Intrathymic IL-7: the where, when, and why of IL-7 signaling during T cell development

The thymus is the birthplace of all T lineage cells. But the thymus is also a cradle as it provides the environment for further maturation and differentiation of immature thymocytes. While many factors contribute to make the thymus a unique place for T cell development, here we review the essential role of intrathymic interleukin-7 (IL-7). In the absence of IL-7 signaling, survival, proliferation and differentiation of immature thymocytes are all severely impaired. Consequently, IL-7 is critical to nurture and guide T precursor cells through the diverse steps of thymic maturation. Interestingly, even as IL-7 signaling is such a critical factor, IL-7 signaling must be also actively suppressed during specific stages of T cell differentiation. These contradictory observations are puzzling but can be satisfactorily explained when understanding the developmental context of IL-7 signaling. In this regard, here we will discuss the spatiotemporal expression of intrathymic IL-7 and address the stage-specific effects of IL-7 signaling in developing thymocytes. Specifically, we will review other facets of intrathymic IL-7 beyond its role as a pro-survival factor and so clarify and reaffirm the unique role of IL-7 as a prime factor in T cell development and differentiation.

Genetic and epigenetic regulation of the organic cation transporter 3, SLC22A3

Human organic cation transporter 3 (OCT3 and SLC22A3) mediates the uptake of many important endogenous amines and basic drugs in a variety of tissues. OCT3 is identified as one of the important risk loci for prostate cancer, and is markedly underexpressed in aggressive prostate cancers. The goal of this study was to identify genetic and epigenetic factors in the promoter region that influence the expression level of OCT3. Haplotypes that contained the common variants, g.-81G>delGA (rs60515630) (minor allele frequency 11.5% in African American) and g.-2G>A (rs555754) (minor allele frequency>30% in all ethnic groups) showed significant increases in luciferase reporter activities and exhibited stronger transcription factor-binding affinity than the haplotypes that contained the major alleles. Consistent with the reporter assays, OCT3 messenger RNA expression levels were significantly higher in Asian (P<0.001) and Caucasian (P<0.05) liver samples from individuals who were homozygous for g.-2A/A in comparison with those homozygous for the g.-2G/G allele. Studies revealed that the methylation level in the basal promoter region of OCT3 was associated with OCT3 expression level and tumorigenesis capability in various prostate cancer cell lines. The methylation level of the OCT3 promoter was higher in 62% of prostate tumor samples compared with matched normal samples. Our studies demonstrate that genetic polymorphisms in the proximal promoter region of OCT3 alter the transcription rate of the gene and may be associated with altered expression levels of OCT3 in human liver. Aberrant methylation contributes to the reduced expression of OCT3 in prostate cancer.

αβ T cell receptors that do not undergo major histocompatibility complex-specific thymic selection possess antibody-like recognition specificities

Major histocompatibility complex (MHC) restriction is the cardinal feature of T cell antigen recognition and is thought to be intrinsic to αβ T cell receptor (TCR) structure because of germline-encoded residues that impose MHC specificity. Here, we analyzed αβTCRs from T cells that had not undergone MHC-specific thymic selection. Instead of recognizing peptide-MHC complexes, the two αβTCRs studied here resembled antibodies in recognizing glycosylation-dependent conformational epitopes on a native self-protein, CD155, and they did so with high affinity independently of MHC molecules. Ligand recognition was via the αβTCR combining site and involved the identical germline-encoded residues that have been thought to uniquely impose MHC specificity, demonstrating that these residues do not only promote MHC binding. This study demonstrates that, without MHC-specific thymic selection, αβTCRs can resemble antibodies in recognizing conformational epitopes on MHC-independent ligands.

Statin treatment use in diabetic patients with breast cancer: A potential C-reactive protein mediated benefit

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Background: Statin treatment has not yet been evaluated in relation to breast cancer (BC) prognosis in diabetes mellitus (DM) patients. Reported decreased survival following BC in women with metabolic syndrome, led us to investigate whether specific statin therapy may lead to improved BC survival. Reported associations between elevated C-reactive protein (CRP) levels at the time of diagnosis with worse cancer prognosis, and CRP-lowering properties of statin treatment in non-cancer patients, led us to investigate whether statin use is associated with lower CRP levels at the time of BC diagnosis and with improved BC outcomes.

Methods: All DM patients newly diagnosed with BC between 2003 and 2007 (Roswell Park Cancer Institute) were retrospectively reviewed (n = 225). BC pathology, outcomes, existing comorbidities and drug therapy were documented. Follow up began at BC diagnosis and ended with first confirmed recurrence and/or death, or last date of follow-up. Hazard ratios (HR) and 95% confidence intervals (CI)s representing the association between statins, BC and a defined event were computed with Cox proportional hazards model. CRP plasma levels were determined by enzyme-linked immunosorbent assay in specimens donated at the time of BC diagnosis. A total of 98 study patients, DM+BC, and their matched controls, BC only (n = 196) were analyzed.

Results: After a median follow up of 30 months, patients receiving statins for cholesterol management were found to have better disease-free survival (HR 0.27, 95% CI: 0.10, 0.71, X2 = 7.31, p = 0.06), and lower overall mortality (HR 0.23, 95% CI: 0.08, 0.66, X2 = 7.80, p = 0.05) compared to patients not receiving any cholesterol management medication. CRP levels have ranged between 0.2 and 21 mg/L and clinically relevant levels ( > 3mg/L) were noted in the study group.

Conclusions: This study explored for the first time the association between statin therapy and BC prognosis in DM. We observed improved outcomes in statin-treated patients. While we currently analyze statin therapy in relationship with baseline CRP levels and BC prognosis, our existing findings suggest that statins have the potential to improve BC outcomes potentially through lowering overall inflammation.

CD8-EOMEShigh T cells define a subpopulation of CD8 memory cells that restore CD127high expression after cART treatment in HIV infected patients. (105.27)

After acute viral infection a small population of effector CD8 T cells upregulate CD127 expression and develop into long lived resting memory T cells. During chronic infections, such as HIV, there is an accumulation of CD8 T cells with effector/memory-like phenotype. These observations led to the hypothesis that there is a developmental impairment in the long lived resting memory T cells within that setting. The transcription factors RUNX3 and Eomesodermin (EOMES) are important in the development of long lived memory CD8 T cells. We studied the dynamics of CD127 expression, RUNX3 and EOMES in patients with HIV infection and different levels of viremia. Consistent with other reports, CD127 expression was decreased in the memory CD8 T cell subset. The CD8 memory CD127low T cells showed increased expression of RUNX3 and EOMES mRNA, as well as effector molecules perforin and granzyme B. In patients with suppressed viremia, we could identify two populations of CD8 T cells expressing EOMEShigh and EOMESint. The EOMESint cells showed a short-lived effector phenotype (perforin+, granzyme B+, CD127low) and the EOMEShigh cells showed a memory-like phenotype (perforin-, CD127high). These results suggest that in human CD8 T cells, EOMES is necessary for the maintenance of long lived memory CD8 T cells and its expression was influenced by HIV-RNA levels and the associated inflammatory environment (R=0.4, p=0.01). These findings provide new insights into the pathogenesis of HIV infection.

Suppression of Cytokine Signaling 4 (SOCS4) is a novel immunomodulatory molecule in T cells (63.14)

Preventing excessive cytokine signaling is critical for a functional immune system. Molecules of the Suppressor Of Cytokine Signaling (SOCS) family play a crucial role in regulating cytokine response, and here we show that SOCS4 is a novel SOCS family member that regulates immune function in T cells. We found that SOCS4 mRNA is highly expressed in the thymus, and specifically in pre-selection CD4, CD8 double positive (DP) thymocytes. TCR signaling significantly downreglated both SOCS4 mRNA and protein expression in DP thymocytes, which also correlated with lower SOCS4 expression in mature thymocytes and in peripheral T cells. Furthermore, T lineage specific overexpression of SOCS4 resulted in impaired T cell development in the thymus, which was presumably induced by a developmental block at the DN stage. Interestingly, SOCS4 overexpression did not result in inhibition of proximal cytokine receptor signaling such as STAT5 or STAT3 phosphorylation as would be expected from other conventional suppressors of cytokine signaling such as SOCS1 or SOCS3. These data suggest that SOCS4 might utilize another mechanism to modulate T cell reactivity. To asses this question, we have generated SOCS4 transgenic mice expressing a transgenic TCR. Preliminary results show further impairment in T cell development in these mice which detailed mechanisms are currently under investigation. Collectively, this study uncovers SOCS4 as a new immunomodulatory molecule in T cells.

Seeing is believing: illuminating the source of in vivo interleukin-7

Interleukin-7 (IL-7) is an essential cytokine for T cells. However, IL-7 is not produced by T cells themselves such that T cells are dependent on extrinsic IL-7. In fact, in the absence of IL-7, T cell development in the thymus as well as survival of naive T cells in the periphery is severely impaired. Furthermore, modulating IL-7 availability in vivo either by genetic means or other experimental approaches determines the size, composition and function of the T cell pool. Consequently, understanding IL-7 expression is critical for understanding T cell immunity. Until most recently, however, the spatiotemporal expression of in vivo IL-7 has remained obscured. Shortage of such information was partly due to scarce expression of IL-7 itself but mainly due to the lack of adequate reagents to monitor IL-7 expression in vivo. This situation dramatically changed with a recent rush of four independent studies that describe the generation and characterization of IL-7 reporter mice, all utilizing bacterial artificial chromosome transgene technology. The emerging consensus of these studies confirmed thymic stromal cells as the major producers of IL-7 but also identified IL-7 reporter activities in various peripheral tissues including skin, intestine and lymph nodes. Strikingly, developmental and environmental cues actively modulated IL-7 reporter activities in vivo suggesting that IL-7 regulation might be a new mechanism of shaping T cell development and homeostasis. Collectively, the availability of these new tools opens up new venues to assess unanswered questions in IL-7 biology in T cells and beyond.

NKT cell-dependent regulation of secondary antigen-specific, conventional CD4+ T cell immune responses

NKT cells are considered to be innate-like regulatory cells. However, their regulatory functions in adaptive immune responses have not been studied in detail. In this study, we investigated the immunoregulatory functions of NKT cells during the secondary phase of an Ag-specific CD4(+) T cell response. When compared with OVA-specific effector CD4(+) T cells adoptively transferred into NKT cell-deficient naive CD1d(-/-) mice, the same T cells transferred into naive CD1d(+/-) mice exhibited substantially stronger immune responses on OVA challenge. The enhanced immune response of the transferred CD4(+) T cells in the presence of NKT cells correlated with an increase in their proliferation in vivo. In addition, T cells transferred into CD1d(+/-) recipients showed enhanced cytokine productions relative to T cells in CD1d(-/-) recipients. To elucidate the physiological relevance of the regulatory role of NKT cells in a disease setting, OVA-specific asthma was induced in recipient mice after adoptive transfer of OVA-specific CD4(+) T cells. CD1d(+/-) recipients showed stronger asthmatic phenotypes in all indications when compared with CD1d(-/-) recipients. Taken together, these results suggest that NKT cells are critical for the regulation of Ag-specific, conventional CD4(+) T cells during the secondary phase of an adaptive immune response.

The presence of CD8+ invariant NKT cells in mice

Invariant natural killer T (iNKT) cells develop in the thymus upon recognition of CD1d expressed on developing thymocytes. Although CD4 and CD8 coreceptors are not directly involved in the interaction between CD1d and the T cell receptors (TCRs) of iNKT cells, a conspicuous lack of CD8(+) iNKT cells in mice raised the question of whether CD8(+) iNKT cells are excluded due to negative selection during their thymic development, or if there is no lineage commitment for the development of murine CD8(+) iNKT cells. To address this question, we analyzed iNKT cell-specific TCR V alpha 14(+) transgenic mice, where the V alpha 14 transgene forces the generation of iNKT cells. This allows detailed study of the iNKT cell repertoire. We were able to identify CD8(+) iNKT cells which respond to the NKT cell-specific glycolipid ligand alpha-galactosylceramide. Unlike conventional iNKT cells, CD8(+) iNKT cells produce predominantly IFN-gamma but not IL-4 upon antigen stimulation. We also confirmed the presence of CD8(+) iNKT cells in wild type mice. Our results suggest that CD8(+) NKT cells do exist in mice, although their population size is quite small. Their Th1-skewed phenotype might explain why the population size of this subtype needs to be controlled tightly.