Inclusion Criteria:

1. Signed informed consent must be obtained prior to conducting any study procedure.

2. Patients must be greater than or equal to 18 years old and weigh greater than or
equal to 40 kg (88 lb).

3. Patients must have received an allogeneic hematopoietic BMT or PBSCT with
myeloablative or reduced-intensity conditioning and have a new onset of acute GvHD,
Grades II to III, which includes the skin and developed within 100 days following an
allo-HPCT.

4. Patients must have received an allogeneic hematopoietic BMT or PBSCT from a related
or unrelated donor that is matched at a minimum at the HLA-A, -B, and -DR loci (i.e.,
at least a 6 out of 6 match). HLA-A and -B match should be determined by serologic
testing, and HLA-DR should be matched by molecular methods.

5. Patients must be receiving only a calcineurin inhibitor at study entry as part of
their acute GvHD prophylactic regimen. Patients may have received additional
immunosuppressants for acute GvHD prophylaxis prior to study entry.

6. Patients must have a Karnofsky performance greater than or equal to 50.

7. Patients must be able and willing to comply with all study procedures.

8. Patients must receive, or must have received, the first corticosteroid dose of
approximately 2.0 mg/kg/day but no more than 2.5 mg/kg/day (methylprednisolone
equivalent) within 24 hours of the initial diagnosis of Grade II to III acute GvHD.
(Up to 2.5 mg/kg/day is allowed for inadvertent dosing fluctuations for reasons other
than lack of response.)

9. Female patients must be one of the following: postmenopausal, surgically incapable
of bearing children, practicing an acceptable method of birth control (acceptable
methods include hormonal contraceptives, intrauterine device, and spermicide and
barrier). Abstinence or partner/spouse sterility may also qualify at the
Investigator's discretion. If a female patient is of childbearing potential, she
must have a negative urine pregnancy test at screening. Male patients must also
commit to using adequate contraceptive precautions (condoms). All patients (both
males and females of childbearing potential) must commit to using adequate
contraceptive precautions throughout their participation in the study and for at
least 3 months following their last ECP treatment.

Exclusion Criteria:

1. Patients who have been diagnosed with chronic GvHD, including de novo chronic GvHD,
prior to 100 days following an allo-HPCT.

2. Patients who have received donor lymphocyte infusions.

3. Patients with uncontrolled life-threatening infections.

4. Patients who have a white blood cell (WBC) count < 1.5 x 10^9/L (1,500/mcL).

5. Patients who have a platelet count < 20.0 x 10^9/L (20,000/mcL), despite platelet
transfusion.

6. Patients whose total bilirubin is greater than or equal to 22 mg/dL.

7. Patients who have an International Normalized Ratio (INR) greater than or equal to 2.

8. Patients who are enrolled in any concomitant investigation for the treatment of acute
GvHD.

9. Patients who are unable to tolerate the extracorporeal volume shifts associated with
ECP treatment due to the presence of any of the following conditions: uncompensated
congestive heart failure, pulmonary edema, severe chronic obstructive pulmonary
disease, severe asthma, renal failure, hepatic encephalopathy, or hepatorenal
syndrome.

10. Female patients whose hemoglobin (Hgb) is < 8.5 g/dL or male patients whose Hgb is <
10.0 g/dL at screening, despite packed red blood cell transfusion.

11. Patients who have a poor tolerability of venipuncture or a lack of adequate venous
access for required treatments and blood sampling.

12. Patients who have a known hypersensitivity or allergy to Oxsoralen (methoxsalen).

13. Patients who have a known hypersensitivity or allergy to both heparin and citrate
products.

14. Female patients who are pregnant and/or lactating.

15. Patients who have co-existing melanoma, basal cell or squamous cell skin carcinoma,
aphakia, photosensitive disease (e.g., porphyria, systemic lupus erythematosus, or
albinism), white blood cell count > 25,000 cells/mm3, previous splenectomy, or
coagulation disorders.