DNA Genotypic Conservation During Phenotypic Switch from T-cell Acute Lymphoblastic Leukaemia to Acute Myeloblastic Leukaemia

De novo acute myeloid leukemia with near-pentaploidy: diploid karyotype and lymphoblastic phenotype at relapse

Hyperploidy is a rare finding in leukemias, with isolated cases of tetraploidy reported in acute myeloblastic and acute lymphblastic leukemias. We report the first case of acute myeloid leukemia with near-pentaploidy (5 n+/-) which was present in 100% of metaphases at diagnosis. By light microscopy, the leukemic blasts were exceptionally large and coarsely granulated. Following one cycle of induction chemotherapy, complete morphologic and cytogenetic remission was documented. Four weeks later relapse occured, at which time the karyotype was diploid and the morphological and immunophenotypic characteristics were those of a lymphoid leukemia. However, the presence of three aberrant chromosomes (5q+, 6q+ and 20q+) confirmed that this was clonal evolution of the original myeloid leukemia. To the best of our knowledge, this case represents the first report of near-pentaloidy in de novo, pretreatment human leukemia.

A biclonal large granular lymphocyte (LGL)/NK-associated (NKa) disorder of CD4+ and CD8+ lymphocyte subpopulations characterized by the simultaneous presence of distinct TCR rearrangements

This communication reports a patient with concomitant expansions of CD4+ and CD8+ large granular lymphocytes. Immunological analyses revealed that the abnormally increased CD4+ LGL fraction was phenotypically similar to other reported persistent CD4+ LGL expansions, whereas the phenotypic profile for the CD8+ LGL component was unusual. Of particular note was the finding that both the CD4+ and CD8+ LGL fractions showed high membrane CD45RO isoform expression, thus suggesting their 'primed' status. Molecular biology studies of immunomagnetically fractionated cells using a T gamma 9 TCR gamma gene primer further revealed that the CD4+ and CD8+ components were both clonal but showed different patterns of rearrangement. It is suggested that the simultaneous presence of CD4+ and CD8+ clonal populations are unlikely to have been derived from a common progenitor and that they reflect expansions of functionally restricted subpopulations.

Monoclonal antibody anti-MPO is useful in recognizing minimally differentiated acute myeloid leukaemia

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.

A classification of acute leukaemia for the 1990s

The need for reproducibility in the classification of acute leukaemia has made it necessary to incorporate information derived from new techniques which have become essential for the study of these disorders. In addition to classic morphology and cytochemistry (FAB proposals), it is necessary to add immunology and cytogenetics (MIC proposals), as well as to investigate further the biological and diagnostic significance of molecular events. As a result of these investigations a new group of leukaemias merit recognition as distinct entities. These include three types of ALL with specific chromosome abnormalities, namely, i) t (9;22), ii) t (4;11) and iii) t (1;19) and four subtypes of AML, i) with minimal differentiation or AML-M0, ii) with basophilic precursors or M2Baso, iii) AML (M4/M5) with t (8;16) and iv) AML with trilineage myelodysplasia. Biphenotypic acute leukaemia constitutes also a distinct entity with features of ALL and AML and represents a malignancy probably affecting multipotent stem cells. We propose an objective evaluation system for biphenotypic leukaemias based on a score in which the various lineage markers are graded according to their known specificity.

Relationship between clonality and transformation in acute leukemia

In some cases of acute leukemia an initial potentially leukemogenic genetic alteration can result in clonally derived end-cells normal in appearance and numbers. We refer to this clonal expansion as preleukemia. Subsequent alterations, intrinsic or extrinsic, often referred to as transformation, result in abnormal differentiation and/or growth regulation; we refer to this as leukemia. Several issues are unresolved. Where in the hierarchy of hematopoiesis clonal expansion and transformation occur is unknown. It is quite likely that clonal expansion occurs in cells with considerable self-renewal potential--probably stem or progenitor cells. The precise site may vary in different cases and account for the diverse phenotypes of acute leukemia. How the preleukemia clone comes to dominate hematopoiesis and the fate of the residual normal stem cells and their progeny are also unknown. Likewise, there is controversy whether different models of leukemogenesis operate in different subjects. For example, are older persons or those with occupational exposure to potentially leukomogenic agents more likely to exhibit one pattern of leukomogenesis? Finally, it is unknown whether these diverse models of leukemogenesis respond differently to therapy.