Patients who have relapsed/refractory CLL and require therapy as per iwCLL guidelines will be eligible. Subjects will receive a treatment with ofatumumab and HDMP for three consecutive 4 week cycles. The primary endpoint is to determine the complete response (CR) to therapy and the secondary endpoints will assess the safety and tolerability of the regimen, the impact of the treatment on progression free, treatment free, overall survival, and pharmacokinetics of ofatumumab. Cycles 1-3 will be administered without scheduled interruption every 28 days for a total of 12 weeks of therapy. Patients will receive allopurinol for tumor-lysis prophylaxis and antimicrobial prophylaxis. Blood glucose levels will be monitored immediately after HDMP infusion by finger stick glucometry. Two months following completion of treatment a response assessment will occur per iwCLL guidelines. The treatment will be administered as outpatient, and each cycle will be four weeks in duration.