First-In-Human Clinical Trial Aims to Extend Remission for Children and Young Adults With Leukemia Treated With T-Cell Immunotherapy

Phase 1 pilot study utilizes T-cell antigen presenting cells to prolong the persistence of cancer-fighting chimeric antigen receptor (CAR) T cells, reduce the relapse rate

After phase 1 results of Seattle Children’s Pediatric Leukemia Adoptive Therapy (PLAT-02) trial have shown T-cell immunotherapy to be effective in getting 93 percent of patients with relapsed or refractory acute lymphoblastic leukemia (ALL) into complete initial remission, researchers have now opened a first-in-human clinical trial aimed at reducing the rate of relapse after the therapy, which is about 50 percent. The new phase 1 pilot study, PLAT-03, will examine the feasibility and safety of administering a second T-cell product intended to increase the long-term persistence of the patient’s chimeric antigen receptor (CAR) T cells that were reprogrammed to detect and destroy cancer.

The research team, led by Dr. Mike Jensen at the Ben Towne Center for Childhood Cancer Research at Seattle Children's Research Institute, is exploring this strategy after discovering that of the patients who relapse in the PLAT-02 trial, about half of them have lost their CAR T cells. Lasting persistence of the CAR T cells is critical in combating a recurrence of cancer cells.

“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 Dr. Colleen Annesley, an oncologist at Seattle Children’s and the lead investigator of the PLAT-03 trial. “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 trial, patients will receive “booster” infusions of a second T-cell product, called T antigen-presenting cells (T-APCs). The T-APCs have been genetically modified to express the CD19 target for the cancer-fighting CAR T cells to recognize. Patients will receive a full dose of T-APCs every 28 days for at least one and up to six doses. By stimulating the CAR T cells with a steady stream of target cells to attack, researchers hope the CAR T cells will re-activate, helping to ensure their persistence long enough to put patients into long-term remission.

PLAT-03 is now open to patients who first enroll in phase 2 of Seattle Children’s PLAT-02 trial and who are also identified as being at risk for early loss of their reprogrammed CAR T cells, or those who lose their reprogrammed CAR T cells within six months of receiving them.

The PLAT-03 trial is one of several trials that Seattle Children’s researchers are planning to open within the next year aimed at further improving the long-term efficacy of T-cell immunotherapy. In addition to the current T-cell immunotherapy trial that is open for children with neuroblastoma, researchers also hope to expand this promising therapy to other solid tumor cancers.

“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 Dr. Rebecca Gardner, Seattle Children's oncologist and the lead investigator of the PLAT-02 trial. “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.”

To read about the experience of one of the patients in the PLAT-02 trial, please visit Seattle Children’s On the Pulse blog.

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. If you are interested in supporting the advancement of immunotherapy and cancer research, please visit Strong Against Cancer’s donation page.

For more information on immunotherapy research trials at Seattle Children’s, please call (206) 987-2106 or email immunotherapy@seattlechildrens.org.

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 Hospital and Research Foundation works with the Seattle Children’s Guild Association, the largest all-volunteer fundraising network for any hospital in the country, to gather community support and raise funds for uncompensated care and research.

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