Improved anti-tumor reactivity with monoclonal anti-idiotypic antibody conjugated to syngeneic mouse red blood cells.

An anti-idiotypic (anti-Id) antibody (Ab), by resembling an epitope on an antigenic molecule may serve as a surrogate antigen and induce specific immune reactivity to the natural antigen. Anti-Id Ab are often conjugated to a foreign protein, such as keyhole limpet hemocyanin (KLH) to elicit a stronger response. However, KLH, a potent antigen itself, may provoke unnecessary and undesirable immune reactivity. In this study, syngeneic mouse red blood cells (RBC) were tested as carriers for anti-Id immunization. In a preliminary experiment, BALB/c mice were immunized with normal rat immunoglobulin G (NRIg)-MRBC or NRIg-KLH. Anti-NRIg responses induced by 2-0.2% of NRIg-MRBC (4-0.4 micrograms of NRIg) superseded those induced by NRIg-KLH (50 micrograms of NRIg). Immunization with NRIg-MRBC did not result in autoreactivity against self antigens on autologous RBC. Monoclonal antibody 2F10, which resembles an epitope on mouse mammary tumor virus (MMTV) envelop protein Gp52, was conjugated to MRBC and used as a surrogate antigen for Gp52. Immune sera were tested in cytotoxicity assay against MMT 68H which expresses Gp52. Between 2-4 weeks after the immunization, specific cytotoxic antibodies were detected in mice immunized with 2.0%, 0.2% and 0.02% 2F10-MRBC, with 0.2% 2F10-MRBC being the most effective dose. 2F10 immune sera did not react with autologous RBC. Therefore, MRBC are at least as effective, and may be more effective than KLH as carriers for Ig immunization. Repeated treatment will be feasible since MRBC are not immunogenic.