Seattle Children’s doctors and researchers are leading efforts to better treat leukemia in children and young adults by boosting the immune system with T-cell immunotherapy.

Immunotherapy is an experimental new cancer treatment that stimulates the immune system to fight disease. It is a type of targeted therapy (also known as biotherapy). Our research studies include phase 1 and phase 2 clinical trials. These trials are paving the way for other steps that may turn immunotherapy into a standard treatment for childhood leukemia, and someday even a cure.

FDA-authorized trials at Seattle Children’s are testing T-cell therapy in children and young adults with relapsed or refractory acute leukemia or lymphoma who are not likely to survive with current treatments. These trials are known as Pediatric Leukemia Adoptive Therapy (PLAT).

Doctors hope that when T-cell therapy is fully tested:

  • It will work quickly, so pediatric leukemia treatment takes weeks, not years.
  • It will have milder side effects than other treatments, like chemotherapy.

  • T cells are white blood cells in the immune system that fight infection. In T-cell therapy, we take T cells from the child’s own blood. Using laboratory techniques, we reprogram the T cells to recognize cancer cells, and we grow the reprogrammed T cells into millions of cells. Then, we take the reprogrammed T cells and return them to the child’s body. Once in the body, the T cells seek out and destroy cancer cells without harming normal, healthy cells.

    Our doctors hope T-cell therapy will transform care for some childhood cancers, making treatment more effective, in less time, with milder side effects. We develop clinical trials of novel therapies like this so we can continue to provide the highest level of care for each child.

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    Watch Dr. Michael Jensen describe this new immunotherapy treatment for childhood cancer.

Is T-cell therapy effective?

The clinical trials needed to answer that question are ongoing, but early results are very promising.

In April 2017, Seattle Children's published that 40 of 43 patients treated in the phase 1 PLAT-02 clinical trial achieved complete initial remission.

  • This 93% remission rate was confirmed by highly sensitive tests designed to detect tiny amounts of cancer cells.
  • The 40 patients who have achieved complete remission included children with very high tumor burdens as well as children who were diagnosed with acute lymphoblastic leukemia (ALL) as infants. When they started the clinical trial, patients had less than a 20% chance of survival using current treatments.
  • Of the patients who achieved initial remission, about 50% are still in remission 1 year after therapy. Some are still in remission more than 2 years after therapy. For the patients whose cancer came back (relapsed), researchers have found that their reprogrammed T cells are no longer in their body or the cancer cells have changed so that the T cells cannot find and destroy them.
  • In PLAT-02, the CAR-T cells are reprogrammed to recognize and target CD19, a protein most leukemia cells express. However, in some patients, the leukemia comes back (recurs), and has evolved so that it doesn't express CD19 anymore and can escape the CAR T cells.
  • New trials (PLAT-03 and PLAT-04) are testing methods to make the T cells last longer and prevent the cancer from escaping the T cells, with the aim of consistently providing long-term remission.
  • Our researchers are also working to develop a trial with reprogrammed CAR T cells that can identify CD19 and CD22 proteins simultaneously. This would allow them to target the cancer cells from both angles with the first round of T-cell immunotherapy.

  • After patients receive an infusion of their reprogrammed T cells, some can experience a side effect called cytokine release syndrome (CRS). This usually involves a fever and changes in blood pressure. Other patients can experience neurological side effects that typically involve temporary confusion or being overly tired (lethargy). In rare cases these side effects could be more severe.

    Read about Dr. Rebecca Gardner’s success in limiting these side effects.

What is the goal of the PLAT studies?

PLAT includes phase 1 and phase 2 trials. Phase 1 trials focus on finding out how much of a therapy to give, how to give it, how often to give it and when side effects occur. Phase 2 trials look at whether a therapy is safe and whether it works in people who have a certain disease.

Through the PLAT studies, researchers are working to answer these questions:

  • Is T-cell therapy safe to give to children and young adults with relapsed or refractory acute leukemia or lymphoma?
  • What is the largest dose that children and young adults can stand (the maximum tolerated dose)?
  • Does T-cell therapy work against leukemia?

  • In PLAT-02, the CAR T cells are reprogrammed to recognize and target the CD19 protein expressed by most leukemia cells.

    The first phase of PLAT-02 was important in establishing the safety of this experimental therapy, short-term side effects and the maximum dose of T cells.

    Phase 2 began in June 2016 and is currently enrolling patients. It will demonstrate how this therapy works for a larger group of patients with relapsed or refractory acute leukemia or lymphoma.

    For more information, call 206-987-2106 or send us an email.

  • PLAT-03 is a phase 1 trial that will test the feasibility and safety of giving a series of 1 to 6 “booster” infusions called T cell antigen-presenting cells (T-APCs). These will be given to children and young adults after they receive their initial T-cell therapy on PLAT-02. The infusions of T-APCs are intended to make the patient’s reprogrammed cancer-fighting T cells last longer.

    PLAT-03 is now open to patients who:

    • Are enrolled in phase 2 of Seattle Children’s PLAT-02 trial
    • Are also identified as being at risk for losing their reprogrammed T-cells shortly after T-cell therapy
    • After receiving T cells through PLAT-02, have lost their reprogrammed T cells within 6 months

    For more information, call 206-987-2106 or send us an email.

  • PLAT-04 is a phase 1 trial that tests the safety and feasibility of CAR T cells that have been reprogrammed to target the CD22 protein expressed by some leukemia cells.

    The PLAT-02 trial uses CAR T cells that have been reprogrammed to target the CD19 protein. However, in some patients, the leukemia comes back (recurs) and has evolved so it doesn’t express CD19 anymore, but it continues to express another protein, CD22.

    Our researchers developed PLAT-04 as an investigational treatment option that will hopefully lead to long-term remission for patients whose cancer expresses CD22.

    For more information, call 206-987-2106 or send us an email.

Who can join the PLAT studies?

The PLAT studies are for children and young adults who:

  • Have relapsed or refractory pre-B acute lymphoblastic leukemia (ALL) or other CD19+ or CD22+ acute leukemia or CD19+ non-Hodgkin lymphoma. It is not open to young people with other leukemias or other childhood cancers.
  • Are ages 1 to 26 years old
  • Patients must be enrolled in PLAT-02 in order to be eligible for PLAT-03.

Researchers use many other factors to decide whether a patient can take part in a study (inclusion criteria) or cannot take part (exclusion criteria). The study team at Seattle Children’s can explain what these factors mean for you or your child.

Are there studies for other childhood cancers?

Who is leading the trials?

All are doctors in the Cancer and Blood Disorders Center at Seattle Children’s Hospital. Gardner and Summers are investigators in the Ben Towne Center for Childhood Cancer Research at Seattle Children’s Research Institute.

The PLAT trials use methods developed by Dr. Michael Jensen of the Ben Towne Center for Childhood Cancer Research.

Contact Us

For more information, call 206-987-2106 or send us an email.

Learn More

Updated July 2017.

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