Plasmacytoid dendritic cells activate lymphoid-specific genetic programs irrespective of their cellular origin.
ABSTRACT The developmental origin of type I interferon (IFN)-producing plasmacytoid dendritic cells (PDCs) is controversial. In particular, the rearrangement of immunoglobulin heavy chain (IgH) genes in murine PDCs and the expression of pre-T cell receptor alpha (pTalpha) gene by human PDCs were proposed as evidence for their "lymphoid" origin. Here we demonstrate that PDCs capable of IFN production develop efficiently from both myeloid- and lymphoid-committed progenitors. Rearranged IgH genes as well as RAG transcripts were found in both myeloid- and lymphoid-derived PDCs. The human pTalpha transgenic reporter was activated in both myeloid- and lymphoid-derived PDCs at a level comparable to pre-T cells. PDCs were the only cell population that activated murine RAG1 knockin and human pTalpha transgenic reporters outside the lymphoid lineage. These results highlight a unique developmental program of PDCs that distinguishes them from other cell types including conventional dendritic cells.
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ABSTRACT: Pioneering work with the Bcr-Abl inhibitor, imatinib, demonstrated a requirement for constant Bcr-Abl inhibition to achieve maximal therapeutic benefit in treating chronic myeloid leukemia (CML), establishing a paradigm that has guided further drug development for this disease. Surprisingly, the second-generation Bcr-Abl inhibitor, dasatinib, was reported to be clinically effective with once-daily dosing, despite a short (3- to 5-hour) plasma half-life. Consistent with this observation, dasatinib treatment of progenitor cells from chronic-phase CML patients for 4 hours, followed by washout, or continuously for 72 hours both resulted in an induction of apoptosis and a reduction in the number of clonogenic cells. Such acute treatments with clinically achievable dasatinib concentrations also irreversibly committed Bcr-Abl+ CML cell lines to apoptotic cell death. Potent transient Bcr-Abl inhibition using the alternative inhibitor, nilotinib, also resulted in cell death. These findings demonstrate that in vitro assays designed to model in vivo pharmacokinetics can predict clinical efficacy. Furthermore, they challenge the widely held notion that continuous target inhibition is required for optimal efficacy of kinase inhibitors.Blood 09/2009; 114(16):3459-63. · 9.78 Impact Factor
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ABSTRACT: Recent studies have shown that NK-dendritic cell (DC) interaction plays an important role in the induction of immune response against tumors and certain viruses. Although the effect of this interaction is bidirectional, the mechanism or molecules involved in this cross-talk have not been identified. In this study, we report that coculture with NK cells causes several fold increase in IL-12 production by Toxoplasma gondii lysate Ag-pulsed DC. This interaction also leads to stronger priming of Ag-specific CD8+ T cell response by these cells. In vitro blockade of NKG2D, a molecule present on human and murine NK cells, neutralizes the NK cell-induced up-regulation of DC response. Moreover, treatment of infected animals with Ab to NKG2D receptor compromises the development of Ag-specific CD8+ T cell immunity and reduces their ability to clear parasites. These studies emphasize the critical role played by NKG2D in the NK-DC interaction, which apparently is important for the generation of robust CD8+ T cell immunity against intracellular pathogens. To the best of our knowledge, this is the first work that describes in vivo importance of NKG2D during natural infection.The Journal of Immunology 08/2007; 179(1):590-6. · 5.52 Impact Factor
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ABSTRACT: Dendritic cells (DC) play a pivotal role in the initiation of T cell responses and earlier studies have shown that their survival is important for the generation of effective immune responses. Cytotoxic T lymphocytes (CTL) and natural killer T (NKT) cells have been proposed to regulate the survival of antigen presenting DC through their ability to kill cells expressing specific antigen via secretion of perforin, a protein contained in cytotoxic granules. Perforin knockout (PKO) mice generate amplified immune responses to DC immunization, suggesting a link between defective cytotoxicity and increased T cell responses. The studies in this thesis used PKO mice and in vivo models of CD8+T cells and NKT cell immune responses to determine whether CTL and NKT cells eliminate DC in a perforin-dependent manner, and whether DC elimination is a mechanism to regulate T cell responses. During a primary influenza infection C57BL/6 and PKO mice generated a similar influenza specific CD8+ immune response. No significant difference in the percentage of influenza epitope PA224-233 specific T cells was observed between C57BL/6 and PKO mice during a secondary influenza infection, but PKO mice had a significantly reduced T cell response directed towards the dominant influenza epitope, NP366-374. The reduced T cell response in PKO mice was not due to differences in activation or differentiation status of specific T cells compared to C57BL/6 mice. Therefore, the extended DC survival in PKO after secondary influenza viral infection, recently reported by other authors, does not appear to correlate with increased expansion of virus specific CD8+T cells in infected mice. The role of NKT cells in DC elimination was assessed in vivo using the NKT cell ligand a-Galactosylceramide (a-GalCer). Injection of a-GalCer in C57BL/6 mice induced a dramatic decline in the number of splenic CD8+DC. A similar decrease in CD8+DC numbers was observed in PKO mice, suggesting that the mechanism of DC loss did not involve perforinmediated killing. In contrast, treatment with a TNF-a neutralizing antibody substantially reduced the decline in CD8+DC numbers. This reduction in splenic CD8+DC occurred as early as 15 hr after a-GalCer treatment, and did not affect generation of CD8+T cell responses or the ability of a-GalCer treatment to provide tumour protection. Taken together, these results suggest that multiple cells and mechanisms can regulate DC survival in vivo. CTL regulate DC survival in vivo in a perforin-dependent manner, but this does not necessarily affect the magnitude of the resulting immune responses. NKT cells also affect the survival of DC in vivo, but in a perforin-independent, cytokine-dependent manner. These findings provide additional knowledge about the in vivo involvement of perforin in regulating DC survival by CTL and NKT cells and the effects this has on T cell responses.