After about five years of testing in humans, an experimental cell therapy that boosts the immune system continues to produce long remissions in many patients with a variety of advanced blood cancers, says a team of researchers at the University of Pennsylvania and Children's Hospital of Philadelphia.

The team, led by Penn gene therapy pioneer Carl June, presented the latest results last week at the annual meeting of the American Society of Hematology.

The personalized immunotherapy is complex and takes weeks to produce; it involves removing and engineering each patient's own disease-fighting T cells to attack the white blood cells that turn malignant in certain leukemias and lymphomas. The engineered T cells are then multiplied and put back into the patient.

Pharmaceutical giant Novartis is partnering with Penn to commercialize the therapy, which last year received the U.S. Food and Drug Administration's "breakthrough" designation, intended to expedite approval. This winter, Penn expects to open the Center for Advanced Cellular Therapeutics, a 30,000-square-foot facility being built in collaboration with Novartis to double production capacity for the T cell therapy.

The latest results show that the therapy continues to work best in pediatric acute lymphoblastic leukemia. Of the first 59 children and young adults treated, 55 (94 percent) had a complete response, meaning their cancer disappeared. However, cancer eventually returned in 20 of those complete responders (36 percent). In 13 children who relapsed, the cancer returned by growing in white blood cells that the T cells were not programmed to attack.

With a median follow-up of one year (meaning half were followed for a less than a year, and half for more than a year), 34 pediatric patients remain in complete remission. (The first child treated, Emily Whitehead, 10, of Philipsburg, PA, has been cancer-free more than three and a half years. Her parents, Kari and Tom, this year  established a foundation in her name to raise money for childhood cancer research.

The T cell therapy has also been used in 28 adults with three types of non-Hodgkin lymphoma that had stopped responding to conventional treatments.  Of those 28 adults, 14, or half, had complete remissions, and several more had partial responses. After a median follow-up of 14 months, the blood cancers had not progressed in more than half of the patients who responded.

Although the rates and durations of responses are impressive compared to conventional treatments, the T cell therapy also causes severe and occasionally life-threatening toxicities in the majority of patients. The researchers presented data from a study in which they found certain chemical markers were elevated in the blood of patients who became critically ill. In the future, the researchers hope to identify patients likely to need a drug that acts as an antidote to the T cell therapy toxicities.

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