Inclusion Criteria:

All patients age > =18 who have been diagnosed with Multiple Myeloma and are scheduled for
autologous peripheral blood hematopoietic stem cell transplant (AHSCT) will be screened
for eligibility.

Patients must fulfill all of the following inclusion criteria to be eligible for this
study:

1. Diagnosis of Multiple Myeloma

2. Age >=18 and no more than 70 years.

3. Able to understand and sign a consent form.

4. Can collect peripheral blood stem cells with a CD34+ cell dose of at least 5.0 x
106/kg. The CD34 molecule is a Cluster of Differentiation molecule present on
hematopoietic stem cells.

5. Conditioning regimen to be high dose Melphalan at a dose of 200mg/m2.

6. Karnofsky Performance Score (KPS) >60 or ECOG (Eastern Cooperative Oncology Group)
performance status <=2

7. Kidney function:Creatinine <2.0 mg/dl or creatinine clearance >50 ml/min

8. Heart function: Ejection fraction >45%

9. Liver function tests :Serum bilirubin, alanine aminotransferase (ALT), aspartate
aminotransferase (AST) less than 3 X upper limit of normal

10. Lung function tests: Forced Vital Capacity (FVC), Forced Expiratory Volume in One
Second (FEV1) or Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) >45%
predicted

Exclusion Criteria:

1. Age <18 years or > 70 years

2. Previous exposure to denileukin diftitox.

3. Patients with documented uncontrolled central nervous system (CNS) disease.

4. Previous AHSCT.

5. Significant organ dysfunction deemed to be inappropriate for autologous
transplantation.