Targeting stromal cell sialylation reverses T cell mediated immunosuppression in the tumor microenvironment

Immunosuppressive tumor microenvironments (TME) reduce the effectiveness of immune responses in cancer. Mesenchymal stromal cells (MSC), precursors to cancer-associated fibroblasts (CAFs), dictate tumor progression by enhancing immune cell suppression in colorectal cancer (CRC). Hyper-sialylation of glycans promotes immune evasion in cancer through binding of sialic acids to their receptors, Siglecs, expressed on immune cells that results in inhibition of effector functions. The role of sialylation in dictating MSC/CAF immunosuppression in the TME is unknown. In this study, we show that tumor-conditioned stromal cells have increased sialyltransferase expression, a2,3/6-linked sialic acid and Siglec ligands. Tumor-conditioned stromal cells and CAFs induce exhausted immunomodulatory PD-1, Siglec-7 and Siglec-9-expressing T cell phenotypes. In vivo, targeting stromal cell sialylation reverses stromal cell-mediated immunosuppression, as evidenced by infiltration of CD25 and granzyme B-expressing T cells in the tumor and draining lymph node. Targeting stromal cell sialylation may overcome immunosuppression in the CRC TME. Overall design: RNA sequencing of untreated murine mesenchyaml stromal cells (MSCs) (n=3) compared to CT26 tumor conditioned media (TCM)-conditioned MSCs (n=3)