Inclusion Criteria:

- Patient must be a recipient of aT cell depleted unrelated or HLA mis-matched related
HSCT for the treatment of a malignancy or immunodeficiency disease.

- Patients must have an ANC > or = to 1500 cells/ul on the day of first treatment.

- Patients with acute or chronic leukemia, or MDS prior to transplant must be in
remission defined as <5% blasts in the bone marrow.

- Patient with must be in remission.

- Patient must be Hepatitis B surface antigen negative pre transplant.

- Patients must have adequate cardiac function defined as a left ventricular ejection
fraction at rest of >50% documented pre-transplant.

- Patient may be of either gender and of any ethnic background.

- Patient may be of any age. There is no upper age restriction.

- Patients or their guardians must be able to understand the nature and risk of the
proposed study and be able to sign consent.

Exclusion Criteria:

- Karnofsky score <70%

- Female patients who are pregnant or lactating.

- Evidence of EBV-LPD or circulating EBV copy number >1000.

- Active uncontrolled bacterial or fungal infection.

- Prior history of Hepatitis B infection or Hepatitis B surface antigen positivity pre
transplant.

- HIV-1,2 sero-positive patients.

- Patients or guardians not signing informed consent.

- Patients with prior allergic reaction to Rituximab or other murine monoclonal
antibody.

- Patients taking other investigational agents under another protocol unless discussed
and approved in advance by Genentech and the IDEC Therapeutic Director.