[Abstract unavailable

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Dendritic cells (DCs) are the sentinel antigen-presenting cells of the immune system; such that their productive interface with the dying cancer cells is crucial for proper communication of the “non-self” status of cancer cells to the adaptive immune system. Efficiency and the ultimate success of such a communication hinges upon the maturation status of the DCs, attained following their interaction with cancer cells. Immature DCs facilitate tolerance toward cancer cells (observed for many apoptotic inducers) while fully mature DCs can strongly promote anticancer immunity if they secrete the correct combinations of cytokines [observed when DCs interact with cancer cells undergoing immunogenic cell death (ICD)]. However, an intermediate population of DC maturation, called semi-mature DCs exists, which can potentiate either tolerogenicity or pro-tumorigenic responses (as happens in the case of certain chemotherapeutics and agents exerting ambivalent immune reactions). Specific combinations of DC phenotypic markers, DC-derived cytokines/chemokines, dying cancer cell-derived danger signals, and other less characterized entities (e.g., exosomes) can define the nature and evolution of the DC maturation state. In the present review, we discuss these different maturation states of DCs, how they might be attained and which anticancer agents or cell death modalities (e.g., tolerogenic cell death vs. ICD) may regulate these states.

Accumulating data indicates that following anti-cancer treatments, cancer cell death can be perceived as immunogenic or tolerogenic by the immune system. The former is made possible due to the ability of certain anti-cancer modalities to induce immunogenic cell death (ICD) that is associated with the emission of damage-associated molecular patterns (DAMPs), which assist in unlocking a sequence of events leading to the development of anti-tumour immunity. In response to ICD inducers, activation of endoplasmic reticulum (ER) stress has been identified to be indispensable to confer the immunogenic character of cancer cell death, due to its ability to coordinate the danger signalling pathways responsible for the trafficking of vital DAMPs and subsequent anti-cancer immune responses. However, in recent times, certain processes apart from ER stress have emerged (e.g., autophagy and possibly viral response-like signature), which have the ability to influence danger signalling. In this review, we discuss the molecular nature, emerging plasticity in the danger signalling mechanisms and immunological impact of known DAMPs in the context of immunogenic cancer cell death. We also discuss key effector mechanisms modulating the interface between dying cancer cells and the immune cells, which we believe are crucial for the therapeutic relevance of ICD in the context of human cancers, and also discuss the influence of experimental conditions and animal models on these. The ultimate outcome of an immune response to cancer cell death (i.e., anti-tumourigenic, pro-tumourigenic or autoimmunity or different combinations of these) tends to be complex and may depend on a number of factors like the type of the cancer cells that die and their in vivo location, the type of cell death pathway they follow to die, the types of immune cells that phagocytose them or interact with them and, last but not the least, whether a cancer antigen is recognized or not. Tolerogenicity towards cell death, as happens predominantly when cancer cells undergo physiological apoptosis (after treatment with most anti-cancer therapies), depends on a number of factors including the presence of immunosuppressive factors, absence or inactivation of DAMPs, induction of tolerogenic dendritic cells (DCs), 'suboptimal' activation of CD8 þ T cells only and apoptotic 'mimicry'.Accentuated immunogenicity exhibited by cancer cells undergoing immunogenic cell death (ICD; after treatment with selected anti-cancer therapies), depends on a number of factors like emission of DAMPs (i.e., surface exposure of certain chaperones, secretion or release of certain nucleotides and endokines), presence of immunostimulatory factors, induction of DC maturation (both phenotypic and functional) and optimal activation of CD4 þ ab, CD8 þ ab and gd T-cell responses. Certain DAMPs are actively trafficked during ICD by danger signalling pathways, which are instigated and regulated by a complex interplay between endoplasmic reticulum (ER) stress, reactive oxygen species (ROS) production and cert...