Dissecting the Efficacy and Immunogenicity of TLR7 Agonist–Antibody Conjugates through the Lens of Fc Effector Function, Conjugation Strategies, and Linker Cleavability

The advent of immuno-oncology therapeutics has given rise to antibody-drug conjugates (ADC) designed to selectively activate pattern recognition receptors such as Toll-Like Receptors (TLRs). In contrast to classical ADC technology, these Immune Stimulating Antibody Conjugates (ISACs) are widely reported to rely on Fcγ-mediated uptake and noncleavable linkers. Herein, we systematically study the impact of Fc effector function, linker cleavability, and conjugation strategy on the efficacy and immunogenicity of a series of TLR7 agonist-based ISACs. We demonstrate that the combination of FcγR-ablation and incorporation of a cleavable linker results in increased stimulation of myeloid cells, enhanced efficacy, and improved tolerability as compared to traditional ISAC designs. Interestingly, we found that all ISAC designs exhibited evidence of antidrug-antibody (ADA) induction. We found that the combination of a cleavable linker, a highly permeable TLR7 agonist payload, and ablation of FcγR binding results in ISACs that exhibit particularly favorable properties for continued development.