First-in-Human Study in Healthy Subjects with the Noncytotoxic Monoclonal Antibody OSE-127, a Strict Antagonist of IL-7Rα.

OSE-127 is a humanized mAb targeting the IL-7Rα-chain (CD127), under development for inflammatory and autoimmune disease treatment. It is a strict antagonist of the IL-7R pathway, is not internalized by target cells, and is noncytotoxic. In this work, a first-in-human, phase I, randomized, double-blind, placebo-controlled, single-center study was carried out to determine the safety, pharmacokinetics, pharmacodynamics, and immunogenicity of OSE-127 administration. Sixty-three healthy subjects were randomly assigned to nine groups: six single ascending dose groups with i.v. administration (0.002-10 mg/kg), a single s.c. treatment group (1 mg/kg), and two double i.v. injection groups (6 or 10 mg/kg). Subjects were followed during <146 d. OSE-127's pharmacokinetic half-life after a single dose increased from 4.6 (1 mg/kg) to 11.7 d (10 mg/kg) and, after a second dose, from 12.5 (6 mg/kg) to 16.25 d (10 mg/kg). Receptor occupancy was ≥95% at doses ≥0.02 mg/kg, and this saturation level was maintained >100 d after two i.v. infusions at 10 mg/kg. IL-7 consumption was inhibited by OSE-127 administration, as demonstrated by a decreased IL-7 pathway gene signature in peripheral blood cells and by ex vivo T lymphocyte restimulation experiments. OSE-127 was well tolerated, with no evidence of cytokine-release syndrome and no significant alteration of blood lymphocyte counts or subset populations. Altogether, the observed lack of significant lymphopenia or serious adverse events, concomitant with the dose-dependent inhibition of IL-7 consumption by target cells, highlights that OSE-127 may show clinical activity in IL-7R pathway-involved diseases.

SIRPα/CD47 axis controls the maintenance of transplant tolerance sustained by myeloid-derived suppressor cells.

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature hematopoietic precursors known to suppress immune responses. Interaction of SIRP alpha (SIRPα), expressed by myeloid cells, with the ubiquitous receptor CD47 is an important immune checkpoint of the innate response regulating macrophages and dendritic cells functions. We previously described that MDSC expressing SIRPα accumulated after transplantation and maintained kidney allograft tolerance. However, the role of the SIRPα/CD47 axis on MDSC function remained unknown. Here, we found that blocking SIRPα or CD47 with monoclonal antibodies (mAbs) induced differentiation of MDSC into myeloid cells overexpressing MHC class II, CD86 costimulatory molecule and increased secretion of macrophage-recruiting chemokines (eg, MCP-1). Using a model of long-term kidney allograft tolerance sustained by MDSC, we observed that administration of blocking anti-SIRPα or CD47 mAbs induced graft dysfunction and rejection. Loss of tolerance came along with significant decrease of MDSC and increase in MCP-1 concentration in the periphery. Graft histological and transcriptomic analyses revealed an inflammatory (M1) macrophagic signature at rejection associated with overexpression of MCP-1 mRNA and protein in the graft. These findings indicate that the SIRPα-CD47 axis regulates the immature phenotype and chemokine secretion of MDSC and contributes to the induction and the active maintenance of peripheral acquired immune tolerance.

IL-15 Trans-Signaling with the Superagonist RLI Promotes Effector/Memory CD8+ T Cell Responses and Enhances Antitumor Activity of PD-1 Antagonists.

Tumors with the help of the surrounding environment facilitate the immune suppression in patients, and immunotherapy can counteract this inhibition. Among immunotherapeutic strategies, the immunostimulatory cytokine IL-15 could represent a serious candidate for the reactivation of antitumor immunity. However, exogenous IL-15 may have a limited impact on patients with cancer due to its dependency on IL-15Rα frequently downregulated in cancer patients. In this work, we studied the antitumor activity of the IL-15 superagonist receptor-linker-IL-15 (RLI), designed to bypass the need of endogenous IL-15Rα. RLI consists of human IL-15 covalently linked to the human IL-15Rα sushi(+) domain. In a mouse model of colorectal carcinoma, RLI as a stand-alone treatment could limit tumor outgrowth only when initiated at an early time of tumor development. At a later time, RLI was not effective, coinciding with the strong accumulation of terminally exhausted programmed cell death-1 (PD-1)(high) T cell Ig mucin-3(+) CD8(+) T cells, suggesting that RLI was not able to reactivate terminally exhausted CD8(+) T cells. Combination with PD-1 blocking Ab showed synergistic activity with RLI, but not with IL-15. RLI could induce a greater accumulation of memory CD8(+) T cells and a stronger effector function in comparison with IL-15. Ex vivo stimulation of tumor-infiltrated lymphocytes from 16 patients with renal cell carcinoma demonstrated 56% of a strong tumor-infiltrated lymphocyte reactivation with the combination anti-PD-1/RLI compared with 43 and 6% with RLI or anti-PD-1, respectively. Altogether, this work provides evidence that the sushi-IL-15Rα/IL-15 fusion protein RLI enhances antitumor activity of anti-PD-1 treatment and is a promising approach to stimulate host immunity.

Tumor targeting of the IL-15 superagonist RLI by an anti-GD2 antibody strongly enhances its antitumor potency.

Immunocytokines (ICKs) targeting cytokines to the tumor environment using antibodies directed against a tumor-associated antigen often have a higher therapeutic index than the corresponding unconjugated cytokines. Various ICKs displaying significant antitumoral effects in several murine tumor models have already been developed, and some of them, in particular interleukin (IL)-2-based ICKs, are in Phase II clinical trials. Although sharing common biological activities with IL-2 in vitro, IL-15 is now considered as having a better potential in antitumor immunotherapeutical strategies and has been shown to be less toxic than IL-2 in preclinical studies. We previously developed the fusion protein RLI, linking a soluble form of human IL-15Rα-sushi+ domain to human IL-15. RLI showed better biological activities than IL-15 in vitro as well as higher antitumoral effects in vivo in murine and human cancer models. Here, we investigated, in the context of an ICK, the effect of associating RLI with an antibody targeting the GD2 ganglioside, a validated tumoral target expressed on many neurectodermal tumors. Anti-GD2-RLI fully retained the cytokine potential of RLI and the antibody effector functions (antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity). It displayed strong antitumor activities in two syngeneic cancer models in immunocompetent mice (subcutaneous EL4 and metastatic NXS2). Its therapeutic potency was higher than those of RLI and anti-GD2 alone or in combination. We suggest that this is related to its bifunctional (cytokine and antibody) nature.

CLEC-1 is a death sensor that limits antigen cross-presentation by dendritic cells and represents a target for cancer immunotherapy.

Tumors exploit numerous immune checkpoints, including those deployed by myeloid cells to curtail antitumor immunity. Here, we show that the C-type lectin receptor CLEC-1 expressed by myeloid cells senses dead cells killed by programmed necrosis. Moreover, we identified Tripartite Motif Containing 21 (TRIM21) as an endogenous ligand overexpressed in various cancers. We observed that the combination of CLEC-1 blockade with chemotherapy prolonged mouse survival in tumor models. Loss of CLEC-1 reduced the accumulation of immunosuppressive myeloid cells in tumors and invigorated the activation state of dendritic cells (DCs), thereby increasing T cell responses. Mechanistically, we found that the absence of CLEC-1 increased the cross-presentation of dead cell-associated antigens by conventional type-1 DCs. We identified antihuman CLEC-1 antagonist antibodies able to enhance antitumor immunity in CLEC-1 humanized mice. Together, our results demonstrate that CLEC-1 acts as an immune checkpoint in myeloid cells and support CLEC-1 as a novel target for cancer immunotherapy.

Selective SIRPα blockade reverses tumor T cell exclusion and overcomes cancer immunotherapy resistance.

T cell exclusion causes resistance to cancer immunotherapies via immune checkpoint blockade (ICB). Myeloid cells contribute to resistance by expressing signal regulatory protein-α (SIRPα), an inhibitory membrane receptor that interacts with ubiquitous receptor CD47 to control macrophage phagocytosis in the tumor microenvironment. Although CD47/SIRPα-targeting drugs have been assessed in preclinical models, the therapeutic benefit of selectively blocking SIRPα, and not SIRPγ/CD47, in humans remains unknown. We report a potent synergy between selective SIRPα blockade and ICB in increasing memory T cell responses and reverting exclusion in syngeneic and orthotopic tumor models. Selective SIRPα blockade stimulated tumor nest T cell recruitment by restoring murine and human macrophage chemokine secretion and increased anti-tumor T cell responses by promoting tumor-antigen crosspresentation by dendritic cells. However, nonselective SIRPα/SIRPγ blockade targeting CD47 impaired human T cell activation, proliferation, and endothelial transmigration. Selective SIRPα inhibition opens an attractive avenue to overcoming ICB resistance in patients with elevated myeloid cell infiltration in solid tumors.

Toward efficient drug screening by homogeneous assays based on the development of new fluorescent vasopressin and oxytocin receptor ligands.

A series of fluorescent ligands designed for vasopressin and oxytocin G protein-coupled receptors was synthesized and characterized to develop fluorescence polarization or homogeneous time-resolved fluorescence (HTRF) binding assays. These ligands, labeled with europium pyridine-bis-bipyridine cryptate or with Alexa 488,546,647 selectively bound to the vasopressin V1a and oxytocin receptors with high affinities and exhibited antagonistic properties. The affinities of several unlabeled ligands determined by our homogeneous assays on membrane preparations or on intact cells into 96- and 384-well plate formats were similar to those determined by usual radioligand binding methods. Compared to other binding assays, the polarization and HTRF binding assays are nonradiaoactive, therefore safer to perform, yet very sensitive and homogeneous, therefore easier and faster to automate. These methods are thus suitable for efficient drug high-throughput screening procedures and can easily be applied to other G protein-coupled receptor models.

Highly potent anti-CD20-RLI immunocytokine targeting established human B lymphoma in SCID mouse.

Rituximab (RTX), a chimeric IgG1 monoclonal antibody directed against the CD20 antigen, has revolutionized the treatment of B-cell malignancies. Nevertheless, the relapsed/refractory rates are still high. One strategy to increase the clinical effectiveness of RTX is based on antibody-cytokine fusion protein (immunocytokine; ICK) vectorizing together at the tumor site the antibody effector activities and the cytokine co-signal required for the generation of cytotoxic cellular immunity. Such ICKs linking various antibody formats to interleukin (IL)-2 are currently being investigated in clinical trials and have shown promising results in cancer therapies. IL-15, a structurally-related cytokine, is now considered as having a better potential than IL-2 in antitumor immunotherapeutic strategies. We have previously engineered the fusion protein RLI, linking a soluble form of human IL-15Rα-sushi+ domain to human IL-15. Compared with IL-15, RLI displayed better biological activities in vitro and higher antitumor effects in vivo in murine and human cancer models. In this study, we investigated the advantages of fusing RLI to RTX. Anti-CD20-RLI kept its binding capacity to CD20, CD16 and IL-15 receptor and therefore fully retained both antibody effector functions (ADCC and CDC), and the cytokine potential of RLI. In a severe combined immunodeficiency (SCID) mouse model of disseminated residual lymphoma, anti-CD20-RLI was found to induce long-term survival of 90% of mice up to at least 120 days whereas RLI and RTX, alone or in combination, just delayed the disease onset (100% of death at 28, 40 and 51 days respectively). These findings suggest that such ICK could improve the clinical efficacy of RTX, particularly in patients with refractory B-cell lymphoma.