Short-term treatment with immune system-suppressing drugs allows human embryonic stem cells to survive and even prosper in mice, according to School of Medicine researchers. The group, led by associate professor Joseph Wu, published its findings in Cell Stem Cell yesterday.

Without such an immune-suppressing technique, animals’ immune systems recognize the stem cells as foreign and rapidly eliminate them. This is a barrier to stem cell transplants in humans as well.

The recent discovery could allow humans to accept stem cell transplants without constantly having to take immunosuppressant drugs, which open the doors to infections and side effects like hypertension and ulcers.

Most current animal and human experiments on the viability of transplanted stem cells study the long-term use of immunosuppressants. The study, spearheaded by medical student Jeremy Pearl, took a different approach, looking at a drug class called “co-stimulatory receptor blocking agents” that trains the immune system to ignore the transplanted cells.

To test their method, the researchers injected embryonic stem cells from mice into the legs of other mice with different genetic backgrounds. Researchers found that the stem cells did very well with spaced-out doses of blocking agents. In the past, cells died after 28 days with traditional immunosuppressants and 21 with no treatment.

The findings add to the debate about the relative merits of induced pluripotent stem (iPS) cells, which can be tailored to a patient’s immune system, and embryonic stem cells. The academic community has not settled whether iPS cells, which are derived from skin cells or other adult cells that normally do not divide into cells of a different type, can differentiate into new tissues as well as embryonic cells. The iPS cells are costly and time-consuming to produce, but in theory they allow researchers to avoid the ethical quandaries associated with embryonic stem cells and, given federal restrictions, are more available.

The researchers will next experiment with a wider variety of drug concentrations and types and start testing the technique in larger animals.

–Tyler Brown