Betty Joe

Cutting Edge: In Vivo Trogocytosis as a Mechanism of Double Negative Regulatory T Cell-Mediated Antigen-Specific Suppression

Recent data have demonstrated that treatment with αβ-TCR+CD3+CD4−CD8−NK1.1− double negative (DN) regulatory T cells (Tregs) inhibits autoimmune diabetes and enhances allotransplant and xenotransplant survival in an Ag-specific fashion. However, the mechanisms whereby DN Tregs suppress Ag-specific immune responses remain largely unknown. In this study, we demonstrate that murine DN Tregs acquire alloantigen in vivo via trogocytosis and express it on their cell surface. Trogocytosis requires specific interaction of MHC-peptide on APCs and Ag-specific TCR on DN Tregs, as blocking this interaction prevents DN Treg-mediated trogocytosis. Acquisition of alloantigen by DN Tregs was required for their ability to kill syngeneic CD8+ T cells. Importantly, DN Tregs that had acquired alloantigen were cytotoxic toward Ag-specific, but not Ag-nonspecific, syngeneic CD8+ T cells. These data provide new insight into how Tregs mediate Ag-specific T cell suppression and may enhance our ability to use DN Tregs as a therapy for transplant rejection and autoimmune diseases.

IL-10 Induces Regulatory T Cell Apoptosis by Up-Regulation of the Membrane Form of TNF-α

Numerous studies have demonstrated the role of regulatory T (Treg) cells in peripheral tolerance. Nevertheless, how the survival and death of Treg cells is controlled is largely unknown. In this study, we investigated the mechanisms involved in regulating the homeostasis of a subset of Ag-specific αβTCR+ CD4−CD8− double negative (DN) Treg cells. We demonstrate that DN Treg cells are naturally resistant to TCR cross-linking-induced apoptosis. Administration of exogenous IL-10 renders DN Treg cells susceptible to apoptosis, and abolishes their suppressive function. Furthermore, TCR cross-linking of DN Treg cells in the presence of IL-10 leads to the up-regulation of the membrane-bound but not the soluble form of TNF-α. Interaction of membrane bound TNF-α with TNFR2 sends death signals to DN Treg cells. Blocking their interaction can reverse the effects of IL-10 on DN Treg cells. These results provide insights into the mechanisms that regulate the function and homeostasis of DN Treg cells.

Adoptive immunotherapy of cancer using ex vivo expanded human γδ T cells: A new approach

gammadelta T cells can be an option for adoptive immunotherapy of cancer. The major obstacle to clinical application of gammadelta T cells is their low number and lack of a reliable method to expand them consistently and efficiently. We were able to expand gammadelta T cells with high purity in all donors regardless of their starting repertoire of gammadelta T cells. These ex vivo expanded gammadelta T cells are in early differentiation stage, can efficiently kill various tumors and inhibit growth of human lung cancer xenografts. This new approach for ex vivo expansion of human gammadelta T cells will open new horizons for clinical use of these cells.

NKG2D regulates production of soluble TRAIL by ex vivo expanded human γδ T cells.

Soluble TRAIL (sTRAIL) can be produced by myeloid‐derived cells to kill cancer cells. Whether this mechanism is used by T cells, and if so, how sTRAIL production is regulated, remains unclear. Our previous studies showed that ex vivo expanded human γδ T cells express TRAIL and NK receptor group 2 (R2), member D (NKG2D), and possess potent anticancer activities both in vitro and in vivo. Here, we investigated in greater detail the mechanisms by which γδ T cells utilize TRAIL and NKG2D to kill lung cancer cells. We demonstrate that human lung cancer cells express TRAIL R2 and NKG2D ligands. Blocking TRAIL or NKG2D during γδ T‐cell‐lung cancer cell co‐cultures significantly reduced γδ T‐cell‐mediated cytotoxicity. Cross‐linking NKG2D with anti‐NKG2D antibody to mimic ligand binding promoted γδ T cells to produce sTRAIL, which induced apoptosis in lung cancer cells through TRAIL R2. Either neutralizing sTRAIL or blocking lung cancer cell TRAIL R2 significantly reduced γδ T‐cell‐mediated cytotoxicity to lung cancer cells. This study demonstrates that γδ T cells can mediate anticancer immunity via NKG2D‐regulated production of sTRAIL.

Anti-leukemia effect of ex vivo expanded DNT cells from AML patients: a potential novel autologous T-cell adoptive immunotherapy

CD3+CD56−, CD4 and CD8 double negative T (DNT) cells comprise 1–3% of peripheral blood (PB) mononuclear cells. Their role in tumor immunity remains largely unknown due to their limited numbers and lack of effective methods to expand them. Here we developed a novel protocol by which DNT cells can be expanded ex vivo to therapeutic levels in 2 weeks from 13 of 16 acute myeloid leukemia (AML) patients during chemotherapy-induced complete remission. The expanded DNT cells expressed similar or higher levels of interferon-γ and tumor necrosis factor-α and Granzyme B as that seen in bulk activated CD8T cells from the same patient but significantly higher levels of perforin. The expanded DNT cells could effectively kill both allogeneic and autologous primary CD34+ leukemic blasts isolated from PB of AML patients in a perforin-dependant manner. These results demonstrate, for the first time, that DNT cells from AML patients can be expanded ex vivo even after intensive chemotherapy, and are effective at killing both allogeneic and autologous primary leukemic blasts. These findings warrant studies further exploring the potential of DNT cells as a novel adjuvant immunotherapy to decrease the risk of relapse in patients with AML and, perhaps, other cancers.

Human Vδ1-T cells regulate immune responses by targeting autologous immature dendritic cells

Recent studies suggest that tissue resident Vδ1-T cells may downregulate immune responses in human beings. However, the function of peripheral blood Vδ1-T cells and their mechanisms of action remain largely unknown because of their limited numbers and the difficulties encountered in expanding these cells. In this study, we provide direct evidence demonstrating that peripheral human Vδ1-T cells can abrogate adaptive immune responses by direct killing of autologous dendritic cells through a perforin-mediated pathway. These findings advance our basic understanding of this unique T-cell subset.

Autocrine IFNγ Controls the Regulatory Function of Lymphoproliferative Double Negative T Cells

TCRαβ+ CD4−CD8−NK− double negative T cells (DN T cells) can act as regulatory T cells to inhibit allograft rejection and autoimmunity. Their role in graft-versus-host disease and mechanisms of suppression remain elusive. In this study, we demonstrate that DN T cells can inhibit CD4+ T cell-mediated GVHD in a semi-allogeneic model of bone marrow transplantation. Furthermore, we present evidence of a novel autocrine IFNγ signaling pathway in Fas-deficient C57BL/6.lpr (B6.lpr) DN T cells. B6.lpr DN T cells lacking IFNγ or its receptor were impaired in their ability to suppress syngeneic CD4+ T cells responding to alloantigen stimulation both in vitro and in vivo. Autocrine IFNγ signaling was required for sustained B6.lpr DN T cell IFNγ secretion in vivo and for upregulation of surface Fas ligand expression during TCR stimulation. Fas ligand (FasL) expression by B6.lpr DN T cells permitted lysis of activated CD4+ T cells and was required for suppression of GVHD. Collectively, our data indicate that DN T cells can inhibit GVHD and that IFNγ plays a critical autocrine role in controlling the regulatory function of B6.lpr DN T cells.