Inclusion Criteria:

- Signed informed consent

- Relapsed or refractory B-CLL after at least one prior course of therapy with
fludarabine

- Circulating lymphocytes expressing CD20

- Peripheral blood lymphocyte count > 5,000/µL

- ECOG performance status ≤ 2

- Life expectancy ≥ 3 months

- Negative blood pregnancy test before inclusion for women of childbearing potential

- Medically acceptable method of birth control throughout the study for women of
childbearing potential

- Being considered as reliable and capable of adhering to the protocol and compliant
with study procedures

- Covered by healthcare insurance

Exclusion Criteria:

- Transformation of CLL into a high grade lymphoma

- Allogeneic stem cell transplantation < 6 months before enrolment

- Prior treatment with anti-CD20 monoclonal antibodies < 6 months before enrolment

- Prior treatment with alemtuzumab < 2 months before enrolment

- Treatment with any IMP or participation in a clinical study within 30 days prior to
enrolment

- Known severe anaphylactic or other hypersensitivity reactions secondary to a prior
exposure to murine antibodies or to any component of LFB-R603

- Patient with prior treatment or concomitant medication that may interfere with the
interpretation of the study data

- Patient with a concomitant malignancy other than basal cell carcinoma of the skin, or
in situ carcinoma of the cervix or the breast

- Patient with serious non-malignant disease, active infection requiring systemic
antibiotic, antifungal or antiviral drug or physical examination or laboratory
abnormalities, that would compromise protocol objectives

- Positive serology to HIV, HCV or presence of HBs Ag

- Creatinine clearance, calculated according to Cockroft -Gault formula < 60 mL/min

- ALT and /or AST level > 1.5 times the upper limit of normal

- Pregnancy or breastfeeding