CLEC-1 Restrains Acute Inflammatory Response and Recruitment of Neutrophils following Tissue Injury

The inflammatory response is a key mechanism for the elimination of injurious agents but must be tightly controlled to prevent additional tissue damage and progression to persistent inflammation. C-type lectin receptors expressed mostly by myeloid cells play a crucial role in the regulation of inflammation by recognizing molecular patterns released by injured tissues. We recently showed that the C-type lectin receptor CLEC-1 is able to recognize necrotic cells. However, its role in the acute inflammatory response following tissue damage had not yet been investigated. We show in this study, in a mouse model of liver injury induced by acetaminophen intoxication, that Clec1a deficiency enhances the acute immune response with increased expression of Il1b, Tnfa, and Cxcl2 and higher infiltration of activated neutrophils into the injured organ. Furthermore, we demonstrate that Clec1a deficiency exacerbates tissue damage via CXCL2-dependent neutrophil infiltration. In contrast, we observed that the lack of CLEC-1 limits CCL2 expression and the accumulation, beyond the peak of injury, of monocyte-derived macrophages. Mechanistically, we found that Clec1a-deficient dendritic cells increase the expression of Il1b, Tnfa, and Cxcl2 in response to necrotic cells, but decrease the expression of Ccl2. Interestingly, treatment with an anti-human CLEC-1 antagonist mAb recapitulates the exacerbation of acute immunopathology observed by genetic loss of Clec1a in a preclinical humanized mouse model. To conclude, our results demonstrate that CLEC-1 is a death receptor limiting the acute inflammatory response following injury and represents a therapeutic target to modulate immunity.

Abstract 2957: CD127 is expressed by acute lymphoblastic leukemias and is efficiently targeted by the IL7R-antagonist OSE-127 through macrophage-mediated antibody dependent phagocytosis

Acute lymphoblastic leukemia (ALL) arises from the uncontrolled proliferation of precursor B or T cells (B- or T-ALL). Novel immunotherapies are urgently needed to reduce polychemotherapy-related toxicities and to target relapsed/refractory disease. The Interleukin 7 receptor (IL7R) plays a pivotal role in the development of ALL through mutations leading to constitutive activation of the oncogenic IL7R pathway or through overexpression of the receptor. The IL7Rα chain (CD127)-targeting antibody OSE-127 is a full antagonist of the IL7R pathway with an excellent safety profile (NCT03980080), currently evaluated in phase 2 trials in inflammatory and autoimmune diseases (NCT04882007, NCT04605978). We previously reported in vivo efficacy of OSE-127 in CD127+ ALL patient-derived xenografts (PDXs) and synergy with standard of care polychemotherapy, but we had not evaluated CD127 protein expression in ALL patient cells. Moreover, the mechanism of action underlying OSE-127’s anti-leukemic activity remained to be fully elucidated. Here we show that CD127 is expressed by >84% ALL patients and that OSE-127 efficiently targets CD127 not only via its IL7R antagonist activity but also through macrophage-mediated antibody dependent phagocytosis (ADCP). First, CD127 surface expression was prospectively measured by flow cytometry in 372 diagnostic ALL patient samples. We detected CD127-positivity (defined as ≥10% CD127+ blasts) in 84.4% (314/372) cases, of which 39.5% (147/372) were CD127hi (≥ 50% CD127+ blasts). CD127 expression was higher in T- than in B-ALL. Among B-ALL, highest expression was detected in E2A-PBX1+ and BCR-ABL-like ALLs. Mechanistically, OSE-127 blocked STAT5 phosphorylation in IL7-responsive ALL-PDX cells, leading to decreased cell survival and proliferation. Surprisingly, we detected high in vivo efficacy of OSE-127 therapy in IL7-unresponsive PDXs (e.g., unable to induce phosphorylation of STAT5 upon ex vivo IL7 stimulation or with IL7R mutation-induced constitutive phosphorylation of STAT5). We uncovered that OSE-127 induced macrophage-mediated ADCP of CD127+ ALL cells in vitro. Accordingly, treatment of IL7-unresponsive, but OSE-127-sensitive models with an OSE-127-LALAPG variant (conserving IL7R-antagonistic properties but lacking ADCP activity due to Fc-inactivating mutations) did not impact leukemia development, thereby substantiating that ADCP contributes to the anti-leukemic efficacy of OSE-127. In fact, ADCP levels induced by OSE-127 treatment in vitro correlated with its capacity to reduce ALL blasts in the blood of PDX mice in vivo. Altogether, through its dual mode of action, OSE-127 may represent a powerful novel immunotherapy option for ALL patients, including cases with dysregulated IL7R signaling, particularly in combination with standard of care polychemotherapy.

Citation Format: Irene Baccelli, Lennart Lenk, Anna Laqua, Dorothee Winterberg, Anna Dietterle, Frederique Corallo, Julien Taurelle, Emma Narbeburu, Beat Bornhauser, Jean-Pierre Bourquin, Fotini Vogiatzi, Simon Raffel, Martin Schrappe, Gunnar Cario, Monika Brüggemann, Denis M Schewe, Nicolas Poirier. CD127 is expressed by acute lymphoblastic leukemias and is efficiently targeted by the IL7R-antagonist OSE-127 through macrophage-mediated antibody dependent phagocytosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2957.

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.

Partitioning the structural features that underlie expansin-like and elicitor activities of cerato-platanin

Cerato-platanin family (CPF) proteins are produced by fungi and elicit defences when applied to plants, behaving as PAMPs/MAMPs. CPF proteins share structural similarity to plant and bacterial expansins, and have been demonstrated, in some cases, to possess expansin-like loosening activity on cellulose. This is the case of cerato-platanin (CP), the founder of the CPF, which shows both eliciting and cellulose-loosening activities, raising the question as to whether the expansin-like activity may be responsible for defence activation. To pinpoint structural and thermodynamic features underlying eliciting and expansin-like activity of CP, we carried out site-directed mutagenesis targeting separately net charge (N84D mutation), conformational stability (V63A mutation), or conserved position previously shown to affect expansin-like activity in CP (D77A mutation), and characterized wild-type protein and its variants. Removing or adding negative charges on the protein surface led to reducing or increasing, respectively, the expansin-like activity. The activity was instead not affected by mutations affecting protein fold and stability. In contrast, all the mutants showed reduced capacity to elicit defences in plants. We conclude that the expansin-like activity of CP depends on net charge and ability to (weakly) bind cellulose, whereas the eliciting activity on plants does not depend on the cellulose-loosening activity.

Accumulation patterns of endogenous β-aminobutyric acid during plant development and defence in Arabidopsis thaliana

We recently discovered that β-aminobutyric acid (BABA), a molecule known for its ability to prime defences in plants, is a natural plant metabolite. However, the role played by endogenous BABA in plants is currently unknown. In this study we investigated the systemic accumulation of BABA during pathogen infection, levels of BABA during plant growth and development and analysed mutants possibly involved in BABA transport or regulation. BABA was quantified by LC-MS using an improved method adapted from a previously published protocol. Systemic accumulation of BABA was determined by analysing non-infected leaves and roots after localised infections with Plectosphaerella cucumerina or Pseudomonas syringae pv. tomato (Pst) DC3000 avrRpt2. The levels of BABA were also quantified in different plant tissues and organs during normal plant growth, and in leaves during senescence. Mutants affecting amino acid transport (aap6, aap3, prot1 and gat1), γ-aminobutyric acid levels (pop2) and senescence/defence (cpr5-2) were analysed. BABA was found to accumulate only locally after bacterial or fungal infection, with no detectable increase in non-infected systemic plant parts. In leaves, BABA content increased during natural and induced senescence. Reproductive organs had the highest levels of BABA, and the mutant cpr5-2 produced constitutively high levels of BABA. Synthetic BABA is highly mobile in the receiving plant, whereas endogenous BABA appears to be produced and accumulated locally in a tissue-specific way. We discuss a possible role for BABA in age-related resistance and propose a comprehensive model for endogenous and synthetic BABA.

A novel approach for the identification of efficient combination therapies in primary human acute myeloid leukemia specimens

Appropriate culture methods for the interrogation of primary leukemic samples were hitherto lacking and current assays for compound screening are not adapted for large-scale investigation of synergistic combinations. In this study, we report a novel approach that efficiently distills synthetic lethal interactions between small molecules active on primary human acute myeloid leukemia (AML) specimens. In single-dose experiments and under culture conditions preserving leukemia stem cell activity, our strategy considerably reduces the number of tests needed for the identification of promising compound combinations. Initially conducted with a selected library of 5000 small molecules and 20 primary AML specimens, it reveals 5 broad classes of sensitized therapeutic target pathways along with their synergistic patient-specific fingerprints. This novel method opens new avenues for the development of AML personalized therapeutics and may be generalized to other tumor types, for which in vitro cancer stem cell cultures have been developed.

Prognostic impact of changes in circulating tumor cells (CTC) in metastatic breast cancer (MBC)

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Background: To prospectively assess the prognostic value of CTC counts at baseline and after one cycle of therapy and their kinetics for response, progression-free (PFS), and overall survival (OS) in MBC. Methods: MBC patients underwent CTC enumeration (CellSearch, Veridex) at baseline (CTCBL), after one cycle of a new line of therapy (CTC1C), and at progression (CTCPD). CTC status was classified as negative (neg (−)) or positive (pos (+)) for <5 and ≥5 CTC/7.5 ml peripheral blood, respectively. CTC kinetics (CTCKIN) from CTCBL to CTC1C were classified as favorable if CTCs remained neg (neg>neg) or became neg (pos>neg), or as unfavorable (neg>pos or pos>pos). Tumor response was assessed every 2–3 months using RECIST criteria. CTC status and kinetics were associated with outcome using log-rank and Fisher’s exact tests. Results: Of 326 patients enrolled (median age (range) at first diagnosis: 50 (23–81) years), 115/326 (35%) were CTCBL+, 51/162 (31%) were CTC1C+, and 39/108 (36%) were CTCPD+. Median follow-up was 15.9 months (mos). Median PFS and OS were significantly reduced in CTCBL+ compared to CTCBL− patients (PFS, 4.3 vs. 7.1 mos, p = .019; OS, 15.0 mos vs. not reached (nr), p <.001) and for CTC1C+ compared to CTC1C− patients (p <.001 for PFS and OS). CTCKIN were predictive of progressive disease as best response (neg>neg, 33%; pos>neg, 38%; pos>pos, 60%; neg>pos, 75%; p = .040). PFS and OS for patients with unfavorable CTCKIN were significantly shorter than for favorable CTCKIN (PFS, 3.7 vs. 6.8 mos, p <.001; OS, 7.8 mos vs. nr, p <.001). Conclusions: CTC at baseline, CTC after one cycle and CTC kinetics are highly predictive of outcome in MBC. Serial CTC enumeration could serve as a useful adjunct to standard diagnostic tests in tailoring therapy. Further details of CTCPD will be presented at the meeting. Clinical trial information: S-295/2009.

Circulating tumor cells in metastatic breast cancer: Are they a strong and independent predictor of poor progression-free and overall survival?

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Background: Circulating tumor cells (CTCs) are detected in 30–60% of patients with metastatic breast cancer (MBC). The aim of this prospective multi-center study was to evaluate the impact of CTCs on progression free survival (PFS) and overall survival (OS) in a large cohort of 486 patients with progressive metastatic disease. Methods: CTC levels were determined for 486 patients at nine German University Breast Cancer Centers between 12/2007 and 06/2011. Samples of 7.5 ml blood were taken before initiation of a new line of therapy and CTCs were enumerated using the CellSearch System (Veridex LLC, Raritan, NJ, USA). CTC status (≥ 5 CTCs vs. < 5 CTCs per 7.5 ml blood) was assessed as a prognostic factor for PFS and OS using univariate (log-rank test) and multivariate (Cox regression model) statistical methods. Results: CTCs were detected in 205/486 (42%) patients. The median CTC count was 2 (range 0–6380) per 7.5 ml blood. The presence of ≥ 5 CTCs/7.5 ml blood did not correlate with any of the established clinicopathological factors except estrogen receptor status (p = 0.038). PFS and OS were both significantly shorter in patients with ≥ 5 CTCs/7.5 ml than in those with < 5 CTCs/7.5 ml blood. PFS was 5.0 [95% CI 4.1–5.8] months vs.7.6 [95% CI 5.9–9.3] months, p < 0.001; and OS was 15.0 [95% CI 13.5–16.5] months vs. 18.3 [95% CI 17.4–19.2] months, p < 0.001. In the multivariate analysis considering all clinicopathological factors and the CTC status, independent predictors of reduced OS and PFS were site of metastasis (visceral vs. bone), number of metastatic sites (multiple sites vs. one site), and CTC status. Conclusions: The presence of ≥ 5 CTCs/7.5 ml blood is a strong and independent predictor of poor PFS and OS in patients with MBC.