Pfizer, Bristol revive Cancer drugs that rev up immune system

Some of the most heralded new cancer drugs fight the disease by removing brakes on the immune system. Now a few leading drug makers are paying attention to a second, opposing force: medicines that accelerate the immune system's attack.
Pfizer Inc, which is lagging rivals in the lucrative field of cancer immunotherapies, has been the first to report early data of an "accelerator" treatment that targets a protein called 4-1BB. It has at least five other Phase I studies underway or in planning stages in solid tumor cancers and lymphomas, which are blood cancers.
Bristol-Myers Squibb Co is hot on Pfizer's heels with a handful of early-stage trials of its own 4-1BB antibody. Others, including Johnson & Johnson and AbbVie Inc are doing early testing of their antibodies prior to starting human trials.
4-1BB, also known as CD137, and its connection to the immune system was identified more than 20 years ago by scientists at the University of California San Diego. The approach was largely abandoned in 2008 after early clinical trials of a Bristol therapy showed dangerous signs of liver damage.
Scientists eventually realized that significantly lower doses of a 4-1BB antibody, given at the right time, could achieve the desired anti-cancer effect without the toxicity.
They now believe immune system accelerator therapies could work for many types of cancers, bolstering an arsenal of new medications that are changing the field of oncology.