Enhancement of Tumour-Specific Immune Responses In Vivo by ‘MHC Loading-Enhancer’ (MLE)

BACKGROUND:Class II MHC molecules (MHC II) are cell surface receptors displaying short protein fragments for the surveillance by CD4+ T cells. Antigens therefore have to be loaded onto this receptor in order to induce productive immune responses. On the cell surface, most MHC II molecules are either occupied by ligands or their binding cleft has been blocked by the acquisition of a non-receptive state. Direct loading with antigens, as required during peptide vaccinations, is therefore hindered. PRINCIPAL FINDINGS:Here we show, that the in vivo response of CD4+ T cells can be improved, when the antigens are administered together with 'MHC-loading enhancer' (MLE). MLE are small catalytic compounds able to open up the MHC binding site by triggering ligand-release and stabilizing the receptive state. Their enhancing effect on the immune response was demonstrated here with an antigen from the influenza virus and tumour associated antigens (TAA) derived from the NY-ESO-1 protein. The application of these antigens in combination with adamantane ethanol (AdEtOH), an MLE compound active on human HLA-DR molecules, significantly increased the frequency of antigen-specific CD4+ T cells in mice transgenic for the human MHC II molecule. Notably, the effect was evident only with the MLE-susceptible HLA-DR molecule and not with murine MHC II molecules non-susceptible for the catalytic effect of the MLE. CONCLUSION:MLE can specifically increase the potency of a vaccine by facilitating the efficient transfer of the antigen onto the MHC molecule. They may therefore open a new way to improve vaccination efficacy and tumour-immunotherapy

CD70/CD27 signaling promotes blast stemness and is a viable therapeutic target in acute myeloid leukemia.

Aberrant proliferation, symmetric self-renewal, increased survival, and defective differentiation of malignant blasts are key oncogenic drivers in acute myeloid leukemia (AML). Stem cell gene signatures predict poor prognosis in AML patients; however, with few exceptions, these deregulated molecular pathways cannot be targeted therapeutically. In this study, we demonstrate that the TNF superfamily ligand-receptor pair CD70/CD27 is expressed on AML blasts and AML stem/progenitor cells. CD70/CD27 signaling in AML cells activates stem cell gene expression programs, including the Wnt pathway, and promotes symmetric cell divisions and proliferation. Soluble CD27, reflecting the extent of CD70/CD27 interactions in vivo, was significantly elevated in the sera of newly diagnosed AML patients and is a strong independent negative prognostic biomarker for overall survival. Blocking the CD70/CD27 interaction by mAb-induced asymmetric cell divisions and differentiation in AML blasts and AML stem/progenitor cells inhibited cell growth and colony formation and significantly prolonged survival in murine AML xenografts. Importantly, hematopoietic stem/progenitor cells from healthy BM donors express neither CD70 nor CD27 and were unaffected by blocking mAb treatment. Therefore, targeting CD70/CD27 signaling represents a promising therapeutic strategy for AML

Getting by with a little help from the right CD4+ T cells

Tumor infiltration by effector cells is essential for the efficacy of T cell-based immunotherapeutic approaches against brain malignancies. We found that tumor-associated antigen (TAA)-specific CD8+ T cells are optimally recruited to neoplastic lesions when co-administered with TH1 polarized CD4+ T cells that are also TAA-specific. However, in vitro TH1 polarization is not required for the long-term therapeutic efficacy of the combined transfer of CD4+ and CD8+ T cells

Synergy between CD8 T cells and Th1 or Th2 polarised CD4 T cells for adoptive immunotherapy of brain tumours

The feasibility of cancer immunotherapy mediated by T lymphocytes is now a clinical reality. Indeed, many tumour associated antigens have been identified for cytotoxic CD8 T cells, which are believed to be key mediators of tumour rejection. However, for aggressive malignancies in specialised anatomic sites such as the brain, a limiting factor is suboptimal tumour infiltration by CD8 T cells. Here we take advantage of recent advances in T cell biology to differentially polarise CD4 T cells in order to explore their capacity to enhance immunotherapy. We used an adoptive cell therapy approach to work with clonal T cell populations of defined specificity. Th1 CD4 T cells preferentially homed to and accumulated within intracranial tumours compared with Th2 CD4 T cells. Moreover, tumour-antigen specific Th1 CD4 T cells enhanced CD8 T cell recruitment and function within the brain tumour bed. Survival of mice bearing intracranial tumours was significantly prolonged when CD4 and CD8 T cells were co-transferred. These results should encourage further definition of tumour antigens recognised by CD4 T cells, and exploitation of both CD4 and CD8 T cell subsets to optimise T cell therapy of cancer

MLE enhance the T cell response against NY-ESO-1 protein.

<p>(A) Determination of T cell response by intracellular cytokine staining. HLA-DR1tg mice were s.c. primed with 10 µg NY-ESO-1 protein in IFA/CpG supplemented with (right panel) or without AdEtOH (middle panel). The specific T cell response was determined by intracellular flow cytometry staining 12 days after priming. Lymph node cells were restimulated for 6 h in the presence of 10 µg NY-ESO-1 protein or control peptide (left panel) together with αCD28 antibody. 3 µg/ml Brefeldin A was added for the last 2 h. Intracellular IFNγ-production was analyzed on CD4+ CD154+ double positive T cells. Numbers indicate frequency of CD4+ CD154+ IFNγ+ cells among total CD4+ cells. Data is representative of two independent experiments. (B) Dose-response. Groups of 5 mice were primed with 10 µg NY-ESO-1 protein emulsified in IFA/CpG supplemented with (open circle) or without AdEtOH (closed circle). 12 days after vaccination 1×10⁶ Lymph node cells were <i>ex vivo</i> challenged with titrated amounts of NY-ESO-1 protein and IFNγ-detection was carried out 48 hrs later using an Elispot assay. Spot numbers represent single IFNγ+ cells.</p

Vaccination in presence of MLE increases the number of antigen-specific IFNγ-producing T cells.

<p>(A) Determination of IFNγ in an Elispot assay. 12 days after vaccination, 1×10⁶ lymph node cells from mice primed with 3 µg HA 306–318 in IFA/CpG supplemented without (left panel) or with AdEtOH (right panel) were incubated with titrated amounts of HA306–318 peptide on a plate coated with α-IFNγ antibody. Detection was carried out 48 hrs later by determining the spot number in each well. Spots represent single IFNγ+ cells. (B) Statistical analysis of the T cell response. Summarized Elispot data obtained from groups of BALB/c mice (left panel, n = 10) and HLA-DR1tg mice (right panel, n = 9) were analyzed using <i>student's t</i> test.</p

Influence of MLE on the class II MHC peptide-loading of dendritic cells.

<p>(A) Cell surface loading. HLA-DR4 expressing dendritic cells (DC) generated from the bone marrow of HLA-DR4 transgenic mice were incubated for 4 h with medium alone (left panel) or with 5 µg/ml biotinylated HA 306–318 peptide in the absence (middle panel) or presence of 250 µM AdEtOH, the model MLE compound used throughout this study (right panel). Contour plots are shown for DC after staining with anti-HLA-DR antibody (→ MHC expression) and streptavidin (→ peptide load). Mean peptide loading (MFI of streptavidin signal) is indicated. (B) CD4+ T cell response. DC from HLA-DR4tg mice (left panel) and from HLA-DR1tg mice (right panel) were pulsed for 4 h with indicated amounts of HA 306–318 peptide in the absence (open circle) and presence (closed circle) of 250 µM AdEtOH. The cells were used to challenge HA 306–318 specific, HLA-DR4-restricted 8475/94 cells and HLA-DR1-restricted EvHA/X5 T cell hybridoma cells, respectively. Background proliferation was measured in absence of peptide (dashed line).</p

MLE enhances the T cell response against NY-ESO-1 derived epitopes.

<p>(A) Cell surface loading of NY-ESO-1 epitopes. L929 fibroblasts transfected with HLA-DR1 (left panel) or HLA-DR4 (right panel) were incubated for 4 h with titrated amounts of NY-ESO-1 89–101 or NY-ESO-1 119–143, respectively. Loading was performed in the absence (closed circles) or presence (open circles) of 250 µM AdEtOH. Non-transfected L929 cells were used as a negative control (left side). Peptide loading was determined by analyzing the mean fluorescence of the streptavidin-signal gated on a distinct expression of HLA-DR. Background fluorescence was detected in the absence of biotinylated peptide (dashed line). (B) Detection of tumour-specific T cell response <i>in vivo</i>. Groups of HLA-DR1tg (left panel, n = 13) or HLA-DR4tg (right panel, n = 10) mice were s.c. primed with 5 µg of the respective NY-ESO-1 epitopes in IFA/CpG supplemented with or without AdEtOH. 12 days after vaccination, 1×10⁶ Lymph node cells were incubated with titrated amounts of NY-ESO-1 89–101 or NY-ESO-1 119–143, respectively. IFNγ-detection was carried out 48 hrs later using an Elispot assay and summarized data were analyzed using <i>student's t</i> test.</p

Immune Infiltration of Spontaneous Mouse Astrocytomas Is Dominated by Immunosuppressive Cells from Early Stages of Tumor Development

International audienceImmune infiltration of advanced human gliomas has been shown, but it is doubtful whether these immune cells affect tumor progression. It could be hypothesized that this infiltrate reflects recently recruited immune cells that are immediately overwhelmed by a high tumor burden. Alternatively, if there is earlier immune detection and infiltration of the tumor, the question arises as to when antitumor competency is lost. To address these issues, we analyzed a transgenic mouse model of spontaneous astrocytoma (GFAP-V(12)HA-ras mice), which allows the study of immune interactions with developing glioma, even at early asymptomatic stages. T cells, including a significant proportion of Tregs, are already present in the brain before symptoms develop, followed later by macrophages, natural killer cells, and dendritic cells. The effector potential of CD8 T-cells is defective, with the absence of granzyme B expression and low expression of IFN-gamma, tumor necrosis factor, and interleukin 2. Overall, our results show an early defective endogenous immune response to gliomas, and local accumulation of immunosuppressive cells at the tumor site. Thus, the antiglioma response is not simply overwhelmed at advanced stages of tumor growth, but is counterbalanced by an inhibitory microenvironment from the outset. Nevertheless, we determined that effector molecule expression (granzyme B, IFN-gamma) by brain-infiltrating CD8 T-cells could be enhanced, despite this unfavorable milieu, by strong immune stimuli. This potential to modulate the strong imbalance in local antiglioma immunity is encouraging for the development and optimization of future glioma immunotherapies. (C)2010 AACR