Hybrid acute leukemia

Optimal therapeutic strategies for mixed phenotype acute leukemia

PURPOSE OF REVIEW

Mixed phenotype acute leukemia (MPAL) encompasses a rare group of clinically, immunophenotypically, and genetically diverse leukemias. Diagnosing and treating these patients remains challenging. In recent years, systematic efforts have been made to better define the genetic landscape of MPAL. These insights allow better understanding of the pathophysiology of MPAL, have the potential for a more biologically meaningful classification and may promote targeted, novel approaches to treat these leukemias.

RECENT FINDINGS

Recent studies suggest that MPALs originate in a multipotent primitive cell, demonstrate large genetic diversity and include subgroups that may benefit from targeted therapy. Recent data support the use of ALL-type induction followed by allogeneic stem cell transplantation in first remission for most adults. Novel targeted approaches hold promise for treatment of MPAL; however, some may unpredictably select for clonal expansion of cells from a different lineage than observed at presentation.

SUMMARY

A biologically and genetically driven classification of MPAL may yield more accurate prognosis and potentially direct therapy in patients with MPAL. Prospective efforts that incorporate targeted approaches based on genetics and immunophenotype are warranted.

Mixed phenotype acute leukemia: outcomes with allogeneic stem cell transplantation. A retrospective study from the Acute Leukemia Working Party of the EBMT

Mixed phenotype acute leukemias are infrequent and considered high risk. The optimal treatment approach and the role of allogeneic hematopoietic stem cell transplantation are not entirely clear. In this study, we investigated 519 patients with mixed phenotype acute leukemia in first complete remission who underwent allogeneic hematopoietic stem cell transplantation between 2000 and 2014, and who were reported to the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplantation (EBMT). Median age was 38.1 years (range 18–75). Cytogenetics classified 49.3% as poor risk. At three years, relapse incidence was 31.4% (26.9–35.9), non-relapse mortality was 22.1% (18.4–26.1), the leukemia-free survival was 46.5% (41.7–51.4), and the overall survival was 56.3% (51.5–61.2). At six months, 32.5% had developed acute graft-versus-host disease, while at three years, 37.5% had developed chronic graft-versus-host disease (32.6–42.3). In a multivariate analysis, age and year of transplant had a strong impact on outcome. Myeloablative conditioning using total body irradiation correlated with a better leukemia-free survival. Our study suggests that mixed phenotype acute leukemia is potentially sensitive to graft-versus-leukemia and thus can benefit from allogeneic hematopoietic stem cell transplantation with a potential for cure.

Allogeneic Hematopoietic Cell Transplantation for Patients with Mixed Phenotype Acute Leukemia

Acute biphenotypic leukemias or mixed phenotype acute leukemias (MPAL) are rare and considered high risk. The optimal treatment and the role of allogeneic hematopoietic stem cell transplantation (alloHCT) are unclear. Most prior case series include only modest numbers of patients who underwent transplantation. We analyzed the outcome of 95 carefully characterized alloHCT patients with MPAL reported to the Center for International Blood and Marrow Transplant Research between 1996 and 2012. The median age was 20 years (range, 1 to 68). Among the 95 patients, 78 were in first complete remission (CR1) and 17 were in second complete remission (CR2). Three-year overall survival (OS) of 67% (95% confidence interval [CI], 57 to 76), leukemia-free survival of 56% (95% CI, 46 to 66), relapse incidence of 29% (95% CI, 20 to 38), and nonrelapse mortality of 15% (95% CI, 9 to 23) were encouraging. OS was best in younger patients (<20 years), but no significant differences were observed between those 20 to 40 years of age and those who were 40 years or older. A matched-pair analysis showed similar outcomes comparing MPAL cases to 375 acute myelogenous leukemia or 359 acute lymphoblastic leukemia cases. MPAL patients had more acute and a trend for more chronic graft-versus-host disease. No difference was observed between patients who underwent transplantation in CR1 versus those who underwent transplantation in CR2. AlloHCT is a promising treatment option for pediatric and adult patients with MPAL with encouraging long-term survival.

Immunophenotyping of leukemia

Modern immunophenotyping of hematological malignancies by flow cytometry is assisted by a wide array of easily accessible monoclonal antibodies, by antibodies conjugated to diverse fluorochromes, and by reliable techniques for cell membrane permeabilization. Simultaneous assessment of multiple surface and intracellular markers at diagnosis reduces the number of cells required, helps the identification of the malignant cells and determines the degree of immunophenotypic heterogeneity of the malignant cell population. A few critical markers are sufficient to establish the lineage association in the majority of cases of acute and chronic leukemias and lymphomas. More extensive immunophenotyping can provide information about the cells' stage of differentiation, assess the expression of prognostically important features, and determine clonality. The identification of leukemia-associated immunophenotypes can be used for monitoring minimal residual disease during therapy. The presence of cells expressing these phenotypes in patients who are in clinical remission is associated with an increased risk of relapse.

Effect of thrombopoietin on acute myelogenous leukemia blasts

It has been shown that the expression of c-mp1, which is a specific receptor for thrombopoietin (TPO), is restricted to the surface of megakaryocytes, platelets, human CD34+ progenitor cells and human erythroid/megakaryocytic leukemic cell lines. Recently, however, it has been reported that some acute myelogenous leukemia (AML) blasts expressed c-mp1 on their cell surface and proliferated in response to TPO. We therefore investigated the effect of thrombopoietin on the growth of leukemic blasts from patients with CD7-positive acute myelogenous leukemia (AML), which is a distinct biological and clinical subtype of AML. Significant growth responses of leukemic blasts to TPO were seen in 10/10 CD7+ and 7/20 CD7- AML cases using 3H-thymidine incorporation, while synergistic stimulatory effects of TPO with stem cell factor (SCF), interleukin-3 (IL-3), granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor were observed in both groups. In a leukemic blast colony assay, significant growth response to TPO was observed in 5/6 CD7+ and 4/17 CD7- AML cases examined. Furthermore, the expression of c-mp1 seemed to be higher in CD7+ AML cases than in CD7- cases, suggesting a relationship between the expression of c-mp1 and the proliferative response to TPO. These findings imply that CD7+ leukemic blasts express functional TPO receptors and proliferate in response to TPO. Thus CD7 expression on AML blasts may indicate the involvement of leukemic progenitors at an early stage of multipotent hemopoietic stem cells. In this review, we discuss the effect of TPO on AML blasts, especially in CD7+ AML cases.

Strategies in the treatment of acute myelogenous leukemia

The current treatment of acute myelogenous leukemia is far from satisfactory despite some recent advances. This review focuses on current strategies designed to improve treatment outcome. With advances in molecular biology, the definition of a complete remission should be redefined as a molecular remission where any abnormal gene rearrangement has disappeared or a clonal remission with morphologic characteristics of a complete remission, but with detectable genetics or molecular abnormalities. Abnormal gene rearrangements permit the detection of minimal residual disease, the significance of which remains to be determined. New drug development remains an important area of research and several new drugs are active in acute myelogenous leukemia. These include etoposide, idarubicin, mitoxantrone and carboplatin. Various combinations are undergoing clinical trials. Prognostic factors which predict for outcome include phenotyping, cytogenetics, cytokinetics, drug resistance and age. Proto-oncogene expression as a predictor of response is under investigation. Post-induction therapy remains controversial and approaches have included allogeneic bone marrow transplantation, autologous bone marrow transplantation with or without purging, intensive consolidation and maintenance programs. The superiority of one approach over the other has not been firmly established. Differentiating agents such as all-trans retinoic acid, and growth factors, the latter for supportive care, or recruitment of leukemic cells into the cycle are being investigated. Understanding the mechanisms of drug resistance should lead to the development of new approaches. Thus, with knowledge generated in many areas, the future should bring increasing success in treating AML.

Rapid production of diversity during the progression of a mixed lineage leukaemia

A leukaemia presenting with two morphologically different blast populations failed to respond to either antimyeloid or antilymphoid treatment and showed a rapid clinical progression. Immunophenotyping provided good evidence for two blast populations, one lymphoid and the other lymphoid with granulocyte monocytic markers. Two different gene rearrangements within JH were also observed with band densities corresponding to the sizes of the two blast cell populations. A t(19; 22) translocation was observed in almost all cells at presentation one of which evolved into a subclone, becoming dominant in the terminal phase of the disease. We show here both the clonal evolution and clonal competition that occurred in this leukaemia and suggest that the potential of the tumour stem line for rapidly producing diversity was the reason for the resistance to treatment.

Phenotypic and genotypic switch in Philadelphia-positive, BCR-positive blast crisis of chronic myeloid leukemia

We report a case of Ph1-positive, bcr-positive chronic myeloid leukemia blast crisis (CML-BC) which at presentation showed a mixed myeloid/B-lymphoid immunophenotype along with TdT positivity and, at the molecular level, an oligoclonal rearrangement of the immunoglobulin heavy chain (IgH) gene region. After obtaining a successful remission, at the time of relapse the patient underwent a phenotypic and genotypic switch from mixed to myeloid phenotype, characterized by the loss of the lymphoid markers and TdT expression and by a germline configuration of the IgH gene region. The same bcr rearrangement was, however, found in both phases of the disease, supporting the suggestion of a true phenotypic and genotypic conversion. This report confirms that the neoplastic event in CML may take place at an early multipotent stem-cell level, prior to a well-defined phenotypic and genotypic lineage expression. Moreover, it is suggested that different factors (chemotherapy? growth factors?) may have either eradicated the bcr+/IgH+ clone and promoted the growth of bcr+/IgH- leukemic cells or, alternatively, supported the lymphoid differentiation program and induced a myeloid lineage shift.

Possible evidence for genomic imprinting in childhood acute myeloblastic leukaemia associated with monosomy for chromosome 7

Monosomy or deletion of chromosome 7 is a frequent finding in both de novo and secondary acute myeloid leukaemia (AML) and myelodysplastic syndromes (MDS). Based on analysis of deletions of chromosome 7 in such patients, it has been suggested that there is a critical region of the chromosome lying within bands q21-q31. We have examined bone marrow and peripheral blood samples from 10 patients with MDS, AML and biphenotypic acute leukaemia who had monosomy for or rearrangement of chromosome 7, seeking evidence of non-random allele loss that might suggest the presence of imprinted genes on the chromosome. Bone marrow cells from one patient with the infant monosomy 7 syndrome had loss of maternal alleles as did two patients with biphenotypic leukaemia. Five out of five patients with MDS and both patients with de novo AML had loss of paternal alleles. One of the latter patients had a del(7) (q31q36) rather than monosomy 7. These findings suggest that imprinting of a gene(s) on chromosome 7, within the bands q31-q36, may be of importance in MDS and AML. Despite the reported increased incidence of AML amongst relatives of patients with cystic fibrosis (CF) the gene for which lies in chromosome region 7q31, none of the patients nor parents studied here appeared to be carriers of the most common gene mutation seen in patients with CF, the delta F508.

Surface marker analysis and karyotype distinguish acute biphenotypic leukemia from acute myelogenous leukemia expressing terminal deoxynucleotidyl transferase

Surface phenotyping by flow cytometry and cytochemical study were used to identify 15 adult patients with acute leukemia displaying ambiguous phenotypes. Differences were found in the blast cell karyotype and immunoglobulin gene rearrangements of terminal deoxynucleotidyl transferase (TdT)-positive acute myelogenous leukemia (AML) and biphenotypic leukemia expressing B lymphoid and myeloid markers. The karyotypic abnormalities, t(9;22) and t(4;11), were noticed in acute biphenotypic leukemia, and were consistently associated with rearrangement at the immunoglobulin locus. Furthermore, coexpression of CD19/CD20 and either myeloperoxidase or myeloid surface markers were predictive of finding the t(9;22) or t(4;11) karyotype. Patients with TdT-positive AML, on the other hand, were less likely to show rearrangement at the immunoglobulin locus, and did not have the t(9;22) or t(4;11). Instead, a variety of nonrandom karyotypic abnormalities were seen, including trisomy 13. Unlike common AML, the majority of TdT-positive cases demonstrated an abnormal karyotype with duplications and/or deletions present in all cases. In no instance was trisomy 8, t(8;21), t(15;17), or any other isolated translocation identified. The authors therefore suggest that immunophenotyping, when combined with cytochemical analysis of TdT and myeloperoxidase or Sudan black B, may aid in the characterization of subgroups of atypical acute leukemia, such that alternate approaches to therapy can be evaluated.

Simultaneous occurrence of myelomonocytic leukemia and multiple myeloma: involvement of common leukemic progenitors and their developmental abnormality of "lineage infidelity"

We investigated the origin of leukemic progenitors in a case of the simultaneous occurrence of myelomonocytic leukemia and multiple myeloma (IgG-kappa). At presentation, myeloperoxidase and nonspecific esterase-positive myelomonocytic cells had proliferated up to 12.2 x 10(9)/liter in the peripheral blood. Bone marrow cell differentials revealed the coexistence of myelomonocytic cells (30%) and atypical plasmacytoid cells (26%). Myelomonocytic cells in peripheral blood expressed both myeloid antigens (CD11b, CD13, CD14, CD15, CD33) and T/B-lymphoid antigens (CD2, CD4, CD5, CD7, CD10, PCA-1). Bone marrow mononuclear cells (BMMC) could be divided into PCA-1 strongly positive and PCA-1 weakly positive populations, which were considered to represent myeloma cells and myelomonocytic cells, respectively; the former were CD2-positive (CD2+), CD14-, and CD15-, whereas the latter were CD2+, CD14+, and CD15+. Immunohistochemical analysis revealed that, in addition to plasmacytoid cells, a minority of myelomonocytic cells showed a positive reaction for IgG staining, and production of IgG was observed in the culture supernatant of CD14+ myelomonocytic cells in peripheral blood. Southern blot analysis revealed the presence of two identical rearrangement bands of immunoglobulin heavy chain gene in both BMMC containing myeloma cells and myelomonocytic cells and CD14+ myelomonocytic cells in peripheral blood. In a long-term methylcellulose assay, peripheral blood mononuclear cells produced large compact colonies consisting of macrophages and IgG+ plasmacytoid cells (M phi/P colonies), while BMMC produced a different type of colonies consisting of CD14+ myelomonoblasts, macrophages, and IgG+ plasma cells (Mb/M phi/P colonies) in addition to M phi/P colonies. Recloning experiments showed that primary Mb/M phi/P colonies gave rise to both secondary M phi/P and Mb/M phi/P colonies. These observations strongly suggest that common leukemic progenitors provide both myeloma and myelomonocytic leukemia cells, and the mechanism of "lineage infidelity" is probably involved in the development of their "bilineal" differentiation.

Down's syndrome and mixed acute leukemia in infants

The routine use of panels of monoclonal antibodies has been complementary to the French-American-British (FAB) leukemia classification, and has unmasked the occurrence of mixed acute leukemia (myeloid-lymphoid). It is widely accepted that children with Down's syndrome (DS) have a high incidence of acute leukemia. There is an extensive body of literature emphasizing the cytogenetic findings in these children. However, information as to the immunophenotype is often limited to the lymphoid surface determinants. The authors report two children with DS whose leukemic blasts were studied with a panel of 17 monoclonal antibodies (myeloid, lymphoid, and megakaryocytic) by flow cytometric examination and were classified as biphenotypic acute leukemia. The blast population coexpressed myeloid and T-cell surface markers. The lymphoid origin was ruled out on the basis of negative terminal deoxynucleotidyl transferase and molecular analysis demonstrating germline configuration for the JH and beta TCR genes.

CD34 antigen expression in children with Philadelphia chromosome-positive acute lymphoblastic leukemia

One characteristic of Philadelphia chromosome (Ph')-positive acute leukemia is the occasional presence of both lymphoid and myeloid features in the same leukemia. This phenomenon supports the theory that this subtype of acute leukemia arises from lymphoid-myeloid stem cell, pluripotent progenitors. Very few reports, however, describe the immunophenotype, especially CD34 antigen, of Ph'-positive acute lymphoblastic leukemia (ALL). It has been shown that CD34, the human progenitor cell antigen, is found on 1% or less of normal human bone marrow cells, approximately 30% of acute leukemias, and multipotent progenitor cells; CD34 is not found on normal peripheral blood cells. A high frequency of CD34 expression was found in children with Ph'-positive ALL: CD34 was positive for all six patients tested, and one had an acute mixed-lineage leukemia. These findings suggest the involvement of a pluripotent stem cell in Ph'-positive ALL.

MY4 expression on B-lymphocyte malignancies may be associated with a more adverse prognosis

We have noted what other preliminary reports have also described as a new specificity of the MY4 monoclonal antibody from Coulter Immunology which previously was designated to only have myelogenous CD14 specificity. The MY4 marker appears to characterize a subpopulation of some B-lymphocytic malignancies that are CD19, CD20, surface immunoglobulin as well as MY4 positive. The results occurred when other myelogenous markers such as CD11b, CD13 and CD33 were unreactive. Another monoclonal antibody marker of CD14 specificity, MO2, did not demonstrate a similar reactivity. Various other monoclonal antibodies of the same IgGI subclass as MY4 were also not reactive and thereby excludes non-specific adsorption as an explanation of the results. The six patients described in this report represented five non-Hodgkin's lymphoma cases and one chronic lymphocytic leukemia case. Fifteen B-lymphocytic leukemias and 30 other B-lymphocytic non-Hodgkin's lymphomas analysed during the same period were not MY4 positive. In reviewing the clinical course of the six patients compared to the general behavior of these types of malignancies and making a speculative generalization from the small group of cases, the MY4 antigen appeared to be expressed by low to intermediate grade B-lymphocytic malignancies of a type that were more rapidly progressive and/or had a greater tendency to undergo a transformation of their malignancy. Two of the three transformed cases were proceeded by chronic lymphocytic leukemia.

Application of the avidin-biotin-peroxidase complex technique for ultraimmunocytochemical characterization of leukemic cells

For simultaneous demonstration of cellular ultrastructure, myeloperoxidase activity, and presence of a membrane-bound antigen in a given blood cell, we examined three different fixatives: periodate-lysine-paraformaldehyde (PLP) and paraformaldehyde and glutaraldehyde for their applicability to preembedding electron microscopic immunocytochemistry using monoclonal antibodies and the avidin-biotin-peroxidase complex (ABC) technique. This procedure was examined in samples from 3 normal volunteers and 29 patients with acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), lymphosarcoma cell leukemia (LSCL), blastic phase of chronic myelogenous leukemia (CML-BC), or other unclassified leukemias. PLP fixation preserved the immunoreactivity of surface glycoproteins as well as immunoglobulins to the most satisfactory extent. Leukemic cells fixed with PLP maintained their fine structural details, so that we could identify their cytoplasmic organelles, although glutaraldehyde produced the best preservation of cellular ultrastructure. In three patients with ALL, our method revealed that a significant portion of blasts possessed both lymphoid surface antigens and peroxidase-positive cytoplasmic granules. Our method was also useful in identifying the lineage of peroxidase-negative leukemic cells, including monoblastic leukemia and megakaryoblastic leukemia cells. Ultraimmunocytochemistry using PLP fixation and the ABC technique may be a promising strategy for determining the nature of blastic cells that remain unclear after a conventional work-up, for characterizing leukemic cells in patients with a relatively low blast cell count in the bone marrow or peripheral blood, and for estimating the presence and frequency of leukemia with multilineage expression.

Acute 'bilineal-biphenotypic' leukaemia

We describe a unique case of hybrid leukaemia with bilineal and biphenotypic features. The coexistence of lymphoblasts and monoblasts was determined morphologically and cytochemically. Immunofluorescence and immunohistochemical analysis revealed that each blast population had both T lymphoid (CD2, cytoplasmic CD3) and myeloid (CD11, CD13, CD15) markers. Southern blot analysis of DNA extracted from the lymph node biopsy demonstrated the presence of monoclonal rearrangement of the TcR-C beta gene. Cytogenetic analysis of the bone marrow cells showed a karyotype of 48, XY, 7q+ in all of the metaphases examined. These observations are suggestive of a monoclonal origin for these two distinct blast populations.

Undifferentiated acute leukemia and lineage infidelity (difficulties in classification and management)

The acute leukemias have been considered to represent a clonal expansion of a malignant transformed hematopoietic progenitor cell with adherence to either the myeloid or lymphoid lineage--"lineage fidelity." Lineage fidelity has been challenged by the demonstration of lineage switching or mixed-lineage leukemias. We describe a 7 year old male who presented with undifferentiated acute leukemia and nasopharyngeal and cervical masses. His blasts had the morphologic appearance of myeloblasts (FAB M1) and were positive solely for the myeloid antigen CD15. He entered a complete remission (CR) with acute nonlymphocytic leukemia therapy. At first relapse he had evidence of mixed-lineage leukemia with B-cell lymphoid and myeloid phenotypes. He again relapsed from a second CR with Burkitt-cell leukemia. Cytogenetic findings showed a consistent 14q+, 17p+ abnormality in the blasts and nasopharyngeal mass. The t(8;14) associated with Burkitt's lymphoma was found in the mass tissue only following passage in the nude mouse. Our patient demonstrates that limitations still exist in our ability to classify acute leukemia. That leukemic transformation occurred in a multipotential progenitor cell leading to undifferentiated leukemia at diagnosis and/or that chemotherapy can influence the genetic programs of leukemic cells leading to the evidence of mixed-lineage leukemia and lineage switching is supported.

The in-vitro response of CD2-positive acute myelogenous leukemia to proliferation and differentiation inducing agents

Acute mixed lineage leukemias (MLL) are a heterogeneous group of acute leukemias that express morphologic and/or immunophenotypic features of more than one hematopoietic cell line. The ontogenetic significance of this mixed lineage expression is unclear. We therefore studied the conviction of the lineage commitment in a group of MLL by examining the in-vitro response of five CD2+ (E-rosette receptor) acute myelogenous leukemia (AML) to a panel of proliferation and differentiation-inducing agents. Three of the five CD2+ AML were TdT-positive. Antigen receptor gene studies revealed no rearrangements at either the T beta or immunoglobulin heavy chain gene loci in any case. When blast-enriched cell populations were placed in short term suspension cultures with PHA, IL-2, PHA + IL-2, GM-CSF or TPA, three of the leukemias responded in a similar fashion while the remaining two cases showed no response. In the three MLL that responded to the in-vitro culture manipulations, features indicative of differentiation along the monocytic lineage pathway were observed. This differentiation was not pronounced in the presence of the phorbol ester TPA, and was manifested by loss of CD2 and CD7 expression, continued expression of myeloid antigens, and the development by the blasts of morphologic and cytochemical characteristics of monocytic cells. None of the five MLL showed any evidence of induced maturation along the T-lymphocyte line of differentiation with any of the agents used. rGM-CSF was the only exogenously added agent to induce proliferation; the proliferative response was slight and was seen in only one of the five leukemias. Therefore, the phenotypic expression of CD2 and CD7 in blasts from MLL is not indicative of irreversible commitment to T-lymphocyte development. The in-vitro loss of T-cell antigens in concert with the development of monocytic features in three of the five CD2+ AML in this study suggests the leukemic cells were preferentially committed to a non-lymphoid lineage differentiation pathway.

Multiple lineage reactivity in childhood leukemia

The leukemia cells from 63 children with acute leukemia were evaluated by flow cytometry with a panel of monoclonal antibodies that included lymphoid and myeloid lineage-specific antigens. Surface markers from patients with acute lyphocytic leukemia (ALL) did not correlate with their FAB classification except for L3 leukemia. Myeloid leukemias of FAB class M1-M4 were positive for CD13 and CD33, whereas CD14 and MY8 were only detected in FAB class M4 leukemia. Mixed leukemias were subclassified as intralineage (B+T+) or interlineage (B+ or T+/M+). Interlineage leukemias represented 5.6% of ALLs, and all patients are alive after treatment with ALL protocols. Interlineage mixed leukemias represent 7.9% of all leukemias occurring in 3.7% of ALLs and 33% of acute myeloid leukemias (AMLs). All children with mixed interlineage leukemias are alive after treatment with the protocol for the dominant leukemia; however, follow-up periods are too short to predict final outcome. The high proportion of mixed interlineage leukemias in AMLs supports Greaves' theory of lineage promiscuity, that is, there is a normal period of hematopoietic development when individual cells co-express multiple lineage antigens on the cell surface.

Clinical characteristics of hybrid leukemia: report of five cases

We studied clinical and biological features of five cases of hybrid leukemia. Three of the five patients were classified as biphenotypic leukemia because of the coexpression of myeloid/B lymphoid markers in patients 1 (FAB M2) and 2 (FAB CMMoL) and myeloid/T lymphoid markers in patient 3 (FAB M4). Patient 4 was identified as bilineal-biphenotypic leukemia because acute myelogenous leukemia (AML) (FAB M4) and acute lymphoblastic leukemia (ALL) (FAB L1) coexisted and each population coexpressed myeloid and T lymphoid markers. Patient 5 was identified as bilineal leukemia due to the conversion from AML (FAB M1) to ALL (FAB L1) at an interval of 3 months. The Philadelphia (Ph1) chromosome was negative in all cases. A leukemic blast colony formation using cell line 5637 conditioned medium as a stimulator was obtained in all four patients examined. Three of the five patients had been suffering from so-called stem cell disorders such as aplastic anemia in patient 2, trilineage myelodysplasia in patient 4 and refractory anemia with excess of blasts in transformation in patient 5. The pre-existing impairment of pluripotent stem cell was probably the background of these hybrid leukemia. Hybrid leukemia appears to have an inferior prognosis: an AML-directed chemotherapy resulted in a low remission rate (2/5) with a short duration of relapse free survival (1/2) and an ALL-directed chemotherapy produced no remission (0/3). Chronological phenotypic analysis revealed that hybrid features of leukemic blasts disappeared at the time of relapse in patient 1 and progression to AML in patient 2. Monitoring of lineage-associated markers should be required for the management of hybrid leukemia.

Unusual immunophenotypes in acute leukaemias: incidence and clinical correlations

The incidence and clinical implications of unusual patterns of expression of leucocyte differentiation antigens in acute leukaemia were assessed on 568 newly diagnosed paediatric and adult cases undergoing immunophenotyping with a panel of monoclonal antibodies at a single centre. Among patients with the precursor B (common) form of acute lymphoblastic leukaemia (ALL), the major variant seen was the group of 15 cases with expression of myeloid surface antigens. 4.5% of ALL cases tested with antibody to CD-11b were positive, 5.1% were CD-13+, and 10.8% CD-33+. All 15 patients achieved a complete remission with chemotherapy, with six of eight children and four of seven adults remaining disease free. A smaller proportion (1.5%) of precursor B ALL patients showed expression of the T lineage marker, CD-7. The only significant variant seen in the precursor T-ALL group was expression of HLA-DR antigen, which was found in five of 35 cases; although all responded to treatment, only one remains a disease-free survivor. Among patients with acute myeloid leukaemia (AML), expression of the lymphoid markers terminal transferase (TdT) and CD-7 were commonly seen (22.2% and 28.4% respectively of cases tested). Other lymphoid markers detected on AML cases were CD2 (11.1%), CD-10 (1%) and CD-19 (4.4%). These results confirm that examples of lineage infidelity are regularly seen in large series of patients with acute leukaemia. Prospective studies using uniform treatment protocols are required to establish whether these patients have significantly different disease outcomes.

Treatment of adult acute lymphoblastic leukaemia using an intensive chemotherapy protocol

A total of 25 evaluable adult patients with acute lymphoblastic leukaemia (ALL) were treated with an intensive chemotherapy regime modified from the L17/L17M protocol of the Sloan-Kettering Hospital. There were 18 men and 7 women; their median age was 36 years (range, 13-78). Seven cases had L1 morphology and 18, L2. The immunophenotype was common-ALL in 10, null-ALL in 9, T-ALL in 4 and B-ALL in 1. Of the 25 patients, 14 (56%) achieved a complete remission (CR). The causes of induction failure were partial remission (PR) only in 7 (28%) and hypoplastic death in 4 (16%). Of the 14 CR patients, 11 (78.6%) relapsed. Five patients developed CNS disease. The median disease-free survival and overall survival were only 9 and 13 months, respectively. As the follow-up periods of the surviving patients were short, late relapses may still occur and the overall treatment result is likely to be worse on longer follow-up. The possible causes of this disappointing result are discussed.

Immunophenotyping in the classification of acute leukemia in adults. Interpretation of multiple lineage reactivity

Fifty-nine adult patients with acute leukemia were classified using a combination of the French-American-British (FAB) criteria and characterization by immunophenotyping using flow cytometric study. The authors identified 51 patients with acute myeloblastic leukemia and eight with acute lymphoblastic leukemia. This procedure permitted lineage assignment in leukemias that otherwise might have been unclassifiable. In addition, the authors demonstrated that the leukemic blasts of 29% of patients with myeloblastic disease exhibited one or more T-cell antigens on their surface. The use of immunophenotyping has greatly enhanced the authors' ability to correctly identify the lineage of acute leukemias. The data, however, must be interpreted with caution with respect to diagnosing acute mixed lineage leukemias and must be integrated with the morphologic and cytochemical evaluation of traditional classification schemes. The possible significance of T-cell markers in myeloblastic leukemia is discussed.

T-cell receptor gene rearrangement and its expression in human myeloid leukemia cell lines

ML cell lines (ML-1, -2, and -3) were derived from the cells of a patient with acute myelocytic leukemia preceded by a T-cell malignant lymphoma. A deletion of chromosome 11 (11q-) was common to the affected cells in both neoplastic phases. We report here that the three ML cell lines have DNA rearrangements of the T-cell receptor (TcR)-beta and gamma-chain genes in addition to immunoglobulin heavy-chain gene rearrangement, though they do not have TcR gene messages. The findings presented here indicate that ML cell lines could be used as models for the elucidation of the bilineal nature of hematopoietic neoplastic cells, though they have a biphenotypic (myelomonocytic/T-cell) marker expression.

Interest of simultaneous ultrastructural characterization of morphology, cytochemistry and immune phenotype in a case of putative hybrid acute leukaemia

A case of acute leukaemia is reported in which blast cells expressed some B-related antigens (namely the CALLA antigen) and no peroxidase activity at the optical level; however, some mature granular cells contained Auer rods. Simultaneous characterization of ultrastructural morphology, cytochemistry and immune phenotype was performed. There was an apparent mutual exclusion in the expression of myeloperoxidase activity and the CALLA antigen, and a heterogeneity in the CALLA expression among the blastic population. These results disagree with the hypothesis of a true biphenotypic leukaemia and demonstrate a complete heterogeneity between the lymphoblastoid cells and the myeloid ones. The interest of such a simple combined method in a case of putative hybrid acute leukaemia is emphasized.

Routine immunophenotyping of acute leukaemias

Recent progress in immunophenotyping includes the availability of monoclonal antibodies (MAbs), knowledge of specificity and reactivity patterns of these reagents, and the technical improvements and standardization of immunofluorescence and immunocytology staining procedures, including flow cytometry. These advances have contributed significantly to the establishment of immunophenotyping as an essential diagnostic tool in the differential diagnosis of types of acute leukaemia. Immunophenotyping allows for the objective and reproducible distinction of acute lymphoblastic leukaemia (ALL) from acute myeloblastic leukaemia (AML) and of T-lineage from B-lineage ALL. Immunologically defined ALL and AML subtypes have been found to convey prognostic significance. Using cell lineage-specific and differentiation stage-specific MAbs, cases of T- and B-lineage ALL and of AML can be further classified into a number of different subtypes. Routine immunophenotyping concentrates on the diagnostic enquiry into a few major, clinically relevant subtypes; only a limited number of crucial reagents are employed that are commercially available. The simplification and standardization of discriminatory immunomarker panels make immunophenotyping a reliable diagnostic instrument for the provision of critical data to make a differential diagnosis. An effort to identify the nature and origin of the blast cells precisely, immunological typing definitely plays an important part in the multiple-marker analysis of acute leukaemia (morphology, cytochemistry, karyotyping, genotyping) for applied diagnostic and fundamental research purposes.

Analysis of peroxidase-negative acute unclassifiable leukemias by monoclonal antibodies. 1. Acute myelogenous leukemia and acute myelomonocytic leukemia

In this study, pretreatment peripheral and/or bone marrow blasts from 12 patients with acute unclassifiable leukemia (AUL) expressing the myeloid-related cell-surface antigen (CD 11) were isolated for further analysis. Despite a lack of myeloperoxidase (MPO) activity, 1 patient's blasts contained cytoplasmic Auer rods. The circulating blasts from another patient expressed MPO while maintaining the same surface phenotype during 20 months of clinical follow-up. In addition, the blasts from 3 cases demonstrated both myelomonocytic and monocyte-specific surface antigens, whereas the remaining 9 cases completely lacked any monocyte-specific antigen detectable by monoclonal antibodies, Mo2, My4 and Leu M3 (CD 14). The first case eventually was diagnosed as acute myelomonocytic leukemia and the second as acute myelogenous leukemia by means of immunophenotypic analysis using flow cytometry (FACS IV). In addition, the presence of MPO protein was identified in the cytoplasm of blast cells from 5 patients with AUL by means of a cytoplasmic immunofluorescence test using a monoclonal antibody (MA1). Our study indicates that non-T, non-B AUL expressing OKM1 (CD 11) antigens include acute leukemias which are unequivocally identifiable as being of either myeloid or myelomonocytic origin. However, further investigations, including immunophenotypic and cytoplasmic analysis, ultrastructural cytochemistry and gene analysis with molecular probes (tests applicable to normal myeloid cells), are necessary in order to determine the actual origin of blasts and to recognize the differentiation stages of the various types of leukemic cells from patients with undifferentiated forms of leukemia.

Terminal deoxynucleotidyl transferase and HLA-DR expression appear unrelated to prognosis of acute myeloid leukaemia

Mononuclear cells from peripheral blood or bone marrow from 314 patients with acute myeloid leukaemia were examined for the presence of nuclear terminal deoxynucleotidyl transferase (304 patients), surface membrane expression of HLA-DR (314 patients) and the common acute lymphoblastic leukaemia antigen (281 patients). All patients were treated with identical remission induction chemotherapy, and morphological diagnosis was carried out in a central laboratory. The overall complete remission rate was 70%. There were no significant correlations between the immunological markers and complete remission rate, duration of remission, or survival.

Simultaneous expression of activated lymphoid cell-associated and granulocytic cell-associated antigens on Hodgkin's and Reed-Sternberg cells in Hodgkin's disease

The surface antigens of Hodgkin cells and Reed-Sternberg cells (H- and R-S cells), including lacunar cells, were analyzed with a large panel of monoclonal and polyclonal antibodies by an immunohistochemical method and an immunoelectron microscopic technique. H- and R-S cells in each histologic subtype of nodular sclerosis, mixed cellularity and lymphocyte depletion were stained similarly with anti-Leu-M1, anti-Leu-11b, TG8, anti-HLA-DR, anti IL-2R, RSC-1 (Ki-1) and anti-alpha-1-antitrypsin, but not with other antibodies examined. These findings suggest the following: (1) H- and R-S cells of nodular sclerosis, mixed cellularity and lymphocyte depletion are not heterogeneous, at least in terms of surface antigen expression, and (2) H- and R-S cells may be lymphoid cells which simultaneously express activated lymphoid cell-associated antigens (e.g., HLA-DR, RSC-1 and IL-2R) and granulocytic cell-associated antigens (e.g., Leu-M1 and TG8).

Tetraploidy and Y chromosome loss in acute mixed-lineage leukemia

An unusual case of acute leukemia with mixed phenotype was followed up from diagnosis to death for about 12 months. The first cytogenetic examination revealed about 80% of the bone marrow cells in the diploid and 20% in the tetraploid range. After two courses of induction therapy, complete remission was achieved within 2 months. At this time the tetraploid cells were reduced to 3%, but 50% of the mitoses showed a Y chromosome loss, while the other mitoses had a diploid karyotype. Early intensification therapy was given 6 weeks later with slow recovery of blood counts. After four months a sharp decrease of the number of Y-missing mitoses was observed, while the marrow remained in full remission. Two months later a relapse occurred and the patient died. At this time the -Y clone had dropped to 2% and the tetraploid clone was totally absent. We conclude from these findings that the diploid clone was the most malignant one, whereas the -Y cells were probably not directly involved in the leukemic process.

Terminal deoxynucleotidyl transferase positive acute myeloid leukaemia: an association with immature myeloblastic leukaemia

The morphology, membrane markers and ultrastructural cytochemistry of 39 cases of acute myeloid leukaemia (AML) with variable proportion (10-99%) of terminal deoxynucleotidyl transferase (TdT) positive blasts was compared with that of 134 cases of TdT negative AML. The incidence of TdT positive AML was 22.5% and this was significantly higher in poorly differentiated myeloblastic (M0 and M1) types (54%) than in all other FAB subtypes (10%; P less than 0.001). Our findings suggest heterogeneity among TdT positive cases. Whilst the majority correspond to genuine TdT positive AML in which evidence for exclusive myeloid nature was demonstrated by phenotypic, cytochemical and ultrastructural markers, a distinct minority (22%) of cases had mixtures of lymphoid and myeloid blasts. A change in phenotype occurred in three out of six cases studied in relapse. There was no difference in the incidence of immunoglobulin (Ig) gene rearrangement between TdT positive (two out of 12) and TdT negative (one out of 11) cases, although published data suggests that Ig gene rearrangement is significantly more common in TdT positive cases. The determination of TdT in AML allows the identification of cases of mixed acute leukaemia which probably represent proliferations of multipotent progenitor cells. The majority of TdT positive cases, nevertheless, correspond to immature types of myeloblastic leukaemia which may constitute a clinically distinct subgroup.

Mixed acute leukaemias

In recent years immunophenotyping and analysis of clonal rearrangement of immunoglobulin and T-cell antigen receptor genes have proved valuable for the diagnosis and classification of leukaemia. These techniques aid in the assignment of cell lineage in cases of acute leukaemia in which the standard FAB criteria of morphology and cytochemistry do not reveal clear lymphoid or myeloid phenotype. These new techniques have also revealed that the leukaemic blasts in a sizable minority of otherwise typical cases of acute leukaemia express 'inappropriate' lineage-associated markers and have been termed mixed acute leukaemias. The spectrum of characteristics encompassed by mixed acute leukaemias ranges from fairly common cases expressing one or two inappropriate markers to the more extreme, rare cases of acute leukaemia termed 'hybrid' in which a truly scrambled picture is seen. A subgroup of these mixed cases have two distinct populations of blasts, e.g. one lymphoid and the other myeloid. These observations raise a number of issues about the cell of origin of these leukaemias and about the mechanisms controlling the developmental regulation of expression of different lineage-associated markers. In addition, accumulating evidence suggests that inappropriate expression of markers may identify sub-groups of both acute myeloid and lymphoblastic leukaemia with an inferior prognosis.

First-line diagnosis based on immunological phenotyping in suspected acute leukemia: a prospective study

In a prospective analysis of the diagnostic value of immunophenotyping in acute leukemias (ALs), all patients admitted to a pediatric and a haematological department suspected of AL were examined consecutively with a selected panel of monoclonal antibodies (Mabs) against leucocyte differentiation antigens during an 8-month period. A total of 189 samples obtained from blood, bone marrow, spinal fluid and lymph nodes in 120 cases were all analysed blindly. The results were correlated with a routine morphological/cytochemical evaluation. Differing results were obtained in seven out of 38 cases in which the immunologically defined diagnosis was acute myeloid leukemia (AML), and in one out of 21 cases with the primary diagnosis acute lymphoid leukemia (ALL). Immunological phenotyping disclosed two cases of hybrid leukemia, one case of biphenotypic and one case of bilineal leukemia. No evidence of malignancy was found in 36 cases, 30 cases of blood and bone marrow and six cases of spinal fluids, in every case in accordance with the pathological examination. These results demonstrate that a first-line immunological evaluation of bone marrow, blood and spinal fluid from patients suspected of AL is highly capable of discriminating between different malignant and nonmalignant haematological diseases and also between various types of leukemias. The immunological methods do, however, require a sufficient amount of material which was a limiting factor in 14 out of 120 examinations, mainly from patients treated with several cycles of cytostatics. It is concluded that immunophenotyping can be used as a first-line diagnostic tool in malignant haematological diseases.

Abnormalities of chromosome 12p13 and malignant proliferation of eosinophils: a nonrandom association

Four patients representing a spectrum of haematological malignancies are reported. Two patients had Philadelphia chromosome negative myeloproliferative disorders, one had acute lymphoblastic leukaemia and one had eosinophilic leukaemia. In each case eosinophilia was present and demonstrated to be part of the malignancy by the association of clonally abnormal metaphases with eosinophil granules. Abnormalities involving the short arm of chromosome 12 (12p13) were a constant feature in all four cases and therefore a nonrandom association between this chromosome region and malignant eosinophil proliferation is proposed.

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.

Acute leukemia with chromosome translocation (4;11): 7 new patients and analysis of 71 cases

Clinical and laboratory features of seven patients with acute leukemia associated with the (4;11) chromosome translocation are presented. Leukemic blasts of these patients showed lymphoid morphology in 6 (although 1 was treated for monoblastic leukemia 3 years earlier) and monocytoid morphology in 1, were positive for TdT and HD 37 (CD 19) in 6 patients, whereas weak expression of CALLA was seen in only 1 patient and T-lineage-associated antigens in none. Leukemic blasts from four patients showed the simultaneous expression of B-lymphoid and myeloid antigens, suggesting leukemogenesis in a very early multipotent progenitor cell. In 2 patients an isochromosome of the long arm of No. 7 chromosome was found in the leukemic karyotypes in addition to t (4; 11) (q 21; q 23); in one instance present at diagnosis, in the other one occurring at relapse. In one other patient leukemia karyotype also demonstrated trisomy 8. Leukemic cells of three patients were investigated by molecular genetics and demonstrated immunoglobulin gene rearrangements for the Ig heavy chain sequences but not for the light chain constant regions and T cell receptor sequences. All patients were treated by intensive chemotherapy. Four of the 7 patients are in continuous complete remission. The longest event-free survival time (over 2 1/2 years) was seen in one patient who had also DOWN-syndrome. Including these 7 patients a clinical analysis of 71 patients with t (4; 11) acute leukemia was made, emphasizing the following characteristics at diagnosis: female sex (62%), age under 2 years (49%), leukocyte count over 100 X 10(9)/1 (61%), splenomegaly (80%), CNS-disease (11%). Survival of over 2 years was reported in less than 15% of the patients. It remains to be seen if risk-adapted treatment can alter the course of this early B-precursor acute leukemia with hitherto very bad prognosis.

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.

Hybrid biphenotypic acute leukemia with extreme hypodiploidy

A patient diagnosed as having acute lymphoblastic leukemia (L2) relapsed 4 months later and was found to have morphologic and immunologic evidence of a biphenotypic hybrid acute leukemia. Chromosome analysis at relapse showed two abnormal clones, one with marked hypodiploidy and the other with exactly double the hypodiploid clone. It is considered that this is an example of a hybrid lymphoblastic/nonlymphoblastic leukemia with unique karyotype.

Hybrid leukaemia of T cell and myeloid lineages: cytogenetic distinction from second (induced) malignancy

The therapeutic and prognostic implications of relapse and clonal evolution of leukaemia are substantially different from those of secondary (induced) malignancy. This report documents the case of a patient who presented with apparent acute non-lymphocytic leukaemia (ANLL) following therapy for acute (T-cell) lymphoblastic leukaemia (ALL) 4 years previously. Morphologically and cytochemically the cells were of myeloid type, but the cell markers showed a T cell lineage. Cytogenetic studies confirmed that this was a relapse of T cell ALL with a phenotypic change, rather than a second malignancy induced by chemotherapy. A 14q deletion present at initial diagnosis recurred at relapse, with the addition of cells with complete deletion of chromosome 14, indicating clonal evolution.