Seattle Children's has announced that 39 of 42 patients treated in a phase I clinical trial using genetically reprogrammed T cells to treat relapsed or refractory acute lymphoblastic leukemia (ALL) have achieved complete remission, showing no detectable leukemia cells in the most sensitive tests. Patients treated in the trial, known as Pediatric Leukemia Adoptive Therapy-02 (PLAT-02), had less than a 20% chance of survival upon enrollment using current treatments. Seattle Children's will launch phase II of the trial this month, with the aim to enroll 70 patients in the next year.

"Seeing 93% of our patients achieve complete remission is incredibly promising," said Seattle Children's oncologist, Dr. Rebecca Gardner, lead investigator for the trial. "We have patients who are still in remission two years after receiving this therapy. While we still have a lot of work to do, our findings give us tremendous hope as this therapy offers children, who are otherwise unlikely to survive, a real chance at achieving remission."

The PLAT-02 trial includes patients with ALL who have relapsed after a bone marrow transplant, or who are unable to get into remission to proceed with a bone marrow transplant. Using T-cell immunotherapy, the research team led by Dr. Mike Jensenat the Ben Towne Center for Childhood Cancer Research at Seattle Children's Research Institute reprograms a patient's T cells so they can hunt down and destroy cancer cells wherever they are hiding in the body.

Gardner, who is also an investigator in the Center for Clinical and Translational Research, said they have been successful in reprogramming and growing T cells for all patients who have enrolled in the trial, a promising finding as similar trials have experienced difficultly producing T cells for all patients.

Another key finding from phase I is that of the patients who achieved initial remission, about 50% are still in remission one year after therapy. For the patients that relapsed, researchers have found that their reprogrammed T cells are no longer present or the cancer has evolved to circumvent the T cells.

"Now that we know we can harness the power of the immune system to successfully get patients into remission, we are working to ensure the T cells remain a long-term defense against cancer for all of our patients," Gardner said. "Our ultimate goal is to fully develop this therapy so we can offer it to newly-diagnosed patients, reducing the need for toxic therapies and minimizing the length of treatment from months or years, to only weeks. We also believe ALL is the tip of the iceberg work is already underway to apply immunotherapy to other forms of pediatric cancers, like neuroblastoma."

The first phase of PLAT-02 was integral in establishing the safety of the therapy and the optimal dose of T cells. Phase II will demonstrate how this therapy works for a larger group of patients.