The Role of Trogocytosis in the Modulation of Immune Cell Functions

Generation of chimeric antigen receptor-macrophages by using human induced pluripotent stem cells

Cancer immunotherapy using chimeric antigen receptor (CAR) cells shows high therapeutic efficacy against several types of leukemia. Among acute lymphoblastic leukemias (ALLs), B cell-derived ALL can be cured by CAR-expressing T cells (CAR-Ts); however, CAR-T cells cannot be simply applied for T cell-derived ALL (T-ALL) because antigens expressed by T-ALL cells, but not by CAR-T cells, have not yet been identified. To apply CAR-T therapy for T-ALL, gene editing of CAR-T cells is required to avoid attacking CAR-T cells themselves. Alternatively, CAR-expressing macrophages (CAR-Ms) have proven to be effective against various cancers, suggesting that CAR-Ms may also be effective against T-ALL. Recently, we developed an efficient differentiation induction system to generate a large number of macrophages from human induced pluripotent stem cells (iPSCs). Here, we asked whether these human iPSC-derived macrophages (iPS-MACs) can be used to develop and evaluate CAR-based immunotherapy against T-ALLs. When non-transduced iPS-MACs were co-cultured with human T-ALL-derived cells, the iPS-MACs appeared to phagocytose parts of T-ALL cells; this method of phagocytosis operated mainly through incorporation of small, "bite-sized" vesicles derived from the T-ALL cells into iPS-MACs (similar to trogocytosis). By contrast, when CAR-expressing iPS-MACs were co-cultured with T-ALL cells, iPS-MACs engulfed the whole T-ALL cell. Thus, our differentiation induction system may be a promising tool for building up CAR-M therapy for T-ALLs.

A "poly-matter network" conception of biological inheritance

Here we intend to shift the "DNA- and information-centric" conception of biological inheritance, with the accompanying exclusion of any non-DNA matter, to a "poly-matter network" framework which, in addition to DNA, considers the action of other cellular membranous constituents. These cellular structures, in particular organelles and plasma membranes, express "landscapes" of specific topologies at their surfaces, which may become altered in response to certain environmental factors. These so-called "membranous environmental landscapes" (MELs), which replicate by self-organization / autopoiesis rather than self-assembly, are transferred from donor to acceptor cells by various - vesicular and non-vesicular - mechanisms and exert novel features in the acceptor cells. The "DNA-centric" conception may be certainly explanatorily sufficient for the transfer of heritable phenotype variation to acceptor cells following the copying of DNA in donor cells and thereby for the phenomenon of biological inheritance of traits. However, it is not causally sufficient. With the observation of phenotype variation, as initially manifested during bacterial transformation, the impact of environmental factors, such as nutrition and stress, in the differential regulation of gene expression has been widely accepted and resulted in intense efforts to resolve the underlying epigenetic mechanisms. However, these are explained under a conceptual frame where the DNA (and associated proteins) are the only matter of inheritance. In contrast, it is our argumentation that inheritance can only be adequately understood as the transfer of DNA in concert with non-DNA matter in a "poly-matter network" conception. The adequate inclusion of the transfer of non-DNA matter is still a desideratum of future genetic research, which may pave the way for the experimental elucidation not only of how DNA and membrane matter act in concert to enable the inheritance of innate traits, but also whether they interact for that of acquired biological traits. Moreover, the "poly-matter network" conception may open new perspectives for an understanding of the pathogenesis of "common complex" diseases.

The origin of human CD20+ T cells: a stolen identity?

Human T cells expressing CD20 play an important role in the defense against virus and cancer and are central in the pathogenesis of both malignancies and various autoimmune disorders. Therapeutic modulation of CD20+ T cells and the CD20 expression level is therefore of significant interest. In rodents, CD20 on T cells is likely the product of an active transfer of CD20 from a donor B cell interacting with a recipient T cell in a process termed trogocytosis. Whether the same applies to human CD20+ T cells is highly debated. Investigating this dispute showed that human CD20- T cells could achieve CD20 along with a series of other B-cell markers from B cells through trogocytosis. However, none of these B-cell markers were co-expressed with CD20 on human CD20+ T cells in blood or inflamed CSF, implying that additional mechanisms may be involved in the development of human CD20+ T cells. In support of this, we identified true naïve CD20+ T cells, measured endogenous production of CD20, and observed that CD20 could be inherited to daughter cells, contradicting that all human CD20+ T cells are a product of trogocytosis.

Trogocytosis in CAR immune cell therapy: a key mechanism of tumor immune escape

Immune cell therapy based on chimeric antigen receptor (CAR) technology platform has been greatly developed. The types of CAR immune cell therapy have expanded from T cells to innate immune cells such as NK cells and macrophages, and the diseases treated have expanded from hematological malignancies to non-tumor fields such as infectious diseases and autoimmune diseases. Among them, CAR-T and CAR-NK therapy have observed examples of rapid remission in approved clinical trials, but the efficacy is unstable and plagued by tumor resistance. Trogocytosis is a special phenomenon of intercellular molecular transfer that is common in the immune system and is achieved by recipient cells through acquisition and internalization of donor cell-derived molecules and mediates immune effects. Recently, a novel short-term drug resistance mechanism based on trogocytosis has been proposed, and the bidirectional molecular exchange between CAR immune cells and tumor cells triggered by trogocytosis partially explains the long-term relapse phenomenon after treatment with CAR immune cells. In this review, we summarize the research progress of trogocytosis in CAR immunotherapy, discuss the influencing factors of trogocytosis and its direct and indirect interference with CAR immune cells and emphasize that the interference of trogocytosis can further release the potential of CAR immune cell therapy.

Human OX40L-CAR-Tregs target activated antigen-presenting cells and control T cell alloreactivity

Regulatory T cells (Tregs) make major contributions to immune homeostasis. Because Treg dysfunction can lead to both allo- and autoimmunity, there is interest in correcting these disorders through Treg adoptive transfer. Two of the central challenges in clinically deploying Treg cellular therapies are ensuring phenotypic stability and maximizing potency. Here, we describe an approach to address both issues through the creation of OX40 ligand (OX40L)-specific chimeric antigen receptor (CAR)-Tregs under the control of a synthetic forkhead box P3 (FOXP3) promoter. The creation of these CAR-Tregs enabled selective Treg stimulation by engagement of OX40L, a key activation antigen in alloimmunity, including both graft-versus-host disease and solid organ transplant rejection, and autoimmunity, including rheumatoid arthritis, systemic sclerosis, and systemic lupus erythematosus. We demonstrated that OX40L-CAR-Tregs were robustly activated in the presence of OX40L-expressing cells, leading to up-regulation of Treg suppressive proteins without induction of proinflammatory cytokine production. Compared with control Tregs, OX40L-CAR-Tregs more potently suppressed alloreactive T cell proliferation in vitro and were directly inhibitory toward activated monocyte-derived dendritic cells (DCs). We identified trogocytosis as one of the central mechanisms by which these CAR-Tregs effectively decrease extracellular display of OX40L, resulting in decreased DC stimulatory capacity. OX40L-CAR-Tregs demonstrated an enhanced ability to control xenogeneic graft-versus-host disease compared with control Tregs without abolishing the graft-versus-leukemia effect. These results suggest that OX40L-CAR-Tregs may have wide applicability as a potent cellular therapy to control both allo- and autoimmune diseases.

Multiple myeloma and the potential of new checkpoint inhibitors for immunotherapy

Multiple myeloma (MM), a cancer of the bone marrow, is categorized as the second most common hematological malignancy of adults in the Western world. Despite dramatic improvements in immunotherapies in the field of cancers, MM immunotherapy has not been promising until now. Recent clinical studies of immune checkpoint inhibitor therapy, either alone or in combination with anticancer drugs, showed excessive side effects or low efficacy, particularly in advanced MM patients. In this context, lymphocyte levels of exhaustion markers play a pivotal role in the MM tumor microenvironment (TME). Hence in the present review, the mechanisms relevant to MM of five inhibitory molecules including T-cell immunoreceptor with Ig and ITIM domains (TIGIT), T-cell immunoglobulin, and mucin domain 3 (Tim-3), lymphocyte activation gene-3 (LAG-3), V-domain Ig Suppressor of T-cell activation and killer immunoglobulin-like receptors along with bispecific T-cell antibodies (BsAbs) will be discussed. Further, we summarized the underlying biology of these checkpoints in cancer and their rapidly emerging role in pathways in MM along with presenting recent clinical trials in context.

Triple Negative Breast Cancer Cells Acquire Lymphocyte Proteins and Genomic DNA During Trogocytosis with T Cells

Trogocytosis is the process by which a recipient cell siphons small membrane fragments and proteins from a donor cell and may be utilized by cancer cells to avoid immune detection. We observed lymphocyte specific protein expressed by TNBC cells via immunofluorescence imaging of patient samples. Image analysis of CD45RA expression, a T cell specific protein, revealed that all stages of TNBCs express CD45RA. Flow cytometry revealed TNBC cells trogocytose CD45 protein from T cells. We also showed that the acquisition of these lymphoid markers is contact dependent. Confocal and super-resolution imaging further revealed CD45 + spherical structures containing T cell genomic DNA inside TNBC cells after co-culture. Trogocytosis between T cells and TNBC cells altered cancer cell gene expression. Our results revealed that CD45 is obtained by TNBC cells from T cells via trogocytosis and that TNBC cells express CD45 intracellularly and on the membrane.

Teaser

TNBC cells acquire small spherical structures from T cells containing lymphocyte-specific membrane proteins and genomic DNA.

The dual nature of TDC - bridging dendritic and T cells in immunity

TDC are hematopoietic cells with unique features that provide intriguing insights into the interplay between innate and adaptive immunity. They express a combination of conventional dendritic cell (DC) and T-cell markers and are found in secondary lymphoid organs (SLOs), lungs and liver of naïve mice, as well as in human blood. When analyzed ex vivo, TDC can behave either as DCs or as T cells, depending on the provided stimuli. Notably, TDC numbers and activation significantly increase in SLOs following viral infection, suggesting a potential role for TDC in antiviral immune responses. In this review, we discuss the properties of these fascinating cells, which call for more investigation on their physiological role during immune responses to both pathogens and tumors.

Receptor transfer between immune cells by autoantibody-enhanced, CD32-driven trogocytosis is hijacked by HIV-1 to infect resting CD4 T cells

Immune cell phenotyping frequently detects lineage-unrelated receptors. Here, we report that surface receptors can be transferred from primary macrophages to CD4 T cells and identify the Fcγ receptor CD32 as driver and cargo of this trogocytotic transfer. Filamentous CD32+ nanoprotrusions deposit distinct plasma membrane patches onto target T cells. Transferred receptors confer cell migration and adhesion properties, and macrophage-derived membrane patches render resting CD4 T cells susceptible to infection by serving as hotspots for HIV-1 binding. Antibodies that recognize T cell epitopes enhance CD32-mediated trogocytosis. Such autoreactive anti-HIV-1 envelope antibodies can be found in the blood of HIV-1 patients and, consistently, the percentage of CD32+ CD4 T cells is increased in their blood. This CD32-mediated, antigen-independent cell communication mode transiently expands the receptor repertoire and functionality of immune cells. HIV-1 hijacks this mechanism by triggering the generation of trogocytosis-promoting autoantibodies to gain access to immune cells critical to its persistence.

Emerging Strategies to Overcome Current CAR-T Therapy Dilemmas - Exosomes Derived from CAR-T Cells

Adoptive T cells immunotherapy, specifically chimeric antigen receptor T cells (CAR-T), has shown promising therapeutic efficacy in the treatment of hematologic malignancies. As extensive research on CAR-T therapies has been conducted, various challenges have emerged that significantly hampered their clinical application, including tumor recurrence, CAR-T cell exhaustion, and cytokine release syndrome (CRS). To overcome the hurdles of CAR-T therapy in clinical treatment, cell-free emerging therapies based on exosomes derived from CAR-T cells have been developed as an effective and promising alternative approach. In this review, we present CAR-T cell-based therapies for the treatment of tumors, including the features and benefits of CAR-T therapies, the limitations that exist in this field, and the measures taken to overcome them. Furthermore, we discuss the notable benefits of utilizing exosomes released from CAR-T cells in tumor treatment and anticipate potential issues in clinical trials. Lastly, drawing from previous research on exosomes from CAR-T cells and the characteristics of exosomes, we propose strategies to overcome these restrictions. Additionally, the review discusses the plight in large-scale preparation of exosome and provides potential solutions for future clinical applications.

Dendritic cells overcome Cre/Lox induced gene deficiency by siphoning cytosolic material from surrounding cells

In a previous report, keratinocytes were shown to share their gene expression profile with surrounding Langerhans cells (LCs), influencing LC biology. Here, we investigated whether transferred material could substitute for lost gene products in cells subjected to Cre/Lox conditional gene deletion. We found that in human Langerin-Cre mice, epidermal LCs and CD11b+CD103+ mesenteric DCs overcome gene deletion if the deleted gene was expressed by neighboring cells. The mechanism of material transfer differed from traditional antigen uptake routes, relying on calcium and PI3K, being susceptible to polyguanylic acid inhibition, and remaining unaffected by inflammation. Termed intracellular monitoring, this process was specific to DCs, occurring in all murine DC subsets tested and human monocyte-derived DCs. The transferred material was presented on MHC-I and MHC-II, suggesting a role in regulating immune responses.

Transfer of membrane(s) matter(s)-non-genetic inheritance of (metabolic) phenotypes?

Glycosylphosphatidylinositol-anchored proteins (GPI-APs) are anchored at the outer phospholipid layer of eukaryotic plasma membranes exclusively by a glycolipid. GPI-APs are not only released into extracellular compartments by lipolytic cleavage. In addition, certain GPI-APs with the glycosylphosphatidylinositol anchor including their fatty acids remaining coupled to the carboxy-terminus of their protein components are also detectable in body fluids, in response to certain stimuli, such as oxidative stress, radicals or high-fat diet. As a consequence, the fatty acid moieties of GPI-APs must be shielded from access of the aqueous environment by incorporation into membranes of extracellular vesicles or into micelle-like complexes together with (lyso)phospholipids and cholesterol. The GPI-APs released from somatic cells and tissues are transferred via those complexes or EVs to somatic as well as pluripotent stem cells with metabolic consequences, such as upregulation of glycogen and lipid synthesis. From these and additional findings, the following hypotheses are developed: i) Transfer of GPI-APs via EVs or micelle-like complexes leads to the induction of new phenotypes in the daughter cells or zygotes, which are presumably not restricted to metabolism. ii) The membrane topographies transferred by the concerted action of GPI-APs and interacting components are replicated by self-organization and self-templation and remain accessible to structural changes by environmental factors. iii) Transfer from mother cells and gametes to their daughter cells and zygotes, respectively, is not restricted to DNA and genes, but also encompasses non-genetic matter, such as GPI-APs and specific membrane constituents. iv) The intergenerational transfer of membrane matter between mammalian organisms is understood as an epigenetic mechanism for phenotypic plasticity, which does not rely on modifications of DNA and histones, but is regarded as molecular mechanism for the inheritance of acquired traits, such as complex metabolic diseases. v) The missing interest in research of non-genetic matter of inheritance, which may be interpreted in the sense of Darwin's "Gemmules" or Galton's "Stirps", should be addressed in future investigations of the philosophy of science and sociology of media.

Trogocytosis drives red blood cell antigen loss in association with antibody-mediated immune suppression

ABSTRACT

Red blood cell (RBC) alloimmunization to paternal antigens during pregnancy can cause hemolytic disease of the fetus and newborn (HDFN). This severe and potentially fatal neonatal disorder can be prevented by the administration of polyclonal anti-D through a mechanism referred to as antibody-mediated immune suppression (AMIS). Although anti-D prophylaxis effectively prevents HDFN, a lack of mechanistic clarity has hampered its replacement with recombinant agents. The major theories behind AMIS induction in the hematologic literature have classically centered around RBC clearance; however, antigen modulation/loss has recently been proposed as a potential mechanism of AMIS. To explore the primary mechanisms of AMIS, we studied the ability of 11 different antibodies to induce AMIS, RBC clearance, antigen loss, and RBC membrane loss in the HOD (hen egg lysozyme-ovalbumin-human Duffy) murine model. Antibodies targeting different portions of the HOD molecule could induce AMIS independent of their ability to clear RBCs; however, all antibodies capable of inducing a strong AMIS effect also caused significant in vivo loss of the HOD antigen in conjunction with RBC membrane loss. In vitro studies of AMIS-inducing antibodies demonstrated simultaneous RBC antigen and membrane loss, which was mediated by macrophages. Confocal live-cell microscopy revealed that AMIS-inducing antibodies triggered RBC membrane transfer to macrophages, consistent with trogocytosis. Furthermore, anti-D itself can induce trogocytosis even at low concentrations, when phagocytosis is minimal or absent. In view of these findings, we propose trogocytosis as a mechanism of AMIS induction.

Intruders or protectors - the multifaceted role of B cells in CNS disorders

B lymphocytes are immune cells studied predominantly in the context of peripheral humoral immune responses against pathogens. Evidence has been accumulating in recent years on the diversity of immunomodulatory functions that B cells undertake, with particular relevance for pathologies of the central nervous system (CNS). This review summarizes current knowledge on B cell populations, localization, infiltration mechanisms, and function in the CNS and associated tissues. Acute and chronic neurodegenerative pathologies are examined in order to explore the complex, and sometimes conflicting, effects that B cells can have in each context, with implications for disease progression and treatment outcomes. Additional factors such as aging modulate the proportions and function of B cell subpopulations over time and are also discussed in the context of neuroinflammatory response and disease susceptibility. A better understanding of the multifactorial role of B cell populations in the CNS may ultimately lead to innovative therapeutic strategies for a variety of neurological conditions.

The Biological Significance of Trogocytosis

Trogocytosis is the intercellular transfer of membrane and membrane-associated proteins between cells. Trogocytosis is an underappreciated phenomenon that has historically routinely been dismissed as an artefact. With a greater understanding of the process and the implications it has on biological systems, trogocytosis has the potential to become a paradigm changer. The presence on a cell of molecules they don't endogenously express can alter the biological activity of the cell and could also lead to the acquisition of new functions. To better appreciate this phenomenon, it is important to understand how these intercellular membrane exchanges influence the function and activity of the donor and the recipient cells. In this chapter, we will examine how the molecules acquired by trogocytosis influence the biology of a variety of systems including mammalian fertilization, treatment of hemolytic disease of the newborn, viral and parasitic infections, cancer immunotherapy, and immune modulation.

Effectiveness and safety of amivantamab in EGFR exon 20 insertion (E20I) mutations in non-small cell lung cancer (NSCLC)

Background

In non-small cell lung cancer (NSCLC), the epidermal growth factor receptor (EGFR) mutation is a representative oncogenic driver mutation. Only about 12% of EGFR mutation patients have the exon 20 insertion mutation, which is the third most frequent mutation among EGFR mutation NSCLC. Amivantamab, an EGFR and MET proto-oncogene, receptor tyrosine kinase (MET) bispecific antibody, was approved for NSCLC patients with the EGFR exon 20 insertion (E20I) mutation. In this study, we described the real-world, single-center efficacy and safety data of amivantamab in E20I mutation patients.

Methods

This study included metastatic NSCLC patients with EGFR E20I mutations. From January 2018 to June 2022, patients with EGFR E20I mutations who were treated with amivantamab were analyzed at Samsung Medical Center as part of the clinical trial or the early access program (EAP). We collected the patients' characteristics [age, sex, smoking history, location of mutation, sites of metastasis, programmed death-ligand 1 (PD-L1) expression status, etc.] and analyzed progression-free survival (PFS) and overall survival (OS) stratified by PD-L1 expression status, co-mutation such as tumor protein p53 (TP53), and metastasis sites.

Results

A total of 42 patients were analyzed, of which 16 patients were enrolled in the phase 1 study, and 26 patients received amivantamab through EAP. There were 14 (33%) patients with partial remission, 18 (43%) patients with stable disease, and 10 (24%) patients with disease progression. The objective response rate (ORR) was 33%, and the disease control rate (DCR) was 76%. PFS was analyzed by dividing the near and far loop for 31 patients whose mutation location was known. The two groups had no statistically significant difference in PFS [median (range): 11.8 (2.3-21.3) vs. 11.3 (3.4-19.2) months, P=0.69]. For 29 patients with TP53 mutation data, there was no significant difference in PFS between the two groups [median (range): 5.9 (0-18.0) vs. 12.6 (6.9-18.3) months, P=0.11]. When analyzing PFS in 37 patients with PD-L1 expression data, PD-L1 (+) patients showed a poor prognosis [median (range): 11.3 (5.0-17.6) vs. 19.5 (5.3-33.7) months, P=0.04; hazard ratio (HR), 0.44; 95% confidence interval (CI): 0.20-0.98].

Conclusions

The efficacy of amivantamab was confirmed for the real-world population for EGFR E20I-mutated NSCLC. PD-L1 status could be a poor predictive factor, which should be further validated.

Targeting KIR as a novel approach to improve CAR-NK cell function

Chimeric antigen receptor (CAR) NK cells are demonstrating promising activity in clinical trials and possess a favorable safety profile compared to CAR-T cells. The Killer cell Immunoglobulin-like Receptors (KIR) have a critical role in the control of NK cell function, and recently, this family of activating and inhibitory receptors have been targeted to improve CAR-NK function. These strategies include the utilisation of inhibitory KIR to reduce trogocytosis-associated NK cell fratricide, the downregulation of inhibitory KIR on CAR-NK cells to alleviate HLA mediated suppression, the selection of CAR-NK cell donors enriched for activating KIR, and the use of activating KIR intracellular domains within novel CAR constructs. These pre-clinical studies demonstrate the potential utility of targeting the KIR to improve CAR-NK cell efficacy and patient outcomes.

The direct transfer approach for transcellular drug delivery

A promising paradigm for drug administration that has garnered increasing attention in recent years is the direct transfer (DT) of nanoparticles for transcellular drug delivery. DT requires direct cell-cell contact and facilitates unidirectional and bidirectional matter exchange between neighboring cells. Consequently, DT enables fast and deep penetration of drugs into the targeted tissues. This comprehensive review discusses the direct transfer concept, which can be delineated into the following three distinct modalities: membrane contact-direct transfer, gap junction-mediated direct transfer (GJ-DT), and tunneling nanotubes-mediated direct transfer (TNTs-DT). Further, the intercellular structures for each modality of direct transfer and their respective merits and demerits are summarized. The review also discusses the recent progress on the drugs or drug delivery systems that could activate DT.

Outsmarting trogocytosis to boost CAR NK/T cell therapy

Chimeric antigen receptor (CAR) NK and T cell therapy are promising immunotherapeutic approaches for the treatment of cancer. However, the efficacy of CAR NK/T cell therapy is often hindered by various factors, including the phenomenon of trogocytosis, which involves the bidirectional exchange of membrane fragments between cells. In this review, we explore the role of trogocytosis in CAR NK/T cell therapy and highlight potential strategies for its modulation to improve therapeutic efficacy. We provide an in-depth analysis of trogocytosis as it relates to the fate and function of NK and T cells, focusing on its effects on cell activation, cytotoxicity, and antigen presentation. We discuss how trogocytosis can mediate transient antigen loss on cancer cells, thereby negatively affecting the effector function of CAR NK/T cells. Additionally, we address the phenomenon of fratricide and trogocytosis-associated exhaustion, which can limit the persistence and effectiveness of CAR-expressing cells. Furthermore, we explore how trogocytosis can impact CAR NK/T cell functionality, including the acquisition of target molecules and the modulation of signaling pathways. To overcome the negative effects of trogocytosis on cellular immunotherapy, we propose innovative approaches to modulate trogocytosis and augment CAR NK/T cell therapy. These strategies encompass targeting trogocytosis-related molecules, engineering CAR NK/T cells to resist trogocytosis-induced exhaustion and leveraging trogocytosis to enhance the function of CAR-expressing cells. By overcoming the limitations imposed by trogocytosis, it may be possible to unleash the full potential of CAR NK/T therapy against cancer. The knowledge and strategies presented in this review will guide future research and development, leading to improved therapeutic outcomes in the field of immunotherapy.

MHC cross-dressing in antigen presentation

Dendritic cells (DCs) orchestrate T cell responses by presenting antigenic peptides on major histocompatibility complex (MHC) and providing costimulation and other instructive signals. Professional antigen presenting cells (APCs), including DCs, are uniquely capable of generating and presenting peptide antigens derived from exogenous proteins. In addition to these canonical cross-presentation and MHC-II presentation pathways, APCs can also display exogenous peptide/MHC (p/MHC) acquired from neighboring cells and extracellular vesicles (EVs). This process, known as MHC cross-dressing, has been implicated in the regulation of T cell responses in a variety of in vivo contexts, including allogeneic solid organ transplantation, tumors, and viral infection. Although the occurrence of MHC cross-dressing has been clearly demonstrated, the importance of this antigen presentation mechanism continues to be elucidated. The contribution of MHC cross-dressing to overall antigen presentation has been obfuscated by the fact that DCs express the same MHC alleles as all other cells in the host, making it difficult to distinguish p/MHC generated within the DC from p/MHC acquired from another cell. As a result, much of what is known about MHC cross-dressing comes from studies using allogeneic organ transplantation and bone marrow chimeric mice, though recent development of mice bearing conditional knockout MHC and β2-microglobulin alleles should facilitate substantial progress in the coming years. In this review, we highlight recent advances in our understanding of MHC cross-dressing and its role in activating T cell responses in various contexts, as well as the experimental insights into the mechanism by which it occurs.

slan+ Monocytes Kill Cancer Cells Coated in Therapeutic Antibody by Trogoptosis

Monocytes positive for 6-Sulfo LacNAc (slan) are a major subset of nonclassical CD14dimCD16+ monocytes in humans. We have shown that slan+ cells infiltrate lymphomas and elicit an antibody-dependent cellular cytotoxicity (ADCC) of neoplastic B cells mediated by the anti-CD20 therapeutic rituximab. Herein, by performing blocking experiments and flow cytometry analyses, as well as confocal microscopy and live-cell imaging assays, we extended the findings to other humanized antibodies and deciphered the underlying effector mechanism(s). Specifically, we show that, after coculture with target cells coated with anti-CD20 or anti-CD38, slan+ monocytes mediate trogocytosis, a cell-cell contact dependent, antibody-mediated process that triggers an active, mechanic disruption of target cell membranes. Trogocytosis by slan+ monocytes leads to a necrotic type of target cell death known as trogoptosis, which, once initiated, was partially sustained by endogenous TNFα. We also found that slan+ monocytes, unlike natural killer (NK) cells, mediate a direct ADCC with all types of anti-CD47 analyzed, and this was independent of their IgG isotype. The latter findings unveil a potentially relevant contribution by slan+ monocytes in mediating the therapeutic efficacy of anti-CD47 in clinical practice, which could be particularly important when NK cells are exhausted or deficient in number. Overall, our observations shed new light on the cytotoxic mechanisms exerted by slan+ monocytes in antibody-dependent tumor cell targeting and advance our knowledge on how to expand our therapeutic arsenal for cancer therapy.

CD4+CD25+FOXP3+ regulatory T cells: a potential "armor" to shield "transplanted allografts" in the war against ischemia reperfusion injury

Despite the advances in therapeutic interventions, solid organ transplantation (SOT) remains the "gold standard" treatment for patients with end-stage organ failure. Recently, vascularized composite allotransplantation (VCA) has reemerged as a feasible treatment option for patients with complex composite tissue defects. In both SOT and VCA, ischemia reperfusion injury (IRI) is inevitable and is a predominant factor that can adversely affect transplant outcome by potentiating early graft dysfunction and/or graft rejection. Restoration of oxygenated blood supply to an organ which was previously hypoxic or ischemic for a period of time triggers cellular oxidative stress, production of both, pro-inflammatory cytokines and chemokines, infiltration of innate immune cells and amplifies adaptive alloimmune responses in the affected allograft. Currently, Food and Drug Administration (FDA) approved drugs for the treatment of IRI are unavailable, therefore an efficacious therapeutic modality to prevent, reduce and/or alleviate allograft damages caused by IRI induced inflammation is warranted to achieve the best-possible transplant outcome among recipients. The tolerogenic capacity of CD4+CD25+FOXP3+ regulatory T cells (Tregs), have been extensively studied in the context of transplant rejection, autoimmunity, and cancer. It was not until recently that Tregs have been recognized as a potential cell therapeutic candidate to be exploited for the prevention and/or treatment of IRI, owing to their immunomodulatory potential. Tregs can mitigate cellular oxidative stress, produce anti-inflammatory cytokines, promote wound healing, and tissue repair and prevent the infiltration of pro-inflammatory immune cells in injured tissues. By using strategic approaches to increase the number of Tregs and to promote targeted delivery, the outcome of SOT and VCA can be improved. This review focuses on two sections: (a) the therapeutic potential of Tregs in preventing and mitigating IRI in the context of SOT and VCA and (b) novel strategies on how Tregs could be utilized for the prevention and/or treatment of IRI.

Settling the uncertainty about unconventional circulating tumor cells: Epithelial-to-mesenchymal transition, cell fusion and trogocytosis

Circulating tumor cells (CTCs) were first described 150 years ago. The so-called "classical" CTC populations (EpCAM+/CK+/CD45-) have been fully characterized and proposed as the most representative CTC subset, with clinical relevance. Nonetheless, other "atypical" or "unconventional" CTCs have also been identified, and their critical role in metastasis formation was demonstrated. In this chapter we illustrate the studies that led to the discovery of unconventional CTCs, defined as CTCs that display both epithelial and mesenchymal markers, or both cancer and immune markers, also in the form of hybrid cancer-immune cells. We also present biological explanations for the origin of these unconventional CTCs: epithelial to mesenchymal transition, cell-cell fusion and trogocytosis. We believe that a deeper knowledge on the biology of CTCs is needed to fully elucidate their role in cancer progression and their use as cancer biomarkers.

NK cells in peripheral blood carry trogocytosed tumor antigens from solid cancer cells

The innate immune lymphocyte lineage natural killer (NK) cell infiltrates tumor environment where it can recognize and eliminate tumor cells. NK cell tumor infiltration is linked to patient prognosis. However, it is unknown if some of these antitumor NK cells leave the tumor environment. In blood-borne cancers, NK cells that have interacted with leukemic cells are recognized by the co-expression of two CD45 isoforms (CD45RARO cells) and/or the plasma membrane presence of tumor antigens (Ag), which NK cells acquire by trogocytosis. We evaluated solid tumor Ag uptake by trogocytosis on NK cells by performing co-cultures in vitro. We analyzed NK population subsets by unsupervised dimensional reduction techniques in blood samples from breast tumor (BC) patients and healthy donors (HD). We confirmed that NK cells perform trogocytosis from solid cancer cells in vitro. The extent of trogocytosis depends on the target cell and the antigen, but not on the amount of Ag expressed by the target cell or the sensitivity to NK cell killing. We identified by FlowSOM (Self-Organizing Maps) several NK cell clusters differentially abundant between BC patients and HD, including anti-tumor NK subsets with phenotype CD45RARO+CD107a+. These analyses showed that bona-fide NK cells that have degranulated were increased in patients and, additionally, these NK cells exhibit trogocytosis of solid tumor Ag on their surface. However, the frequency of NK cells that have trogocytosed is very low and much lower than that found in hematological cancer patients, suggesting that the number of NK cells that exit the tumor environment is scarce. To our knowledge, this is the first report describing the presence of solid tumor markers on circulating NK subsets from breast tumor patients. This NK cell immune profiling could lead to generate novel strategies to complement established therapies for BC patients or to the use of peripheral blood NK cells in the theranostic of solid cancer patients after treatment.

Targeted Nanocarriers Co-Opting Pulmonary Intravascular Leukocytes for Drug Delivery to the Injured Brain

Ex vivo-loaded white blood cells (WBC) can transfer cargo to pathological foci in the central nervous system (CNS). Here we tested affinity ligand driven in vivo loading of WBC in order to bypass the need for ex vivo WBC manipulation. We used a mouse model of acute brain inflammation caused by local injection of tumor necrosis factor alpha (TNF-α). We intravenously injected nanoparticles targeted to intercellular adhesion molecule 1 (anti-ICAM/NP). We found that (A) at 2 h, >20% of anti-ICAM/NP were localized to the lungs; (B) of the anti-ICAM/NP in the lungs >90% were associated with leukocytes; (C) at 6 and 22 h, anti-ICAM/NP pulmonary uptake decreased; (D) anti-ICAM/NP uptake in brain increased up to 5-fold in this time interval, concomitantly with migration of WBCs into the injured brain. Intravital microscopy confirmed transport of anti-ICAM/NP beyond the blood-brain barrier and flow cytometry demonstrated complete association of NP with WBC in the brain (98%). Dexamethasone-loaded anti-ICAM/liposomes abrogated brain edema in this model and promoted anti-inflammatory M2 polarization of macrophages in the brain. In vivo targeted loading of WBC in the intravascular pool may provide advantages of coopting WBC predisposed to natural rapid mobilization from the lungs to the brain, connected directly via conduit vessels.

Dendritic Cells Overcome Cre/Lox Induced Gene Deficiency by Siphoning Material From Neighboring Cells Using Intracellular Monitoring-a Novel Mechanism of Antigen Acquisition

Macrophages and dendritic cells (DCs) in peripheral tissue interact closely with their local microenvironment by scavenging protein and nucleic acids released by neighboring cells. Material transfer between cell types is necessary for pathogen detection and antigen presentation, but thought to be relatively limited in scale. Recent reports, however, demonstrate that the quantity of transferred material can be quite large when DCs are in direct contact with live cells. This observation may be problematic for conditional gene deletion models that assume gene products will remain in the cell they are produced in. Here, we investigate whether conditional gene deletions induced by the widely used Cre/Lox system can be overcome at the protein level in DCs. Of concern, using the human Langerin Cre mouse model, we find that epidermal Langerhans cells and CD11b+CD103+ mesenteric DCs can overcome gene deletion if the deleted gene is expressed by neighboring cells. Surprisingly, we also find that the mechanism of material transfer does not resemble known mechanisms of antigen uptake, is dependent on extra- and intracellular calcium, PI3K, and scavenger receptors, and mediates a majority of material transfer to DCs. We term this novel process intracellular monitoring, and find that it is specific to DCs, but occurs in all murine DC subsets tested, as well as in human DCs. Transferred material is successfully presented and cross presented on MHC-II and MHC-I, and occurs between allogeneic donor and acceptors cells-implicating this widespread and unique process in immunosurveillance and organ transplantation.

Global Impact of Monoclonal Antibodies (mAbs) in Children: A Focus on Anti-GD2

Monoclonal antibodies (mAbs), as the name implies, are clonal antibodies that bind to the same antigen. mAbs are broadly used as diagnostic or therapeutic tools for neoplasms, autoimmune diseases, allergic conditions, and infections. Although most mAbs are approved for treating adult cancers, few are applicable to childhood malignancies, limited mostly to hematological cancers. As for solid tumors, only anti-disialoganglioside (GD2) mAbs are approved specifically for neuroblastoma. Inequities of drug access have continued, affecting most therapeutic mAbs globally. To understand these challenges, a deeper dive into the complex transition from basic research to the clinic, or between marketing and regulatory agencies, is timely. This review focuses on current mAbs approved or under investigation in pediatric cancer, with special attention on solid tumors and anti-GD2 mAbs, and the hurdles that limit their broad global access. Beyond understanding the mechanisms of drug resistance, the continual discovery of next generation drugs safer for children and easier to administer, the discovery of predictive biomarkers to avoid futility should ease the acceptance by patient, health care professionals and regulatory agencies, in order to expand clinical utility. With a better integration into the multimodal treatment for each disease, protocols that align with the regional clinical practice should also improve acceptance and cost-effectiveness. Communication and collaboration between academic institutions, pharmaceutical companies, and regulatory agencies should help to ensure accessible, affordable, and sustainable health care for all.

CTLA4 depletes T cell endogenous and trogocytosed B7 ligands via cis-endocytosis

CD28 and CTLA4 are T cell coreceptors that competitively engage B7 ligands CD80 and CD86 to control adaptive immune responses. While the role of CTLA4 in restraining CD28 costimulatory signaling is well-established, the mechanism has remained unclear. Here, we report that human T cells acquire antigen-presenting-cell (APC)-derived B7 ligands and major histocompatibility complex (MHC) via trogocytosis through CD28:B7 binding. Acquired MHC and B7 enabled T cells to autostimulate, and this process was limited cell-intrinsically by CTLA4, which depletes B7 ligands trogocytosed or endogenously expressed by T cells through cis-endocytosis. Extending this model to the previously proposed extrinsic function of CTLA4 in human regulatory T cells (Treg), we show that blockade of either CD28 or CTLA4 attenuates Treg-mediated depletion of APC B7, indicating that trogocytosis and CTLA4-mediated cis-endocytosis work together to deplete B7 from APCs. Our study establishes CTLA4 as a cell-intrinsic molecular sink that limits B7 availability on the surface of T cells, with implications for CTLA4-targeted therapy.

(Patho)Physiology of Glycosylphosphatidylinositol-Anchored Proteins II: Intercellular Transfer of Matter (Inheritance?) That Matters

Glycosylphosphatidylinositol (GPI)-anchored proteins (APs) are anchored at the outer leaflet of the plasma membrane (PM) bilayer by covalent linkage to a typical glycolipid and expressed in all eukaryotic organisms so far studied. Lipolytic release from PMs into extracellular compartments and intercellular transfer are regarded as the main (patho)physiological roles exerted by GPI-APs. The intercellular transfer of GPI-APs relies on the complete GPI anchor and is mediated by extracellular vesicles such as microvesicles and exosomes and lipid-free homo- or heteromeric aggregates, and lipoprotein-like particles such as prostasomes and surfactant-like particles, or lipid-containing micelle-like complexes. In mammalian organisms, non-vesicular transfer is controlled by the distance between donor and acceptor cells/tissues; intrinsic conditions such as age, metabolic state, and stress; extrinsic factors such as GPI-binding proteins; hormones such as insulin; and drugs such as anti-diabetic sulfonylureas. It proceeds either "directly" upon close neighborhood or contact of donor and acceptor cells or "indirectly" as a consequence of the induced lipolytic release of GPI-APs from PMs. Those displace from the serum GPI-binding proteins GPI-APs, which have retained the complete anchor, and become assembled in aggregates or micelle-like complexes. Importantly, intercellular transfer of GPI-APs has been shown to induce specific phenotypes such as stimulation of lipid and glycogen synthesis, in cultured human adipocytes, blood cells, and induced pluripotent stem cells. As a consequence, intercellular transfer of GPI-APs should be regarded as non-genetic inheritance of (acquired) features between somatic cells which is based on the biogenesis and transmission of matter such as GPI-APs and "membrane landscapes", rather than the replication and transmission of information such as DNA. Its operation in mammalian organisms remains to be clarified.

Trogocytosis and cross-dressing in antigen presentation

Antigen (Ag)-presenting cells capture or synthesize Ags that are processed into peptides bound and displayed on the plasma membrane by major histocompatibility complex (MHC) molecules. Here, we review a mechanism that enables cells to present Ag-loaded MHC molecules that they have not produced themselves, namely trogocytosis. During trogocytosis, a cell acquires fragments from another living cell without, in most cases, affecting the viability of the donor cell. The trogocytic cell can incorporate into its own plasma membrane (becoming cross-dressed) proteins acquired from the donor cell, including intact Ag and MHC molecules. Trogocytosis and cross-dressing expand the immunological functions that immune and nonimmune cells are able to carry out, with both beneficial and deleterious consequences.

Advancements in CAR-NK therapy: lessons to be learned from CAR-T therapy

Advancements in chimeric antigen receptor engineered T-cell (CAR-T) therapy have revolutionized treatment for several cancer types over the past decade. Despite this success, obstacles including the high price tag, manufacturing complexity, and treatment-associated toxicities have limited the broad application of this therapy. Chimeric antigen receptor engineered natural killer cell (CAR-NK) therapy offers a potential opportunity for a simpler and more affordable "off-the-shelf" treatment, likely with fewer toxicities. Unlike CAR-T, CAR-NK therapies are still in early development, with few clinical trials yet reported. Given the challenges experienced through the development of CAR-T therapies, this review explores what lessons we can apply to build better CAR-NK therapies. In particular, we explore the importance of optimizing the immunochemical properties of the CAR construct, understanding factors leading to cell product persistence, enhancing trafficking of transferred cells to the tumor, ensuring the metabolic fitness of the transferred product, and strategies to avoid tumor escape through antigen loss. We also review trogocytosis, an important emerging challenge that likely equally applies to CAR-T and CAR-NK cells. Finally, we discuss how these limitations are already being addressed in CAR-NK therapies, and what future directions may be possible.

MHC-dressing on dendritic cells: Boosting anti-tumor immunity via unconventional tumor antigen presentation

Dendritic cells are crucial for anti-tumor immune responses due to their ability to activate cytotoxic effector CD8⁺ T cells. Canonically, in anti-tumor immunity, dendritic cells activate CD8⁺ T cells in a process termed cross-presentation. Recent studies have demonstrated that another type of antigen presentation, MHC-dressing, also serves to activate CD8⁺ T cells against tumor cell-derived antigens. Understanding MHC-dressing's specific contributions to anti-tumor immunity can open up novel therapeutic avenues. In this review, we summarize the early studies that identified MHC-dressing as a relevant antigen presentation pathway before diving into a deeper discussion of the biology of MHC-dressing, focusing in particular on which dendritic cell subsets are most capable of performing MHC-dressing and how MHC-dressing compares to other forms of antigen presentation. We conclude by discussing the implications MHC-dressing has for anti-tumor immunity.

Basophils control T cell priming through soluble mediators rather than antigen presentation

Basophils play an important role in the development of type 2 immunity and have been linked to protective immunity against parasites but also inflammatory responses in allergic diseases. While typically classified as degranulating effector cells, different modes of cellular activation have been identified, which together with the observation that different populations of basophils exist in the context of disease suggest a multifunctional role. In this review we aim to highlight the role of basophils play in antigen presentation of type 2 immunity and focus on the contribution basophils play in the context of antigen presentation and T cell priming. We will discuss evidence suggesting that basophils perform a direct role in antigen presentation and relate it to findings that indicate cellular cooperation with professional antigen-presenting cells, such as dendritic cells. We will also highlight tissue-specific differences in basophil phenotypes that might lead to distinct roles in cellular cooperation and how these distinct interactions might influence immunological and clinical outcomes of disease. This review thus aims to consolidate the seemingly conflicting literature on the involvement of basophils in antigen presentation and tries to find a resolution to the discussion whether basophils influence antigen presentation through direct or indirect mechanisms.

A Case Study of Chimeric Antigen Receptor T Cell Function: Donor Therapeutic Differences in Activity and Modulation with Verteporfin

BACKGROUND

Chimeric antigen receptor (CAR) T cells have recently been demonstrated to extract and express cognate tumor antigens through trogocytosis. This process may contribute to tumor antigen escape, T cell exhaustion, and fratricide, which plays a central role in CAR dysfunction. We sought to evaluate the importance of this effect in epidermal growth factor receptor variant III (EGFRvIII) specific CAR T cells targeting glioma.

METHODS

EGFRvIII-specific CAR T cells were generated from various donors and analyzed for cytotoxicity, trogocytosis, and in vivo therapeutic activity against intracranial glioma. Tumor autophagy resulting from CAR T cell activity was evaluated in combination with an autophagy inducer (verteporfin) or inhibitor (bafilomycin A1).

RESULTS

CAR T cell products derived from different donors induced markedly divergent levels of trogocytosis of tumor antigen as well as PD-L1 upon engaging target tumor cells correlating with variability in efficacy in mice. Pharmacological facilitation of CAR induced-autophagy with verteporfin inhibits trogocytic expression of tumor antigen on CARs and increases CAR persistence and efficacy in mice.

CONCLUSION

These data propose CAR-induced autophagy as a mechanism counteracting CAR-induced trogocytosis and provide a new strategy to innovate high-performance CARs through pharmacological facilitation of T cell-induced tumor death.

Single-cell RNA sequencing reveals the suppressive effect of PPP1R15A inhibitor Sephin1 in antitumor immunity

Protein phosphatase 1 regulatory subunit 15A (PPP1R15A) is an important factor in the integrated stress response (ISR) in mammals and may play a crucial role in tumorigenesis. In our studies, we found an inhibitor of PPP1R15A, Sephin1, plays a protumorigenic role in mouse tumor models. By analyzing the single-cell transcriptome data of the mouse tumor models, we found that in C57BL/6 mice, Sephin1 treatment could lead to higher levels of ISR activity and lower levels of antitumor immune activities. Specifically, Sephin1 treatment caused reductions in antitumor immune cell types and lower expression levels of cytotoxicity-related genes. In addition, T cell receptor (TCR) repertoire analysis demonstrated that the clonal expansion of tumor-specific T cells was inhibited by Sephin1. A special TCR + macrophage subtype in tumor was identified to be significantly depleted upon Sephin1 treatment, implying its key antitumor role. These results suggest that PPP1R15A has the potential to be an effective target for tumor therapy.

T-Cell Mediated Immunity in Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and frequently lethal skin cancer with neuroendocrine characteristics. MCC can originate from either the presence of MCC polyomavirus (MCPyV) DNA or chronic ultraviolet (UV) exposure that can cause DNA mutations. MCC is predominant in sun-exposed regions of the body and can metastasize to regional lymph nodes, liver, lungs, bone, and brain. Older, light-skinned individuals with a history of significant sun exposure are at the highest risk. Previous studies have shown that tumors containing a high number of tumor-infiltrating T-cells have favorable survival, even in the absence of MCPyV DNA, suggesting that MCPyV infection enhances T-cell infiltration. However, other factors may also play a role in the host antitumor response. Herein, we review the impact of tumor infiltrating lymphocytes (TILs), mainly the CD4⁺, CD8⁺, and regulatory T-cell (Tregs) responses on the course of MCC, including their role in initiating MCPyV-specific immune responses. Furthermore, potential research avenues related to T-cell biology in MCC, as well as relevant immunotherapies are discussed.

Blockade of CD47 enhances the antitumor effect of macrophages in renal cell carcinoma through trogocytosis

Immune checkpoint inhibitors and vascular endothelial growth factor receptor tyrosine kinase inhibitors (VEGFR TKIs) are mainstream treatments for renal cell carcinoma (RCC). Both T cells and macrophages infiltrate the tumor microenvironment of RCC. CD47, an immune checkpoint of macrophages, transmits the “don’t eat me” signal to macrophages. We propose a novel therapeutic strategy that activates the antitumor effect of macrophages. We found that CD47 was expressed in patients with RCC, and high CD47 expression was indicative of worse overall survival in datasets from The Cancer Genome Atlas. We observed that CD47-blocking antibodies enhanced the antitumor effect of macrophages against human RCC cell lines. Trogocytosis, rather than phagocytosis, occurred and was promoted by increased cell-to-cell contact between macrophages and RCC cells. Trogocytosis induced by CD47 blockade occurred in the presence of CD11b integrin signaling in macrophages and was augmented when RCC cells were exposed to VEGFR TKIs, except for sunitinib. In conclusion, this study presents evidence that anti-CD47 blocking antibodies improve the antitumor effect of macrophages in RCC. In combination with VEGFR TKIs, CD47 blockade is a potential therapeutic strategy for patients with RCC.

KIR-based inhibitory CARs overcome CAR-NK cell trogocytosis-mediated fratricide and tumor escape

Trogocytosis is an active process that transfers surface material from targeted to effector cells. Using multiple in vivo tumor models and clinical data, we report that chimeric antigen receptor (CAR) activation in natural killer (NK) cells promoted transfer of the CAR cognate antigen from tumor to NK cells, resulting in (1) lower tumor antigen density, thus impairing the ability of CAR-NK cells to engage with their target, and (2) induced self-recognition and continuous CAR-mediated engagement, resulting in fratricide of trogocytic antigen-expressing NK cells (NKTROG+) and NK cell hyporesponsiveness. This phenomenon could be offset by a dual-CAR system incorporating both an activating CAR against the cognate tumor antigen and an NK self-recognizing inhibitory CAR that transferred a 'don't kill me' signal to NK cells upon engagement with their TROG+ siblings. This system prevented trogocytic antigen-mediated fratricide, while sparing activating CAR signaling against the tumor antigen, and resulted in enhanced CAR-NK cell activity.

Trogocytosis in innate immunity to cancer is an intimate relationship with unexpected outcomes

Trogocytosis is a cellular process whereby a cell acquires a membrane fragment from a donor cell in a contact-dependent manner allowing for the transfer of surface proteins with functional integrity. It is involved in various biological processes, including cell-cell communication, immune regulation, and response to pathogens and cancer cells, with poorly defined molecular mechanisms. With the exception of eosinophils, trogocytosis has been reported in most immune cells and plays diverse roles in the modulation of anti-tumor immune responses. Here, we report that eosinophils acquire membrane fragments from tumor cells early after contact through the CD11b/CD18 integrin complex. We discuss the impact of trogocytosis in innate immune cells on cancer progression in the context of the evidence that eosinophils can engage in trogocytosis with tumor cells. We also discuss shared and cell-specific mechanisms underlying this process based on in silico modeling and provide a hypothetical molecular model for the stabilization of the immunological synapse operating in granulocytes and possibly other innate immune cells that enables trogocytosis.

•

Trogocytosis in innate immune cells can regulate immune responses to cancer

•

Eosinophils engage in trogocytosis with tumor cells via CD11b/CD18 integrin complex

•

CD11b/CD18 integrin, focal adhesion molecules and actin network enable trogocytosis

Molecular targeted therapy for anticancer treatment

Since the initial clinical approval in the late 1990s and remarkable anticancer effects for certain types of cancer, molecular targeted therapy utilizing small molecule agents or therapeutic monoclonal antibodies acting as signal transduction inhibitors has served as a fundamental backbone in precision medicine for cancer treatment. These approaches are now used clinically as first-line therapy for various types of human cancers. Compared to conventional chemotherapy, targeted therapeutic agents have efficient anticancer effects with fewer side effects. However, the emergence of drug resistance is a major drawback of molecular targeted therapy, and several strategies have been attempted to improve therapeutic efficacy by overcoming such resistance. Herein, we summarize current knowledge regarding several targeted therapeutic agents, including classification, a brief biology of target kinases, mechanisms of action, examples of clinically used targeted therapy, and perspectives for future development.

ATF3 and CH25H regulate effector trogocytosis and anti-tumor activities of endogenous and immunotherapeutic cytotoxic T lymphocytes

Effector trogocytosis between malignant cells and tumor-specific cytotoxic T lymphocytes (CTLs) contributes to immune evasion through antigen loss on target cells and fratricide of antigen-experienced CTLs by other CTLs. The mechanisms regulating these events in tumors remain poorly understood. Here, we demonstrate that tumor-derived factors (TDFs) stimulated effector trogocytosis and restricted CTLs' tumoricidal activity and viability in vitro. TDFs robustly altered the CTL's lipid profile, including depletion of 25-hydroxycholesterol (25HC). 25HC inhibited trogocytosis and prevented CTL's inactivation and fratricide. Mechanistically, TDFs induced ATF3 transcription factor that suppressed the expression of 25HC-regulating gene-cholesterol 25-hydroxylase (CH25H). Stimulation of trogocytosis in the intratumoral CTL by the ATF3-CH25H axis attenuated anti-tumor immunity, stimulated tumor growth, and impeded the efficacy of chimeric antigen receptor (CAR) T cell adoptive therapy. Through use of armored CAR constructs or pharmacologic agents restoring CH25H expression, we reversed these phenotypes and increased the efficacy of immunotherapies.

Neutrophil trogocytosis during their trans-endothelial migration: role of extracellular CIRP

Background

Neutrophils are the most abundant innate immune cells in the circulating blood, and they act as the first responder against bacterial and fungal infection. However, accumulation of activated neutrophils can cause severe inflammation and tissue damage. Recently, neutrophil trogocytosis or membrane transfer with neighboring cells was reported to modulate immune responses. Extracellular cold-inducible RNA binding protein (eCIRP) is a newly identified damage-associated molecular pattern (DAMP). eCIRP can activate neutrophils to be more pro-inflammatory. This study aimed to identify the role of eCIRP in neutrophil trogocytosis during their trans-endothelial migration.

Methods

A trans-endothelial migration (TEM) assay using bone marrow neutrophils and mouse primary lung vascular endothelial cells was conducted using transwell chambers and neutrophil trogocytosis was assessed in vitro. In an in vivo mouse model of acute lung injury, neutrophil trogocytosis was assessed from bronchoalveolar lavage fluid.

Results

In TEM assay, the trogocytosis of neutrophils occurred during trans-endothelial migration and eCIRP significantly increased the percentage of these neutrophils. The trogocytosed neutrophils acquired the endothelial membrane containing junctional adhesion molecule-C (JAM-C) and VE-cadherin, and these membrane patches were polarized by Mac-1 binding. Furthermore, eCIRP-induced JAM-C positive trogocytosed neutrophils are more pro-inflammatory than the JAM-C negative counterpart. JAM-C positive trogocytosed neutrophils were also observed in the bronchoalveolar lavage fluid of a mouse model of acute lung injury.

Conclusion

These data suggest that during the paracellular trans-endothelial migration of neutrophils in response to inflammation, eCIRP induces trogocytosis of neutrophils, and the trogocytosed neutrophils exhibit an exaggerated pro-inflammatory phenotype promoting acute lung injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00515-3.

FcγR-Mediated Trogocytosis 2.0: Revisiting History Gives Rise to a Unifying Hypothesis

There is increasing interest in the clinical implications and immunology of trogocytosis, a process in which the receptors on acceptor cells remove and internalize cognate ligands from donor cells. We have reported that this phenomenon occurs in cancer immunotherapy, in which cells that express FcγR remove and internalize CD20 and bound mAbs from malignant B cells. This process can be generalized to include other reactions including the immune adherence phenomenon and antibody-induced immunosuppression. We discuss in detail FcγR-mediated trogocytosis and the evidence supporting a proposed predominant role for liver sinusoidal endothelial cells via the action of the inhibitory receptor FcγRIIb2. We describe experiments to test the validity of this hypothesis. The elucidation of the details of FcγR-mediated trogocytosis has the potential to allow for the development of novel therapies that can potentially block or enhance this reaction, depending upon whether the process leads to unfavorable or positive biological effects.

Glycoengineered anti-CD39 promotes anticancer responses by depleting suppressive cells and inhibiting angiogenesis in tumor models

Immunosuppressive cells accumulating in the tumor microenvironment constitute a formidable barrier that interferes with current immunotherapeutic approaches. A unifying feature of these tumor-associated immune and vascular endothelial cells appears to be the elevated expression of ectonucleotidase CD39, which in tandem with ecto-5'-nucleotidase CD73, catalyzes the conversion of extracellular ATP into adenosine. We glycoengineered an afucosylated anti-CD39 IgG2c and tested this reagent in mouse melanoma and colorectal tumor models. We identified major biological effects of this approach on cancer growth, associated with depletion of immunosuppressive cells, mediated through enhanced Fcγ receptor-directed (FcγR-directed), antibody-dependent cellular cytotoxicity (ADCC). Furthermore, regulatory/exhausted T cells lost CD39 expression, as a consequence of antibody-mediated trogocytosis. Most strikingly, tumor-associated macrophages and endothelial cells with high CD39 expression were effectively depleted following antibody treatment, thereby blocking angiogenesis. Tumor site-specific cellular modulation and lack of angiogenesis synergized with chemotherapy and anti-PD-L1 immunotherapy in experimental tumor models. We conclude that depleting suppressive cells and targeting tumor vasculature, through administration of afucosylated anti-CD39 antibody and the activation of ADCC, comprises an improved, purinergic system-modulating strategy for cancer therapy.

Measuring trogocytosis between ovarian tumor and natural killer cells

Trogocytosis is an active transport mechanism by which one cell extracts a plasma membrane fragment with embedded molecules from an adjacent cell in a contact-dependent process leading to the acquisition of a new function. Our protocol, which has general applicability, consolidates and optimizes existing protocols while highlighting key experimental variables to demonstrate that natural killer (NK) cells acquire the tetraspanin CD9 by trogocytosis from ovarian tumor cells. For complete details on the use and execution of this protocol, please refer to Gonzalez et al. (2021).

Overcome tumor relapse in CAR T cell therapy

Chimeric antigen receptor (CAR) T cell therapy is a novel therapeutic approach that uses gene editing techniques and lentiviral transduction to engineer T cells so that they can effectively kill tumors. However, CAR T cell therapy still has some drawbacks: many patients who received CAR T cell therapy and achieve remission, still had tumor relapse and treatment resistance, which may be due to tumor immune escape and CAR T cell dysfunction. To overcome tumor relapse, more researches are being done to optimize CAR T cell therapy to make it more precise and personalized, including screening for more specific tumor antigens, developing novel CAR T cells, and combinatorial treatment approaches. In this review, we will discuss the mechanisms as well as the progress of research on overcoming plans.

Cancer cells resist antibody-mediated destruction by neutrophils through activation of the exocyst complex

BACKGROUND

Neutrophils kill antibody-opsonized tumor cells using trogocytosis, a unique mechanism of destruction of the target plasma. This previously unknown cytotoxic process of neutrophils is dependent on antibody opsonization, Fcγ receptors and CD11b/CD18 integrins. Here, we demonstrate that tumor cells can escape neutrophil-mediated cytotoxicity by calcium (Ca2+)-dependent and exocyst complex-dependent plasma membrane repair.

METHODS

We knocked down EXOC7 or EXOC4, two exocyst components, to evaluate their involvement in tumor cell membrane repair after neutrophil-induced trogocytosis. We used live cell microscopy and flow cytometry for visualization of the host and tumor cell interaction and tumor cell membrane repair. Last, we reported the mRNA levels of exocyst in breast cancer tumors in correlation to the response in trastuzumab-treated patients.

RESULTS

We found that tumor cells can evade neutrophil antibody-dependent cellular cytotoxicity (ADCC) by Ca2+-dependent cell membrane repair, a process induced upon neutrophil trogocytosis. Absence of exocyst components EXOC7 or EXOC4 rendered tumor cells vulnerable to neutrophil-mediated ADCC (but not natural killer cell-mediated killing), while neutrophil trogocytosis remained unaltered. Finally, mRNA levels of exocyst components in trastuzumab-treated patients were inversely correlated to complete response to therapy.

CONCLUSIONS

Our results support that neutrophil attack towards antibody-opsonized cancer cells by trogocytosis induces an active repair process by the exocyst complex in vitro. Our findings provide insight to the possible contribution of neutrophils in current antibody therapies and the tolerance mechanism of tumor cells and support further studies for potential use of the exocyst components as clinical biomarkers.

NK Cells Acquire CCR5 and CXCR4 by Trogocytosis in People Living with HIV-1

NK cells play a major role in the antiviral immune response, including against HIV-1. HIV-1 patients have impaired NK cell activity with a decrease in CD56^dim NK cells and an increase in the CD56⁻CD16⁺ subset, and recently it has been proposed that a population of CD56⁺NKG2C⁺KIR⁺CD57⁺ cells represents antiviral memory NK cells. Antiretroviral therapy (ART) partly restores the functional activity of this lymphocyte lineage. NK cells when interacting with their targets can gain antigens from them by the process of trogocytosis. Here we show that NK cells can obtain CCR5 and CXCR4, but barely CD4, from T cell lines by trogocytosis in vitro. By UMAP (Uniform Manifold Approximation and Projection), we show that aviremic HIV-1 patients have unique NK cell clusters that include cells expressing CCR5, NKG2C and KIRs, but lack CD57 expression. Viremic patients have a larger proportion of CXCR4⁺ and CCR5⁺ NK cells than healthy donors (HD) and this is largely increased in CD107⁺ cells, suggesting a link between degranulation and trogocytosis. In agreement, UMAP identified a specific NK cell cluster in viremic HIV-1 patients, which contains most of the CD107a⁺, CCR5⁺ and CXCR4⁺ cells. However, this cluster lacks NKG2C expression. Therefore, NK cells can gain CCR5 and CXCR4 by trogocytosis, which depends on degranulation.