A new wave of experimental cancer drugs that directly recruit the immune system's powerful T cells are proving to be immensely effective weapons against tumors, potentially transforming the $100 billion global market for drugs that fight the disease.

But top oncology researchers are concerned about the two emerging technologies, citing dangers seen repeatedly in clinical trials including the potentially fatal buildup of toxic debris from killed tumor cells and damage to healthy tissue. Such side effects could block regulatory approval if they aren’t controlled, researchers and drug company executives said in interviews with Reuters.

In some trials, the two new approaches, known as CAR T cells and bispecific antibodies, have eliminated all traces of blood cancers in 40 percent to 90 percent of patients who had no remaining options. The drugs could reap annual sales in the tens of billions of dollars for their manufacturers, especially if they can also eliminate solid tumors in such terminally ill patients.

CAR T cells, or chimeric antigen receptor T cells, are T cells that have been removed from the body and attached through genetic engineering to an antibody fragment that recognizes a specific tumor protein. T cells are an especially powerful disease-fighting kind of white blood cell. The result is a drug with the killing power of a greatly enhanced T cell, combined with the tumor-spotting ability of an antibody.

Bispecific antibodies are a twist on conventional antibodies, Y-shaped proteins whose two arms grasp for the same protein target found on cancer cells.

With bispecifics, one arm of the antibody typically grasps a cancer cell while the other arm takes hold of T cells, bringing the mortal enemies into contact. The T cell punches holes into the adjacent tumor cell and injects deadly enzymes. Conventional antibodies, by contrast, don't directly recruit T cells.

"Unleashing the killing power of the T cell directly on the tumor cells allows a large increase in potency of these antibodies," said Dr. David Scheinberg, chairman of molecular pharmacology at Memorial Sloan Kettering Cancer Center.

Investor excitement over these therapies have helped boost interest from companies including Amgen Inc and Roche and have fueled a jump in share prices of smaller firms such as Kite Pharma Inc, Juno Therapeutics and Bluebird Bio.

"We take patients that have failed every treatment, every chemo combination, that have just two to six months to live. You give them a CAR, and within 3 to 4 weeks you can see massive tumors melting away," said Arie Belldegrun, chief executive officer of Kite. The company went public in June and announced a partnership with Amgen earlier this month.

CAR T cells could cost $300,000 to $500,000 per patient, if approved, making them among the world's most expensive drugs and testing the ability of insurers to pay for them, said Les Funtleyder of E Squared Asset Management. The hedge fund owns shares of Kite Pharma. Bispecific antibodies could command prices of $200,000 or higher, he said.

The potency of the experimental drugs comes with some dangerous potential side effects. In the killing process, inflammatory chemicals from the medicines and the tumor cells, called cytokines, are released into the bloodstream and can cause fever, low blood pressure and rapid heartbeat that can be life-threatening.

The drugs, because of their unique structure and how they work, make it harder to predict whether they will go astray, said Dr. Bindu George, team leader of the U.S. Food and Drug Administration's Office of Cellular, Tissue and Gene Therapies, who called CAR T drugs perhaps the most interesting new technology.

Most CAR T cells and bispecific antibodies in development identify blood cancer cells by a specific protein, CD19, found on the surfaces of lymphomas and leukemias. Because the same protein can also be found on non-cancerous cells, the drugs can go off track and attack healthy tissues.

"Our biggest concern would be an off-target toxicity that wasn't expected and we didn't know the cause of it," George said. In that case, "we might have to ask (the drugmaker) for additional information, how the toxicity happened, what organ it was, and literally go back to the drawing board."

  

TAMING A POWERFUL DRUG

Researchers have used anti-inflammation medications to tame some of the adverse reactions, not always successfully. A study of CAR T cell treatment sponsored by Juno for patients with aggressive non-Hodgkin's lymphoma was briefly put on hold after two people died.

Unlike antibodies, which are excreted from the body within days or weeks, engineered CAR T cells are expected to circulate for years or even a lifetime in the bloodstream, potentially providing lasting benefits, but also risks.

"You can start to reject normal tissues; it can kill organs or cause autoimmune disease, and you don't want that," said Zelig Eshhar, a professor emeritus of the Weizmann Institute in Israel who pioneered the CAR approach.

To reduce that danger, researchers are attempting to build "suicide switches" into CAR T cells to turn them off after they have wiped out all signs of cancer.

At least 30 bispecific antibodies are believed to be in development, including ones from Roche, Johnson & Johnson, AbbVie and Eli Lilly.

A growing number of drugmakers are also racing to develop the first CAR T therapies, including Kite, Novartis, Juno, Cellectis and its partner Pfizer Inc, and Bluebird, in partnership with Celgene Corp.

   

EXPENSIVE OPTION

The FDA in December approved the first bispecific, Amgen's $178,000 Blincyto for acute lymphoblastic leukemia (ALL) that did not respond to previous treatment. The cancer, prevalent in children, is diagnosed each year in an estimated 6,020 Americans, killing about a fourth of them.

One third of patients in the Amgen study had no detectable cancer for nearly seven months after receiving the drug through a month-long infusion.

A main hope for Blincyto is that it will keep patients alive until they can receive stem cell transplants, their best chance of a possible cure.

CAR technology may also come to the rescue where few options remain.

"If doctors and specialists learn how to control this very powerful gun, CAR T cells could save hundreds of thousands of people in the United States," said Ori Hershkowitz, a Tel Aviv-based fund manager with Sphera Funds, which owns shares of Kite and rival CARs developer Novartis.

A Novartis trial showed 27 of 30 children and adults with ALL had no signs of the disease after being treated with its CAR T drug. Some 78 percent of patients were still alive six months after treatment, while some sustained remission for up to two years.

But everyone in the study developed cytokine release syndrome, including a severe form of it in 27 percent of patients.

"It certainly needs to be watched and evaluated," said Usman Azam, global head of cell therapies for Novartis. He still believes the drug’s benefits provide "compelling hope that you can potentially cure patients."

Roche's Genentech unit is conducting a mid-stage trial of a bispecific antibody to treat head and neck cancer and colorectal cancer. It is studying a dozen others in preclinical trials against cancer, Alzheimer's disease and inflammatory diseases.

Paul Carter, a Genentech executive, was cautious about the prospects.

"It's too early to say whether this will be a home run, although there's optimism it will be at least a base hit that will help us figure out how to go further."