Single-cell transcriptomic unveils tumor-mediated reprogramming of neutrophils and their unique vulnerability that inhibits metastasis.

Abstract

Neutrophils are protumorigenic and prometastatic in tumor-bearing mice. Comprehensive single-cell RNA sequencing analyses on various tissues of naïve and tumor-bearing MMTV-PyMT (mouse mammary tumor virus-polyoma middle T antigen) mice unraveled a neutrophil reprogramming process and uncovered a strategy to selectively target reprogrammed neutrophils. Transcriptional reprogramming of neutrophils in tumor-bearing mice is initiated in the bone marrow (BM) by granulocyte colony-stimulating factor (G-CSF). Among the seven neutrophil clusters in the BM, the abundance of one cluster is markedly increased whereas another cluster is diminished in tumor-bearing mice. This reprogramming endures across tissue types including blood, tumor microenvironment, and the metastatic niche in the lungs. Thus, in all tissues tested, neutrophils derived from tumor-bearing mice are transcriptionally distinct from those derived from naïve mice. Among the genes that are markedly induced are members of the <i>Ifitm</i> family. We leverage this facet to selectively target reprogrammed neutrophils through treatment with Rapalink-1-an mTOR (mechanistic target of rapamycin) inhibitor-whose intake is greatly enhanced by IFITM proteins. Reprogrammed neutrophils selectively uptake Rapalink-1, which selectively eradicate them in vivo and normalized the neutrophil-to-lymphocyte ratio in tumor-bearing mice without affecting naïve neutrophils. Last, Rapalink-1 inhibited metastasis of a Rapalink-1-resistant tumor. Thus, Rapalink-1 not only could affect the primary tumor but also selectively eliminates tumor-reprogrammed neutrophils to diminish metastasis.