US regulators have approved a second form of gene therapy to fight cancer. The treatment, called Yescarta, is the first immunotherapy on the US market for certain kinds of non-Hodgkin lymphoma (NHL), a cancer that attacks the lymph nodes.

Known as a chimeric antigen receptor (CAR) T cell therapy, Yescarta modifies a patient's white blood cells so they can attack and kill lymphoma.

The treatment is expected to cost about $373,000, and is only approved for people who have relapsed twice after at least two other kinds of treatment.

‘Today marks another milestone in the development of a whole new scientific paradigm for the treatment of serious diseases,’ FDA Commissioner Scott Gottlieb said in a statement late Wednesday.

‘In just several decades, gene therapy has gone from being a promising concept to a practical solution to deadly and largely untreatable forms of cancer,’ he added.

‘This approval demonstrates the continued momentum of this promising new area of medicine.’

The FDA approved the first gene therapy against cancer in August, a leukemia treatment called Kymriah, made by Novartis. Its cost is estimated at $475,000.

Yescarta was initially developed by researchers at the National Cancer Institute in Washington, DC. A deal was struck with Kite Pharma to develop the drug. Gilead Pharmaceuticals purchased Kite for $11.9 billion this year.

About 3,500 patients in the United States may be candidates for treatment with Yescarta, including those with diffuse large B-cell lymphoma (DLBCL), the most common type of Non-Hodgkin lymphoma in adults.

Patients must first have their immune cells removed, then modified in a lab for re-infusion.

Side effects can be severe, even fatal, particularly in the first couple of weeks after treatment.

These include cytokine release syndrome (CRS), when the body reacts negatively to the infusion of CAR-T ‘cells causing high fever and flu-like symptoms,’ as well as the risk of brain damage.

‘Both CRS and neurologic toxicities can be fatal or life-threatening,’ the FDA warned.

‘Other side effects include serious infections, low blood cell counts and a weakened immune system.’

In a trial involving more than 100 patients with refractory or relapsed large B-cell lymphoma, 51 percent went into complete remission after treatment with Yescarta, according to the FDA.