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SummaryMonoclonal antibody (mAb) drugs that stimulate antitumor immunity are transforming cancer treatment but require optimization for maximum clinical impact. Here, we show that, unlike other immunoglobulin isotypes, human IgG2 (h2) imparts FcγR-independent agonistic activity to immune-stimulatory mAbs such as anti-CD40, -4-1BB, and -CD28. Activity is provided by a subfraction of h2, h2B, that is structurally constrained due its unique arrangement of hinge region disulfide bonds. Agonistic activity can be transferred from h2 to h1 by swapping their hinge and CH1 domains, and substitution of key hinge and CH1 cysteines generates homogenous h2 variants with distinct agonistic properties. This provides the exciting opportunity to engineer clinical reagents with defined therapeutic activity regardless of FcγR expression levels in the local microenvironment.

Therapeutic antibodies have transformed cancer therapy, unlocking mechanisms of action by engaging the immune system. Unfortunately, cures rarely occur and patients display intrinsic or acquired resistance. Here, we demonstrate the therapeutic potential of targeting human (h) FcγRIIB (CD32B), a receptor implicated in immune cell desensitization and tumor cell resistance. FcγRIIB-blocking antibodies prevented internalization of the CD20-specific antibody rituximab, thereby maximizing cell surface accessibility and immune effector cell mediated antitumor activity. In hFcγRIIB-transgenic (Tg) mice, FcγRIIB-blocking antibodies effectively deleted target cells in combination with rituximab, and other therapeutic antibodies, from resistance-prone stromal compartments. Similar efficacy was seen in primary human tumor xenografts, including with cells from patients with relapsed/refractory disease. These data support the further development of hFcγRIIB antibodies for clinical assessment.

Complement and FcγR effector pathways are central triggers of immune inflammation; however, the exact mechanisms for their cooperation with effector cells and their nature remain elusive. In this study we show that in the lung Arthus reaction, the initial contact between immune complexes and alveolar macrophages (AM) results in plasma complement-independent C5a production that causes decreased levels of inhibitory FcγRIIB, increased levels of activating FcγRIII, and highly induced FcγR-mediated TNF-α and CXCR2 ligand production. Blockade of C5aR completely reversed such changes. Strikingly, studies of pertussis toxin inhibition show the essential role of Gi-type G protein signaling in C5aR-mediated control of the regulatory FcγR system in vitro, and analysis of the various C5aR-, FcγR-, and Gi-deficient mice verifies the importance of Gαi2-associated C5aR and the FcγRIII-FcγRIIB receptor pair in lung inflammation in vivo. Moreover, adoptive transfer experiments of C5aR- and FcγRIII-positive cells into C5aR- and FcγRIII-deficient mice establish AM as responsible effector cells. AM lacking either C5aR or FcγRIII do not possess any such inducibility of immune complex disease, whereas reconstitution with FcγRIIB-negative AM results in an enhanced pathology. These data suggest that AM function as a cellular link of C5a production and C5aR activation that uses a Gαi2-dependent signal for modulating the two opposing FcγR, FcγRIIB and FcγRIII, in the initiation of the inflammatory cascade in the lung Arthus reaction.

Graphical Abstract Highlights d Anti-4-1BB IgG2a depletes intratumoral Treg cells; IgG1 promotes CD8 T cell function d The efficacy of anti-4-1BB mIgG1 and anti-4-1BB mIgG2a depends on different FcgRs d Optimal tumor therapy requires sequential anti-4-1BB IgG2a and IgG1 or PD-1 blockade d Hinge-engineered anti-4-1BB mIgG2a/h2B mAb harnesses both mechanisms of action