CHICAGO (Reuters) - Promising new data on blood and bone marrow cancer therapies that re-engineer immune system cells are convincing more doctors of the validity of the approach, according to Reuters interviews at the world’s biggest annual oncology meeting. Chimeric antigen receptor T-cell, or CAR-T, therapies extract immune system T-cells from an individual patient, alter their DNA to better spot and kill cancer cells, and infuse them back into the same patient.

Investors had been closely watching the fortunes of CAR-T developers, including Kite Pharma Inc and Bluebird Bio Inc. This week, the therapies took center stage at the American Society of Clinical Oncology (ASCO) annual meeting, with new results on their use for multiple myeloma patients.

The science “is quite revolutionary,” said Dr. Michael Sabel, chief of surgical oncology at University of Michigan Health Systems, who is not involved in the trials.

“We have struggled for years with the idea of getting T-cells to actually recognize the cancer cell and form that bond, that latch, that allows it to be an effective killing cell,” he said. “We are now seeing that advance.”

CAR-T therapies are expected to reach the U.S. market for the first time this year. U.S. regulators are reviewing treatments from Kite and Novartis AG which target a protein called CD19 found in lymphoma and leukemia, achieving remission in more than 80 percent of patients with advanced-stage disease.

CAR-Ts can also pose serious risks, including a potentially life-threatening inflammatory condition, though researchers said at ASCO they have become more confident in managing though side effects.

“What used to be a sideshow has moved on to the main stage,” said Nick Leschly, chief executive officer at Bluebird Bio. The company, which is developing a therapy with Celgene Corp, gave an update on its clinical trial of multiple myeloma patients who had exhausted other options. All 15 patients evaluated so far have responded to the treatment, and 27 percent had a complete remission, Bluebird said.

Shares of Bluebird are up 17 percent so far this week. BMO Capital Markets estimated sales of the therapy, bb2121, could reach $3.6 billion annually.

A relatively unknown company, Nanjing Legend Biotech, also surprised ASCO participants with a small CAR-T trial in patients with advanced multiple myeloma. All 35 patients enrolled so far have responded to the treatment. Of the 19 patients followed for more than four months, 14 saw complete remission.

Most trial patients experienced cytokine release syndrome (CRS), a potentially life-threatening inflammatory condition, but researchers said the side effect was temporary and manageable in most patients.

Dr. Frank Fan, chief scientific officer at Nanjing Legend Biotech, a unit of Genscript Biotech Corp, said the company plans to enroll a total of 100 patients in the Chinese trial and to start a similar U.S. trial in early 2018.

Juno Therapeutics Inc scrapped its initial CAR-T candidate for acute lymphoblastic leukemia (ALL) after five patient deaths. The company said at ASCO that early trial results for a different CAR-T found that 66 percent of non-Hodgkin lymphoma patients responded to the drug, and 18 percent suffered severe neurological side effects. One patient died, although the company said the death was not attributed to the CAR-T treatment.

Data from Kite showed remission in 73 percent of 11 patients with relapsed ALL who took its CAR-T treatment axi-cel. It plans to launch a Phase 2 trial in the fourth quarter, possibly at a lower dose.

Globally, there are more than 183 clinical CAR-T trials underway, said Dr. Carl June, professor in immunotherapy at the University of Pennsylvania’s Perelman School of Medicine, and one of the first researchers in the CAR-T field. ASCO awarded June the David A. Karnofsky Memorial Award, its highest scientific prize, this week.

“This takes immuno-oncology to another level,” June told a packed lecture hall on Sunday.