OUTLINE: This is a randomized study. Patients are stratified by prior bone marrow transplantation (yes vs no) and by prior pneumococcal vaccine (Pnu-Immune-23) (yes vs no or unknown). Patients are randomized to one of two treatment arms: Arm I: Patients receive Haemophilus influenzae b vaccine (Hib TITER) and Pnu-Immune-23 on day 1 during week 1. Patients who have received Pnu-Immune-23 within the past 3 years receive Hib TITER but no Pnu-Immune-23. Patients receive low dose interleukin-12 (IL-12) subcutaneously (SQ) twice a week during weeks 1 and 2. Beginning on day 1 of week 3, patients receive high dose IL-12 SQ twice a week for an additional 12 weeks. Arm II: Patients receive Hib TITER and Pnu-Immune-23 as in arm I. Patients undergo observation during weeks 1-4, then receive low dose IL-12 SQ twice a week during weeks 5 and 6. Beginning on day 1 of week 7, patients receive high dose IL-12 SQ twice a week for an additional 12 weeks. Both arms: Patients without disease progression may continue to receive high dose IL-12 for an additional 14 weeks. Patients are followed every 3 months for the first 2 years, every 6 months for the next 3 years, and then annually thereafter until death.