SummaryAnti-CD40 monoclonal antibodies (mAbs) that promote or inhibit receptor function hold promise as therapeutics for cancer and autoimmunity. Rules governing their diverse range of functions, however, are lacking. Here we determined characteristics of nine hCD40 mAbs engaging epitopes throughout the CD40 extracellular region expressed as varying isotypes. All mAb formats were strong agonists when hyper-crosslinked; however, only those binding the membrane-distal cysteine-rich domain 1 (CRD1) retained agonistic activity with physiological Fc gamma receptor crosslinking or as human immunoglobulin G2 isotype; agonistic activity decreased as epitopes drew closer to the membrane. In addition, all CRD2-4 binding mAbs blocked CD40 ligand interaction and were potent antagonists. Thus, the membrane distal CRD1 provides a region of choice for selecting CD40 agonists while CRD2-4 provides antagonistic epitopes.

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.

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

CTLA-4 is a crucial immune regulator that mediates both negative costimulation signals to T cells, and regulatory T (Treg)-cell extrinsic control of effector responses.Here we present evidence supporting a novel mechanism for this extrinsic suppression, executed by the alternatively spliced soluble CTLA-4 isoform (sCTLA-4). Analyses of human T cells in vitro show that sCTLA-4 secretion can be increased during responses, and has potent inhibitory properties, since isoform-specific blockade of its activity significantly increased Ag-driven proliferation and cytokine (IFN-γ, IL-17) secretion. Treg cells were demonstrated to be a prominent source of sCTLA-4, which contributed to suppression in vitro when their numbers were limiting. The soluble isoform was also produced by, and inhibited, murine T cells responding to Ag in vitro, and blockade of its activity in vivo protected against metastatic spread of melanoma in mice. We conclude that sCTLA-4 is an important immune regulator, responsible for at least some of the inhibitory effects previously ascribed to the membrane-bound isoform. These results suggest that the immune system exploits the different CTLA-4 isoforms for either intrinsic or extrinsic regulation of T-cell activity. Keywords: CD4 + T cells r Costimulatory molecules r Immune regulation r Treg cellsAdditional supporting information may be found in the online version of this article at the publisher's web-site Introduction CTLA-4 is an important regulator of T-cell responses [1][2][3][4]. Its critical role is highlighted by CTLA-4 knockout mice, which develop a fatal lymphoproliferative disorder soon after birth, arising from a profound failure of T-cell homeostasis [5,6]. Despite these potent effects, the activities of CTLA-4 are only partially understood.CTLA-4 shares sequence homology and B7 ligands (CD80/CD86) with the costimulatory molecule, CD28, but differs by delivering inhibitory, rather than activating, signals to the T cells on which it is expressed as a receptor [7,8]. Upregulation of CTLA-4 on activated T cells provides a mechanism for negative Correspondence: Dr. Frank J. Ward e-mail: mmd475@abdn.ac.uk feedback to control their responses. However, not all its regulatory effects are explained by inhibitory costimulation, since CTLA-4 can also suppress activated effector T-cell populations without the need for them to express it [9,10]. This latter, cell-extrinsic mechanism has been largely attributed to CD4 + regulatory T (Treg)-cell subsets, which constitutively express high levels of CTLA-4, and require it for their regulatory function [11][12][13][14][15][16].How Treg cells might use CTLA-4 to regulate effector T-cell responses remains controversial. It has been suggested that CTLA-4 on Treg cells binds B7 and thus blocks CD28-mediated effector T-cell costimulation, or that it induces inhibitory mechanisms in the APC such as the IDO tryptophan catabolic enzyme * These authors contributed equally to this work.www.eji-journal.eu Eur. J. Immunol. 2013. 43: 1274-1285 Immunomodulation 1275 cas...