BackgroundTumor progression is accompanied by dramatic remodeling of the surrounding extracellular matrix leading to the formation of a tumor-specific ECM, which is often more collagen-rich and of increased stiffness. The altered ECM of the tumor supports cancer growth and metastasis, but it is unknown if this effect involves modulation of T cell activity. To investigate if a high-density tumor-specific ECM could influence the ability of T cells to kill cancer cells, we here studied how T cells respond to 3D culture in different collagen densities.MethodsT cells cultured in 3D conditions surrounded by a high or low collagen density were imaged using confocal fluorescent microscopy. The effects of the different collagen densities on T cell proliferation, survival, and differentiation were examined using flow cytometry. Cancer cell proliferation in similar 3D conditions was also measured. Triple-negative breast cancer specimens were analyzed for the number of infiltrating CD8+ T cells and for the collagen density. Whole-transcriptome analyses were applied to investigate in detail the effects of collagen density on T cells. Computational analyses were used to identify transcription factors involved in the collagen density-induced gene regulation. Observed changes were confirmed by qRT-PCR analysis.ResultsT cell proliferation was significantly reduced in a high-density matrix compared to a low-density matrix and prolonged culture in a high-density matrix led to a higher ratio of CD4+ to CD8+ T cells. The proliferation of cancer cells was unaffected by the surrounding collagen-density. Consistently, we observed a reduction in the number of infiltrating CD8+ T-cells in mammary tumors with high collagen-density indicating that collagen-density has a role in regulating T cell abundance in human breast cancer.Whole-transcriptome analysis of 3D-cultured T cells revealed that a high-density matrix induces downregulation of cytotoxic activity markers and upregulation of regulatory T cell markers. These transcriptional changes were predicted to involve autocrine TGF-β signaling and they were accompanied by an impaired ability of tumor-infiltrating T cells to kill autologous cancer cells.ConclusionsOur study identifies a new immune modulatory mechanism, which could be essential for suppression of T cell activity in the tumor microenvironment.Electronic supplementary materialThe online version of this article (10.1186/s40425-019-0556-6) contains supplementary material, which is available to authorized users.

Lactic acidosis is common to most solid tumors and has been found to affect infiltrating immune cells. Here we document effector phase inhibition of cytotoxic T cells (CTLs) involving complete blockage of cytokine production and partial impairment of lytic granule exocytosis. Lactic acidosis impaired TCR‐triggered phosphorylation of JNK, c‐Jun and p38, while not affecting MEK1 and ERK. The select targeting of signaling proteins involved in IFNγ production (JNK/c‐Jun, p38) without affecting those jointly used in cytokine regulation and granule exocytosis (MEK1/ERK) explains the observed split effect of lactic acidosis on the CTL responses. CTL inhibition by lactic acidosis showed fast dynamics with immediate onset and reversion. Functional recovery by neutralizing the extracellular pH despite continuous presence of lactate holds promise that CTL activity can be improved in the milieu of solid tumors with appropriate anti‐acidosis treatment, thereby increasing the efficacy of adoptive T cell therapy.

Our study demonstrates that tumor-derived heat shock protein (HSP)70 chaperones a tyrosinase peptide and mediates its transfer to human immature dendritic cells (DCs) by receptor-dependent uptake. Human tumor-derived HSP70 peptide complexes (HSP70-PC) thus have the immunogenic potential to instruct DCs to cross-present endogenously expressed, nonmutated, and tumor antigenic peptides that are shared among tumors of the melanocytic lineage for T cell recognition. T cell stimulation by HSP70-instructed DCs is dependent on the Ag bound to HSP70 in that only DCs incubated with HSP70-PC purified from tyrosinase-positive (HSP70-PC/tyr+) but not from tyrosinase-negative (HSP70-PC/tyr−) melanoma cells resulted in the specific activation of the HLA-A*0201-restricted tyrosinase peptide-specific cytotoxic T cell clone. HSP70-PC-mediated T cell stimulation is very efficient, delivering the tyrosinase peptide at concentrations as low as 30 ng/ml of HSP70-PC for T cell recognition. Receptor-dependent binding of HSP70-PC and active cell metabolism are prerequisites for MHC class I-restricted cross-presentation and T cell stimulation. T cell stimulation does not require external DC maturation signals (e.g., exogenously added TNF-α), suggesting that signaling DC maturation is an intrinsic property of the HSP70-PC itself and related to receptor-mediated binding. The cross-presentation of a shared human tumor Ag together with the exquisite efficacy are important new aspects for HSP70-based immunotherapy in clinical anti-cancer vaccination strategies, and suggest a potential extension of HSP70-based vaccination protocols from a patient-individual treatment modality to its use in an allogeneic setting.

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Roquin proteins preclude spontaneous T cell activation and aberrant differentiation of T follicular helper (Tfh) or T helper 17 (Th17) cells. Here we showed that deletion of Roquin-encoding alleles specifically in regulatory T (Treg) cells also caused the activation of conventional T cells. Roquin-deficient Treg cells downregulated CD25, acquired a follicular Treg (Tfr) cell phenotype, and suppressed germinal center reactions but could not protect from colitis. Roquin inhibited the PI3K-mTOR signaling pathway by upregulation of Pten through interfering with miR-17∼92 binding to an overlapping cis-element in the Pten 3' UTR, and downregulated the Foxo1-specific E3 ubiquitin ligase Itch. Loss of Roquin enhanced Akt-mTOR signaling and protein synthesis, whereas inhibition of PI3K or mTOR in Roquin-deficient T cells corrected enhanced Tfh and Th17 or reduced iTreg cell differentiation. Thereby, Roquin-mediated control of PI3K-mTOR signaling prevents autoimmunity by restraining activation and differentiation of conventional T cells and specialization of Treg cells.

Heat shock proteins (HSP) when released into the extracellular milieu can act simultaneously as a source of antigen due to their ability to chaperone peptides and as a maturation signal for dendritic cells, thereby inducing DCs to cross-present antigens to CD8+ T-cells. HSP can also act independently from associated peptides, stimulating the innate immune system. Previous results regarding the activation of NK cells by HSP70 cell surface expression on tumour cells and soluble HSP70 will be further covered elsewhere within this issue. For cross-presentation, HSP70-peptide complexes (HSP70-PC) were used from two human melanoma cell lines that differ in the expression of the tumour-associated antigen tyrosinase. Purified HSP70-PC consists of both the constitutively expressed HSC70 and the inducible HSP70. HSP70-peptide complexes purified from tyrosinase positive (HSP70-PC/tyr+) human melanoma cells, incubated with immature DCs, results in the activation of HLA-*A0201-restricted tyrosinase peptide-specific T-cells. Receptor-mediated uptake of HSP70-PC by DCs and intracellular transport are required for efficient MHC class I restricted cross-presentation of chaperoned peptides. Demonstration of HSP70-PC mediated cross-presentation of such non-mutated naturally expressed tumour antigens is of special clinical interest with regard to hyperthermia. Tumour regression and improved local control have been shown within clinical phase II/III trials integrating regional hyperthermia combined with radiation and/or chemotherapy in multimodal treatment strategies. According to the proposed concept, local necrosis induced by hyperthermic treatment induces the release of HSPs, followed by uptake, processing and presentation of associated peptides by DCs. By acting as chaperone and a signal for DC maturation, HSP70-PC might efficiently prime circulating T-cells. Therefore, upregulating HSP70 and causing local necrosis in tumour tissue by hyperthermia offers great potential as a new approach to directly activate the immune system.

Heat shock proteins (HSPs) have shown promise for the optimization of protein-based vaccines because they can transfer exogenous antigens to dendritic cells and at the same time induce their maturation. Great care must be exercised in interpretating HSP-driven studies, as by-products linked to the recombinant generation of these proteins have been shown to mediate immunological effects. We generated highly purified human recombinant Hsp70 and demonstrated that it strongly enhances the cross-presentation of exogenous antigens resulting in better antigen-specific T cell stimulation. Augmentation of T cell stimulation was a direct function of the degree of complex formation between Hsp70 and peptides and correlated with improved antigen delivery to endosomal compartments. The Hsp70 activity was independent of TAP proteins and was not inhibited by exotoxin A or endosomal acidification. Consequently, Hsp70 enhanced cross-presentation of various antigenic sequences, even when they required different post-uptake processing and trafficking, as exemplified by the tumor antigens tyrosinase and Melan-A/MART-1. Furthermore, Hsp70 enhanced cross-presentation by different antigen-presenting cells (APCs), including dendritic cells and B cells. Importantly, enhanced cross-presentation and antigen-specific T cell activation were observed in the absence of innate signals transmitted by Hsp70. As Hsp70 supports the cross-presentation of different antigens and APCs and is inert to APC function, it may show efficacy in various settings of immune modulation, including induction of antigen-specific immunity or tolerance.Cytotoxic CD8 T cells have an essential role in cellular immunity in that they destroy infected or malignantly transformed cells. They are activated by the recognition of complexes of major histocompatibility complex (MHC) 4 class I and antigenic peptides present on the surface of antigen-presenting cells (APC). Conventionally, the antigenic peptides presented by MHC class I are derived from endogenous cytosolic antigens. In specialized situations, MHC class I molecules additionally present peptides derived from exogenous antigens. This noncanonical MHC class I presentation, which is referred to as cross-presentation, requires that the exogenous antigen is internalized by APCs, subsequently enzymatically processed into peptides, and channeled into the MHC class I loading pathway (1, 2). Cross-presentation is crucial for the generation of CD8 T cell responses against antigens that are not endogenously produced by APCs, such as tumor antigens and pathogen-derived proteins. In an applied setting, cross-presentation is the required pathway for the generation of protein-based vaccines that are intended to stimulate antigen-specific CD8 responses. Critical parameters that define the efficacy of a vaccine are the amount of delivered antigen and the context in which the antigen is presented to the T cells. As the physiological capacity of APCs to cross-present antigen is generally low (3), there is significant interest to de...

Uromodulin/Tamm-Horsfall protein is not immunostimulatory in the tubular lumen, but through unknown mechanisms it can activate dendritic cells and promote inflammation in the renal interstitium. Here, we noted that uromodulin isolated from human urine aggregates to large, irregular clumps with a crystal-like ultrastructure. These uromodulin nanoparticles activated isolated human monocytes to express costimulatory molecules and to secrete the mature proinflammatory cytokines, including IL-1b. Full release of IL-1b in response to uromodulin depended on priming of pro-IL-1b expression by Toll-like receptors, TNF-a, or IL-1a. In addition, uromodulininduced secretion of mature IL-1b depended on the NLRP3 inflammasome, its linker molecule ASC, and pro-IL-1b cleavage by caspase-1. Activation of NLRP3 required phagocytosis of uromodulin particles into lysosomes, cathepsin leakage, oxidative stress, and potassium efflux from the cell. Taken together, these data suggest that uromodulin is a NLRP3 agonist handled by antigen-presenting cells as an immunostimulatory nanoparticle. Thus, in the presence of tubular damage that exposes the renal interstitium, uromodulin becomes an endogenous danger signal. The inability of renal parenchymal cells to secrete IL-1b may explain why uromodulin remains immunologically inert inside the luminal compartment of the urinary tract.