Transcriptional regulation of the IL-7Rα gene by dexamethasone and IL-7 in primary human CD8 T cells.

Interleukin-7 is essential for the development and maintenance of T cells, and the expression of the IL-7 receptor is tightly regulated at every stage of the T cell's lifespan. In mature CD8 T cells, IL-7 plays important roles in cell survival, peripheral homeostasis, and cytolytic function. The IL-7 receptor alpha-chain (CD127) is expressed at high levels on naïve and memory cells, but it is rapidly downregulated upon IL-7 stimulation. In this study, we illustrate the dynamicity of the CD127 promoter and show that it possesses positive as well as negative regulatory sites involved in upregulating and downregulating CD127 expression, respectively. We cloned the CD127 gene promoter and identified key cis-regulatory elements required for CD127 expression in mature resting primary CD8 T cells. The core promoter necessary for efficient basal transcription is contained within the first 262 bp upstream of the TATA box. Additional positive regulatory elements are located between -1200 and -2406 bp, conferring a further 2- to 4-fold enhancement in gene expression. While transcription of the CD127 gene is increased directly through a glucocorticoid response element located between -2255 and -2269 bp upstream of the TATA box, we identified a suppressive region that lies upstream of 1760 bp from the TATA box, which is likely involved in the IL-7-mediated suppression of CD127 transcription. Finally, we illustrated IL-7 does not bias alternative splicing of CD127 transcripts in primary human CD8 T cells.

IL-7 downregulates IL-7Rα expression in human CD8 T cells by two independent mechanisms.

Interleukin (IL)-7 is an essential nonredundant cytokine, and throughout the lifespan of a T-cell signaling via the IL-7 receptor influences cell survival, proliferation and differentiation. It is therefore no surprise that expression of the IL-7 receptor alpha-chain (CD127) is tightly regulated. We have previously shown that IL-7 downregulates expression of CD127 at the cell surface and now elucidate the kinetics of that suppression and demonstrate that IL-7 downregulates CD127 transcripts and surface protein in primary human CD8 T cells by two separate pathways. We show that IL-7 induces the initial reduction in cell-surface CD127 protein independent of transcriptional suppression, which is delayed by 40-60 min. Although IL-7-mediated downregulation of CD127 transcripts is dependent on Janus kinase (JAK)/STAT5, the early downregulation of surface CD127 protein is independent of JAK activity. The data further illustrate that low levels of IL-7 induce smaller and transient decreases in CD127 transcripts and surface protein, whereas higher concentrations induce more profound and sustained suppression. Such flexibility in receptor expression likely allows for fine-tuned immune responses in human CD8 T cells in different microenvironments and in response to different immunological challenges.

The prognostic value of FoxP3+ tumor-infiltrating lymphocytes in cancer: a critical review of the literature.

CD8+ tumor-infiltrating lymphocytes (TIL) are associated with survival in a variety of cancers. A second subpopulation of TIL, defined by forkhead box protein P3 (FoxP3) expression, has been reported to inhibit tumor immunity, resulting in decreased patient survival. On the basis of this premise, several groups are attempting to deplete FoxP3+ T cells to enhance tumor immunity. However, recent studies have challenged this paradigm by showing that FoxP3+ T cells exhibit heterogeneous phenotypes and, in some cohorts, are associated with favorable prognosis. These discrepant results could arise from differences in study methodologies or the biologic properties of specific cancer types. Here, we conduct the first systematic review of the prognostic significance of FoxP3+ T cells across nonlymphoid cancers (58 studies from 16 cancers). We assessed antibody specificity, cell-scoring strategy, multivariate modeling, use of single compared with multiple markers, and tumor site. Two factors proved important. First, when FoxP3 was combined with one additional marker, double-positive T cells were generally associated with poor prognosis. Second, tumor site had a major influence. FoxP3+ T cells were associated with poor prognosis in hepatocellular cancer and generally good prognosis in colorectal cancer, whereas other cancer types were inconsistent or understudied. We conclude that FoxP3+ T cells have heterogeneous properties that can be discerned by the use of additional markers. Furthermore, the net biologic effects of FoxP3+ T cells seem to depend on the tumor site, perhaps reflecting microenvironmental differences. Thus, depletion of FoxP3+ T cells might enhance tumor immunity in some patient groups but be detrimental in others.

Soluble HIV Tat protein removes the IL-7 receptor alpha-chain from the surface of resting CD8 T cells and targets it for degradation.

IL-7 signaling is essential to CD8 T cell development, activation, and homeostasis. We have previously shown decreased expression of the IL-7R alpha-chain (CD127) on CD8 T cells in HIV(+) patients and that this downregulation is mediated at least in part by the HIV Tat protein. We show in this study that CD127 has a prolonged t(1/2) in resting CD8 T cells and continuously recycles on and off the cell membrane. We also demonstrate soluble Tat protein significantly decreases the t(1/2) of CD127. Soluble Tat is taken up from the medium and accumulates in CD8 T cells with a peak of 6 h. Once inside the cell, Tat exits the endosomes during their normal acidification and enters the cytosol. Tat then translocates to the inner leaflet of the cell membrane, where it binds directly to the cytoplasmic tail of CD127, inducing receptor aggregation and internalization through a process dependent on microtubules. Tat appears to then target CD127 for degradation via the proteasome. By removing CD127 from the cell surface, the HIV Tat protein is thus able to reduce IL-7 signaling and impair CD8 T cell proliferation and function.

Interleukin-7 receptor expression on CD8 T-cells is downregulated by the HIV Tat protein.

We have previously shown decreased expression of the interleukin (IL)-7 receptor alpha-chain (CD127) on CD8 T-cells in HIV-infected patients and an apparent recovery of this receptor in those receiving antiretroviral therapy with sustained viral suppression. Here, we demonstrate that the HIV Tat protein specifically downregulates cell surface expression of CD127 on human CD8 T-cells in a dose- and time-dependent manner. The effects of Tat on CD127 expression could be blocked with anti-Tat monoclonal antibodies or by preincubating Tat with heparin. Tat had no effect on the expression of other cell surface proteins examined, including CD132, or on cell viability over 72 hours. Further, CD127 expression was not altered by other HIV proteins, including gp160 or Nef. Preincubation of purified CD8 T-cells with Tat protein inhibited CD8 T-cell proliferation and perforin synthesis after stimulation with IL-7. Because IL-7 signaling is essential for optimal CD8 T-cell proliferation and function, the downregulation of CD127 and apparent inhibition of cytotoxic activity by Tat may play an important role in HIV-induced immune dysregulation and impaired cell-mediated immunity.