Yesterday afternoon, one of the biggest announcements in the history of stem cell research came down: The Food and Drug Administration approved the first clinical trial of injecting embryonic stem cells into a human being. The Geron Corp., based in California, officially said this morning that it has the FDA's go-ahead to begin the first stage of testing with up to 10 patients suffering serious spinal cord injuries.

The treatment is called GRNOPC1, and the procedure isn't any less complicated to articulate: "The ultimate goal for the use of GRNOPC1 is to achieve restoration of spinal cord function by the injection of hESC-derived oligodendrocyte progenitor cells directly into the lesion site of the patient's injured spinal cord," Thomas Okarma, Geron's CEO, says in the company's announcement. Here's a general translation for those of us who didn't attend biomedical school.

Let's start with what Geron is fighting: Demyelination. Myelin is the protective substance that sheaths nerve cells called axons, increasing the speed at which signals travel down them. Some severe spinal injuries result in a breakage of the myelin sheath, which interrupts the signals. Cells called oligodendrocytes produce myelin for your central nervous system, and Geron's plan involves using oligodendrocyte progenitor cells. These progenitor cells should grow into oligodendrocytes once injected into the spinal area, Okarma hopes, and help to recreate the lost protective myelin.

The process is an intrusive one. In phase one, researchers plan to find patients with severe spinal cord injuries that were inflicted between 7 and 14 days before the stem cell injections. The first injection will pump in about 2,000,000 cells—fewer than have been used, relative to size, in animal trials, because phase one trials have to ensure that the procedure is safe. The researchers have done 24 rodent experiments in which the procedure successfully restores some myelin. —Andrew Moseman