DISEASE CHARACTERISTICS: Polyclonal or monoclonal B-cell lymphoproliferative disorder while under pharmacologic immune suppression for control of either allograft rejection or autoimmune disease Measurable disease as defined by one of the following: At least 1 tumor mass measuring 1.0 cm in largest dimension Greater than 25% marrow involvement Quantifiable extranodal disease Expression of CD20 antigen confirmed by biopsy or fine needle aspirate Progression of disease or stable disease following reduction of immunosuppressive medication and antiviral therapy Inability to further reduce immunosuppressive medication