Human stem cells restore movement in monkey after spinal cord injury
After four failed attempts, researchers have finally figured out how to place a graft of human stem cells into a monkey’s spinal cord to create new cells and promote healing. There were a number of challenges that slowed the success—surgery required a large amount of helpful proteins to act as a sort of “glue” for the stem cell graft, the surgical table had to be tilted just far enough so that cerebral spinal fluid would not wash the graft away, and the monkey required a large amount of immunosuppression so that its body would not immediately reject the human cells.
Surgery itself has not been nearly the biggest challenge. After a spinal injury, the body quickly organizes a web of structural molecules around the damaged site, minimizing the possibility for stem cells to extend new axon branches, and limiting the amount of beneficial molecules and other growth factors for the stem cells. To beat this barrier, neuroscientists have been testing cocktails of special molecules that could boost stem cell survival once implanted. After testing unsuccessfully on rats, researchers moved to monkeys without much hope. However, the monkey treated managed to surprise everyone.
As early as two months after surgery, the monkey had a massive amount of new neuronal branches growing from the injured site. The stem cells had developed into mature neurons, and some branches traveled as far as what would be the length of two spinal cord fragments in humans. Furthermore, the new branches were connecting with the monkey’s undamaged cells. The connections made between the human neural graft and the monkey’s own axons are promising evidence that transplanted stem cells can create the connections necessary to allow renewed voluntary arm movements in humans.
Nine months later, the monkey can now grasp basic objects. This is a major breakthrough for regenerative medicine, and the move from rodents to primates is an exciting development with a promising future.