β-endorphin primes NK cells and NK-derived Extracellular Vesicle to enhance anti-tumor cytotoxicity

Psychoneuroimmunology suggests that positive physiological states, including laughter, could affect anti-tumor immunity, but the underlying mechanisms remain unclear. Here, we investigated whether {beta}-endorphin (BE), an endogenous opioid peptide associated with positive physiological stimuli, modulates Natural Killer (NK) cell cytotoxicity and the anti-tumor activity of NK-derived extracellular vesicles (EVs). Using NK-92 cells, we assessed cytotoxicity against JIMT1 breast cancer cells, CD107a mobilization, cytotoxic activity of conditioned medium (CM), and EV yield, cargo, and function. BE enhanced NK-92-mediated killing of JIMT1 cells without increasing CD107a mobilization, suggesting that improved cytotoxicity was not driven by classical degranulation. Consistently, CM from BE-treated NK cells retained contact-independent cytotoxicity. NK-EVs were enriched in granzyme B and perforin following BE treatment exhibiting enhanced cytotoxicity against JIMT1 and BW tumor cells. BE also increased the cytotoxic activity of primary human NK cells, and BE-conditioned NK-EVs primed naive NK-92 cells for enhanced tumor killing. These findings indicate that BE enhances NK anti-tumor immunity by remodeling the cytotoxic secretome and generating EVs that act as both direct cytotoxic effectors and mediators of NK cell priming. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=119 HEIGHT=200 SRC="FIGDIR/small/741417v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@16d4026org.highwire.dtl.DTLVardef@18e91fcorg.highwire.dtl.DTLVardef@1124baeorg.highwire.dtl.DTLVardef@268d0e_HPS_FORMAT_FIGEXP M_FIG C_FIG Proposed neuroendocrine-immune model linking positive physiological stimuli, NK cell-derived extracellular vesicles (EVs), and anti-tumor activity. Laughter is depicted as a conceptual upstream trigger of hypothalamic-pituitary signaling leading to {beta}-endorphin (BE) release. BE conditioning enhanced NK-92 cytotoxicity and the anti-tumor activity of NK-derived EVs, consistent with granzyme B and perforin enrichment and supporting EV-mediated contact-independent cancer cell killing.