RATIONALE: Biological therapies, such as fusion protein cytokine therapy, 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. Giving fusion protein cytokine therapy together with rituximab may kill more cancer cells.