Complement C5

Class

Complement C5 inhibitor (RNA aptamer)

Complement C5 is a protein at a key junction of the complement system, a cascade of blood proteins that helps the immune system recognize and destroy pathogens and clear damaged cells. However it is triggered, the cascade converges on an enzyme complex that cleaves C5 into two pieces: C5a, which signals and recruits inflammatory cells, and C5b, which assembles into a pore-forming structure that ruptures target cell membranes. Blocking C5 prevents formation of both pieces, reducing inflammation and cell destruction while leaving earlier cascade steps, such as tagging of pathogens for clearance, largely functional. This matters in diseases driven by inappropriate complement activation: conditions where blood cells are destroyed prematurely, kidney disorders involving small-vessel clotting, neuromuscular disease where complement damages the nerve-muscle junction, and retinal disease where local complement activity contributes to progressive tissue loss. C5 can be inhibited through several distinct approaches: antibodies that bind the circulating protein, RNA-based agents that lower its production in the liver, and aptamers, folded RNA molecules that bind proteins much as antibodies do, each suited to different dosing schedules or tissue targets, such as direct delivery into the eye.