More than 90 percent of children and young adults with acute lymphoblastic leukemia, or ALL, are in remission after treatment as part of a promising Seattle Children’s clinical trial, researchers reported.

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A year ago, Meagan Mullanix was waiting to see whether the experimental therapy would work, whether her own genetically reprogrammed immune-system cells could truly target and destroy the cancer that nearly killed her.

Today, the 23-year-old returning college student is cancer-free, with no evidence of the acute lymphoblastic leukemia, or ALL, that first struck when she was 17, and then came raging back — even after chemotherapy treatments and a bone-marrow transplant.

“I’m feeling great. I’m coming up on my year on April 25 and it looks like I’ll make it,” said Mullanix, one of the first patients enrolled in a Seattle Children’s clinical trial that uses genetically modified T-cells, a form of white blood cell, to target the deadly cancer in patients from toddlers to young adults.

Of 22 participants in the trial that began in January 2014, 20 have achieved complete remission, according to tests designed to detect minute traces of cancer cells.

That’s more than 90 percent success in the patients with the most serious prognoses, those with high tumor burdens or who were diagnosed as babies, according to data released Tuesday at the annual meeting of the American Association for Cancer Research (AACR).

“These results are extremely encouraging,” said Dr. Mike Jensen, director of the Ben Towne Center for Childhood Cancer Research at Seattle Children’s Research Institute, who will present the results.

Also encouraged is Dr. Rebecca Gardner, the Seattle Children’s pediatric cancer expert who is leading the trial of the cutting-edge procedure now performed at a handful of sites nationwide.

In the first phase, she has focused on the sickest ALL patients, those who have relapsed after chemotherapy treatment or bone-marrow transplant, who typically have just a 10 percent to 20 percent chance of survival. But the new results have been so promising, the procedure is being considered as a potential front-line treatment.

“This gives us hope that, eventually, we’ll be able to use this therapy in patients who are newly diagnosed, reducing the need for toxic therapies and bone-marrow transplants,” Gardner said.

Dr. Jonathan Lopez discusses scans of Meagan Mullanix’s brain with Meagan and her mother, Sally Mullanix. Meagan, 23, was diagnosed with cancer at age 17, failed treatment twice, including a bone-marrow transplant.  (Mark Harrison / The Seattle Times)
Dr. Jonathan Lopez discusses scans of Meagan Mullanix’s brain with Meagan and her mother, Sally Mullanix. Meagan, 23, was diagnosed with cancer at age 17, failed treatment twice, including a bone-marrow transplant. (Mark Harrison / The Seattle Times)

The protocol works by removing millions of T-cells from the patient and then using a viral vector to introduce antibodylike proteins called CARs, or chimeric antigen receptors, to the cells. The re-engineered cells are designed to target a protein on the surface of malignant B-cells known as CD19. The modified T-cells are returned to the patient, where they bind to the B-cells, destroying them — and the cancer.

“It basically tricks the T-cell into killing what you want it to kill,” Gardner said.

A future trial in adults is planned using a cell product candidate known as JCAR017, manufactured by Juno Therapeutics, a biomedical firm in Seattle.

In Mullanix’s case, it took only 10 days for her reprogrammed cells to eliminate the cancer.

“Her T-cells did a fantastic job of growing and expanding,” Gardner said.

In fact, her cells proliferated so strongly that Mullanix developed one of the signature signs that the treatment is taking hold, a so-called “cytokine storm.”

That occurs when the natural chemicals flood from the cells in the immune system as they are activated, causing high fevers, chills and other symptoms.

“Her body replicated the cells so quickly, it created a firestorm in her brain,” said Sally Mullanix, 56, Meagan’s mother.

Meagan Mullanix’s reaction was so severe that doctors had to shut down her engineered T-cells or risk death. It left her with lingering neurological problems that have led to seizures. She takes medication now to control it but could require surgery in the future, said her mom.

Those complications have kept Meagan Mullanix from fully launching back into her life. She’s waiting for the all-clear to drive again, for instance, six months after her last seizure. She stays home a lot, making her feel “cooped-up,” and says she can’t wait to head back to a local community college in the fall.

But the young woman who’s been grappling with the disease since high school said she’s not complaining.

“I’m cancer-free, so that’s great,” she said.

The results of the new trial are “very good news,” said Dr. Stephen J. Forman, a cancer expert and stem-cell transplant specialist at The City of Hope National Medical Center in Duarte, Calif.

Although he’s not involved with this trial, he and Jensen have worked closely together, he said, and they’ve mused about whether the treatment could substitute for chemotherapy in children and adults with ALL.

“It simply puts the question out there, is it possible to use this therapy in the front part of therapy?” he said.

For Meagan Mullanix, who endured five years of harsh therapies, using the protocol as a first step instead of a last resort for the disease would be ideal.

“That is honestly what I was hoping for when I first found out about the treatment,” she said. “I wish it were available to everyone.”