VIF-Ig: a novel fc framework for ADCC by incorporation of VHH unit

Antibody-dependent cellular cytotoxicity is a key mechanism for antibody-based therapeutics, and current engineering strategies to enhance ADCC primarily rely on two approaches: Fc mutations to improve the antibody's intrinsic CD16a affinity, or the fusion of binding-modules targeting NK cell receptors. The former often compromises antibody stability and induces CD16a downregulation; the latter occupies sites critical for target association and limits the assembly of multi-specific therapeutics. Here, we introduce a novel Fc engineering approach wherein the CH2 domain of the Fc region is replaced with an anti-NKp46 VHH named VIF-Ig. It has been reported that NKp46 expression remains unaltered after NK cell activation across various tumor microenvironments, addressing a key limitation of CD16a-dependent strategies. The novel molecules exhibit potent ADCC, high thermal stability, and retain FcRn binding for favorable pharmacokinetic profiles. Furthermore, we demonstrate that VIF-Ig can accommodate VHHs to target various epitopes. Thus, this versatile modular platform is suitable for developing next-generation NK cell or even other cell engagers with enhanced efficacy and tunable specificity, especially for emerging multi-specific immune cell engagers.