Targeting of a developmentally regulated epitope of CD43 for the treatment of acute leukemia

Previously, we developed a JL1 mouse monoclonal antibody that specifically recognizes the leukemic cells of T, B, and myeloid lineages, but not the peripheral blood cells and pluripotent hematopoietic stem cells. Here, we identified that JL1 mAb recognized a specific epitope of human CD43 and validated its potential as an anti-leukemic targeting agent. After the comprehensive screening of JL1 Ag in the human thymocyte cDNA library, multiple fusion gene constructs encoding human CD43 were generated to identify its specific epitope to JL1 antibody. JL1 antibody interacted with a developmentally regulated and non-glycosylated epitope of the human CD43 extracellular domain (AA 73-81, EGSPLWTSI). In an in vivo leukemia model using NOD/SCID mice injected with CCRF-CEM7 cells, JL1 antibody induced effective cytotoxicity in tumor cells and prolonged survival (p < 0.05). Saporin conjugation to JL1 antibody effectively depleted tumor cells in in vitro cytotoxic assays and also prolonged survival in a leukemic mouse model (p < 0.001). These preclinical results further support the therapeutic potential of the JL1 antibody in the management of acute leukemia.

[Immunophenotyping characteristics of biphenotypic acute leukemia and analysis of curative effect]

This study was aimed to investigate the immunophenotyping characteristics of biphenotypic acute leukemia (BAL) and to analyze its curative efficacy. The four-color direct immunofluorescence staining and CD45/SSC gating analysis of flow cytometry were used to detect the cells of bone marrow and peripheral blood of 45 doubtful cases of BAL, and the immunophenotyping was performed according to the European Group for the Immunological Classification of Leukemia (EGIL) score criterion. The results showed that among 45 doubtful cases of BAL, the co-expression of cCD79a and cMPO was observed in 23 cases of My/B-ALL, with highest level of CD19 expression, followed by CD10; the co-expression of cCD3 and cMPO was observed in 18 cases of My/T-ALL, with highest level of CD7 expression, followed by CD5; the co-expression of cCD3 and cCD79a was found in 4 cases of T/B. Out of 45 cases of BAL, 30 cases showed cTdT expression, 25 cases showed CD34 expression, 31 cases showed CD117 expression. The results also indicated that the expression rate of CD33 was higher than that of CD13 in antigen expression of My/B-ALL and My/T-ALL patients. The complete remission (CR) rate of My/B-ALL with My/T-ALL CD34(+) was lower than that of My/B-ALL with CD34(-), the CR rate of My/B-ALL with CD34(+) was lower than that of My/T-ALL with CD34(-). It is concluded that the co-expression of My/B-ALL antigen has been found to be most common, then followed by My/T-All. cCD3, cCD79a, cMPO have important value for diagnosing and identifying of BAL. The flow cytometry with four-color direct immunofluorescence staining is most specific method for diagnosis of BAL. The clinical prognosis of BAL with low cell differentiation is poor.

[Study on the clinical characteristics of 32 patients with mixed phenotype acute leukemia]

OBJECTIVE

To investigate the clinical and biological characteristics and prognosis of mixed phenotype acute leukemia (MPAL).

METHODS

Thirty two patients were diagnosed as MPAL by bone marrow examination, immunophenotyping, cytogenetic and molecular assay and were treated with combined chemotherapy regimens for both acute lymphoblastic and acute myeloid leukemia. Two cases were received allogeneic hematopoietic stem cell transplantation (allo-HSCT).

RESULTS

(1) The incidence of MPAL in acute leukemias was 2.6%. There were 16 cases (50.0%) of mixed myeloid and B-lymphoid (M/B), 14(43.8%) myeloid and T-lymphoid (M/T), one each (3.1%) of trilineage (M/B/T) and B- and T-lymphoid (B/T) phenotype. (2) The positive rates of CD34 and HLA-DR were 87.5% and 62.5%, respectively. (3) Abnormal karyotypes were detected in 70.0% of 30 MPAL patients, which were structural and numerical abnormalities including t(9;22), 11q23 and complex karyotypes. (4) The total complete remission (CR) rate was 75.0% and the overall survival (OS) and disease-free survival (DFS) at 2 years were 14.8% and 14.2% respectively. The CR rates for M/B and M/T cases were 75.0% and 71.4% respectively. No statistical difference was observed in OS and DFS between M/B and M/T cases.

CONCLUSIONS

MPAL is a rare type of acute leukemia with a high heterogeneity. The unfavorable indicators of MPAL may be factors such as abnormal karyotypes, high expression of CD34 and extramedullary infiltration. Combined regimens and more intensive therapy including allo-HSCT might contribute to improving survival.

Candida krusei fungemia in an immunocompromised patient

Candida krusei is an emerging fungal pathogen found primarily in immunocompromised patients. Intrinsic resistance to fluconazole and decreasing susceptibility to other anti-fungal agents are problematic. When colonization occurs, dissemination may follow rapidly. We present a case of a patient with acute lymphoblastic leukemia who, despite being treated prophylactically with fluconazole, developed disseminated C. krusei.

Diagnosis of biphenotypic acute leukemia: a paradigmatic approach

Biphenotypic acute leukemia (BAL), or acute leukemia with a single population of blasts coexpressing markers of two different lineages, is a rare clinical entity. To define BAL, a scoring system was proposed by the European Group of Immunological Markers for Leukemias (EGIL) in 1995. However, increasing evidence suggests that this system has limitations, as acknowledged by the 2008 World Health Organization (WHO) Classification of Tumors of Hematopoietic and Lymphoid Tissues. Although substantially improved in relation to the EGIL, the new WHO Classification is still not optimal for guiding the clinical management of patients with BAL. We propose a new paradigmatic approach to defining BAL based on recent clinical studies of BAL and advances in immunologic marker definition and cytogenetics, and applied our new approach to 8 cases of "BAL" among a cohort of 742 new acute leukemias in our Cancer Center. By our new criteria, 6 cases were reclassified as acute lymphoblastic leukemia (ALL), while only 2 were still classified as BAL. Our approach is also supported by analyses of the BAL cases previously reported by other institutions.

[Study on the clinical characteristics of adult biphenotypic acute leukaemia]

OBJECTIVE

To analyze the clinical and biological characteristics and prognosis of adult biphenotypic acute leukaemia (BAL).

METHODS

Immunophenotypes were analyzed using multicolor flow cytometry, karyotype analysis by short-term culture R-banding technique. The chemotherapy regimens were accordingly for acute lymphoblastic leukaemia (ALL), acute myeloid leukaemia (AML) or for both ALL and AML. Patients with Ph (+) or bcr-abl (+) were treated with Imatinib.

RESULTS

(1) The incidence of BAL in acute leukaemias was 6.7%, with a male predominance and 52.3% of BAL patients had WBC > or = 30 x 10(9)/L and 16.9% WBC > or = 100 x 10(9)/L. (2) Percentages of coexpression of myeloid and B lymphoid antigens were 81.5%, of myeloid and T lymphoid antigens 10.8%, of myeloid, B- and T lymphoid antigens 4.6%, and of B and T lymphoid antigens 3.1%. (3) Normal and abnormal karyotypes accounted for 41.5% and 58.5%, respectively in 53 BAL patients with karyotype analysis. The rate of Ph (+) or bcr-abl (+) was 32.1%. (4) 31 (56.4%) of 65 patients achieved complete remission (CR), but CR rate was only 35.3% for Ph (+) or bcr-abl (+) cases.

CONCLUSION

(1) High white blood cell count and coexpression of myeloid/B lymphoid antigens are common in BAL. (2) Abnormal karyotypes and Ph (+) or bcr-abl( +) often happen. (3) The treatment outcome of BAL is poor.

[Biphenotypic and bilineal acute leukemias]

Human acute leukemias (AL) are classified as myeloid or lymphoid according to cytomorphology and the expression of leukocyte differentiation antigens/CD-markers. However, in the minority of cases leukemic cells express markers of more than one lineage, which has led to the introduction of a new subgroup of acute leukemias termed mixed or biphenotypic acute leukemias (BAL). In an effort to distinguish between BAL and those AL with aberrant expression of markers of other lineage, the European Group for the Immunological Characterization of Acute Leukemias (EGIL) has proposed a scoring system in which CD-markers are assigned a score of 0.5, 1.0 or 2.0, depending on the specificity of a particular antigen for myeloid, B- and/or T-lymphoid lineage, respectively. The new WHO classification of hematologic tumors has adopted the EGIL criteria for BAL and introduced a new group of AL termed 'AL of ambiguous lineage'. In addition to BAL in which a single cell population expresses both myeloid and lymphoid differentiation markers, this new group of leukemias also comprises cases that present with two separate blast populations (acute bilineal leukemia, aBLL). In general, BAL accounts for less than 5% of all AL cases, whereas aBLL is a rare disease constituting 1%-2% of AL cases that contains B- or T-lymphoid along with myeloid blasts. Chromosome abnormalities are frequent in both entities with a relatively high incidence of Philadelphia chromosome and rearrangements involving 11q23, especially in cases with B- and myeloid involvement. Other biological features include CD34 expression and multi-drug resistance P-glycoprotein overexpression. The prognosis of BAL and aBLL is unfavorable, with poor prognostic factors being age, high WBC and the presence of Philadelphia chromosome. Unfortunately, optimal therapy is not known, although regimens designed for acute lymphoblastic leukemia may result in a better response rate. Collaborative studies are needed for better understanding of the biology of these entities and establishment of standard therapeutic protocols.

[Cytomorphology of acute mixed leukemia]

Biphenotypic acute leukemias (AL) with blasts expressing both myeloid and lymphoid antigens are grouped with undifferentiated AL and bilineal AL in the group of AL of ambiguous lineage. Not all AL with myeloid and lymphoid antigens (ALMy+Ly) are true biphenotypic AL. According to EGIL scoring system, true biphenotypic ALMy+Ly are those with a sum of antigens 2 or more points for both myeloid and lymphoid lineage or for B and T lineage. The aim of this study was to compare cytomorphology and immunophenotype of AL to better understand the relation of certain AL morphology, immunophenotype, cytogenetics and molecular biology of biphenotypic AL.

PATIENTS AND METHODS

The study included a group of 169 AL patients treated from 1985 till 1991, and a group of 102 AL patients treated from 1993 till 1996 at Zagreb University Hospital Center. Bone marrow and peripheral blood of the two groups of AL patients were analyzed according to Pappenheim (May-Grunwald-Giemsa), cytochemical and alkaline phosphatase-anti-alkaline phosphatase (APAAP) immunocytochemical staining. Flow cytometry immunophenotyping of bone marrow was also done in both patient groups.

RESULTS AND DISCUSSION

In the group of 169 adult AL patients, 116 were cytomorphologically classified as acute myeloblastic leukemias (AML), 35 as acute lymphoblastic leukemias (ALL) and 18 as acute undifferentiated leukemias (ANLM). In 6 (3.4%) of 169 AL patients, blasts expressed both myeloid and lymphoid antigens. In the group of 102 AL patients there were 19 (18.6%) ALMy+Ly. In 64 patients cytomorphologically classified into AML subgroup out of 102 AL patients, there were 15 (14.7%/102; 23.4%/64) AML with lymphoid antigens (AMLLy+). In 35 patients cytomorphologically diagnosed as ALL and 3 as ANLM out of 102 AL, there were 4 (3.9%/102; 10.5%/38) ALL with myeloid antigens (ALLMy+). The incidence of mixed AL in 102 AL was more consistent with other studies, pointing to the necessity of myeloperoxidase (MPO), CD7 and TdT determination as part of standard immunophenotyping for better recognition of mixed AL.

CONCLUSION

In both groups of 169 and 102 AL patients, the majority of AL cases were cytomorphologically classified as AML. In the group of 169 patients there were 5 AMLLy+ and in the group of 102 patients there were 15 AMLLy+. In one ANLM,My+ out of 169 AL and also one ANLM,My+ out of 102 AL, blasts were cytomorphologically undifferentiated; in 3 ALLMy+ of 102 AL blasts expressed lymphoid morphology. According to EGIL scoring system, among 15 AMLLy+ of 102 AL there were 4 true biphenotypic ALMy+Ly (1 M1, 2 M3, 1 M4), and in 4 ALMy+Ly with undifferentiated and lymphoid morphology there were 2 true biphenotypic AL (1 L2; 1 ANLM). In 3 ALLB+T out of 35 ALL, one was interlineal biphenotypic AL. These observations are consistent with other studies and WHO determinations indicating that the majority of true biphenotypic leukemias are associated with immature monoblastic or myeloid cytomorphology or with lymphoid or undifferentiated characteristics, but may also express any AML cytomorphology type. Thus, there is no direct correlation of leukemic cell cytomorphology and biphenotypic AL immunophenotype.

[Clinical characteristics and immunophenotypes of mixed-lineage acute leukemia]

The aim of study was to analyze the clinical, biological features, treatment outcome and prognosis of mixed-lineage acute leukemia (MAL). 48 MAL patients diagnosed according to European Group of International Leukemia (EGIL) scoring system were retrospectively analyzed and the analysis results were compared with that from 68 cases of AML and 61 cases of ALL. The results showed that the incidence of MAL in acute leukemia was 9.6%. Morphologically, the subtypes of M(1) and M(2) were predominant in AML, while L(2) in ALL. The median of white blood cell count in MAL was significantly higher than that of non-mixed-lineage cases (AML and ALL) observed during the same period (P < 0.05). The incidences of enlargement of liver, spleen and lymphonodes in MAL were higher than those in AML. The difference was significant (P < 0.01) and was not significant compared with those in ALL (P > 0.05). Coexpression of myeloid and B lymphoid antigens in MAL patients was predominant, its rate was 70.9%. The coexpression rate of T lymphoid and myeloid antigens was 20.8%, coexpression of B, T lymphoid and myeloid antigens was 8.3%. CD34 was expressed in 79.2% of MAL cases, it was higher than those expressed in AML (54.4%) and ALL (52.5%) (P < 0.01), which suggests that MAL might originate from malignant transformation of hematopoietic stem cells. Cytogenetic analysis revealed normal and abnormal karyotypes in 32.1% and 67.9% of MAL cases respectively. In MAL Ph chromosome abnormality incidence was 25% and was significantly higher than that in AML group (0%) (P < 0.01), but was not statistical defference with that in ALL group (16.7%) (P > 0.05). The completed remission rate of MAL was 38.1%, lower than CR rate in AML (70.8%) and ALL (72.2%) respectively (P < 0.01). Treatment outcomes were negatively related to the expression of CD34 antigen and Ph chromosome. It is concluded that MAL is supposed to be originated from stem cells, coexpression of lymphoid/myeloid antigens is the major feature of MAL which accompanies many poor prognosis factors and lower CR rate. Appropriate chemotherapeutic strategy should be further searched.

Acute lymphoblastic leukemia with the phenotype of a putative B-cell/T-cell bipotential precursor

Biphenotypic acute leukemias (BALs) are uncommon. Most are of myeloid-B-cell or myeloid-T-cell lineage. We report herein a 70-year-old man with an unusual acute leukemia where the blasts expressed both B- and T-lymphoid markers. He presented to us with an enlarging cutaneous tumor. The presenting peripheral blood and bone marrow aspirate showed 40% and 90% blasts, respectively, which were negative for the usual cytochemical stains. The flow cytometric analysis revealed that the blasts were positive for CD19, CD20, CD22, cytoplasmic (Cyt) CD79a, CD10, Cyt CD3, CD5, CD7, CD4, HLA-DR, TdT, and were negative for myeloid markers. According to the scoring system from the European Group for the Immunological Characterization of Acute Leukaemias (EGIL), this case was an unequivocal B-cell/T-cell BAL. Conventional cytogenetic analysis revealed 46XY [t(4;11)(q31;q13), add(8)(q24), der(9)del(9)(p21)del(9)(q32q34), -13, +mar] in all 25 metaphases analyzed. Fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) for 11q23 rearrangements as well as t(9;22) were negative. PCR for both TCR-gamma and IgH gene analyses revealed polyclonal rearrangements. We postulate that this case of BAL might have arisen from the putative common lymphoid progenitor cell.

Successful treatment of bcr/abl-positive acute mixed lineage leukemia by unmanipulated bone marrow transplantation from an HLA-haploidentical (3-antigen-mismatched) cousin

We describe a patient with bcr/abl-positive acute mixed lineage leukemia who successfully underwent transplantation in primary induction failure, using unmanipulated bone marrow from a human leukocyte antigen (HLA)-haploidentical cousin. The tumor burden was successfully reduced by the administration of imatinib mesylate (STI571) before transplantation. As graft-versus-host disease (GVHD) prophylaxis, a combination of tacrolimus and a short course of methotrexate, methylprednisolone, and mycophenolate mofetil was used. Hematopoietic reconstitution was rapid, and acute GVHD was limited to the skin (grade I). The patient is still in complete remission past day +400. This successful case suggests that HLA-haploidentical transplantation using unmanipulated marrow from a distantly related relative can be considered for patients in urgent situations who do not have HLA-identical donors.

Facilitation of functional compartmentalization of bone marrow cells in leukemic mice by biological response modifiers: an immunotherapeutic approach

Biological Response Modifiers (BRMs) including interleukin-2 (IL-2), interferon-gamma (IFN-gamma) and sheep erythrocytes (SRBC) protected N,N'-ethylnitrosourea (ENU) induced leukaemic mice. Two cell types from the bone marrow were isolated in density specific gradient representing two distinct compartments, the low density cells being more CD34 positive than the high density group. Investigations with the functional efficacy of such compartments revealed significant improvement of cytotoxic efficacy and phagocytic burst at the high density compartment (HDC) level. The high density compartment was found to be more responsive towards the BRMs compared to the cells of the low density compartment (LDC). It was suggested that use of BRMs in vivo can stimulate a potent functional progenitor compartmentalization in normal as well as leukaemic mice. These observations are expected to help a logistic approach towards combined BRM therapy at the clinical level.

[Concurrence of cytochemical and immune patterns of different cell lines in cases of acute leukemia]

Mixed, bilineal, biclonal and hybrid leukemias are synonymous, differing from biphenotypical ones. Mixed acute leukemia is defined by the coincidence of 1) two cytochemical markers of different lineage, or 2) one of them with more than one opposite immunological marker, or 3) more than one immunological marker opposite to another immunological lineage. Seven cases of mixed acute leukemia are presented, two of which showed posttreatment switching. It is concluded that mixed acute leukemias are associated with a poor prognosis, and therapeutic criteria are defined.

Correlation of morphological FAB classification and immunophenotyping: value in recognition of morphological, cytochemical and immunological characteristics of mixed leukaemias

Correlation between the FAB classification and immunophenotype was studied in 169 consecutive adult patients with acute leukaemia (AL). The lineage of leukaemic cells could be determined in the majority of cases, whereas 3 patients (1.8%) remained unclassified. In 22 out of 71 patients (31%) with acute myeloid leukaemia (AML) FAB M1 and M2 types, and in 5 out of 16 patients (31%) with chronic myeloid leukaemia (CML) in myeloid blast crisis, leukaemic cells did not express myeloid lineage-related markers, indicating asynchronous expression of cell markers in a substantial proportion of patients. Flow cytometric two-colour immunofluorescence revealed mixed AL immunophenotype in 6 out of 169 patients (3.4%). This group included five CD2+AML (5% of AML tested) and one undifferentiated AL expressing CD10(CALLA), CDw65(VIM-2). The former group included FAB M1, M2, M3 and M4 forms of AML with a single cell population, and an AML M2 patient with both cytochemically and immunologically two separate populations of leukaemic cells. This further illustrates the heterogeneity of the target cell(s) for leukaemogenesis and the level of differentiation of AML cells. However, there was no difference in the treatment response and the remission duration between AML patients and patients with mixed phenotype AML.

[Mixed myelocytic and lymphocytic acute leukemia. Case report]

A patient with acute mixed myelocytic and lymphocytic leukemia is reported. The patient showed two populations of malignant myeloid and lymphoid cells with predominance of myeloid lineage. According to the present knowledge, it is hypothesized that its origin is at a pluripotent transformed stem cell which has the capability of differentiating through myeloid and lymphoid lineages. Its maturation is arrested at certain level, thus raising two monoclonal populations simultaneously in the same patient. The treatment should be combined with drugs used in acute myeloblastic and lymphoblastic leukemia. The response to chemotherapy is generally poor.

[Biphenotypic acute leukemia. Clinical, morphological, cytochemical and immunophenotypic studies]

The blast cells from 2 cases of acute leukemic patients classified as M1 type by FAB criterion simultaneously expressed lymphoid markers such as SmIgG, CD19, CD20, DR, PAS in case 1 and CD9, CD10, DR, PAS in case 2. The blast cells of these two cases also expressed CD38 antigen. The data on phenotype and cytochemistry in these two cases fulfil the criteria of biphenotypic acute leukemia proposed by Dr. Gale. The problems in diagnosis, treatment and prognosis of this kind of mixed acute leukemia were discussed.

Characterization of childhood acute leukemia with multiple myeloid and lymphoid markers at diagnosis and at relapse

To define the clinical and biologic significance of childhood acute mixed-lineage leukemia diagnosed by stringent criteria, we studied 25 cases of acute lymphoblastic leukemia expressing greater than or equal to 2 myeloid-associated antigens (My+ ALL), and 16 cases of acute myeloid leukemia expressing greater than or equal to 2 lymphoid associated antigens (Ly+ AML). These cases represented 6.1% of 410 newly diagnosed ALLs (two treatment protocols) and 16.8% of 95 AMLs (two protocols). T-lineage--associated antigens were identified in 9 of the My+ ALL cases and in 14 of those classified as Ly+ AML; all but 1 of the 19 cases that could be subclassified had an early thymocyte stage of differentiation. The My+ ALL cases had an increased frequency of French-American-British (FAB) L2 morphology (36%); the Ly+ AML cases were characterized by FAB M1 or M2 morphology, low levels of myeloperoxidase reactivity and combined populations of myeloperoxidase-positive large blasts and small blasts generally of hand-mirror morphology. Karyotypic abnormalities included t(9;22)(q34;q11) in three cases of My+ ALL, 11q23 translocations in two cases of My+ ALL, and 14q32 translocations in three My+ ALL and five Ly+ AML cases. Mixed-lineage expression lacked prognostic significance in either ALL or AML; however, the findings indicate that some patients with Ly+ AML may respond to prednisone, vincristine, and L-asparaginase after failing on protocols for myeloid leukemia. At relapse, two My+ ALLs had converted to AML and two Ly+ AMLs to ALL; one case in each group showed complete replacement of the original karyotype. Acute mixed-lineage leukemia does not adequately describe the heterogeneity of the cases identified in this study and should be replaced by a set of more restrictive terms that indicate the unique biologic features of these leukemias.

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.

Reconstitution of an active surface CD2 by DNA transfer in CD2-CD3+ Jurkat cells facilitates CD3-T cell receptor-mediated IL-2 production

To investigate the requirements for CD2 expression in the activation of T lymphocytes via the CD3-TCR complex, we produced and characterized a series of CD2-variants of the IL-2 producing Jurkat leukemia cell line, J32 (surface phenotype, CD2+, CD3+, CD28+). These mutants were derived by radiation and immunoselection, and were cloned under limiting dilution conditions. A total of 3 out of 30 of these mutants selectively lost the expression of both CD2 surface molecules and CD2 mRNA, and retained the expression of the CD3-TCR complex and the CD28 molecule. A mitogenic combination of anti-CD2 antibodies (9.6 + 9-1) failed to stimulate activation of these variants as measured by mobilization of intracellular Ca2+ and by IL-2 production. The CD2- mutants stimulated with anti-CD3 or anti-TCR mAb revealed an 8- to 32-fold decrease in IL-2 production and IL-2 mRNA accumulation as compared with the parental cells. No alteration of CD3-TCR-induced mobilization of intracellular Ca2+ was observed in the CD2- mutants. Reconstitution of CD2 expression by gene transfer in two J32 CD2- mutants restored IL-2 production and IL-2 mRNA accumulation in responses to both anti-CD2 and anti-CD3-TCR mAb. These results are the first direct demonstration of the requirement for CD2 molecules in optimizing IL-2 response in human T cells stimulated via CD3-TCR complex.

Mixed-lineage leukemia and asynchronous antigen expression

Considerable confusion exists regarding the definition of acute mixed-lineage leukemia. We have proposed a list of strict criteria, limiting the term acute mixed-lineage leukemia to those patients whose blast cells co-express lymphoid and myeloid characteristics. This system includes cytochemical, immunologic, molecular, and cytogenetic characteristics that are strongly associated with either lymphoid or myeloid lineages. As more information becomes available, the criteria for mixed-lineage leukemia will undoubtedly change. Identification of patients with mixed-lineage leukemia and metachronous leukemia (lineage switch) is important for determining the prognostic implications of these findings. Care must be taken in identifying cases of metachronous leukemia because of the increased incidence of second malignancies following aggressive therapy. Evidence of a recurrence of the original clone must be obtained before metachronous leukemia can be diagnosed. As with mixed-lineage and metachronous leukemias, the potential clinical and prognostic implications of lymphoid leukemias with antigenic asynchrony should be identified. The asynchronous antigen expression in leukemic lymphoblasts may provide a means for detecting minimal residual disease. Detection of minimal residual leukemia is possible because these blasts differ from the predominant population of normal lymphoid cells in their expression of cell surface markers. Study of the mechanisms that lead to these unusual leukemias may result in better understanding of the processes that underlie both normal hematopoietic differentiation and leukemogenesis. An understanding of these leukemias may also permit identification of cases that are destined to fail current therapies so that more intensive or selective therapy can be instituted for such children. Curing the 30% of children with ALL that relapse despite our best efforts should be one of the top priorities for pediatric oncologists.

Karyotypic patterns in acute mixed lineage leukemia

We performed cytogenetic and immunologic studies of blast cells from 13 children with acute mixed lineage leukemia (AMLL) to discern patterns of chromosome alteration and antigen expression that would assist in classification of this disease entity. Six patients with 11q23 translocations--including four with the t(11;19), one with the t(9;11), and one with the t(1;11)--were characterized by a young age and hyperleukocytosis. A B cell-associated antigen (CD19) and HLA-DR antigens were expressed by blast cells from all patients; only one case was positive for the common acute lymphocytic leukemia antigen (CALLA, CD10). A myeloid-associated antigen (CD13) was expressed by blast cells from one patient at diagnosis and from another at relapse; it was also expressed by cells from the remaining four patients after brief in vitro culture without addition of differentiating agents. Four patients with t(9;22)(q34;q11) were characterized by an older age and hyperleukocytosis. Each of these cases was positive for CD13, CD19, and HLA-DR, and three were positive for CALLA. The 11q23 translocation was associated with CALLA- ALL marked by a myeloid phenotype, whereas the t(9;22) occurred in cases of acute myeloid leukemia with a CALLA+ lymphoid phenotype. One case had a 7q35-q36 translocation, which involves the region of the T cell receptor beta-chain gene. Our results suggest that karyotypic alterations can be used to refine the classification of AMLL.

Hybrid acute leukemia in an HIV-antibody-positive patient

Although the great majority of acute leukemias have been designated as being of lymphocytic or myelocytic origin, recent reports have described elements of both in some patients. We describe here the first case of hybrid acute leukemia in an HIV-antibody-positive patient as well as the first hybrid involving B-cell (Burkitt) acute lymphocytic leukemia and acute myelomonocytic leukemia proven by cytochemical, immunologic, and cytogenetic methods. This case illustrates the increasingly complex difficulties in the diagnosis and treatment of AIDS-related malignancies.