Factor VIII light chain domains of recombinant Factor VIII Fc fusion protein impact Fc effector function and CD16+ NK cell activation

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Presentation Time: 03:15 PM - 04:30 PM
Poster Board Number: B858
Abstract ID: 4402

Presenting Author:
Basil Golding , Office Director at FDA, Center for Biologics Eval. and Research (CBER)

Abstract:

Recombinant Factor VIII-Fc fusion protein (rFVIIIFc) is an enhanced half-life therapeutic protein used for the management of hemophilia A. Recent studies demonstrated that rFVIIIFc interacts with Fc gamma receptors (FcγR) resulting in the activation or inhibition of FcγR-expressing immune cells. We demonstrated that rFVIIIFc activates natural killer (NK) cells via Fc-mediated interactions with CD16, which can lead to the lysis of an anti-FVIII B cell clone. Here, we used human NK cell lines and primary NK cells to study the role of the FVIII moiety in rFVIIIFc-mediated NK cell activation. Activation of NK cells with rFVIIIFc was probed at the molecular level, using antibodies against FVIII, Fc, or CD16. Besides the Fc-CD16 interaction, we identified the FVIII light chain as playing a key role in the activation of CD16+ NK cells by rFVIIIFc. The use of antibodies that are FVIII domain-specific demonstrated that blocking FVIII C1 or C2 domains, unlike blocking of FVIII heavy chain, inhibited rFVIIIFc-mediated CD16+ NK cell activation. We therefore propose that FVIII light chain-mediated membrane binding results in tethering of the fusion protein to the cell surface and allows for Fc-CD16 interactions to proceed, resulting in NK cellular activation. These findings suggest that novel Fc fusion proteins with the C1/C2 domains of FVIII light chain and relevant ligand can potentially be designed to target and promote lysis of unwanted B cells or cancer cells.