Compartmentalized role of xCT in supporting pancreatic tumor growth, inflammation and mood disturbance in mice.

xCT (Slc7a11), the specific subunit of the cystine/glutamate antiporter system xc-, is present in the brain and on immune cells, where it is known to modulate behavior and inflammatory responses. In a variety of cancers -including pancreatic ductal adenocarcinoma (PDAC)-, xCT is upregulated by tumor cells to support their growth and spread. Therefore, we studied the impact of xCT deletion in pancreatic tumor cells (Panc02) and/or the host (xCT-/- mice) on tumor burden, inflammation, cachexia and mood disturbances. Deletion of xCT in the tumor strongly reduced tumor growth. Targeting xCT in the host and not the tumor resulted only in a partial reduction of tumor burden, while it did attenuate tumor-related systemic inflammation and prevented an increase in immunosuppressive regulatory T cells. The latter effect could be replicated by specific xCT deletion in immune cells. xCT deletion in the host or the tumor differentially modulated neuroinflammation. When mice were grafted with xCT-deleted tumor cells, hypothalamic inflammation was reduced and, accordingly, food intake improved. Tumor bearing xCT-/- mice showed a trend of reduced hippocampal neuroinflammation with less anxiety- and depressive-like behavior. Taken together, targeting xCT may have beneficial effects on pancreatic cancer-related comorbidities, beyond reducing tumor burden. The search for novel and specific xCT inhibitors is warranted as they may represent a holistic therapy in pancreatic cancer.

Multimeric immunotherapeutic complexes activating natural killer cells towards HIV-1 cure.

BACKGROUND: Combination antiretroviral therapy (cART) has dramatically extended the life expectancy of people living with HIV-1 and improved their quality of life. There is nevertheless no cure for HIV-1 infection since HIV-1 persists in viral reservoirs of latently infected CD4+ T cells. cART does not eradicate HIV-1 reservoirs or restore cytotoxic natural killer (NK) cells which are dramatically reduced by HIV-1 infection, and express the checkpoint inhibitors NKG2A or KIR2DL upregulated after HIV-1 infection. Cytotoxic NK cells expressing the homing receptor CXCR5 were recently described as key subsets controlling viral replication. METHODS: We designed and evaluated the potency of "Natural killer activating Multimeric immunotherapeutic compleXes", called as NaMiX, combining multimers of the IL-15/IL-15Rα complex with an anti-NKG2A or an anti-KIR single-chain fragment variable (scFv) to kill HIV-1 infected CD4+ T cells. The oligomerization domain of the C4 binding protein was used to associate the IL-15/IL-15Rα complex to the scFv of each checkpoint inhibitor as well as to multimerize each entity into a heptamer (α form) or a dimer (ß form). Each α or ß form was compared in different in vitro models using one-way ANOVA and post-hoc Tukey's tests before evaluation in humanized NSG tg-huIL-15 mice having functional NK cells. RESULTS: All NaMiX significantly enhanced the cytolytic activity of NK and CD8+ T cells against Raji tumour cells and HIV-1+ ACH-2 cells by increasing degranulation, release of granzyme B, perforin and IFN-γ. Targeting NKG2A had a stronger effect than targeting KIR2DL due to higher expression of NKG2A on NK cells. In viral inhibition assays, NaMiX initially increased viral replication of CD4+ T cells which was subsequently inhibited by cytotoxic NK cells. Importantly, anti-NKG2A NaMiX enhanced activation, cytotoxicity, IFN-γ production and CXCR5 expression of NK cells from HIV-1 positive individuals. In humanized NSG tg-huIL-15 mice, we confirmed enhanced activation, degranulation, cytotoxicity of NK cells, and killing of HIV-1 infected cells from mice injected with the anti-NKG2A.α NaMiX, as compared to control mice, as well as decreased total HIV-1 DNA in the lung. CONCLUSIONS: NK cell-mediated killing of HIV-1 infected cells by NaMiX represents a promising approach to support HIV-1 cure strategies.

Push-Through Filtration of Emulsified Adipose Tissue Over a 500-µm Mesh Significantly Reduces the Amount of Stromal Vascular Fraction and Mesenchymal Stem Cells.

BACKGROUND: Mechanical isolation of the stromal vascular fraction (SVF) separates the stromal component from the parenchymal cells. Emulsification is currently the most commonly used disaggregation method and is effective in disrupting adipocytes and fragmenting the extracellular matrix (ECM). Subsequent push-through filtration of emulsified adipose tissue removes parts of the ECM that are not sufficiently micronized, thereby further liquifying the tissue. OBJECTIVES: The aim of this study was to investigate whether filtration over a 500-µm mesh filter might affect the SVF and adipose-derived mesenchymal stem cell (MSC) quantity in emulsified lipoaspirate samples by removing ECM fragments. METHODS: Eleven lipoaspirate samples from healthy nonobese women were harvested and emulsified in 30 passes. One-half of the sample was filtered through a 500-µm mesh filter and the other half was left unfiltered. Paired samples were processed and analyzed by flow cytometry to identify cellular viability, and SVF and MSC yield. RESULTS: Push-through filtration reduced the number of SVF cells by a mean [standard deviation] of 39.65% [5.67%] (P < .01). It also significantly reduced MSC counts by 48.28% [6.72%] (P < .01). Filtration did not significantly affect viability (P = .118). CONCLUSIONS: Retention of fibrous remnants by push-through filters removed ECM containing the SVF and MSCs from emulsified lipoaspirates. Processing methods should aim either to further micronize the lipoaspirate before filtering or not to filter the samples at all, to preserve both the cellular component carried within the ECM and the inductive properties of the ECM itself.

Autologous dendritic cell vaccination against HIV-1 induces changes in natural killer cell phenotype and functionality.

Although natural killer (NK) cells have been studied in connection with dendritic cell (DC)-based vaccination in the field of cancer immunology, their role has barely been addressed in the context of therapeutic vaccination against HIV-1. In this study, we evaluated whether a therapeutic DC-based vaccine consisting of monocyte-derived DCs electroporated with Tat, Rev and Nef encoding mRNA affects NK cell frequency, phenotype and functionality in HIV-1-infected individuals. Although the frequency of total NK cells did not change, we observed a significant increase in cytotoxic NK cells following immunisation. In addition, significant changes in the NK cell phenotype associated with migration and exhaustion were observed together with increased NK cell-mediated killing and (poly)functionality. Our results show that DC-based vaccination has profound effects on NK cells, which highlights the importance of evaluating NK cells in future clinical trials looking at DC-based immunotherapy in the context of HIV-1 infection.

Evaluation of functional candidate biomarkers of non-genotoxic hepatocarcinogenicity in human liver spheroid co-cultures.

Validated in vitro assays for testing non-genotoxic carcinogenic potential of chemicals are currently not available. Consequently, the two-year rodent bioassay remains the gold standard method for the identification of these chemicals. Transcriptomic and proteomic analyses have provided a comprehensive understanding of the non-genotoxic carcinogenic processes, however, functional changes induced by effects at transcriptional and translational levels have not been addressed. The present study was set up to test a number of proposed in vitro biomarkers of non-genotoxic hepatocarcinogenicity at the functional level using a translational 3-dimensional model. Spheroid cultures of human hepatocytes and stellate cells were exposed to 5 genotoxic carcinogenic, 5 non-genotoxic carcinogenic, and 5 non-carcinogenic chemical compounds and assessed for oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, apoptosis, and inflammation. The spheroid model could capture many of these events triggered by the genotoxic carcinogenic chemicals, particularly aflatoxin B1 and hydroquinone. Nonetheless, no clear distinction could be made between genotoxic and non-genotoxic hepatocarcinogenicity. Therefore, spheroid cultures of human liver cells may be appropriate in vitro tools for mechanistic investigation of chemical-induced hepatocarcinogenicity, however, these mechanisms and their read-outs do not seem to be eligible biomarkers for detecting non-genotoxic carcinogenic chemicals.

Qualitative plasma viral load determination as a tool for screening of viral reservoir size in PWH.

OBJECTIVES: Suppression of viral replication in patients on antiretroviral therapy (ART) is determined by plasma viral load (pVL) measurement. Whenever pVL reaches values below the limit of quantification, the qualitative parameter 'target detected' or 'target not detected' is available but often not reported to the clinician. We investigated whether qualitative pVL measurements can be used to estimate the viral reservoir size. DESIGN: The study recruited 114 people with HIV (PWH) who are stable on ART between 2016 and 2018. The percentage of pVL measurements qualitatively reported as 'target detected' (PTD) within a 2-year period was calculated. METHODS: t-DNA and US-RNA were used to estimate viral reservoir size and were quantified on peripheral blood mononuclear cells (PBMCs) using droplet digital PCR. RESULTS: A median of 6.5 pVL measurements over a 2-year period was evaluated for each participant to calculate PTD. A positive correlation was found between t-DNA and PTD (r = 0.24; P = 0.011) but not between US-RNA and PTD (r = 0.1; P = 0.3). A significantly lower PTD was observed in PWH with a small viral reservoir, as estimated by t-DNA less than 66 copies/106 PBMCs and US-RNA less than 10 copies/106 PBMCs, compared with PWH with a larger viral reservoir (P = 0.001). We also show that t-DNA is detectable whenever PTD is higher than 56% and that ART regimen does not affect PTD. CONCLUSION: Our study shows that PTD provides an efficient parameter to preselect participants with a small viral reservoir based on already available pVL data for future HIV cure trials.

Efficient Induction of Antigen-Specific CD8+ T-Cell Responses by Cationic Peptide-Based mRNA Nanoparticles.

A major determinant for the success of mRNA-based vaccines is the composition of the nanoparticles (NPs) used for formulation and delivery. Cationic peptides represent interesting candidate carriers for mRNA, since they have been shown to efficiently deliver nucleic acids to eukaryotic cells. mRNA NPs based on arginine-rich peptides have previously been demonstrated to induce potent antigen-specific CD8+ T-cell responses. We therefore compared the histidine-rich amphipathic peptide LAH4-L1 (KKALLAHALHLLALLALHLAHALKKA) to the fully substituted arginine variant (LAH4-L1R) for their capacity to formulate mRNA and transfect dendritic cells (DCs). Although both peptides encapsulated mRNA to the same extent, and showed excellent uptake in DCs, the gene expression level was significantly higher for LAH4-L1. The LAH4-L1-mRNA NPs also resulted in enhanced antigen presentation in the context of MHC I compared to LAH4-L1R in primary murine CD103+ DCs. Both peptides induced DC maturation and inflammasome activation. Subsequent ex vivo stimulation of OT-I splenocytes with transfected CD103+ DCs resulted in a high proportion of polyfunctional CD8+ T cells for both peptides. In addition, in vivo immunization with LAH4-L1 or LAH4-L1R-mRNA NPs resulted in proliferation of antigen-specific T cells. In conclusion, although LAH4-L1 outperformed LAH4-L1R in terms of transfection efficiency, the immune stimulation ex vivo and in vivo was equally efficient.

Oncolytic Herpes Simplex Virus Type 1 Induces Immunogenic Cell Death Resulting in Maturation of BDCA-1+ Myeloid Dendritic Cells.

Recently, a paradigm shift has been established for oncolytic viruses (OVs) as it was shown that the immune system plays an important role in the specific killing of tumor cells by OVs. OVs have the intrinsic capacity to provide the right signals to trigger anti-tumor immune responses, on the one hand by delivering virus-derived innate signals and on the other hand by inducing immunogenic cell death (ICD), which is accompanied by the release of various damage-associated molecules from infected tumor cells. Here, we determined the ICD-inducing capacity of Talimogene laherparepvec (T-VEC), a herpes simplex virus type 1 based OV, and benchmarked this to other previously described ICD (e.g., doxorubicin) and non-ICD inducing agents (cisplatin). Furthermore, we studied the capability of T-VEC to induce the maturation of human BDCA-1+ myeloid dendritic cells (myDCs). We found that T-VEC treatment exerts direct and indirect anti-tumor effects as it induces tumor cell death that coincides with the release of hallmark mediators of ICD, while simultaneously contributing to the maturation of BDCA-1+ myDCs. These results unequivocally cement OVs in the category of cancer immunotherapy.

Lifespan extension with preservation of hippocampal function in aged system xc--deficient male mice.

The cystine/glutamate antiporter system xc- has been identified as the major source of extracellular glutamate in several brain regions as well as a modulator of neuroinflammation, and genetic deletion of its specific subunit xCT (xCT-/-) is protective in mouse models for age-related neurological disorders. However, the previously observed oxidative shift in the plasma cystine/cysteine ratio of adult xCT-/- mice led to the hypothesis that system xc- deletion would negatively affect life- and healthspan. Still, till now the role of system xc- in physiological aging remains unexplored. We therefore studied the effect of xCT deletion on the aging process of mice, with a particular focus on the immune system, hippocampal function, and cognitive aging. We observed that male xCT-/- mice have an extended lifespan, despite an even more increased plasma cystine/cysteine ratio in aged compared to adult mice. This oxidative shift does not negatively impact the general health status of the mice. On the contrary, the age-related priming of the innate immune system, that manifested as increased LPS-induced cytokine levels and hypothermia in xCT+/+ mice, was attenuated in xCT-/- mice. While this was associated with only a very moderate shift towards a more anti-inflammatory state of the aged hippocampus, we observed changes in the hippocampal metabolome that were associated with a preserved hippocampal function and the retention of hippocampus-dependent memory in male aged xCT-/- mice. Targeting system xc- is thus not only a promising strategy to prevent cognitive decline, but also to promote healthy aging.

T-cell subsets in the skin and their role in inflammatory skin disorders.

T lymphocytes (T cells) are major players of the adaptive immune response. Naive T cells are primed in the presence of cytokines, leading to polarization into distinct T-cell subsets with specific functions. These subsets are classified based on their T-cell receptor profile, expression of transcription factors, surface cytokine and chemokine receptors, and their cytokine production, which together determine their specific function. This review provides an overview of the various T-cell subsets and their function in several inflammatory skin disorders ranging from allergic inflammation to skin tumors. Moreover, we highlight similarities of T-cell responses across different skin disorders, demonstrating the presence of similar and opposing functions for the different T-cell subsets. Finally, we discuss the effects of currently available and promising therapeutic approaches to harness T cells in inflammatory skin diseases for which efficacy next to unwanted side effects provide new insights into the pathophysiology of skin disorders.

Unraveling the Effects of a Talimogene Laherparepvec (T-VEC)-Induced Tumor Oncolysate on Myeloid Dendritic Cells.

T-VEC, a HSV-1 derived oncolytic virus, is approved for the treatment of advanced melanoma. The mechanisms that underly the systemic anti-tumor effect that is seen following intratumoral injection have not yet been studied but are likely to be mediated by myeloid dendritic cells (myDC) that initiate an adaptive immune response. In this study we could demonstrate that T-VEC is non-toxic for human myDC. T-VEC and a T-VEC oncolysate of melanoma cell lines were able to mature human myDC. myDC were able to take up lysed melanoma cells and cross-present melanoma-derived tumor antigens to antigen-specific T cells. Our results support the possible role of myDC as mediators of an adaptive anti-tumor effect and intratumoral co-administration of T-VEC plus autologous myDC could be a complementary treatment option. A clinical trial that investigates this hypothesis is currently ongoing.

Layer-by-Layer technique as a versatile tool for gene delivery applications.

Introduction: Gene therapy is a breakthrough medical field which focuses on the therapeutic delivery of recombinant nucleic acids in order to treat or prevent a broad spectrum of diseases. However, a number of important obstacles remain before its wide introduction into clinical practice can be envisaged. One of the biggest bottlenecks is the lack of efficient and safe delivery technologies, particularly, for in vivo distribution. Above and beyond standard requirements for carriers, the delivery systems for gene therapy ideally use a hit-and-run principle (to minimize off-target effect and display of immunogenic moieties). None of the currently used viral vectors fulfills all of these requirements. Therefore, the growing variety of non-viral delivery platforms represents a promising alternative.Areas covered: This review summarizes the Layer-by-Layer (LbL) approaches that can be effectively used for the gene delivery, considering various examples with the transfer of pDNA, mRNA, siRNA as well as genome-editing tools. Ex vivo gene modification of clinically relevant cells and clinical aspects for possible application of LbL systems in gene therapy are also underlined.Expert opinion: The LbL technique provides broad opportunities for the delivery of genetic material for various purposes and offers promise for future clinical application in gene therapy.

Off the beaten path: Novel mRNA-nanoformulations for therapeutic vaccination against HIV.

Over the last few years, immunotherapy for HIV in general and therapeutic vaccination in particular, has received a tremendous boost, both in preclinical research and in clinical applications. This interest is based on the evidence that the immune system plays a crucial role in controlling HIV infection, as shown for long-term non-progressors and elite controllers, and that immune responses can be manipulated towards targeting conserved epitopes. So far, the most successful approach has been vaccination with autologous dendritic cells (DCs) loaded ex vivo with antigens and activation signals. Although this approach offers much promise, it also comes with significant drawbacks such as the requirement of a specialized infrastructure and expertise, as well as major challenges for logistics and storage, making it extremely time consuming and costly. Therefore, methods are being developed to avoid the use of ex vivo generated, autologous DCs. One of these methods is based on mRNA for therapeutic vaccination. mRNA has proven to be a very promising vaccine platform, as the coding information for any desired protein, including antigens and activation signals, can be generated in a very short period of time, showing promise both as an off-the-shelf therapy and as a personalized approach. However, an important drawback of this approach is the short half-life of native mRNA, due to the presence of ambient RNases. In addition, proper immunization requires that the antigens are expressed, processed and presented at the right immunological site (e.g. the lymphoid tissues). An ambivalent aspect of mRNA as a vaccine is its capacity to induce type I interferons, which can have beneficial adjuvant effects, but also deleterious effects on mRNA stability and translation. Thus, proper formulation of the mRNA is crucially important. Many approaches for RNA formulation have already been tested, with mixed success. In this review we discuss the state-of-the-art and future trends for mRNA-nanoparticle formulations for HIV vaccination, both in the prophylactic and in the therapeutic setting.

Neuroprotection by Insulin-like Growth Factor-1 in Rats with Ischemic Stroke is Associated with Microglial Changes and a Reduction in Neuroinflammation.

We and others have shown that insulin-like growth factor-1 (IGF-1) is neuroprotective when administered systemically shortly following stroke. In the current study, we addressed the hypothesis that microglia mediate neuroprotection by IGF-1 following ischemic stroke. Furthermore, we investigated whether IGF-1 modulates pro- and anti-inflammatory mediators in ischemic brain with a special reference to microglia. Ischemic stroke was induced in normal conscious Wistar rats by infusing the vasoconstrictor, endothelin-1 (Et-1), next to middle cerebral artery (MCA). IGF-1 (300 µg) was injected subcutaneously (SC) at 30 and 120 min following stroke. Microglial inhibitor, minocycline, was injected intraperitoneally (IP) at 1 h before stroke (25 mg/kg) and 11 h after stroke (45 mg/kg). Post-stroke IGF-1 treatment reduced the infarct size and increased the sensorimotor function which coincided with an increase in the number of ameboid microglia in the ischemic cortex. Minocycline treatment abrogated the increase in ameboid microglia by IGF-1, while the effect of IGF-1 in the reduction of infarct size was only partially affected. IGF-1 suppressed mRNA expression of inducible nitric oxide synthase (iNOS) and interleukin (IL)-1ß in the ischemic hemisphere, while in purified microglia, only iNOS expression levels were reduced. Our findings show that microglia are a target for IGF-1 and that neuroprotection by IGF-1 coincides with down-regulation of inflammatory mediators which could be instrumental to the beneficial effects.

Intranodal administration of mRNA encoding nucleoprotein provides cross-strain immunity against influenza in mice.

BACKGROUND: Current human influenza vaccines lack the adaptability to match the mutational rate of the virus and therefore require annual revisions. Because of extensive manufacturing times and the possibility that antigenic alterations occur during viral vaccine strain production, an inherent risk exists for antigenic mismatch between the new influenza vaccine and circulating viruses. Targeting more conserved antigens such as nucleoprotein (NP) could provide a more sustainable vaccination strategy by inducing long term and heterosubtypic protection against influenza. We previously demonstrated that intranodal mRNA injection can induce potent antigen-specific T-cell responses. In this study, we investigated whether intranodal administration of mRNA encoding NP can induce T-cell responses capable of protecting against a heterologous influenza virus challenge. METHODS: BALB/c mice were immunized in the inguinal lymph nodes with different vaccination regimens of mRNA encoding NP. Immune responses were compared with NP DNA vaccination via IFN-γ ELISPOT and in vivo cytotoxicity. For survival experiments, mice were prime-boost vaccinated with 17 µg NP mRNA and infected with 1LD50 of H1N1 influenza virus 8 weeks after boost. Weight was monitored and viral titers, cytokines and immune cell populations in the bronchoalveolar lavage, and IFN-γ responses in the spleen were analyzed. RESULTS: Our results demonstrate that NP mRNA induces superior systemic T-cell responses against NP compared to classical DNA vaccination. These responses were sustained for several weeks even at low vaccine doses. Upon challenge infection, vaccination with NP mRNA resulted in reduced lung viral titers and improved recovery from infection. Finally, we show that vaccination with NP mRNA affects the immune response in infected lungs by lowering immune cell infiltration while increasing the fraction of T cells, monocytes and MHC II+ alveolar macrophages within immune infiltrates. This change was associated with altered levels of both pro- and anti-inflammatory cytokines. CONCLUSIONS: These findings suggest that intranodal vaccination with NP mRNA induces cross-strain immunity against influenza, but also highlight a paradox of influenza immunity, whereby robust immune responses can provide protection, but can also transiently exacerbate symptoms during infection.

Immune checkpoint blockade combined with IL-6 and TGF-ß inhibition improves the therapeutic outcome of mRNA-based immunotherapy.

Improved understanding of cancer immunology has provided insight into the phenomenon of frequent tumor recurrence after initially successful immunotherapy. A delicate balance exists between the capacity of the immune system to control tumor growth and various resistance mechanisms that arise to avoid or even counteract the host's immune system. These resistance mechanisms include but are not limited to (i) adaptive expression of inhibitory checkpoint molecules in response to the proinflammatory environment and (ii) amplification of cancer stem cells, a small fraction of tumor cells possessing the capacity for self-renewal and mediating treatment resistance and formation of metastases after long periods of clinical remission. Several individual therapeutic agents have so far been developed to revert T-cell exhaustion or disrupt the cross-talk between cancer stem cells and the tumor-promoting microenvironment. Here, we demonstrate that a three-arm combination therapy-consisting of an mRNA-based vaccine to induce antigen-specific T-cell responses, monoclonal antibodies blocking inhibitory checkpoint molecules (PD-1, TIM-3, LAG-3), and antibodies targeting IL-6 and TGF-ß-improves the therapeutic outcome in subcutaneous TC-1 tumors and significantly prolongs survival of treated mice. Our findings point to a need for a rational development of multidimensional anticancer therapies, aiming at the induction of tumor-specific immunity and simultaneously targeting multiple resistance mechanisms.

Dendritic cell immunotherapy followed by cART interruption during HIV-1 infection induces plasma protein markers of cellular immunity and neutrophil recruitment.

OBJECTIVES: To characterize the host response to dendritic cell-based immunotherapy and subsequent combined antiretroviral therapy (cART) interruption in HIV-1-infected individuals at the plasma protein level. DESIGN: An autologous dendritic cell (DC) therapeutic vaccine was administered to HIV-infected individuals, stable on cART. The effect of vaccination was evaluated at the plasma protein level during the period preceding cART interruption, during analytical therapy interruption and at viral reactivation. Healthy controls and post-exposure prophylactically treated healthy individuals were included as controls. METHODS: Plasma marker ('analyte') levels including cytokines, chemokines, growth factors, and hormones were measured in trial participants and control plasma samples using a multiplex immunoassay. Analyte levels were analysed using principle component analysis, cluster analysis and limma. Blood neutrophil counts were analysed using linear regression. RESULTS: Plasma analyte levels of HIV-infected individuals are markedly different from those of healthy controls and HIV-negative individuals receiving post-exposure prophylaxis. Viral reactivation following cART interruption also affects multiple analytes, but cART interruption itself only has only a minor effect. We find that Thyroxine-Binding Globulin (TBG) levels and late-stage neutrophil numbers correlate with the time off cART after DC vaccination. Furthermore, analysis shows that cART alters several regulators of blood glucose levels, including C-peptide, chromogranin-A and leptin. HIV reactivation is associated with the upregulation of CXCR3 ligands. CONCLUSIONS: Chronic HIV infection leads to a change in multiple plasma analyte levels, as does virus reactivation after cART interruption. Furthermore, we find evidence for the involvement of TBG and neutrophils in the response to DC-vaccination in the setting of HIV-infection.

Oncolytic virus-induced cell death and immunity: a match made in heaven?

Our understanding of the mechanisms responsible for cancer development has increased enormously over the last decades. However, for many cancers, this has not been translated into a significant improvement in overall survival, and overall mortality remains high. Treatment for many malignancies remains based on surgery, chemotherapy, and radiotherapy. Significant progress has been made toward the development of more specific, more potent, and less invasive treatment modalities, but such targeted therapies remain the exception for most cancers. Thus, cancer therapies based on a different mechanism of action should be explored. The immune system plays an important role in keeping tumor growth at bay. However, in many cases, these responses are not strong enough to keep tumor growth under control. Thus, immunotherapy aims to boost the immune system to suppress tumor growth efficiently. This has been demonstrated by the recent successes of immune checkpoint therapy in several cancers. Oncolytic viruses (OVs) are another exciting class of immunotherapy agent. As well as replicating selectively within and killing tumor cells, OVs are able to elicit potent anti-tumor immune responses. Therapeutic vaccination with OVs, also referred to as cancer virotherapy, can thus be tailored to elicit vigorous cellular immune responses and even target individual malignancies in a personalized manner. In this review, we will describe the intricate link among oncolytic virotherapy, tumor immunology, and immunogenic cell death (ICD) and discuss ways to harness optimally their potential for future cancer therapy.