Researchers begin first-in-human trial of T-cell immunotherapy in children with leukemia

By Liz Meszaros, MDLinx
Published May 10, 2017

Key Takeaways

Researchers have begun a first-in-human, phase 1, pilot study looking at whether T-cell antigen presenting cells can prolong the persistence of cancer-fighting chimeric antigen receptor (CAR) T cells and thus reduce relapse rates in children and young adults with leukemia.

Their study comes on the heels of results from the phase 1 Seattle Children’s Pediatric Leukemia Adoptive Therapy (PLAT-02) trial, in which researchers demonstrated that T-cell immunotherapy was effective in inducing complete initial remission in 93% of patients with relapsed or refractory acute lymphoblastic leukemia (ALL).

The new study, PLAT-03, is designed to assess the feasibility and safety of administering a second T-cell product in children and young adults to increase the long-term persistence of CAR T cells that had been reprogrammed to detect and destroy cancer. Researchers decided on this strategy after discovering that about 50% of patients who relapsed in the PLAT-02 trial had lost their CAR T cells.

The presence of these cells is essential in fighting cancer cell recurrence.

“While it’s promising that we’re able to get these patients who are very sick back into remission, we’re also seeing that the loss of the CAR T cells in some patients may be opening the door for the cancer to return,” said lead investigator Colleen Elizabeth Annesley, MD, oncologist, Seattle Children’s Hospital, Seattle, WA. “We’re pleased to now be able to offer patients who have lost, or are at risk of losing, their cancer-fighting T cells an option that will hopefully lead to them achieving long-term remission.”

In the PLAT-03 study, patients will receive “booster” infusions of a second T-cell product—T antigen-presenting cells (T-APCs), which have been genetically modified to express the CD19 target recognized by CAR T cells. It is through this stimulation of the CAR T cells with consistent target cells to attack that researchers hope to reactivate them and ensure that they survive long enough to put patients into long-term remission.

PLAT-03 is open for patients enrolled in phase 2 of the PLAT-02 trial who are at risk for early reprogrammed CAR T cell loss or those who lost reprogrammed cells within 6 months of receiving them.

The PLAT-03 study is one of several that researchers from Seattle Children’s Hospital have planned during the next year, with the goal of improving long-term efficacy of T-cell immunotherapy.

“We are pleased to be at a pivotal point where we are now looking at several new strategies to further improve CAR T-cell immunotherapy so it remains a long-term defense for all of our patients,” said lead investigator of PLAT-02, Rebecca Gardner, MD, Seattle Children's oncologist. “We’re also excited to be working to apply this therapy to several other forms of pediatric cancer beyond ALL, with the hope that T-cell immunotherapy becomes a first line of defense, reducing the need for toxic therapies and minimizing the length of treatment to only weeks.”

The T-cell immunotherapy trials at Seattle Children’s are funded in part by Strong Against Cancer, a national philanthropic initiative with worldwide implications for potentially curing childhood cancers. For more information on immunotherapy research trials at Seattle Children’s, please call (206) 987-2106 or email

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