Leukocytes as a reservoir of circulating oncogenic DNA and regulatory targets of tumor-derived extracellular vesicles

Essentials Tumor-bearing mice were employed to follow oncogenic HRAS sequences in plasma, and blood cells. Cancer DNA accumulated in leukocytes above levels detected in exosomes, platelets and plasma. Extracellular vesicles and nucleosomes are required for uptake of tumor DNA by leukocytes. Uptake of tumor-derived extracellular vesicles by leukocytes triggers coagulant phenotype.

SUMMARY

Background Tumor-derived extracellular vesicles (EVs) and free nucleosomes (NSs) carry into the circulation a wealth of cancer-specific, bioactive and poorly understood molecular cargoes, including genomic DNA (gDNA). Objective Here we investigated the distribution of extracellular oncogenic gDNA sequences (HRAS and HER2) in the circulation of tumor-bearing mice. Methods and Results Surprisingly, circulating leukocytes (WBCs), especially neutrophils, contained the highest levels of mutant gDNA, which exceeded the amount of this material recovered from soluble fractions of plasma, circulating EVs, platelets, red blood cells (RBCs) and peripheral organs, as quantified by digital droplet PCR (ddPCR). Tumor excision resulted in disappearance of the WBC-associated gDNA signal within 2-9 days, which is in line with the expected half-life of these cells. EVs and nucleosomes were essential for the uptake of tumor-derived extracellular DNA by neutrophil-like cells and impacted their phenotype. Indeed, the exposure of granulocytic HL-60 cells to EVs from HRAS-driven cancer cells resulted in a selective increase in tissue factor (TF) procoagulant activity and interleukin 8 (IL-8) production. The levels of circulating thrombin-antithrombin complexes (TAT) were markedly elevated in mice harboring HRAS-driven xenografts. Conclusions Myeloid cells may represent a hitherto unrecognized reservoir of cancer-derived, EV/NS-associated oncogenic gDNA in the circulation, and a possible novel platform for liquid biopsy in cancer. In addition, uptake of this material alters the phenotype of myeloid cells, induces procoagulant and proinflammatory activity and may contribute to systemic effects associated with cancer.

IL-12-independent Th1-type immune responses to respiratory viral infection: requirement of IL-18 for IFN-gamma release in the lung but not for the differentiation of viral-reactive Th1-type lymphocytes

We demonstrated that IL-12 was induced during primary or secondary pulmonary adenoviral infection in wild-type (wt) mice. However, cellular responses were not compromised in the lungs of IL-12-/- mice. The level of IFN-gamma in the lung was similar in wt and IL-12-/- mice during pulmonary viral infection. Upon Ag stimulation in vitro, lymphocytes from draining lymph nodes or spleen of infected IL-12-/- mice released large amounts of IFN-gamma, but not IL-4, which were comparable to those released by wt lymphocytes. Furthermore, a predominantly IgG2a response to adenoviral infection was unimpaired in IL-12-/- mice. These significant anti-adenoviral Th1-type responses in IL-12-/- mice led to an efficient clearance of virus-infected cells in the lung. Whether IL-18 was involved in IL-12-independent anti-adenoviral immune responses was investigated. Abrogation of endogenous IL-18 by an Ab resulted in diminished IFN-gamma release and lymphocytic infiltrate in the lung during adenoviral infection. Nevertheless, the development of lymphocytes of the Th1 phenotype was unimpaired in the absence of both IL-12 and IL-18. In contrast to their intact ability to mount Th1-type responses to viral infection, IL-12-/- mice suffered impaired Th1-type immune responses to pulmonary mycobacterial infection. Our findings suggest that IL-12, although induced, is not required for Th1-type responses to respiratory viral infection, in contrast to mycobacterial infection. IL-18 is required for the optimal release of IFN-gamma in the lung during viral infection, but is not required for the generation of virus-reactive Th1-type lymphocytes. Th1 differentiation during respiratory adenoviral infection may involve molecules different from IL-12 or IL-18.