Specific immunosuppression of human anti-murine antibody responses in hu-PBL-SCID mice

Severe combined immunodeficient (SCID) mice were reconstituted with normal human peripheral blood leukocytes (PBLs) and were shown to produce a human anti-mouse immunoglobulin antibody response on immunization with heat-treated murine monoclonal IgG1 antibody to ovalbumin, referred to as ha-Mab-2. The human anti-mouse antibody response was proportional to the number of B cells and mononuclear cells transferred from a given batch of PBL. However, pretreatment of hu-PBL-SCID mice with a tolerogenic covalent conjugate of monomethoxypolyethylene glycol (mPEG) and Mab-2 suppressed this response on subsequent injections of ha-Mab-2, and this suppression was shown to be antigen-specific, i.e., it did not suppress the antibody response to ovalbumin and did not affect the level of production of human immunoglobulin of hu-PBL-SCID mice. The suppression was due to the generation of human suppressor CD8⁺ T (Ts) cells, which down regulated CD4⁺ helper T cells in an antigen and HLA class I specific manner, i.e., these findings were in accord with the previously shown immunosuppressive effect of tolerogenic mPEG conjugates in normal mice.