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.</jats:p

Fcγ receptor dependency of agonistic CD40 antibody in lymphoma therapy can be overcome through antibody multimerization

Immunomodulatory mAbs, led by the anti-CTLA4 mAb ipilimumab, are an exciting new class of drugs capable of promoting anticancer immunity and providing durable control of some tumors. Close analysis of a number of agents has revealed a critical yet variable role for Fc? receptors in their efficacy. In this article, we reveal that agonistic anti-CD40 mAbs have an absolute requirement for cross-linking by inhibitory Fc?RIIB when used systemically to treat established BCL1 syngeneic lymphoma, and therapy is lost when using a mouse IgG2a mAb not cross-linked by Fc?RIIB. Furthermore, in Fc?RIIB-deficient mice the lymphoma itself can provide Fc?RIIB to cross-link anti-CD40 on neighboring cells, and only when this is blocked does therapy fail. The dependence on Fc?RIIB for immunostimulatory activity was not absolute, however, because when anti-CD40 mAbs were administered systemically with the TLR3 agonist polyinosinic:polycytidylic acid or were given subcutaneously, activatory Fc?R could also provide cross-linking. Using this mechanistic insight, we designed multimeric forms of anti-CD40 mAb with intrinsic Fc?R-independent activity that were highly effective in the treatment of lymphoma-bearing mice. In conclusion, Fc?R-independent anti-CD40 activation is a viable strategy in vivo. These findings have important translational implications, as humans, unlike mice, do not have IgG that binds strongly to Fc?RIIB; therefore Fc?R-independent derivatives represent an attractive therapeutic optio