RATIONALE: Monoclonal antibodies such as rituximab can locate tumor cells and either kill them or deliver tumor-killing substances to them without harming normal cells. Drugs used in chemotherapy use different ways to stop cancer cells from dividing so they stop growing or die. Colony-stimulating factors such as filgrastim may increase the numbers of immune cells found in bone marrow or peripheral blood and may help a person's immune system recover from the side effects of chemotherapy. Combining chemotherapy with rituximab and filgrastim may kill more cancer cells.