Subsets Of Antigen-presenting Cells Research Articles

(Not) Home alone: Antigen presenting cell - T Cell communication in barrier tissues.

Priming of T cells by antigen presenting cells (APCs) is essential for T cell fate decisions, enabling T cells to migrate to specific tissues to exert their effector functions. Previously, these interactions were mainly explored using blood-derived cells or animal models. With great advances in single cell RNA-sequencing techniques enabling analysis of tissue-derived cells, it has become clear that subsets of APCs are responsible for priming and modulating heterogeneous T cell effector responses in different tissues. This composition of APCs and T cells in tissues is essential for maintaining homeostasis and is known to be skewed in infection and inflammation, leading to pathological T cell responses. This review highlights the commonalities and differences of T cell priming and subsequent effector function in multiple barrier tissues such as the skin, intestine and female reproductive tract. Further, we provide an overview of how this process is altered during tissue-specific infections which are known to cause chronic inflammation and how this knowledge could be harnessed to modify T cell responses in barrier tissue.

Interplay between plasmacytoid dendritic cells and tumor-specific T cells in peripheral blood influences long-term survival in non-small cell lung carcinoma.

Plasmacytoid dendritic cells (pDCs) represent a subset of antigen-presenting cells that play an ambivalent role in cancer immunity. Here, we investigated the clinical significance of circulating pDCs and their interaction with tumor-specific T cell responses in patients with non-small cell lung cancer (NSCLC, n = 126) . The relation between intratumoral pDC signature and immune checkpoint inhibitors efficacy was also evaluated. Patients with NSCLC had low level but activated phenotype pDC compared to healthy donors. In overall population, patients with high level of pDC (pDChigh) had improved overall survival (OS) compared to patients with pDClow, median OS 30.4 versus 20.7months (P = 0.013). This clinical benefit was only observed in stage I to III patients, but not in metastatic disease. We showed that patients harboring pDChigh profile had high amount of Th1-diffentiation cytokine interleukin-12 (IL-12) in blood and had functional T cells directed against a broad range of tumor antigens. Furthermore, a high pDC signature in the tumor microenvironment was associated with improved clinical outcome in patients treated with anti-PD-(L)1 therapy. Overall, this study showedthatcirculating pDChigh is associated with long-term OSin NSCLC and highlighted the predictive value of intratumor pDC signature in the efficacy of immune checkpoint inhibitors.

Characterisation of the immune microenvironment of cutaneous squamous cell carcinoma in immunosuppression.

Cutaneous squamous cell carcinoma (cSCC) is a common cancer. Systemic immunosuppression with drugs such as Prednisone results in more aggressive disease. We hypothesise that more aggressive disease in immunosuppression is the result of immune changes in the tumor microenvironment. We characterised T cell, phagocytic and antigen presenting cell subsets in cSCC and determined if these infiltrates were altered by immunosuppressive therapy. We found a dominant "CD8 profile" in the centre of cSCC lesions, with CD8 cells correlating with Tbet, FoxP3, OX40 and "M2-like" macrophages, whereas a "Tbet and granulocyte profile" with associated inflammation predominated at the margin of the tumor. Individuals on systemic immunosuppressive therapy had lesions that were comparable in size, stage and number of vessels to immune competent individuals; however, the number of CD11c positive cells in the lesion centre was significantly reduced. We conclude that cSCC lesions are immunologically heterogeneous across the lesion and that systemically immunosuppressed individuals have reduced CD11c positive cells in the centre of the lesion. The role and detailed phenotype of CD11c positive cells in cSCC lesions warrant further investigation.

MTORC1 signaling in antigen-presenting cells of the skin restrains CD8+ Tcell priming.

How mechanistic target of rapamycin complex 1 (mTORC1), a key regulator of cellular metabolism, affects dendritic cell (DC) metabolism and Tcell-priming capacity has primarily been investigated invitro, but how mTORC1 regulates this invivo remains poorly defined. Here, using mice deficient for mTORC1 component raptor in DCs, we find that loss of mTORC1 negatively affects glycolytic and fatty acid metabolism and maturation of conventional DCs, particularly cDC1s. Nonetheless, antigen-specific CD8+ Tcell responses to infection are not compromised and are even enhanced following skin immunization. This is associated with increased activation of Langerhans cells and a subpopulation of EpCAM-expressing cDC1s, of which the latter show an increased physical interaction with CD8+ Tcells in situ. Together, this work reveals that mTORC1 limits CD8+ Tcell priming invivo by differentially orchestrating the metabolism and immunogenicity of distinct antigen-presenting cell subsets, which may have implications for clinical use of mTOR inhibitors.

Abstract 1373: PeptidePCR: Direct identification of cancer vaccine targets from scant clinical samples

Abstract Background: Peptides presented by Human Leukocyte antigen (HLA) class I and II molecules form an important component of the adaptive immune response against tumors. Identifying HLA-bound peptides is therefore crucial to understand the specificity of T cell responses in cancer. Due to sample limitations, it is often difficult or impossible to confirm epitope presentation in clinical biopsy material. To develop truly personal medicine, target epitopes need to be directly identified or validated in patient tumors at the peptide antigen level. Methodology: We have developed a microscale HLA immunoprecipitation protocol which when combined with a tandem mass tag (TMT)-based barcoding approach was able to identify HLA-bound peptides. HLA-complexes were affinity purified from either cultured cells, patient-derived xenograft or melanoma biopsies and the peptide cargo was tagged using TMT barcodes and analyzed using high-resolution mass spectrometry. Like primers in PCR, the carrier peptides and multiplexing of samples amplifies the signal enabling sensitive detection. Results: By using this strategy, we identified HLA-bound peptides from as few as ~1000 cultured cells. We demonstrate the clinical utility of this approach by confirming the presentation of around 1000 peptides from a challenging melanoma biopsy (~1-20mg in total), including 11 well-known T-cell response-inducing epitopes and other potential epitopes derived from Melanoma-associated antigens and neoantigens. Conclusion: This strategy will be useful for studying peptidome subsets in other clinical samples where the amount of tissue available via sampling is limiting, including biopsies taken for autoimmune diseases and infections, or to sample rare cell types in tissue/cell samples, such as different antigen-presenting cell subsets. The approach can directly isolate antigens that are already presented by HLA molecules, thereby increasing the precision of personalized approaches to cancer treatment with less than 1-week turnaround times. Citation Format: Sri H. Ramarathinam, Pouya Faridi, Angela Peng, Pacman Szeto, Nicholas C. Wong, Andreas Behren, Mark Shackleton, Anthony W. Purcell. PeptidePCR: Direct identification of cancer vaccine targets from scant clinical samples [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1373.

184-OR: Antigen-Presenting Cells Can Generate Hybrid Peptides Identified in Type 1 Diabetes

Type 1 Diabetes (T1D) is an autoimmune disease characterized by selective loss of pancreatic β-cells. Aberrant reactivity to insulin and insulin precursor peptides has long been considered important in the pathogenesis of T1D. Recently, T cells recognizing hybrid insulin peptides (HIPs) have been described, first in a rodent model and later in human T1D. A HIP is a CD4 T-cell epitope that is formed by the post-translational fusion of two peptide fragments with at least one of the peptide fragments derived from insulin or a precursor. HIP formation can occur intra- or intermolecularly. The role of these HIPs in the pathogenesis of T1D remains unclear. Others have proposed that HIPs are formed in β-cells during crinophagy of secretory granules. As ultrastructural studies have demonstrated that β-cells can transfer secretory vesicles to local antigen presenting cells (APCs) , we hypothesized that APCs could similarly generate HIPs via protease mediated transpeptidation. To test this, we manufactured peptide-containing nanocarriers mimicking β-cell secretory vesicles to transfer selected peptides to APCs in both mouse and human in vitro systems utilizing donor APCs and CD4 TCR transgenic T cells or a CD4 transductant reporter cells respectively. Here, we demonstrate the subsets of APCs which are capable of intramolecular and intermolecular HIP formation. We further demonstrate that this formation can be blocked by proteosome inhibition. Our study identifies a novel mechanism for the generation of HIPs recognized in T1D. Disclosure S.A.Khokhar: None. M.Liu: None. J.L.Gaglia: Advisory Panel; Dompé, Regeneron Pharmaceuticals Inc., Consultant; Vertex Pharmaceuticals Incorporated, Research Support; Avotres Inc., Dompé, Janssen Research & Development, LLC, Provention Bio, Inc., Stock/Shareholder; Vertex Pharmaceuticals Incorporated. Funding National Institutes of Health 5P30DK036836JDRF 5-ECR-2016-186-A-N

Central tolerance is impaired in the middle-aged thymic environment.

One of the earliest hallmarks of immune aging is thymus involution, which not only reduces the number of newly generated and exported T cells, but also alters the composition and organization of the thymus microenvironment. Thymic T‐cell export continues into adulthood, yet the impact of thymus involution on the quality of newly generated T‐cell clones is not well established. Notably, the number and proportion of medullary thymic epithelial cells (mTECs) and expression of tissue‐restricted antigens (TRAs) decline with age, suggesting the involuting thymus may not promote efficient central tolerance. Here, we demonstrate that the middle‐aged thymic environment does not support rapid motility of medullary thymocytes, potentially diminishing their ability to scan antigen presenting cells (APCs) that display the diverse self‐antigens that induce central tolerance. Consistent with this possibility, thymic slice assays reveal that the middle‐aged thymic environment does not support efficient negative selection or regulatory T‐cell (Treg) induction of thymocytes responsive to either TRAs or ubiquitous self‐antigens. This decline in central tolerance is not universal, but instead impacts lower‐avidity self‐antigens that are either less abundant or bind to TCRs with moderate affinities. Additionally, the decline in thymic tolerance by middle age is accompanied by both a reduction in mTECs and hematopoietic APC subsets that cooperate to drive central tolerance. Thus, age‐associated changes in the thymic environment result in impaired central tolerance against moderate‐avidity self‐antigens, potentially resulting in export of increasingly autoreactive naive T cells, with a deficit of Treg counterparts by middle age.

Single Cell Sequencing of Myeloid Cells in Human Hypertension

Hypertension is a major modifiable risk factor for death and cardiovascular disease, yet its causes are largely unknown. Monocytes and monocyte‐derived dendritic cells (DCs) are activated in hypertension producing cytokines that drive T cell activation. Moreover, DCs from hypertensive mice promote hypertension when adoptively transferred into normotensive mice. The specific human subsets of antigen presenting cells (APCs) that promote human hypertension have yet to be described at a single cell level. We isolated total peripheral blood mononuclear cells (PBMCs) from normotensive (n=5) and hypertensive (n=4) human subjects. We sorted for HLA‐DR+ and CD19‐ cells by magnetic bead separation. Single cell sequencing was performed on a 10x Chromium platform. After performing quality controls, we found a total of 10 clusters that were expressed in both normotensive and hypertensive human subjects. KEGG Pathway analysis on all HLA‐DR+ myeloid cells revealed that pathways associated with oxidative phosphorylation, toll‐like receptor signaling and interleukin (IL)‐17 signaling were increased in hypertensive subjects. Conversely, pathways associated with antigen processing and presentation and cell adhesion molecules were enriched in normotensive subjects. Hypertensive subjects had a significant increase in CD14+ CD36+ monocytes compared to controls (p=0.009). Conversely, CD14+ CD36‐ monocytes and plasmacytoid DCs were significantly reduced in hypertensive subjects (p=0.002 and p=0.0008, respectively). Of particular interest were a cluster of pro‐inflammatory monocytes with expression of CD14 CCL3, IL1B, CD83, TNF, and SGK1. Within this cluster, CXCL8, the gene encoding interleukin (IL)‐8, and CCL3 were significantly increased in hypertensive subjects compared to controls (adjusted p value = 3.0E‐106and 2.0E‐107, respectively). Further studies are needed to investigate CXCL8 (IL‐8) and its role in myeloid cell activation and human hypertension.

Instructive Cues of Thymic T Cell Selection.

A high diversity of αβ T cell receptors (TCRs), capable of recognizing virtually any pathogen but also self-antigens, is generated during T cell development in the thymus. Nevertheless, a strict developmental program supports the selection of a self-tolerant T cell repertoire capable of responding to foreign antigens. The steps of T cell selection are controlled by cortical and medullary stromal niches, mainly composed of thymic epithelial cells and dendritic cells. The integration of important cues provided by these specialized niches, including (a) the TCR signal strength induced by the recognition of self-peptide-MHC complexes, (b) costimulatory signals, and (c) cytokine signals, critically controls T cell repertoire selection. This review discusses our current understanding of the signals that coordinate positive selection, negative selection, and agonist selection of Foxp3+ regulatory T cells. It also highlights recent advances that have unraveled the functional diversity of thymic antigen-presenting cell subsets implicated in T cell selection.

Analysis of immune response induction mechanisms implicating the dose-sparing effect of transcutaneous immunization using a self-dissolving microneedle patch

Transcutaneous immunization (TCI) is an effective vaccination method that is easier and less painful than the conventional injectable vaccination method. We previously developed self-dissolving microneedle patches (sdMN) and demonstrated that this TCI method has a high vaccination efficacy in mice and humans. To elucidate the mechanism of immune response induction, which is the basis for the efficacy and safety of TCI with sdMN, we examined the local reaction of the skin where sdMN was applied and the kinetics and differentiation status of immune cells in the draining lymph nodes (DLNs). We found that gene expression of the proinflammatory cytokine Il1b and the downstream transcription factor Irf7 was markedly upregulated in skin tissues after sdMN application. Moreover, activation of Langerhans cells and CD207− dermal dendritic cells, which are subsets of antigen-presenting cells (APCs) in the skin, and their migration to the DLNs were promoted. Furthermore, the activated APC subsets promoted CD4+ T cell and B cell differentiation and the formation of germinal centers, which are the sites of high-affinity antibody production. These phenomena associated with sdMN application may contribute to the efficient production of antigen-specific antibodies after TCI using sdMN. These findings provide essential information regarding immune response induction mechanisms for the development and improvement of TCI preparations.

461. Classical Antigen Presenting Cell Activation Correlates with T Cell Immunity and COVID-19 Severity

BackgroundThe initial response of immune cells against respiratory viruses often determines the severity and duration of disease. The early trajectory of the immune response during infection with SARS-CoV-2 remains poorly understood. Dysregulation of innate immune factors that facilitate viral clearance and the adaptive response, such as type I interferons, have been implicated in severe COVID-19. However, collection of biological samples during the first seven days post-symptom onset has posed a logistical challenge, limiting our knowledge surrounding the immune responses that drive protection versus immunopathology.MethodsFrom March 2020, Military Health System beneficiaries presenting with a positive SARS-CoV-2 test, a COVID-19 like illness, or a high-risk SARS-CoV-2 exposure at nine military medical treatment facilities across the United States were eligible for enrollment in our longitudinal cohort study, which included collection of respiratory sample, sera, plasma, and peripheral blood mononuclear cells (PBMCs). Twenty-five SARS-CoV-2 infected study participants provided samples with in the first seven days of symptom onset, fifteen of whom were hospitalized with COVID-19. We employed multiparameter spectral flow cytometry to comprehensively analyze the early trajectory of the innate and adaptive immune responses.ResultsWe discovered that early activation of critical antigen presenting cell subsets was impaired upon comparing inpatients with outpatients, correlating with decreased antigen-experienced T cell responses. Specifically, we noted reduced expression of key costimulatory molecules, CD80 and CD86, on conventional dendritic cells that are required for viral antigen-specific T cell priming. Reduction in CD38, a marker of activation was also observed on inpatient dendritic cell subsets.ConclusionReduced antigen presenting cell activation and expression of ligands that facilitate T cell engagement may impede the efficient clearance of SARS-CoV-2, coinciding with more severe disease in our cohort. Further analysis of the functional activation of early innate immune responses triggered by SARS-CoV-2 may unveil new immune biomarkers and therapeutic targets to predict and prevent severe disease associated with inadequate T cell immunity.Disclosures Simon Pollett, MBBS, Astra Zeneca (Other Financial or Material Support, HJF, in support of USU IDCRP, funded under a CRADA to augment the conduct of an unrelated Phase III COVID-19 vaccine trial sponsored by AstraZeneca as part of USG response (unrelated work))

Identification of Antigen Presenting Cell Subsets Supporting Human Tfh Differentiation.

CD4+ T follicular helper (Tfh) cells are essential for initiating and regulating efficient humoral responses in secondary lymphoid organs. Tfh polarization and differentiation is driven by multiple stimuli delivered by antigen presenting cells (APCs). APCs represent a complex population of immune cells, comprising several subpopulations (dendritic cells and macrophages) that are distinguished by their phenotype, ontogeny, and functions. In order to better identify and understand the role of the different APC subsets in human Tfh biology, we have used in vitro assays based on the co-culture of APCs and T cells. This chapter describes two complementary protocols. The first protocol describes an assay to study the capacity of APCs to drive Tfh polarization from naive CD4+ T cells. The second protocol is designed to address the role of APCs in modulating effector functions of mature Tfh cells.

Time-Dependent Serial Changes of Antigen-Presenting Cell Subsets in the Ocular Surface Are Distinct between Corneal Sterile Inflammation and Allosensitization in a Murine Model.

The kinetics of antigen-presenting cells (APCs) vary depending on their resident tissues and the manner of immunization. We investigated the long-term changes in mature APC and T-cell subsets over 4 weeks in the ocular surface in murine models of corneal quiescent or potent sterile inflammation, and allosensitization using partial (PT), syngeneic (Syn), and allogeneic (Allo) corneal transplantation. In PT, CD11bintCD11chiMHCIIhiCD86hi cells increased until 4 weeks with an increase in IFNγhi T cells. In Syn, both CD11bintCD11chiMHCIIhiCD86hi and CD11bhiCD11chiMHCIIhiCD86hi APC subsets increased until 4 weeks with a brief increase in CD69hi T cells at 2 weeks. In Allo, CD11bintCD11chiMHCIIhiCD86hi and CD11bhiCD11chiMHCIIhiCD86hi APC subsets increased until 4 weeks, and an early increase in CD69hi T cells was observed at 2 weeks followed by a late increase in IFNγhi T cells at 4 weeks. The frequency of the IFNγhi T cell subset was positively correlated with the frequency of the CD11bintCD11chiMHCIIhiCD86hi subset, indicating the existence of APC–T cell interaction in the ocular surface. Together, the results indicate that allosensitization in mature APCs leads to T-cell activation in the ocular surface, whereas sterile inflammation merely induces a brief and non-specific T-cell activation in the ocular surface.

Tunable heat shock protein-mediated NK cell responses are orchestrated by STAT1 in Antigen Presenting Cells

The release of Heat Shock Proteins (HSPs) from aberrant cells can initiate immune responses following engagement of the HSPs with antigen presenting cells (APCs). This is an important mechanism for cancer immunosurveillance and can also be modeled by vaccination with HSPs through various routes, targeting specific APCs expressing the HSP receptor CD91. Immunological outcomes can be varied as a result of the broad expression of CD91 in different dendritic cell and macrophage populations. We investigated the cellular response of different APCs to the prototypical immunogenic HSP, gp96, in the context of Th1 immunity. Although APCs generally express similar levels of the HSP receptor CD91, we uncovered APC-distinct, downstream signaling pathways activating STAT1, and differential STAT1 induced genes. As a result of this differential and unique signaling we determined that gp96-activated macrophages, but not DCs are capable of activating NK cells to produce IFN-gamma. These data demonstrate that different APC subsets elicit unique intracellular signaling responses to HSPs which result in different patterns of downstream cellular activation and immune responses. Collectively this provides a novel tunable and autochthonous immune response to extracellular HSPs which has important implications on the development of immunity to cancer and infectious disease, as well as homeostasis.

A positive feedback loop reinforces the allergic immune response in human peanut allergy.

Food allergies are a leading cause of anaphylaxis, and cellular mechanisms involving antigen presentation likely play key roles in their pathogenesis. However, little is known about the response of specific antigen-presenting cell (APC) subsets to food allergens in the setting of food allergies. Here, we show that in peanut-allergic humans, peanut allergen drives the differentiation of CD209+ monocyte-derived dendritic cells (DCs) and CD23+ (FcєRII) myeloid dendritic cells through the action of allergen-specific CD4+ T cells. CD209+ DCs act reciprocally on the same peanut-specific CD4+ T cell population to reinforce Th2 cytokine expression in a positive feedback loop, which may explain the persistence of established food allergy. In support of this novel model, we show clinically that the initiation of oral immunotherapy (OIT) in peanut-allergic patients is associated with a decrease in CD209+ DCs, suggesting that breaking the cycle of positive feedback is associated with therapeutic effect.

T cell infiltration on local CpG-B delivery in early-stage melanoma is predominantly related to CLEC9A+CD141+ cDC1 and CD14+ antigen-presenting cell recruitment

BackgroundWe previously reported CpG-B injection at the primary tumor excision site prior to re-excision and sentinel node biopsy to result in immune activation of the sentinel lymph node (SLN), increased...

Antigen-Presenting Cells in Food Tolerance and Allergy.

Food allergy now affects 6%–8% of children in the Western world; despite this, we understand little about why certain people become sensitized to food allergens. The dominant form of food allergy is mediated by food-specific immunoglobulin E (IgE) antibodies, which can cause a variety of symptoms, including life-threatening anaphylaxis. A central step in this immune response to food antigens that differentiates tolerance from allergy is the initial priming of T cells by antigen-presenting cells (APCs), primarily different types of dendritic cells (DCs). DCs, along with monocyte and macrophage populations, dictate oral tolerance versus allergy by shaping the T cell and subsequent B cell antibody response. A growing body of literature has shed light on the conditions under which antigen presentation occurs and how different types of T cell responses are induced by different APCs. We will review APC subsets in the gut and discuss mechanisms of APC-induced oral tolerance versus allergy to food identified using mouse models and patient samples.

MTORC1 Signalling in Antigen-Presenting Cells of the Skin Restrains CD8+ T Cell Priming

Mechanistic target of rapamycin complex 1 (mTORC1), a key sensor and regulator of cellular metabolism, has primarily been shown in vitro to affect various aspects of dendritic cell (DC) biology. However, our understanding of how mTORC1 regulates DC metabolism and their T cell-priming capacity in vivo remains limited. Here, using mice deficient in mTORC1 component raptor in DCs (CD11cΔraptor), we found that loss of mTORC1 selectively compromises glucose uptake, mitochondrial fitness and cellular maturation, particularly MHCI expression, of type 1 conventional DCs. Nonetheless, antigen-specific CD8+ T cell responses to infection were not compromised and even enhanced following skin immunization in CD11cΔraptor mice. This was associated with potentiated costimulatory molecule expression and IL-12 production specifically by Langerhans cells in CD11cΔraptor mice. Together, this work reveals that mTORC1 differentially orchestrates metabolism and immunogenicity of distinct antigen-presenting cell subsets, to limit CD8+ T cell priming in vivo, which may have implications for clinical use of mTOR inhibitors.

Comprehensive Phenotyping of Human Dendritic Cells and Monocytes.

Professional antigen-presenting cells (APCs), which include dendritic cells (DCs) and monocytes are essential for inducing and steering adaptive T-cell responses. Recent technological developments in single-cell analysis have significantly advanced our understanding of APC subset heterogeneity. To accurately resolve this functional diversity and to account for tissue-specific adaptation, novel phenotyping markers have been described more recently. While some of these largely overlap with traditionally used markers, more fine-grained phenotyping might be essential during inflammatory settings, where the traditional distinction between monocytes and dendritic cells has become blurred. Within this phenotype report, we provide a concise overview of traditional and recently described markers for the phenotyping of DCs and monocytes in the human system.

Cross-dressing of CD8α+ Dendritic Cells with Antigens from Live Mouse Tumor Cells Is a Major Mechanism of Cross-priming.

Live cells are the most abundant sources of antigen in a tumor-bearing host. Here, we used live tumor cells as source of antigens to investigate the mechanism underlying their immunogenicity in murine tumor models. The live tumor cells were significantly more immunogenic than irradiated or apoptotic tumor cells. We examined the interaction of live and apoptotic tumor cells with major subsets of antigen-presenting cells, i.e., CD8α+ dendritic cells (DC), CD8α- DCs, plasmacytoid DCs, and CD169+ macrophages at skin draining lymph nodes. The CD8α+ DCs captured cell-associated antigens from both live and apoptotic tumor cells, whereas CD169+ macrophages picked up cell-associated antigens mostly from apoptotic tumor cells. Trogocytosis and cross-dressing of membrane-associated antigenic material from live tumor cells to CD8α+ DCs was the primary mechanism for cross-priming of tumor antigens upon immunization with live cells. Phagocytosis of apoptotic tumor cells was the primary mechanism for cross-priming of tumor antigens upon immunization with apoptotic or irradiated cells. These findings clarify the mechanism of cross-priming of cancer antigens by DCs, allowing for a greater understanding of antitumor immune responses.