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.