A novel CD16A-nanobody platform overcomes Fc polymorphism limitations for potent and broad-spectrum NK cell engager therapeutics

CD16A (FcgammaRIIIA) is the key activating receptor on natural killer (NK) cells mediating antibody-dependent cellular cytotoxicity (ADCC), an important mechanism for therapeutic antibodies to eliminate tumor cells. Both IgG1-Fc and low-fucose Fc formats exhibit poor affinity for the common CD16A-158F allele, found in ~85% of the population, creating a major barrier to broad and potent NK cell-mediated tumor killing. CD16A-based NK cell engagers overcome this limitation by directly bridging NK cells to tumor antigens with high-affinity CD16A-binding domains, enabling potent, Fc-independent ADCC. Here, we present an optimized NK engager platform incorporating a proprietary CD16A nanobody in an optimized antibody format. This platform demonstrates superior in vitro and in vivo efficacy compared to low-fucose Fc-enhanced formats across multiple programs, including PD-L1/CD16A bispecific and CDH17/EGFR/CD16A trispecific antibodies. The B117-1 antibody format achieves 50-100-fold higher CD16A avidity, with strong binding to both CD16A-158V and CD16A-158F alleles. In contrast, amivantamab, despite its low-fucose Fc enhancement, exhibits significantly weaker ADCC activity in donors carrying CD16A-158F alleles. Extensive format screening revealed that NK cell activation is heavily influenced by the spatial distance between the tumor antigen-binding Fab and the anti-CD16A nanobody: longer distance impairs the bulky CD45 phosphatase exclusion from the immunological synapse, leading to significantly reduced cytotoxicity. Consequently, the widely adopted Morrison-type antibody consistently underperformed compared to architectures with shorter CD16A-TAA-Fab spacing. Immunogenicity assessment in PBMCs from 45 HLA-diverse healthy donors showed low anti-drug antibody (ADA) rates for IBI3019, which incorporates the CD16A nanobody platform. The ADA rate is comparable to that of trastuzumab and significantly lower than atezolizumab. The CD16A nanobody integrates seamlessly into the antibody architecture, offering superior stability over scFv formats and straightforward CMC manufacturing akin to standard bispecifics, without specialized glycoengineering or licensing. This versatile, high-performance platform exemplifies the next-generation NK cell engagers, delivering broad patient coverage and superior therapeutic potential.