Quantifying the Dual Effect of Antitumor and Pro-Tumor Human Neutrophils on Natural Killer Cell Behaviors in a Microphysiological System.

Neutrophils, the most abundant immune cells in humans, can promote the progression of many solid tumors. Neutrophils in solid tumor tissues can contribute to immunosuppression and resistance to immunotherapy partially by inhibiting the antitumor activity of natural killer (NK) cells, a group of innate immune cells known as the first line of defense against cancer. Studies in mice show that neutrophils are functionally plastic and can be polarized by molecular cues to show either an antitumor "N1" or a pro-tumor "N2" phenotype. However, the crosstalk between neutrophils and NK cells in human cancer is not well characterized, especially as to how different subtypes of neutrophils could influence NK cell behaviors differently. In this study, we engineered a human cell-based microphysiological system to quantify the distinct effects of antitumor N1-like and pro-tumor N2-like neutrophil subtypes on NK cell behaviors including migration and tumor cytotoxicity. We found that NK cells showed preferential migration toward N1-like neutrophils over N2-like neutrophils, although they showed lower motility in terms of speed, displacement, and directionality after migration toward N1-like neutrophils in comparison to N2-like neutrophils. Moreover, N1-like neutrophils restored the NK cell cytotoxicity against pancreatic tumor spheroids, while N2-like neutrophils suppressed it, although both neutrophil subtypes inhibited NK cell infiltration into tumor spheroids. Our study reveals the dual role of human neutrophils in modulating NK cell behaviors and sheds new light on the nuanced crosstalk between different immune cell types, suggesting the reprogramming of neutrophils to enhance the antitumor functions of NK cells as a potential immunotherapy strategy for cancer.