term effect on T-cells. In this report we describe the development and refinement of an in vitro assay for measuring the long-term effect of IL7, more specifically on CD4+ T-cells, while the assay could be adapted to look at CD8+ T-cells. PBMCs and/or purified CD4+ T-cells stained with VPD450 (cell cycle dye) were expanded for 5 days using the mitogen Phytohemagglutinin and/or CD3/CD28 agonists. This resulted in cell proliferation (VPD450 dilution) and activation-induced cell death (7-AAD uptake) which was rescued by the addition of IL7, resulting in cell survival over a further 5 days. JAK-inhibitor (Tofactinib) or a blocking anti-IL7Rα antibody (clone R34.34) abolished cell survival suggesting antagonism, while another antibody (clone A019D5) displayed an agonist effect. These results were confirmed at the proximal signalling level using an IL7/STAT5-luciferase reporter assay. This novel assay for a biological long term effect may be useful for the characterisation of potential therapeutic drugs targeting the IL7/IL7R in CD4+ T-cells.

Modulation of Signaling Mediated by TSLP and IL-7 in Inflammation, Autoimmune Diseases, and Cancer

Thymic Stromal Lymphopoietin (TSLP) and Interleukin-7 (IL-7) are widely studied cytokines within distinct branches of immunology. On one hand, TSLP is crucially important for mediating type 2 immunity at barrier surfaces and has been linked to widespread allergic and inflammatory diseases of the airways, skin, and gut. On the other hand, IL-7 operates at the foundations of T-cell and innate lymphoid cell (ILC) development and homeostasis and has been associated with cancer. Yet, TSLP and IL-7 are united by key commonalities in their structure and the structural basis of the receptor assemblies they mediate to initiate cellular signaling, in particular their cross-utilization of IL-7Rα. As therapeutic targeting of TSLP and IL-7 via diverse approaches is reaching advanced stages and in light of the plethora of mechanistic and structural data on receptor signaling mediated by the two cytokines, the time is ripe to provide integrated views of such knowledge. Here, we first discuss the major pathophysiological roles of TSLP and IL-7 in autoimmune diseases, inflammation and cancer. Subsequently, we curate structural and mechanistic knowledge about receptor assemblies mediated by the two cytokines. Finally, we review therapeutic avenues targeting TSLP and IL-7 signaling. We envision that such integrated view of the mechanism, structure, and modulation of signaling assemblies mediated by TSLP and IL-7 will enhance and fine-tune the development of more effective and selective approaches to further interrogate the role of TSLP and IL-7 in physiology and disease.

Model-Based Characterization of the Pharmacokinetics, Target Engagement Biomarkers, and Immunomodulatory Activity of PF-06342674, a Humanized mAb Against IL-7 Receptor-α, in Adults with Type 1 Diabetes

IL-7 receptor-α (IL-7Rα) blockade has been shown to reverse autoimmune diabetes in the non-obese diabetic mouse by promoting inhibition of effector T cells and consequently altering the balance of regulatory T (T_reg) and effector memory (T_EM) cells. PF-06342674 is a humanized monoclonal antibody that binds to and inhibits the function of IL-7Rα. In the current phase 1b study, subjects with type 1 diabetes (T1D) received subcutaneous doses of either placebo or PF-06342674 (1, 3, 8 mg/kg/q2w or 6 mg/kg/q1w) for 10 weeks and were followed up to 18 weeks. Nonlinear mixed effects models were developed to characterize the pharmacokinetics (PK), target engagement biomarkers, and immunomodulatory activity. PF-06342674 was estimated to have 20-fold more potent inhibitory effect on T_EM cells relative to T_reg cells resulting in a non-monotonic dose-response relationship for the T_reg:T_EM ratio, reaching maximum at ~ 3 mg/kg/q2w dose. Target-mediated elimination led to nonlinear PK with accelerated clearance at lower doses due to high affinity binding and rapid clearance of the drug-target complex. Doses ≥ 3 mg/kg q2w result in sustained PF-06342674 concentrations higher than the concentration of cellular IL-7 receptor and, in turn, maintain near maximal receptor occupancy over the dosing interval. The results provide important insight into the mechanism of IL-7Rα blockade and immunomodulatory activity of PF-06342674 and establish a rational framework for dose selection for subsequent clinical trials of PF-06342674. Furthermore, this analysis serves as an example of mechanistic modeling to support dose selection of a drug candidate in the early phases of development.

Interleukin-7 receptor blockade by an anti-CD127 monoclonal antibody in nonhuman primate kidney transplantation

IL-7 is an important cytokine for T cell lymphopoiesis. Blockade of the IL-7 signaling pathway has been shown to induce long-term graft survival or graft tolerance in murine transplant models through inhibiting T cell homeostasis and favoring immunoregulation. In this study, we assessed for the first time the effects of a blocking anti-human cluster of differentiation 127 (CD127) mAb administered in combination with low-dose tacrolimus or thymoglobulin in a life-sustaining kidney allograft model in baboons. Contrary to our expectation, the addition of an anti-CD127 mAb to the treatment protocols did not prolong graft survival compared to low-dose tacrolimus alone or thymoglobulin alone. Anti-CD127 mAb administration led to full CD127 receptor occupancy during the follow-up period. However, all treated animals lost their kidney graft between 1 week and 2 weeks after transplantation. Unlike in rodents, in nonhuman primates, anti-CD127 mAb treatment does not decrease the absolute numbers of lymphocyte and lymphocyte subsets and does not effectively inhibit postdepletional T cell proliferation and homeostasis, suggesting that IL-7 is not a limiting factor for T cell homeostasis in primates.

Flip the coin: IL-7 and IL-7R in health and disease

The cytokine IL-7 and its receptor, IL-7R, are critical for T cell and, in the mouse, B cell development, as well as differentiation and survival of naive T cells, and generation and maintenance of memory T cells. They are also required for innate lymphoid cell (ILC) development and maintenance, and consequently for generation of lymphoid structures and barrier defense. Here we discuss the central role of IL-7 and IL-7R in the lymphoid system and highlight the impact of their deregulation, placing a particular emphasis on their 'dark side' as promoters of cancer development. We also explore therapeutic implications and opportunities associated with either positive or negative modulation of the IL-7-IL-7R signaling axis.

IL-7 receptor influences anti-TNF responsiveness and T cell gut homing in inflammatory bowel disease

It remains unknown what causes inflammatory bowel disease (IBD), including signaling networks perpetuating chronic gastrointestinal inflammation in Crohn's disease (CD) and ulcerative colitis (UC), in humans. According to an analysis of up to 500 patients with IBD and 100 controls, we report that key transcripts of the IL-7 receptor (IL-7R) pathway are accumulated in inflamed colon tissues of severe CD and UC patients not responding to either immunosuppressive/corticosteroid, anti-TNF, or anti-α4β7 therapies. High expression of both IL7R and IL-7R signaling signature in the colon before treatment is strongly associated with nonresponsiveness to anti-TNF therapy. While in mice IL-7 is known to play a role in systemic inflammation, we found that in humans IL-7 also controlled α4β7 integrin expression and imprinted gut-homing specificity on T cells. IL-7R blockade reduced human T cell homing to the gut and colonic inflammation in vivo in humanized mouse models, and altered effector T cells in colon explants from UC patients grown ex vivo. Our findings show that failure of current treatments for CD and UC is strongly associated with an overexpressed IL-7R signaling pathway and point to IL-7R as a relevant therapeutic target and potential biomarker to fill an unmet need in clinical IBD detection and treatment.

Anti-IL-7 receptor α monoclonal antibody (GSK2618960) in healthy subjects - a randomized, double-blind, placebo-controlled study

Aim

Interleukin (IL)‐7 signalling modulates T cell activity and is implicated in numerous autoimmune diseases. The present study investigated the safety, pharmacokinetics, target engagement, pharmacodynamics and immunogenicity of GSK2618960, an IL‐7 receptor‐α subunit (CD127) monoclonal antibody.

Methods

A double‐blind (sponsor‐unblind) study of a single intravenous infusion of either GSK2618960 (0.6 mg kg^–1 or 2.0 mg kg^–1) or placebo was carried out in 18 healthy subjects over 24 weeks.

Results

GSK2618960 was well tolerated; there were no serious or significant adverse events. The observed half‐life was 5 (±1) days (2.0 mg kg^–1), with nonlinear pharmacokinetics. Full receptor occupancy (>95%) was observed until day 8 (0.6 mg kg^–1) and day 22 (2.0 mg kg^–1). Maximal inhibition of IL‐7‐mediated signal transducer and activator of transcription 5 (STAT5) phosphorylation was observed in 5/6 subjects until day 22 (2.0 mg kg^–1). Mean circulating IL‐7 and soluble receptor (CD127) levels were increased above baseline during days 2 and 15 (0.6 mg kg^–1) and days 2 and 22 (2.0 mg kg^–1). No meaningful changes were observed in absolute numbers or proportions of immune cell populations or inflammatory cytokine profiles (IL‐6, tumour necrosis factor‐α, interferon‐γ, IL‐2). Persistent antidrug antibodies (ADAs) were detected in 5/6 subjects administered a dose of 0.6 mg kg^–1 (neutralizing in 2/6) and in 6/6 subjects administered 2.0 mg kg^–1 (neutralizing in 5/6).

Conclusion

GSK2618960 was well tolerated and blocked IL‐7 receptor signalling upon full target engagement. Although there was no discernible impact on peripheral T cell subsets in healthy subjects, GSK2618960 may effectively modulate the autoinflammatory activity of pathogenic T cells in diseased tissue. A relatively short half‐life is likely the result of target‐mediated rather than ADA‐mediated clearance.

IL-7 receptor blockade blunts antigen-specific memory T cell responses and chronic inflammation in primates

Targeting the expansion of pathogenic memory immune cells is a promising therapeutic strategy to prevent chronic autoimmune attacks. Here we investigate the therapeutic efficacy and mechanism of new anti-human IL-7Rα monoclonal antibodies (mAb) in non-human primates and show that, depending on the target epitope, a single injection of antagonistic anti-IL-7Rα mAbs induces a long-term control of skin inflammation despite repeated antigen challenges in presensitized monkeys. No modification in T cell numbers, phenotype, function or metabolism is observed in the peripheral blood or in response to polyclonal stimulation ex vivo. However, long-term in vivo hyporesponsiveness is associated with a significant decrease in the frequency of antigen-specific T cells producing IFN-γ upon antigen restimulation ex vivo. These findings indicate that chronic antigen-specific memory T cell responses can be controlled by anti-IL-7Rα mAbs, promoting and maintaining remission in T-cell mediated chronic inflammatory diseases.