Deadly pancreatic tumours evade attack by the immune system by developing a stroma — a shell of connective tissue enmeshed with white blood cells that suppress the immune response. Robert Vonderheide at the University of Pennsylvania in Philadelphia and his team now report a way to reverse this immune suppression.

The authors studied 21 patients undergoing chemotherapy for pancreatic cancer, and added an antibody that stimulates a protein called CD40 to their treatment regimen. CD40 is known to activate certain types of immune cell, including tumour-specific T cells. Tumours in four of the patients regressed.

The scientists repeated the treatment regime in mice genetically engineered to develop similar pancreatic cancers. About 30% of mouse tumours regressed, with holes appearing in the stroma. Surprisingly, the immune cell responsible for killing tumour and stroma cells was not the T cell but the macrophage.

Science 331, 1612–1616 (2011)