Illustration showing monoclonal antibodies (blue) being used to treat sickle cell anaemia. Sickle cell anaemia is an inherited blood disease in which the red blood cells contain an abnormal form of haemoglobin (bloods oxygen-carrying pigment) that causes the blood cells to become sickle-shaped, rather than round. Sickle cells cannot move through small blood vessels as easily as normal cells and so can cause blockages. This prevents oxygen from reaching the tissues, causing severe pain and organ damage. Monoclonal antibodies (mAbs) are proteins produced by cloned cells that are engineered to target specific substances. In this case, the drug works by inhibiting P-selectin, which reduces the adhesion of red blood cells, white blood cells, and platelets to the walls of blood vessels. This helps alleviate pain crises caused by reduced blood flow due to sickle cell anaemia.