Moloney leukemia virus-induced cell surface antigen mimicry by monoclonal antibodies.

We have investigated antigen-independent modulation of immune responses by monoclonal antibodies directed against both viral and nonviral antigens. BALB/c mice were immunized with monoclonal IgM (i.e. Ab1) specific for either Moloney murine leukemia virus-induced cell surface antigen (MCSA) or the hapten 2,4-dinitrophenyl (DNP). Injection with either Ab1 activated a functional idiotypic (Id) network as evidenced by production of both anti-Id (Ab2) antibodies and anti-anti-Id (Ab3) antibodies. A subset of induced Ab3 (designated Ab1'), exhibited specificity for antigen (virus or DNP). In mice immunized with anti-Id antibodies (Ab2), production of Ab3 and Ab1' was also observed. In the MCSA system, antibody-induced Ab1' responses were effective in protecting mice from tumor development upon subsequent challenge with live virus. Furthermore, antigen-independent modulation of immunity to both viral and nonviral antigens was found to be thymus-dependent. Similar findings in other viral systems suggest that antibody-induced activation of Id networks may prove a viable alternative vaccine strategy that can elicit antigen-specific responses, and in some cases protection, in the apparent absence of exposure to antigen.

Thymus-dependent network responses to a monoclonal cross-reactive antiidiotypic antibody.

BALB/c mice were inoculated i.p. with a cross-reactive anti-Idiotypic mAb (designated FD5-1) in the absence of Ag or adjuvants. Injection with unmodified FD5-1 resulted in the induction of serum antibodies reactive with both FD5-1 (Ab3) and the hapten DNP (Ab1'). Endpoint titers of the Ab3 response showed an increase in serum IgM, which was dose-responsive to both the number of injections and the amount of FD5-1 antibody injected. The serum IgM Ab3 response was found to be thymus dependent and idiotypically specific for FD5-1. Athymic mice injected with FD5-1 were unable to produce a serum IgM Ab3 response, whereas their euthymic littermates produced strong Ab3 responses. Serum Ab3 responses and Ab1' were detectable only in the IgM isotype; no specific IgG responses were observed. Indeed, IgG recognized by FD5-1 appeared to be suppressed by FD5-1. Injection of mice with FD5-1 modulated serum IgM responses to DNP, (4-hydroxy-3-nitrophenyl)acetyl (NP), 4-ethoxymethylene-2-phenyloxazol-5-one (OX), phosphorylcholine (PC), and alpha 1,3-dextran (DEX) in a thymus-dependent manner. FD5-1 injection induced IgM responses against DNP, (4-hydroxy-3-nitrophenyl)acetyl (NP), 4-ethoxymethylene-2-phenyloxazol-5-one, and DEX but decreased IgM binding to PC. No detectable Ab1' responses to any of the aforementioned molecules were found when the same sera were probed for IgG. The specificity of serum Ab1' from FD5-1-injected mice was evaluated by antigenic inhibition. Binding of serum Ab1' to DNP-BSA was inhibitable by DNP-lysine, whereas equivalent concentrations of lysine alone had no inhibitory effect. The antigenic specificity of IgM from normal serum binding to PC-BSA was demonstrated by inhibition with free PC, and the binding of Ab1' from FD5-1-injected mice to DEX-coated plates was shown to be inhibitable by DEX. We have described in vivo network perturbation in adult BALB/c mice injected with anti-Id antibody in the absence of Ag or adjuvants. Our findings show that injection of the cross-reactive anti-Id FD5-1 can induce thymus-dependent Ag-specific responses. In two systems where FD5-1 functions as an anti-anti-anti-Id antibody (PC and DEX), thymus-dependent responses were also observed. FD5-1 injection suppressed antibodies binding to PC, whereas DEX-specific responses were induced.

Thymus-dependent antiidiotype and anti-antiidiotype responses to a dinitrophenyl-specific monoclonal antibody.

BALB/c mice were inoculated i.p. with graded doses of a DNP-specific, IgM mAb (designated 57.1). Injection with unmodified 57.1 in the absence of adjuvants resulted in the generation of an anti-Id response (Ab2) and an anti-anti-Id response (Ab3). The generation of serum anti-Id antibodies was found to be thymus dependent. Nude mice immunized with 57.1 were unable to produce a serum Ab2 response above nonimmunized controls whereas euthymic mice receiving identical doses of 57.1 produced strong Ab2 responses. To examine the specificity of serum anti-Id, sera from mice receiving 57.1 were screened against a panel of mAb representing at least five distinct VH gene families. Serum titers were significantly higher against 57.1 than against any of the other antibodies in the panel. Three of the antibodies in this panel bind FD5-1, a monoclonal anti-Id (Ab2) that also binds 57.1. However, sera from mice receiving 57.1 bound 57.1 only. Thus, the serum Ab2 response appears to be highly specific for idiotopes on 57.1. The predominant isotype of these anti-Id antibodies was IgG1. The number of isotypes detected increased in a dose dependent manner with all IgG subclasses having anti-Id specificity in sera from animals receiving the higher doses of 57.1. Further analysis of the serum demonstrated that approximately 8% of the Ab2 response was paratope-specific (inhibitable by the monovalent hapten DNP-lysine). The same sera were analyzed for the presence of Ab3 by binding to the monoclonal anti-Id antibody FD5-1. Lower serum titers of Ab3 were generated in comparison to serum titers of Ab2. Analysis of the binding specificity of the Ab3 response revealed that DNP-BSA was able to partially inhibit the binding of serum IgM and IgG Ab3 to FD5-1. A subset of the Ab3 response. Ab1' that is specific for DNP was observed in a direct binding assay where detectable amounts of DNP binding IgM, IgG1, and IgG3 isotypes were present. We have thus described a complete circuit (Ab1----Ab2----Ab3) of antibodies within the Id network by immunizing animals with an unmodified mAb in the absence of Ag or adjuvants.

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.