Mesenchymal stem cells (MSCs) are being intensively investigated as future therapeutics for various human diseases. One of the most important challenges to the clinical application of MSCs is the possibility of malignant transformation during long-term in vitro culturing. However, there have been no reports on the tumorigenicity of salivary gland-derived MSCs following long-term in vitro culturing. Here, we isolated a single clonal glandular stem cell from human parotid gland stem cells (hpGSCs) using a modified sub-fractionation culturing method. The possibility of malignant transformation of these cells following long-term culturing was evaluated under in vitro and in vivo culture conditions. Single clonal glandular stem cells from the human parotid gland have unique multipotent MSCs traits. hpGSCs at passage 18 stained strongly for β-galactosidase expression and long-term culture of hpGSCs led to a reduction in telomerase activity. hpGSCs could not survive in a soft agar environment and did not cause tumor formation in a xenograft mouse model. In addition, expression of salivary cancer-related oncogenes was not elevated in hpGSCs following the long-term culture. In conclusion, we demonstrated that there is no possibility of acquiring a malignant transformation during long-term in vitro cell expansion of hpGSC.

中文翻译：

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来源于人腮腺的单克隆腺干细胞在长期体外培养过程中不会出现恶性表型。

间充质干细胞 (MSCs) 正在被深入研究作为各种人类疾病的未来疗法。MSCs 临床应用面临的最重要挑战之一是长期体外培养过程中可能发生恶性转化。然而，长期体外培养后唾液腺来源的MSCs的致瘤性尚未见报道。在这里，我们使用改良的亚分级培养方法从人腮腺干细胞 (hpGSCs) 中分离出单克隆腺体干细胞。在体外和体内培养条件下评估这些细胞长期培养后恶性转化的可能性。来自人类腮腺的单克隆腺干细胞具有独特的多能 MSC 特征。第 18 代的 hpGSC 对 β-半乳糖苷酶表达强烈染色，长期培养 hpGSC 导致端粒酶活性降低。hpGSCs 不能在软琼脂环境中存活，并且不会在异种移植小鼠模型中引起肿瘤形成。此外，在长期培养后，hpGSCs 中唾液癌相关癌基因的表达没有升高。总之，我们证明了在 hpGSC 的长期体外细胞扩增过程中不可能发生恶性转化。