Destruction of cancer cells by therapeutic antibodies occurs, at least in part, through antibody-dependent cellular cytotoxicity (ADCC), and this can be mediated by various Fc-receptor-expressing immune cells, including neutrophils. However, the mechanism(s) by which neutrophils kill antibody-opsonized cancer cells has not been established. Here, we demonstrate that neutrophils can exert a mode of destruction of cancer cells, which involves antibody-mediated trogocytosis by neutrophils. Intimately associated with this is an active mechanical disruption of the cancer cell plasma membrane, leading to a lytic (i.e., necrotic) type of cancer cell death. Furthermore, this mode of destruction of antibody-opsonized cancer cells by neutrophils is potentiated by CD47-SIRPα checkpoint blockade. Collectively, these findings show that neutrophil ADCC toward cancer cells occurs by a mechanism of cytotoxicity called trogoptosis, which can be further improved by targeting CD47-SIRPα interactions.

Monoclonal antibodies are among the most promising therapeutic agents for treating cancer. Therapeutic cancer antibodies bind to tumor cells, turning them into targets for immune-mediated destruction. We show here that this antibody-mediated killing of tumor cells is limited by a mechanism involving the interaction between tumor cell-expressed CD47 and the inhibitory receptor signal regulatory protein-α (SIRPα) on myeloid cells. Mice that lack the SIRPα cytoplasmic tail, and hence its inhibitory signaling, display increased antibody-mediated elimination of melanoma cells in vivo. Moreover, interference with CD47-SIRPα interactions by CD47 knockdown or by antagonistic antibodies against CD47 or SIRPα significantly enhances the in vitro killing of trastuzumab-opsonized Her2/Neu-positive breast cancer cells by phagocytes. Finally, the response to trastuzumab therapy in breast cancer patients appears correlated to cancer cell CD47 expression. These findings demonstrate that CD47-SIRPα interactions participate in a homeostatic mechanism that restricts antibody-mediated killing of tumor cells. This provides a rational basis for targeting CD47-SIRPα interactions, using for instance the antagonistic antibodies against human SIRPα described herein, to potentiate the clinical effects of cancer therapeutic antibodies.antibody-dependent cellular cytotoxicity | neutrophil | immunoreceptor | Fc-receptor

Key Points Human CARD9 deficiency is characterized by a selective neutrophil killing defect, resulting in invasive candidiasis.

Key Points Human neutrophils use 2 independent mechanisms for the killing of unopsonized and serum-opsonized C albicans. Unopsonized Candida killing depends on CR3 and CARD9 but not dectin-1; opsonized Candida killing on FcγR, PKC, and NADPH oxidase activity.

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Key Points Activated neutrophils can suppress T-cell proliferation in a CD11b-dependent multistep process involving ROS production and degranulation. MDSC activity results in nonapoptotic T-cell damage.

The NLRP3 inflammasome can be activated by pathogen-associated molecular patterns or endogenous danger-associated molecular patterns. The activation of the NLRP3 inflammasome results in proteolytic activation and secretion of cytokines of the interleukin-1 (IL-1) family. The precise mode of activation of the NLRP3 inflammasome is still elusive, but has been postulated to be mediated by reactive oxygen species (ROS) generated by an NADPH oxidase. Using primary cells from chronic granulomatous disease (CGD) patients lacking expression of p22 phox , a protein that is required for the function of Nox1-4, we show that cells lacking NADPH oxidase activity are capable of secreting normal amounts of IL-1␤. Thus, we provide evidence that activation of the NLRP3 inflammasome does not depend on ROS generated from an NADPH oxidase. (Blood. 2010;115(26): 5398-5400) IntroductionInflammasomes are specialized intracellular protein complexes responsible for regulating the proteolytic activation of proinflammatory cytokines of the interleukin-1 (IL-1) family. 1 The central components of inflammasomes, the Nod-like receptor (NLR) proteins, act as sensors for exogenous (microbial) or endogenous danger signals. Importantly, inappropriate activation of inflammasomes, due to activating mutations in the NLRs or an excess of danger signals can lead to autoinflammatory disorders such as chronic infantile neurologic cutaneous and articular syndrome, or the more common reactions in gout. 1 The best-studied NLR, NLRP3, forms inflammasomes that mediate the release of IL-1␤ and related cytokines by, for example, macrophages. The NLRP3 inflammasome can be activated by pathogen-associated molecular patterns such as lipopolysaccharide (LPS) or muramyl dipeptide, or endogenous danger-associated molecular patterns such as uric acid. 1 The precise mode of activation of the NLRP3 inflammasome is still elusive, but it has been postulated, in reports by Dostert et al, to be dependent on reactive oxygen species (ROS) generated by an NADPH oxidase. 2,3 In these reports, the authors show an inhibitory effect on IL-1␤ secretion by knockdown of p22 phox , a protein that is part of the catalytic core of several NADPH oxidases.The catalytic core of NADPH oxidases contains a member of the Nox family of proteins. 4 All members of the Nox1-4 subfamily form a heterodimer with the common p22 phox subunit. In the case of Nox2, p22 phox functions as a docking site for the regulatory protein p47 phox , and indirectly for p67 phox , and p40 phox ; the small GTPase Rac binds to p67 phox and serves as a switch for Nox2 activation. 4 For Nox1 and 3, p47 phox and p67 phox homologs are probably involved in this activation. 4 Nox4 is believed not to be regulated by p47 phox and p67 phox or their homologs, and p22 phox is not a conditio sine qua non for its activity but Nox4 activity seems to be clearly enhanced by association with p22 phox4 . The best-studied NADPH oxidase is the phagocyte NADPH oxidase, a microbicidal enzyme that contains Nox2 (gp91 phox ) and p22 phox an...

Disclosure of potential conflict of interest: S. Gray has received travel support from Medtronic. E. Holbrook has consultant arrangements with 480 Biomedical and has provided expert testimony for Margol & Margol PA. B. S. Bleier has received grants from MEEI Curing Kids Fund and Cook Medical; has consultant arrangements with Olympus, Canon, and Storz; has provided expert testimony on ENT-related cases; has a patent for P-gp inhibition for chronic rhinosinusitis and receives royalties from this patent; and has stock/stock options in Interscope. The rest of the authors declare that they have no relevant conflicts of interest.