University life is a different experience for different people. For some, it’s about learning skills, acquiring knowledge, or making friends and contacts. For others, it may broaden their idea of what’s possible. “As an undergraduate, you sometimes bop along until something excites you,” says John Gearhart, who received his bachelor’s degree in horticulture in 1964. “For me it was a genetics course. I discovered that genetics really turned me on—the idea that all of the life around us is controlled by subcellular entities called genes.”

Today, Gearhart is an internationally acclaimed developmental geneticist who, in 1997, became the first scientist to grow human stem cells in a lab dish. A professor of gynecology and obstetrics at The Johns Hopkins University School of Medicine, he also directs the country’s largest federally funded research program on Down’s syndrome and runs Hopkins’ Preimplantation Genetic Diagnosis Program, a service for couples who carry the genes for genetically based diseases such as hemophilia, Tay-Sachs, and cystic fibrosis. In this program, he explains, couples undergo in vitro fertilization. This allows them to have their embryos examined and ensures that only healthy embryos are transferred to the uterus.

But it’s Gearhart’s research on human stem cells that has the most far-reaching implications. “Stem-cell biology is based on the idea that you can recover undifferentiated cells in the body—from the embryo, the fetus, and bone marrow—and manipulate them to form new tissues,” Gearhart explains. “Stem cells contain the genetic information to become virtually any cell in the human body. They’re just waiting for some signal in their environment to tell them what to become.”

As was Gearhart in the early 1960s. His first research project was in horticulture professor Dick Craig’s lab, working with the genes responsible for the color of geraniums. “My dad had a farm in the mountains outside Blairsville and I wanted to develop bigger and better apples and peaches,” he says, laughing. Although he soon learned that isolating genes wasn’t the shrewd way to improve fruit, genetics continued to be the thread he would follow through his academic career, from geraniums to corn to fruit flies to mice to—finally—humans.

Now, he’s transplanting stem cells into mice, where they develop into neurons, blood cells, and heart cells that actually grow and function. “We can create a spinal cord injury, for instance, then transplant the cells into the mouse and show that they restore some ambulatory capacity. The cells can integrate into the heart muscle and strengthen a weak heart. We’ve even been able to reconstitute blood that’s been lethally irradiated.” The next step is to transplant the cells into humans. “In three to five years, we should be in clinical trials for spinal cord injuries and Parkinson’s disease,” he says. “It’s an exciting time.”

But stem-cell research is not without controversy. Gearhart has spoken before the United States Congress, the French Parliament, the German Bundenstag, and other world leaders as they develop policies concerning the use of these cells. The global publicity also has been difficult for Gearhart on a personal level. “We’ve received thousands of requests from patients for the transplantations,” he says. “They want to be first, they want to get in line. These people are very sick, or they have a family member who is very sick. They won’t be able to come back in five or ten years when the therapy’s ready. It’s really hard to hear their stories.”

In the early 1960s, when Gearhart was studying horticulture, genetics was in its infancy. All scientists knew was that genes are composed of molecules called DNA and make RNA before forming protein. “Genetics still tantalizes me,” he says. “We’ve sequenced the human genome, but we still don’t know how genes work. We still don’t know how—out of 70,000 genes—you form an organism.”