Granulysin- and granzyme-dependent elimination of myeloid cells by therapeutic ova-specific type 1 regulatory T cells.

The intrinsic immunosuppressive properties of regulatory T (Treg) cells can be harnessed for therapeutic approaches aiming at down-modulating harmful immune reactions. In this context, expanded type 1 Treg cells (Tr1 cells) specific for ovalbumin (ova-Tr1 cells) have been tested for clinical efficacy in the treatment of autoimmune disorders such as refractory Crohn's disease (CD). The clinical use of these therapeutic products warrants exploration of their mechanism of action. Here, we identified a relationship between the CD activity index and the expression of lytic molecules by the ova-Tr1 cells administered in the previously reported First-in-Man study [Crohn's And Treg cells Study 1 (CATS1) study]. Accordingly, ova-Tr1 cells were found to carry granules containing high levels of lytic molecules, including multiple granzymes and granulysin. These cells displayed a T-cell receptor (TCR)-independent cytotoxic activity, which was preferentially directed toward myeloid cell lines and monocyte-derived dendritic cells. Upon contact with myeloid cells, ova-Tr1 cells induced their apoptosis via a perforin-independent and a granulysin/granzyme-dependent mechanism. As compared to CD8+ cytotoxic T cells, ova-Tr1 cells required more time to lyse target cells and displayed a more gradual lytic activity over time. Notably, this activity was sustained over days resulting in the control of myeloid cell populations at a relatively low ratio. Our study reveals that ova-Tr1 cells are endowed with a sustained cytotoxic activity that relies on a unique combination of granulysin and granzymes and that preferentially eliminates myeloid target cells in a TCR-independent manner.

The co-receptor BTLA negatively regulates human Vγ9Vδ2 T-cell proliferation: a potential way of immune escape for lymphoma cells.

Vγ9Vδ2 cells, the major γδ T-cell subset in human peripheral blood, represent a T-cell subset that displays reactivity against microbial agents and tumors. The biology of Vγ9Vδ2 T cells remains poorly understood. We show herein that the interaction between B- and T-lymphocyte attenuator (BTLA) and herpesvirus entry mediator (HVEM) is a major regulator of Vγ9Vδ2 T-cell proliferation control. BTLA was strongly expressed at the surface of resting Vγ9Vδ2 T cells and inversely correlated with T-cell differentiation. BTLA-HVEM blockade by monoclonal antibodies resulted in the enhancement of Vγ9Vδ2 T-cell receptor-mediated signaling, whereas BTLA-HVEM interaction led to a decrease in phosphoantigen-mediated proliferation by inducing a partial S-phase arrest. Our data also suggested that BTLA-HVEM might participate in the control of γδ T-cell differentiation. In addition, the proliferation of autologous γδ T cells after exposition to lymphoma cells was dramatically reduced through BTLA-HVEM interaction. These data suggest that HVEM interaction with BTLA may play a role in lymphomagenesis by interfering with Vγ9Vδ2 T-cell proliferation. Moreover, BTLA stimulation of Vγ9Vδ2 T cells appears as a new possible mechanism of immune escape by lymphoma cells.

PD-1 is a novel regulator of human B-cell activation.

The outcome of the adaptive immune response is determined by the integration of both positive and negative signals, respectively, induced upon the triggering of co-signaling receptors. One of them, programmed cell death 1 (PDCD1/PD-1) has largely been shown to be involved in the negative regulation of T-cell activation. However, PD-1 is also expressed on human B cells, and its role(s) in the process of human B-cell activation remains uncertain thus far. In this study, we describe the expression of PD-1 on the major human B-cells subsets isolated from peripheral blood and lymph nodes. We showed that PD-1 was expressed on naive B cells, was differentially expressed on peripheral IgM memory as compared with memory B cells and was lost on germinal center B cells. Expression of PD-1 ligands (PD-Ls) was induced by TLR9 activation. Finally, we showed that PD-1 was recruited to the B-cell receptor upon triggering. We determined that during TLR9 activation, blockade of PD-1/PD-Ls pathways indeed increased B-cell activation, proliferation and the production of inflammatory cytokines. Altogether, our results show, that, as reported in T cells, PD-1/PD-Ls complexes acted as inhibitors of the B-cell activation cascade and highlight the importance of devising future therapies able to modulate lymphocyte activation through the targeting of the PD-1/PD-Ls pathways.

Human Vγ9Vδ2 T cells specifically recognize and kill acute myeloid leukemic blasts.

Vγ9Vδ2 T cells are attractive candidates for antileukemic activity. The analysis of Vγ9Vδ2 T cells in newly diagnosed acute myeloid leukemia (AML) patients revealed that their absolute cell numbers were normal in the blood as well as in the bone marrow but showed a striking imbalance in the differentiation subsets, with preponderance of the effector memory population. This unusual phenotype was restored after removal of leukemic cells in patients, which reached complete remission after chemotherapy, suggesting that leukemic cells might be involved in the alteration of γδ T cell development in AML. Accordingly, coculture between AML cells and Vγ9Vδ2 T cells induced selection of effector cells. In accordance with their effector memory status, in vitro proliferation of Vγ9Vδ2 T cells was reduced compared with normal controls. Nevertheless, Vγ9Vδ2 T cells efficiently killed autologous AML blasts via the perforin/granzyme pathway. The ligands for DNAM-1 were expressed by AML cells. We showed that killing of AML blasts was TCR and DNAM-1 dependent. Using a xenotransplantation murine model, we showed that Vγ9Vδ2 T cells homed to the bone marrow in close proximity of engrafted leukemic cells and enhanced survival. These data demonstrate that Vγ9Vδ2 T cells are endowed with the ability to interact with and eradicate AML blasts both in vitro and in a mouse model. Collectively, our data revealed that Vγ9Vδ2 T cells have a potent antileukemic activity provided that optimal activation is achieved, such as with synthetic TCR agonists. This study enhances the interest of these cells for therapeutic purposes such as AML treatment.

Bromohydrin pyrophosphate enhances antibody-dependent cell-mediated cytotoxicity induced by therapeutic antibodies.

In human blood, 1% to 5% of lymphocytes are gammadelta T cells; they mostly express the gammadelta T-cell receptor (TCR)Vgamma9, recognize nonpeptide phosphoantigens (PAgs) produced by microbes and tumor cells, and mediate different modes of lytic activities directed against tumor target cells. Antibody-dependent cell-mediated cytotoxicity (ADCC) mediated by cytolytic lymphoid cells is essential for the clinical activity of anticancer monoclonal antibodies (mAbs), but whether PAgs affect ADCC by gammadelta T cells is unknown. Here we report that, in association with the CD20(+)-specific mAb rituximab (RTX), the synthetic PAg bromohydrin pyrophosphate (BrHPP) increased TCRVgamma9(+) cell binding to CD20(+) lymphoma cells in vitro. This combination activated phospho-ZAP70 and phospho-ERK1/2 signaling in TCRVgamma9(+) cells and strongly enhanced their ADCC activity. We obtained similar results with BrHPP in the context of the mAbs alemtuzumab and trastuzumab. Furthermore, BrHPP enhanced RTX-mediated depletion of CD20(+) cells in vitro from peripheral blood mononuclear cells of healthy subjects and enhanced ADCC by gammadelta T cells from patients with chronic lymphocytic leukemia. In cynomolgus macaques, a regimen combining RTX, BrHPP, and IL2 activated TCRVgamma9(+) lymphocytes and enhanced B-cell depletion from blood and lymph nodes. Thus, the combination with BrHPP PAg is able to improve the efficacy of cancer immunotherapy by therapeutic mAbs.

Lipophilic fluorochrome trackers of membrane transfers between immune cells.

Cell-to-cell transfers of membrane molecules between lymphoid cells (sometimes referred to as trogocytosis) is frequent and has multiple physiological consequences. Although difficult to visualize through the tracking of defined cell surface proteins, this process can be readily monitored by inserting PKH or CellVue Maroon fluorochromes into the plasma membranes of donor cells. We discuss here parameters that determine its detection by a flow-cytometry-based in vitro assay and present examples of application, including time-lapse video-microscopy analysis of transfers at the immunological synapse. By combining detection of cell-to-cell transfer and of cell surface CD107, it is possible to discriminate lymphoid cells binding target cells with and without perforin release. This could prove useful for identifying cells that destruct known target cells in autoimmune pathologies.

BTN3A molecules considerably improve Vγ9Vδ2T cells-based immunotherapy in acute myeloid leukemia.

Given their recognized ability to kill acute myeloid leukemia (AML) blasts both in vitro and in vivo, Vγ9Vδ2 T cells are of growing interest in the design of new strategies of immunotherapy. We show that the Butyrophilin3A (BTN3A, CD277) subfamily is a critical determinant of Vγ9Vδ2 TCR-mediated recognition of human primary AML blasts ex vivo. Moreover, anti-BTN3A 20.1 agonist monoclonal antibodies (mAbs) can trigger BTN3A on AML blasts leading to further enhanced Vγ9Vδ2 T cell-mediated killing, but this mAb had no enhancing effect upon NK cell-mediated killing. We show that monocytic differentiation of primary AML blasts accounts for their AminoBisphosphonate (N-BP)-mediated sensitization to Vγ9Vδ2 T cells. In addition, anti-BTN3A 20.1 mAbs could specifically sensitize resistant blasts to Vγ9Vδ2 T cells lysis and overcome the poor effect of N-BP treatment on those blasts. We confirmed the enhancement of Vγ9Vδ2 T cells activity by anti-BTN3A 20.1 mAb using a human AML xenotransplantation mouse model. We showed that anti-BTN3A 20.1 mAb combined with Vγ9Vδ2 T cells immunotherapy could increase animal survival and decrease the leukemic burden in blood and bone marrow. These findings could be of great interest in the design of new immunotherapeutic strategies for treating AML.

Inhibition of Noninfectious Uveitis Using Intravenous Administration of Collagen II-Specific Type 1 Regulatory T Cells.

PURPOSE: To evaluate the therapeutic potential of Col-Treg, a collagen II-specific type 1 regulatory T-cell immunotherapy for the treatment of noninfectious uveitis (NIU). METHODS: Col-Treg cells were produced from collagen II-specific T cell receptor (TCR) transgenic mice or peripheral blood of healthy donors. Phenotypic characterization was performed by flow cytometry, and cytokine secretion was evaluated with Flowcytomix or ELISA. In vitro functional characterization included ATP hydrolysis, cytotoxicity, and contact-independent T-cell suppression and plasticity assays. Col-Treg migration was assessed by quantitative PCR specific to Col-Treg TCR. Col-Treg cells were administered intravenously in mice displaying experimental autoimmune uveitis (EAU) induced by interphotoreceptor retinoid-binding protein (IRBP) immunizations. Efficacy of Col-Treg was assessed by ophthalmology, histology, and immunohistochemistry. RESULTS: Mice Col-Treg cells displayed identity features of type 1 Treg cells with expression of CD25, FoxP3, low surface expression of CD127, and cytokine secretion profile (IL-10(high), IL-4(low), IFN-γ(int)). In vitro functional assays demonstrated Col-Treg suppressive capacity via soluble factor-dependent immunosuppression, cytotoxicity, and ATP hydrolysis. Col-Treg cells expressed granzyme B, CD39, and glucocorticoid-induced TNF-related protein (GITR). Administration of Col-Treg in EAU mice inhibited clinical and morphologic signs of uveitis and decreased ocular leukocyte infiltration. Col-Treg cells homed in the ocular tissues 24 hours after intravenous injection. Human Col-Treg cells were comparable to mice Col-Treg cells in identity and function and did not show the capacity to differentiate into Th17 cells in vitro. CONCLUSIONS: These results demonstrate the therapeutic potential of Col-Treg cells as a targeted approach for the treatment of NIU and the feasibility of translating this approach to the human clinical setting.

BTLA, a key regulator of Vγ9Vδ2 T-cell proliferation.

Although in the last few years γδ T lymphocytes have been the subject of growing interest as potential anticancer immunotherapeutics, how the proliferative and effector responses of these cells are regulated remains unclear. We have recently reported that the co-receptor B and T lymphocyte associated (BTLA) inhibits the proliferation of human Vγ9Vδ2 T cells, potentially underpinning a mechanism of immune escape by lymphoma cells.

CpG-ODN-induced sustained expression of BTLA mediating selective inhibition of human B cells.

BTLA (B- and T-lymphocyte attenuator) is a prominent co-receptor that is structurally and functionally related to CTLA-4 and PD-1. In T cells, BTLA inhibits TCR-mediated activation. In B cells, roles and functions of BTLA are still poorly understood and have never been studied in the context of B cells activated by CpG via TLR9. In this study, we evaluated the expression of BTLA depending on activation and differentiation of human B cell subsets in peripheral blood and lymph nodes. Stimulation with CpG upregulated BTLA, but not its ligand: herpes virus entry mediator (HVEM), on B cells in vitro and sustained its expression in vivo in melanoma patients after vaccination. Upon ligation with HVEM, BTLA inhibited CpG-mediated B cell functions (proliferation, cytokine production, and upregulation of co-stimulatory molecules), which was reversed by blocking BTLA/HVEM interactions. Interestingly, chemokine secretion (IL-8 and MIP1ß) was not affected by BTLA/HVEM ligation, suggesting that BTLA-mediated inhibition is selective for some but not all B cell functions. We conclude that BTLA is an important immune checkpoint for B cells, as similarly known for T cells.

Immunotherapy of acute myeloid leukemia based on γδ T cells.

A current major challenge of acute myeloid leukemia research is to develop immunotherapeutic strategies that would be employable in all patients. We recently reported that appropriately stimulated γδ T cells are fully capable of mediating cytotoxicity against leukemic blasts.

Emerging concepts for the treatment of hematological malignancies with therapeutic monoclonal antibodies.

The development of therapeutic monoclonal antibodies (mAbs) has revolutionized the treatment of cancer along the last ten years. The best examples of their therapeutic efficacies have been obtained with rituximab for the treatment of CD20+ B-cell Non-Hodgkin Lymphoma (B-NHL), and several others antibodies with optimized bioactivities are now being developed for the treatment of various malignant hemopathies. We review here the main drugs developed in this field, and present some emerging concepts able to improve the bioactivities of the next generation of therapeutic mAbs.