Identification and characterization of human immunodeficiency virus type 1 gag-pol fusion protein in transfected mammalian cells

Three human immunodeficiency virus type 1 (HIV-1) mutants were constructed with mutations in their protease genes: AH2-pSVL, with an in-phase deletion; BH27-pSVL, with an out-of-phase deletion creating a stop codon immediately after the deletion site; and CA-pSVL, with a point mutation creating an Asp-to-Ala substitution at the putative protease active site. The wild-type, HXB2-pSVL, and the mutated viral genomes were used to transfect COS-M6 cells and to produce virions. Immunoblotting assays with a monoclonal antibody (MAb) specific for p24 showed that all three mutant contained a gag precursor, Pr56gag, with AH2 and CA expressing an extra band of about 160 kDa. Similar assays with a MAb specific for HIV-1 reverse transcriptase (RT) also revealed a 160-kDa protein from AH2 and CA virions and two mature p66 and p51 RT subunits from HXB2 virions. In addition, HXB2, AH2, and CA but not BH27 virions exhibited RT activity. The same protein in the 160-kDa band seemed to possess both p24 and RT components, since the MAb against p24 was able to immunoadsorb RT antigen and enzymatic activity. These results indicate that the HIV-1 gag-pol fusion protein produced in mammalian cells expressed significant RT activity.

Transfectomas expressing both secreted and membrane-bound forms of chimeric IgE with anti-viral specificity

Because of the lack of a cell line expressing on surface and secreting human IgE of known Ag specificity, the construction of a transfectoma line possessing such properties would be useful for studying the roles of surface IgE and the effects of anti-IgE antibodies on IgE-producing B cells. Toward this goal, the human genomic DNA segment encompassing the two exons encoding the membrane anchor peptide of epsilon-chain and their flanking regions was sequenced. Hybrid epsilon and kappa genomic DNA comprising the C regions of human epsilon- and kappa-chains and the H and L chain V regions of the murine mAb BAT123, which reacts with the gp120 envelope protein of HIV-1, were constructed. Mammalian expression vectors containing these fusion genes were used to transfect murine myeloma Sp2/0 cells, and transfectants stably expressing on surface and secreting into culture medium chimeric IgE were obtained. The chimeric IgE showed identical Ag-binding properties as the murine mAb BAT123. Acting in concert with the specific peptide Ag polyvalently coupled to a protein carrier, the chimeric antibody could induce histamine release from human blood basophils. These results demonstrate the potential utility of the transfectoma cells and the chimeric IgE in studying the roles of membrane-bound IgE and effects of anti-IgE antibodies on IgE-producing B cells.

Transfectomas expressing both secreted and membrane-bound forms of chimeric IgE with anti-viral specificity

Because of the lack of a cell line expressing on surface and secreting human IgE of known Ag specificity, the construction of a transfectoma line possessing such properties would be useful for studying the roles of surface IgE and the effects of anti-IgE antibodies on IgE-producing B cells. Toward this goal, the human genomic DNA segment encompassing the two exons encoding the membrane anchor peptide of epsilon-chain and their flanking regions was sequenced. Hybrid epsilon and kappa genomic DNA comprising the C regions of human epsilon- and kappa-chains and the H and L chain V regions of the murine mAb BAT123, which reacts with the gp120 envelope protein of HIV-1, were constructed. Mammalian expression vectors containing these fusion genes were used to transfect murine myeloma Sp2/0 cells, and transfectants stably expressing on surface and secreting into culture medium chimeric IgE were obtained. The chimeric IgE showed identical Ag-binding properties as the murine mAb BAT123. Acting in concert with the specific peptide Ag polyvalently coupled to a protein carrier, the chimeric antibody could induce histamine release from human blood basophils. These results demonstrate the potential utility of the transfectoma cells and the chimeric IgE in studying the roles of membrane-bound IgE and effects of anti-IgE antibodies on IgE-producing B cells.

Two isoforms of human membrane-bound alpha Ig resulting from alternative mRNA splicing in the membrane segment

Antibodies specific for membrane-bound Ig (mIg) but not for their secreted forms would be useful not only for studying the function of mIg but also for modulating B cell activities in vivo. We have proposed that the extracellular portions of the membrane anchor peptides of mIg can be used as antigenic sites for isotype-specific targeting of B cells. Clones containing the genes of human Ig alpha 1 or alpha 2 subclasses were isolated from a genomic DNA library. The gene segments encoding the membrane peptides and their flanking regions were amplified by polymerase chain reaction, subcloned into plasmid pUC19, and the DNA sequences were determined. Human alpha 1 and alpha 2 genes, like murine alpha gene, each has only one membrane exon. The sequences of the human alpha 1 and alpha 2 genes are almost identical in the membrane peptide-coding region. The mRNA from a human mIgA-expressing B cell line, DAKIKI, was isolated, its cDNA prepared, and the segments spanning the membrane peptide-coding region and a part of the constant domain 3 amplified by polymerase chain reaction. DNA sequences revealed that there are two isoforms of alpha 1-chain, resulting from the alternative splicing of the third constant domain of H chain to two acceptor sites in the membrane exon. One isoform has a segment of 32 and the other 26 amino acid residues in the extracellular portion of the membrane peptide. These segments may serve as isotype-specific antigenic epitopes for antibody targeting of mIgA-bearing B cells.

Two isoforms of human membrane-bound alpha Ig resulting from alternative mRNA splicing in the membrane segment

Antibodies specific for membrane-bound Ig (mIg) but not for their secreted forms would be useful not only for studying the function of mIg but also for modulating B cell activities in vivo. We have proposed that the extracellular portions of the membrane anchor peptides of mIg can be used as antigenic sites for isotype-specific targeting of B cells. Clones containing the genes of human Ig alpha 1 or alpha 2 subclasses were isolated from a genomic DNA library. The gene segments encoding the membrane peptides and their flanking regions were amplified by polymerase chain reaction, subcloned into plasmid pUC19, and the DNA sequences were determined. Human alpha 1 and alpha 2 genes, like murine alpha gene, each has only one membrane exon. The sequences of the human alpha 1 and alpha 2 genes are almost identical in the membrane peptide-coding region. The mRNA from a human mIgA-expressing B cell line, DAKIKI, was isolated, its cDNA prepared, and the segments spanning the membrane peptide-coding region and a part of the constant domain 3 amplified by polymerase chain reaction. DNA sequences revealed that there are two isoforms of alpha 1-chain, resulting from the alternative splicing of the third constant domain of H chain to two acceptor sites in the membrane exon. One isoform has a segment of 32 and the other 26 amino acid residues in the extracellular portion of the membrane peptide. These segments may serve as isotype-specific antigenic epitopes for antibody targeting of mIgA-bearing B cells.

Monoclonal anti-idiotypic antibody mimicking the principal neutralization site in HIV-1 GP120 induces HIV-1 neutralizing antibodies in rabbits

A murine mAb BAT123 (Ab1) directing to the principal neutralization site of human T cell leukemia virus (HTLV)-IIIB gp120 (amino acid residue 308-322) was used to generate syngeneic anti-Id mAb (Ab2). Among the Ab2, a mAb AB19-4 was characterized by both serologic and biologic methods to be paratope-specific (Ab2 beta), bearing the internal image of the neutralization site. AB19-4 was found to bind specifically to BAT123 and also to its mouse-human chimeric form in ELISA. The binding of AB19-4 to BAT123 was specifically inhibited by HTLV-IIIB gp120 and the synthetic epitope peptides of HTLV-IIIB and HTLV-IIIMN defined by BAT123. AB19-4 also inhibited the binding of BAT123 to HTLV-IIIB-infected H9 cells in flow cytometric studies. Polyclonal goat and sheep antisera against HTLV-IIIB gp120 reacted specifically with AB19-4, suggesting that AB19-4 may recognize cross-species idiotopes. Rabbits immunized with purified AB19-4 generated anti-anti-Id antibodies (Ab3) that reacted specifically with HTLV-IIIB gp120 and the BAT123-binding epitope peptides of HTLV-IIIB and HTLV-IIIMN. The Ab3 bound to H9 cells infected by HTLV-IIIB or HTLV-IIIMN and inhibited the infection of CEM cells by HTLV-IIIB or HTLV-IIIMN, whereas BAT123 also bound H9 cells infected by HTLV-IIIB or HTLV-IIIMN but neutralized only HTLV-IIIB. Our data suggest that AB19-4 mimics the neutralization site on HIV-1 gp120 defined by BAT123. The induction of immunity to HIV using internal-image Ab2 to HIV-neutralizing antibodies may provide a viable approach for developing effective vaccines for AIDS.

Monoclonal antibodies specific for human IgE-producing B cells: a potential therapeutic for IgE-mediated allergic diseases

Monoclonal antibodies (MAbs) specific for surface antigens of lymphocytes are being used to target and deplete tumorous or normal lymphocytes in vivo. Here, we report evidence for the existence of antigenic epitopes on IgE that are accessible on IgE-secreting B cells but not on other cells bearing IgE. Among 42 murine MAbs specific for human IgE, two were shown by fluorescence flow cytometric analyses to bind to IgE-secreting cell lines but not to IgE bound to high-affinity IgE.Fc receptors (Fc epsilon RI) on basophils or low-affinity IgE receptors (Fc epsilon RII) on other cell types. Neither could they induce histamine release from basophils of various donors even under very permissive conditions. These antibodies may be useful for targeting IgE-secreting B cells in patients suffering from IgE-mediated allergies.

Preliminary crystallographic analysis of the Fab fragment of an antibody against HIV gp120

Single crystals of the Fab fragment of a murine monoclonal antibody BAT123 (IgG1, kappa) raised against a dominant neutralizing determinant of gp120 of HIV that are suitable for X-ray structural analysis have been obtained. The thick prismatic plate crystals belong to space group P2(1)2(1)2 with unit cell dimensions of a = 177.42 A, b = 37.36 A and c = 73.30 A.

Immunoconjugates that neutralize HIV virions kill T cells infected with diverse strains of HIV-1

Two murine monoclonal antibodies, G3.519, recognizing the CD4-binding region, and BAT123, a variable region of gp120 of human immunodeficiency virus, were chemically coupled to pokeweed antiviral protein isolated from seeds (PAP-S). The immunoconjugates were purified by Sephacryl S-200 gel filtration and Mono S ion exchange chromatography. Immunoconjugate G3.519-PAP-S specifically killed human T cells, H9, infected with three diverse HIV-1 strains, HTLV-IIIB, -IIIMN, and -IIIRF. Inhibition of thymidine incorporation by the immunoconjugate was concentration-dependent, with the ID50 ranging from 1.4 x 10(-10) M to 1.7 x 10(-9) M. Immunoconjugate BAT123-PAP-S was effective in killing H9 cells infected with HTLV-IIIB (ID50 = 4.3 x 10(-11) M) and -IIIMN (ID50 = 4.7 x 10(-10) M), but not -IIIRF. Both immunoconjugates did not inhibit thymidine incorporation in uninfected H9 cells up to a concentration of 5.3 x 10(-8) M, and their cytotoxic activities could be competitively blocked by the respective unconjugated antibodies. The immunoconjugates retained the ability to neutralize HIV virions to infect T cells and to prevent the syncytium formation. These in vitro studies suggest that the use of immunoconjugates capable of killing HIV-infected T cells and neutralizing virus may provide an alternative treatment for HIV-infected persons.

Immunoconjugates that neutralize HIV virions kill T cells infected with diverse strains of HIV-1

Two murine monoclonal antibodies, G3.519, recognizing the CD4-binding region, and BAT123, a variable region of gp120 of human immunodeficiency virus, were chemically coupled to pokeweed antiviral protein isolated from seeds (PAP-S). The immunoconjugates were purified by Sephacryl S-200 gel filtration and Mono S ion exchange chromatography. Immunoconjugate G3.519-PAP-S specifically killed human T cells, H9, infected with three diverse HIV-1 strains, HTLV-IIIB, -IIIMN, and -IIIRF. Inhibition of thymidine incorporation by the immunoconjugate was concentration-dependent, with the ID50 ranging from 1.4 x 10(-10) M to 1.7 x 10(-9) M. Immunoconjugate BAT123-PAP-S was effective in killing H9 cells infected with HTLV-IIIB (ID50 = 4.3 x 10(-11) M) and -IIIMN (ID50 = 4.7 x 10(-10) M), but not -IIIRF. Both immunoconjugates did not inhibit thymidine incorporation in uninfected H9 cells up to a concentration of 5.3 x 10(-8) M, and their cytotoxic activities could be competitively blocked by the respective unconjugated antibodies. The immunoconjugates retained the ability to neutralize HIV virions to infect T cells and to prevent the syncytium formation. These in vitro studies suggest that the use of immunoconjugates capable of killing HIV-infected T cells and neutralizing virus may provide an alternative treatment for HIV-infected persons.

Effect of bismuth subsalicylate on Clostridium difficile colitis in hamsters

The therapeutic effect of bismuth subsalicylate (BSS, Pepto-Bismol) in Clostridium difficile colitis was studied in golden Syrian hamsters. C. difficile was fed to the hamsters by orogastric intubation 2-3 days after their arrival. Clindamycin (1.5 mg per animal) was given intraperitoneally 4 days later. Twenty-four hours after challenge with clindamycin, animals were given BSS at dosages of 5, 10, and 15 mg twice daily for 5 days by orogastric intubation. Controls included untreated animals and those given 5 mg of vancomycin once daily by intubation. Delay in the time of death was observed in all BSS-treated animals and was statistically significant on days 4-6 in those receiving 15 mg twice daily. Vancomycin produced a greater delay in death than did BSS. Our study suggests that BSS at a dosage of 15 mg twice daily has some therapeutic effect on C. difficile colitis in hamsters.

A chimeric mouse-human antibody that retains specificity for HIV gp120 and mediates the lysis of HIV-infected cells

Murine mAb BAT123, which was made against the envelope glycoprotein gp120 of HTLV-IIIB strain of HIV type 1 (HIV-1), is capable of neutralizing HTLV-IIIB in vitro. It also inhibits the fusion between uninfected CD4+ cells and HIV-1-infected cells to form syncytia. As a step to explore the potential utility of the anti-HIV antibody in vivo, we have constructed a mouse-human chimeric antibody by rDNA techniques. The chimeric antibody, which bears the variable domains of mouse antibody BAT123 and constant domains Cr1 and C kappa of human Ig retains the Ag specificity of BAT123 as determined by its reactivity with HIV-1-infected H9 cells, gp120 in Western blot analysis, and the oligopeptide recognized by BAT123. The antiviral activities of the chimeric antibody in neutralizing HIV-1 infection as well as inhibiting the syncytia formation are also found identical to those of the parent murine antibody. Moreover, in the presence of human blood mononuclear cells, the chimeric antibody but not BAT123 (mouse IgG1) induces antibody-dependent cellular cytotoxicity. The findings point to the potential usefulness of the chimeric antibody in treating patients infected with HIV-1.

A chimeric mouse-human antibody that retains specificity for HIV gp120 and mediates the lysis of HIV-infected cells

Murine mAb BAT123, which was made against the envelope glycoprotein gp120 of HTLV-IIIB strain of HIV type 1 (HIV-1), is capable of neutralizing HTLV-IIIB in vitro. It also inhibits the fusion between uninfected CD4+ cells and HIV-1-infected cells to form syncytia. As a step to explore the potential utility of the anti-HIV antibody in vivo, we have constructed a mouse-human chimeric antibody by rDNA techniques. The chimeric antibody, which bears the variable domains of mouse antibody BAT123 and constant domains Cr1 and C kappa of human Ig retains the Ag specificity of BAT123 as determined by its reactivity with HIV-1-infected H9 cells, gp120 in Western blot analysis, and the oligopeptide recognized by BAT123. The antiviral activities of the chimeric antibody in neutralizing HIV-1 infection as well as inhibiting the syncytia formation are also found identical to those of the parent murine antibody. Moreover, in the presence of human blood mononuclear cells, the chimeric antibody but not BAT123 (mouse IgG1) induces antibody-dependent cellular cytotoxicity. The findings point to the potential usefulness of the chimeric antibody in treating patients infected with HIV-1.

Role of human immunodeficiency virus type 1-specific protease in core protein maturation and viral infectivity

It is generally believed that the gag gene product of human immunodeficiency virus type 1 (HIV-1) is processed into several core proteins by a virus-specific protease. We used deletion mutation analysis to study the role of HIV-specific protease in the processing of core proteins and its requirement for viral infectivity. Several mutant genomes with deletions in the protease gene were constructed. A mammalian cell line, COS-M6, transfected with the wild-type viral genome was shown to produce virions containing processed core proteins, while COS-M6 cells transfected with two mutated genomes could express only the core protein precursor, Pr56gag. The wild-type transfectant produced infectious virus; both transfectants expressing the mutated genomes also produced virions, and one of them still retained reverse transcriptase activity. However, the mutant viral particles were devoid of infectivity. Virions with a distinct central core and an electron-dense nucleoid budded out from the plasma membrane of COS-M6 cells transfected with the wild-type genome. In contrast, noninfectious virions that budded either into cytoplasmic vacuoles or out from the plasma membrane of COS-M6 cells transfected with mutant genomes contained ring-shaped nucleoids. These results indicate that the HIV-1 protease plays a role not only in the maturation of the core proteins but also in the assembly of the virus and thus is required for viral infectivity.

Detection and purification of a recombinant human B lymphotropic virus (HHV-6) in the baculovirus expression system by limiting dilution and DNA dot-blot hybridization

A recombinant virus Ac373-HB was detected and purified from the transfection mixture of wild type and recombinant virus in the baculovirus expression system using a combination of limiting dilution and DNA dot-blot hybridization. This method allows for a quick and convenient way of detection and purification of recombinant virus without the need to use a plaque purification step. It is generally applicable to other expression systems besides the baculovirus system described here.

Treatment of Clostridium difficile colitis in hamsters with a lipopeptide antibiotic, LY146032

LY146032, an acidic lipopeptide antibiotic which inhibits the biosynthesis of cell wall peptidoglycan, was found to be effective in delaying death in a hamster model of pseudomembranous colitis. A dose of 0.05 mg/day was effective. The equivalent protection with vancomycin required a dose 100-fold higher, i.e., 5 mg/day.

Effects of feeding lactobacillus GG on lethal irradiation in mice

Mice exposed to 1400 rads of total body irradiation experienced 80%-100% mortality in 2 wk. Bacteremia was demonstrated in all dead animals. Feeding Lactobacillus GG strain reduced Pseudomonas bacteremia and prolonged survival time in animals colonized with this organism. In animals not colonized with Pseudomonas, feeding Lactobacillus GG also produced some reduction in early deaths, and there was less Gram-negative bacteremia in these animals compared with controls.

Expression of human interleukin-2 receptor cDNA in E. coli

cDNAs for human interleukin-2 receptor were recently cloned and sequenced (Leonard et al., 1984, Nature 311, 626-631; Nikaido et al., 1984, Nature 311, 631-635; Cosman et al., Nature 312, 768-771). In the studies reported here, we describe the expression of a cDNA clone for the human interleukin-2 receptor in E. coli using an "open reading frame" expression vector pMR100. The inserted cDNA was expressed in E. coli transformants as a tripartite fusion polypeptide fused to the lambda cI protein at its amino terminus and to beta-galactosidase at its carboxy terminus. We demonstrate that the bacterially produced IL-2 receptor protein can bind to IL-2.

Determination of human T cell activity in response to allogeneic cells and mitogens. An immunochemical assay for gamma-interferon is more sensitive and specific than a proliferation assay

T lymphocytes proliferate and secrete lymphokines in response to allogeneic cells, mitogens and other stimuli. Cell proliferation as measured by [3H]thymidine ([3H]Tdr) incorporation into DNA has been routinely used to determine T cell responses in research and clinical laboratories. We have compared the sensitivity of an immunoradiometric assay (IRMA) for human gamma-interferon (IFN-gamma) (Chang et al., 1984), with that of the conventional [3H]Tdr incorporation assay in the measurement of T cell responses to antigens and mitogens in culture. Peripheral blood mononuclear cells (PBMs) were incubated in the presence and absence of phytohemagglutinin (PHA) or mononuclear cells from another individual for various periods of time. The culture fluids were collected for determining IFN-gamma and the cells were assayed for [3H]Tdr incorporation. Results of measurements were expressed in terms of stimulation indices. Both IFN-gamma secretion and thymidine incorporation were measurable in mixed lymphocyte cultures after incubation for 3 days, and in PHA stimulated culture after 24 h of incubation. The stimulation indices reflecting increased gamma-interferon were found to be more pronounced and more consistent than those of [3H]Tdr incorporation.

Expression of the protein encoded by the 3' open reading frame of human T-cell lymphotropic virus type III in bacteria: demonstration of its immunoreactivity with human sera

The genome of human T-cell lymphotropic virus type III/lymphadenopathy-associated virus (HTLV-III/LAV), the infectious agent etiologically associated with the acquired immunodeficiency syndrome, contains, in addition to the genes for the polymerase, core, and envelope proteins, several open reading frames. To investigate whether the 3' open reading frame (3' orf) located between the envelope gene and the 3' long terminal repeat is a gene expressed in vivo in infected individuals, we inserted a fragment of 3' orf in a prokaryotic expression vector. The protein product synthesized in bacteria was purified and allowed to react with sera from individuals infected with human T-cell lymphotropic virus type III as indicated by seropositivity for other viral proteins. Two-thirds of the sera, regardless of the clinical status of the individuals, reacted with the purified protein indicating that 3' orf is a viral gene the product of which is immunogenic in vivo. A polyclonal rabbit antiserum reacting against the 3' orf gene product was obtained by serial injection of rabbits with the purified bacterial protein. The antiserum recognized a 27-kDa protein in the human T-cell lymphotropic virus type III-infected lymphocytes.