CD47-SIRPα Controls ADCC Killing of Primary T Cells by PMN Through a Combination of Trogocytosis and NADPH Oxidase Activation.

Immunotherapies targeting the "don't eat me" myeloid checkpoint constituted by CD47 SIRPα interaction have promising clinical potential but are limited by toxicities associated with the destruction of non-tumor cells. These dose-limiting toxicities demonstrate the need to highlight the mechanisms of anti-CD47-SIRPα therapy effects on non-tumor CD47-bearing cells. Given the increased incidence of lymphopenia in patients receiving anti-CD47 antibodies and the strong ADCC (antibody-dependent cellular cytotoxicity) effector function of polymorphonuclear cells (PMNs), we investigated the behavior of primary PMNs cocultured with primary T cells in the presence of anti-CD47 mAbs. PMNs killed T cells in a CD47-mAb-dependent manner and at a remarkably potent PMN to T cell ratio of 1:1. The observed cytotoxicity was produced by a novel combination of both trogocytosis and a strong respiratory burst induced by classical ADCC and CD47-SIRPα checkpoint blockade. The complex effect of the CD47 blocking mAb could be recapitulated by combining its individual mechanistic elements: ADCC, SIRPα blockade, and ROS induction. Although previous studies had concluded that disruption of SIRPα signaling in PMNs was limited to trogocytosis-specific cytotoxicity, our results suggest that SIRPα also tightly controls activation of NADPH oxidase, a function demonstrated during differentiation of immature PMNs but not so far in mature PMNs. Together, our results highlight the need to integrate PMNs in the development of molecules targeting the CD47-SIRPα immune checkpoint and to design agents able to enhance myeloid cell function while limiting adverse effects on healthy cells able to participate in the anti-tumor immune response.

The Multiple Roles of Trogocytosis in Immunity, the Nervous System, and Development.

Trogocytosis is a general biological process that involves one cell physically taking small parts of the membrane and other components from another cell. In trogocytosis, one cell seems to take little "bites" from another cell resulting in multiple outcomes from these cell-cell interactions. Trogocytosis was first described in protozoan parasites, which by taking pieces of host cells, kill them and cause tissue damage. Now, it is known that this process is also performed by cells of the immune system with important consequences such as cell communication and activation, elimination of microbial pathogens, and even control of cancer cells. More recently, trogocytosis has also been reported to occur in cells of the central nervous system and in various cells during development. Some of the molecules involved in phagocytosis also participate in trogocytosis. However, the molecular mechanisms that regulate trogocytosis are still a mystery. Elucidating these mechanisms is becoming a research area of much interest. For example, why neutrophils can engage trogocytosis to kill Trichomonas vaginalis parasites, but neutrophils use phagocytosis to eliminate already death parasites? Thus, trogocytosis is a significant process in normal physiology that multiple cells from different organisms use in various scenarios of health and disease. In this review, we present the basic principles known on the process of trogocytosis and discuss the importance in this process to host-pathogen interactions and to normal functions in the immune and nervous systems.

Evolution of Antibodies to Native Trimeric Envelope and Their Fc-Dependent Functions in Untreated and Treated Primary HIV Infection.

People living with HIV (PLWH) develop both anti-envelope-specific antibodies, which bind the closed trimeric HIV envelope present on infected cells, and anti-gp120-specific antibodies, which bind gp120 monomers shed by infected cells and taken up by CD4 on uninfected bystander cells. Both antibodies have an Fc portion that binds to Fc receptors on several types of innate immune cells and stimulates them to develop antiviral functions. Among these Fc-dependent functions (FcDFs) are antibody-dependent (AD) cellular cytotoxicity (ADCC), AD cellular trogocytosis (ADCT), and AD phagocytosis (ADCP). In this study, we assessed the evolution of total immunoglobulin G (IgG), anti-gp120, and anti-envelope IgG antibodies and their FcDFs in plasma samples from antiretroviral therapy (ART)-naive subjects during early HIV infection (28 to 194 days postinfection [DPI]). We found that both the concentrations and FcDFs of anti-gp120 and anti-envelope antibodies increased with time in ART-naive PLWH. Although generated concurrently, anti-gp120-specific antibodies were 20.7-fold more abundant than anti-envelope-specific antibodies, both specificities being strongly correlated with each other and FcDFs. Among the FcDFs, only ADCP activity was inversely correlated with concurrent viral load. PLWH who started ART at >90 DPI showed higher anti-envelope-specific antibody levels and ADCT and ADCP activities than those starting ART at<90 DPI. However, in longitudinally collected samples, ART initiation at >90 DPI was accompanied by a faster decline in anti-envelope-specific antibody levels, which did not translate to a faster decline in FcDFs than for those starting ART at <90 DPI. IMPORTANCE Closed-conformation envelope is expressed on the surface of HIV-infected cells. Antibodies targeting this conformation and that support FcDFs have the potential to control HIV. This study tracked the timing of the appearance and evolution of antibodies to closed-conformation envelope, whose concentration increased over the first 6 months of infection. Antiretroviral therapy (ART) initiation blunts further increases in the concentration of these antibodies and their and FcDFs. However, antibodies to open-conformation envelope also increased with DPI until ART initiation. These antibodies target uninfected bystander cells, which may contribute to loss of uninfected CD4 cells and pathogenicity. This report presents, for the first time, the evolution of antibodies to closed-conformation envelope and their fate on ART. This information may be useful in making decisions on the timing of ART initiation in early HIV infection.

Mechanisms Driving Neutrophil-Induced T-cell Immunoparalysis in Ovarian Cancer.

T-cell activation and expansion in the tumor microenvironment (TME) are critical for antitumor immunity. Neutrophils in the TME acquire a complement-dependent T-cell suppressor phenotype that is characterized by inhibition of T-cell proliferation and activation through mechanisms distinct from those of myeloid-derived suppressor cells. In this study, we used ascites fluid supernatants (ASC) from patients with ovarian cancer as an authentic component of the TME to evaluate the effects of ASC on neutrophil function and mechanisms for neutrophil-driven immune suppression. ASC prolonged neutrophil life span, decreased neutrophil density, and induced nuclear hypersegmentation. Mass cytometry analysis showed that ASC induced 15 distinct neutrophil clusters. ASC stimulated complement deposition and signaling in neutrophils, resulting in surface mobilization of granule constituents, including NADPH oxidase. NADPH oxidase activation and phosphatidylserine signaling were required for neutrophil suppressor function, although we did not observe a direct role of extracellular reactive oxygen species in inhibiting T-cell proliferation. Postoperative surgical drainage fluid also induced a complement-dependent neutrophil suppressor phenotype, pointing to this effect as a general response to injury. Like circulating lymphocytes, ASC-activated neutrophils caused complement-dependent suppression of tumor-associated lymphocytes. ASC-activated neutrophils adhered to T cells and caused trogocytosis of T-cell membranes. These injury and signaling cues resulted in T-cell immunoparalysis characterized by impaired NFAT translocation, IL2 production, glucose uptake, mitochondrial function, and mTOR activation. Our results demonstrate that complement-dependent priming of neutrophil effector functions in the TME induces a T-cell nonresponsiveness distinct from established checkpoint pathways and identify targets for immunotherapy.See related Spotlight by Cassatella, p. 725.