Detection of normal and chimeric nucleophosmin in human cells

In anaplastic large-cell lymphoma (ALCL), the (2;5) chromosomal translocati on creates a fusion gene encoding the 80-kD NPM-ALK hybrid protein. This re port describes three new monoclonal antibodies, two of which recognize, by Western blotting, the N-terminal portion of NPM present in the NPM-ALK fusi on protein and also in two other NPM fusion proteins (NPM-RAR alpha and NPM -MLF1). The third antibody recognizes the C-terminal portion (deleted in NP M-ALK) and reacts only with wild-type NPM. The three antibodies immunostain wild-type NPM (in paraffin-embedded normal tissue samples) in cell nuclei and in the cytoplasm of mitotic cells, cerebral neurones, exceptionally, sh ow diffuse cytoplasmic labeling. In contrast to normal tissues, the two ant ibodies against the N-terminal portion of NPM labeled the cytoplasm of neop lastic cells, in four ALK-positive ALCL, reflecting their reactivity with N PM-ALK fusion protein, whereas the antibody to the C-terminal NPM epitope l abeled only cell nuclei. Immunocytochemical labeling with these antibodies can therefore confirm that an ALK-positive lymphoma expresses NPM-ALK (rath er than a variant ALK-fusion protein) and may also provide evidence For chr omosomal anomalies involving the NPM gene other than the classical (2;5) tr anslocation. (C) 1999 by The American Society of Hematology.