Scientists at the Stanford University School of Medicine and at the University of California, San Francisco report isolating stem cells from human testes. Though the cells bear a striking resemblance to embryonic stem cells, the researchers caution against viewing them as one and the same.
The testes stem cells have different patterns of gene expression and regulation and they do not proliferate and differentiate as aggressively as human embryonic stem cells, the team points out. They note that these stem cells seem to hover somewhere between true pluripotency and tissue-specific multipotency exhibited by many types of adult stem cells. The researchers thus termed the cells multipotent germline stem cells.
The investigators used cells obtained via biopsies conducted to diagnose infertility in 19 men. Each patient’s cells were cultured in a manner similar to human embryonic stem cells.
Of the 19 samples, two yielded cell lines with many characteristics of the pluripotent cells, according to the scientists. One of the two patients from whom the cell lines were derived withdrew from the study, and his samples were discarded.
Further study on the remaining cell line indicated that it expressed many but not all genes associated with pluripotency. The cells could also be induced to differentiate into nontesticular neural cell precursors and expressed the telomerase enzyme essential to keep pluripotent cells young and unspecialized.
When the investigators examined the cells’ patterns of methylation, however, they found that the newly derived cell line was less thoroughly methylated as compared to human embryonic stem cells in one region and more heavily methylated than human embryonic stem cells in another region.
Finally, when the researchers injected the human stem cells into mice with compromised immune systems, they showed only a limited ability to form a teratoma, which is a hallmark of true pluripotency, the research team explains.
Together, the results suggest that the stem cells isolated from male testes have some, but not all the characteristics of true pluripotent cells. “It’s not yet possible to completely recreate human embryonic stem cells from germline cells,” asserts Renee Reijo-Pera, Ph.D., director of Stanford’s Center for Human Embryonic Stem Cell Research and Education and co-senior author. “These cells differ in gene expression, methylation, and in their ability to form teratomas.”
The findings, published in the January issue of Stem Cells, are in contrast to those reported in a recent Nature paper, according to the scientists. That study concluded that the cells were in fact as pluripotent as embryonic stem cells.