Development of a Tumor-Specific Multivalent CD40 Agonist Antibody FAPxCD40 for Cancer Therapy: Balancing Efficacy and Toxicity.

CD40 agonist antibodies are reported to augment tumor antigen presentation and have shown potential antitumor efficacy in clinical trials. Nevertheless, the limited efficacy and on-target, off-tumor toxicity restrict the further development of these antibodies. We hypothesize that the toxicity could be overcome by activating CD40 specifically through tumor-specific antigens. Additionally, limited efficacy can be improved through the strategic construction of CD40 bispecific antibodies (bsAb) to refine the degree of CD40 clustering. Therefore, we developed anti-FAPxCD40 bsAbs with varying valences of anti-CD40 moieties, including bivalent FAPxCD40-2, tetravalent FAPxCD40-4, and hexavalent FAPxCD40-6. The tetravalent design of FAPxCD40-4 led to efficient activation of antigen-presenting cells and T-cell priming in the presence of FAP. The antitumor activity and toxicity of FAPxCD40-4 were tested in the CD40-humanized mFAP-MC38 xenograft model. Compared with non-tumor-targeting CD40 agonist or bivalent bsAbs, FAPxCD40-4 displayed potent antitumor activity and negligible toxicity at low doses, indicating an ideal therapeutic window. Our results demonstrated that the valences of the anti-CD40 moieties in bsAbs can be modulated to optimize CD40 activation and enlarge the therapeutic window of this type of molecules.