Injection of human stem cells into mice with tumors slowed down tumor growth, researchers have found. Human mesenchymal stem cells (MSCs), isolated from bone marrow, caused changes in blood vessels supplying the tumor. This modification of blood supply seemed to impact tumor growth.

Treating cancer with stem cells has been controversial. Some studies have found that stem cells force tumors to enter programmed cell death, while other studies suggest that stem cells actually promote tumor growth by inducing infiltration of new blood vessels.

Researchers at INSERM groups at Université Joseph Fourier in collaboration with CHU de Grenoble decided to investigate these conflicting hypotheses. They studied the impact of MSCs on already established subcutaneous or lung metastasis in mice. To do this, the scientists engrafted nude mice with luciferase-positive mouse adenocarcinoma cells (TSA-Luc+) to obtain subcutaneous or lung tumors. MSCs were then injected into the periphery of the subcutaneous tumors or delivered by systemic intravenous injection in mice bearing either subcutaneous tumors or lung metastasis.

For both the subcutaneous and lung tumors, injection of MSCs reduced cell division, consequently slowing the rate of tumor growth. Part of the mode of action of stem cells therefore appears to be due to angiogenesis, but the mechanism behind this is still unclear.

“We found that MSCs altered vasculature inside the tumor—although new blood vessels were generated, overall they were longer and fewer than in untreated tumors,” explains Claire Rome, Ph.D., of the Université Joseph Fourier, who led this study. “This could be restricting the oxygen and nutrients to the tumor, limiting cell division. Our study confirms others that propose that stem cells, in particular MSCs, might be one way forward in treating cancer.”

“One of the interesting questions this study raises is when MSCs promote tumor growth and when they restrict it,” adds Celia Gomes from the University of Coimbra. “The answer seems to be timing—this study looks at already established tumors, while others, which find that MSCs increase growth, tend to be investigating new tumors. This is a first step in the path to identifying exactly which patients might benefit from stem cell therapy and which will not.”

This study was published today in Stem Cell Research & Therapy, in a paper titled “The dual effect of MSCs on tumour growth and tumour angiogenesis”.

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