This is a humanized IgG4 antibody using the same sequences as the therapeutic antibody sutimlimab. It is designed to target C1s and inhibit the activation of the classical complement pathway, part of the innate immune system against infection. The pathway is triggered by C1, a multimolecular complex composed of the recognition protein C1q and two serine proteases, C1r and C1s. Sutimlimab blocks C1s and halts C1-activated hemolysis in cold agglutinin disease, to prevent the abnormal destruction of healthy red blood cells. By selectively inhibiting the classical pathway upstream at C1s, it does not inhibit the lectin and alternative complement pathways.