There have been many different preparative regimens used for patients with SCIDS or severe T-cell immunodeficiency syndromes. Some patients have gotten no preparative regimen, while others have gotten only antithymocyte globulin (ATG; immune proteins made in horses that, when given, will kill lymphocytes). Still other patients have gotten conventional chemotherapy. In children treated with nothing or ATG alone, there is an increased risk of graft failure or only partial engraftment. When this happens, patients need life-long therapy with immunoglobulins to support the immune system. Children treated with chemotherapy generally have full immune recovery, but also may have major side effects from the chemotherapy. The side effects include infection, organ failure and infertility.