Generation of tumor-targeted antibody–CpG conjugates

A number of monoclonal antibodies against tumor-associated antigens have been developed for the treatment of cancer. The anti-tumor effects of such antibodies can be enhanced by conjugation to immune stimulatory ligands, such as the toll-like receptor 9 agonist CpG oligodeoxynucleotides (CpG). The present study describes methods for the conjugation of CpG to two clinically approved monoclonal antibodies (rituximab and trastuzumab) via a Sulfo-EMCS maleimide linker. This conjugation method yielded stable joining of CpG and antibody (molar range 2.2–4.3:1). Immunofluorescence studies showed intact antigen-specific antibody binding of the immunoconjugates, that were comparable to unmodified antibody. Furthermore, antibody–CpG conjugates demonstrated improved (rituximab) or equivalent (trastuzumab) immune stimulatory activity compared to free CpG in vitro. These studies demonstrate the feasibility of antibody–CpG immunoconjugates and provide the foundation for future in vivo immunotherapy evaluation.