Summary Despite the crucial role of tissue-resident memory T (Trm) cells in protective immunity, their priming remains poorly understood. Here, we have shown differential priming requirements for Trm versus circulating memory CD8+ T cells. In vaccinia cutaneous-infected mice, DNGR-1-mediated crosspresentation was required for optimal Trm cell priming but not for their skin differentiation or for circulating memory T cell generation. DNGR-1+ dendritic cells (DCs) promoted T-bet transcription factor induction and retention of CD8+ T cells in the lymph nodes (LNs). Inhibition of LN egress enhanced Trm cell generation, whereas genetic or antibody blockade of DNGR-1 or specific signals provided during priming by DNGR-1+ DCs, such as interleukin-12 (IL-12), IL-15 or CD24, impaired Trm cell priming. DNGR-1 also regulated Trm cell generation during influenza infection. Moreover, protective immunity depended on optimal Trm cell induction by DNGR-1+ DCs. Our results reveal specific priming requirements for CD8+ Trm cells during viral infection and vaccination.

Dendritic cells (DCs) control innate and adaptive immunity by patrolling tissues to gather antigens and danger signals derived from microbes and tissue. Subsequently, DCs integrate those environmental cues, orchestrate immunity or tolerance, and regulate tissue homeostasis. Recent advances in the field of immunometabolism highlight the notion that immune cells markedly alter cellular metabolic pathways during differentiation or upon activation, which has important implications on their functionality. Previous studies showed that active oxidative phosphorylation in mitochondria is associated with immature or tolerogenic DCs, while increased glycolysis upon pathogen sensing can promote immunogenic DC functions. However, new results in the last years suggest that regulation of DC metabolism in steady state, after immunogenic activation and during tolerance in different pathophysiological settings, may be more complex. Moreover, ontogenically distinct DC subsets show different functional specializations to control T cell responses. It is, thus, relevant how metabolism influences DC differentiation and plasticity, and what potential metabolic differences exist among DC subsets. Better understanding of the emerging connection between metabolic adaptions and functional DC specification will likely allow the development of therapeutic strategies to manipulate immune responses.

Background The manipulation of dendritic cells (DCs) for cancer vaccination has not reached its full potential, despite the revolution in cancer immunotherapy. DCs are fundamental for CD8+ T cell activation, which relies on cross-presentation of exogenous antigen on MHC-I and can be fostered by immunogenic cancer cell death. Translational and clinical research has focused on in vitro-generated monocyte-derived DCs, while the vaccination efficacy of natural conventional type 1 DCs (cDC1s), which are associated with improved anti-tumor immunity and specialize on antigen cross-presentation, remains unknown. Methods We isolated primary spleen mouse cDC1s and established a protocol for fast ex vivo activation and antigen-loading with lysates of tumor cells that underwent immunogenic cell death by UV irradiation. Natural tumor antigen-loaded cDC1s were transferred and their potential for induction of endogenous CD8+ and CD4+ T cell responses in vivo, cancer prevention and therapy were assessed in three grafted cancer models. Further, we tested the efficacy of natural cDC1 vaccination in combination and comparison with anti-PD-1 treatment in two “wildtype” tumor models not expressing exogenous antigens. Results Herein, we reveal that primary mouse cDC1s ex vivo loaded with dead tumor cell-derived antigen are activated and induce strong CD8+ T cell responses from the endogenous repertoire upon adoptive transfer in vivo through tumor antigen cross-presentation. Notably, cDC1-based vaccines enhance tumor infiltration by cancer-reactive CD8+ and CD4+ T cells and halt progression of engrafted cancer models, including tumors that are refractory to anti-PD-1 treatment. Moreover, combined tumor antigen-loaded primary cDC1 and anti-PD-1 therapy had strong synergistic effects in a PD-1 checkpoint inhibition susceptible cancer model. Conclusions This preclinical proof-of-principle study is first to support the therapeutic efficacy of cancer immunotherapy with syngeneic dead tumor cell antigen-loaded mouse cDC1s, the equivalents of the human dendritic cell subset that correlates with beneficial prognosis of cancer patients. Our data pave the way for translation of cDC1-based cancer treatments into the clinic when isolation of natural human cDC1s becomes feasible. Electronic supplementary material The online version of this article (10.1186/s40425-019-0565-5) contains supplementary material, which is available to authorized users.

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BackgroundElimination of cancer cells by some stimuli like chemotherapy and radiotherapy activates anticancer immunity after the generation of damage‐associated molecular patterns, a process recently named immunogenic cell death (ICD). Despite the recent advances in cancer immunotherapy, very little is known about the immunological consequences of cell death activated by cytotoxic CD8+T (Tc) cells on cancer cells, that is, if Tc cells induce ICD on cancer cells and the molecular mechanisms involved.MethodsICD induced by Tc cells on EL4 cells was analyzed in tumor by vaccinating mice with EL4 cells killedin vitroorin vivoby Ag-specific Tc cells. EL4 cells and mutants thereof overexpressing Bcl-XLor a dominant negative mutant of caspase-3 and wild-type mice, as well as mice depleted of Tc cells and mice deficient in perforin, TLR4 and BATF3 were used.Ex vivocytotoxicity of spleen cells from immunized mice was analyzed by flow cytometry. Expression of ICD signals (calreticulin, HMGB1 and interleukin (IL)-1β) was analyzed by flow cytometry and ELISA.ResultsMice immunized with EL4.gp33 cells killed in vitro or in vivo by gp33-specific Tc cells were protected from parental EL4 tumor development. This result was confirmed in vivo by using ovalbumin (OVA) as another surrogate antigen. Perforin and TLR4 and BATF3-dependent type 1 conventional dendritic cells (cDC1s) were required for protection against tumor development, indicating cross-priming of Tc cells against endogenous EL4 tumor antigens. Tc cells induced ICD signals in EL4 cells. Notably, ICD of EL4 cells was dependent on caspase-3 activity, with reduced antitumor immunity generated by caspase-3–deficient EL4 cells. In contrast, overexpression of Bcl-XLin EL4 cells had no effect on induction of Tc cell antitumor response and protection.ConclusionsElimination of tumor cells by Ag-specific Tc cells is immunogenic and protects against tumor development by generating new Tc cells against EL4 endogenous antigens. This finding helps to explain the enhanced efficacy of T cell-dependent immunotherapy and provide a molecular basis to explain the epitope spread phenomenon observed during vaccination and chimeric antigen receptor (CAR)-T cell therapy. In addition, they suggest that caspase-3 activity in the tumor may be used as a biomarker to predict cancer recurrence during T cell-dependent immunotherapies.

Tissue-resident memory CD8+ T (Trm) cells define a distinct non-recirculating subset. Trm cells constitute a first line of defense against local infections in barrier tissues, but they are also found in non-barrier tissues and play a role in antitumor immunity. Their differentiation in tissues and their phenotypical, transcriptional, and functional characteristics are the object of active research. Herein, we will discuss the potential existence of committed CD8+ Trm precursors and the genealogy of memory CD8+ T cell subsets. In addition to the priming of naive T cells, there is some plasticity of antigen-experienced effector and memory T cell subsets to generate Trm precursors. Local inflammation, antigen presentation, and cytokines drive Trm differentiation. It is of prime interest how specific dendritic cell subsets modulate priming and differentiation of Trm cells, as well as their reactivation within tissues. Research on how we can manipulate generation of memory T cells subsets is key for improved vaccination strategies.

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