The treatment involves removing immune system cells known as T cells from each patient and genetically modifying the cells in the laboratory to attack and kill leukemia cells.
"We're entering a new frontier in medical innovation with the ability to reprogram a patient's own cells to attack a deadly cancer", said FDA Commissioner Dr. Scott Gottlieb.
"Kymriah is a first-of-its-kind treatment approach that fills an important unmet need for children and young adults with this serious disease", said Peter Marks, M.D., Ph.D., director of the FDA's Center for Biologics Evaluation and Research (CBER).
With the treatments available now, fewer than 10 percent of patients with the relapsed, hard-to-treat leukemia are alive five years after diagnosis.
Kymriah is one type of so-called CAR-T cancer therapies.
Kymriah will include strict guidelines for use in children up to 25 years old with relapsed acute lymphoblastic leukemia.
In approving Kymriah, the FDA warned that it has the potential to cause severe side effects, including cytokine release syndrome, an overreaction to the activation and proliferation of immune cells that causes high fever and flu-like symptoms, and neurological events.
The Food and Drug Administration called the approval historic.
The market for the breakthrough drug is relatively small; about 600 children a year in the US may be candidates. Novartis stock remained relatively flat after the approval.
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Kymriah is a genetically-modified autologous T-cell immunotherapy.
Novartis' therapy is one of two cutting-edge treatments for blood cancers are poised to get approved by the end of the year.
Therapies that would operate in similar ways - engineering the immune system's T cells to fight disease more effectively - are under investigation for a host of other conditions, including HIV/AIDS, genetic and autoimmune disorders and other forms of cancer. The trial found that of the 51 patients with DLBCL, 23 had either a complete response (meaning cancer had disappeared completely) or a partial response (meaning their tumour displayed signs that it was shrinking).
In a separate action, the FDA has also expanded the approval of tocilizumab (Actemra) for the treatment of vehicle T-cell-induced severe or life-threatening CRS in patients 2 years of age or older.
First developed by the University of Pennsylvania, Kymriah uses the 4-1BB costimulatory domain in its vehicle to enhance cellular responses as well as persistence of the treatment after it is infused into the patient, which may be associated with long-lasting remissions in patients.
The T-cell therapy was first tested at Penn in 2010, in three adults with advanced chronic lymphocytic leukemia.
Oncologists described the drug, made by Novartis and marketed as Kymriah, as revolutionary, but critics anxious the first-of-its-kind cancer treatment could usher in a new class of ultra-expensive medications.
The FDA said it has granted 76 applications for trials involving experimental CAR-T therapies. The cells will be frozen and shipped to Novartis' plant in Morris Plains, N.J., where they will be bioengineered and multiplied, refrozen, and shipped back to be infused into the patient. Patients will be followed for 15 years to evaluate the long-term safety of Kymriah.