Monoclonal Antibody Anti-MPO is Useful in Recognizing Minimally Differentiated Acute Myeloid Leukaemia

Abstract

The enzyme myeloperoxidase (MPO) is the most specific marker of myeloid lineage. The recognition of acute myeloid leukaemia (AML) with minimally differentiation (AML-M0) is established with methods that include myeloid markers CD13/CD33 and detection of MPO in blast cells by immunological techniques or electron microscopy cytochemistry (EM). We have analysed the presence of MPO in leukaemic blast cells by conventional cytochemistry and immunological methods using a monoclonal antibody anti-MPO (CLB-MPO1) in 121 cases of acute leukaemia. The aim of the study was to investigate the sensitivity of this McAb to identify AML-M0, as CD13/CD33 can be expressed in some cases of acute lymphoblastic leukaemia (ALL) and EM cytochemistry is not always available in many laboratories. Anti-MPO was positive in all cases of AML (M1-M5) which were positive by Sudan Black B reaction in similar or higher percentage ratio for each case, although in some of them did not label with CD13/CD33 tested by IF and IPc techniques. Based on the anti-MPO positivity, 5 out of 10 cases called undifferentiated leukaemia (AUL) were reclassified as AML-M0, though 4 cases were CD13/CD33 negative. Furthermore, after analysing the anti-MPO expression among 32 cases of ALL, we had to reclassify four of them as acute biphenotypic leukaemia. We conclude that anti-MPO is a very sensitive and reliable tool in AML diagnosis and has an important role in distinguishing minimally differentiated AML and biphenotypic acute leukaemia from AUL and ALL.

Minimally differentiated acute myeloid leukemia (AML-MO): a distinct clinico-biologic entity with poor prognosis

“…In our experience, 100% of 23 patients affected by AML-M0 showed anti-MPO positivity as compared with CD13 and CD33, which were both not expressed in 13% of the cases [6,12]. In the study of Praxedes et al [16], based on the anti-MPO positivity, five out of ten leukemias called undifferentiated (AUL) were reclassified as AML-M0, though four of them were CD13/CD33 negative. The authors concluded that anti-MPO is a very sensitive and reliable tool in AML diagnosis and has a pivotal role in distinguishing AML-M0 and byphenotypic acute leukemia from AUL and ALL.…”

“…The recognition of AML-M0 is also established with methods that include detection of MPO in blast cells by immunological techniques [6,7,10,14,15]. MPO is localized in the primary granules of myeloid cells, and its synthesis occurs early on the differentiation pathway [14,16,17]; it therefore is a good candidate as a specific immunological target for AML. A study involving 140 patients affected by AL (90 AML, 50 ALL) has confirmed the sensitivity and specificity of anti-MPO when used in immunocytochemistry with the APAAP method [8].…”

Acute Myeloid Leukemia With Minimal Differentiation:A Multiple Parameter Study

“…Some classification systems 13 and some studies have placed great weight on finding anti-MPO positivity in making a diagnosis of AML-MO, even to the point of relying on anti-MPO to classify cases as AML-MO in the absence of any other evidence of myeloid differentiation. 8 We would caution against overinterpretation of anti-MPO positivity in the absence of CD13 or CD33 antigen expression, because we and others have seen anti-MPO-positive blasts in AJCP • January 1998 Acute Myelo otherwise classic cases of ALL. [14][15][16] This finding suggests that some lymphoblasts may contain rudimentary or precursor forms of MPO that cannot be modified to a functional enzyme.…”

“…Certainly some studies have shown up to 100% of AML-MO cases with anti-MPO positivity, suggesting that an early form of the MPO enzyme can be detected before its cytochemical expression. [8][9][10] The absence of MPO, however, as detected by in situ hybridization for MPO messenger RNA has been noted in a high (50%) proportion of cases of AML-MO, 12 raising questions about the validity of a high rate of anti-MPO detection in AML-MO. Some classification systems 13 and some studies have placed great weight on finding anti-MPO positivity in making a diagnosis of AML-MO, even to the point of relying on anti-MPO to classify cases as AML-MO in the absence of any other evidence of myeloid differentiation.…”

“…3 Subsequent authors have sometimes modified this definition by including cases that had anti-MPO positive blasts by immunologic methods but failed to express any other myeloid marker, such as CD13 or CD33. 8 Other AML-MO studies included cases with blasts showing nonspecific esterase staining. 9 ' 10 We chose to exclude cases with any myeloid cytochemical staining in the blasts, because these cases would appear to represent AML with at least some cytochemical evidence of lineage maturation.…”