A Randomized, Open-Label, Phase II Multicenter Study of High-Dose Immunosuppressive Therapy Using Total Body Irradiation, Cyclophosphamide, ATGAM, and Autologous Transplantation With Auto-CD34+HPC Versus Intravenous Pulse Cyclophosphamide for the Treatment of Severe Systemic Sclerosis (SCSSc-01)

Inclusion Criteria:

- Severe systemic sclerosis (SSc) as defined by the American College of Rheumatology
(ACR)

- SSc, including extensive skin and internal organ involvement involving either the
lungs or the kidneys, that threatens participant's life

- Willingness to use accepted methods of contraception for at least 15 months after
starting study treatment

Exclusion Criteria:

- Lung, heart, liver, or kidney impairment that would interfere with the study or
compromise participant's survival

- Active blood vessel dilation in the stomach (Active Gastric Antral Vascular
Ectasia/GAVE, also known as "watermelon stomach"). Patients found to have this
disorder at study screening can receive treatment outside the study and then be
re-screened. For more information about this study criterion, refer to the study
protocol.

- Previous treatment with cyclophosphamide, as defined by: a) prior IV cyclophosphamide
administration for more than 6 months OR a total cumulative IV dose greater than 3
g/m2; b) prior oral cyclophosphamide administration for more than 4 months,
regardless of dose; or c) combination of prior oral and IV cyclophosphamide
administration for more than 6 months, independent of dose.

- Steroid therapy at doses of greater than 10 mg/day, or more than 2 pulses for
concurrent illnesses within prior 12 months

- Unwillingness or inability to discontinue certain disease-modifying antirheumatic
drugs (DMARDs) for the treatment of SSc

- Presence of clinically significant rheumatic diseases other than scleroderma
requiring significant immunosuppression

- Any active uncontrolled infection that would interfere with high-dose therapy or
pulse cyclophosphamide regimens

- Hepatitis B virus infected

- Hepatitis C virus infected

- HIV infected

- Blood abnormalities

- Diagnosis of cancer within 2 years prior to study entry. Participants with adequately
treated squamous cell skin cancer, basal cell carcinoma, and carcinoma in situ are
not excluded.

- Other comorbid illnesses with an estimated life expectancy of less than 5 years

- Defective formation of bone marrow cells (myelodysplasia)

- Uncontrolled hypertension

- History of hypersensitivity to murine or E. coli proteins

- History of noncompliance with prior medical care

- History of substance abuse within 5 years prior to study entry

- Pregnancy