Last year marked a first for engineered antibodies–the European Commission approved a new cancer drug called Removab (catumaxomab), an antibody specially designed to grab both cancer cells and immune cells in such a way that the immune cell can kill the cancer cell. (The drug is undergoing testing for U.S. Food and Drug Administration approval.)

Now a handful of similarly complex molecules, dubbed “bispecific antibodies” for their ability to target two things at once, are in clinical trials. The two arms of these antibodies work together in different ways to treat cancer or other diseases, by bringing together two types of cells, as with Removab, by targeting two different types of receptors on the surface of a cell, or even using one arm to deliver drugs to specific cells targeted by the other.

Scientists say the two-front attack can make existing cancer therapeutics more powerful and help combat drug resistance, an issue for some targeted cancer therapies. “If you can wrap two treatments into one molecule, you have a potentially more active drug and can take it to the FDA more quickly,” says Carlos Barbas, chair of the Skaggs Institute for Chemical Biology at the Scripps Research Institute in La Jolla, CA.

While the concept of bispecific antibodies has been around for decades, the approach has only recently shown clinical success. The field has been driven forward by new ways of designing and making the antibodies, which take advantage of advances in protein engineering, as well as the success of single-target antibodies, such as herceptin, that are already on the market. “The European approval of the Trion antibody provides proof of principle that this technology works,” said Tariq Ghayur, senior principle scientist at Abbott Laboratories, in Worcester, MA, at a conference in Boston organized by the Massachusetts Biotechnology Council on Wednesday. “I think in the next few years, we’ll see lots of advances in this area.”

Herceptin, an antibody used to treat some types of breast and other cancers, has been one of the earliest successful examples of targeted cancer treatment. Given primarily to women whose cancers overexpress a receptor called HER2, the antibody binds to the receptor, encouraging the immune system to attack the cell.