A monoclonal immunoglobulin G1 antibody with potential antineoplastic activity. Siplizumab binds to CD2, a specific receptor found in T cells and NK cells, thereby triggering a host immune response that results in lysis of CD2+ cells, selective suppression of the immune system, and control of activated T cell growth. Check for active clinical trialsusing this agent. or A substance being studied in the treatment of certain types of T-cell lymphoma. It is also being studied in the prevention of organ or tissue rejection after a kidney and/or bone marrow transplant. Siplizumab binds to a protein called CD2, which is found on some types of immune cells and cancer cells. This may help suppress the body’s immune response and it may help kill cancer cells. Siplizumab is a type of monoclonal antibody. Also called MEDI-507.