Targeting Sialidase to PD1 Enhances T cell Function and Tumor Control
Brett M. Garabedian, Eleanor E. Bashian, Xiaoshuang Wang, Andrew J. Thompson, James C. Paulson
Abstract
Immune therapies targeting the PD1 axis have transformed outcomes in cancer treatment by enhancing T cell-mediated immune responses. However, many tumors evade immune clearance through orthogonal escape mechanisms. Excessive production of immunosuppressive sialic acid-containing glycans (sialoglycans) can impair immune surveillance by recruiting inhibitory Siglecs to the immune synapse where, like PD1, they act as checkpoints for cell activation. Sialic acids can also impact T cell activation by dampening the ligation of the costimulatory receptor CD28 with its ligands. This polypharmacology implicates sialoglycans as a linchpin of tumor immunity that can be targeted to further improve outcomes of PD1 therapies. In this work we conjugated sialidase to anti-PD1 (αPD1-S) to selectively degrade sialic acids on immune cells expressing PD1. Glycan profiling confirmed targeted desialylation, and functional assays demonstrated enhancements to T cell activation and cytotoxic capacity. In a melanoma model, αPD1-S promoted inflammatory macrophage polarization and reduced T cell exhaustion, collectively restricting melanoma growth beyond anti-PD1 (αPD1) alone. By simultaneously blocking PD1 and degrading sialoglycans, αPD1-S provides a novel strategy to enhance T cell-mediated immune responses and improve tumor control in refractory cancers.