• Time to engraftment and incidence of graft failure [ Time Frame: 100 days post-HCT ] [ Designated as safety issue: Yes ]
  
• Incidence of grade II-IV graft vs. host disease [ Time Frame: 100 days post-HCT ] [ Designated as safety issue: Yes ]
  

• Incidence of grade 3 and 4 regimen related toxicity [ Time Frame: 100 days post-HCT ] [ Designated as safety issue: Yes ]
  
• Estimate of disease-free survival [ Time Frame: 1 year, 3 yrs post-HCT ] [ Designated as safety issue: No ]
  

Procedure: Stem Cell Transplant
Transplantation of hematopoietic stem cells (bone marrow, cord blood, peripheral blood stem cells) following myeloablative conditioning regimen
Procedure: In-vivo T-cell Depletion
Rabbit ATG (Thymoglobulin) is use for in-vivo T cell depletion.
Drug: busulfan, cyclophosphamide, and antithymocyte globulin (ATG)
Busulfan iv for 4 days followed by cyclophosphamide iv for 4 days. rabbit ATG is given for 4 doses pre-transplant.

Subjects will begin chemotherapy as a preparative regimen, which is intended to completely eliminate their defective immune system and bone marrow. The preparative regimen consists of the chemotherapy drugs (busulfan, cyclophosphamide, and antithymocyte globulin (ATG)).

Transplantation: subjects will then have a source of blood stem cells (bone marrow) from their donor administered into their catheter. Medication will be given to help prevent Graft-Versus Host Disease (GVHD). The ATG will help to deplete the donor stem cells of the type of cells that can cause GVHD and will also help to promote engraftment of the new stem cells.

Recovery Phase: The second phase of treatment consists of a period after transplantation during which we wait for the return of bone marrow function. This usually takes two to four weeks. Subjects will be given a blood cell growth factor, G-CSF, to help speed recovery of the white blood cells and potentially decrease the risk of infection and decrease the time until the bone marrow recovers.

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.

• 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, 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 HIV.
• Age > 55 years.
• Not providing informed consent.