Resolution of infection promotes a state of dormancy and long survival of CD4 memory T cells.

Memory T cells survive throughout the lifetime of an individual and are protective upon recall. It is not clear how memory T cells can live so long. Here, we demonstrate that at the resolution of a viral infection, low levels of antigen are captured by B cells and presented to specific CD4(+) memory T cells to render a state of unresponsiveness. We demonstrate in two systems that this process occurs naturally during the fall of antigen and is associated with a global gene expression program initiated with the clearance of antigen. Our study suggests that in the absence of antigen, a state of dormancy associated with low-energy utilization and proliferation can help memory CD4(+) T cells to survive nearly throughout the lifetime of mice. The dormant CD4(+) memory T cells become activated by stimulatory signals generated by a subsequent infection. We propose that quiescence might be a mechanism necessary to regulate long-term survival of CD4 memory T cells and to prevent cross-reactivity to self, hence autoimmunity.

A survey of methylated candidate tumor suppressor genes in nasopharyngeal carcinoma.

Nasopharyngeal carcinoma (NPC) is a rare malignancy with unique genetic, viral and environmental characteristic that distinguishes it from other head and neck carcinomas. The clinical management of NPC remains challenging largely due to the lack of early detection strategies for this tumor. In our study, we have sought to identify novel genes involved in the pathogenesis of NPC that might provide insight into this tumor's biology and could potentially be used as biomarkers. To identify these genes, we studied the epigenetics of NPC by characterizing a panel of methylation markers. Eighteen genes were evaluated by quantitative methylation-specific polymerase chain reaction (PCR) in cell lines as well as in tissue samples including 50 NPC tumors and 28 benign nasopharyngeal biopsies. Significance was evaluated using Fisher's exact test and quantitative values were optimized using cut off values derived from receiver-operator characteristic curves. The methylation status of AIM1, APC, CALCA, deleted in colorectal carcinomas (DCC), DLEC, deleted in liver cancer 1 (DLC1), estrogen receptor alpha (ESR), FHIT, KIF1A and PGP9.5 was significantly associated with NPC compared to controls. The sensitivity of the individual genes ranged from 26 to 66% and the specificity was above 92% for all genes except FHIT. The combination of PGP9.5, KIF1A and DLEC had a sensitivity of 84% and a specificity of 92%. Ectopic expression of DCC and DLC1 lead to decrease in colony formation and invasion properties. Our results indicate that methylation of novel biomarkers in NPC could be used to enhance early detection approaches. Additionally, our functional studies reveal previously unknown tumor suppressor roles in NPC.

Gene expression profiling reveals early cellular responses to intracellular magnetic labeling with superparamagnetic iron oxide nanoparticles.

With MRI (stem) cell tracking having entered the clinic, studies on the cellular genomic response toward labeling are warranted. Gene expression profiling was applied to C17.2 neural stem cells following superparamagnetic iron oxide/PLL (poly-L-lysine) labeling over the course of 1 week. Relative to unlabeled cells, less than 1% of genes (49 total) exhibited greater than 2-fold difference in expression in response to superparamagnetic iron oxide/PLL labeling. In particular, transferrin receptor 1 (Tfrc) and heme oxygenase 1 (Hmox1) expression was downregulated early, whereas genes involved in lysosomal function (Sulf1) and detoxification (Clu, Cp, Gstm2, Mgst1) were upregulated at later time points. Relative to cells treated with PLL only, cells labeled with superparamagnetic iron oxide/PLL complexes exhibited differential expression of 1399 genes. Though these differentially expressed genes exhibited altered expression over time, the overall extent was limited. Gene ontology analysis of differentially expressed genes showed that genes encoding zinc-binding proteins are enriched after superparamagnetic iron oxide/PLL labeling relative to PLL only treatment, whereas members of the apoptosis/programmed cell death pathway did not display increased expression. Overexpression of the differentially expressed genes Rnf138 and Abcc4 were confirmed by quantitative real-time polymerase chain reaction. These results demonstrate that, although early reactions responsible for iron homeostasis are induced, overall neural stem cell gene expression remains largely unaltered following superparamagnetic iron oxide/PLL labeling.

Mouse ES cell-derived cardiac precursor cells are multipotent and facilitate identification of novel cardiac genes.

Although the differentiation of ES cells to cardiomyocytes has been firmly established, the extent to which corresponding cardiac precursor cells can contribute to other cardiac populations remains unclear. To determine the molecular and cellular characteristics of cardiac-fated populations derived from mouse ES (mES) cells, we isolated cardiac progenitor cells (CPCs) from differentiating mES cell cultures by using a reporter cell line that expresses GFP under the control of a cardiac-specific enhancer element of Nkx2-5, a transcription factor expressed early in cardiac development. This ES cell-derived CPC population initially expressed genetic markers of both stem cells and mesoderm, while differentiated CPCs displayed markers of 3 distinct cell lineages (cardiomyocytes, vascular smooth muscle cells, and endothelial cells)--Flk1 (also known as Kdr), c-Kit, and Nkx2-5, but not Brachyury--and subsequently expressed Isl1. Clonally derived CPCs also demonstrated this multipotent phenotype. By transcription profiling of CPCs, we found that mES cell-derived CPCs displayed a transcriptional signature that paralleled in vivo cardiac development. Additionally, these studies suggested the involvement of genes that we believe were previously unknown to play a role in cardiac development. Taken together, our data demonstrate that ES cell-derived CPCs comprise a multipotent precursor population capable of populating multiple cardiac lineages and suggest that ES cell differentiation is a valid model for studying development of multiple cardiac-fated tissues.

Chronic CD4+ T-cell activation and depletion in human immunodeficiency virus type 1 infection: type I interferon-mediated disruption of T-cell dynamics.

The mechanism of CD4(+) T-cell depletion during chronic human immunodeficiency virus type 1 (HIV-1) infection remains unknown. Many studies suggest a significant role for chronic CD4(+) T-cell activation. We assumed that the pathogenic process of excessive CD4(+) T-cell activation would be reflected in the transcriptional profiles of activated CD4(+) T cells. Here we demonstrate that the transcriptional programs of in vivo-activated CD4(+) T cells from untreated HIV-positive (HIV(+)) individuals are clearly different from those of activated CD4(+) T cells from HIV-negative (HIV(-)) individuals. We observed a dramatic up-regulation of cell cycle-associated and interferon-stimulated transcripts in activated CD4(+) T cells of untreated HIV(+) individuals. Furthermore, we find an enrichment of proliferative and type I interferon-responsive transcription factor binding sites in the promoters of genes that are differentially expressed in activated CD4(+) T cells of untreated HIV(+) individuals compared to those of HIV(-) individuals. We confirm these findings by examination of in vivo-activated CD4(+) T cells. Taken together, these results suggest that activated CD4(+) T cells from untreated HIV(+) individuals are in a hyperproliferative state that is modulated by type I interferons. From these results, we propose a new model for CD4(+) T-cell depletion during chronic HIV-1 infection.