Monoclonal IgM antibodies that inhibit primary Moloney murine sarcoma growth.

Monoclonal IgM antibodies with specificity for Moloney murine sarcoma virus (M-MuSV)-Moloney murine leukemia virus (M-MuLV) from two hybridoma clones have been isolated and characterized. The monoclonal antibodies have specificity for a cytoplasmic and cell surface Friend-Moloney-Rauscher group-specific antigen. Immunoelectron microscopy revealed antibody binding to the surface of virus-expressing cells but not to the budding virus particles. Treatment of M-MuSV-injected mice with monoclonal IgM anti-M-MuSV significantly inhibited tumor growth compared to virus-inoculated animals receiving either saline or MOPC 104E. Nude mice exhibited delayed tumor induction following treatment with the monoclonal antibodies but ultimately died from tumor growth. Virus-injected euthymic mice that were treated with monoclonal IgM anti-M-MuSV generated a potentiated spleen cell-mediated cytotoxicity against Moloney sarcoma cells compared to virus-infected treated with saline. This potentiation of cytotoxicity remained after trypsinization of the spleen cells and thus was probably not due to passively adsorbed monoclonal antibody. The antibodies alone or in the presence of complement did not neutralize M-MuLV. The IgM antibodies induced specific tumor cell cytotoxicity in vitro mediated by complement spleen cells, lymph node cells, or thymus cells. In conclusion, two monoclonal IgM anti-M-MuSV antibodies that bind to the tumor cell surface did not neutralize virus can inhibit primary M-MuSV-induced tumor growth in vivo. The regression event appeared to involve heterogeneous mechanisms. Complete regression remained thymus dependent even with passive antibody therapy, but significant tumor growth inhibition was produced independent of T-cells. In vitro these IgM antibodies induced complement and cell-mediated cytotoxicity.

Effects of DNA synthesis inhibitors on early antigen expression following primary infection or superinfection by Epstein-Barr virus.

Seven lymphoid cell lines previously characterized with respect to their resident Epstein-Barr virus (EBV) genome content were infected or superinfected with concentrated EBV from supernatant of the P3HR-1 cell line. Immunofluorescence assays were conducted on smears 48 hours after infection, using human sera containing antibodies to EBV early antigen (EA). Two EBV nuclear antigen (EBNA) negative cell lines containing no detectable resident EBV DNA and five EBNA positive cell lines containing EBV genomes were tested. The cell lines did not spontaneously express EBV EA (i.e., they were non-producers). All cell lines responded to infection or superinfection with EBV by expressing EA. Treatment of the cell lines with arabinosylcytosine (Ara-C) 10 micrograms/ml, at the time of infection resulted in significant decreases in the number of cells expressing detectable EA after drug treatment in all cell lines (72 +/- 5 percent inhibition of EA expression). Experiments were also conducted with hydroxyurea (HU) and phosphonoacetic acid (PAA). It was found that treatment with HU (100 micrograms/ml) inhibited EA production in cell lines containing EBV genome copies by 81 percent as compared to the superinfected cultures receiving no drug. In primary infection of EBNA negative cell lines, HU had minimal effects. PAA (100 micrograms/ml), on the other hand, had very little effect on EA expression following superinfection of cell lines harboring the EBV genome, but reduced the EA expression after primary infection of EBNA negative cell lines by 70 to 80 percent. All drugs were used at concentrations having little effect on RNA and protein synthesis. However, HU and Ara-C significantly reduced DNA synthesis and cell division in the treated cultures.

Complementation between infecting Epstein-Barr virus and intrinsic viral genomes in human lymphoid cell lines.

13 human lymphoid cell lines previously characterized in terms of their intrinsic Epstein-Barr virus (EBV) genome content were infected or superinfected with EBV from the supernatant of P3HR-1 cells. The cell lines included 2 lymphoma cell lines that contain no detectable EBV genomes and 11 cell lines containing intrinsic EBV genomes. All the cell lines responded to EBV infection by expressing early antigen (EA). The number of EA-positive cells in the cultures was proportional to the viral concentration used for infection or superinfection. However, cell lines containing multiple intrinsic EBV genomes expressed higher amounts of EA-positive cells. Evaluation of EA expression versus the number of intrinsic EBV genome copies per cell in each line revealed EA to increase as the intrinsic EBV genome content of the cell lines increased in a nonlinear curve that was described by an exponential logistic function. The coefficient of determination R2 for this curve was greater than 0.9 for multiple experiments. The data suggest that 80-90% of the virus in P3HR-1 is defective and requires intrinsic viral genomes for expression of EA. Transactivation or complementation between intrinsic EBV genomes and infecting virus is supported by these observations.