Faculty Bibliography

The RUNX1/AML1 gene is the most frequently mutated gene in human leukemia. Conditional deletion of Runx1 in adult mice results in an increase of hematopoietic stem cells (HSCs), which serve as target cells for leukemia; however, Runx1(-/-) mice do not develop spontaneous leukemia. Here we show that maintenance of Runx1(-/-) HSCs is compromised, progressively resulting in HSC exhaustion. In leukemia development, the stem cell exhaustion was rescued by additional genetic changes. Retroviral insertional mutagenesis revealed Evi5 activation as a cooperating genetic alteration and EVI5 overexpression indeed prevented Runx1(-/-) HSC exhaustion in mice. Moreover, EVI5 was frequently overexpressed in human RUNX1-related leukemias. These results provide insights into the mechanism for maintenance of pre-leukemic stem cells and may provide a novel direction for therapeutic applications

Passage through the beta-selection developmental checkpoint requires productive rearrangement of segments of the T cell antigen receptor-beta gene (Tcrb) and formation of a pre-TCR on the surface of CD4(-)CD8(-) thymocytes. How other receptors influence betabeta-selection is less well understood. Here we define a new role for the chemokine receptor CXCR4 during T cell development. CXCR4 functionally associated with the pre-TCR and influenced beta-selection by regulating the steady-state localization of immature thymocytes in thymic subregions, by facilitating optimal pre-TCR-induced survival signals, and by promoting thymocyte proliferation. We also characterize functionally relevant signaling molecules downstream of CXCR4 and the pre-TCR in thymocytes. Our data designate CXCR4 as a costimulator of the pre-TCR during beta-selection

Forkhead box P3 (FOXP3)(+)CD4(+)CD25(+) inducible regulatory T (iT reg) cells play an important role in immune tolerance and homeostasis. In this study, we show that the transforming growth factor-beta (TGF-beta) induces the expression of the Runt-related transcription factors RUNX1 and RUNX3 in CD4(+) T cells. This induction seems to be a prerequisite for the binding of RUNX1 and RUNX3 to three putative RUNX binding sites in the FOXP3 promoter. Inactivation of the gene encoding RUNX cofactor core-binding factor-beta (CBFbeta) in mice and small interfering RNA (siRNA)-mediated suppression of RUNX1 and RUNX3 in human T cells resulted in reduced expression of Foxp3. The in vivo conversion of naive CD4(+) T cells into Foxp3(+) iT reg cells was significantly decreased in adoptively transferred Cbfb(F/F) CD4-cre naive T cells into Rag2(-/-) mice. Both RUNX1 and RUNX3 siRNA silenced human T reg cells and Cbfb(F/F) CD4-cre mouse T reg cells showed diminished suppressive function in vitro. Circulating human CD4(+) CD25(high) CD127(-) T reg cells significantly expressed higher levels of RUNX3, FOXP3, and TGF-beta mRNA compared with CD4(+)CD25(-) cells. Furthermore, FOXP3 and RUNX3 were colocalized in human tonsil T reg cells. These data demonstrate Runx transcription factors as a molecular link in TGF-beta-induced Foxp3 expression in iT reg cell differentiation and function

The transcription factor Foxp3 has an indispensable role in establishing stable transcriptional and functional programs of regulatory T cells (T(reg) cells). Loss of Foxp3 expression in mature T(reg) cells results in a failure of suppressor function, yet the molecular mechanisms that ensure steady, heritable Foxp3 expression in the T(reg) cell lineage remain unknown. Using T(reg) cell-specific gene targeting, we found that complexes of the transcription factors Runx and CBFbeta were required for maintenance of Foxp3 mRNA and protein expression in T(reg) cells. Consequently, mice lacking CBFbetab exclusively in the T(reg) cell lineage had a moderate lymphoproliferative syndrome. Thus, Runx-CBFbeta complexes maintain stable high expression of Foxp3 and serve as an essential determinant of T(reg) cell lineage stability

The gastrointestinal tract of mammals is inhabited by hundreds of distinct species of commensal microorganisms that exist in a mutualistic relationship with the host. How commensal microbiota influence the host immune system is poorly understood. We show here that colonization of the small intestine of mice with a single commensal microbe, segmented filamentous bacterium (SFB), is sufficient to induce the appearance of CD4(+) T helper cells that produce IL-17 and IL-22 (Th17 cells) in the lamina propria. SFB adhere tightly to the surface of epithelial cells in the terminal ileum of mice with Th17 cells but are absent from mice that have few Th17 cells. Colonization with SFB was correlated with increased expression of genes associated with inflammation and antimicrobial defenses and resulted in enhanced resistance to the intestinal pathogen Citrobacter rodentium. Thus, manipulation of this commensal-regulated pathway may provide new opportunities for enhancing mucosal immunity and treating autoimmune disease

CD4(+)Foxp3(+) regulatory T cells (Treg cells) are known to control the progression of autoimmune diabetes, but when, where, and how they exert their influence in this context are questions still under vigorous debate. Exploiting a transgene encoding the human diphtheria toxin receptor, we punctually and specifically ablated Foxp3(+) cells in the BCD2.5/NOD mouse model of autoimmune diabetes. Strikingly, overt disease developed within 3 days. The earliest detectable event was the activation of natural killer (NK) cells directly within the insulitic lesion, particularly the induction of Ifng gene expression within 7 hours of Treg cell ablation. Interferon-gamma had a strong impact on the gene-expression program of the local CD4(+) T effector cell population, unleashing it to aggressively attack the islets, which was required for the development of diabetes. Thus, Treg cells regulate pancreatic autoimmunity in situ through control of a central innate immune system player, NK cells

Signaling through the T cell antigen receptor (TCR) is important for the homeostasis of naive and memory CD4(+) T cells. The significance of TCR signaling in regulatory T (Treg) cells has not been systematically addressed. Using an Ox40-cre allele that is prominently expressed in Treg cells, and a conditional null allele of the gene encoding p56(Lck), we have examined the importance of TCR signaling in Treg cells. Inactivation of p56(Lck) resulted in abnormal Treg homeostasis characterized by impaired turnover, preferential redistribution to the lymph nodes, loss of suppressive function, and striking changes in gene expression. Abnormal Treg cell homeostasis and function did not reflect the involvement of p56(Lck) in CD4 function because these effects were not observed when CD4 expression was inactivated by Ox40-cre.The results make clear multiple aspects of Treg cell homeostasis and phenotype that are dependent on a sustained capacity to signal through the TCR

The differentiation of naive CD4(+) T cells into lineages with distinct effector functions has been considered to be an irreversible event. T helper type 1 (Th1) cells stably express IFN-gamma, whereas Th2 cells express IL-4. The discovery and investigation of two other CD4(+) T cell subsets, induced regulatory T (iTreg) cells and Th17 cells, has led to a rethinking of the notion that helper T cell subsets represent irreversibly differentiated endpoints. Accumulating evidence suggests that CD4(+) T cells, particularly iTreg and Th17 cells, are more plastic than previously appreciated. It appears that expression of Foxp3 by iTreg cells or IL-17 by Th17 cells may not be stable and that there is a great degree of flexibility in their differentiation options. Here, we will discuss recent findings that demonstrate the plasticity of CD4(+) T cell differentiation and the biological implications of this flexibility

Upon encountering antigen in the context of antigen presenting cells, naive CD4(+) T cells undergo differentiation into effector T helper (Th) cells, which can secrete high levels of cytokines and other immunomodulators to mediate host defense and tissue inflammation. During the past three years, the immunology field has witnessed an explosion of research advances in the biology of Th17 cells, the most recently described subset of T helper cells, which play crucial roles in host immunity and inflammation. Here we review emerging data on transcriptional regulatory networks that govern the differentiation program of Th17 cells, and focus on how the orphan nuclear receptor RORgammat coordinates this process in concert with diverse cytokine-induced transcription factors