 - Clear CD19 expression must be uniformly detected on 75 or more of malignant cells from either bone marrow or a leukemia or lymphoma mass by flow cytometry or immunohistochemistry. These assays must be performed at the National Institutes of Health. It is preferable but not required that the specimen used for CD19 determination comes from a sample that was obtained after the patient s most recent treatment. If paraffin embedded unstained samples of bone marrow involved with malignancy or a lymphoma mass are available, these can be shipped to the NIH for CD19 staining; otherwise, new biopsies will need to be performed for determination of CD19 expression. 