A BISPECIFIC MOLECULE TARGETING CD40 AND TUMOR ANTIGEN MESOTHELIN ENHANCES TUMOR-SPECIFIC IMMUNITY

Agonistic CD40 monoclonal antibodies (mAbs) have demonstrated some clinical activity, but with dose-limiting toxicity. To reduce systemic toxicity, we developed a bispecific molecule that was maximally active in the presence of a tumor antigen and had limited activity in the absence of the tumor antigen. LB-1 is a bispecific molecule containing single-chain Fv domains targeting mouse CD40 and the tumor antigen mesothelin. LB-1 exhibited enhanced activity upon binding to cell surface mesothelin but was less potent in the absence of mesothelin binding. In a mouse model implanted with syngeneic 4T1 tumors expressing cell surface mesothelin, LB-1 demonstrated comparable antitumor activity as an agonistic CD40 mAb but did not cause elevation of serum cytokines and liver enzymes as was observed in anti-CD40-treated mice. The results from our study of LB-1 were used to develop a human cross-reactive bispecific molecule (ABBV-428) that targeted human CD40 and mesothelin. ABBV-428 demonstrated enhanced activation of antigen-presenting cells and T cells upon binding to cell surface mesothelin, and inhibition of cultured or implanted PC3 tumor cell growth after immune activation. Although expression of cell surface mesothelin is necessary, the bispecific molecules induced immune-mediated antitumor activity against both mesothelin+ and mesothelin- tumor cells. ABBV-428 represents a class of bispecific molecules with conditional activity dependent on the binding of a tumor specific antigen, and such activity could potentially maximize antitumor potency while limiting systemic toxicity in clinical studies.