Some leukemia patients who had exhausted other treatment options have no trace of the disease more than four years after being treated with an experimental type of therapy called CAR T cells in a small pilot study at the University of Pennsylvania.

The 14-patient study, which began in the summer of 2010, enrolled patients who had failed to benefit from standard treatments for chronic lymphocytic leukemia (CLL), a cancer of white blood cells that most commonly affects adults.

They were given one treatment with CTL019, a therapy developed by the university and licensed to Swiss drugmaker Novartis AG. Patients have since been monitored to assess durability of the therapy's benefits.

The treatment is made by taking immune system soldiers called T cells from the body, genetically modifying them to have cancer-spotting abilities of antibodies, and then infusing the altered cells back into the patient.

The first patient to receive the therapy is cancer-free after five years and another of the first three enrolled patients also remains in remission, the university said on Wednesday.

All signs of cancer disappeared in four patients, or 29 percent, but one of them died almost two years after therapy due to an unrelated infection.

"The durability of the remissions we have observed in this study are remarkable and have given us great hope that personalized cell therapies are going to be important options for patients," said Dr. David Porter, director of blood and marrow transplantation at the university's Abramson Cancer Center.

Another four patients achieved some reduction in tumors, with responses lasting an average of about seven months.

Six patients, or 43 percent, failed to respond to therapy, and their leukemia progressed within one to nine months.

Novartis plans next year to seek marketing approval of CTL019 to treat pediatric patients with another cancer of the white blood cells, acute lymphoblastic leukemia. Although it can occur in adults, it is the most common type of cancer in children.

Novartis is considered in the lead among a handful of companies racing to develop and launch CAR T cells to treat blood cancers, including Kite Pharma Inc, Juno Therapeutics Inc and Bluebird Bio Inc.

But the therapies can cause a life-threatening inflammation called cytokine release syndrome, which was seen in all patients who responded to CTL019 in the University of Pennsylvania study.

All patients recovered from the inflammation, including some treated with steroids.