Regenerative medicine is a field that is still very much in its infancy. "Before stem cells can lie used routinely, there is a great deal more that researchers have to learn," reports one embryonic stem cell researcher. "We still don’t know what signals are required to make the stem cells mature into specific tissue types. It’s also only educated guessing at this point about how to avoid tumor formation or rejection after transplanting stem cells into a new host. You might say that Nature holds her cards close." (Potten et al 2006)
The rejection issue is being researched at Stanford University, utilizing strains of laboratory mice for testing. Dr.Vlicha Drukker has been part of an international research team examining the immune response that might be launched against transplanted stem cells. "We used two experimental platforms to examine the in vivo immune system response toward transplanted stem cells," said Dr. Drukkcr. "First, mice with both normal and iminunodcficieiit immune systems were used to identify T cells as the major component that causes rejection." T cells are a subset of leukocytes, or white blood cells. They can be thought of as the "hunter-killer" cells that swarm an infection. "Second," said Drukkcr, "mice that were conditioned to carry peripheral blood leukocytes from human origin were used to test the response toward undifferentiated and differentiated human embryonic stem cells." (Potten et al 2006)
Using this model, Drukker’s research team detected only a minute immune response toward both undifferentiated and differentiated stem cells over the course of a month. "Our data showed that stem cells evade immune destruction due to a low immuno stimulatory potential," said Drukkcr. (Potten et al 2006) If this feat is replicated in human stem cell transplants, then the possibilities for healing damaged organs and tissue without fear of rejection greatly expands the range of possibilities for stem cell therapies.
