Detection of immunogenic cell death and its relevance for cancer therapy

Abstract

Chemotherapy, radiation therapy, as well as targeted anticancer agents can induce clinically relevant tumor-targeting immune responses, which critically rely on the antigenicity of malignant cells and their capacity to generate adjuvant signals. In particular, immunogenic cell death (ICD) is accompanied by the exposure and release of numerous damage-associated molecular patterns (DAMPs), which altogether confer a robust adjuvanticity to dying cancer cells, as they favor the recruitment and activation of antigen-presenting cells. ICD-associated DAMPs include surface-exposed calreticulin (CALR) as well as secreted ATP, annexin A1 (ANXA1), type I interferon, and high-mobility group box 1 (HMGB1). Additional hallmarks of ICD encompass the phosphorylation of eukaryotic translation initiation factor 2 subunit-α (EIF2S1, better known as eIF2α), the activation of autophagy, and a global arrest in transcription and translation. Here, we outline methodological approaches for measuring ICD markers in vitro and ex vivo for the discovery of next-generation antineoplastic agents, the development of personalized anticancer regimens, and the identification of optimal therapeutic combinations for the clinical management of cancer.

Fig. 1. Main hallmarks of ICD.

Different inducers of immunogenic cell death (ICD) have been shown to elicit incompletely overlapping molecular signatures with respect to ICD biomarkers. This not only reinforces the need for the simultaneous assessment of multiple surrogate ICD biomarkers in the context of screening campaigns, but also identifies an originally unsuspected diversity in the molecular and cellular mechanisms supporting adaptive immunity downstream of danger signaling. ANXA1, annexin A1; CALR, calreticulin, CXCL10, C-X-C motif chemokine ligand 10; ECP, extracorporeal photochemotherapy; HHP, high hydrostatic pressure; HMGB1, high-mobility group box 1; IFN, interferon; IL-1β (official name: IL1B), interleukin 1 beta; IL-17 (official name: IL17), interleukin 17; PDT, photodynamic therapy.

Fig. 2. Main methodological approaches to measure ICD biomarkers in vitro.

The main hallmarks of immunogenic cell death (ICD) can be assessed by flow cytometry, (immuno)fluorescence microscopy, immunoblotting, or luminometry, based on a variety of different approaches. ANXA1, annexin A1; CALR, calreticulin, CXCL10, C-X-C motif chemokine ligand 10; HMGB1, high-mobility group box 1; IFN, interferon; IL-1β (official name: IL1B), interleukin 1 beta; IL-17 (official name: IL17), interleukin 17; RUSH, retention using selective hooks.

Fig. 3. ICD inducers from HCS campaigns to the bedside.

Several high-content screening (HCS) campaigns have led to the discovery of novel immunogenic cell death (ICD) inducers that have entered clinical testing, either alone (A), or combined with immune checkpoint inhibitors (B). ICD induction is also being harnessed for the generation of dendritic cell (DC)-based vaccines for therapeutic purposes (C). Finally, biomarkers of ICD may be used to stratify patient populations and hence identify individuals with an elevated likelihood to respond to treatment and/or subjects that would benefit from strategies correcting existing defects in ICD signaling (D). HHP, high hydrostatic pressure.