Development of a flow cytometric method to detect the presence of mutated nucleophosmin 1 in acute myeloid leukemia

Objective/Background Nucleophosmin 1 (NPM1) plays multiple roles in cell growth and proliferation. Deletion/insertion mutations in exon 12 of NPM1 (NPM1-DIM), commonly found in patients with acute myeloid leukemia (AML), alter the C-terminal amino acids and disrupt the normal nucleocytoplasmic shuttling function of the protein, which in turn leads to disease pathogenesis. However, this altered function as a result of NPM1-DIM positivity is actually associated with a significantly better response to therapy and overall survival, and thus it is of clinical relevance to investigate the mutation status at diagnosis. Our objective was to design a reliable flow cytometry assay to detect mutated NPM1 in peripheral blood (PB) samples from AML patients, using a polyclonal mutation-specific antibody. Methods A commercially available NPM1 mutation-specific polyclonal antibody in combination with a secondary goat antirabbit antibody was used to detect the C-terminal-mutated NPM1 by flow cytometry. OCI/AML3 (+) cell line and clinical PB controls were used to optimize the assay and determine sensitivity, reliability, and reproducibility parameters. The assay was then tested on a small cohort of 12 AML patients at diagnosis and compared with NPM1-DIM testing on a standard polymerase chain reaction (PCR) platform. Results Flow cytometry using the polyclonal antibody was able to reliably detect mutated NPM1 populations of at least 10%. Using an objective analysis of the mean fluorescent intensity, clear positive and negative mutated cell populations could be distinguished using the clinical AML samples. From the analysis of 12 patients, 2 were found to be positive using this assay, which corresponded with conventional PCR methodology. Conclusions Flow cytometry may be used to detect NPM1 C-terminal mutations in AML patients using a polyclonal anti-NPM1 antibody, allowing rapid mutation status determination at diagnosis.