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Seattle Children's T-Cell Immunotherapy Clinical Trial for Children With Relapsed Leukemia Shows 93% Complete Remission Rate

Phase 1 findings show 39 out of 42 patients achieved complete remission; Phase 2 of the trial to launch this month

Seattle Children's announced today that 39 of 42 patients treated in a Phase 1 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 2 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, who is the lead investigator for the trial and will present the Phase 1 results at the American Society of Clinical Oncology (ASCO) Annual Meeting on Sunday, June 5. "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 Jensen at 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 1 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 2 will demonstrate how this therapy works for a larger group of patients.

To learn about the experience of one of the patients who participated in the trial, please visit Seattle Children’s On the Pulse blog.

If you are interested in supporting the advancement of immunotherapy and cancer research at Seattle Children’s, please visit our donation page.

For more information on immunotherapy research trials at Seattle Children's, please call (206) 987-2106 or email

About Seattle Children’s

Seattle Children’s mission is to provide hope, care and cures to help every child live the healthiest and most fulfilling life possible. Together, Seattle Children’s Hospital, Research Institute and Foundation deliver superior patient care, identify new discoveries and treatments through pediatric research, and raise funds to create better futures for patients.

Ranked as one of the top children’s hospitals in the country by U.S. News & World Report, Seattle Children’s serves as the pediatric and adolescent academic medical center for Washington, Alaska, Montana and Idaho – the largest region of any children’s hospital in the country. As one of the nation’s top five pediatric research centers, Seattle Children’s Research Institute is internationally recognized for its work in neurosciences, immunology, cancer, infectious disease, injury prevention and much more. Seattle Children’s Foundation, along with Seattle Children’s Guild Association – the largest all volunteer fundraising network for any hospital in the country – works with our generous community to raise funds for lifesaving care and research.

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