Germ-line configuration of the immunoglobulin heavy chain gene in a case of B cell precursor acute lymphoblastic leukemia

A 20-year-old man was admitted to our hospital because of fever and knee joint pain on March 20, 1986. Physical examination revealed generalized lymphadenopathy and hepatomegaly. White blood cell count was 32,800 microliters with 74.4% blast cells. Bone marrow was hypercellular with 93.6% blast cells. Blast cells were weakly positive for acid phosphatase and PAS stainings but were negative for peroxidase, sudan black B and esterase stainings. Cell surface marker analysis of blast cells disclosed that they were positive for anti-HLA-DR, CD19, CD24, CD33 and CD38, but were negative for CD10 and CD20. Cytoplasmic immunoglobulin of blast cells was negative and TdT activity by immunofluorescent method was positive. Chromosomal analysis of bone marrow samples revealed normal karyotype. Therefore, this case was diagnosed as having acute lymphoblastic leukemia (L2) and achieved complete remission with LVP therapy consisting of 1-asparaginase, vincristine and prednisolone. Gene analysis of blast cells disclosed germ-line configuration of both the immunoglobulin heavy chain gene and T cell receptor beta chain gene. We speculated that the phenotype of leukemic cells might precede the genotype in some cases of acute leukemia.     

Philadelphia-positive acute mixed leukemia with monosomy 7

A 26-year-old male was admitted to our hospital because of fever and leukocytosis. On admission, a white blood cell count was 28,300/microliters with 46.5% blast cells and 16.0% atypical monocytoid cells, a hemoglobin level 13.7 g/dl, and a platelet count 15.0 X 10(4)/microliters. Bone marrow contained 58.8% of peroxidase-negative blast cells. He was diagnosed as acute lymphoblastic leukemia (ALL L2) according to the FAB classification. Chromosome analysis revealed the marrow cells to contain 45, XY, -7, t(9; 22) (q34; q11). On surface marker analysis, the leukemic cells were positive for both lymphoid (CD10) and myeloid markers (CD13). Two color flow-cytometric analysis showed two distinct populations with CD10 and CD1 3, respectively. Rearrangements of both immunoglobulin heavy chain and T cell receptor beta-chain were observed. The "breakpoint cluster region" on chromosome 22 was not rearranged. On the basis of these findings, we thought this case being acute mixed leukemia. He was refractory to AdVP therapy and BHAC-DMP therapy. He is now under treatment with A-Triple-V therapy.     

Interleukin-1 alpha also induces granulocyte-macrophage colony-stimulating factor in immature normal bone marrow cells.

The cytokine interleukin-1 (IL-1) plays a role in the regulation of normal as well as leukemic hematopoiesis. In acute myeloid leukemia (AML), IL-1 induces autocrine granulocyte/macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor (TNF) production, and these factors may then synergistically induce proliferation in AML blast cells. In this report, we show that IL-1 stimulates DNA synthesis of highly enriched normal bone marrow blast cells (CD34 positive, adherent cell depleted, CD3/CD14/CD15 negative). The stimulative effect of IL-1 can be blocked with neutralizing anti-TNF alpha and anti-GM-CSF antibodies and, most efficiently, by the combination of anti-TNF alpha and anti-GM-CSF, but not with anti-G-CSF antibody, suggesting that IL-1-induced proliferation was initiated through TNF and GM-CSF release. Concentrations of TNF and GM-CSF increased in the culture medium of normal bone marrow blast cells after IL-1 induction. Of the IL-1-induced cells, 12% were positive for GM-CSF mRNA by in situ hybridization, as opposed to 6% of non-induced cells. Thus, in addition to its effect on leukemic blast cells, IL-1 also acts on normal marrow blast cells. We propose a scheme where IL-1 stimulation of normal bone marrow blast cells leads to the induction of TNF alpha and GM-CSF, which in association stimulate DNA synthesis efficiently according to a paracrine or autocrine mechanism within the marrow blast cell compartment.     

Induction of Complete Remission of Hypoplastic Leukemia with Antithymocyte Globulin

A 13-year-old boy was admitted to a local hospital because of pancytopenia. A bone marrow aspiration and biopsy revealed severely hypocellular marrow with no obvious leukemic cells. The diagnosis was severe aplastic anemia, and the patient was treated with antithymocyte globulin and cyclosporin A. A trilineage response was obtained, and the patient became transfusion-independent within 2 weeks. Two months later, the peripheral blood count normalized with an increased bone marrow cellularity. However, the patient was readmitted 5 months later for recurrence of the pancytopenia. A bone marrow aspiration revealed hypocellular marrow with morphologically blastoid cells. A surface marker study revealed the presence of a single clone that was positive for CD7, CD33, CD34, and HLA-DR. A diagnosis of hypoplastic leukemia was made on the basis of morphology and the surface marker studies. Retrospectively, the laboratory findings were the same as those seen at the onset of the disease. The patient did not respond to combination chemotherapy consisting of vincristine, prednisolone, cyclophosphamide, L-asparaginase, and doxorubicin, but administration of etoposide resulted in complete remission. An in vitro study revealed that >95% of the leukemic cells of this patient could be lysed after an incubation with antithymocyte globulin and human AB serum or baby rabbit serum. These findings suggest the efficacy of antithymocyte globulin in treating certain hypoplastic leukemias.     

Human malignancy-associated nucleolar antigen as a marker for tumor cells in patients with acute leukemia

Tumor burden in adult patients with acute leukemia is assessed using the percentage of blast cells in the bone marrow or blood. It is clear, however, that not all blast cells are leukemic cells, especially during rapid marrow regeneration. Similarly, some leukemia cell lines have been shown to differentiate in vitro, and the same process also occurs in vivo. Therefore, the leukemic burden may be due to more differentiated cells as well as to blast cells. The purpose of this study was to investigate whether the human malignancy-associated nucleolar antigen (HMNA) could be used as a marker for leukemic cells and to examine its potential as a diagnostic tool. The proportion of HMNA-positive cells in the bone marrow of patients with acute leukemia was determined by indirect immunofluorescence with antibodies to HMNA and was compared with the differential counts routinely made in the clinic laboratory. The percentages of HMNA-positive cells among the nucleated cells in the marrow of 72 patients with clinical evidence of leukemia were significantly higher (range 9%-98%, median 83%) than those observed for nonleukemic individuals (range less than 0.05%-2.5%, median 1%) or for fractions of marrow cells from normal volunteers enriched for normal early progenitor cells (less than or equal to 2%). Patients with leukemia in remission had a lower percentage of HMNA- positive cells (range 0%-83%, median 3%). The percentage of HMNA- positive cells increased as patients approached relapse. Although the percentage of HMNA-positive cells was related to the percentage of blast cells in the bone marrow of the patients with leukemia, some partially differentiated cells were also HMNA-positive in some specimens, and some blastic cells were HMNA-negative in other specimens. These studies indicate the potential usefulness of HMNA as a marker for leukemic cells.     

Unusual karyotypic changes and B cell involvement in a case of lymph node blast crisis of chronic myelogenous leukemia

A patient with Philadelphia chromosome (Ph1) positive chronic myelogenous leukemia (CML) entered a blast crisis localized to lymph nodes. On light microscopy, by morphology and histochemical staining, the blasts were undifferentiated. In spite of terminal deoxynucleotidyl transferase positivity, some of the lymph node cells expressed a myeloid differentiation antigen, OKM1, and were peroxidase positive by transmission electron microscopy (TEM). However, the majority of cells were peroxidase negative on TEM and expressed OKT-10, a marker found on both primitive myeloid and lymphoid cells. Cultures of lymph node cells stimulated with Epstein-Barr virus or lipopolysaccharide (LPS) revealed the Ph1, indicating B cell involvement in the CML. T cells from cultures stimulated with L4-phytohemagglutinin and T cell growth factor were negative for the Ph1. In unstimulated lymph node cells, the uncomplicated Ph1 could not be demonstrated; instead, a unique complex karyotype involving a masked Ph1 was identified in these and the LPS cultures. This karyotype was not found in bone marrow (BM) metaphase cells. Instead, BM cells showed either the simple Ph1 or the Ph1 with a rearrangement involving chromosomes 13 and 20. The patient had transient responses to three chemotherapy regimens, two of which were designed to treat acute lymphocytic leukemia, but he died 8 months after disease acceleration without BM blast crisis. These findings are compatible with an extramedullary blast crisis originating in a primitive cell with both myeloid and lymphoid characteristics.     

Lineage switch on recurrence from minimally differentiated acute leukemia (M0) to acute megakaryocytic leukemia (M7)

Phenotypic switch in acute leukemia is a rare phenomenon. We report on a female infant with minimally differentiated acute leukemia (M 0) which underwent a lineage switch on relapse. In March 1997, a 1-year-8-month old girl was admitted to our hospital with a high-grade fever and generalized purpura. Bone marrow showed 84% blasts. The blasts were negative for peroxidase, periodic acid-Schiff and alpha-naphthyl butyrate esterase. Immunophenotypic analyses of the blast cells were positive for CD 13, CD 33 antigens, as well as CD 34. Lymphoid markers all were negative. Though some blasts morphologically demonstrated cytoplasmic blebs, CD 41 was negative and ultrastructural platelet peroxidase was absent. Based on these hematological features, the patient was diagnosed as having AML-M 0. She was treated according to the Children's Cancer and Leukemia Study Group schedule and a complete remission was achieved 1.5 months after starting induction therapy. However, she relapsed in spite of continued chemotherapy in July 1997, when the cytomorphological pattern changed and the patient was diagnosed both morphologically and immunologically as having M 7. Electron microscopy revealed platelet peroxidase (+) and CD 41 (+). Cytogenetic studies on relapse demonstrated inv(3) (q 21 p 25). We attempted aggressive reinduction therapy, but without effect. The patient simultaneously developed severe pneumonia and died in February, 1998. A lineage switch on relapse and resistance to chemotherapy may be associated with the occurrence of genetic aberration.     

Successful treatment with cladribine for hypoplastic hairy cell leukemia after long-term neutropenia

A 34-year-old woman was admitted to the hospital because of swelling of her right knee, and the result of the laboratory tests indicated anemia and leukocytopenia. A bone marrow examination showed dissemination of small to medium-sized abnormal lymphocytes with abundant and pale blue cytoplasm and a circumferential "hairy" projection in the hypocellular bone marrow. These cells were positive for tartrate-resistant acid phosphatase (TRAP) and for CD 19, CD 20, CD 25, CD 103 and SmIg kappa. The patient was diagnosed as having hypoplastic hairy cell leukemia and received cladribine (2-CdA) for seven days via continuous intravenous injection. The minimum white blood cell count was 300/microl at seven days after starting the therapy (day 7) and the neutrophil count recovered to more than 1500/microl on day 118. The patient achieved complete remission on day 140 without any episodes of severe infection and has remained in complete remission for more than one year. The treatment of hypocellular HCL with 2-CdA might be useful.     

Minimally differentiated acute nonlymphocytic leukemia: a distinct entity

Ten of 136 consecutive adult patients with previously untreated acute leukemia had morphologically undifferentiated leukemia by light microscopy. Leukemic cells from these patients were characterized by agranular cytoplasm, negative histochemical staining with sudan black (SB) and nonspecific esterase, and absent lymphoid cell surface markers and therefore were not classifiable according to the French-American-British (FAB) system. Electron microscopy with myeloperoxidase (MPO) staining revealed the presence of peroxidase positive cytoplasmic granules and endoplasmic reticulum in eight of the nine patients studied. Cells from the patient who was negative for MPO were also negative for platelet peroxidase. A series of monoclonal antibodies to myeloid antigens also revealed myeloid features with all patients having at least one myeloid differentiation antigen present on the surface of their cells. Common acute lymphoblastic leukemia (ALL) antigen was absent in the nine patients tested. Cytogenetic analysis of blast cells was abnormal in seven patients on whom adequately banded chromosomes were obtained although there were no consistent abnormalities. No patient had a Ph1 chromosome. Only two of the ten patients achieved a complete remission. Morphologically undifferentiated leukemia may have myeloid features when studied by transmission electron microscopy or with monoclonal antibodies for cell surface markers. Such studies should be performed when the leukemia cannot be classified using either light microscopy or lymphoid cell surface markers. Such patients infrequently achieve remission with standard therapy and constitute a distinct entity.     

Basophilic differentiation of leukemic cells in a patient with acute leukemia carrying minor bcr/abl chimeric mRNA

A 77-year-old woman was referred to our hospital because of leukocytosis and leukoblastosis in September 1999. She was healthy except for hypertension, and no abnormal findings in the peripheral blood had been observed up to December 1998. Physical examination revealed neither hepatosplenomegaly nor superficial lymphadenopathy. A bone marrow film showed massive proliferation of blast cells (87.8%), some of which contained coarse basophilic granules (38.6%). The cells were negative for peroxidase and esterase (alpha-naphtyl butyrate and ASD-chloroacetate) staining, but the granules showed metachromasia upon toluidine blue staining. As immunophenotypic analysis of the cells showed double positive for CD13/CD19 but negativity for CD33, this case did not meet the diagnostic criteria for biphenotypic acute leukemia. Chromosome and gene analysis showed positivity for the Ph1 chromosome with minor bcr/abl chimeric mRNA. A homogenate of the peripheral mononuclear cells demonstrated a high concentration of histamine. Electron microscopy analysis confirmed that some of the blast cells contained dense granules, which closely resembled "immature basophil granules" morphologically. These results suggested that the blast cells showed basophilic differentiation. As the clinical course and peripheral blood findings were different from blastic crisis of chronic myelogenous leukemia (CML) and CML with minor bcr/abl chimeric mRNA, the present case was diagnosed as "multiphenotypic acute leukemia", a type of acute basophilic leukemia classified by Duchayne.     

Discordant patterns of chromosome changes and myeloblast proliferation during the terminal phase of chronic myeloid leukemia.

A patient with Ph1 positive chronic myeloid leukemia (CML) developed blastic transformation which by morphologic criteria appeared to be localized to the lymphatic system. Chromosome analysis at this time, however, revealed new chromosomal abnormalities in addition to the existing Ph1 in all tissues studied (lymph node, blood, and bone marrow) consisting primarily of extra chromosome numbers 19 and 9 and a second Ph1. Therapy resulted in clinical remission with significant decrease in the aneuploid cell lines. However, these reappeared with recurrence of the blast crisis. Colony formation in semisolid culture of blood and marrow cells at the time of initial blast crisis yielded growth patterns characteristic of CML. On recurrence of the blast crisis after therapy, growth patterns were characteristic of CML in blast crisis or acute myeloblastic leukemia even though blood and marrow still showed relatively low levels of myeloblasts and promyelocytes. Possible explanations are discussed for the disparity in distribution between morphologic and chromosomal abnormalities in this patient.     

Expression of a myeloid marker on TdT-positive acute lymphocytic leukemic cells: evidence by double-fluorescence staining

The expression of a myeloid-specific antigen was detected on TdT- positive blast cell populations in two cases of childhood acute lymphocytic leukemia. Double-fluorescence staining by using the monoclonal antibody, VIM-D5, which is specific for cells of myeloid origin, in combination with TdT antiserum revealed that a distinct portion of the blast cells carried both markers. The finding represents the first direct demonstration of this specific biphenotype in leukemic cells and was interpreted as the abnormal expression of a myeloid antigen on lymphoid blast cells.     

Hypocellular bone marrow with increased blasts

Twenty patients with hypocellular bone marrow and increased blasts (HBMIB) were reviewed. The median age was 60 years with a male:female ratio of 17:3. History of alcohol abuse was noted in 30%, potential exposure to toxic chemicals in 20%, second malignancies in 20%, and aplastic anemia in 25%. Pancytopenia with marrow hypocellularity and increased marrow blast cells were characteristic hematopathologic features. Marrow hypocellularity was moderate to severe (less than or equal to 25%) in over half of the cases and mild to moderate (greater than 25, less than or equal to 35%) in the remainder. Blast cells were the predominant cellular elements in the marrow displaying scanty to moderate amounts of cytoplasm, round to oval nuclei, and one or more nucleoli. Special stains were performed in 19 cases. Blast cells morphologically displayed myeloid features, but Sudan black B and/or peroxidase positivity was noted in only ten patients. The overall mortality was high, especially in patients undergoing chemotherapy. At 1 year follow-up, 11 patients had received chemotherapy and eight of these eleven were dead compared to three of nine patients dead in those not receiving chemotherapy. Only two patients developed "overt" leukemia evidenced by hypercellular marrow and over 30% blast cells in the peripheral blood. HBMIB is a distinct clinicopathologic entity characterized by severe marrow failure and a low response rate to chemotherapy.     

Fas ligand is highly expressed in acute leukemia and during the transformation of chronic myeloid leukemia to blast crisis.

Fas ligand (FasL) induces apoptosis in susceptible Fas-bearing cells and is critically involved in regulating T-cell immune responses. It is highly expressed in several human malignancies, and a role in the suppression of antitumor immune responses has been suggested. We evaluated FasL expression in leukemia and normal hematopoietic cells. By Western blotting, all acute leukemic cell lines (n = 9) and primary samples of acute leukemic marrow (n = 4) revealed high levels of FasL. In contrast, much weaker signals were observed in samples of normal marrow (n = 5), and either weak or intermediate expression was seen in chronic myeloid leukemia (CML) in chronic phase (n = 7). Additional leukemic samples were examined by immunohistochemistry. Staining for FasL was negative in 7 of 9 cases of chronic-phase CML, whereas all cases of CML in blast crisis (n = 6), acute lymphoblastic leukemia (n = 6), and acute myeloid leukemia (n = 11) stained strongly in 60 to 100% of nucleated cells. FasL+ leukemic cell lines did not trigger Fas-mediated apoptosis in either Jurkat cells or activated human T lymphocytes, possibly related to the intracellular location of the ligand. Western analysis of normal marrow subpopulations revealed that most FasL in marrow mononuclear cells was expressed by CD7+ lymphocytes. FasL also was strongly expressed in CD34+ hematopoietic progenitor cells from both normal and chronic-phase CML marrow, suggesting a correlation with primitive maturation stage. In summary, high levels of FasL expression were associated with aggressive biologic behavior in leukemia, including transformation of CML to blast crisis. This could potentially represent a response to loss of proapoptotic Fas signaling, which is known to occur in acute leukemic blasts.     

Extramedullary diseases as presenting features of aleukemic acute monocytic leukemia]

We present a case of acute monocytic leukemia presenting with extramedullary disease clinically resembling lymphoma. A 36 year-old man presented with arthralgia and was found to have skin eruption, nasopharyngeal mass, hepatosplenomegaly and superficial lymphadenopathy. The biopsies of those lesions as well as bone marrow revealed infiltration of CD45 positive large atypical cells and were interpreted as malignant lymphoma. At that time blood film showed leuko-erythroblastic picture, but no atypical cells were noted. He was treated with CHOP followed by VEPA chemotherapy and achieved partial remission. Four months later headache and double vision occurred with the same atypical cell in the cerebrospinal fluid. The cells were identified as monoblasts by cytochemistry and immunophenotype. The diagnosis of aleukemic acute monocytic leukemia was made and its CNS involvement was successfully treated with chemotherapy with DHAP and intrathecal MTX. However, two months later, blasts finally appeared in the peripheral blood and the patient died of multiorgan failure eight months after presentation. The blasts were positive for T cell markers (CD2, 4, 8) and NK marker (NKH-1) as well as monocytic markers. This finding, together with those by other investigators, may indicate the association between these immunophenotypes and extramedullary manifestations of acute monocytic leukemia.     

Decreased natural killer cell activity versus normal natural killer cell markers in mononuclear cells from patients with smouldering leukemia

Peripheral blood (PB) and bone marrow mononuclear cells from 23 patients with smouldering leukemia were analyzed for natural killer (NK) cell activity and various surface cell markers. Significantly reduced NK activity was detected in the patients' PB compared with the activity in the healthy controls (p less than 0.0005). A similar difference in NK cell activity between the 2 groups was also observed in bone marrow mononuclear cells (p = 0.005). In contrast, no significant differences in cells positive for the NK cell markers Leu-7 and Leu-11b were found between patients and controls, either in PB or in bone marrow. The patients' PB and bone marrow mononuclear cells had, however, a reduced percentage and absolute number of Leu 3a+ and T8+ cells. Patients with smouldering leukemia have immunological derangements which may make them predisposed for the later development of florid leukemia.     

Early T-cell features in blast crisis of Ph1-positive chronic myeloid leukaemia

A patient with Ph1-positive chronic myeloid leukaemia (CML) presented in extramedullary blast crisis. Whereas the peripheral blood and bone marrow features were consistent with the chronic phase of CML, study of the enlarged lymph nodes demonstrated massive replacement by Ph1-positive blast cells of lymphoblastic morphology. Such blast cells showed diffuse acid phosphatase positivity, were positive for TdT, and had an enzyme pattern (adenosin-deaminase, purine-nucleosidephosphorilase and lactate-dehydrogenase) typical of immature T-cells. To further characterize the phenotype of the blast cells, they were analyzed for surface markers using a panel of monoclonal antibodies selected to identify differentiation antigens of T cells, B cells and myeloid cells. The results of the latter analysis were consistent with an early T-cell origin of the blast cells, since they were positive for TdT, CRIS1 (T1), E rosettes and OKT10, and were negative for OKT3, Leu3 and OKT8. These features demonstrate that T-cell markers may also be expressed in blast crisis of CML and provide evidence that T-cells may share a common stem cell with myeloid and B-cells in CML.     

Establishment of a novel human megakaryoblastic leukemia cell line, MEG- 01, with positive Philadelphia chromosome

A megakaryoblastic cell line, designated MEG-01, was established from the bone marrow of a patient with blast crisis of Philadelphia (Ph1) chromosome-positive chronic myelogenous leukemia. MEG-01 cells grew in single-cell suspension with a doubling time of 36 to 48 hours. Under the usual culture conditions, approximately half of the cells adhered to the culture flask with extention of pseudopods. MEG-01 cells were positive for the periodic acid-Schiff reaction, alpha-naphthyl acetate esterase, and acid phosphatase, and negative for myeloperoxidase, alpha- naphthyl butyrate esterase, naphthol AS-D chloroacetate esterase, and alkaline phosphatase. Ultrastructural platelet peroxidase was positive in MEG-01 cells. Cytoplasmic factor VIII (FVIII)-related antigen was weakly positive in larger MEG-01 cells by both an indirect immunofluorescent technique with monoclonal antibodies and a direct immunoperoxidase technique using horseradish peroxidase-conjugated conventional rabbit anti-human FVIII antibody. Platelet glycoprotein (GP) IIb/IIIa antigen was uniformly demonstrated on the surface of MEG- 01 cells by both indirect immunofluorescent and immunoperoxidase techniques using antiplatelet GP IIb/IIIa monoclonal antibodies; platelet GP lb antigen was demonstrated only in the cytoplasm of larger MEG-01 cells. MEG-01 cells possessed no markers for B or T lymphocytes or for myeloid cells. Chromosome analysis of this cell line revealed a human male hyperdiploid karyotype with a modal chromosome number of 56 to 58. The Ph1 chromosome was observed in all karyotypes analyzed. This novel human megakaryoblastic cell line may provide a useful model for the study of human megakaryopoiesis and of the biosynthetic mechanisms of proteins unique to megakaryocytic lineage.     

Acute myeloid leukemia with mediastinal myeloid sarcoma refractory to acute myeloid leukemia therapy but responsive to l-asparaginase

We report the case of a 14-year-old female with acute myeloid leukemia (AML) and myeloid sarcomas (MS) in the anterior mediastinum and around numerous bones. Laboratory tests showed a white blood cell count of 4.0?×?10(9)/l with 7.0?% blasts. Computed tomography revealed a mediastinal mass and pleural effusion; pleural effusion cytology was negative for malignant cells. In addition, disseminated intravascular coagulation (DIC) was present. Following DIC therapy, thoracoscopic and bone marrow biopsies were performed. Immunostaining and surface marker analysis revealed that the blast cells were positive for cytoplasmic myeloperoxidase, CD4, CD7, CD33, CD44, CD117, and HLA-DR, but negative for CD34 and CD56. Karyotype was normal. MS associated with AML was diagnosed. Multidrug chemotherapy for AML was completely ineffective, and MS continued to progress. Immunohistochemistry revealed that the blasts were negative for asparagine synthetase (AS); therefore, chemotherapy including L: -asparaginase was initiated. After the first administration of L: -asparaginase, the patient's condition improved; however, she subsequently developed tumor lysis syndrome and sepsis, which eventually led to death. Aggressive MS in childhood is rare and refractory to existing AML chemotherapy. Chemotherapy including L: -asparaginase may prove to be effective in such cases, especially those in which blast cells show negative AS expression.     

Membrane receptors for interleukin 2 on hematopoietic precursors in chronic myeloid leukemia

In this report we present data on the expression of IL2 receptors on chronic phase CML cells. Using an anti IL2 receptor monoclonal antibody (McAb aIL2r) in indirect immunofluorescence we found significant proportions (42.2% +/- 19.7 SD) of the CML cells (previously depleted of E rosetting T cells) to be IL2 receptor positive following incubation in suspension for 18 hours at 37 degrees C. Noninduced cells did not express IL2 receptors. After induction the aIL2r positive and negative cell subpopulations were sorted and analyzed separately for morphology, lineage specific cell surface markers, and clonogenic cell numbers. The IL2 receptor positive CML subpopulations mainly contained blast cells and monocytes and revealed reactivity with myeloid McAbs but not with T cell, B cell, platelet, or erythroid markers. Clonogenic cells (CFU-GEMM, BFUe, and CFU-GM) were selectively recovered from aIL2r positive CML cells and thus were IL2 receptor positive. The addition of recombinant IL2 (rIL2) to CFU-GM and BFUe cultures, in concentrations from 50 to 500 U/mL, did not influence the efficiency of colony formation. Binding of a radiolabeled IL2 preparation to the in vitro activated CML cells indicated the presence of low affinity receptors for IL2. In contrast to CML, normal human marrow cells were consistently aIL2r nonreactive. Thus, IL2 receptor inducibility is a characteristic feature of CML clonogenic cells, which they share with AML, but not with normal marrow progenitors. The role of IL2 receptors in the regulation of proliferation of CML cells requires further investigation.