WASHINGTON, Jan. 23 (Xinhua) -- The U.S. Food and Drug Administration (FDA) has approved the first human trials of human embryonic stem cell research, authorizing researchers to test whether the cells are safe to use in spinal injury patients, U.S. biotech firm Geron Corp. announced Friday.

    The tests could begin by summer, said Dr. Thomas Okarma, president and CEO of the Geron Corp. The trials will use human stem cells authorized for research by then President George W. Bush in 2001. The patients will be those with the most severe spinal cord injuries, called complete spinal cord injuries.

    The primary purpose of the trial will be to see whether injecting these cells into patients is safe, but Okarma said researchers will also look for any signs of recovery. Scientists will monitor the patients for a year after the injections to see if they are regaining any function below the injured point.

    Whatever its outcome, the study will mark a new chapter in the history of embryonic-stem-cell research in the United States -- a field where debate spilled out of the laboratory long ago and into national politics. While some overseas doctors claim to use human embryonic stem cells in their clinics, stem-cell experts said they knew of no previous human studies that use such cells.

    The trials will involve eight to 10 patients who are completely paralyzed below the third to 10th vertebra, and who sustained their spinal cord injury within seven to 14 days. The tests will use stem cells cultured from embryos left over in fertility clinics, which otherwise would have been discarded.

    Using the stem cells, researchers have developed cells called oligodendrocytes, which are precursors to nerve cells and which produce a protective layer around nerve cells known as myelin. Researchers will inject these nerve cells directly into the part of the spine where the injury occurred.

    Embryonic stem cells are blank cells found in four- to five-day-old embryos, which have the ability to turn into any cell in the body. However, when stem cells are removed, the embryo is destroyed -- which has made this one of the most controversial medical research fields in the past decade.

    Federal research funds were prohibited for embryonic stem-cell research until August 2001, when Bush approved spending for research using only already-existing cell lines. Scientists later discovered that fewer than two dozen of those lines were useful for research, but abortion opponents opposed any legislation that would lift Bush's restrictions, and Bush twice vetoed congressional efforts to roll back his rules.

    President Obama is expected to loosen the restrictions, which many researchers and advocates have complained severely set back work toward curing disease such as Alzheimer's, Parkinson's and diabetes.