 Rituximab is a type of drug known as a therapeutic antibody. Therapeutic antibodies are laboratory-created substances that attach onto a protein on the surface of a cell. After binding to the cell, the therapeutic antibody can block the growth of the tumor andor trigger the bodys immune system to attack the target, and can also sensitize a cancer cell to chemotherapy. Rituximab is approved by the Food and Drug Administration FDA for the treatment of CLLSLL. 