Both the B and T cells are derived ultimately from cells in the bone marrow called stem cells. When the stem cells are missing or defective, the individual fails to form B cells and T cells. This condition is known as severe combined immunodeficiency disease (SCID). Confinement to a sterilized plastic bubble used to be required for these individuals because they are unable to mount immune defenses against any antigens. The typical treatment option for SCID is a bone marrow transplant.
