Is stem cell regenerative therapy effective for herniated discs? if so, where are the leading research centers in the field?

Not so much: There is hope that stem cells will someday be used to treat symptomatic degenerative discs; but herniated discs are different. When your disc herniated, inflammatory cells migrate into the area and have the capability if resorting the herniated fragment approximately 80-90 percent if the time. Stem cells have not been shown to improve that process at this point.