An example of the sort of immune system engineering that is presently taking place in the laboratory: "Until this research, we thought the immune system needed to attack the cancer directly in order to be effective. Now we know that isn't necessarily so. Attacking the dense tissues surrounding the cancer is another approach, similar to attacking a brick wall by dissolving the mortar in the wall. Ultimately, the immune system was able to eat away at this tissue surrounding the cancer, and the tumors fell apart as a result of that assault. These results provide fresh insight to build new immune therapies for cancer. ... pancreatic cancer patients received standard gemcitabine chemotherapy with an experimental antibody [that] binds and stimulates a cell surface receptor called CD40, which is a key regulator of T-cell activation. The team initially hypothesized that the CD40 antibodies would turn on the T cells and allow them to attack the tumor. The treatment appeared to work, with some patients' tumors shrinking substantially and the vast majority of tumors losing metabolic activity after therapy, although all of the responding patients eventually relapsed. When the researchers looked at post-treatment tumor samples, obtained via biopsy or surgical removal, there were no T cells to be seen. Instead, they saw an abundance of another white blood cell known as macrophages. ... When the investigators treated mice that developed pancreatic cancer with gemcitabine in combination with CD40 antibodies, the results looked like those of the human trial. Some mouse tumors shrank and were found to be loaded with macrophages but contained few or no T cells. Closer inspection showed that the macrophages were attacking what is known as the tumor stroma, the supporting tissue around the tumor. Pancreatic tumors secrete chemical signals that draw macrophages to the tumor site, but if left to their own devices, these macrophages would protect the tumor. However, treating the mice (or patients) with CD40 antibodies seemed to flip that system on its head. ... It is something of a Trojan horse approach. The tumor is still calling in macrophages, but now we've used the CD40 receptor to re-educate those macrophages to attack - not promote - the tumor."