Stem Cell Transplant for Immunologic or Histiocytic Disorders

Inclusion Criteria: Patients with immunodeficiencies or histiocytic disorders 0-35 years of age with an acceptable stem cell donor and disease characteristic defined by the following: Patients with histocytic disorders (hemophagocytic lymphohistiocytosis of any etiology and refractory Langerhans cell histiocytosis) who do not meet eligibility criteria for a myeloablative transplant procedure Patients with immunodeficiency disorders in whom residual immune function may not require a fully myeloablative preparative regimen or patient is ineligible for standard myeloablative preparative regimen (any form of severe combined immunodeficiency [SCID], or other immunodeficiency with T cell defect) Patients with immunodeficiency disorders that have had poor outcome with myeloablative stem cell transplants (including, but not limited to, common variable immunodeficiency [CVID], Wiskott Aldrich Syndrome [WAS] if > 5 years of age, ataxia telangiectasia) Patients with immunodeficiencies or histocytic disorders that require a second stem cell transplant (SCT) for any reason Exclusion Criteria: Karnofsky or Lansky performance score <70 Glomerular filtration rate (GFR)<30% predicted Cardiac function <50% normal by echocardiogram Serum creatinine > 2x normal for age/weight Pregnant or lactating females Active serious infection that has not had an adequate course of therapy pre-SCT. Any patient with acquired immune deficiency syndrome (AIDS) or AIDS-related complex (ARC) or human immunodeficiency virus (HIV) seropositivity