Aaron and Christal Walker live in dread that their daughter will get sick, and in dread that she won't.

Six days ago, Avrey Walker, 9, of Redmond, Ore., became the seventh child to receive an experimental gene therapy for leukemia at Children's Hospital of Philadelphia.

She will soon suffer several days of fevers, nausea, headaches, maybe worse - if the therapy works as it should, marshalling her immune T cells to fight her cancer.

Four of the first five children to undergo treatment and get lab results are cancer-free, according to their families and doctors.

"The doctors said it would take seven to 10 days" for the flulike reaction to begin, Avrey's father said last weekend. "So we're just waiting and watching intently."

The medical and human drama of the T-cell therapy, developed at the University of Pennsylvania, is unfolding in ways the defy the staid traditions of scientific research. On Monday, the New England Journal of Medicine fast-tracked online publication of a paper about Children's first two pediatric patients. But those results - and more - have been out for months, released by the researchers at a conference, or by the families.

The first pediatric patient, Emily Whitehead, 7, of Phillipsburg, Pa., who remains in remission after almost dying, was the subject of worldwide headlines in December.

And last week, the larger story - the harnessing of the immune system to fight cancer after decades of trying - broadened beyond Penn and Children's.

Researchers at Memorial Sloan-Kettering Cancer Center in New York published results from five adult leukemia patients treated with an experimental T-cell therapy much like Penn's. Three of them have been in remission for up to two years; one went into remission but died of a blood clot; and one relapsed and died.

Penn's therapy has worked in adults, too, but those seven patients, who had complete or partial remissions, had a less aggressive form of the disease called chronic myelogenous leukemia.

Sloan-Kettering's results are very impressive, Penn researcher David Porter said.

Penn's team, led by Carl June, will soon collaborate with Sloan-Kettering to see which version of the T-cell therapy works better, Porter said.

The two groups use slightly different viral "vectors" to deliver a therapeutic gene into the T cells. That gene programs the T cells to recognize and kill B cells, the blood component that turns malignant in the leukemias.

"One of the issues is how much does the vector contribute to the patient's response," Porter said. "So we'll trade vectors, then give patients T cells made from both vectors."

Penn is also adapting its T-cell therapy to treat solid tumors such as ovarian cancer. Meanwhile, the early success - although in a small number of patients - is stimulating the field of immunotherapy.

Researchers at the National Cancer Institute and at least three major medical centers are planning or conducting clinical trials of T-cell therapies like Penn's.

Industry is investing, too. Novartis Pharmaceuticals is partnering with Penn. And biotech power Celgene announced this month a "strategic collaboration" on T-cell therapy research with Baylor College of Medicine in Houston.

Aaron Walker hopes it is the beginning of the end of trying to save children like Avrey using toxic, debilitating chemotherapy and radiation.

"My goal," he said, "is to let other families know that there's something out there besides years of suffering."

Contact Marie McCullough at 215-854-2720 or mmccullough@phillynews.com.