Mild Reduction-Mediated NK Cell Membrane Modification for ROS Scavenging Efficacy Overcome Immunosuppressive Tumor Microenvironment

Solid tumors are characterized by a metabolically dysregulated tumor microenvironment (TME) enriched with reactive oxygen species (ROS), which suppresses immune cell function. Natural killer (NK) cells are promising effectors in cancer immunotherapy due to their intrinsic cytotoxicity without prior antigen sensitization. However, oxidative stress impairs NK cell cytotoxicity by reducing degranulation, interferon-γ production, and survival. Therefore, maintaining NK cell redox balance is a crucial obstacle to achieving optimal therapeutic results in ROS-rich TMEs. Here, we proposed a straightforward, non-genetic ex vivo membrane modification approach to reinforce the redox balance of NK cells via ROS scavenging. Using tris(2-carboxyethyl)phosphine (TCEP), a mild reducing agent, we selectively introduced free thiol groups onto the exterior surface of NK cell plasma membranes. The engineered surface-thiol-riched NK cells (STR-NK) demonstrated (1) increased membrane thiols, (2) efficiently eliminated extracellular ROS, (3) attenuated intracellular ROS accumulation, and (4) preserved cytotoxicity-associated gene expression under oxidative stress. Importantly, STR-NK cells maintained potent cytotoxicity against diverse solid tumor cells despite the presence of ROS. Overall, this uncomplicated and scalable surface redox modulation approach enhances NK cell anticancer activity under oxidative stress, offering a promising strategy to improve NK cell-based cancer immunotherapies in ROS-enriched solid TMEs.