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WASHINGTON -- The FDA on Wednesday for treatment of certain pediatric and young adult patients with relapsed or refractory B-cell precursor acute lymphoblastic leukemia.

Calling it a "historic action," the agency said the approval marks the "first gene therapy available in the United States."

The treatment, to be tradenamed Kymriah and carrying the generic name tisagenlecleucel, is sold by Novartis. The company said it will charge $475,000 for the one-time treatment.

In this type of therapy, patients' own immune cells are modified ex vivo to include a gene for the CAR protein, which directs them to attack leukemia cells carrying the CD19 antigen.

An FDA advisory committee had unanimously recommended the approval at a meeting last month.

However, tisagenlecleucel (also known as CTL019) can cause severe side effects, particularly a condition called cytokine release syndrome (CRS) that can become life-threatening.

The FDA is including a boxed warning for CRS and, in an unusual move, also approved a new indication for the rheumatologic drug tocilizumab (Actemra) as a treatment for CRS. The agency said that 69% of patients developing the condition during CAR T-cell trials "had complete resolution of CRS within 2 weeks following one or two doses" of tocilizumab, which inhibits interleukin-6.

In a call with the media, FDA Commissioner Scott Gottlieb, MD, discussed the “cross-agency approach” involved in this approval, with both the Oncology Center for Excellence and the Center for Biologics Evaluation and Research collaborating. Gottlieb said that this “more collaborative scientific model for review” will be employed in the future, as the agency is committing to “expediting new and groundbreaking therapies.”

Gottlieb noted that there are currently more than 550 investigational new drug applications for gene therapy products, including 76 related to CAR T-cells.

Peter Marks, MD, director of the Center for Biologics Evaluation and Research at the FDA, said that CAR T-cells may have the potential to treat different types of diseases and cancers, including solid tumors, certain infections and autoimmune disease. He added that potential use of these treatments to treat hemologic malignancies, adult forms of leukemia and certain types of non-Hodgkins lymphoma are “not yet approved and are currently investigational.”

In a statement, the American Hematology Society’s president, Kenneth Anderson, MD, applauded the approval but noted that it’s just the first step down a long road.

“While the importance of CAR-T cannot be overstated, this approval only pertains to a small population of children,” Anderson said. “More research is needed to make this therapy more effective for a broader population, to reduce the severe side effects that patients experience during treatment, and ultimately to find a broader application beyond blood cancers. Continued research will also lead to improved manufacturing of large numbers of cells, which is necessary to make this therapy accessible to more patients.”

Gottlieb said that a post-marketing study would be required for tisagenlecleucel and called it a crucial part of the “new, accelerated pathways to approval.” He said he is “very confident” that the FDA has the resources to ensure that companies fulfill their post-marketing commitments.

In addition to the boxed warning and post-marketing study, the FDA is also requiring a Risk Evaluation and Mitigation Strategy that includes mandatory training in CRS and its management for all personnel "involved in the prescribing, dispensing, or administering" tisagenlecleucel. Clinics must also certify that they have tocilizumab on hand for immediate administration.

Novartis had received breakthrough therapy and priority review designations on tisagenlecleucel.

Staff writer Molly Walker contributed to this report.

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