The immunogenicity of antibody aggregates in a novel transgenic mouse model

Protein aggregates have been discussed as a potential risk factor related to immunogenicity. Here we developed a novel human IgG transgenic (tg) mouse system expressing a mini-repertoire of human IgG1 antibodies (Abs) for the assessment of immunogenic properties of human mAb preparations.

Transgenic mice were generated using germline versions of the human Ig heavy chain γ1 (IgH-γ1), and the human Ig light chain (IgL) κ and λ genes. Only the soluble form of human IgH-γ1 was used to avoid expression of the membrane Ig-H chain and concomitant allelic exclusion of endogenous murine Ig genes. IgG1 aggregates were generated by different stress conditions such as process-related, low pH and exposure to artificial light.

The expression of human Ig proteins induced immunological tolerance to a broad range of human IgG1 molecules in the tg mice. Immunization with IgG1 aggregates demonstrated that soluble oligomers induced by significant light-exposure and carrying neo-epitopes induced a strong immune response in tg mice. In contrast, Ab aggregates alone and monomers with neo-epitopes were not immunogenic.

This mouse model is able to recognize immunogenic modifications of human IgG1. While the degree of stress-induced aggregation varies for different mAbs, our findings using a particular mAb (mAb1) demonstrate that non-covalently modified aggregates do not break tolerance, contrary to widely held opinion. The immunogenic potential of soluble aggregates of human IgG strongly depends on the presence of neo-epitopes resulting from harsh stress conditions, i.e. extensive exposure to artificial light.