Death, danger & immunity: Fundamental mechanisms linking pathogenic or iatrogenic cell death events to immune responses

Immunogenic cell death inducers for enhanced cancer immunotherapy

Inducing the immunogenic cell death (ICD) of cancer cells is an important method to improve the immunogenicity of tumor cells for enhanced cancer immunotherapy. Therefore, we discuss the ICD process and then highlight various ICD inducers and strategies for triggering the ICD of cancer cells. We hope that this Feature Article will inspire readers to develop more effective ICD inducers.

Sensing Tissue Damage by Myeloid C-Type Lectin Receptors

After both sterile and infectious insults, damage is inflicted on tissues leading to accidental or programmed cell death. In addition, events of programmed cell death also take place under homeostatic conditions, such as in embryo development or in the turnover of hematopoietic cells. Mammalian tissues are seeded with myeloid immune cells, which harbor a plethora of receptors that allow the detection of cell death, modulating immune responses. The myeloid C-type lectin receptors (CLRs) are one of the most prominent families of receptors involved in tailoring immunity after sensing dead cells. In this chapter, we will cover a diversity of signals arising from different forms of cell death and how they are recognized by myeloid CLRs. We will also explore how myeloid cells develop their sentinel function, exploring how some of these CLRs identify cell death and the type of responses triggered thereof. In particular, we will focus on DNGR-1 (CLEC9A), Mincle (CLEC4E), CLL-1 (CLEC12A), LOX-1 (OLR1), CD301 (CLEC10A) and DEC-205 (LY75) as paradigmatic death-sensing CLRs expressed by myeloid cells. The molecular processes triggered after cell death recognition by myeloid CLRs contribute to the regulation of immune responses in pathologies associated with tissue damage, such as infection, autoimmunity and cancer. A better understanding of these processes may help to improve the current approaches for therapeutic intervention.

Mitoxantrone-Loaded Nanoparticles for Magnetically Controlled Tumor Therapy-Induction of Tumor Cell Death, Release of Danger Signals and Activation of Immune Cells

Stimulating the patient’s immune system represents a promising therapeutic strategy to fight cancer. However, low immunogenicity of the tumor cells within an immune suppressive milieu often leads to weak anti-tumor immune responses. Additionally, the immune system may be impaired by accompanying aggressive chemotherapies. We show that mitoxantrone, bound to superparamagnetic iron oxide nanoparticles (SPIONs) as the transport system, can be magnetically accumulated in adherent HT-29 colon carcinoma cells, thereby inducing the same cell death phenotype as its soluble counterpart, a chemotherapeutic agent and prototypic inductor of immunogenic cell death. The nanoparticle-loaded drug induces cell cycle stop, apoptosis and secondary necrosis in a dose- and time-dependent manner comparable to the free drug. Cell death was accompanied by the release of interleukin-8 and damage-associated molecular patterns (DAMPs) such as HSP70 and ATP, which fostered chemotactic migration of monocytes and maturation of dendritic cells. We furthermore ensured absence of endotoxin contaminations and compatibility with erythrocytes and platelets and investigated the influence on plasma coagulation in vitro. Summarizing, with magnetic enrichment, mitoxantrone can be accumulated at the desired place, sparing healthy peripheral cells and tissues, such as immune cells. Conserving immune competence in cancer patients in the future might allow combined therapeutic approaches with immune therapies (e.g., checkpoint inhibitors).

Quantitative determination of phagocytosis by bone marrow-derived dendritic cells via imaging flow cytometry

Immunogenic cell death (ICD), induced by certain anticancer chemotherapeutics, leads to the emission of danger associated molecular patterns (DAMP) by cancer cells, which facilitates the attraction, activation and maturation of dendritic cells (DC) as well as the subsequent priming of effector T cells. In this context calreticulin (CALR) exposed at an early stage of ICD at the surface of the cancer cells serves as phagocytic signal and triggers the formation of immunological synapses between malignant cells and DC. Subsequent phagocytosis facilitates the transfer of tumor associated antigen and thus depicts a fundamental step in the generation of anticancer immunity. Here we provide an imaging flowcytometric protocol for the quantification of ICD-associated DC phagocytosis of cancer cells. As compared to the traditional flowcytometry-based analysis, the presented method offers additional means of differentiation between the transient formation of immunological synapses and the final DC-mediated phagocytosis of cancer cells.

Quantification of eIF2alpha phosphorylation during immunogenic cell death

Immunogenic cell death (ICD) is a particular modality of cell death that can be triggered by selected anticancer chemotherapeutics. Tumor cells undergoing ICD can induce an adaptive anticancer immune response that targets residual cancer cells with the same antigenic profile. The activation of a full-blown immune response against the tumor antigen is preceded by the release or exposure of danger associated molecular patterns (DAMPs) by tumor cells that stimulate the attraction, activation and maturation of dendritic cells and eventually the antigen-specific priming of cytotoxic T lymphocytes (CTLs). The phosphorylation of the eukaryotic translation initiation factor (EIF2A) is a pathognomonic characteristic of ICD, which governs the release/exposure of DAMPs such as ATP and calreticulin and thus the immunogenicity of cell death. Here we describe techniques to detect eIF2alpha phosphorylation for the assessment of ICD.