"The Potential Is Immeasurable"

When Hwang Woo Suk, one of South Korea's leading cloning experts, hit a frustrating patch in his research last year, a neurosurgeon colleague suggested he spend time with some patients who might benefit from stem-cell research. Hwang met a young couple with a tragic tale. The day after their wedding, the newlyweds went hiking. The husband slipped on a mountain trail and injured his spine. In the five years since the accident, the man hadn't been able to walk or go to the bathroom without his wife's help.

"I realized these people are not living," Hwang, 51,...