Interaction of sialylated glycans with Siglec receptors on suppressive myeloid cells

In spite of the impressive advances in cancer immunotherapy that have entered the clinics, only a subset of patients benefits from current treatment strategies and many fail to achieve a durable response. Most treatment regimens are T cell-centric and neglect the role of the suppressive tumor microenvironment (TME) that drives various resistance mechanisms. Myeloid cells are the most abundant immune cells found in the TME and include immunosuppressive subsets such as myeloid-derived suppressor cells (MDSCs). In addition, overexpression of sialoglycans within the TME can drive tumor progression via various mechanisms. Hypersialylation can, for example, enhance immune evasion via interaction with sialic acid-binding immunoglobulin-like lectin (Siglec) receptors on tumor-infiltrating immune cells. Here, we tested the role of sialic acid on MDSCs and their interaction with Siglec receptors. We found that MDSCs derived from the blood of lung cancer patients and tumor- bearing mice strongly express inhibitory Siglec receptors. In murine cancer models of emergency myelopoiesis, Siglec-E knockout on myeloid cells resulted in prolonged survival and increased infiltration of activated T cells. Targeting suppressive myeloid cells by blocking Siglec receptors or desialylation led to a strong reduction of their suppressive potential. We further identified CCL2 as a mediator involved in T cell suppression upon the interaction of sialoglycans and Siglec receptors on MDSCs. Our results provide mechanistic insights into how sialylated glycans inhibit anti-cancer immunity by facilitating CCL2 expression. This interaction marks a new potential target to limit the suppressive capacity of the TME and induce anti-tumor response

Two Flow Cytometric Approaches of NKG2D Ligand Surface Detection to Distinguish Stem Cells from Bulk Subpopulations in Acute Myeloid Leukemia

Within the same patient, absence of NKG2D ligands (NKG2DL) surface expression was shown to distinguish leukemic subpopulations with stem cell properties (so called leukemic stem cells, LSCs) from more differentiated counterpart leukemic cells that lack disease initiation potential although they carry similar leukemia specific genetic mutations. NKG2DL are biochemically highly diverse MHC class I-like self-molecules. Healthy cells in homeostatic conditions generally do not express NKG2DL on the cell surface. Instead, expression of these ligands is induced upon exposure to cellular stress (e.g., oncogenic transformation or infectious stimuli) to trigger elimination of damaged cells via lysis through NKG2D-receptor-expressing immune cells such as natural killer (NK) cells. Interestingly, NKG2DL surface expression is selectively suppressed in LSC subpopulations, allowing these cells to evade NKG2D-mediated immune surveillance. Here, we present a side-by-side analysis of two different flow cytometry methods that allow the investigation of NKG2DL surface expression on cancer cells i.e., a method involving pan-ligand recognition and a method involving staining with multiple antibodies against single ligands. These methods can be used to separate viable NKG2DL negative cellular subpopulations with putative cancer stem cell properties from NKG2DL positive non-LSC

Targeting the Siglec-sialic acid axis promotes antitumor immune responses in preclinical models of glioblastoma

Glioblastoma (GBM) is the most aggressive form of primary brain tumor, for which effective therapies are urgently needed. Cancer cells are capable of evading clearance by phagocytes such as microglia- and monocyte-derived cells through engaging tolerogenic programs. Here, we found that high expression of sialic acid-binding immunoglobulin-like lectin 9 (Siglec-9) correlates with reduced survival in patients with GBM. Using microglia- and monocyte-derived cell-specific knockouts of Siglec-E, the murine functional homolog of Siglec-9, together with single-cell RNA sequencing, we demonstrated that Siglec-E inhibits phagocytosis by these cells, thereby promoting immune evasion. Loss of Siglec-E on monocyte-derived cells further enhanced antigen cross-presentation and production of pro-inflammatory cytokines, which resulted in more efficient T cell priming. This bridging of innate and adaptive responses delayed tumor growth and resulted in prolonged survival in murine models of GBM. Furthermore, we showed the combinatorial activity of Siglec-E blockade and other immunotherapies demonstrating the potential for targeting Siglec-9 as a treatment for patients with GBM

The Combination of MiRNA-196b, LCN2, and TIMP1 is a Potential Set of Circulating Biomarkers for Screening Individuals at Risk for Familial Pancreatic Cancer

Individuals at risk (IAR) of familial pancreatic cancer (FPC) are good candidates for screening. Unfortunately, neither reliable imaging modalities nor biomarkers are available to detect high-grade precursor lesions or early cancer. Circulating levels of candidate biomarkers LCN2, TIMP1, Glypican-1, RNU2-1f, and miRNA-196b were analyzed in 218 individuals with sporadic pancreatic ductal adenocarcinoma (PDAC, n = 50), FPC (n = 20), chronic pancreatitis (n = 10), IAR with relevant precursor lesions (n = 11) or non-relevant lesions (n = 5), 20 controls, and IAR with (n = 51) or without (n = 51) lesions on pancreatic imaging. In addition, corresponding duodenal juice samples were analyzed for Glypican-1 (n = 144) enrichment and KRAS mutations (n = 123). The panel miR-196b/LCN2/TIMP1 could distinguish high-grade lesions and stage I PDAC from controls with absolute specificity and sensitivity. In contrast, Glypican-1 enrichment in serum exosomes and duodenal juice was not diagnostic. KRAS mutations in duodenal juice were detected in 9 of 12 patients with PDAC and only 4 of 9 IAR with relevant precursor lesions. IAR with lesions on imaging had elevated miR-196b/LCN2/TIMP1 levels (p = 0.0007) and KRAS mutations in duodenal juice (p = 0.0004) significantly more often than IAR without imaging lesions. The combination miR-196b/LCN2/TIMP1 might be a promising biomarker set for the detection of high-grade PDAC precursor lesions in IAR of FPC families