Inclusion Criteria

- INCLUSION CRITERIA: PATIENT

Ages greater than or equal to 2 to 80.

Wt greater than 40 kg.

Patients with systemic mastocytosis proven by a bone marrow biopsy and one of the
following:

Category I disease with poor prognosis secondary to extensive bone marrow involvement of
mast cells (i.e. greater than 50 percent of the bone marrow cavity replaced by mast cells)
and evidence of a bone marrow failure state defined as presence of one of the following
for greater than or equal to 2 months:

- Neutrophil count less than 500/ mm3.

- Platelet count less than 20,000/mm3.

- Dependency on transfusion of RBC or platelets.

Category II disease with an associated hematologic disorder:

- Myelodysplastic syndromes.

- Myeloproliferative states except essential thrombocytosis or polycythemia vera.

- Increased blasts in peripheral blood or bone marrow greater than 10 percent.

- Bone marrow failure states as described above.

Category III disease with enlarged peripheral lymph nodes with histopathological evidence
of the replacement of the entire lymph node architecture with mast cells and/or
accompanying peripheral eosinophilia. We also consider aggressive systemic mastocytosis
with local tissue invasion as category III disease.

Category IV disease with mast cell leukemia, characterized by the presence of malignant
mast cells in the peripheral blood, which constitute greater than 10 percent of the
nucleated cells.

No major organ dysfunction precluding transplantation.

DLCO greater than or equal to 65 percent predicted.

Left ventricular ejection fraction of greater than or equal to 40%.

ECOG performance status of 0 or 1.

Life expectancy of more than 3 months.

HLA-identical sibling available as donor.

Patients or their parent(s)/responsible guardian(s) must be able to comprehend the
investigational nature of the study and be willing to sign an informed consent.

INCLUSION CRITERIA: DONOR

HLA identical family donor, (only HLA identical).

Weight greater than or equal to 18 kg.

Age less than or equal to 80 years old.

Informed consent given.

EXCLUSION CRITERIA: PATIENT (Any of the following)

Pregnant or lactating

Age less than 2 or age greater than 80 years.

Weight less than or equal to 40 kg.

ECOG performance status of 2 or more.

Psychiatric disorder or mental deficiency severe as to make compliance with the BMT
treatment unlikely, and making informed consent impossible.

Major anticipated illness or organ failure incompatible with survival from PBSC
transplant.

DLCO less than 65 percent predicted.

Left ventricular ejection fraction less than 40%.

Baseline GFR less than 50ml/min: measured or calculated by the following formula: GFR =
{(140-age) x body weight in kg}/72 x serum creatinine (for females, multiply by 0.85).

Serum bilirubin greater than 4 mg/dl, transaminases greater than 5 times the upper limit
of normal.

Other malignant diseases liable to relapse or progress within 5 years.

Life expectancy of less than 3 months.

EXCLUSION CRITERIA: DONOR (Any of the following)

Pregnant or lactating.

Donor unfit to receive G-CSF and undergo apheresis (Uncontrolled hypertension, history of
congestive heart failure or unstable angina, thrombocytopenia).

HIV positive. Donors who are positive for HBV, HCV or HTLV-1 may be used if the
risk-benefit ratio is considered acceptable by the patient and investigator.

Weight greater than 18 kg.

Age greater than 2 or less than 80 years.