Natural killer (NK) cells have cytotoxic effects on tumor cells and viral pathogens. NK cell-derived exosomes (NK-exosomes) also express typical NK cell markers and cytotoxic molecules, therefore, exert anti-tumor and immune homeostatic activities. In this study, canine NK-exosomes separated from cytotoxic NK cell supernatant carried specific markers such as CD81, Alix, and Perforin 1. We examined the anti-tumor effects of NK-exosomes in an experimental murine model using the canine mammary carcinoma cells, REM134. REM134 cells were xenografted of mammary fat pad of mice. CD133, Bmi-1, MMP-3, IL-6, TNF-α, and PCNA are useful as a molecular marker for tumorigenesis and metastasis. The treatment of canine NK-exosomes inhibited tumor growth and significantly (p<0.01) downregulated the expression of Bmi-1, MMP-3, IL-6, TNF-α, and PCNA in REM134-treated mice. Also, the expression of CD133, potent cancer stem cell marker, was significantly downregulated in the canine NK-exosomes-treated mice compared with that of the tumor group. Collectively, these results suggested that canine NK-exosomes has a potential capacity for regulation of cancer progression and metastasis against canine mammary carcinoma.

Canine mammary tumors account for ~30% of all tumors in the female dogs and approximately 50% of the tumors are malignant. Exosomes have been the focus of great interest, as they appear to be involved in numerous important cellular processes. In this study, we examined the anti-tumor effects of canine mesenchymal stem cells-derived exosomes (MSC-exosomes) in an experimental murine mammary tumor model using canine mammary carcinoma cells, REM134. The MSC-exosomes were injected tumor site and tail vein of REM134 xenografted mice. We found that tumor size of the MSC-exosomes-treated group decreased compared to those of the only tumor group in REM134-driven tumorigenic mouse model. In addition, the MSC-exosomes-treated tumor group showed meaningfully reduced expression levels of the MMP-3, IL-1β, IL-6, and TNF-α compared to those in the tumor group. Specifically, we confirmed that the expression level of the CD133, potent cancer stem cell (CSC) markers, decreased in the MSC-exosomes-treated tumor group compared to the tumor group. This study suggests that the MSC-exosomes exhibited anti-tumor effects through downregulating CSC-related markers in the canine mammary tumor murine model. Further study is needed in the future, and we are conducting research on the detailed anti-tumor mechanism of the MSC-exosomes.