1. A 66-year-old male presents with chronic fatigue. On examination, the patient is noted to have lymphadenopathy and an enlarged liver and spleen. Laboratory examination reveals a white blood cell count of 25,000/mL with 93% lymphocytes; the lymphocytes appear small and mature. Both the hematocrit and platelet counts are within normal limits; however, hypogammaglobulinemia is also noted. Which of the following agents is indicated for treatment of this patient's condition?