Purification and characterization of fetal hematopoietic cells that express the common acute lymphoblastic leukemia antigen (CALLA)

Fetal hematopoietic cells that express the common acute lymphoblastic leukemia antigen (CALLA) were purified from both fetal liver and fetal bone marrow by immune rosetting with sheep erythrocytes coated with rabbit anti-mouse immunoglobulin and by fluorescence-activated cell sorting. Dual fluorescence techniques disclosed that these cells were heterogenous with respect to the expression of a series of differentiation and activation antigens defined by monoclonal antibodies. Thus, whereas all CALLA+ cells were Ia+ and expressed two activation antigens, J2 and T10, only 30-50% expressed B1 antigen. Furthermore, using methanol-fixed cells, it could be shown that approximately 20% contained intracytoplasmic mu chains (cyto-mu) and that approximately 15% were positive for the terminal transferase enzyme (TdT) marker. The CALLA+ fetal cells thus closely resemble the childhood acute lymphoblastic leukemia cell with respect to surface marker phenotype. A population of CALLA- cells devoid of mature erythroid and myeloid surface markers was found to contain higher numbers of TdT+ cells but lower numbers of cyto-mu, B1, and Ia+ cells than the CALLA+ subset. In vitro analysis of normal, purified CALLA+ cells demonstrated that incubation at 37 degrees C with J5 monoclonal antibody specific for CALLA resulted in the specific modulation of surface antigen. Similar results have previously been obtained with CALLA+ tumor cells. Although phenotypic analysis of CALLA+ cells suggests that these cells are relatively immature lymphoid cells, CALLA+ cells do not appear to contain either myeloid precursor cells (CFU-G/M) or the earliest lymphoid stem cells.

Differentiation patterns in the blastic phase of chronic myeloid leukemia

The surface antigen phenotype of 30 patients with the blast phase of chronic myeloid leukemia (CML) was determined using a panel of monoclonal antibodies recognizing differentiation antigens of normal myeloid, erythroid, megakaryocyte, and lymphoid cells. Ten patients' cells expressed a phenotype corresponding to an immature myeloid cell and were felt to have "myeloid" blast crisis. None of these myeloid leukemias were TdT+ or responded to vincristine (V) and prednisone (P). Eleven patients expressed a phenotype similar to acute lymphoblastic leukemia cells and probably reflect maturation to an early B lymphocyte. All of these "lymphoid" leukemias were TdT+, and 67% of evaluable patients had a complete response to V and P. One leukemia had the phenotype of an erythroleukemia, one patient's cells expressed the phenotype of megakaryoblastic leukemia, and one leukemia had populations of both myeloid and lymphoid blasts. Six leukemias did not express surface markers characteristic of any lineage and were termed "undifferentiated." This group was heterogeneous with respect to TdT expression, but no patient had a complete response to V and P. Determination of surface antigen phenotype in CML blast crisis thus provides clinically useful information for the structuring of treatment protocols.

Interferon-induced changes in expression of antigens defined by monoclonal antibodies on malignant and nonmalignant mononuclear hematopoietic cells

The effect of alpha interferon (alpha IFN) on the expression of histocompatibility--as well as differentiation antigens on normal and malignant hematopoietic mononuclear cells--were investigated by cell cytofluorometry using a panel of monoclonal antibodies (MoAbs). An increase in the expression of HLA-antigens detected by beta 2-Microglobulin (beta 2-M) could be demonstrated for peripheral blood mononuclear cells, non-T cells, Null cells, activated T cells, fetal thymocytes, adherent cells, and on four malignant non-T lymphoblastoid cell lines. In contrast, no significant differences were observed in the expression of antigens specific for B-lymphocytes (B1), T-lymphocytes (T3, T4, T6, T8, T11), NK-cells (901) and adherent cells (Mo1-4). Likewise, the expression of Ia-antigens remained unaltered on non-T cells, Null cells, and monocytes. The only other effect of IFN was an increase in the number as well as the amount of lymphocytes expressing the T10 antigen. It thus seems that the enhancing effect of IFN on resting cells of the immune system is highly selective. On the four lymphoblastoid cell lines, the expression of the common acute lymphoblastic leukemia antigen (CALLA) was significantly decreased concomitantly with the increase in MHC-antigens. On the other hand, the density of both a HLA-D related Ia antigen (I2) and a B-lymphocyte differentiation antigen (B1) remained unaltered following IFN treatment. The implications of these findings are discussed.

Generation of a cloned NK cell line derived from the "null cell" fraction of human peripheral blood

The present studies were designed to determine the conditions for generation of human NK clones. First the "null cell" (NC) fraction of human peripheral blood mononuclear cells, which contains the NK effectors, was purified using negative selection with anti-T3, anti-T8, anti-B1, and anti-Mo2 monoclonal antibodies. Subsequently, NC were cloned by limiting dilution using a combination of phytohemagglutinin (PHA) and lymphocyte-conditioned medium (LCM) as an initial stimulus. Colonies could be easily obtained with this procedure, but the maintenance of long-term growth of the cultures represented a major problem. A cloned cell line termed JT1 was generated and has been proliferating continuously in culture for more than 6 mo. The phenotype of JT1 cells was analyzed several times with a series of monoclonal antibodies. These cells did not express surface markers related to thymic (T3-, T4-, T8-, T11-), B cells (B1-, J5-), or myelomonocytic (Mo1-, Mo2-, MY7-) differentiation. In contrast, 95% of JT1 cells reacted with the anti-T10 monoclonal antibody. T9, Ia, and J2 antigens were also present on JT1 cells, but their expression appeared variable from one determination to another. This cloned cell line maintains a strong cytotoxicity against common NK targets, such as K562 and Molt 4 cell lines, and a moderate ADCC activity. In addition, after several months in culture, JT1 cells are still capable of being regulated by interferon, because this lymphokine rapidly enhances cytotoxicity against K562 cells.

Generation of a cloned NK cell line derived from the "null cell" fraction of human peripheral blood

The present studies were designed to determine the conditions for generation of human NK clones. First the "null cell" (NC) fraction of human peripheral blood mononuclear cells, which contains the NK effectors, was purified using negative selection with anti-T3, anti-T8, anti-B1, and anti-Mo2 monoclonal antibodies. Subsequently, NC were cloned by limiting dilution using a combination of phytohemagglutinin (PHA) and lymphocyte-conditioned medium (LCM) as an initial stimulus. Colonies could be easily obtained with this procedure, but the maintenance of long-term growth of the cultures represented a major problem. A cloned cell line termed JT1 was generated and has been proliferating continuously in culture for more than 6 mo. The phenotype of JT1 cells was analyzed several times with a series of monoclonal antibodies. These cells did not express surface markers related to thymic (T3-, T4-, T8-, T11-), B cells (B1-, J5-), or myelomonocytic (Mo1-, Mo2-, MY7-) differentiation. In contrast, 95% of JT1 cells reacted with the anti-T10 monoclonal antibody. T9, Ia, and J2 antigens were also present on JT1 cells, but their expression appeared variable from one determination to another. This cloned cell line maintains a strong cytotoxicity against common NK targets, such as K562 and Molt 4 cell lines, and a moderate ADCC activity. In addition, after several months in culture, JT1 cells are still capable of being regulated by interferon, because this lymphokine rapidly enhances cytotoxicity against K562 cells.

Induction of human B cell antigens in non-T cell acute lymphoblastic leukemia

Leukemic cells from 70% of patients with Ia+CALLA+ non-T cell acute lymphoblastic leukemia (ALL) express an antigen (B1) found on all normal B lymphocytes. In this study, ALL cells that do not express the B1 antigen were studied in an attempt to further elucidate the cellular lineage of these tumors. Non-T cell ALL lines and tumor cells isolated from patients with non-T cell ALL that are Ia + CALLA + B1- were studied in vitro with a variety of agents known to promote cellular differentiation. Phorbol diester (TPA) or phytohemagglutinin conditioned leukocyte culture media were capable of inducing the expression of B1 on all four non-T cell ALL lines tested. In contrast, B1 could not be induced under the identical conditions on a promyelocytic leukemia line or a T cell lymphoblastic leukemia line. With the induction of B1 on non-T cell ALL lines, cytoplasmic mu-heavy chain (c mu) became undetectable, whereas the expression of CALLA and Ia were unchanged. The expression of B1 was accompanied by a decrease of cellular proliferation and DNA synthesis, but not significant morphologic changes were noted. In addition, no other B or T cell antigens were detected. The cellular origin of non-T cell ALL was further investigated using tumor cells isolated from leukemic patients. Tumor cells from eight patients with Ia + CALLA + B1-c mu- ALL could be induced in vitro with TPA to express both B1 and c mu. In contrast, cells from five patients with Ia + CALLA-B1-c mu- non-T cell ALL could not be induced with TPA to express CALLA, B1 or c mu. These studies suggest that the non-T cell ALL are heterogeneous and represent a spectrum of early B cell differentiation including the pre- pre-B cell (Ia + CALLA + B1-c mu-), the intermediate pre-B cell (Ia + CALLA +B1 + c mu-), and finally the "true" pre-B cell (Ia + CALLA + B1 + c mu+). The cellular origin of the remaining Ia + CALLA-B1-c mu- form of non-T cell ALL (20%) is still unknown.

Autologous bone-marrow transplantation in CALLA-positive acute lymphoblastic leukemia after in-vitro treatment with J5 monoclonal antibody and complement

A monoclonal antibody (J5) specific for the common acute-lymphoblastic-leukaemia antigen (CALLA) was used for in-vitro pre-treatment of bone-marrow before autologous transplantation in four patients with CALLA-positive acute lymphoblastic leukaemia (ALL) in relapse, who did not have HLA-compatible donors. After remission induction and intensification, bone-marrow cells were harvested, treated with J5 antibody and rabbit complement, and cryopreserved in liquid nitrogen. Patients received ablative chemotherapy and total-body irradiation before reinfusion of autologous J5-treated bone marrow. The transplantation protocol was well tolerated, and engraftment of normal myeloid cells occurred in all for patients. Two patients have continued in unmaintained remission with complete haematopoietic reconstitution for more than 1 year after autologous transplantation.

Monoclonal antibody-ricin A chain conjugate selectively cytotoxic for cells bearing the common acute lymphoblastic leukemia antigen

The toxic subunit of ricin has been conjugated by a disulfide bound to a monoclonal murine antibody (J-5) specific for the common acute lymphoblastic leukemia antigen (CALLA) expressed on human lymphoblastic cells. Both the monoclonal antibody and ricin A chain retained their original biological activity after conjugation. The ricin A chain portion of this conjugate effectively inhibited protein synthesis in a cell-free rabbit reticulocyte lysate system. Its antibody-combining site attached to the membrane of CALLA-bearing cells, whereupon both components of the molecule, antibody and A chain, could be detected using fluorescein-labeled antibody probes directed against either mouse F(ab')2 or ricin A chain. This conjugate proved to be a potent cytotoxin for CALLA-positive Nalm-1 cells growing in vitro and produced 50% inhibition of proliferation at levels of 2 x 10(-10) M. In contrast, CALLA-negative cell lines were unaffected until levels of conjugate approached 10(-6) M. When tested for cytotoxic action on Nalm-1 cells, the composite conjugate molecule was at least 2000 times more effective than J-5 antibody alone, ricin A chain alone, or a noncovalent mixture of these components. Cytotoxicity of the conjugate could be blocked completely by addition of antibodies specific for either mouse immunoglobulin or ricin A chain. Direct comparison of the in vitro cytotoxicity of CALLA-directed univalent Fab versus bivalent F(ab')2 carriers of ricin A chain revealed 70-fold greater efficacy for the latter conjugate. This differential could not be accounted for by differences in A chain activity or binding affinity for the cell membrane but appeared related to the ability of the multivalent agent to induce modulation and internalization of CALLA determinants. No overt toxic effects were noted when the F(ab')2-A chain conjugate was administered i.v. to rabbits at levels as high as 20 mg/kg single injection or 5 mg/kg for 5 days. The unique specificity characteristics and high potency of this cytotoxic conjugate indicate that it has significant therapeutic potential for the treatment of CALLA-bearing human leukemias and lymphomas.

Utilization of monoclonal antibodies in the treatment of leukemia and lymphoma

The generation of murine monoclonal antibodies reactive with human leukemia and lymphoma cells has recently led to clinical trials that have begun to evaluate the use of these reagents in the treatment of various leukemias and lymphomas. Several of these studies have demonstrated that infusion of monoclonal antibody can cause the rapid and specific clearance of leukemic cells from the peripheral blood. Intravenously administered antibody also rapidly binds to bone marrow lymphoblasts, and in one instance, has resulted in the partial regression of tumor cell infiltrates in lymph nodes and skin. Unfortunately, clinically significant responses have not in general been achieved, but these clinical studies have identified specific factors that result in the development of resistance to antibody-mediated lysis in vivo. These factors include the presence of circulating antigen, antigenic modulation, reactivity of monoclonal antibody with normal cells, immune response to murine antibody, and the inefficiency of natural immune effector mechanisms. Current research is now being directed towards developing methods to circumvent each of these obstacles. Future clinical studies utilizing antibodies in vitro or with different specificity may demonstrate greater therapeutic efficacy. In addition, monoclonal antibodies can be used as carriers of other cytotoxic agents and in conjunction with other agents that will reduce the total load. Monoclonal antibodies represent new and powerful reagents that may in the near future become an additional therapeutic modality for patients with malignant disease.

Comparative expression of T9, T10, and Ia antigens on activated human T cell subsets

In the present study, the expression of three surface molecules T9, T10, and Ia, which are found on activated T lymphocytes, was examined utilizing monoclonal antibodies and indirect immunofluorescence. These antigens were shown to appear on T lymphocytes in a defined temporal sequence which was dependent on the specific triggering stimulus. Moreover, when T cells were fractionated into individual subsets of T4+ inducer and T8+ cytotoxic/suppressor lymphocytes, the expression of all three molecules was restricted to the T4+ subset following soluble antigen stimulation. By contrast, both subsets expressed these surface determinants following mitogen or alloantigen stimulation. The above results suggest that there may be successive stages in the T cell activation process associated with the appearance of unique cell surface antigens and further support the view that various triggering stimuli activate T cell populations differently.

Use of monoclonal antibodies as diagnostic and therapeutic reagents in acute lymphoblastic leukemia

A monoclonal antibody specific for a common acute lymphoblastic leukemia (ALL) antigen has been generated and characterized. This antibody (J-5) is reactive with leukemic cells from most patients with non-T-cell ALL and some patients with chronic myelocytic leukemia in blast crisis. J-5 antibody is not reactive with leukemic cells from patients with either T-cell ALL, chronic lymphocytic leukemia, acute myeloblastic leukemia, or stable-phase chronic myelocytic leukemia. In addition to diagnostic applications, anti-common ALL antigen monoclonal antibody has been used to study the effect of specific serotherapy in the treatment of ALL. In the first patient with ALL treated with J-5 antibody, a 90% reduction in circulating lymphoblasts occurred within 1 hr of starting antibody infusion. Despite continued serotherapy, however, lymphoblasts persisted in peripheral blood and bone marrow. Analysis of cell surface markers during serotherapy suggested that resistance to antibody-mediated lysis in vivo may have been due to antigenic modulation of leukemic cells in response to J-5 monoclonal antibody.

Expression of myeloid differentiation antigens on normal and malignant myeloid cells

A series of monoclonal antibodies have been characterized that define four surface antigens (MY3, MY4, MY7, and MY8) of human myeloid cells. They were derived from a fusion of the NS-1 plasmacytoma cell line with splenocytes from a mouse immunized with human acute myelomonocytic leukemia cells. MY3 and MY4 are expressed by normal monocytes and by greater than 90% of patients with acute monocytic leukemia or acute myelomonocytic leukemia, but are detected much less often on other types of myeloid leukemia. MY7 is expressed by granulocytes, monocytes, and 5% of normal bone marrow cells. 79% of all acute myeloblastic leukemia (AML) patients tested (72 patients) express MY7 without preferential expression by any AML subtype. MY8 is expressed by normal monocytes, granulocytes, all peroxidase-positive bone marrow cells, and 50% of AML patients. MY3, MY4, and MY8 define myeloid differentiation antigens in that they are not detected on myeloid precursor cells and appear at discrete stages of differentiation. These antigens are not expressed by lymphocytes, erythrocytes, platelets, or lymphoid malignancies. The monoclonal antisera defining these antigens have been used to study differentiation of normal myeloid cells and malignant cell lines.

Expression of common acute lymphoblastic leukemia antigen (CALLA) by lymphomas of B-cell and T-cell lineage

Previous studies have demonstrated that the common acute lymphoblastic leukemia antigen (CALLA) is expressed by leukemic cells from approximately 80% of patients with non-T-cell ALL and 30%-50% of patients with chronic myelocytic leukemia in blast crisis. A small number of normal bone marrow and fetal liver cells also express CALLA, but the functional role of this molecule is unknown. In the present study, we have used a monoclonal antibody (J5) specific for CALLA to study the expression of this antigen in non-Hodgkin's lymphomas. Within the B-cell lymphomas, it was found the CALLA was expressed by almost all Burkitt's and nodular poorly differentiated lymphocytic lymphomas. Within the T-cell lymphomas, CALLA was expressed in 40% of patients with lymphoblastic lymphoma. Three of 3 Burkitt's lymphoma cell lines and three of eight T-lymphoblast cell lines were also found to express CALLA. Normal spleen, lymph node, and thymus cells were not reactive with J5 antibody. These findings indicate that expression of CALLA is not limited to relatively undifferentiated leukemic lymphoblasts but also occurs in more differentiated lymphoid malignancies. However, normal differentiated lymphoid cells in lymph node, spleen, and thymus, which have a phenotype similar to that of lymphoma cells, do not appear to express CALLA.

Human cell lines express multiple populations of Ia-like molecules

Three monoclonal antibodies have been used to isolate Ia-like antigens from three human cell lines; two of which are thought to be homozygous at the HLA-D/DR locus. Complete extraction of the Ia antigens identified by one antibody leaves those recognized by the two remaining antibodies in three parallel sets of experiments, indicating that the antigenic determinants recognized by these antibodies are present on three different populations of Ia molecules from cells of single individuals. These three populations of Ia-like molecules may reflect serologic variants of the product of a single genetic locus or may represent the products of as many as three nonallelic genetic regions. Demonstration of the existence of these multiple populations of Ia-like molecules on presumed homozygous typing cells indicates that this antigenic system is much more complex than has been generally realized. Further study may clarify the relationship between HLA-D/DR type and susceptibility to a variety of diseases and ultimately lead to better matches and improved survival for allogenic transplants. Since the HLA-D region is intimately involved in regulation of the immune response and susceptibility to a variety of diseases, use of monoclonal antibodies specific for discrete Ia antigens, the only identified products of the HLA-D region, may facilitate dissection of its many biological functions.

Absence of common ALL antigen on normal bipotent myeloid, erythroid, and granulocyte progenitors

The presence of the common acute lymphoblastic leukemia antigen (CALLA) on leukemic cells from the great majority of patients with non-T cell acute lymphoblastic leukemia and chronic myelogenous leukemia in blast crisis suggests that CALLA could be differentiation antigen expressed by normal lymphoid and myeloid stem cells. Treatment with a murine monoclonal anti-CALLA antibody and complement lysed CALLA-positive leukemic cells quantitatively, whereas similar treatment of nucleated cells from peripheral blood and bone marrow failed to affect the expression, in semisolid culture, of CFU-G/E, BFU-E, CFU-E, or CFU-C. These data suggest that CALLA is not a normal differentiation antigen of the myeloid bipotent cell or its committed progenitors.

Serotherapy of acute lymphoblastic leukemia with monoclonal antibody

We tested the efficacy of passive serotherapy in the treatment of acute lymphoblastic leukemia in four patients who had relapsed while receiving standard chemotherapeutic agents. Each patient received multiple intravenous infusions of J-5 monoclonal antibody specific for common acute lymphoblastic leukemia antigen (CALLA). In the three patients with circulating leukemic cells, there was a rapid decrease in circulating blasts that began immediately after antibody infusion, but not all leukemic cells were cleared, and remaining cells appeared to be resistant to further serotherapy. Although J-5 antibody was also demonstrable on bone marrow lymphoblasts immediately after antibody infusion in one patient, there was no change in bone marrow cellularity or differential during serotherapy. Analysis of the cell surface phenotype of leukemic cells during serotherapy and in vitro studies with patient cells suggests that resistance to serotherapy was mediated in part by antigenic modulation of CALLA in response to J-5 antibody.

Cell surface characterization of malignant T cells from lymphoblastic lymphoma using monoclonal antibodies: evidence for phenotypic differences between malignant T cells from patients with acute lymphoblastic leukemia and lymphoblastic lymphoma

A series of monoclonal antibodies was used for the characterization of malignant T cells from 21 patients with lymphoblastic lymphoma (LL). The tumor population from these patients showed a marked degree of phenotypic heterogeneity and a proportion (one-third) of patients had tumor cells that did not conform exactly with the cells normally detected in the thymus. However, these cell populations could be related to the early or common or late thymocyte population (about one-third of the patients in each category). This contrast, with the characterization of malignant T cells from 43 patients with acute lymphoblastic leukemia (ALL) that could be related to either early or common thymocytes, with an exception of two patients categorized as having a tumor population related to late thymocytes. Further phenotypic differences between cells from ALL and LL could be demonstrated by investigation with two additional monoclonal antibodies, A50 and U4. Among patients with malignant T cells related to common thymocyte, 0/12 patients with ALL had cells recognized by A50, where 5/8 patients with LL had A50+ cells. Among patients with early thymocytes, only patients with ALL had cells recognized by U4. In addition, 5 LL patients had cells reactive with J5, a monoclonal antibody recognizing the common ALL antigen (CALLA). Since CALLA was found on cells related to common and late thymocytes, CALLA is neither lineage specific, nor can it be viewed as being peculiar to malignant lymphoid cells arrested at very immature stages of differentiation.

Surface antigens on malignant Sézary and T-CLL cells correspond to those of mature T cells

Tumor cells from eight adult patients with T-cell chronic malignancies were investigated with a series of monoclonal antibodies recognizing T-cell differentiation antigens. This series allowed definition of discrete subpopulations of mature T cells with functional specialization. All six patients with Sézary syndrome and one patient with T-chronic lymphocytic leukemia had cells with the same phenotype as normal helper/inducer T cells, whereas the other patient with T-chronic lymphocytic leukemia had cell with the same phenotype as normal cytotoxic/suppressor T cells. Some clinical manifestations observed in these patients may reflect retention of functional activities by their malignant cells.

Fate of a common acute lymphoblastic leukemia antigen during modulation by monoclonal antibody

Modulation of a human common acute lymphoblastic leukemia antigen (CALLA) by specific monoclonal antibody (J5) has been studied with the immune precipitation method to identify radiolabeled antigen. Surfaces of leukemic cells have been labeled using 125I both before and after modulation by J5 antibody for different time intervals. Leukemic cells have also been metabolically labeled with 35S-methionine before modulation. These studies indicate that the 100,000-dalton glycoprotein expressing CALLA (gp 100-CALLA) cannot be detected in cells that were modulated with J5 antibody before surface labeling but that it is easily detectable in cells that were surface labeled before modulation for 10 hr. At later time points, gp 100-CALLA is selectively lost from cells that were surface labeled before modulation. Gp 100-CALLA is not detected in the supernatants from cultures of these modulated cells. We conclude that gp 100-CALLA is rapidly internalized during modulation and that CALLA is degraded. Gp 100-CALLA is not shed into the culture media, nor does it remain on the cell surface in an altered form. Incubation of leukemic cells with antisera to beta2-microglobulin or IgM does not affect the expression of gp 100-CALLA.

Fate of a common acute lymphoblastic leukemia antigen during modulation by monoclonal antibody

Modulation of a human common acute lymphoblastic leukemia antigen (CALLA) by specific monoclonal antibody (J5) has been studied with the immune precipitation method to identify radiolabeled antigen. Surfaces of leukemic cells have been labeled using 125I both before and after modulation by J5 antibody for different time intervals. Leukemic cells have also been metabolically labeled with 35S-methionine before modulation. These studies indicate that the 100,000-dalton glycoprotein expressing CALLA (gp 100-CALLA) cannot be detected in cells that were modulated with J5 antibody before surface labeling but that it is easily detectable in cells that were surface labeled before modulation for 10 hr. At later time points, gp 100-CALLA is selectively lost from cells that were surface labeled before modulation. Gp 100-CALLA is not detected in the supernatants from cultures of these modulated cells. We conclude that gp 100-CALLA is rapidly internalized during modulation and that CALLA is degraded. Gp 100-CALLA is not shed into the culture media, nor does it remain on the cell surface in an altered form. Incubation of leukemic cells with antisera to beta2-microglobulin or IgM does not affect the expression of gp 100-CALLA.

A unique cell surface antigen identifying lymphoid malignancies of B cell origin

A monoclonal antibody (anti-B1) specific for a unique B cell surface differentiation antigen was used to characterize the malignant cells from patients with leukemias or lymphomas. All tumor cells from patients with lymphomas or chronic lymphocytic leukemias, bearing either monoclonal kappa lambda light chain, expressed the B1 antigen. In contrast, tumor cells from T cell leukemias and lymphomas or acute myeloblastic leukemia were unreactive. Approximately 50% of acute lymphoblastic leukemias (ALL) of non-T origin and 50% of chronic myelocytic leukemia in blast crisis were also anti-B1 reactive. moreover, 21 of 28 patients with the common ALL antigen (CALLA) positive form of ALL were anti-B1 positive, whereas 0 of 13 patients with CALLA negative ALL were reactive. These observations demonstrate that an antigen present on normal B cells is expressed on the vast majority of B cell lymphomas and on approximately 75% of CALLA positive ALL, suggesting that these tumors may share a common B cell lineage.