Monoclonal antibodies against myeloperoxidase are valuable immunological reagents for the diagnosis of acute myeloid leukaemia.

Whereas the diagnosis of acute lymphoid leukaemia greatly depends on immunophenotyping on the leukaemic cells, the diagnosis of acute myeloid leukaemia (AML) is still only based on morphological and cytochemical criteria. Here we describe that with a monoclonal antibody, directed against myeloperoxidase (MPO), the immunological diagnosis of AML is possible in most cases. A monoclonal antibody against lactoferrin (LF) was used to detect more mature myeloperoxidase-containing cells. Of the cell samples tested from 206 different patients with AML, 95% were found to express myeloperoxidase in more than 15% of lactoferrin-negative cells. Compared with other myeloid-reactive monoclonal antibodies (VIM2, anti-CD13, anti-CD14, anti-CD15 and anti-CD33), a higher diagnostic sensitivity and specificity for AML was found. No significant correlation with the FAB classification was found. In most patients, more MPO-positive cells were detected by the monoclonal antibody than by the cytochemical staining. This could be due to the recognition of enzymatically inactive precursor forms of myeloperoxidase by the antibody. The use of anti-myeloperoxidase monoclonal antibodies for the diagnosis of AML has the advantage that objective quantification is possible.