Virus or tumor Ag-derived peptides that are displayed by MHC class I molecules are attractive starting points for vaccine development because they induce strong protective and therapeutic cytotoxic T cell responses. In thus study, we show that the MHC binding and consequent T cell reactivity against several HLA-A*02 restricted epitopes can be further improved through the incorporation of nonproteogenic amino acids at primary and secondary anchor positions. We screened more than 90 nonproteogenic, synthetic amino acids through a range of epitopes and tested more than 3000 chemically enhanced altered peptide ligands (CPLs) for binding affinity to HLA-A*0201. With this approach, we designed CPLs of viral epitopes, of melanoma-associated Ags, and of the minor histocompatibility Ag UTA2-1, which is currently being evaluated for its antileukemic activity in clinical dendritic cell vaccination trials. The crystal structure of one of the CPLs in complex with HLA-A*0201 revealed the molecular interactions likely responsible for improved binding. The best CPLs displayed enhanced affinity for MHC, increasing MHC stability and prolonging recognition by Ag-specific T cells and, most importantly, they induced accelerated expansion of antitumor T cell frequencies in vitro and in vivo as compared with the native epitope. Eventually, we were able to construct a toolbox of preferred nonproteogenic residues with which practically any given HLA-A*02 restricted epitope can be readily optimized. These CPLs could improve the therapeutic outcome of vaccination strategies or can be used for ex vivo enrichment and faster expansion of Ag-specific T cells for transfer into patients.
Endogenous type I IFN production after innate immune recognition of tumor cells is critical for generating natural adaptive immune responses against tumors in vivo. We recently have reported that targeting low doses of IFN-? to the tumor microenvironment using tumor-specific mAbs can facilitate antitumor immunity, which could be augmented further with PD-L1/PD-1 blockade. However, sustained high doses of type I IFNs in the tumor microenvironment, which are potently therapeutic alone, may function through distinct mechanisms. In the current report, we demonstrate that high-dose intratumoral type I IFNs indeed exerted a profound therapeutic effect in the murine B16 model, which unexpectedly did not increase T cell responses. Moreover, bone marrow chimeras revealed a role for type I IFN signaling on nonhematopoietic cells, and most of the therapeutic effect was retained in mice deficient in T, B, and NK cells. Rather, the tumor vasculature was ablated with high-dose intratumoral IFN-?, and conditional deletion of IFN-?/?R in Tie2-positive vascular endothelial cells eliminated most of the antitumor activity. Therefore, the major component of the antitumor activity of sustained high doses of type I IFNs occurs through a direct antiangiogenic effect. Our data help resolve conditions under which distinct antitumor mechanisms of type I IFNs are operational in vivo.
Minor histocompatibility antigens are highly immunogenic polymorphic peptides playing crucial roles in the clinical outcome of HLA-identical allogeneic stem cell transplantation. Although the introduction of genome-wide association-based strategies significantly accelerated the identification of minor histocompatibility antigens over the past years, more efficient, rapid and robust identification techniques are required for a better understanding of the immunobiology of minor histocompatibility antigens and for optimal clinical application in the treatment of hematological malignancies. To develop a strategy that can overcome the drawbacks of all earlier developed strategies, we now integrated our previously developed genetic correlation analysis methodology with the comprehensive genomic databases from the 1000 Genomes Project. We show that the data set of the 1000 Genomes Project is suitable to identify all of the previously known minor histocompatibility antigens. Moreover, we demonstrate the power of this novel approach by the identification of the new HLA-DP4 restricted minor histocompatibility antigen UTDP4-1, which despite extensive efforts could not be identified using any of the previously developed biochemical, molecular biological or genetic strategies. The 1000 Genomes Project-based identification of minor histocompatibility antigens thus represents a very convenient and robust method for the identification of new targets for cancer therapy after allogeneic stem cell transplantation.
Knowledge of the accurate copy number of HLA class I presented ligands is important in fundamental and clinical immunology. Currently, the best copy number determinations are based on mass spectrometry, employing single reaction monitoring (SRM) in combination with a known amount of isotopically labeled peptide. The major drawback of this approach is that the losses during sample pretreatment, i.e. immunopurification and filtration steps, are not well defined and must, therefore, be estimated. In addition, such losses can vary for individual peptides. Therefore, we developed a new approach in which isotopically labeled peptide-MHC monomers (hpMHC) are prepared and added directly after cell lysis, i.e. before the usual sample processing. Using this approach, all losses during sample processing can be accounted for and allows accurate determination of specific MHC class I-presented ligands. Our study pinpoints the immunopurification step as the origin of the rather extreme losses during sample pretreatment and offers a solution to account for these losses. Obviously, this has important implications for accurate HLA-ligand quantitation. The strategy presented here can be used to obtain a reliable view of epitope copy number and thus allows improvement of vaccine design and strategies for immunotherapy.
Tumor escape from immune-mediated destruction has been associated with immunosuppressive mechanisms that inhibit T cell activation. Although evidence for an active immune response, including infiltration with CD8(+) T cells, can be found in a subset of patients, those tumors are nonetheless not immunologically rejected. In the current report, we show that it is the subset of T cell-inflamed tumors that showed high expression of three defined immunosuppressive mechanisms: indoleamine-2,3-dioxygenase (IDO), PD-L1/B7-H1, and FoxP3(+) regulatory T cells (T(regs)), suggesting that these inhibitory pathways might serve as negative feedback mechanisms that followed, rather than preceded, CD8(+) T cell infiltration. Mechanistic studies in mice revealed that up-regulated expression of IDO and PD-L1, as well as recruitment of T(regs), in the tumor microenvironment depended on the presence of CD8(+) T cells. The former was driven by interferon-? and the latter by a production of CCR4-binding chemokines along with a component of induced proliferation. Our results argue that these major immunosuppressive pathways are intrinsically driven by the immune system rather than being orchestrated by cancer cells, and imply that cancer immunotherapy approaches targeting negative regulatory immune checkpoints might be preferentially beneficial for patients with a preexisting T cell-inflamed tumor microenvironment.
T cell anergy is one of the mechanisms contributing to peripheral tolerance, particularly in the context of progressively growing tumors and in tolerogenic treatments promoting allograft acceptance. We recently reported that early growth response gene 2 (Egr2) is a critical transcription factor for the induction of anergy in vitro and in vivo, which was identified based on its ability to regulate the expression of inhibitory signaling molecules diacylglycerol kinase (DGK)-? and -?. We reasoned that other transcriptional targets of Egr2 might encode additional factors important for T cell anergy and immune regulation. Thus, we conducted two sets of genome-wide screens: gene expression profiling of wild type versus Egr2-deleted T cells treated under anergizing conditions, and a ChIP-Seq analysis to identify genes that bind Egr2 in anergic cells. Merging of these data sets revealed 49 targets that are directly regulated by Egr2. Among these are inhibitory signaling molecules previously reported to contribute to T cell anergy, but unexpectedly, also cell surface molecules and secreted factors, including lymphocyte-activation gene 3 (Lag3), Class-I-MHC-restricted T cell associated molecule (Crtam), Semaphorin 7A (Sema7A), and chemokine CCL1. These observations suggest that anergic T cells might not simply be functionally inert, and may have additional functional properties oriented towards other cellular components of the immune system.
For tumor antigen-specific T cells to effectively control the growth of cancer cells in vivo, they must gain access to, and function within, the tumor microenvironment. While tumor antigen-based vaccines and T cell adoptive transfer strategies can result in clinical benefit in a subset of patients, most of the patients do not respond clinically. Even for tumor-infiltrating lymphocyte (TIL)-based adoptive transfer for patients with metastatic melanoma, which can provide tumor shrinkage in around 50% of treated individuals, many patients are not eligible, in part because there are not sufficient TIL present in the resected tumor. Thus, the denominator is in fact larger, and it has been suggested that absence of TIL may be a marker for poor efficacy of immunotherapies in general. While qualitative and/or quantitative features of the T cells are important considerations for efficacy, a major component of primary resistance likely can be attributed to the tumor microenvironment. Data are accumulating suggesting that two major categories of immune resistance within the tumor microenvironment may exist: failure of T cell trafficking due to low levels of inflammation and lack of chemokines for migration, and dominant suppression through immune inhibitory mechanisms. New therapeutic interventions are being guided by these observations, and preliminary clinical success is validating this working model.
IgG FcRs are important mediators of immunity and play a key role during Ab-based immunotherapy. Within the leukocyte IgG receptor family, only Fc?RI is capable of IgG binding with high affinity. Fc?RI exists as a complex of a ligand binding ?-chain and an FcR ?-chain. The receptors ?-chain can, furthermore, elicit several functions independent of the ITAM-bearing FcR ?-chain. Functional implications of high-affinity IgG binding and mechanisms underlying FcR ?-chain-independent signaling remain unclear to this day. In this paper, we provide an overview of past literature on Fc?RI and address the implications of recently described interactions between cytosolic proteins and the Fc?RI ?-chain, as well as cytokine-enhanced Fc?RI immune complex binding. Furthermore, an analysis of potential polymorphisms within the FCGR1A gene is provided.
The molecular identification of tumor antigens initially catalyzed substantial enthusiasm for the development of tumor antigen-based vaccines for the treatment of cancer. However, numerous vaccine approaches in melanoma and other cancers have yielded a low rate of clinical response, despite frequent induction of specific T cells as detected in the peripheral blood. This observation has prompted several investigators to begin interrogating the tumor microenvironment for biologic correlates to tumor response versus resistance. Evidence is beginning to emerge suggesting that distinct subsets of tumors may exist that reflect distinct categories of immune escape. Lack of chemokine-mediated trafficking, poor innate immune cell activation, and the presence of specific immune suppressive mechanisms can be found to characterize subsets of tumors. A non-inflamed tumor phenotype may predict for resistance to cancer vaccines, suggesting a possible predictive biomarker and patient enrichment strategy. But in addition, characterization of these subsets may pave the way for catering therapeutic interventions toward the biologic features of the tumor in individual patients.
The essential role of CD4(+) T cells as helpers of anticancer immunity is indisputable. Little is known, however, about their capacity to serve as effector cells in cancer treatment. Therefore, we explored the efficacy of immunotherapy with sole CD4(+) cytotoxic human T cells directed at a hematopoietic-restricted minor histocompatibility antigen (mHag).
Identification of minor histocompatibility antigens (mHag) with classic methods often requires sophisticated technologies, determination, and patience. We here describe and validate a nonlaborious and convenient genetic approach, based on genome-wide correlations of mHag zygosities with HapMap single-nucleotide polymorphism genotypes, to identify clinical relevant mHags within a reasonable time frame.
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