CD16A Shedding Regulates Innate Cell Engager-Induced Serial Killing by Natural Killer Cells

Natural killer (NK) cells can protect from tumor-transformed cells using a fine-tuned machinery of activating and inhibiting receptors. An important activating receptor is Fc gamma receptor IIIa (FcγRIIIA or CD16A), which can trigger antibody-dependent cellular cytotoxicity (ADCC) when recognizing antibody-opsonized target cells. One strategy to boost ADCC responses may be achieved by inhibiting activation-induced shedding of CD16A from the NK cell surface. However, previous preclinical studies have shown contrasting results regarding the effectiveness and limitations of this approach. Here, microchip-based live cell-imaging was used to assess the consequences of CD16A shedding inhibition on the dynamics of NK cell cytotoxicity. The bispecific innate cell engager acimtamig (AFM13) was superior to IgG1 monoclonal antibodies in ADCC and in increasing the fraction of cytotoxic NK cells and serial killers. Under conditions where CD16A shedding was inhibited, acimtamig still triggered ADCC; however, the ability to promote serial killing was reduced and associated with impaired NK cell detachment from target cells. These results demonstrate that CD16A shedding represents an intrinsic feature of NK cell biology that is critical to sustain the antitumoral cytotoxicity of NK cells. This has implications for CD16A engineering of NK cell products and their combination with CD16A-directed NK cell engagers.