Sutimlimab

Hemolysis associated with cold agglutinin disease is driven by the activation of the complement system. Cold agglutinins transiently bind erythrocytes as they circulate through cooler parts of the body (e.g. the extremities) - as they circulate back to warmer areas, C1q esterase activates C4 and C2, which generates C3 convertase, an enzyme which cleaves C3 into C3a and C3b. At this stage, the erythrocytes tagged with C3b can be sequestered by macrophages in the reticuloendothelial system, ultimately leading to extravascular hemolysis. Alternatively, C3b may be further cleaved into C3c and C3d - if complement activation continues past the C3 step, the membrane attack complex with C5b-C9 may form, which causes intravascular hemolysis.

Sutimlimab is a humanized IgG4 monoclonal antibody targeted at the complement C1s subunit, a serine protease responsible for the activation of the classic complement pathway. By inhibiting the complement cascade at the level of C1s, sutimlimab prevents the deposition of complement opsinins on erythrocytes, thus preventing their eventual hemolysis.