Normal chicken cells (chf-) express a surface antigen which cross-reacts with determinants of the major envelope glycoprotein (gp85) of avian myeloblastosis virus

Isolation of complementary DNA clones encoding the human lymphocyte glycoprotein T1/Leu-1

The T1/Leu-1/CD5 molecule, a human T-cell surface glycoprotein of relative molecular mass (Mr) 67,000, has been implicated in the proliferative response of activated T cells and in T-cell helper function. A similar involvement in T-cell proliferation has been reported for Ly-1, the murine homologue of T1. Here we report the complete amino-acid sequence of the T1 precursor molecule deduced from complementary DNA clones. The protein contains a classical signal peptide; a 347-amino-acid extracellular segment; a transmembrane region; and a 93-amino-acid intracellular segment. The extracellular segment contains many cysteine residues and is composed of two related structural domains separated by a proline/threonine-rich region. The T1 molecule has structural features characteristic of other receptor molecules.

In vitro growth inhibition of murine leukemia cells by antibody specific for the major envelope glycoprotein (gp71) of Friend leukemia virus

An in vitro complement (C')-independent growth cytostasis model is described in which the replication of Friend leukemia virus (FLV)-induced erythroleukemia cells (of the FLC-745 cell line) is inhibited by goat serum directed against the major FLV envelope glycoprotein, gp71. The cytostatic effect is reversible, with the degree of this reversibility dependent on both the concentration and duration of exposure to immune serum. The inhibitory factor in heat-activated goat anti-FLV gp71 (delta G alpha FLV gp71) serum has been identified as virus-specific IgG antibody, and F(ab')2 fragments of this antibody are highly effective in suppressing FLC-745 cell growth. Studies with various murine leukemia and lymphoma cell lines, as well as with a panel of antisera directed against various murine oncornaviruses or viral proteins, have demonstrated that antibodies reactive with the group or type determinants of FLV gp71 are capable of mediating cytostasis. Under conditions of antibody-mediated growth inhibition of FLC-745 cells, specific modulation of gp71 expression is followed by nonspecific modulation of H-2d antigen expression. In addition, considerable cell death occurs in cytostatic cultures which is accompanied by continued division (as measured by DNA synthesis) of a portion of the cell population. Cytofluorimetric analysis of nuclei from growth-inhibited FLC-745 cells demonstrates a diminution in the frequency of cells in the G2/M phase of the cell cycle. It is suggested that antibody-mediate FLC-745 cell growth inhibition operates via a blockade of the cell cycle which prevents most cells in the population from traversing G2/M. While these blocked cells appear to be subject to slow cytolysis by a C'-independent mechanism, a portion of the cells escape this blockade and continue to replicate, thus offsetting the death of the former cells to yield a relatively constant density of viable cells for at least 72-96 h of growth inhibition. The possible relevance of this in vitro phenomenon to in vivo passive therapy against FLV-induced disease with G alpha FLV gp71 and similar antisera is briefly considered.

Human cell surface proteins selectively assembled into vesicular stomatitis virus virions

Vesicular stomatitis virus (VSV) selectively assembled proteins from human cells into progeny virions. These proteins can be surface labeled before infection with 125I, and when purified virus was examined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, only two or three bands of proteins (Mr around 100K) were seen. Antisera to these proteins were produced, using as immunizing antigen VSV tsO45 mutant, defective in assembly of G protein, which had been made at the nonpermissive temperature in the three human tumor cell lines, HeLa (cervical carcinoma), T47D (breast carcinoma), and HMB2 (melanoma). After absorption with wild-type VSV, each of the antisera displayed a different pattern of reactivity; at least three antigenic specificities were detected. Two of them, corresponding to antigens selected by VSV from HeLa and T47D, were to some extent related and they showed an association mainly with epithelial cell-derived gynecological tumors, but they were absent in carcinomas of lung or of digestive tract. These (or related) antigens were expressed in a lower level in some normal tissues, mainly in ovaries. Antigen(s) assembled by VSV from the melanoma cell line was entirely different and appeared to be associated with cell growth. The grounds for selective assembly of these specific proteins by VSV are not clear; they either share with viral surface glycoproteins some physical or structural properties, which are critical for incorporation into the viral envelope, or conceivably they even may represent uncleaved precursor proteins coded by env genes of incomplete genomes of endogenous human retroviruses.

Transformation-defective Rous sarcoma virus mutants with altered p19 of the gag gene and their inhibitory effect on host cell growth

Mutants (PH2010, PH2011, PH2012) of Rous sarcoma virus which have a growth-inhibitory effect on chicken embryo fibroblasts were isolated from a temperature-sensitive mutant of the Schmidt-Ruppin strain of Rous sarcoma virus (tsNY68). The growth rate of fibroblasts infected with these viruses was about 50 to 60% of that of uninfected fibroblasts. A morphological difference between mutant-infected and uninfected fibroblasts was observed at logarithmic phase but not at stationary phase. Neither the protein p60src nor its associated protein kinase activity was significantly detected by an immunoprecipitation assay in the cells infected with these mutants. Analysis of the unintegrated DNA of the mutant PH2010 showed that a sequence of about 1.4 kilobase pairs at the src gene region is deleted. Further examination of the viral structural proteins in infected cells as well as in virions by immunoprecipitation and peptide mapping revealed that the molecular size of the Pr76 gag protein of the mutant RSV is smaller than that of the mutant tsNY68 because of partial deletion at the p19 gag gene. The peptide maps suggest that the deleted region of the altered p19 of the mutant is near the carboxy terminal of p19. The amount of Prgp92env synthesized in the mutant-infected cells was about fivefold more than that in tsNY68-infected cells.

A monoclonal antibody reactive with a second epitope of the 67,000-dalton human T cell antigen

Hybridomas were produced against the T-cell CLL derived-cell line, SKW3, by the fusion of hyperimmune spleen cells with P3 myeloma cells. One clone, designated DU-SKW3-1, was shown to produce a murine IgG2b antibody reactive with an antigen expressed on normal thymocytes and peripheral blood T cells. This antigen was not detected on human B cells, erythrocytes, monocytes, granulocytes, or platelets. D-SKW3-1 also reacted with T-ALL, T-CLL, and B-CLL cells, but did not react with common ALL or acute myelocytic or monocytic leukemias. Immunoprecipitation of lactoperoxidase-iodinated, detergent-solubilized PBL demonstrated that DU-SKW3-1 reacted with a protein with an apparent mass of 67,000 daltons (p67), which had identical mobility to the antigen precipitated by L17F12, Cocapping experiments suggested that DU-SKW3-1 and L17F12 detected the same molecule: however, DU-SKW3-1 was unable to block the binding of L17F12. In addition, DU-SKW3-1 reacted with the T lymphocytes of both the great apes and old world monkeys, in contrast to L17F12 and two other p67 monoclonals, T101 and 10.2, which reacted only with the cells of the great apes. This data suggests that DU-SKW3-1 may react with a second, less phylogenetically restricted epitope on the p67 T cell-/CLL-associated molecule.

Characterization and distribution of a 24,000-molecular weight antigen defined by a monoclonal antibody (DU-ALL-1) elicited to common acute lymphoblastic leukemia (cALL) cells

A monoclonal antibody (DU-ALL-1) was generated to common acute lymphoblastic leukemia (cALL) cells by microcytotoxicity and indirect immunofluorescence, DU-ALL-1 reacted only with cALL cell lines and not with the other hematopoietic cell lines tested. Peripheral blood lymphocytes, monocytes, granulocytes and mitogen-activated lymphocytes did not react significantly with this antibody. However, platelets (100%) and normal bone marrow cells (8.5%) reacted with DU-ALL-1. Microcytotoxicity testing of human leukemia cells showed that DU-ALL-1 reacted with cells from a majority of null and pre-B ALL patients (63/77) and with cells from some patients with acute myeloblastic leukemia (4/7) and T-ALL (4/20). DU-ALL-1 was generally non-reactive with cells from patients with B-cell leukemias (2/16) and chronic myelogenous leukemia in blast crisis (0/4). By an indirect immunoperoxidase technique, DU-ALL-1 reacted with a variety of non-hematopoietic tissues, including smooth and cardiac muscle and epithelia from several organs. The DU-ALL-1 antigen had an apparent mol. wt of 24,000 and did not bind to lectins or label with [3H]glucosamine. Thus, DU-ALL-1 defines a 24,000-mol. wt protein which is absent from most peripheral blood mononuclear cells, is expressed on normal platelets and several non-hematopoietic tissues, and may be a useful for subclassifying leukemias.

Distribution of common acute lymphoblastic leukemia antigen in nonhematopoietic tissues

The common acute lymphoblastic leukemia antigen (CALLA), as defined by J-5 murine monoclonal antibodies, was detected on renal tubular and glomerular cells from fetal and adult donors by an indirect immunoperoxidase technique. CALLA could also be detected on epithelial cells of the fetal small intestine and on myoepithelial cells of adult breast but not on myoepithelial cells of the salivary gland. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of immunoprecipitated 125I-labeled membrane antigens from dissociated renal cells demonstrated that the antigen migrated as a 90,000 mol wt antigen rather than the 98,000-100,000 mol wt antigen noted on CALLA-positive tissue culture cell lines. The data suggest that the determinant defined by the J-5 monoclonal antibody is neither a lymphoid cell-specific differentiation antigen nor a leukemia-specific antigen.

Avian myeloblastosis virus proteins in leukemic chicken myeloblasts

We have analyzed the avian myeloblastosis virus proteins in two types of leukemic myeloblasts: established myeloblastic cell lines (DU 1765 and DU 11157) and leukemic myeloblasts obtained from the peripheral blood of a leukemic C/E Spafas chicken (no. 21957). Using monospecific antisera for immunoprecipitation and polyacrylamide gel electrophoresis, we have detected gag gene-related proteins in the myeloblasts. The DU 1765 and DU 11157 cells contained a p100 protein which possessed antigenic determinants of the viral proteins p27, p19, p15, and p12. The p100 was not found in leukemic myeloblasts from Spafas chickens, and pulse-chase experiments showed that the p100 was not a precursor for the viral proteins. However, the p100 is present in uninfected line 15 chicken embryos. A pr76-like protein was identified in DU 1765 cells but migrated slightly further into gels than the pr76 of Spafas-derived leukemic myeloblasts. The Spafas-derived myeloblasts produced a pr60, whereas the DU 1765 cells contained instead a related protein of 62,000 daltons. Using anti-avian myeloblastosis virus gp85 sera, a glycoprotein of 120,000 daltons (gp120) was detected in all the tested leukemic myeloblasts. The gp120 was also present, in low amounts, in uninfected embyonic spleen and yolk sac cells. The anti-gp85 sera also precipitated a 27,000-dalton protein (h27) in these same cells. Both the gp120 and h27 could not be detected in either uninfected or myeloblastosis-associated virus-infected fibroblasts. Limited peptide hydrolysis revealed that h27 is different from the viral structural protein p27. In conclusion, monospecific antisera for gag and env gene products of avian myeloblastosis virus did not precipitate any unique or aberrant avian myeloblastosis virus protein from leukemic myeloblasts.

env Gene of Rous sarcoma virus: identification of the gene product by cell-free translation

Cell-free translation of polyadenylic acid-selected, denatured virion 70S RNA of the Schmidt-Ruppin strain of Rous sarcoma virus (subgroup A) yields a 64,000-Mr polypeptide which is specifically immunoprecipitated by a group-specific serum raised against envelope glycoprotein gp85. This polypeptide is not synthesized from the virion RNA of the replication-defective mutant rdNY8SR-A, which contains an extensive deletion within the envelope (env) gene. From this genetic evidence we conclude that the 64,000-Mr polypeptide represents the nonglycosylated product of the env gene and propose the designation of P64env. The 64,000-Mr polypeptide is translated from a 26S to 28S polyadenylated RNA species, whereas the p60src product is synthesized from a 20S to 22S RNA, and both Pr76gag and P180gag-pol are synthesized predominately from 34S RNA. The product of the env gene of Rous-associated virus-2 was also identified by cell-free translation.