Tetra- and Hexavalent Siglec-8 Ligands Modulate Immune Cell Activation.

Carbohydrate-binding proteins are generally characterized by poor affinities for their natural glycan ligands, predominantly due to the shallow and solvent-exposed binding sites. To overcome this drawback, nature has exploited multivalency to strengthen the binding by establishing multiple interactions simultaneously. The development of oligovalent structures frequently proved to be successful, not only for proteins with multiple binding sites, but also for proteins that possess a single recognition domain. Herein we present the syntheses of a number of oligovalent ligands for Siglec-8, a monomeric I-type lectin found on eosinophils and mast cells, alongside the thermodynamic characterization of their binding. While the enthalpic contribution of each binding epitope was within a narrow range to that of the monomeric ligand, the entropy penalty increased steadily with growing valency. Additionally, we observed a successful agonistic binding of the tetra- and hexavalent and, to an even larger extent, multivalent ligands to Siglec-8 on immune cells and modulation of immune cell activation. Thus, triggering a biological effect is not restricted to multivalent ligands but could be induced by low oligovalent ligands as well, whereas a monovalent ligand, despite binding with similar affinity, showed an antagonistic effect.

Changes of peripheral T cell subsets in melanoma patients with immune-related adverse events.

Introduction: Immunotherapies have improved the prognosis of many cancer patients including patients with advanced melanoma. Immune checkpoint receptors including CTLA-4 and PD-1 have been established as main therapeutic targets for immunotherapy of melanoma. Although monotherapy is effective in melanoma patients, a dual therapy approach has been shown to be most effective. Dual checkpoint blockade, however, increases substantially the risk for immune-related adverse events (irAEs). Methods: In this study, we characterized peripheral immune cell subsets in patients with anti-PD-1 monotherapy and with dual immune receptors blockade targeting PD-1 and CTLA-4. Results: We found differences in peripheral T cells between patients who developed severe immune-related side effects and patients with mild irAEs. We identified several mainly changes in CD8+ T cell subsets in patients with severe irAE under dual PD-1 and CTLA-4 blockade. Discussion: This work suggests that peripheral immune cell dynamics could be associated with severe immune-related side effects in patients receiving immune checkpoint inhibitors. These changes could be used as future biomarkers in early diagnosis of irAEs.

Targeting cancer glycosylation repolarizes tumor-associated macrophages allowing effective immune checkpoint blockade.

Immune checkpoint blockade (ICB) has substantially improved the prognosis of patients with cancer, but the majority experiences limited benefit, supporting the need for new therapeutic approaches. Up-regulation of sialic acid-containing glycans, termed hypersialylation, is a common feature of cancer-associated glycosylation, driving disease progression and immune escape through the engagement of Siglec receptors on tumor-infiltrating immune cells. Here, we show that tumor sialylation correlates with distinct immune states and reduced survival in human cancers. The targeted removal of Siglec ligands in the tumor microenvironment, using an antibody-sialidase conjugate, enhanced antitumor immunity and halted tumor progression in several murine models. Using single-cell RNA sequencing, we revealed that desialylation repolarized tumor-associated macrophages (TAMs). We also identified Siglec-E as the main receptor for hypersialylation on TAMs. Last, we found that genetic and therapeutic desialylation, as well as loss of Siglec-E, enhanced the efficacy of ICB. Thus, therapeutic desialylation represents an immunotherapeutic approach to reshape macrophage phenotypes and augment the adaptive antitumor immune response.

Siglec Receptors Modulate Dendritic Cell Activation and Antigen Presentation to T Cells in Cancer.

Interactions between sialylated glycans and sialic acid-binding immunoglobulin-like lectin (Siglec) receptors have been recently described as potential new immune checkpoint that can be targeted to improve anticancer immunity. Myeloid cells have been reported to express a wide range of different Siglecs; however, their expression and functions on cancer-associated dendritic cells (DCs) were not fully characterized. We found that classical conventional DCs (cDCs) from cancer patient samples have a high expression of several inhibitory Siglecs including Siglec-7, Siglec-9, and Siglec-10. In subcutaneous murine tumor models, we also found an upregulation of the inhibitory Siglec-E receptor on cancer-associated cDCs. DC lines and bone marrow-derived DCs (BMDCs) with expression of these inhibitory Siglecs showed impaired maturation states on transcriptome and protein level. Furthermore, ablation of these inhibitory Siglecs from DCs enhanced their capability to prime antigen-specific T cells and induce proliferation. Our work provides a deeper understanding of the influence of inhibitory Siglecs on DCs and reveals a potential new target to improve cancer immunotherapy.

The sialoglycan-Siglec glyco-immune checkpoint - a target for improving innate and adaptive anti-cancer immunity.

Introduction: During cancer progression, tumor cells develop several mechanisms to prevent killing and to shape the immune system into a tumor-promoting environment. One of such regulatory mechanism is the overexpression of sialic acid (Sia) on carbohydrates of proteins and lipids on tumor cells. Sia-containing glycans or sialoglycans were shown to inhibit immune effector functions of NK cells and T cells by engaging inhibitory Siglec receptors on the surface of these cells. They can also modulate the differentiation of myeloid cells into tumor-promoting M2 macrophages. Areas covered: We review the role of sialoglycans in cancer and introduce the Siglecs, their expression on different immune cells and their interaction with cancer-associated sialoglycans. The targeting of this sialoglycan-Siglec glyco-immune checkpoint is discussed along with potential therapeutic approaches. Pubmed was searched for publications on Siglecs, sialic acid, and cancer. Expert opinion: The targeting of sialoglycan-Siglec interactions has become a major focus in cancer research. New approaches have been developed that directly target sialic acids in tumor lesions. Targeted sialidases that cleave sialic acid specifically in the tumor, have already shown efficacy; efforts targeting the sialoglycan-Siglec pathway for improvement of CAR T cell therapy are ongoing. The sialoglycan-Siglec immune checkpoint is a promising new target for cancer immunotherapy.

NKp46 Calibrates Tumoricidal Potential of Type 1 Innate Lymphocytes by Regulating TRAIL Expression.

NK cells are a subset of group 1 innate lymphocytes that recognize and eliminate virus-infected and transformed cells. During the course of their development, NK cells acquire a repertoire of activating and inhibitory receptors, which ultimately define their reactivity against target cells. The array of receptors and their specificity during early developmental stages will control and imprint functional properties of NK cells, a process known as "NK cell education." Innate lymphoid cells (ILCs) are a diverse group of lymphocytes, which, like NK cells, do not rely on somatically rearranged Ag receptors for recognition. Among ILC subsets, ILC1s are most like NK cells functionally. Prototypic ILC1s reside in the liver, and a large part of their function is attributed to the expression of TRAIL, a TNF superfamily member with a well-documented antitumor activity. In this article, we show that TRAIL expression on mouse ILC1s is controlled by an activating receptor NKp46, which has been previously shown to control NK cell education. In the absence of NKp46, ILC1s fail to express normal levels of TRAIL on the surface, which results in diminished cytotoxicity toward TRAIL receptor-positive targets. To our knowledge, these findings provide the first evidence of a role of NKp46 in ILC1s that calibrates their antitumor response.

Humic material induces behavioral and global transcriptional responses in the nematode Caenorhabditis elegans.

Humic materials are complex organic molecules constituting the most abundant source of natural organic matter (NOM) in freshwater and soil ecosystems. Recent advances have identified that they interfere with biological systems, via the induction of biotransformation enzymes, the inhibition of photosynthetic oxygen release (in freshwater plants), the production of internal oxidative stress, or through the feminization of fish and amphibians. The nematode model organism Caenorhabditis elegans was chosen to investigate whether a natural and a synthetic humic material induce (i) a behavioral attraction, (ii) the reproduction, and (iii) a response in whole genome transcriptional expression. The phenomenological attractant experiments provided evidence that both humic material sources attract the worm and exert distinct chemical cues. In the reproduction assay, only the highest concentration (32 mg/L DOC of Fuchskuhle NOM, 38 mg/L DOC of HS 1500) resulted in a decrease in brood size, highlighting an overall intrinsic tolerance toward humic material. Finally, oligonucleotide-based whole genome DNA microarray experiments were performed from control and humic material treated worms. Significant transcriptional changes (exceeding a 2-fold increase or decrease) were identified in chemosensors, olfactory receptors, as well as enzymes of the biotransformation system (cytochromes P450, UDP-glucuronosyltransferases, glutathione S-transferases), thereby confirming that humic material is recognized as an environmental signaling chemical.