[illus. 1] Drug developers have launched more than 1,000 combination trials to try to improve patient outcomes with checkpoint inhibitors that harness the body's T cells to kill cancer cells. Until recently, these trials have mostly focused on up-regulating the adaptive immune system--a slow-starting but long-lasting protective network that has to learn the signatures of specific threats before it can use T cells and other mechanisms to defend itself. Recently, however, a few firms have started to explore whether the broader acting, rapid-onset innate immune system might provide the complementary anticancer targets that everyone is looking for.

Merck & Co., for example, launched a trial early in 2017 of its pro-inflammatory STING agonist MK-1454 alone and in combination with the approved checkpoint PD1 blocker pembrolizumab (see Table 1). In September, Novartis and partner Aduro Biotech likewise launched a phase I trial that combines Aduro's STING agonist ADU-S100 with Novartis's experimental PD1 inhibitor PDR001.