Inclusion Criteria:

- Histologically confirmed CLL, DLBCL, FL;

- Karnofsky Performance Status ≥ 70;

- Life expectancy of ≥ 12 weeks;

- Prior radiation therapy provided exposure does not exceed an area of 25% of marrow
space

- Adequate hematological function

- Adequate organ function

Exclusion Criteria:

- Any available standard line of therapy known to be life-prolonging or life-saving;

- No concurrent therapy or therapy within six weeks of first dose of MEDI-551 for
treatment of cancer

- Previous therapy directed against CD19

- Vaccination (other than experimental cancer vaccine therapy) within 28 days prior to
receiving the first dose of MEDI-551;

- History of other invasive malignancy within 5 years except for cervical carcinoma in
situ (CIS), non-melanomatous carcinoma of the skin or ductal carcinoma in situ (DCIS)
of the breast that have been surgically cured;

- Active infection requiring treatment

- Autologous stem cell transplantation within 4 months prior to study entry;

- Allogeneic stem cell transplantation or any other organ transplant;

- Ongoing ≥ Grade 2 toxicities from previous cancer therapies unless specifically
allowed in the Inclusion/Exclusion criteria.

- Use of immunosuppressive medication other than steroids within 28 days before the
first dose of MEDI-551;

- Use of immunosuppressive medication other than steroids within 28 days before the
first dose of MEDI-551 (inhaled and topical corticosteroids are permitted);

- Documented current central nervous system involvement by leukemia or lymphoma;

- Pregnancy or lactation;

- Clinically significant abnormality on ECG.