Natural killer cell-derived extracellular vesicles in cancer: mediators of intercellular communication and tumor immune signaling

Abstract

Natural killer (NK) cells are essential components of innate immunity and play a pivotal role in tumor surveillance through direct cytotoxicity and immune regulation. In recent years, NK-cell-derived extracellular vesicles (NK-EVs) have emerged as a promising cell-free therapeutic modality that preserves key antitumor functions of parental NK cells while overcoming several limitations associated with cell-based immunotherapy. As biologically derived nanovesicles, NK-EVs combine nanoscale delivery properties with a cell-free formulation format and generally low immunogenicity. However, although selected preclinical studies suggest tumor-interacting or target-cell-recognition properties, a broadly applicable intrinsic tumor-targeting capacity—and, in particular, intrinsic blood–brain barrier (BBB) penetration—has not been established for native NK-EVs. This review systematically summarizes the biological characteristics, biogenesis pathways, and molecular cargo of NK-EVs, with particular emphasis on their antitumor mechanisms. Current evidence supports perforin/granzyme-mediated cytotoxicity and Fas/Fas ligand (FasL) signaling as the most established mechanisms of NK-EVs-mediated tumor killing, whereas miRNA-mediated regulation and tumor microenvironment remodeling represent emerging functional pathways requiring further validation. By contrast, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)–death receptor 4/5 (DR4/DR5) signaling remains putative because direct NK-EVs-specific causal evidence is limited. Functionally investigated miRNAs and tumor-microenvironment effects represent context-dependent or emerging pathways whose generalizability across NK-cell sources and preparation conditions requires further validation. Importantly, recent advances in engineering strategies—including parental-cell priming, cargo loading, antigen-recognition engineering, tissue/barrier-targeting modification, biomimetic nanovesicle construction, and formulation-based stabilization. These approaches can alter cargo composition, recipient-cell recognition, or tissue-specific delivery through distinct mechanisms. Improvements achieved by engineered composite platforms should therefore not be conflated with intrinsic properties of native NK-EVs. Nevertheless, major translational challenges remain, including scalable manufacturing, purification and characterization standardization, mechanism-linked potency testing, biodistribution uncertainty, batch comparability, and product-specific regulatory considerations. Overall, NK-EVs should be viewed not only as potential cell-free therapeutic tools but also as specialized mediators of tumor–immune communication that integrate cytotoxic protein transfer, receptor-mediated signaling, RNA-based regulation, and microenvironmental crosstalk.