T-Cell Depletion and Stem Cell Transplant for Immune Deficiencies and Histiocytic Disorders

Inclusion Criteria: * Any patient from birth to \< 55 years of age fulfilling the following criteria will be eligible for this study. * Patients meeting clinical diagnostic criteria for Hemophagocytic Lymphohistiocytosis (HLH) * Patients meeting clinical diagnostic criteria or genetic diagnosis of X-linked lymphoproliferative disorder (XLP) and whose disease is ACTIVE but STABLE, or NON-ACTIVE/QUIESCENT. * Patients with Chediak-Higashi Syndrome who meet the following diagnostic criteria and whose disease is ACTIVE but STABLE, or NON-ACTIVE/QUIESCENT as defined in Appendix V of the study protocol. * Patients with Viral Associated Hemophagocytic Syndrome (VAHS) - if relapsed after other therapy or supportive care. Diagnostic criteria as above for HLH. Disease status must be ACTIVE but STABLE, or NON-ACTIVE/QUIESCENT as defined in Appendix V. It is cautioned that many patients with HLH or familial hemophagocytic lymphohistiocytosis (FHL) will have a viral infection at time of initial presentation and may therefore be misdiagnosed as having VAHS. * Griscelli Syndrome * Primary immune deficiencies with non-genotypic identical donors only. * Progressive Langerhans cell histiocytosis unresponsive to standard therapy. * Other non-malignant hematological disorders in which stem cell transplant with a myeloablative regimen is indicated. * Diamond Blackfan Anemia if transfusion dependent * Schwachman Diamond Syndrome: with cytopenias or transformation to myelodysplastic syndrome (MDS) * Kostman's Syndrome (if ANC \<500 without GCSF support, or transformation to MDS) * Congenital dyserythropoietic anemia if transfusion dependent * Amegakaryocytic thrombocytopenia if baseline platelet counts \<20,000 or requiring transfusions. * Cardiac, hepatic, renal and pulmonary function deemed adequate for high dose chemotherapy with stem cell rescue as per institutional standards. General guidelines are as follows: * Cardiac: Asymptomatic or, if symptomatic, then left ventricular ejection fraction at rest must be \> 40% and must improve with exercise, or shortening fraction by echocardiogram must be within institutional normals * Hepatic: \< 3 x normal SGOT and \< 2.5 mg/dL serum bilirubin * Renal: Serum creatinine within normal range, or if serum creatinine outside normal range then creatinine clearance or glomerular filtration study should be \> 50% of normal. * Pulmonary: Asymptomatic or, if symptomatic, diffusing capacity of the lung for carbon monoxide (DLCO) \> 45% of predicted (corrected for hemoglobin). For children unable to perform pulmonary function testing, then oxygen saturation should be \>95%. * Availability of a suitable allogeneic bone marrow donor as per current institutional guidelines for non-T cell depleted hematopoietic stem cell transplant (HSCT). * Patients who have undergone previous stem cell transplant (SCT) and failed engraftment or who had relapse of their disease are considered eligible if they meet other eligibility criteria and if the second SCT would occur 6 months or more after the first. If the first SCT preparative regimen was of a non-myeloablative intensity then the second SCT could be performed earlier when the acute toxicity from that procedure was resolved. Exclusion Criteria: * Patients who are moribund or whose life expectancy is severely limited by disease other than their underlying disorder. Karnofsky performance status \< 70% or Lansky \< 50% for patients \< 16 years. * Patients with hemophagocytic disorders secondary to underlying malignancy. * Patients who have ACTIVE/UNSTABLE disease as defined in Appendix V. * Significant active infections, including Human Immunodeficiency Virus (HIV). * Age \> 55 years. * Not providing informed consent.