FcγRIIIa Expression Is Not Increased on Natural Killer Cells Expressing the FcγRIIIa-158V Allotype

Abstract

The presence of a valine (V) versus a phenylanaline (F) at position 158 of Fc;RIIIa/CD16a improves the affinity for IgG and is associated with higher therapeutic response to rituximab. Increased CD16 expression on natural killer (NK) cells from donors with the VV or VF versus FF genotype has recently been reported. We indeed observed higher binding of the anti-CD16 monoclonal antibody (mAb) 3G8 on NK cells from V carriers (VV = VF > FF). However, the binding of two other anti-CD16 mAbs, LNK16 and DJ130c, decreased with the number of V allele (VV < VF < FF). CD16 transcript levels were independent on the genotype. Rituximab binding to NK cells from V carriers was higher than its binding to FF NK cells at low concentrations (10 and 100 Mg/mL). However, the difference was nearly completely abolished at saturating concentrations (z1,000 Mg/mL). Finally, nearly 100% of CD16-expressing NK cells displayed a complete down-modulation of the receptor after optimal engagement by plate-bound 3G8, whatever the genotype. By contrast, the percentages of NK cells downmodulating CD16 after competitive engagement of the receptor by plate-bound rituximab increased with the number of V allele (FF, 18.2 F 8.6%; VF, 32.0 F 4.9%; and VV, 42.4 F 9.9%). These results are in discrepancy with the expected increased competition that would result from an increased expression of CD16 on VV and VF NK cells. We conclude that increased binding and functional and clinical responses associated with the high-affinity Fc;RIIIa-158V are unrelated to an increased expression of this allotype. [Cancer Res 2008;68(4):976-80]

ADAM17-Mediated Shedding of FcγRIIIA on Human NK Cells: Identification of the Cleavage Site and Relationship with Activation

“…We and others have previously shown that NK cell FcgRIIIA is downmodulated after incubation with the anti-CD16 mAb 3G8 (3,4) or the Fc portion of rituximab (4,6). Such modulation may result from shedding and/or internalization.…”

“…PBMCs, NK cells, JY cells, NKL cells, and CD16/g-transduced T cells were isolated and/or cultured as previously described (1,4,24,25).…”

“…Shedding is a mechanism for irreversible removal of many transmembrane cell-surface molecules. FcgRIIIA/CD16A is shed upon FcgRIIIA/CD16A-dependent activation of CD56 dim NK cells by anti-CD16 mAb (3,4), a condition in which reversible removal of FcgRIIIA/CD16A resulting from internalization has also been described (5), or by the Fc portion of rituximab (4,6), as well as upon FcgRIIIA/CD16A-independent activation by K562 cells (7) or by phorbol esters such as PMA (2). The identification of the main enzyme involved in the shedding of FcgRIIIA/CD16A represents a critical step toward understanding how FcgRIIIA/ CD16A-dependent functions are regulated.…”

Generation of BiKEs and TriKEs to Improve NK Cell-Mediated Targeting of Tumor Cells

“…Binding affinity appears to be an important component of ADCC. This impression is supported by increased rituximab-driven cytotoxicity of B cell tumors mediated by NK cells containing the CD16A-158VV or VF allotypes which, when compared to the CD16A-158FF allotype, display decreased affinity for the Fc portions of antibodies [30]. Therefore, BiKEs and TriKEs might improve NK cell function by generating a stronger interaction through binding with anti-CD16 than that produced by binding of CD16 to the natural Fc portion of antibodies.…”

Restricted processing of CD16a/Fc γ receptor IIIa N-glycans from primary human NK cells impacts structure and function

“…In-vitro binding studies demonstrated the less common CD16a V158 allotype binds IgG1 with ~5 fold greater affinity compared to CD16a F158 (5). Furthermore, increased binding leads to an increased NK cell response and increased ADCC (6)(7)(8)(9). Current advances in mAb therapy are targeting optimization of NK cell ADCC activity by Fc glycoengineering to improve CD16a binding (4).…”