John M. Pesando

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.

Monoclonal antibodies defining serologically distinct HLA-D/DR related Ia-like antigens in man

Four monoclonal antisera-identifying antigens with the identical tissue distribution and molecular weight of previously described Ia-like antigens were characterized. Two of these antisera, I-1 and I-2, identified antigens expressed on the HLA-D/DR positive cells from all HLA heterozygous individuals. Further characterization on homozygous typing cells (HTCs) demonstrated that I-2 was not reactive with most Dw7 and Dw11 HTCs. Monoclonal antisera, termed I-LR1 and I-LR2, defined polymorphic Ia-like antigens that demonstrated restricted expression on cells from HLA heterozygous individuals. Antigen I-LR1 was expressed on cells from 60% of HLA heterozygotes and its reactivity with HTCs did not conform to any previously described monotypic or supertypic HLA-D/DR pattern. In contrast, I-LR2 was expressed on 40% of HLA heterozygotes and identified only HLA-DR3, 5 and 6 HTCs. Studies of families with HLA recombinants permitted the demonstration that the I-LR1 and I-LR2 antigens are tightly linked to the HLA-D/DR locus. These experiments permit the direct demonstration by immunoprecipitation, linkage studies, and MHC recombinant families that the p29,34 complex in man is closely linked to or is within the HLA-D/DR locus. These studies suggest that the human Ia-like antigens are more heterogeneous than previously demonstrated and that monoclonal antisera will be useful in further defining the structural, genetic, and functional characteristics of these molecules.

Expression of a 26,000-dalton glycoprotein on activated human T cells

Abstract In the present study, we describe the expression of a 26,000-dalton glycoprotein on human T cells following stimulation by either mitogen or alloantigen. This glycoprotein, which is the target antigen of a monoclonal antibody designated J2, is distinct from Ia-like molecules and is not present on resting T cells. We demonstrate GP 26 expression in both major immunoregulatory subsets i.e., T4 + (inducer) and T8 + (cytotoxic/suppressor) following activation and show that the GP 26-bearing cells are not directly responsible for the cytotoxicity generated in MLR. The relationship of the J2 target antigen to other glycoproteins with similar molecular weight which have been described on activated T cells is discussed.

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.

AFTR: A fifth human B-cell-specific surface antigen

We report the identification and characterization of a fifth B-cell-specific surface antigen (AFTR) detected by three murine monoclonal antibodies. AFTR is present on all malignant human B-cell lines tested except those of plasma cells and on malignant B cells from 49/49 patients, including those with pre-B-cell acute lymphoblastic leukemia. Similarly, AFTR is found on all CD19+ B cells from normal bone marrow, peripheral blood, and tonsil, although it is only weakly expressed on Epstein-Barr virus-transformed normal B cells. AFTR is not expressed on T lymphocytes, thymocytes, myelocytes, monocytes, granulocytes, or erythrocytes, or on endothelial or epithelial cells. Isolation of AFTR from surface-iodinated cells by immune precipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals bands at 38 and 42 kd in the acute lymphoblastic leukemia cell lines Laz 221 and NALM-6. Molecular weights of these two bands vary slightly between different B-cell populations but change little under reducing and nonreducing conditions. In contrast, relative intensities of these bands vary considerably between different B-cell populations. Like the B-cell-specific surface immunoglobulin and CD19 antigens, but unlike CD20, expression of AFTR is specifically reduced or modulated when cells are incubated with monoclonal antibodies at 37 degrees C. The molecular weight, behavior, and cellular distribution of AFTR are distinct from those of known B-cell surface antigens. One of these MoAbs (J3-109) is a prototype reagent for the CD72 antigen cluster.

A proposal for the mechanism of carbonic anhydrase action

A new catalytic mechanism is proposed for the hydration of CO2 by the zinc metalloenzyme carbonic anhydrase. This mechanism identifies the group controlling catalytic activity as an active site histidine, in which the protonated imidazole ring coordinates to zinc, losing a proton. Geometric constraints on the histidine unit make the metal-ligand bond a strained and, therefore, labile one. In the hydration reaction, the metal-bound neutral histidine moiety serves as a proton acceptor for the transient ionization of metal-bound water. Zinc-bound hydroxide attacks the carbon of the substrate to generate metal-bound bicarbonate, and the system regenerates itself by losing the elements of carbonic acid.

801 ABSENCE OF COMMON ALL ANTIGEN ON NORMAL PLURIPOTENTIAL MYELOID, ERYTHROID AND GRANULOCYTE PROGENITORS

The common ALL antigen (CALLA) is a unique cell surface glycoprotein detected on the lymphoblasts of most cases of childhood ALL and some B cell tumors to which Ritz et al (Nature 283: 583, 1980) have generated a cytolytic monoclonal antibody (J-5). To determine whether J-5 is distributed on the surfaces of hematopoietic progenitors and with the ultimate purpose of developing a useful approach to autotransplantation, we thrice exposed normal marrow and blood mononuclear cells to J-5 and complement after having determined that such treatment is sufficient to eradicate >99% J-5+ lymphoblasts. The cells were then cultured in both plasma clot and methylcellulose systems to which were added appropriate inducers. Erythroid, granuloid and mixed erythroid/granuloid colony growth was unaffected both with respect to number, size, and morphology. The normal colonies were preserved even in experiments in which J-5+ leukemic cells were added to the normal marrows and lysed during antibody exposure. These results suggest that CALLA is absent from the surface of committed marrow and peripheral blood myeloid progenitors. The antibody is a powerful potential tool for elimination of CALLA+ lymphoblasts from marrow prior to autologous bone marrow transplantation.