RATIONALE: Biological therapies, such as agatolimod sodium, may stimulate the immune system in different ways and stop cancer cells from growing. Monoclonal antibodies, such as rituximab, can block cancer growth in different ways. Some block the ability of cancer cells to grow and spread. Others find cancer cells and help kill them or carry cancer-killing substances to them. Radiolabeled monoclonal antibodies, such as yttrium Y 90 ibritumomab tiuxetan, can find cancer cells and carry cancer-killing substances to them without harming normal cells. Giving agatolimod sodium together with rituximab and yttrium Y 90 ibritumomab tiuxetan may kill more cancer cells.