Inclusion Criteria:

- Patients with Severe Combined Immunodeficiency Syndrome:

- SCID with presence of B lymphocytes

- X-linked SCID (presence of B lymphocytes)

- Autosomal recessive SCID

- Patients with Severe Combined Immunodeficiency Syndrome:

- SCID with absence of T and B lymphocytes

- Patients with Severe Combined Immunodeficiency Syndrome:

- Purine metabolite deficiencies, deficiencies of the purine metabolites

- Adenosine deaminase (ADA) deficiency

- Purine nucleoside phosphorylase (PNP) deficiency

- DONOR: Related donor who is human leukocyte antigen (HLA) genotypically identical at
least at one haplotype and may be genotypically or phenotypically identical for
serological typing for HLA-A, B, C, and at the allele level for DRB1 and DQB1;
related donors other than siblings must be matched at HLA-A, B, and C (at highest
resolution available at the time of donor selection) and at DRB1 and DQB1 by DNA
typing; if more than one HLA-identical sibling is available, priority will be given
to the oldest normal donor

- DONOR: Unrelated donors who are prospectively matched for HLA-A, B, C, DRB1 and DQB1
by DNA typing at the highest resolution routinely available at the time of donor
selection; only a single allele disparity will be allowed for HLA-A, B, or C as
defined by high resolution typing

Exclusion Criteria:

- Patients with viral associated T cell immunodeficiency disorders, such as human
immunodeficiency virus (HIV)

- Patients with other disease or organ dysfunction that would limit survival to less
than 30 days

- DONOR: Identical twin

- DONOR: Pregnancy

- DONOR: HIV seropositive

- DONOR: A positive anti-donor cytotoxic cross match is absolute donor exclusion

- DONOR: Patient and donor pairs homozygous at a mismatched allele in the graft
rejection vector are considered a two-HLA allele mismatch, i.e., the patient is
A*0201, and this type of mismatch is not allowed

- DONOR: < 6 months old, > 75 years old