Inclusion Criteria:

          -  Must have detectable CLL/SLL (> 0.01% leukemia cells present)

          -  Must have received at least 12 months of venetoclax.

          -  Patients may be receiving venetoclax at the time of screening and study entry.

          -  Patients who have discontinued venetoclax more than 6 months prior to study entry must
             still have a disease burden meeting criteria for low risk of TLS (i.e. no lymph node
             greater than 5 cm in diameter; absolute lymphocyte count less than 25 k/uL)

        Exclusion Criteria:

        Evidence of other clinically significant uncontrolled condition(s) including, but not
        limited to:

          -  Uncontrolled and/or active systemic infection (viral, bacterial or fungal)

          -  Chronic hepatitis B virus (HBV) or hepatitis C (HCV) requiring treatment. Note:
             subjects with serologic evidence of prior vaccination to HBV (i.e. hepatitis B surface
             (HBs) antigen negative, anti-HBs antibody positive and anti-hepatitis B core (HBc)
             antibody negative) or positive anti-HBc antibody from intravenous immunoglobulins
             (IVIG) may participate.

          -  Child class B or C cirrhosis

        Treatment with any of the following within 7 days prior to the first dose of cirmtuzumab:

          -  Steroid therapy for anti-neoplastic intent

          -  Biologic agent (monoclonal antibody) within 30 days for anti-neoplastic intent.

          -  Chemotherapy (purine analog or alkylating agent) or target small molecule agent within
             14 days or 5 half-lives (whichever is shorter), or has not recovered to less than
             CTCAE grade 2 clinically significant adverse effect(s)/toxicity(s) of previous
             therapy.

          -  CLL therapy, aside from venetoclax.

          -  History of other malignancy that could affect compliance with the protocol or
             interpretation of results (example: patients with a history of curatively treated
             basal or squamous cell carcinoma of the skin or in situ carcinoma of the cervix are
             generally eligible.)

          -  Women who are pregnant or lactating