STATE COLLEGE, Pa. — A 7-year-old Pennsylvania girl, after a two-year battle with acute lymphoblastic leukemia, became the first child to receive an experimental treatment that used a genetically modified version of her own immune system to fight it off.

Emily “Emma” Whitehead and her parents, Tom and Kari Whitehead of Philipsburg, Pa., turned to experts at the University of Pennsylvania and the Children’s Hospital of Philadelphia for help when chemotherapy failed and she could not remain in remission long enough to receive a bone-marrow transplant.

In April, Emily became the first child have her own T cells – infection-fighting white blood cells in her immune system – genetically engineered to recognize and attack the cancer cells in her body. The doctors removed her T cells through a process similar to blood donation, programmed them to attack her cancer, then grew them and injected them back into her body.

Two months later, tests on Emily had found no cancer and she got to go home.

Since then, the doctors and researchers have been using what they learned from Emily’s case to treat other cancer patients who have run out of conventional options. They described their work over the weekend at the American Society of Hematology’s annual meeting in Atlanta.

Their aim is to eventually replace bone-marrow treatments with the new T cell therapy.

“We are basically trying to treat cancer a whole new way,” said Dr. Stephen Grupp, the pediatric oncologist who treated Emily at the Philadelphia hospital.

T cells are “immune cells in the body that are actually very good at getting rid of cells that don’t belong,” Grupp said, but “unfortunately, cancer is really good at dodging T cells.”

Researchers have been working for years to develop a way to “train” these cells to multiply and attack cancer, similar to a vaccine.

But “all those efforts have been essentially unsuccessful because once you get a big tumor in your body, it’s very hard to marshal up the immune system,” said Michael Kalos, director of the Translational and Correlative Studies Laboratory in Penn’s Perelman School of Medicine.

So researchers decided to attempt to grow the T cells outside the body so there would be plenty to fight off a tumor. This process is known as adoptive T cell transfer, or adoptive immunotherapy.

“So instead of trying to stimulate or trigger a rare cell in somebody’s body by a vaccine, you give them the end product of that, which is a billion cells that are engineered to recognize what you want them to recognize,” Kalos said.

Emily’s form of cancer is leukemia of the B cells, which are another type of white blood cell.

Researchers are “putting in a new gene using a virus. That gene gets incorporated into the actual DNA of the cell and that gene produces a new protein that doesn’t exist in nature,” Grupp said.

The two innovations that make the treatment possible are creating the new protein, and then getting it onto the T cell’s surface.

That protein is called a chimeric antigen receptor, or CAR, and it forces a T cell to go after and bind with a target on a cancer cell.

In Emily’s case, that target is another protein, called CD 19, which is only present on the surface of B cells.

“You could call that the ‘guided missile rationale,’” said Bruce Levine, director of the Clinical Cell and Vaccine Production Facility, because the T cells only kill the B cells. That is different from traditional chemotherapy, which doesn’t have a specific target.

Penn researchers first reported on this type of successful T cell treatment last year. Three adults were treated and two had complete remission. Their cases were detailed in the New England Journal of Medicine and Science Translational Medicine in August 2011.

Two years after treatment, the two adults still have no evidence of disease – they also still have the engineered T cells in their bodies, a major scientific breakthrough, researchers said.

“The problem is that lots of people have figured out how to engineer T cells, lots of people figured out how to grow T cells in a lab, but nobody figured out how to make the cells actually grow in the patient,” Grupp said.

That is, until now.

This weekend, researchers shared new data showing that nine of 12 patients with advanced leukemia in the clinical trial, including Emily and another child after her, responded to treatment.

“When we first treated our first three adults ... the results came back over a period of six weeks, and at that point I knew that my life was forever changed,” said June, director of translational research in Penn’s Abramson Cancer Center.

“We were worried that there was a small number of patients but what we’ve seen has never been seen before. And now ... two years later, the results have held up and we have more patients. ... I was always worried that this is a fluke of small numbers ... but now we know that is wasn’t just a fluke. In April, when Emily got treated, it both confirmed it and then showed that it works in a different kind of cancer.”

June hopes that genetically engineered T cells will one day replace more invasive procedures such as bone-marrow transplants.

The Penn research team is working to expand the study soon with more pediatric and adult patients.