Cellular therapeutics show great promise for the treatment of disease, but few noninvasive techniques exist for monitoring the cells after administration. Here we present a magnetic resonance imaging (MRI) technology that uses perfluoropolyether (PFPE) agents to track cells in vivo. Fluorine MRI selectively images only the labeled cells, and a 'conventional' (1)H image places the cells in their anatomical context. We labeled phenotypically defined dendritic cells (DCs) with PFPE ex vivo and observed efficient intracellular uptake of the PFPE with little effect on DC function. We injected labeled DCs into tissue or intravenously in mice and then tracked the cells in vivo using (19)F MRI. Although we focused on DCs, which are being developed as immunotherapeutics for cancer and autoimmune diseases, this technology should be useful for monitoring a wide range of cell types in vivo.

This article describes an in vivo imaging method for visualizing and quantifying a specific cell population. Cells are labeled ex vivo with a perfluoropolyether nanoparticle tracer agent and then detected in vivo using 19

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Obesity-associated increases in adipose tissue (AT) CD11c+ cells suggest that dendritic cells (DC), which are involved in the tissue recruitment and activation of macrophages, may play a role in determining AT and liver immunophenotype in obesity. This study addressed this hypothesis. With the use of flow cytometry, electron microscopy, and loss-and-gain of function approaches, the contribution of DC to the pattern of immune cell alterations and recruitment in obesity was assessed. In AT and liver there was a substantial, high-fat diet (HFD)–induced increase in DC. In AT, these increases were associated with crown-like structures, whereas in liver the increase in DC constituted an early and reversible response to diet. Notably, mice lacking DC had reduced AT and liver macrophages, whereas DC replacement in DC-null mice increased liver and AT macrophage populations. Furthermore, delivery of bone marrow–derived DC to lean wild-type mice increased AT and liver macrophage infiltration. Finally, mice lacking DC were resistant to the weight gain and metabolic abnormalities of an HFD. Together, these data demonstrate that DC are elevated in obesity, promote macrophage infiltration of AT and liver, contribute to the determination of tissue immunophenotype, and play a role in systemic metabolic responses to an HFD.

Material

Material Supplementary 9.DC1http://www.jimmunol.org/content/suppl/2010/08/16/jimmunol.100074

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T cell receptor (TCR) signal strength determines the differentiation outcome of naïve CD4+ T cells: low signal strength favors Foxp3pos regulatory T cells (Treg) whereas high TCR signals are required to induce IL-2-producing helper T cells (Th). To better understand the signaling requirements for this cell-fate decision, we constructed a logic circuit model of the TCR signaling pathways. A major feature of this model is an incoherent feed-forward loop involving activation of Foxp3 and its inhibition by mTOR, which leads to transient appearance of Foxp3pos cells under simulation conditions that drive IL-2 producing Th cells. This behavior along with the predicted ability of TGF-β to induce Treg despite continued activation of the Akt/mTOR pathway were confirmed experimentally. The latter provides a possible reason for the observed instability of TGF-β-induced Treg. The model also predicted and experiments confirmed that transient high dose Ag stimulation results in three stable T cell fates (Th, Treg, and non-activated) with relative proportions depending on the duration of stimulation. Experimental analysis of the cell population at the time of Ag removal identified three distinct populations based on CD25 abundance and Akt/mTOR activation that correlated with these T cell fates. Further analysis of corresponding simulation trajectories implicated a negative feedback loop involving Foxp3, PTEN, and Akt/mTOR. Taken together, these results suggest that there is a critical period following TCR stimulation during which heterogeneity in the differentiating population leads to increased plasticity of cell fate.