Sialoglycans on human T cells attenuate death programs executed through the Fas pathway

Abstract

T cells are critical executors of adaptive immune responses and their persistence is tightly regulated. Part of this regulation relies on programmed cell death driven by the Tumor Necrosis Factor (TNF) receptor superfamily. The addition of glycans that terminate in the monosaccharide sialic acid (sialoglycans) to these cell death receptors has been shown to attenuate their apoptotic functions. While this is now understood to be a pro-survival mechanism in settings of cancer pathophysiology, the specific roles of sialoglycans in regulating cell death receptor activity on human T cells remains unexplored. This is of particular importance given the rising interest in T cell glycan editing for therapeutic benefit. Here, we address this gap using both immortalized (Jurkat) and primary human T cells deficient in sialoglycans. We found that T cell sialoglycans suppressed apoptosis induced by the Fas receptor (FasR) but not other TNF receptor superfamily members such as TNFR1 and TRAIL-R1. Dynamic reorganization of FasR was increased on sialoglycan-deficient Jurkat cells, suggesting that these glycans limit receptor clustering. This model was further supported by phosphoproteomics results, which confirmed that loss of sialoglycans negatively regulated the pro-survival MAPK/ERK signalling pathway. Finally, we used a recombinant sialic acid cleaving enzyme (sialidase) to confirm that sialoglycans on primary human T cells are bona fide immunophysiological regulators of FasR-driven programmed cell death. Combined, our results demonstrate that sialoglycan remodelling on T cells influences cell fate driven by the Fas pathway and provide motivation to further characterize the immunoregulatory roles of the glycocalyx in health and disease.