Seattle Children's doctors and researchers are leading efforts to better treat leukemia by boosting the immune system with immunotherapy.

Immunotherapy is a new cancer treatment that stimulates a patient's immune system to better fight disease. It is also known as targeted therapy or biotherapy. Our research studies include Phase I and Phase II clinical trials. These trials are paving the way for other steps that may turn immunotherapy into a standard leukemia treatment, and someday even a cure.

Two trials at Seattle Children's are testing T-cell therapy in children and young adults with relapsed or refractory acute lymphoblastic leukemia (ALL) who are not likely to survive with current treatments. These trials are known as pediatric leukemia adoptive therapy (PLAT)-01 and PLAT-02.

Doctors hope that when this new therapy is fully tested:

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

What is T-cell therapy?

T cells are white blood cells in the immune system that fight infection. The goal with PLAT is to reprogram a patient's own T cells so they can seek out and destroy cancer cells wherever they are hiding in the body. 

The steps in this process are:

  1. A blood sample is drawn from the patient at Seattle Children's Hospital. This sample goes to a special part of Seattle Children's Research Institute called the Therapeutic Cell Production Core. Lab staff remove the T cells from the sample, purify them and reprogram them. In this case, "reprogram" means to change the T cells by adding recombinant DNA (genetically modify them). Then, the newly programmed T cells are grown to multiply into billions of new cells.
  2. The changed T cells are put back into the patient's body through an intravenous (IV) infusion .
  3. The change tells the T cells to make a place on their surface (a receptor) that acts like Velcro. This receptor allows the T cells to recognize and bind to a target on the cancer cells (a protein called CD19). When they bind, the T cells can attack the cancer cells as if they were fighting an infection. The receptor that's made on the T cells is called a chimeric antigen receptor (CAR). T cells that have the receptor may be called CAR T cells.
  4. The changed T cells are put back into the patient's body through an IV infusion. The hope is that the changed cells will go to work right away, finding and destroying the cancer cells. The change made to the T cell also "tags" the cells so our research team can track them in the body. If doctors want to stop the action of the T cells later, they can do this with the drug cetuximab, which recognizes the tag.

What are the goals of the studies?

PLAT-01 is a Phase I trial. PLAT-02 is a Phase I and Phase II trial. Phase I 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 II 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 patients with relapsed or refractory ALL?
  • What is the largest dose that patients can stand (the maximum tolerated dose)?
  • Does T-cell therapy work against ALL?

Also, these clinical studies are meant to show that T cells taken from patients can be changed in the same way that T cells were changed in laboratory studies earlier.

Who can join the studies?

The PLAT studies are for patients who:

  • Have relapsed or refractory CD19+ ALL – not other leukemias or other childhood cancers
  • Are ages 1 to 26 years old

Researchers use many other factors to decide whether a patient can take part in a study (inclusion criteria) or cannot take part (exclusion criteria). A full list of these factors for the PLAT studies is at The study team at Seattle Children's can explain what these factors mean for you or your child.

We are currently enrolling patients in a Phase I clinical trial testing T-cell therapy in children and adolescents with recurrent or refractory neuroblastoma.

Who is leading the trials?

Dr. Rebecca Gardner is leading these trials. Both PLAT-01 and PLAT-02 use a method developed by Dr. Michael Jensen of the Ben Towne Center for Childhood Cancer Research at Seattle Children's Research Institute.

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