Haematologic and immunophenotypic profile of acute myeloid leukemia: an experience of Tata Memorial Hospital.

OBJECTIVES: To study the hematologic and immunophenotypic profile of 260 cases of acute myeloid leukemia at diagnosis. MATERIAL AND METHODS: This is a retrospective analysis of 260 cases of AML diagnosed at our institution between 1998 and 2000. Diagnosis was based on peripheral blood and bone marrow examination for morphology cytochemistry and immunophenotypic studies. SPSS software package, version 10, was used for statistical analysis. RESULTS: Seventy-six percent of our cases were adults. The age of the patients ranged from one year to 78 years with a median age of 27.2 years. There were 187 males and 73 females. The commonest FAB subtype, in both children and adults, was AML-M2. The highest WBC counts were seen in AML-M1 and the lowest in AML-M3 (10-97 x 10(9)/L, mean 53.8 x 10(9)/L). The mean values and range for hemoglobin was 6.8 gm/l (1.8 gm/l to 9.2 gm/l), platelet count 63.3 x 10(9)/L (32-83 x 10(9)/L), peripheral blood blasts 41.4% (5 to 77%) and bone marrow blasts 57.6% (34-96%). Myeloperoxidase positivity was highest in the M1, M2 and M3 subtypes. CD13 and CD33 were the most useful markers in the diagnosis of AML. CD14 and CD36 were most often seen in monocytic (38%) and myelomonocytic (44%) leukemias. Lymphoid antigen expression was seen in 15% of cases. CD7 expression was the commonest (11%). CONCLUSION: AML accounted for 39.8% of all acute leukemias at this institution. The most common subtype was AML-M2. Myeloperoxidase stain was a useful tool in the diagnosis of myeloid leukemias. CD13 and CD33 were the most diagnostic myeloid markers.

Production & evaluation of a monoclonal antibody against human myeloperoxidase.

We describe the production of a mouse monoclonal antibody (H2E1) against human myeloperoxidase antigen. After production and characterisation, this antibody was compared with commercially available monoclonal antibodies, cytochemical myeloperoxidase and previously produced polyclonal antibody. Reaction with various cell lines proved that this monoclonal antibody was specific for myeloid lineage. This monoclonal showed positivity in 81.8 per cent of acute myeloid leukaemias whereas the polyclonal antibody was 100 per cent positive. We found that the polyclonal antibody was more sensitive as compared to the monoclonal. This is probably due to the lack of recognition of individual epitopes on the antigen. We recommend the use of antibodies which have different epitope recognition as most specific for myeloperoxidase.

Acute non-lymphocytic leukemia with expression of surface antigen CD7--morphological, cytochemical, immunological and ultrastructural features in eight patients.

Of late, there has been an increase in the number of acute leukemias coexpressing markers believed to be restricted to a single lineage. Eight patients with ANLL whose blast coexpressed the T cell associated CD7 antibody were identified among 462 consecutive ANLL cases. Seven had FAB defined AML according to morphocytochemical criteria, whereas one patient was classified as MO on the basis of ultrastructural studies. The incidence of CD7 positivity was particularly significant in the less differentiated sub-types MO and M1 compared to other FAB sub-groups. Detailed long term studies will be required to realize their biological and clinical significance.

High incidence of meningeal leukemia in lymphoid blast crisis of chronic myelogenous leukemia.

Fifteen patients with lymphoid blast crisis of chronic myelogenous leukemia (LyBC-CML) and five patients with acute lymphoblastic leukemia converting to Philadelphia-positive (Ph+) chronic myeloid leukemia (ALL Ph + CML) were followed. Seven of 15 (46.7%) LyBC-CML patients developed meningeal leukemia within a median period of 6 months (range 2-11 months), while there was no medullary relapse. Five of these responded well to triple intrathecal therapy. In the ALL Ph + CML patients, in spite of central nervous system (CNS) prophylaxis with IT MTX and 18 Gy cranial radiation, two of five patients (40%) experienced meningeal leukemia, one isolated and the other with medullary relapse. The data confirm that LyBC-CML patients experience a high incidence of meningeal leukemia. The role of CNS prophylaxis is not very clear, but its use may delay development and reduce morbidity due to CNS disease.

Phenotypic heterogeneity of erythroblasts in erythroblastic leukemia revealed by monoclonal antibodies.

Eight cases each of erythroleukemia (AML-M6) and erythroblastic crisis of chronic granulocytic leukemia (CGLBC-E) were immunophenotyped with the help of a panel of lineage-associated monoclonal antibodies (McAbs). The latter included those reactive with erythroid progenitor (BFU-E and CFU-E) and erythroid precursors at different stages of maturation. In six of eight cases of AML-M6, erythroblasts revealed an immature phenotype, as evident from reactivity of the blast cells with McAbs directed against the earlier stages of erythroid maturation. One case had the phenotype of CFU-E, and in the remaining case of AML-M6 the erythroblasts showed a "mature" surface antigenic profile. This immunophenotypic spectrum was unrelated to the morphologic maturity of the erythroblasts. In two cases of CGLBC-E, an early erythroblastic phenotype was observed, while in as many cases a "mature" phenotype was present. Four of eight cases, however, revealed a mixed, erythroid plus myeloid phenotype. In one of the four cases, two separate blast populations, which represented erythroblasts and myeloblasts, could be identified. In the remaining three cases the blasts were morphologically homogeneous and undifferentiated. High incidence of HLA-DR positivity in the latter three cases suggests the primitive nature of blasts cells and their closeness to the putative "bipotent" myeloid stem cell. Our study has shown phenotypic heterogeneity of blast cells in AML-M6 and CGLBC-E.

Acute leukemia with coexpression of lymphoid and myeloid phenotypes.

A multiparameter analysis of 706 cases of acute leukemia (AL) over a two-year period revealed only six cases (0.86 per cent) with coexpression of lymphoid and myeloid phenotypes. In three cases, expression of both lymphoid and myeloid markers by the majority of the blast cells suggested a 'biphenotypic' pattern while in the remaining three cases, the lymphoid and myeloid phenotypes were segregated into two morphologically distinct populations of blast cells indicating a 'biclonal' distribution. The poor response to anti-acute lymphoblastic leukemia therapy in five of these six cases underlines the bad prognostic significance of coexpression of lymphoid and myeloid phenotypes in AL. The incidence of 'mixed lineage' phenotype in the present series appears very low.

Myeloid lineage specificity and high sensitivity of monoclonal antibody GM 58/8 proves its usefulness as a diagnostic reagent in acute leukemia.

Monoclonal antibody (MoAb) GM 58/8 was earlier reported to be directed against an antigen expressed by myeloid progenitors (CFU-GM), myeloid precursors, granulocytes, and monocytes. Immunophenotyping of 216 cases of acute leukemia [acute myeloblastic leukemia (AML) = 147 and acute lymphoblastic leukemia (ALL) = 69] and 18 cases of chronic granulocytic leukemia in blast crisis (CGLBC) with this antibody showed that GM 58/8 reacted with 92% of AML cases (M1-M5) and 100% of myeloblastic crisis in CGL cases. All cases of ALL, lymphoblastic crisis in CGL, erythroleukemia, and erythroblastic crisis in CGL were unreactive with GM 58/8. The antibody revealed the myeloid phenotype in an additional 15 cases of otherwise unclassifiable acute leukemia and six cases of CGLBC. Eleven cases of acute "mixed lineage" leukemia were also diagnosed with the help of GM 58/8. The high specificity (100%) and sensitivity (92%) of MoAb GM 58/8 for myeloblastic leukemia is unmatched by almost all previously described myeloid MoAb and proves its usefulness as a single diagnostic reagent for AML and myeloblastic crisis in CGL.