Generation of a human IgG3-streptavidin fusion protein. Implications for the inhibition and elimination of auto-reactive B cells.

Antibodies against self-molecules play a significant role in the development and progression of Systemic Lupus Erythematosus, as well as a number of other autoimmune disorders. Immunosuppressive drugs have been used to control this process. However, they are normally not specific to the offending cell, and can actually suppress beneficial immune responses to pathogens. In this paper a genetically engineered targeting molecule is described, which has the capacity to target antigen-specific B cells for inhibition or elimination. The targeting molecule is a fusion of streptavidin subunit to the constant region of human IgG3 (IgG3-Av). It is demonstrated by ELISA and flow cytometry that IgG3-Av binds biotinylated antigen as well as human Fc gamma receptors present on myeloid cells. It is also shown by confocal microscopy and flow cytometry, that IgG3-Av can mediate Fc receptor-dependent phagocytosis of latex microspheres adsorbed with biotinylated antigen. Furthermore, the IgG3-Av construct can modulate Ca++ flux, characteristic of B cell inhibition as well as ADCC of B cells in an antigen-specific manner. In summary, these studies describe an approach, which has the potential to be used as a treatment to inhibit or remove antigen-specific (auto-reactive) B cells.