Immunotherapy Targeting Inhibitory Fcγ Receptor IIB (CD32b) in the Mouse Is Limited by Monoclonal Antibody Consumption and Receptor Internalization

Abstract

Genetic deficiency of the inhibitory Fc receptor, FcγRIIB (CD32b), has been shown to augment the activity of activatory FcγR and promote mAb immunotherapy. To investigate whether mAbs capable of blocking FcγRIIB have similar capacity, we recently generated a panel of specific anti-mouse FcγRIIB mAbs that do not cross-react with other FcRs, allowing us to study the potential of FcγRIIB as a therapeutic target. Previous work revealed a number of these mAbs capable of eliciting programmed cell death of targets, and in the present study we demonstrated their ability to promote target cell phagocytosis. However, in a variety of murine tumor models, anti-FcγRIIB mAbs demonstrated limited therapeutic activity despite optimized treatment regimens. Unexpectedly, we observed that the anti-FcγRIIB mAbs are rapidly and extensively consumed in vivo, both by the tumor and host cells, including B cells, leading to a precipitous loss from the circulation. Closer analysis revealed that the anti-FcγRIIB mAbs become extensively internalized from the cell surface within 24 h in vivo, likely explaining their suboptimal efficacy. Subsequent studies revealed that anti-FcγRIIB mAb immunotherapy was effective when used against FcγRIIB+ tumors in FcγRIIB−/− recipients, indicating that consumption of the mAb by nontumor cells is the primary limitation of these reagents. Importantly, similar rates of internalization were not seen on human target cells, at least in vitro. These studies further highlight the need to determine the propensity of mAb therapeutics to internalize target receptors and also identify potential key differences between human and mouse cells in this respect.

Antagonistic Human FcγRIIB (CD32B) Antibodies Have Anti-Tumor Activity and Overcome Resistance to Antibody Therapy In Vivo

“…We previously explored an equivalent panel of mFcgRII-specific mAbs (Williams et al, 2012) and observed that they had limited therapeutic benefit due to their rapid consumption in vivo (Williams et al, 2013b). Similar rates of internalization were not seen on human target cells, at least in vitro, in agreement with earlier studies (Rankin et al, 2006).…”

Development and Characterization of Monoclonal Antibodies Specific for Mouse and Human Fcγ Receptors

“…A panel of validated reagents is extremely valuable in assessing the importance of individual FcgR expression levels in diseases in which they are proposed to be modulated. We recently demonstrated that expression of the inhibitory hFcgRIIB accelerates the internalization of rituximab (42) and other mAb (43) from the surface of B cells in a dose-dependent manner that limits their therapeutic efficacy (42,(44)(45)(46). A careful assessment of hFcgRIIB levels in the blood of patients receiving a therapeutic mAb may be an important biomarker of prognostic value.…”

Effect of trastuzumab interchain disulfide bond cleavage on Fcγ receptor binding and antibody-dependent tumour cell phagocytosis

“…ADCP with THP-1 cells and rituximab was also blocked with anti-FcgRI and anti-FcgRII mAbs but not with an anti-FcgRIII mAb (25). THP-1 cells express FcgRIIB as well as FcgRIIA (26), and FcgRIIB inhibits FcgRIA/IIA-mediated phagocytosis (27). However, it is unknown how the inhibitory FcgRIIB is involved in our ADCP system as compared with FcgRIA and FcgRIIA.…”