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

Acute lymphoblastic leukemia (ALL) arises from the uncontrolled proliferation of precursor B or T cells (BCP- or 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 leukemias and T-ALL, where immunotherapy approaches remain scarce. While 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 (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 Lusvertikimab 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 high-risk leukemias. Importantly, Lusvertikimab 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, Lusvertikimab 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). Lusvertikimab-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, Lusvertikimab may represent a novel immunotherapy option for any CD127-positive ALL, particularly in combination with standard-of-care polychemotherapy.

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.

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.

Concerted BAG3 and SIRPα blockade impairs pancreatic tumor growth

The BAG3- and SIRPα- mediated pathways trigger distinct cellular targets and signaling mechanisms in pancreatic cancer microenvironment. To explore their functional connection, we investigated the effects of their combined blockade on cancer growth in orthotopic allografts of pancreatic cancer mt4–2D cells in immunocompetent mice. The anti-BAG3 + anti-SIRPα mAbs treatment inhibited (p = 0.007) tumor growth by about the 70%; also the number of metastatic lesions was decreased, mostly by the effect of the anti-BAG3 mAb. Fibrosis and the expression of the CAF activation marker α-SMA were reduced by about the 30% in animals treated with anti-BAG3 mAb compared to untreated animals, and appeared unaffected by treatment with the anti-SIRPα mAb alone; however, the addition of anti-SIRPα to anti-BAG3 mAb in the combined treatment resulted in a > 60% (p < 0.0001) reduction of the fibrotic area and a 70% (p < 0.0001) inhibition of CAF α-SMA positivity. Dendritic cells (DCs) and CD8+ lymphocytes, hardly detectable in the tumors of untreated animals, were modestly increased by single treatments, while were much more clearly observable (p < 0.0001) in the tumors of the animals subjected to the combined treatment. The effects of BAG3 and SIRPα blockade do not simply reflect the sum of the effects of the single blockades, indicating that the two pathways are connected by regulatory interactions and suggesting, as a proof of principle, the potential therapeutic efficacy of a combined BAG3 and SIRPα blockade in pancreatic cancer.

230 Preclinical efficacy of CLEC-1 antagonist as novel myeloid immune checkpoint therapy for oncology

Background

C-type lectin receptors (CLRs) are powerful pattern recognition receptors shaping immune cell-mediated tissue damage by positively or negatively regulating myeloid cell functions and hence tumor elimination or evasion. We previously reported that the orphan CLR CLEC-1 expressed by dendritic cells (DCs) tempers T cell’s responses in vivo by limiting antigen cross-presentation by cDC1. Furthermore, we observed that CLEC-1 is highly expressed by myeloid cells purified from human tumor microenvironment, in particular tumor-associated macrophages.

Methods

Macrophages were generated from monocytes of healthy volunteers for phagocytosis assays. MC38 and Hepa 1.6 murine tumor cells were implanted in Clec1a KO or KI mice for immunotherapeutic treatment evaluation.

Results

Using newly developed anti-human CLEC-1 monoclonal antibodies (mAbs), we found that antagonist anti-CLEC-1 mAbs with the capacity to block CLEC-1/CLEC-1Ligand interaction, as opposed to non-antagonist CLEC-1 mAbs, increase the phagocytosis of CLEC-1Ligand-positive human tumor cells by human macrophages, in particular when opsonized by tumor-associated antigen mAbs (Rituximab, Cetuximab, Trastuzumab) or with anti-CD47 mAb (Magrolimab). In-vivo, CLEC-1 knock-out (KO) mice (n=19) display significant prolonged survival in monotherapy as compared to wild-type littermates (n=12) in an orthotopic hepatocellular carcinoma (HCC) model and anti-tumor memory responses was demonstrated by tumor rechallenge in cured mice. CLEC1 KO mice also illustrate significant eradication of MC38 colorectal tumors in combination with chemotherapy promoting CLEC-1Ligand expression by tumor cells (n=16 with Gemcitabine or n=11 with Cyclophosphamide). HCC tumor microenvironment analysis after 2 weeks of tumor implantation shows significantly higher number of CD8+ and memory CD8+ T cells with reduced PD1 expression in CLEC1 KO animals (n=16 versus n=12 for KO vs WT mice respectively). Finally, we recently generated human CLEC-1 knock-in mice expressing the extracellular human CLEC1 domain fused to the intracellular mouse CLEC1 tail and confirmed preclinical efficacy in vivo with anti-human CLEC1 antagonist mAb in monotherapy in the orthotopic HCC model.

Conclusions

These data illustrate that CLEC-1 inhibition represents a novel therapeutic target for immuno-oncology modifying T cell immune responses and tumor cell phagocytosis by macrophages.

Abstract 1636: CLEC-1 is a novel myeloid immune checkpoint for cancer immunotherapy limiting tumor cells phagocytosis and tumor antigen cross-presentation

Myeloid cells represent one of the most abundant immune cell types in solid tumors that impede myeloid phagocytosis by triggering “don't eat me” and “don't find me” signals. Recent literature demonstrates that C-type lectin receptors (CLRs) are powerful pattern recognition receptors shaping immune cell-mediated tissue damage by positively or negatively regulating myeloid cell functions and hence tumor elimination or evasion. We previously reported that the orphan CLR CLEC-1 expressed by dendritic cells (DCs) and macrophages (MPs) is enhanced by TGFβ and tempers downstream T cells responses. Furthermore, we observed that CLEC-1 is highly expressed by myeloid cells purified from the human tumor microenvironment, in particular, tumor-associated MPs. We evaluated whether CLEC-1 could also be a receptor for DAMPs and influences phagocytosis. We found that CLEC-1 fusion protein binds specifically to secondary necrotic healthy or tumor cells induced by chemotherapy, radiation (UV, X-ray), or culture stress conditions suggesting that ligands of CLEC-1 are generated upon stress and programmed cell death. Importantly, further to promising results in KO CLEC-1 mice, we observed in vivo that CLEC-1 deficient mice, in contrast to wild-type littermates, eradicate MC38 colorectal tumors in combination with cytotoxic and immunogenic chemotherapy. Importantly, disruption of CLEC-1 signaling by Fc-CLEC-1 fusion protein also promotes tumor eradication. We then generated and identified different anti-human CLEC-1 antagonist monoclonal antibodies (mAbs) with the capacity to block CLEC-1/CLEC-1L interaction. We developed innovative antagonist CLEC-1 mAbs which, in contrast to non-antagonist CLEC-1 control mAb, increase the phagocytosis of CLEC-1L-positive human tumor cells by human TGFβ-polarized DCs or MPs. Indeed, TGFβ-polarized DCs phagocytose more efficiently a NSCLC cell line (A549) as well as Rituximab (anti-CD20 mAb)-opsonized Burkitt lymphoma cells (Raji) when CLEC-1 is antagonized by Abs. Similarly, macrophages significantly more efficiently engulfed human tumors in the presence of CLEC-1 antagonist Abs, in particular when tumor cells were opsonized such as Rituximab-opsonized Raji cells, Cetuximab opsonized colon carcinoma cells (DLD-1; EGFR+) or Trastuzumab opsonized mammary carcinoma cells (SK-BR-3; Her2+). Importantly, we observed both in vitro and in vivo that DCs from Clec1a deficient mice cross-present more efficiently dead cell-associated antigens to CD8+ T cells (OT-1). We generated hCLEC-1 knock-in mice and in vivo preclinical evaluation of CLEC-1 blocking mAbs is ongoing. Altogether, these data illustrate that CLEC-1 broadly notably inhibits tumor-cell phagocytosis and synergized with tumor-targeted cytotoxic monoclonal antibodies in both solid and hematological tumors, and hampers DC antigen cross-presentation.

Citation Format: Vanessa Gauttier, Sabrina Pengam, Marion Drouin, Javier Saenz, Bérangère Evrard, Kevin Biteau, Caroline Mary, Géraldine Teppaz, Ariane Desselle, Virginie Thépénier, Emmanuelle Wilhelm, Elise Chiffoleau, Nicolas Poirier. CLEC-1 is a novel myeloid immune checkpoint for cancer immunotherapy limiting tumor cells phagocytosis and tumor antigen cross-presentation [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 1636.

Agonist anti-ChemR23 mAb reduces tissue neutrophil accumulation and triggers chronic inflammation resolution

Resolution of inflammation is elicited by proresolving lipids, which activate GPCRs to induce neutrophil apoptosis, reduce neutrophil tissue recruitment, and promote macrophage efferocytosis. Transcriptional analyses in up to 300 patients with Inflammatory Bowel Disease (IBD) identified potential therapeutic targets mediating chronic inflammation. We found that ChemR23, a GPCR targeted by resolvin E1, is overexpressed in inflamed colon tissues of severe IBD patients unresponsive to anti-TNFα or anti-α4β7 therapies and associated with significant mucosal neutrophil accumulation. We also identified an anti-ChemR23 agonist antibody that induces receptor signaling, promotes macrophage efferocytosis, and reduces neutrophil apoptosis at the site of inflammation. This ChemR23 mAb accelerated acute inflammation resolution and triggered resolution in ongoing chronic colitis models, with a significant decrease in tissue lesions, fibrosis and inflammation-driven tumors. Our findings suggest that failure of current IBD therapies may be associated with neutrophil infiltration and that ChemR23 is a promising therapeutic target for chronic inflammation.

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.

Interleukin-7/Interferon Axis Drives T Cell and Salivary Gland Epithelial Cell Interactions in Sjögren's Syndrome

OBJECTIVE

Primary Sjögren's syndrome (SS) is characterized by a lymphocytic infiltration of salivary glands (SGs) and the presence of an interferon (IFN) signature. SG epithelial cells (SGECs) play an active role in primary SS pathophysiology. We undertook this study to examine the interactions between SGECs and T cells in primary SS and the role of the interleukin-7 (IL-7)/IFN axis.

METHODS

Primary cultured SGECs from control subjects and patients with primary SS were stimulated with poly(I-C), IFNα, or IFNγ. T cells were sorted from blood and stimulated with IL-7. CD25 expression was assessed by flow cytometry. SG explants were cultured for 4 days with anti-IL-7 receptor (IL-7R) antagonist antibody (OSE-127), and transcriptomic analysis was performed using the NanoString platform.

RESULTS

Serum IL-7 level was increased in patients with primary SS compared to controls and was associated with B cell biomarkers. IL7R expression was decreased in T cells from patients with primary SS compared to controls. SGECs stimulated with poly(I-C), IFNα, or IFNγ secreted IL-7. IL-7 stimulation increased the activation of T cells, as well as IFNγ secretion. Transcriptomic analysis of SG explants showed a correlation between IL7 and IFN expression. Finally, explants cultured with anti-IL-7R antibody showed decreased IFN-stimulated gene expression.

CONCLUSION

These results suggest the presence of an IL-7/IFNγ amplification loop involving SGECs and T cells in primary SS. IL-7 was secreted by SGECs stimulated with type I or type II IFN and, in turn, activated T cells that secrete type II IFN. An anti-IL-7R antibody decreased the IFN signature in T cells in primary SS and could be of therapeutic interest.

Abstract 910: A novel bifunctional anti-PD-1 IL-7 fusion protein to reinvigorate exhausted T cell and disarms Treg suppressive activity

Despite the clinical success of anti-PD(L)1 therapy, the majority of patient remain unresponsive or fail to develop a durable response. We explored a second generation of PD-1 antibody by fusing IL-7 cytokine to the Fc portion, called BiCKI® IL-7. The high affinity of the anti PD-1 antibody will allow the concentration/retention of the drug into the tumor microenvironment and preferentially deliver IL-7 in cis-dependent manner to PD-1+ cells. IL-7 is an optimal target for immunotherapy to preferentially stimulate effector T-cell (Teff) functions over regulatory T-cells (Treg)due to the differential expression of IL-7R and poor capacity of IL-7 to stimulate Treg proliferation. Moreover, It has been published that PD-1 blockades increase IL-7R expression and improve IL-7 signaling in exhausted T-cells rationalizing our combinatorial approach.

Results Our anti PD-1/IL-7 bispecific antibody efficiently blocks the PD-1/PD-L1 and PD-L2 interactions and the PD-1-mediated inhibitory signal (pSHP1) and in parallel activates IL-7R pSTAT5 signaling into T cells. Anti PD-1/IL-7 preferentially binds in cis to T cells coexpressing PD-1 and CD127 enabling a selective activation of primed antigen- experienced T cells over PD1-negative (e.g. naïve) cells. A high affinity/avidity of the molecule was observed using biosensor when both receptor CD127 and PD-1, supporting the cis-targeting activity of the drug. Using in vitro T cell activation bioassay, we observed that IL-7 portion fused to the anti-PD-1 synergizes to enhance TCR mediated signaling (NFAT) through activation of the non-canonical pathway while IL-7 in combination with anti-PD1 (two separates product) has no additive effect. Although IL-7R expression decrease over chronic stimulation of Teff cells, we demonstrated that IL-7 efficiently activates progenitor and some fully-exhausted human T-cells (pSTAT5) and maintain their proliferation and survival capacity. This IL-7R signaling activation was associated with a significant increased IFNγ secretion using ex-vivo fresh human tumor explant culture. A significant higher IFNγ production was obtained with anti PD-1/IL-7compared to anti PD-1 treatment alone, including in non-responder patients to anti-PD1, suggesting that the anti PD-1/IL-7 bispecific can reactivate TILs that are resistant to PD-1 therapy. Knowing that Tregs have a key suppressive function, we also explored the possibility that anti-PD-1/IL-7 affect Treg functions. In a human Treg/Teff coculture assay, anti PD-1/IL-7 abrogates the Treg capacity to inhibit proliferation and IFN-g secretion of CD8+ Teff. Moreover, IL-7 and anti-PD-1/IL-7 does not stimulate Treg proliferation, in contrast to IL-2 and IL-15.

Conclusion Our data validate the therapeutic potential of providing IL-7 signals to overcome PD-1 resistance. The bifunctional anti-PD1/IL-7 favors the T-cell effector over T-regulatory immune balance by stimulating Teff cells and exhausted T-cell, while disarming Tregs suppressive functions.

Citation Format: Aurore Morello, Justine Durand, Virginie Thepenier, Géraldine Teppaz, Margaux Seite, Sabrina Pengam, Caroline Mary, Nicolas Poirier. A novel bifunctional anti-PD-1 IL-7 fusion protein to reinvigorate exhausted T cell and disarms Treg suppressive activity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 910.

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-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.

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.

Abstract 1684: Selective SIRPa blockade potentiates dendritic cell antigen cross-presentation and triggers memory T-cell antitumor responses

Targeting immune checkpoints of the adaptive immunity has shown great therapeutic efficacy to fight cancers, but in a limited proportion of patients. Myeloid cells represent a major immune cell type in many solid tumors, and are often associated with a poor outcome. Interaction of SIRPalpha (SIRPa), expressed by myeloid cells, with the ubiquitous receptor CD47 is an important immune checkpoint of the innate response, involved in the regulation of macrophages and neutrophils functions including phagocytosis. Targeting both adaptive and innate immune cells represents a promising therapeutic strategy against cancer. Here we evaluated the impact of a SIRPa checkpoint inhibitor on adaptive immune responses both in rodents and human settings.

Antagonist anti-SIRPa monoclonal antibody (mAbs) was evaluated in vivo in combination with adaptive immune checkpoint inhibitors (anti-PD-L1 mAb) or costimulatory agent (anti-4-1BB mAb) in an orthotopic hepatocellular carcinoma (HCC) model in immunocompetent mice. Whereas monotherapies have shown a modest clinical effect, combination with SIRPa blockade dramatically enhanced the overall survival with up to 70% of mice in complete remission (p &lt; 0.0001 in both combination: n=15 with anti-41BB and n=11 with anti-PDL1 combination). These cured mice showed robust memory immune response since a second tumor challenge (performed up to one month after treatment withdrawal) was rejected in all mice (p&lt;0.01 n=20). In addition, adaptive transfer of T lymphocytes from 4-1BB combo or sera from PD-L1 combo cured mice in naïve untreated mice protected them from orthotopic HCC development (n=5/6 with T-cell from 4-1BB combo; n=5/5 with sera from PD-L1 combo). Tumor infiltrates analyzed by flow cytometry showed enrichment in effector CD8 T cells with the 4-1BB therapy whereas PD-L1 combination led to an accumulation of memory CD4 T cells. Tumor transcriptional analysis using Nanostring technology revealed higher dendritic cells (DCs) and T cells (mainly TH1) immune signature with reduced exhaustion signature. Finally, we found in vitro that selective blockade of SIRPa during antigen processing by mouse dendritic cells (with ovalbumin protein and TCR-transgenic OT-1 T-cell) or human dendritic cells (with melan-A 25-mer long peptide and human antigen-specific T-cell clone from melanoma patients) significantly increases T-cell activation and cytokine (i.e. IFNg) secretion.

In conclusion, we showed that selective SIRPa antagonist increased dendritic cell tumor-antigen cross-presentation and generated robust antitumor memory response in combination with adaptive immunotherapies.

Citation Format: Vanessa Gauttier, Sabrina Pengam, Justine Durand, Aurore Morello, Sophie Conchon, Bernard Vanhove, Nicolas Poirier. Selective SIRPa blockade potentiates dendritic cell antigen cross-presentation and triggers memory T-cell antitumor responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1684.

Abstract LB-188: Selective targeting of SIRP alpha induces potent memory antitumor immune responses without presenting hematological toxicity

Targeting immune checkpoints of the adaptive immunity has shown great therapeutic efficacy to fight cancers, but in a limited proportion of patients. Myeloid cells represent the most abundant immune cell type in many solid tumors, and are often associated with a poor outcome. Interaction of SIRPalpha (SIRPα), expressed by myeloid cells, with the ubiquitous receptor CD47 is an important immune checkpoint of the innate response, involved in the regulation of macrophages, dendritic cells and neutrophils function (e.g. phagocytosis). Thus, combining immunotherapies targeting both adaptive and innate immune cells represents a promising therapeutic strategy against cancer. Since agents targeting CD47 (anti-CD47 or SIRPa-Fc) recently experienced hematological toxicity (anemia or thrombocytopenia), we evaluated the preclinical safety and efficacy of an antagonistic anti-SIRPa monoclonal antibody (mAb).

Here, we found that administration of anti-SIRPa mAb at high dose (10 mg/kg) in healthy or tumor-bearing mice did not modify red blood cells and platelets numbers, hematocrit and hemoglobin levels, while in parallel anti-CD47 mAbs rapidly induced anemia within three days, owing to the high expression of CD47 on red blood cells. Next, we evaluated the therapeutic potential of antagonist anti-SIRPa mAbs in combination with adaptive immune checkpoint inhibitors (anti-PD-L1 mAb) or an adaptive immune checkpoint agonist (anti-4-1BB mAb) using an orthotopic hepatocellular carcinoma (HCC) preclinical model in immunocompetent mice. Monotherapy with antagonist anti-SIRPa mAbs prolonged survival in 25% of mice but did not induce remission (p&lt;0.01). While PD-1 blockade alone was also poorly effective in this model (MST: 22 days, n=8), combination with SIRPα blockade induced durable remission in 60% of mice (p&lt;0.05). Association of SIRPα blockade with 4-1BB agonist was highly efficient with 80% of long-term remission (p&lt;0.01) while monotherapy with 4-1BB mAb led to tumor elimination in only 26% of mice (ns). Mice presenting a remission after selective SIRPα blockade in combination with PD-L1 or 4-1BB agents acquired a robust memory immune responses mediated, at least, by T lymphocytes since a second tumor challenge (performed up to one month after treatment withdrawal) was always rejected (p&lt;0.01). In addition, adoptive transfer of T lymphocytes from cured mice in naïve untreated mice protected them from orthotopic HCC development.

In conclusion, we showed that targeting selectively SIRPa is devoid of hematological toxicity and that combination of immunotherapies targeting both adaptive and innate immune cells is promising to generate robust antitumor memory immunity.

Citation Format: Vanessa Gauttier, Sabrina Pengam, Sophie Conchon, Bernard Vanhove, Nicolas Poirier. Selective targeting of SIRP alpha induces potent memory antitumor immune responses without presenting hematological toxicity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-188. doi:10.1158/1538-7445.AM2017-LB-188

Anti-CD28 Antibody and Belatacept Exert Differential Effects on Mechanisms of Renal Allograft Rejection

Belatacept is a biologic that targets CD80/86 and prevents its interaction with CD28 and its alternative ligand, cytotoxic T lymphocyte antigen 4 (CTLA-4). Clinical experience in kidney transplantation has revealed a high incidence of rejection with belatacept, especially with intensive regimens, suggesting that blocking CTLA-4 is deleterious. We performed a head to head assessment of FR104 (n=5), a selective pegylated Fab' antibody fragment antagonist of CD28 that does not block the CTLA-4 pathway, and belatacept (n=5) in kidney allotransplantation in baboons. The biologics were supplemented with an initial 1-month treatment with low-dose tacrolimus. In cases of acute rejection, animals also received steroids. In the belatacept group, four of five recipients developed severe, steroid-resistant acute cellular rejection, whereas FR104-treated animals did not. Assessment of regulatory T cell-specific demethylated region methylation status in 1-month biopsy samples revealed a nonsignificant trend for higher regulatory T cell frequencies in FR104-treated animals. Transcriptional analysis did not reveal significant differences in Th17 cytokines but did reveal higher levels of IL-21, the main cytokine secreted by CD4 T follicular helper (Tfh) cells, in belatacept-treated animals. In vitro, FR104 controlled the proliferative response of human preexisting Tfh cells more efficiently than belatacept. In mice, selective CD28 blockade also controlled Tfh memory cell responses to KLH stimulation more efficiently than CD80/86 blockade. Our data reveal that selective CD28 blockade and belatacept exert different effects on mechanisms of renal allograft rejection, particularly at the level of Tfh cell stimulation.

FR104, an antagonist anti-CD28 monovalent fab' antibody, prevents alloimmunization and allows calcineurin inhibitor minimization in nonhuman primate renal allograft

Selective targeting of CD28 might represent an effective immunomodulation strategy by preventing T cell costimulation, while favoring coinhibition since inhibitory signals transmitted through CTLA-4; PD-L1 and B7 would not be affected. We previously showed in vitro and in vivo that anti-CD28 antagonists suppress effector T cells while enhancing regulatory T cell (Treg) suppression and immune tolerance. Here, we evaluate FR104, a novel antagonist pegylated anti-CD28 Fab' antibody fragment, in nonhuman primate renal allotransplantation. FR104, in association with low doses of tacrolimus or with rapamycin in a steroid-free therapy, prevents acute rejection and alloantibody development and prolongs allograft survival. However, when FR104 was associated with mycophenolate mofetil and steroids, half of the recipients rejected their grafts prematurely. Finally, we observed an accumulation of Helios-negative Tregs in the blood and within the graft after FR104 therapy, confirmed by Treg-specific demethylated region DNA analysis. In conclusion, FR104 reinforces immunosuppression in calcineurin inhibitor (CNI)-low or CNI-free protocols, without the need of steroids. Accumulation of intragraft Tregs suggested the promotion of immunoregulatory mechanisms. Selective CD28 antagonists might become an alternative CNI-sparing strategy to B7 antagonists for kidney transplant recipients.