Doctors have successfully used a disabled version of HIV to modify a 7-year-old leukemia patient’s white blood cells to attack her cancer. The breakthrough procedure could potentially replace bone marrow transplant as a leukemia treatment.

Emma Whitehead was selected as a patient for the experimental technique after two years of battling with acute lymphoblastic leukemia, the New York Times reported. Chemotherapy failed to either cure the disease or result in a period of remission long enough for a bone marrow transplant.

The process was previously tested only on adult patients. In April, Whitehead became the first child to undergo the treatment, her medical team revealed during an annual meeting of the American Society of Hematology in Atlanta last weekend. She was also the first patient to be treated for her kind of leukemia.

Doctors from the University of Pennsylvania and the Children's Hospital of Philadelphia manipulated Whitehead’s immune system to make it target cancer cells. They took a batch of her own T cells – a kind of white blood cell – and genetically engineered them to kill the B cells – another kind of white blood cell – responsible for her disease.

To do this, the doctors used a modified and disabled form of HIV, the virus responsible for AIDS, to alter the T cells’ genes, making them produce a protein called a chimeric antigen receptor on their surface. This artificial protein matches another protein encountered only on the surface of B cells. The alteration allows T cells to attach to B cells, and destroy them. The genetically engineered T cells were then injected back into Whitehead’s blood, where they could reproduce on their own.

Two months after the procedure, testing revealed there was no sign of cancer in the girl’s body. The altered T cells were still present in her blood, but in smaller quantities than during treatment. Six months later, Whitehead is still in remission and is now back in school.

The experimental treatment has not yet been fully tested: Whitehead nearly died when the procedure caused a spontaneous high fever, and other near-fatal symptoms.

Not all of the 12 patients in the clinical trial responded to the treatment as well as Whitehead: Three adults with chronic leukemia had complete remissions; four improved their condition, but did not beat the disease completely; one is still in too early a stage to evaluate; two patients saw no effect from the treatment; another child initially responded, but eventually relapsed.

The treatment also kills healthy B cells along with malignant ones, making patients vulnerable to certain types of infections; patients require regular treatments of immune globulins to prevent illness.

T cell therapy appears to be a promising medical breakthrough that may replace older bone marrow treatments, the researchers said. They plan to conduct additional trials with at least a half-dozen patients over the next year.

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