The complement system, part of the immune system, has long been used as a target for interventions in certain rare disease. Apellis Pharmaceuticals is developing therapies to treat rare blood and kidney diseases, but by targeting a different part of the complement system than available therapies do today. We spoke to Cedric Francois, co-founder, president and CEO of Apellis, about the complement system, Apellis’ approach, and why he thinks this will lead to better therapies for these rare diseases.