Immunogenic and Non-immunogenic Cell Death in the Tumor Microenvironment

Programmed cell death in tumor immunity: mechanistic insights and clinical implications

Programmed cell death (PCD) is an evolutionarily conserved mechanism of cell suicide that is controlled by various signaling pathways. PCD plays an important role in a multitude of biological processes, such as cell turnover, development, tissue homeostasis and immunity. Some forms of PCD, including apoptosis, autophagy-dependent cell death, pyroptosis, ferroptosis and necroptosis, contribute to carcinogenesis and cancer development, and thus have attracted increasing attention in the field of oncology. Recently, increasing research-based evidence has demonstrated that PCD acts as a critical modulator of tumor immunity. PCD can affect the function of innate and adaptive immune cells, which leads to distinct immunological consequences, such as the priming of tumor-specific T cells, immunosuppression and immune evasion. Targeting PCD alone or in combination with conventional immunotherapy may provide new options to enhance the clinical efficacy of anticancer therapeutics. In this review, we introduce the characteristics and mechanisms of ubiquitous PCD pathways (e.g., apoptosis, autophagy-dependent cell death, pyroptosis and ferroptosis) and explore the complex interaction between these cell death mechanisms and tumor immunity based on currently available evidence. We also discuss the therapeutic potential of PCD-based approaches by outlining clinical trials targeting PCD in cancer treatment. Elucidating the immune-related effects of PCD on cancer pathogenesis will likely contribute to an improved understanding of oncoimmunology and allow PCD to be exploited for cancer treatment.

Brentuximab Vedotin-Driven Microtubule Disruption Results in Endoplasmic Reticulum Stress Leading to Immunogenic Cell Death and Antitumor Immunity

Brentuximab vedotin, a CD30-directed antibody-drug conjugate (ADC), is approved for clinical use in multiple CD30-expressing lymphomas. The cytotoxic payload component of brentuximab vedotin is monomethyl auristatin E (MMAE), a highly potent microtubule-disrupting agent. Preclinical results provided here demonstrate that treatment of cancer cells with brentuximab vedotin or free MMAE leads to a catastrophic disruption of the microtubule network eliciting a robust endoplasmic reticulum (ER) stress response that culminates in the induction of the classic hallmarks of immunogenic cell death (ICD). In accordance with the induction of ICD, brentuximab vedotin-killed lymphoma cells drove innate immune cell activation in vitro and in vivo. In the "gold-standard" test of ICD, vaccination of mice with brentuximab vedotin or free MMAE-killed tumor cells protected animals from tumor rechallenge; in addition, T cells transferred from previously vaccinated animals slowed tumor growth in immunodeficient mice. Immunity acquired from killed tumor cell vaccination was further amplified by the addition of PD-1 blockade. In a humanized model of CD30+ B-cell tumors, treatment with brentuximab vedotin drove the expansion and recruitment of autologous Epstein-Barr virus-reactive CD8+ T cells potentiating the activity of anti-PD-1 therapy. Together, these data support the ability of brentuximab vedotin and MMAE to drive ICD in tumor cells resulting in the activation of antigen-presenting cells and augmented T-cell immunity. These data provide a strong rationale for the clinical combination of brentuximab vedotin and other MMAE-based ADCs with checkpoint inhibitors.

Silver nanoparticles induce a non-immunogenic tumor cell death

Immunogenic cell death (ICD) is a form of cell death characterized by the release of danger signals required to trigger an adaptive immune response against tumor-associated antigens. Silver nanoparticles (AgNP) display anti-proliferative and cytotoxic effects in tumor cells, but it has not been previously studied whether AgNP act as an ICD inductor. The present study evaluated the in vitro release of calreticulin as a damage-associated molecular pattern (DAMP) associated with the cytotoxicity of AgNP and their in vivo anti-cancer effects. In vitro, mouse CT26 colon carcinoma and MCA205 fibrosarcoma cells were exposed to AgNP and then cell proliferation, adhesion, and release of calreticulin were determined. The results indicated there were time- and concentration-related anti-proliferative effects of AgNP in both the CT26 and MCA205 lines. Concurrently, changes in cell adhesion were detected mainly in the CT26 cells. Regarding DAMP detection, a significant increase in calreticulin was observed only in CT26 cells treated with doxorubicin and AgNP; however, no differences were found in the MCA205 cells. In vivo, the survival and growth of subcutaneous tumors were monitored after vaccination of mice with cell debris from tumor cells treated with AgNP or after intra-tumoral administration of AgNP to established tumors. Consequently, anti-tumoral prophylactic immunization with AgNP-dead cells failed to protect mice from tumor re-challenge; intra-tumor injection of AgNP did not induce a significant effect. In conclusion, there was a noticeable anti-tumoral effect of AgNP in vitro in both CT26 and MCA205 cell lines, accompanied by the release of calreticulin in CT26 cells. In vivo, immunization with cell debris derived from AgNP-treated tumor cells failed to induce a protective immune response in the cancer model mice. Clearly, further research is needed to determine if one could combine AgNP with other ICD inducers to improve the anti-tumor effect of these nanoparticles in vivo.

Intratumoral co-injection of NK cells and NKG2A-neutralizing monoclonal antibodies

NK-cell reactivity against cancer is conceivably suppressed in the tumor microenvironment by the interaction of the inhibitory receptor NKG2A with the non-classical MHC-I molecules HLA-E in humans or Qa-1b in mice. We found that intratumoral delivery of NK cells attains significant therapeutic effects only if co-injected with anti-NKG2A and anti-Qa-1b blocking monoclonal antibodies against solid mouse tumor models. Such therapeutic activity was contingent on endogenous CD8 T cells and type-1 conventional dendritic cells (cDC1). Moreover, the anti-tumor effects were enhanced upon combination with systemic anti-PD-1 mAb treatment and achieved partial abscopal efficacy against distant non-injected tumors. In xenografted mice bearing HLA-E-expressing human cancer cells, intratumoral co-injection of activated allogeneic human NK cells and clinical-grade anti-NKG2A mAb (monalizumab) synergistically achieved therapeutic effects. In conclusion, these studies provide evidence for the clinical potential of intratumoral NK cell-based immunotherapies that exert their anti-tumor efficacy as a result of eliciting endogenous T-cell responses.

Chrysin and chrysin-loaded nanocarriers induced immunogenic cell death on B16 melanoma cells

Induction of immunogenic cell death (ICD) is a promising strategy for cancer immunotherapy. Chrysin, which has potential anticancer effects, faces limitations in clinical applications due to its poor water solubility. This study aimed to formulate chrysin with PEG-poly(α-benzylcarboxylate-ε-caprolactone) (PBCL) nanoparticles (NPs) and assess their anticancer and ICD-inducing potency in melanoma cells, comparing with free chrysin. The co-solvent evaporation method was employed to develop chrysin-loaded NPs. UV spectroscopy, dynamic light scattering, and the dialysis bag method were used to evaluate the encapsulation efficiency (EE), particle size, polydispersity index (PDI), and drug release profile, respectively. The anticancer effects of the drugs were assessed using the MTT and trypan blue exclusion assays. Flow cytometry was employed to evaluate apoptosis and calreticulin (CRT) expression. ELISA and western blotting were used to detect heat shock protein 90 (HSP90), Annexin A1, GRP78 (Glucose-related protein78), and activated protein kinase R-like endoplasmic reticulum kinase (p-PERK). Chrysin-loaded PEG-PBCL NPs (chrysin-PEG-PBCL) showed an EE of 97 ± 1%. Chrysin-PEG-PBCL was 38.18 ± 3.96 nm in size, with a PDI being 0.62 ± 0.23. Chrysin-PEG-PBCL showed an initial burst release, followed by sustained release over 24 h. Chrysin-PEG-PBCL exhibited a significantly stronger anticancer effect in B16 cells. Chrysin-PEG-PBCL was found to be more potent in inducing apoptosis. Both free chrysin and chrysin NPs induced ICD as indicated by an increase in the levels of ICD biomarkers. Interestingly, chrysin NPs were found to be more potent inducers of ICD than the free drug. These findings demonstrate that chrysin and chrysin-PEG-PBCL NPs can induce ICD in B16 cells. PEG-PBCL NPs significantly enhanced the potency of chrysin in inducing ICD compared to its free form.

Mechanisms of cancer cell death induction by triptolide

Drug resistance is a hot topic issue in cancer research and therapy. Although cancer therapy including radiotherapy and anti-cancer drugs can kill malignant cells within the tumor, cancer cells can develop a wide range of mechanisms to resist the toxic effects of anti-cancer agents. Cancer cells may provide some mechanisms to resist oxidative stress and escape from apoptosis and attack by the immune system. Furthermore, cancer cells may resist senescence, pyroptosis, ferroptosis, necroptosis, and autophagic cell death by modulating several critical genes. The development of these mechanisms leads to resistance to anti-cancer drugs and also radiotherapy. Resistance to therapy can increase mortality and reduce survival following cancer therapy. Thus, overcoming mechanisms of resistance to cell death in malignant cells can facilitate tumor elimination and increase the efficiency of anti-cancer therapy. Natural-derived molecules are intriguing agents that may be suggested to be used as an adjuvant in combination with other anticancer drugs or radiotherapy to sensitize cancer cells to therapy with at least side effects. This paper aims to review the potential of triptolide for inducing various types of cell death in cancer cells. We review the induction or resistance to different cell death mechanisms such as apoptosis, autophagic cell death, senescence, pyroptosis, ferroptosis, and necrosis following the administration of triptolide. We also review the safety and future perspectives for triptolide and its derivatives in experimental and human studies. The anticancer potential of triptolide and its derivatives may make them effective adjuvants for enhancing tumor suppression in combination with anticancer therapy.

(-)-Guaiol triggers immunogenic cell death and inhibits tumor growth in non-small cell lung cancer

(-)-Guaiol is a sesquiterpenoid found in many traditional Chinese medicines with potent antitumor activity. However, its therapeutic effect and mechanism in non-small cell lung cancer (NSCLC) have not been fully elucidated. In this study, (-)-Guaiol was found to induce immunogenic cell death (ICD) in NSCLC in vitro. Using (-)-Guaiol in vivo, we found that (-)-Guaiol could suppress tumor growth, increase dendritic cell activation, and enhance T-cell infiltration. Vaccination experiments suggest that cellular immunoprophylaxis after (-)-Guaiol intervention can suppress tumor growth. Previous studies have found that (-)-Guaiol induces apoptosis and autophagy in NSCLC. Apoptosis and autophagy are closely related to ICD. To explore whether autophagy and apoptosis are involved in (-)-Guaiol-induced ICD, we used inhibitors of apoptosis and autophagy. The results showed that the release of damage-associated molecular patterns (DAMPs) was partly reversed after inhibition of apoptosis and autophagy. In conclusion, these results suggested that the (-)-Guaiol triggers immunogenic cell death and inhibits tumor growth in NSCLC.

Spotlight on NLRP6 and Tumor Research Situation: A Potential Cancer Participant

NOD-like receptor family pyrin domain containing 6 (NLRP6) is a new pattern recognition receptor in the mammalian innate immune system. Both the liver and the gut exhibit substantial levels of cytoplasmic expression. It can speed up cell response to endogenous danger signals or exogenous pathogen infection. NLRP6 can function in various ways as an inflammasome or a noninflammasome. The understanding of NLRP6 is steadily increasing thanks to ongoing investigations, but due to discrepancies in how those studies have described their link with tumors, the significance of NLRP6 in the emergence of cancer is still debatable as of this writing. This article will use the structure and function of NLRP6 as the pivotal point and thoroughly explain the present interactions between NLRP6 and tumors and any possible clinical benefits.

Immunogenic cell death after combined treatment with radiation and ATR inhibitors is dually regulated by apoptotic caspases

Introduction

Inhibitors of the ATR kinase act as radiosensitizers through abrogating the G2 checkpoint and reducing DNA repair. Recent studies suggest that ATR inhibitors can also increase radiation-induced antitumor immunity, but the underlying immunomodulating mechanisms remain poorly understood. Moreover, it is poorly known how such immune effects relate to different death pathways such as caspase-dependent apoptosis. Here we address whether ATR inhibition in combination with irradiation may increase the presentation of hallmark factors of immunogenic cell death (ICD), and to what extent caspase activation regulates this response.

Methods

Human lung cancer and osteosarcoma cell lines (SW900, H1975, H460, U2OS) were treated with X-rays and ATR inhibitors (VE822; AZD6738) in the absence and presence of a pan-caspase inhibitor. The ICD hallmarks HMGB1 release, ATP secretion and calreticulin surface-presentation were assessed by immunoblotting of growth medium, the CellTiter-Glo assay and an optimized live-cell flow cytometry assay, respectively. To obtain accurate measurement of small differences in the calreticulin signal by flow cytometry, we included normalization to a barcoded control sample.

Results

Extracellular release of HMGB1 was increased in all the cell lines at 72 hours after the combined treatment with radiation and ATR inhibitors, relative to mock treatment or cells treated with radiation alone. The HMGB1 release correlated largely - but not strictly - with loss of plasma membrane integrity, and was suppressed by addition of the caspase inhibitor. However, one cell line showed HMGB1 release despite caspase inhibition, and in this cell line caspase inhibition induced pMLKL, a marker for necroptosis. ATP secretion occurred already at 48 hours after the co-treatment and did clearly not correlate with loss of plasma membrane integrity. Addition of pan-caspase inhibition further increased the ATP secretion. Surface-presentation of calreticulin was increased at 24-72 hours after irradiation, but not further increased by either ATR or caspase inhibition.

Conclusion

These results show that ATR inhibition can increase the presentation of two out of three ICD hallmark factors from irradiated human cancer cells. Moreover, caspase activation distinctly affects each of the hallmark factors, and therefore likely plays a dual role in tumor immunogenicity by promoting both immunostimulatory and -suppressive effects.

Analysis of immunogenic cell death in atherosclerosis based on scRNA-seq and bulk RNA-seq data

BACKGROUND

Regulated cell death plays a very important role in atherosclerosis (AS). Despite a large number of studies, there is a lack of literature on immunogenic cell death (ICD) in AS.

METHOD

Carotid atherosclerotic plaque single-cell RNA (scRNA) sequencing data were analyzed to define involved cells and determine their transcriptomic characteristics. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, CIBERSORT, ESTIMATE and ssGSEA (Gene Set Enrichment Analysis), consensus clustering analysis, random forest (RF), Decision Curve Analysis (DCA), and the Drug-Gene Interaction and DrugBank databases were applied for bulk sequencing data. All data were downloaded from Gene Expression Omnibus (GEO).

RESULT

mDCs and CTLs correlated obviously with AS occurrence and development (k2(mDCs) = 48.333, P < 0.001; k2(CTL) = 130.56, P < 0.001). In total, 21 differentially expressed genes were obtained for the bulk transcriptome; KEGG enrichment analysis results were similar to those for differentially expressed genes in endothelial cells. Eleven genes with a gene importance score > 1.5 were obtained in the training set and validated in the test set, resulting in 8 differentially expressed genes for ICD. A model to predict occurrence of AS and 56 drugs that may be used to treat AS were obtained with these 8 genes.

CONCLUSION

Immunogenic cell death occurs mainly in endothelial cells in AS. ICD maintains chronic inflammation in AS and plays a crucial role in its occurrence and development. ICD related genes may become drug-targeted genes for AS treatment.

Ferroptosis heterogeneity in triple-negative breast cancer reveals an innovative immunotherapy combination strategy

Treatment of triple-negative breast cancer (TNBC) remains challenging. Deciphering the orchestration of metabolic pathways in regulating ferroptosis will provide new insights into TNBC therapeutic strategies. Here, we integrated the multiomics data of our large TNBC cohort (n = 465) to develop the ferroptosis atlas. We discovered that TNBCs had heterogeneous phenotypes in ferroptosis-related metabolites and metabolic pathways. The luminal androgen receptor (LAR) subtype of TNBC was characterized by the upregulation of oxidized phosphatidylethanolamines and glutathione metabolism (especially GPX4), which allowed the utilization of GPX4 inhibitors to induce ferroptosis. Furthermore, we verified that GPX4 inhibition not only induced tumor ferroptosis but also enhanced antitumor immunity. The combination of GPX4 inhibitors and anti-PD1 possessed greater therapeutic efficacy than monotherapy. Clinically, higher GPX4 expression correlated with lower cytolytic scores and worse prognosis in immunotherapy cohorts. Collectively, this study demonstrated the ferroptosis landscape of TNBC and revealed an innovative immunotherapy combination strategy for refractory LAR tumors.

Silibinin induces immunogenic cell death in cancer cells and enhances the induced immunogenicity by chemotherapy

Introduction: Silibinin is a natural flavonoid compound known to induce apoptosis in cancer cells. Despite silibinin's safety and efficacy as an anticancer drug, its effects on inducing immunogenic cell death (ICD) are largely unknown. Herein, we have evaluated the stimulating effects of silibinin on ICD in cancer cells treated with silibinin alone or in combination with chemotherapy. Methods: The anticancer effect of silibinin, alone or in combination with doxorubicin or oxaliplatin (OXP), was assessed using the MTT assay. Compusyn software was used to analyze the combination therapy data. Western blotting was conducted to examine the level of STAT3 activity. Flow cytometry was used to analyze calreticulin (CRT) and apoptosis. The heat shock protein (HSP70), high mobility group box protein1 (HMGB1), and IL-12 levels were assessed by ELISA. Results: Compared to the negative control groups, silibinin induced ICD in CT26 and B16F10 cells and significantly enhanced the induction of this type of cell death by doxorubicin, and these changes were allied with substantial increases in the level of damage-associated molecular patterns (DAMPs) including CRT, HSP70, and HMGB1. Furthermore, conditioned media from cancer cells exposed to silibinin and doxorubicin was found to stimulate IL-12 secretion in dendritic cells (DCs), suggesting the link of this treatment with the induction of Th1 response. Silibinin did not augment the ICD response induced by OXP. Conclusion: Our findings showed that silibinin can induce ICD and it potentiates the induction of this type of cell death induced by chemotherapy in cancer cells.

Heterologous prime-boost cellular vaccination induces potent antitumor immunity against triple negative breast cancer

Introduction

Triple negative breast cancer (TNBC) is the most aggressive and hard-to-treat subtype of breast cancer, affecting 10-20% of all women diagnosed with breast cancer. Surgery, chemotherapy and hormone/Her2 targeted therapies are the cornerstones of treatment for breast cancer, but women with TNBC do not benefit from these treatments. Although the prognosis is dismal, immunotherapies hold significant promise in TNBC, even in wide spread disease because TNBC is infiltrated with more immune cells. This preclinical study is proposing to optimize an oncolytic virus-infected cell vaccine (ICV) based on a prime-boost vaccination strategy to address this unmet clinical need.

Methods

We used various classes of immunomodulators to improve the immunogenicity of whole tumor cells in the prime vaccine, followed by their infection with oncolytic Vesicular Stomatitis Virus (VSVd51) to deliver the boost vaccine. For in vivo studies, we compared the efficacy of a homologous prime-boost vaccination regimen to a heterologous strategy by treating 4T1 tumor bearing BALB/c mice and further by conducting re-challenge studies to evaluate immune memory responses in surviving mice. Due to the aggressive nature of 4T1 tumor spread (akin to stage IV TNBC in human patients), we also compared early surgical resection of primary tumors versus later surgical resection combined with vaccination.

Results

In vitro results demonstrated that immunogenic cell death (ICD) markers and pro-inflammatory cytokines were released at the highest levels following treatment of mouse 4T1 TNBC cells with oxaliplatin chemotherapy and influenza vaccine. These ICD inducers also contributed towards higher dendritic cell recruitment and activation. With the top ICD inducers at hand, we observed that treatment of TNBC-bearing mice with the influenza virus-modified prime vaccine followed by VSVd51 infected boost vaccine resulted in the best survival. Furthermore, higher frequencies of both effector and central memory T cells along with a complete absence of recurrent tumors were observed in re-challenged mice. Importantly, early surgical resection combined with prime-boost vaccination led to improved overall survival in mice.

Conclusion

Taken together, this novel cancer vaccination strategy following early surgical resection could be a promising therapeutic avenue for TNBC patients.

Efferocytosis drives myeloid NLRP3 dependent inflammasome signaling secretion of IL-1β to promote tumor growth

Caspase-1 signaling in myeloid suppressor cells can promote T-cell independent cancer progression, but the regulation of inflammasome signaling within the highly heterogeneous myeloid population in the tumor milieu remains elusive. To resolve this complexity, single cell transcriptomic profile of Head and Neck Squamous Cell Carcinoma (HNSCC) identified distinct inflammasome-associated genes within specific clusters of tumor-infiltrating myeloid cells. Among these myeloid cells, the sensor protein, NLRP3, and downstream effector IL-1β transcripts were enriched in discreet monocytic and macrophage subtypes in the TME. We showed that deletion of NLRP3, but not AIM2, phenocopied caspase-1/IL-1β dependent tumor progression in vivo. Paradoxically, we found myeloid-intrinsic caspase-1 signaling increased myeloid survival contrary to what would be predicted from the canonical pyroptotic function of caspase-1. This myeloid NLRP3/IL-1β signaling axis promotion of tumor growth was found to be gasdermin D independent. Mechanistically, we found that phagocyte-mediated efferocytosis of dying tumor cells in the TME directly activated NLRP3-dependent inflammasome signaling to drive IL-1β secretion. Subsequently we showed that NLRP3-mediated IL-1β production drives tumor growth in vivo. Dynamic RNA velocity analysis showed a robust directional flow from efferocytosis gene-set ^high macrophages to an inflammasome gene-set ^high macrophage population. We provide a novel efferocytosis-dependent inflammasome signaling pathway which mediates homeostatic tumor cell apoptosis that characterizes chronic inflammation-induced malignancy.

Oxaliplatin Induces Immunogenic Cell Death in Human and Murine Laryngeal Cancer

Background

Cisplatin resistance is observed in patients with laryngeal cancer. The present study was designed to explore the efficacy of oxaliplatin on laryngeal cancer and elucidate the underlying mechanisms.

Methods

Cell viability was determined by using MTT assays. Cell apoptosis was determined by using annexin V and propidium iodide (PI) staining. Flow cytometry and immunofluorescence were applied to determine the levels of calreticulin (CALR) and DiD (1,1-dioctadecyl-3,3,3,3-tetramethylindodicarbocyanine). Flow cytometry was applied to analyze the levels of CD83, CD86, IFN-γ-producing CD8⁺ T cells, and CD4⁺CD25⁺FoxP3⁺ Tregs. The levels of adenosine triphosphate (ATP) were determined by using a chemiluminescent ATP kit and cytokines were determined by using specific enzyme-linked immunosorbent assays (ELISAs). The levels of HMGB1 were determined by using Western blot and ELISA, respectively. The xenograft animal model was constructed to evaluate the antitumor effects of oxaliplatin.

Results

Oxaliplatin inhibited cell growth, promoted cell apoptosis, and induced the levels of CALR, ATP, and high mobility group box protein 1 (HMGB1) in Hep-2 cells. Oxaliplatin-treated Hep-2 cells increased the intensity of DiD and the levels of CD83 and CD86 in dendritic cells (DCs), as well as induced the supernatant IL-6 and TNF-α. Oxaliplatin-treated primary laryngeal cancer cell-pulsed DCs increased the IFN-γ-producing CD8⁺ T cells and suppressed CD4⁺CD25⁺FoxP3⁺ Tregs. In vivo data showed that oxaliplatin suppressed tumor growth and increased the populations of CD86⁺CD80⁺ and CD8⁺CD45⁺ cells in the tumor tissues.

Conclusion

Treatment with oxaliplatin inhibited laryngeal cancer cells by inducing immunogenic cell death.

Apoptotic vesicles ameliorate lupus and arthritis via phosphatidylserine-mediated modulation of T cell receptor signaling

Mesenchymal stem cells (MSCs) influence T cells in health, disease and therapy through messengers of intercellular communication including extracellular vesicles (EVs). Apoptosis is a mode of cell death that tends to promote immune tolerance, and a large number of apoptotic vesicles (apoVs) are generated from MSCs during apoptosis. In an effort to characterize these apoVs and explore their immunomodulatory potential, here we show that after replenishing them systemically, the apoV deficiency in Fas mutant mice and pathological lymphoproliferation were rescued, leading to the amelioration of inflammation and lupus activity. ApoVs directly interacted with CD4⁺ T cells and inhibited CD25 expression and IL-2 production in a dose-dependent manner. A broad range of Th1/2/17 subsets and cytokines including IFNγ, IL17A and IL-10 were suppressed while Foxp3⁺ cells were maintained. Mechanistically, exposed phosphatidylserine (PtdSer/PS) on apoVs mediated the interaction with T cells to disrupt proximal T cell receptor signaling transduction. Remarkably, administration of apoVs prevented Th17 differentiation and memory formation, and ameliorated inflammation and joint erosion in murine arthritis. Collectively, our findings unveil a previously unrecognized crosstalk between MSC apoVs and CD4⁺ T cells and suggest a promising therapeutic use of apoVs for autoimmune diseases.

An Overview on Immunogenic Cell Death in Cancer Biology and Therapy

Immunogenic cell death (ICD) is a modality of regulated cell death that is sufficient to promote an adaptive immune response against antigens of the dying cell in an immunocompetent host. An important characteristic of ICD is the release and exposure of damage-associated molecular patterns, which are potent endogenous immune adjuvants. As the induction of ICD can be achieved with conventional cytotoxic agents, it represents a potential approach for the immunotherapy of cancer. Here, different aspects of ICD in cancer biology and treatment are reviewed.

Strategy to Enhance Anticancer Activity and Induced Immunogenic Cell Death of Antimicrobial Peptides by Using Non-Nature Amino Acid Substitutions

There is an urgent and imminent need to develop new agents to fight against cancer. In addition to the antimicrobial and anti-inflammatory activities, many antimicrobial peptides can bind to and lyse cancer cells. P-113, a 12-amino acid clinically active histatin-rich peptide, was found to possess anti-Candida activities but showed poor anticancer activity. Herein, anticancer activities and induced immunogenic cancer cell death of phenylalanine-(Phe-P-113), β-naphthylalanine-(Nal-P-113), β-diphenylalanine-(Dip-P-113), and β-(4,4′-biphenyl)alanine-(Bip-P-113) substituted P-113 were studied. Among these peptides, Nal-P-113 demonstrated the best anticancer activity and caused cancer cells to release potent danger-associated molecular patterns (DAMPs), such as reactive oxygen species (ROS), cytochrome c, ATP, and high-mobility group box 1 (HMGB1). These results could help in developing antimicrobial peptides with better anticancer activity and induced immunogenic cell death in therapeutic applications.

Biomimetic radiosensitizers unlock radiogenetics for local interstitial radiotherapy to activate systematic immune responses and resist tumor metastasis

Background

Similar to other local therapeutic methods, local interstitial radiotherapy (IRT) also suffers from insufficient systematic immune activation, resulting in tumor metastasis.

Results

Mn-based IRT radiosensitizers consisting of ¹³¹I, MnO₂ and bovine serum albumin (BSA) (¹³¹I-MnO₂-BSA) were engineered. Such Mn-based IRT radiosensitizers successfully unlocked radiogenetics to magnify systematic immune responses of local IRT via remodeling hypoxic and immunosuppressive microenvironments and resist tumor metastasis. The MnO₂ in ¹³¹I-MnO₂-BSA caused decomposition of H₂O₂ enriched in tumors to generate O₂ for alleviating hypoxic microenvironment and removing tumor resistances to IRT. Concurrently, hypoxia mitigation by such radiosensitizers-unlocked radiogenetics can effectively remodel immunosuppressive microenvironment associated with regulatory T (Treg) cells and tumor-associated macrophages (TAMs) infiltration inhibition to induce immunogenic cell death (ICD), which, along with hypoxia mitigation, activates systematic immune responses. More intriguingly, ¹³¹I-MnO₂-BSA-enabled radiogenetics can upregulate PD-L1 expression, which allows anti-PD-L1-combined therapy to exert a robust antitumor effect on primary tumors and elicit memory effects to suppress metastatic tumors in both tumor models (4T1 and CT26).

Conclusions

IRT radiosensitizer-unlocked radiogenetics and the corresponding design principle provide a general pathway to address the insufficient systematic immune responses of local IRT.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01324-w.

Biological Investigation of a Water-Soluble Isoginkgetin-Phosphate Analogue, Targeting the Spliceosome with In Vivo Antitumor Activity

The first total synthesis of the natural product Isoginkgetin as well as four water-soluble Isoginkgetin-phosphate analogues is reported herein. Moreover, the full study of the IP2 phosphate analogue with respect to pharmacological properties (metabolic and plasmatic stabilities, pharmacokinetic, off-target, etc.) as well as in vitro and in vivo biological activities are disclosed herein.

Intravesical immunotherapy with a GM-CSF armed oncolytic vesicular stomatitis virus improves outcome in bladder cancer

A significant proportion of non-muscle invasive bladder cancer cases will progress to muscle invasive disease. Transurethral resection followed by Bacillus Calmette Guerin immunotherapy can reduce this risk, while cystectomy prior to muscle invasion provides the best option for survival. Currently, there are no effective treatments for Bacillus Calmette Guerin refractory disease. A novel oncolytic vesicular stomatitis virus containing the human GM-CSF transgene (VSVd51-hGM-CSF) was rescued and tested as a potential bladder-sparing therapy for aggressive bladder cancer. The existing variant expressing mouse GM-CSF was also used. Measurement of gene expression and protein level alterations of canonical immunogenic cell death associated events on mouse and human bladder cancer cell lines and spheroids showed enhanced release of danger signals and immunogenic factors following infection with VSVd51-m/hGM-CSF. Intravesical instillation of VSVd51-mGM-CSF into MB49 bladder cancer bearing C57Bl/6 mice demonstrated enhanced activation of peripheral and bladder infiltrating effector immune cells, along with improved survival and reduced tumor volume. Importantly, virus-mediated anti-tumor immunity was recapitulated in bladder cancer patient-derived organoids. These results suggest that VSVd51-hGM-CSF is a promising viro/immunotherapy that could benefit bladder cancer patients.

Innate Immunity and Cancer Pathophysiology

Chronic inflammation increases the risk of several cancers, including gastric, colon, and hepatic cancers. Conversely, tumors, similar to tissue injury, trigger an inflammatory response coordinated by the innate immune system. Cellular and molecular mediators of inflammation modulate tumor growth directly and by influencing the adaptive immune response. Depending on the balance of immune cell types and signals within the tumor microenvironment, inflammation can support or restrain the tumor. Adding to the complexity, research from the past two decades has revealed that innate immune cells are highly heterogeneous and plastic, with variable phenotypes depending on tumor type, stage, and treatment. The field is now on the cusp of being able to harness this wealth of data to (a) classify tumors on the basis of their immune makeup, with implications for prognosis, treatment choice, and clinical outcome, and (b) design therapeutic strategies that activate antitumor immune responses by targeting innate immune cells.

A novel prodrug and its nanoformulation suppress cancer stem cells by inducing immunogenic cell death and inhibiting indoleamine 2, 3-dioxygenase

Cancer stem cells (CSCs) present grand challenges for triple-negative breast cancer (TNBC). Conventional chemotherapy drugs, including Camptothecin (CPT), not only cannot eradicate CSCs but also foster a suppressive immune microenvironment for the initiation and proliferation of CSCs. Herein, we report a novel prodrug CPT-SS-NLG919 (CN) and its nanoformulation CN@PLA-HES-FA (CN@PHF), which potently suppress CSCs by regulating CSCs niche in murine TNBC 4T1 tumors. Via inducing immunogenic cell death (ICD) and simultaneous inhibiting indoleamine 2, 3-dioxygenase (IDO), CN and CN@PHF promote DC maturation, decrease Treg cells, mitigate tryptophan consumption, and reduce the amount of IL-6, IL-13, and TGF-β, converting CSCs niche to a hostile condition for CSCs to live in and eliminating CSCs efficiently, thereby inducing efficient tumor inhibition in 4T1 tumor models. Our work represents a new paradigm of eliminating CSCs by regulating tumor immune microenvironment and suggests that CN and its nanoformulation CN@PHF are promising candidates for the treatment of intractable TNBC.

Targeting of the tumor microenvironment by curcumin

The tumor microenvironment (TME) is made up of several cells and molecules that affect the survival of cancer cells. Indeed, certain (immunosuppressive) cells which promote tumors can promote the growth of tumors by stimulating the proliferation of cancer cells and promoting angiogenesis. During tumor growth, antitumoral immunity includes natural killer cells and CD8+ T cells cannot overcome immunosuppressive responses and cancer cell proliferation. In order to achieve the appropriate therapeutic response, we must kill cancer cells and suppress the release of immunosuppressive molecules. The balance between anti-tumor immunity and immunosuppressive cells, such as regulatory T cells (Tregs), cancer-associated fibroblasts, tumor-associated macrophages, and myeloid-derived suppressor cells plays a key role in the suppression or promotion of cancer cells. Curcumin is a plant-derived agent that has shown interesting properties for cancer therapy. It has shown that not only directly inhibit the growth of cancer cells, but can also modulate the growth and activity of immunosuppressant and tumor-promoting cells. In this review, we explain how curcumin modulates interactions within TME in favor of tumor treatment. The potential modulating effects of curcumin on the responses of cancer cells to treatment modalities such as immunotherapy will also be discussed.

Immunogenic Cell Death Induced by Chemoradiotherapy of Novel pH-Sensitive Cargo-Loaded Polymersomes in Glioblastoma

Background

Inducing the immunogenic cell death of tumour cells can mediate the occurrence of antitumour immune responses and make the therapeutic effect more significant. Therefore, the development of treatments that can induce ICD to destroy tumour cells most effectively is promising. Previously, a new type of pH-sensitive polymersome was designed for the treatment of glioblastoma which represents a promising nanoplatform for future translational research in glioblastoma therapy. In this study, the aim of this work was to analyse whether chemoradiotherapy of the novel pH-sensitive cargo-loaded polymersomes can induce ICD.

Methods

Cell death in U87-MG and G422 cells was induced by Au-DOX@PO-ANG, and cell death was analysed by CCK-8 and flow cytometry. The release of CRT was determined by using laser scanning confocal microscopy and flow cytometry. ELISA kits were used to detect the release of HMGB1 and ATP. The dying cancer cells treated with different treatments were cocultured with bone-marrow-derived dendritic cells (BMDCs), and then flow cytometry was used to determine the maturation rate of BMDCs (CD11c+CD86+CD80+) to analyse the in vitro immunogenicity. Tumour vaccination experiments were used to evaluate the ability of Au-DOX@PO-ANG to induce ICD in vivo.

Results

We determined the optimal treatment strategy to evaluate the ability of chemotherapy combined with radiotherapy to induce ICD and dying cancer cells induced by Au-DOX@PO-ANG+RT could induce calreticulin eversion to the cell membrane, promote the release of HMGB1 and ATP, and induce the maturation of BMDCs. Using dying cancer cells induced by Au-DOX@PO-ANG+RT, we demonstrate the efficient vaccination potential of ICD in vivo.

Conclusion

These results identify Au-DOX@PO-ANG as a novel immunogenic cell death inducer in vitro and in vivo that could be effectively combined with RT in cancer therapy.

A [Pt(cis-1,3-diaminocycloalkane)Cl2] analog exhibits hallmarks typical of immunogenic cell death inducers in model cancer cells

The platinum drugs belong to prevailing chemotherapeutics used in the treatment of cancer. At present, however, the search for new anticancer metal-based drugs that operate by the mechanisms distinct from those of the conventional chemotherapeutics is very active. Furthermore, it has been demonstrated that cytotoxic chemotherapy and immunotherapy may exert a highly synergistic anticancer activity. Thus, the development of antitumor platinum and other metal-based drugs that exhibit cytostatic effects and concurrently elicit immunogenic cell death (ICD) has shown promise for cancer treatment. Notably, conventional platinum drug oxaliplatin ([Pt(1R,2R-DACH)(oxalate)], DACH = diaminocyclohexane) is a well-known agent that displays both cytostatic and immune responses. Moreover, it was also demonstrated that even minor derivatization of the unleaving cycloalkyl moiety in oxaliplatin might have a pronounced effect on its immunomodulatory activity. Here, we investigated how replacing the 1R,2R- diaminocyclohexane ring by 1,3-diaminocycloalkane (alkane = butane, pentane, or hexane) affects the ability to evoke secretion of damage-associated molecular patterns characteristic of ICD in model murine colorectal carcinoma cell line CT26. The results indicate that among the investigated [Pt(cis-1,3-diaminocycloalkane)Cl₂] complexes, the complex containing the cyclobutyl moiety exhibits the hallmarks typical of ICD inducers. Thus, [Pt(cis-1,3-diaminocyclobutane)Cl₂] may expand the spectrum of anticancer chemotherapeutics capable of inducing ICD in cancer cells and might be of interest for further (pre)clinical development.

Stimuli-Sheddable Nanomedicine Overcoming Pathophysiological Barriers for Potentiating Immunotherapy of Cancer

Immunotherapy displays potent potential for clinical cancer management by activating the protective immune response; however, the microenvironment of the immunosuppressive tumor restricts the efficiency of immunotherapies. Along with the complex pathophysiological barrier of the solid tumors, successful immunotherapeutic delivery remains a formidable challenge for conventional nanomedicine. Stimuli-sheddable nano vectors may facilitate the delivery of cargoes to tumors with minimal premature cargo leakage in blood circulation while enhancing the tumor penetration of nanomedicines by deshielding the polyethylene glycol (PEG) corona upon endogenous activity such as acidity, enzymes and glutathione, or external stimuli, such as laser irradiation. Throughout this study, researchers overviewed the recent advances of nanomedicine-based cancer immunotherapy using the stimuli-responsive deshielding nano vectors, which allowed researchers to integrate multiple therapeutic regimens for inducing immunogenic cell death. This aided in blocking the immune checkpoints, repolarizing the macrophages, and regulating the kynurenine metabolism. Furthermore, researchers discussed the critical issues in the development of stimuli-sheddable nanoimmunodulators, primarily aimed at speeding up their clinical translation. Finally, researchers provided novel perspectives for improving cancer management with the stimuli-sheddable nanomedicine.

Radiation and adjuvant drug-loaded liposomes target glioblastoma stem cells and trigger in-situ immune response

Background

The radio- and chemo-resistance of glioblastoma stem-like cells (GSCs), together with their innate tumor-initiating aptitude, make this cell population a crucial target for effective therapies. However, targeting GSCs is hardly difficult and complex, due to the presence of the blood-brain barrier (BBB) and the infiltrative nature of GSCs arousing their dispersion within the brain parenchyma.

Methods

Liposomes (LIPs), surface-decorated with an Apolipoprotein E-modified peptide (mApoE) to enable BBB crossing, were loaded with doxorubicin (DOXO), as paradigm of cytotoxic drug triggering immunogenic cell death (ICD). Patient-derived xenografts (PDXs) obtained by GSC intracranial injection were treated with mApoE-DOXO-LIPs alone or concomitantly with radiation.

Results

Our results indicated that mApoE, through the engagement of the low-density lipoprotein receptor (LDLR), promotes mApoE-DOXO-LIPs transcytosis across the BBB and confers target specificity towards GSCs. Irradiation enhanced LDLR expression on both BBB and GSCs, thus further promoting LIP diffusion and specificity. When administered in combination with radiations, mApoE-DOXO-LIPs caused a significant reduction of in vivo tumor growth due to GSC apoptosis. GSC apoptosis prompted microglia/macrophage phagocytic activity, together with the activation of the antigen-presenting machinery crucially required for anti-tumor adaptive immune response.

Conclusions

Our results advocate for radiotherapy and adjuvant administration of drug-loaded, mApoE-targeted nanovectors as an effective strategy to deliver cytotoxic molecules to GSCs at the surgical tumor margins, the forefront of glioblastoma (GBM) recurrence, circumventing BBB hurdles. DOXO encapsulation proved in situ immune response activation within GBM microenvironment.

Metabolic regulation in the immune response to cancer

Metabolic reprogramming in tumor‐immune interactions is emerging as a key factor affecting pro‐inflammatory carcinogenic effects and anticancer immune responses. Therefore, dysregulated metabolites and their regulators affect both cancer progression and therapeutic response. Here, we describe the molecular mechanisms through which microenvironmental, systemic, and microbial metabolites potentially influence the host immune response to mediate malignant progression and therapeutic intervention. We summarized the primary interplaying factors that constitute metabolism, immunological reactions, and cancer with a focus on mechanistic aspects. Finally, we discussed the possibility of metabolic interventions at multiple levels to enhance the efficacy of immunotherapeutic and conventional approaches for future anticancer treatments.

Valproic acid triggers radiation-induced abscopal effect by modulating the unirradiated tumor immune microenvironment in a rat model of breast cancer

An abscopal effect occurs when localized radiotherapy causes the regression of tumors distant from the irradiated site. However, such a clinically detectable abscopal effect from radiotherapy alone is rare. This study investigated whether valproic acid ([VPA], a histone deacetylase inhibitor [HDACi]) treatment can stimulate radiation-induced abscopal effect. We used 7,12-dimethylbenz[a]anthracene, a typical environmental carcinogen, to establish a rat model with multiple breast tumors. Only one tumor received 8 Gy fractionated doses of X-rays (2 Gy daily fractions over four days) and 200 mg/kg VPA was administered intraperitoneally. We monitored the growth of both irradiated and unirradiated tumors after treatments. The unirradiated tumor was collected for hematoxylin and eosin (HE) staining, immunohistochemistry (IHC) (CD8, Granzyme B, Cleaved Caspase-3, BrdU, Ki67, F4/80 and CD68), double immunofluorescence (F4/80 and CD86), Western blot (Cleaved Caspase-3) and qRT-PCR (CD86, CD163, IL-1β, IL-6, IL-12, IL-23, IL-10, TGF-β) analysis. We found ionizing radiation (IR) + VPA treatment inhibited both irradiated and unirradiated tumor growth as compared to IR alone. Such observe abscopal effect was mediated by the recruitment of activated CD8+ T cells into the unirradiated tumor sites, which released Granzyme B to cause tumor cell apoptosis. Furthermore, IR + VPA treatment led to macrophages infiltration into the unirradiated tumor sites and polarization to M1 phenotype, resulted in increased levels of pro-inflammatory cytokines such as IL-1β and IL-12, and decreased levels of anti-inflammatory cytokines such as IL-10 and TGF-β. Our data supports the proposition that VPA may be a potential therapeutic candidate to trigger radiation-induced abscopal effect by modulating the unirradiated tumor immune microenvironment.

The Antisocial Network: Cross Talk Between Cell Death Programs in Host Defense

Nearly all animal cells contain proteins evolved to trigger the destruction of the cell in which they reside. The activation of these proteins occurs via sequential programs, and much effort has been expended in delineating the molecular mechanisms underlying the resulting processes of programmed cell death (PCD). These efforts have led to the definition of apoptosis as a form of nonimmunogenic PCD that is required for normal development and tissue homeostasis, and of pyroptosis and necroptosis as forms of PCD initiated by pathogen infection that are associated with inflammation and immune activation. While this paradigm has served the field well, numerous recent studies have highlighted cross talk between these programs, challenging the idea that apoptosis, pyroptosis, and necroptosis are linear pathways with defined immunological outputs. Here, we discuss the emerging idea of cell death as a signaling network, considering connections between cell death pathways both as we observe them now and in their evolutionary origins. We also discuss the engagement and subversion of cell death pathways by pathogens, as well as the key immunological outcomes of these processes.

Irradiation-Induced Changes in the Immunogenicity of Lung Cancer Cell Lines: Based on Comparison of X-rays and Carbon Ions

Increasing the immunogenicity of tumors is considered to be an effective means to improve the synergistic immune effect of radiotherapy. Carbon ions have become ideal radiation for combined immunotherapy due to their particular radiobiological advantages. However, the difference in time and dose of immunogenic changes induced by Carbon ions and X-rays has not yet been fully clarified. To further explore the immunogenicity differences between carbon ions and X-rays induced by radiation in different "time windows" and "dose windows." In this study, we used principal component analysis (PCA) to screen out the marker genes from the single-cell RNA-sequencing (scRNA-seq) of CD8⁺ T cells and constructed a protein-protein interaction (PPI) network. Also, ELISA was used to test the exposure levels of HMGB1, IL-10, and TGF-β under different "time windows" and "dose windows" of irradiation with X-rays and carbon ions for A549, H520, and Lewis Lung Carcinoma (LLC) cell lines. The results demonstrated that different marker genes were involved in different processes of immune effect. HMGB1 was significantly enriched in the activated state, while the immunosuppressive factors TGF-β and IL-10 were mainly enriched in the non-functional state. Both X-rays and Carbon ions promoted the exposure of HMGB1, IL-10, and TGF-β in a time-dependent manner. X-rays but not Carbon ions increased the HMGB1 exposure level in a dose-dependent manner. Besides, compared with X-rays, carbon ions increased the exposure of HMGB1 while relatively reduced the exposure levels of immunosuppressive factors IL-10 and TGF-β. Therefore, we speculate that Carbon ions may be more advantageous than conventional X-rays in inducing immune effects.

Plasma-Activated Medium Potentiates the Immunogenicity of Tumor Cell Lysates for Dendritic Cell-Based Cancer Vaccines

Autologous dendritic cells (DCs)-based vaccines are considered quite promising for cancer immunotherapy due to their exquisite potential to induce tumor antigen-specific cytotoxic T cells. However, a lack of efficient protocols for inducing immunogenic tumor antigens limits the efficacy of DC-based cancer vaccines. Here, we found that a plasma-activated medium (PAM) induces immunogenic cell death (ICD) in tumor cells but not in an immortalized L929 cell line or human peripheral blood mononuclear cells. PAM induced an accumulation of reactive oxygen species (ROS), autophagy, apoptosis, and necrosis in a concentration-dependent manner. The tumor lysates prepared after PAM treatment displayed increased immunogenicity in a model of human monocyte-derived DCs, compared to the lysates prepared by a standard freezing/thawing method. Mature DCs loaded with PAM lysates showed an increased maturation potential, as estimated by their increased expression of CD83, CD86, CD40, IL-12/IL-10 production, and attenuated PDL1 and ILT-4 expression, compared to the DCs treated with control tumor lysates. Moreover, in co-culture with allogeneic T cells, DCs loaded with PAM-lysates increased the proportion of cytotoxic IFN-γ+ granzyme A+ CD8+ T cells and IL-17A-producing T cells and preserved the Th1 response. In contrast, control tumor lysates-treated DCs increased the frequency of Th2 (CD4+IL-4+), CD4, and CD8 regulatory T cell subtypes, none of which was observed with DCs loaded with PAM-lysates. Cumulatively, these results suggest that the novel method for preparing immunogenic tumor lysates with PAM could be suitable for improved DC-based immunotherapy of cancer patients.

Immune Modulator and Low-Temperature PTT-Induced Synergistic Immunotherapy for Cancer Treatment

Immunotherapy has shown great potential in cancer therapeutics but has limitations of the insufficient activation of dendritic cells (DCs) and immune-suppressive microenvironment. To overcome these obstacles, a cascade synergistic immunotherapy nanosystem (denoted as CpG@PDA-FA) was designed to elevate anticancer immune response. The combination nanosystem including a photothermal agent polydopamine (PDA) and immunomodulator CpG oligodeoxynucleotides (CpG ODNs). On the one hand, polydopamine (PDA) acts as a photothermal agent to induce low-temperature PTT. It leads to immunogenic cell death (ICD), a programmed cell death pathway, which can activate DCs and enhance the antitumor immune response of T cells. On the other hand, CpG ODNs further promote maturation and migration of DCs as well as ameliorates the immunosuppression microenvironment of the tumor (TME). This paper focuses on a cancer synergistic treatment of ICD-induced immunotherapy by low-temperature PTT and ameliorates TME by immunomodulator CpG ODNs. We proved that CpG@PDA-FA NPs realized a remarkable synergistic treatment effect compared with respective single PTT or CpG therapy in the maturation of DCs and activation of T cells. In addition, CpG@PDA-FA NPs also reduced myeloid-derived suppressor cells and regulatory T cells to relieve immunosuppression. Hence, CpG@PDA-FA NPs provide a bidirectional immunotherapy strategy for tumor inhibition and highlight the cascade effects of low-temperature PTT and immunotherapy.

Gutting it Out: Developing Effective Immunotherapies for Patients With Colorectal Cancer

Risk factors for colorectal cancer (CRC) include proinflammatory diets, sedentary habits, and obesity, in addition to genetic syndromes that predispose individuals to this disease. Current treatment relies on surgical excision and cytotoxic chemotherapies. There has been a renewed interest in immunotherapy as a treatment option for CRC given the success in melanoma and microsatellite instable (MSI) CRC. Immunotherapy with checkpoint inhibitors only plays a role in the 4%-6% of patients with MSIhigh tumors and even within this subpopulation, response rates can vary from 30% to 50%. Most patients with CRC do not respond to this modality of treatment, even though colorectal tumors are frequently infiltrated with T cells. Tumor cells limit apoptosis and survive following intensive chemotherapy leading to drug resistance and induction of autophagy. Pharmacological or molecular inhibition of autophagy improves the efficacy of cytotoxic chemotherapy in murine models. The microbiome clearly plays an etiologic role, in some or most colon tumors, realized by elegant findings in murine models and now investigated in human clinical trials. Recent results have suggested that cancer vaccines may be beneficial, perhaps best as preventive strategies. The search for therapies that can be combined with current approaches to increase their efficacy, and new knowledge of the biology of CRC are pivotal to improve the care of patients suffering from this disease. Here, we review the basic immunobiology of CRC, current "state-of-the-art" immunotherapies and define those areas with greatest therapeutic promise for the future.

Cancer-associated adipocytes as immunomodulators in cancer

Cancer-associated adipocytes (CAAs), as a main component of the tumor-adipose microenvironment (TAME), have various functions, including remodeling the extracellular matrix and interacting with tumor cells or infiltrated leukocytes through a variety of mutual signals. Here, we summarize the primary interplay among CAAs, the immune response and cancer with a focus on the mechanistic aspects of these relationships. Finally, unifying our understanding of CAAs with the immune cell function may be an effective method to enhance the efficacy of immunotherapeutic and conventional treatments.

Nanomedicine-mediated induction of immunogenic cell death and prevention of PD-L1 overexpression for enhanced hepatocellular carcinoma therapy

Background

The present study aims to develop a nanoparticle encapsulating doxorubicin (DOX) and programmed death-ligand 1 (PD-L1) siRNA and evaluate its anti-tumor effects on hepatoma carcinoma (HCC).

Methods

Nanoparticle encapsulating DOX and PD-L1 siRNA (NPDOX/siPD-L1) was characterized by dynamic light scattering and transmission electron microscopy. Flow cytometry was applied to analyze cell populations, NPDOX/siPD-L1 internalization, and cell apoptosis. Real-Time (RT)-quantitative reverse transcription (qPCR) and western blotting were used to determine the mRNA and protein levels, respectively. Released ATP was determined using ATP determination kit and cytokines were determined using specific ELISAs. A tumor-bearing animal model was established to evaluate the anti-tumor effects of NPDOX/siPD-L1.

Results

Treatment of NPDOX/siPD-L1 induced immunogenic cell death (ICD) and PD-L1 overexpression in HCC. In vivo study demonstrated that intravenously injection of NPDOX/siPD-L1 significantly inhibited the tumor volume and PD-L1 expressions of tumor tissue in the H22 tumor-bearing animal model. Besides, the treatment of NPDOX/siPD-L1 also regulated the populations of matured dendritic cells and cytotoxic T cells and the productions of cytokines in the tumor tissues.

Conclusion

Taken together, NPDOX/siPD-L1 showed significant anti-tumor effects on HCC by the induction of ICD and inhibition of PD-L1 overexpression.

Combining chemotherapy and autologous peptide-pulsed dendritic cells provides survival benefit in stage IV melanoma patients

BACKGROUND AND OBJECTIVES

We examined retrospectively whether the combination of standard dacarbazine (DTIC) and/or fotemustine chemotherapy and autologous peptide-loaded dendritic cell (DC) vaccination may improve survival of stage IV melanoma patients. Furthermore, a small cohort of long-term survivors was studied in more detail.

PATIENTS AND METHODS

Between 1998 and 2008, 41 patients were vaccinated at least three times with DCs while receiving chemotherapy and compared to all other 168 patients in our database who only received chemotherapy (1993-2008).

RESULTS

Median life expectancy of patients receiving additional DC-vaccination was 18 months, compared to eleven months for patients under standard chemotherapy alone. In contrast to patients with other haplotypes, the HLA-A1/A1 subset of DC-treated patients showed significantly lower median survival (12 vs. 25 months). Autoantibodies were frequently detected in serum of both vaccinated and non-vaccinated patients, and there was no correlation between titers, loss or appearance of autoantibodies and survival. Additionally, phenotyping of DCs and PBMCs also did not reveal any conspicuous correlation with survival.

CONCLUSIONS

Combining standard chemotherapy and DC vaccination appears superior to chemotherapy alone. The impact of HLA haplotypes on survival emphasizes the importance of a careful selection of patients with specific, well-defined HLA haplotypes for future vaccination trials using peptide-pulsed DCs, possibly combined with checkpoint inhibitors.

The Innate Immune Signalling Pathways: Turning RIG-I Sensor Activation Against Cancer

Over the last 15 years, the ability to harness a patient's own immune system has led to significant progress in cancer therapy. For instance, immunotherapeutic strategies, including checkpoint inhibitors or adoptive cell therapy using chimeric antigen receptor T-cell (CAR-T), are specifically aimed at enhancing adaptive anti-tumour immunity. Several research groups demonstrated that adaptive anti-tumour immunity is highly sustained by innate immune responses. Host innate immunity provides the first line of defence and mediates recognition of danger signals through pattern recognition receptors (PRRs), such as cytosolic sensors of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular pattern (DAMP) signals. The retinoic acid-inducible gene I (RIG-I) is a cytosolic RNA helicase, which detects viral double-strand RNA and, once activated, triggers signalling pathways, converging on the production of type I interferons, proinflammatory cytokines, and programmed cell death. Approaches aimed at activating RIG-I within cancers are being explored as novel therapeutic treatments to generate an inflammatory tumour microenvironment and to facilitate cytotoxic T-cell cross-priming and infiltration. Here, we provide an overview of studies regarding the role of RIG-I signalling in the tumour microenvironment, and the most recent preclinical studies that employ RIG-I agonists. Lastly, we present a selection of clinical trials designed to prove the antitumour role of RIG I and that may result in improved therapeutic outcomes for cancer patients.

A Screening of Antineoplastic Drugs for Acute Myeloid Leukemia Reveals Contrasting Immunogenic Effects of Etoposide and Fludarabine

BACKGROUND

Recent evidence demonstrated that the treatment of acute myeloid leukemia (AML) cells with daunorubicin (DNR) but not cytarabine (Ara-C) results in immunogenic cell death (ICD). In the clinical setting, chemotherapy including anthracyclines and Ara-C remains a gold standard for AML treatment. In the last decade, etoposide (Eto) and fludarabine (Flu) have been added to the standard treatment for AML to potentiate its therapeutic effect and have been tested in many trials. Very little data are available about the ability of these drugs to induce ICD.

METHODS

AML cells were treated with all four drugs. Calreticulin and heat shock protein 70/90 translocation, non-histone chromatin-binding protein high mobility group box 1 and adenosine triphosphate release were evaluated. The treated cells were pulsed into dendritic cells (DCs) and used for in vitro immunological tests.

RESULTS

Flu and Ara-C had no capacity to induce ICD-related events. Interestingly, Eto was comparable to DNR in inducing all ICD events, resulting in DC maturation. Moreover, Flu was significantly more potent in inducing suppressive T regulatory cells compared to other drugs.

CONCLUSIONS

Our results indicate a novel and until now poorly investigated feature of antineoplastic drugs commonly used for AML treatment, based on their different immunogenic potential.

Telomere Stress Potentiates STING-Dependent Anti-tumor Immunity

Telomerase is an attractive target for anti-tumor therapy as it is almost universally expressed in cancer cells. Here, we show that treatment with a telomere-targeting drug, 6-thio-2'-deoxyguanosine (6-thio-dG), leads to tumor regression through innate and adaptive immune-dependent responses in syngeneic and humanized mouse models of telomerase-expressing cancers. 6-thio-dG treatment causes telomere-associated DNA damages that are sensed by dendritic cells (DCs) and activates the host cytosolic DNA sensing STING/interferon I pathway, resulting in enhanced cross-priming capacity of DCs and tumor-specific CD8⁺ T cell activation. Moreover, 6-thio-dG overcomes resistance to checkpoint blockade in advanced cancer models. Our results unveil how telomere stress increases innate sensing and adaptive anti-tumor immunity and provide strong rationales for combining telomere-targeting therapy with immunotherapy.

A review of radiation induced abscopal effect: combining radiotherapy and immunotherapy to treat the untreated distant metastatic tumours

Background:

Radiotherapy is an effective and significant mode of definitive cancer treatment with well-established local tumour control success, especially in the treatment of localised tumours. Although, for metastatic disease, the role of radiotherapy has generally been limited to palliation of symptoms. In the treatment of metastatic diseases settings, the radiation therapy technique has always been confronted with the challenge of the simultaneous treatment of all of the various distant metastatic tumour sites, however, some recent evidence suggests that radiotherapy can potentially induce anticancer immune responses whose effectors potentially migrate to distant metastatic tumours to provoke their regression in cancer patients. Thus, unirradiated distant metastatic tumour sites can exhibit a delayed therapeutic response termed the abscopal effect.

Materials and methods:

This paper reports on a review of the abscopal effect, including its biological mechanism, the effect of radiation dose and fractionation regime and the timing of immunotherapy administration on radiotherapy-induced abscopal effect, the enhancement of radiotherapy-induced abscopal effects with immunotherapy, the effect of the location of the irradiated tumour and the radiotherapy of multiple tumour sites on the likelihood and effectiveness of inducing abscopal responses in the preclinical and clinical settings and also reports on some evidence of clinical observations in patients.

Conclusions:

Although abscopal effects of radiotherapy are still relatively rare in patients, it has gained a lot of interest due to recent development and use of immunotherapy strategies incorporating combinations of targeted immunomodulators and immune checkpoint blockade with radiation therapy. The enhancement of cancer immunotherapy could potentially enable the translation of the concept of abscopal effect into the clinics as a new strategy to induce therapeutically effective anti-tumour immune responses in cancer patients. The combination of radiotherapy and immunotherapy has the potential to expand the role of radiotherapy from a purely local tumour control treatment to play a significant role in advanced and metastatic tumour control and this could likely lead to a paradigm shift in the treatment of patients with metastatic cancer.

Site-specific metastasis: A cooperation between cancer cells and the metastatic microenvironment

The conclusion derived from the information provided in this review is that disseminating tumor cells (DTC) collaborate with the microenvironment of a future metastatic organ site in the establishment of organ‐specific metastasis. We review the basic principles of site‐specific metastasis and the contribution of the cross talk between DTC and the microenvironment of metastatic sites (metastatic microenvironment [MME]) to the establishment of the organ‐specific premetastatic niche; the targeted migration of DTC to the endothelium of the future organ‐specific metastasis; the transmigration of DTC to this site and the seeding and colonization of DTC in their future MME. We also discuss the role played by DTC‐MME interactions on tumor dormancy and on the differential response of tumor cells residing in different MMEs to antitumor therapy. Finally, we summarize some studies dealing with the effects of the MME on a unique site‐specific metastasis—brain metastasis.

Non-Thermal Plasma Application in Tumor-Bearing Mice Induces Increase of Serum HMGB1

The application of cold atmospheric plasma (CAP) in cancer therapy could be one of the new anticancer strategies. In the current work, we used cold atmospheric plasma jet for the treatment of cultured cells and mice. We showed that CAP induced the death of MX-7 mouse rhabdomyosarcoma cells with the hallmarks of immunogenic cell death (ICD): calreticulin and heat shock protein 70 (HSP70) externalization and high-mobility group box 1 protein (HMGB1) release. The intensity of HMGB1 release after the CAP treatment correlated directly with the basal extracellular HMGB1 level. Releasing from dying cells, HMGB1 can act as a proinflammatory cytokine. Our in vivo study demonstrated that cold atmospheric plasma induces a short-term two-times increase in serum HMGB1 level only in tumor-bearing mice with no effect in healthy mice. These findings support our hypothesis that CAP-dependent HMGB1 release from dying cancer cells can change the serum HMGB1 level. At the same time, we showed a weak cytokine response to CAP irradiation in healthy mice that can characterize CAP as an immune-safety physical antitumor approach.

HMGB1 in Radiotherapy: A Two Headed Signal Regulating Tumor Radiosensitivity and Immunity

Radiotherapy (RT) is a mainstay of cancer treatment. Recent studies have shown that RT not only directly induces cell death but also has late and sustained immune effects. High mobility group box 1 (HMGB1) is a nuclear protein released during RT, with location-dependent functions. It is essential for normal cellular function but also regulates the proliferation and migration of tumor cells by binding to high-affinity receptors. In this review, we summarize recent evidence on the functions of HMGB1 in RT according to the position, intracellular HMGB1 and extracellular HMGB1. Intracellular HMGB1 induces radiation tolerance in tumor cells by promoting DNA damage repair and autophagy. Extracellular HMGB1 plays a more intricate role in radiation-related immune responses, wherein it not only stimulates the anti-tumor immune response by facilitating the recognition of dying tumor cells but is also involved in maintaining immunosuppression. Factors that potentially affect the role of HMGB1 in RT-induced cytotoxicity have also been discussed in the context of possible therapeutic applications, which helps to develop effective and targeted radio-sensitization therapies.

Recombinant Lactaptin Induces Immunogenic Cell Death and Creates an Antitumor Vaccination Effect in Vivo with Enhancement by an IDO Inhibitor

Natural compounds of various origins are intensively investigated for their antitumor activity. Potential benefits of antitumor therapy can be achieved when cytotoxic agents kill cancer cells and these dying cancer cells drive adoptive immunity to the tumor. This strategy was successfully demonstrated for chemotherapeutic drugs that induce immunogenic type of cell death (ICD) with release of DAMPs (danger associated molecular patterns) and exposure of “eat me” signals. In this study, we demonstrated that recombinant human milk peptide lactaptin (RL2) induces death of cancer cells with ICD hallmarks in vitro with the release of ATP and high-mobility group box 1 protein (HMGB1) and exposure of calreticulin and HSP70 on the external cell membrane. RL2-treated cancer cells were efficiently engulfed by phagocytic cells. Using the syngeneic mouse model, we demonstrated that RL2-treated MX-7 rhabdomyosarcoma cells confer long-term immune-mediated protection against challenge with live MX-7 cells. We also analyzed the combinatorial antitumor effect of vaccination with RL2-treated cells and the inhibition of indoleamine 2,3-dioxygenase (IDO) with ethyl pyruvate. Compared to solo anti-tumor immunization with RL2-treated cells, additional chemical inhibition of IDO demonstrated better long-term antitumor responses than vaccination alone.

Immune checkpoint inhibitors reverse tolerogenic mechanisms induced by melanoma targeted radionuclide therapy

In line with the ongoing phase I trial (NCT03784625) dedicated to melanoma targeted radionuclide therapy (TRT), we explore the interplay between immune system and the melanin ligand [¹³¹I]ICF01012 alone or combined with immunotherapy (immune checkpoint inhibitors, ICI) in preclinical models. Here we demonstrate that [¹³¹I]ICF01012 induces immunogenic cell death, characterized by a significant increase in cell surface-exposed annexin A1 and calreticulin. Additionally, [¹³¹I]ICF01012 increases survival in immunocompetent mice, compared to immunocompromised (29 vs. 24 days, p = 0.0374). Flow cytometry and RT-qPCR analyses highlight that [¹³¹I]ICF01012 induces adaptive and innate immune cell recruitment in the tumor microenvironment. [¹³¹I]ICF01012 combination with ICIs (anti-CTLA-4, anti-PD-1, anti-PD-L1) has shown that tolerance is a main immune escape mechanism, whereas exhaustion is not present after TRT. Furthermore, [¹³¹I]ICF01012 and ICI combination has systematically resulted in a prolonged survival (p < 0.0001) compared to TRT alone. Specifically, [¹³¹I]ICF01012 + anti-CTLA-4 combination significantly increases survival compared to anti-CTLA-4 alone (41 vs. 26 days; p = 0.0011), without toxicity. This work represents the first global characterization of TRT-induced modifications of the antitumor immune response, demonstrating that tolerance is a main immune escape mechanism and that combining TRT and ICI is promising.