BCL6 fine-tunes long-term tumor control.

Sun et al. provide comprehensive evidence that the transcription factor BCL6 functions as a gatekeeper for CD8+ progenitor cell function in tumors and prevents their excessive terminal differentiation, thereby preserving this stem-like population for long-term tumor control.

Identification of a novel enhancer essential for Satb1 expression in TH2 cells and activated ILC2s.

The genome organizer, special AT-rich binding protein-1 (SATB1), functions to globally regulate gene networks during primary T cell development and plays a pivotal role in lineage specification in CD4+ helper-, CD8+ cytotoxic-, and FOXP3+ regulatory-T cell subsets. However, it remains unclear how Satb1 gene expression is controlled, particularly in effector T cell function. Here, by using a novel reporter mouse strain expressing SATB1-Venus and genome editing, we have identified a cis-regulatory enhancer, essential for maintaining Satb1 expression specifically in TH2 cells. This enhancer is occupied by STAT6 and interacts with Satb1 promoters through chromatin looping in TH2 cells. Reduction of Satb1 expression, by the lack of this enhancer, resulted in elevated IL-5 expression in TH2 cells. In addition, we found that Satb1 is induced in activated group 2 innate lymphoid cells (ILC2s) through this enhancer. Collectively, these results provide novel insights into how Satb1 expression is regulated in TH2 cells and ILC2s during type 2 immune responses.

The Majority of the Serine/Threonine Phosphorylation Sites in Bcl11b Protein Are Dispensable for the Differentiation of T Cells.

Posttranslational modification, such as phosphorylation, is an important biological event that modulates and diversifies protein function. Bcl11b protein is a zinc-finger transcription factor that plays a crucial role in early T cell development and the segregation of T cell subsets. Bcl11b possesses at least 25 serine/threonine (S/T) residues that can be phosphorylated upon TCR stimulation. To understand the physiological relevance of the phosphorylation on Bcl11b protein, we replaced S/T residues with alanine (A) by targeting murine Bcl11b gene in embryonic stem cells. By combinational targeting of exons 2 and 4 in the Bcl11b gene, we generated a mouse strain, Bcl11b-phosphorylation site mutation mice, in which 23 S/T residues were replaced with A residues. Such extensive manipulation left only five putative phosphorylated residues, two of which were specific for mutant protein, and resulted in reduced amounts of Bcl11b protein. However, primary T cell development in the thymus, as well as the maintenance of peripheral T cells, remained intact even after loss of major physiological phosphorylation. In addition, in vitro differentiation of CD4+ naive T cells into effector Th cell subsets-Th1, Th2, Th17, and regulatory T-was comparable between wild-type and Bcl11b-phosphorylation site mutation mice. These findings indicate that the physiological phosphorylation on major 23 S/T residues in Bcl11b is dispensable for Bcl11b functions in early T cell development and effector Th cell differentiation.

The Roles of RUNX Proteins in Lymphocyte Function and Anti-Tumor Immunity.

The Runt-related transcription factor (RUNX) family of proteins are crucial for many developmental and immuno-physiological processes. Their importance in cellular and tissue development has been repeatedly demonstrated as they are often found mutated and implicated in tumorigenesis. Most importantly, RUNX have now emerged as critical regulators of lymphocyte function against pathogenic infections and tumorigenic cells, the latter has now revolutionized our current understandings as to how RUNX proteins contribute to control tumor pathogenicity. These multifunctional roles of RUNX in mammalian immune responses and tissue homeostasis have led us to appreciate their value in controlling anti-tumor immune responses. Here, we summarize and discuss the role of RUNX in regulating the development and function of lymphocytes responding to foreign and tumorigenic threats and highlight their key roles in anti-tumor immunity.

Phosphoinositide 3-Kinase p110 Delta Differentially Restrains and Directs Naïve Versus Effector CD8+ T Cell Transcriptional Programs.

Phosphoinositide 3-kinase p110 delta (PI3K p110δ) is pivotal for CD8+ T cell immune responses. The current study explores PI3K p110δ induction and repression of antigen receptor and cytokine regulated programs to inform how PI3K p110δ directs CD8+ T cell fate. The studies force a revision of the concept that PI3K p110δ controls metabolic pathways in T cells and reveal major differences in PI3K p110δ regulated transcriptional programs between naïve and effector cytotoxic T cells (CTL). These differences include differential control of the expression of cytolytic effector molecules and costimulatory receptors. Key insights from the work include that PI3K p110δ signalling pathways repress expression of the critical inhibitory receptors CTLA4 and SLAMF6 in CTL. Moreover, in both naïve and effector T cells the dominant role for PI3K p110δ is to restrain the production of the chemokines that orchestrate communication between adaptive and innate immune cells. The study provides a comprehensive resource for understanding how PI3K p110δ uses multiple processes mediated by Protein Kinase B/AKT, FOXO1 dependent and independent mechanisms and mitogen-activated protein kinases (MAPK) to direct CD8+ T cell fate.

The Role of CD8 Downregulation during Thymocyte Differentiation.

During mammalian T cell development, CD4+CD8+ double-positive (DP) thymocytes must make a lineage choice to become either conventional CD4+ or CD8+ T cells, dependent on their specificity for MHC-II or MHC-I, respectively. Alternatively, DP thymocytes can decide to become innate-like T cells in response to nonclassical MHC-I molecules. A key feature is the downregulation of CD8, which causes transient T cell receptor (TCR) signaling in MHC-I-selected DP thymocytes. Hence, this kinetic signaling model postulates that short or long duration of TCR signals during positive selection can direct the development of cytotoxic or helper T cell lineages. In this opinion article, we discuss the effects of constitutive expression of transgenic CD8 and prolonged TCR signaling on T cell lineage choice in MHC-I selected mouse thymocytes.