FCGR3A and cancer: ELISA was performed to verify the binding activityof the Fc region to the CD16a known as FcγRIIIa, expressed onmast cells, macrophages, and natural killer cells, which activatesantibody-dependent cellular cytotoxicity (ADCC),42 eventually leading to the elimination of primary leukemiccells, cancer cell lines, and cells infected with hepatitis B virus.43 In this study, we determined the binding affinityof anti-HER2 VHH-FcK to CD16a, one of the Fc gamma receptors (FcγRIIIa),and compared it with that of Trastuzumab, using ELISA analysis (Figure 5a).