Inclusion Criteria

          1. Subject must sign an ICF, prior to any screening procedures.

          2. Must have active CLL disease that needs treatment per iwCLL2018

          3. R/R CLL after receiving at least 2 prior lines of systemic antineoplastic therapy,
             including treatment with (or intolerance of) a BTK inhibitor

          4. Has Measurable Disease with ≥5 × 109/L (5,000/μL) B lymphocytes in peripheral blood or
             Presence of measurable lymphadenopathy and/or organomegaly

          5. ECOG performance status score of 0 or 1

          6. Screening flow cytometry evidence of CD20 positivity

          7. Has laboratory parameters as follows:

             a. HBG-≥9.0 g/dL; ANC-≥1.0 x 109/L; Platelets-≥30 x 109/L

          8. Received a cumulative dose of corticosteroids less than the equivalent of 250 mg of
             prednisone within the 2-week period before the first dose

          9. Availability of fresh bone marrow material

         10. Must take prophylaxis for TLS

         11. A woman must be either not of childbearing potential or of childbearing potential and
             practicing a highly effective method of birth control, and must have a negative serum
             beta-human chorionic gonadotropin (beta-hCG) and urine pregnancy test at screening.

         12. A man who is sexually active with a woman of childbearing potential and has not had a
             vasectomy must agree to use a barrier method of birth control.

        Exclusion Criteria

          1. Transformation of CLL to aggressive non-Hodgkin lymphoma

          2. Received prior treatment with a CD3 × CD20 bispecific antibody.

          3. Received any prior allogeneic HSCT or solid organ transplantation.

          4. Received treatment with an anti-cancer biologic including anti-CD20 therapy,
             radio-conjugated or toxin-conjugated antibody or CAR T-cell therapy or investigational
             drug or medical device within 4 weeks, before the first dose.

          5. Received chemotherapy or radiation therapy within 2 weeks of the first dose of
             epcoritamab.

          6. Has autoimmune disease or other diseases that require permanent or high-dose
             immunosuppressive therapy.

          7. Has uncontrolled intercurrent illness.

          8. Toxicities from previous anti-cancer therapies have not resolved to baseline levels or
             to Grade 1 or less except for alopecia and peripheral neuropathy.

          9. Primary central nervous system (CNS) lymphoma or known CNS involvement at screening.

         10. Known past or current malignancy other than inclusion diagnosis

         11. Subject has suspected allergies, hypersensitivity, or intolerance to epcoritamab or
             its excipients.

         12. Subject is unable to tolerate uric acid reducing medications

         13. Has had major surgery within 3 weeks before screening or will not have fully recovered
             from surgery, or has major surgery planned during the time the subject is expected to
             participate in the trial (or within 4 weeks after the last dose of epcoritamab).Known
             history/positive serology for hepatitis B.

         14. Known medical history or ongoing hepatitis C infection that has not been cured.

         15. HIV tested positive at screening.

         16. Is a woman who is pregnant or breast-feeding, or who is planning to become pregnant
             while enrolled in this trial or within 12 months after the last dose of epicoritamab.

         17. Is a man who plans to father a child while enrolled in this trial or within 12 months
             after the last dose of epicoritamab.