Siglec-9 Regulates an Effector Memory CD8+ T-cell Subset That Congregates in the Melanoma Tumor Microenvironment

Abstract

Emerging evidence suggests an immunosuppressive role of altered tumor glycosylation due to downregulation of innate immune responses via immunoregulatory Siglecs. In contrast, human T cells, a major anticancer effector cell, only rarely express Siglecs. However, here, we report that the majority of intratumoral, but not peripheral blood, cytotoxic CD8 þ T cells expressed Siglec-9 in melanoma. We identified Siglec-9 þ CD8 þ T cells as a subset of effector memory cells with high functional capacity and signatures of clonal expansion. This cytotoxic T-cell subset was functionally inhibited in the presence of Siglec-9 ligands or by Siglec-9 engagement by specific antibodies. TCR signaling pathways and key effector functions (cytotoxicity, cytokine production) of CD8 þ T cells were suppressed by Siglec-9 engagement, which was associated with the phosphorylation of the inhibitory protein tyrosine phosphatase SHP-1, but not SHP-2. Expression of cognate Siglec-9 ligands was observed on the majority of tumor cells in primary and metastatic melanoma specimens. Targeting the tumor-restricted, glycosylation-dependent Siglec-9 axis may unleash this intratumoral T-cell subset, while confining T-cell activation to the tumor microenvironment.

Deciphering the transcriptomic landscape of tumor-infiltrating CD8 lymphocytes in B16 melanoma tumors with single-cell RNA-Seq

“…Hence, this cluster was referred to as Effector Memory-like ("EM-like") state (Figure 1 B,C). Note that, while T cells with effector memory phenotype have been previously observed among TILs (Zhang et al, 2018;Haas et al, 2019), EM-like cells have never been characterized at the transcriptomic level on murine tumors, and a gene signature for this population remains to be defined.…”

Human T cell glycosylation and implications on immune therapy for cancer

“…Several recent reports demonstrate the expression of Siglec-9 on tumor-infiltrating cytotoxic CD8 + T cells in multiple types of cancers (colorectal, ovarian and non-small cell lung cancer (NSCLC), and melanoma). 75,76 These Siglec-9-expressing tumor-infiltrating lymphocytes (TILs) as well as Siglec-9 + CD8 + T cells, in lower numbers in the peripheral blood of melanoma patients and healthy donors, exhibited an effector memory phenotype. Co-expression with several known inhibitory T-cell receptors, e.g.…”

“…Despite this inhibitory phenotype, functional responses of Siglec-9 + CD8 + T cells to CD3/C28 costimulation are higher than those observed for their Siglec-9 − counterparts in vitro (Table 2). 76…”

Don’t sugarcoat it: How glycocalyx composition influences cancer progression

“…Mimetics against the sLe x tetrasaccharide along with other ligands have been used in clinical trials for pan selectin inhibition (Chang et al, 2010; Morikis et al, 2017) to treat sickle cell crises, E-selectin inhibition to treat acute myeloid leukemia in bone marrow (Winkler et al, 2012), and combined E-selectin and CXCR4 inhibition (Price et al, 2016) to treat dormant breast cancer. Furthermore, glycan-based therapeutics to cleave sialic acid ligands on cancer cells to prevent siglec-based shielding from immunosurveilance are also entering clinical trials (Haas et al, 2019; Stanczak et al, 2018). While small molecule inhibitors and mimetics have therapeutic applications, they still represent a brute force approach to manipulating glycosylation and lack the precision needed to specifically edit the glycocalyx.…”