Hai-Hui Xue

Differentiation and Persistence of Memory CD8+ T Cells Depend on T Cell Factor 1

T cell factor 1 (TCF-1) is a transcription factor known to act downstream of the canonical Wnt pathway and is essential for normal T cell development. However, its physiological roles in mature CD8(+) T cell responses are unknown. Here we showed that TCF-1 deficiency limited proliferation of CD8(+) effector T cells and impaired their differentiation toward a central memory phenotype. Moreover, TCF-1-deficient memory CD8(+) T cells were progressively lost over time, exhibiting reduced expression of the antiapoptotic molecule Bcl-2 and interleukin-2 receptor beta chain and diminished IL-15-driven proliferation. TCF-1 was directly associated with the Eomes allele and the Wnt-TCF-1 pathway was necessary and sufficient for optimal Eomes expression in naive and memory CD8(+) T cells. Importantly, forced expression of Eomes partly protected TCF-1-deficient memory CD8(+) T cells from time-dependent attrition. Our studies thus identify TCF-1 as a critical player in a transcriptional program that regulates memory CD8 differentiation and longevity.

Repetitive Antigen Stimulation Induces Stepwise Transcriptome Diversification but Preserves a Core Signature of Memory CD8+ T Cell Differentiation

Repetitive antigen stimulation by prime-boost vaccination or pathogen reencounter increases memory CD8(+) T cell numbers, but the impact on memory CD8(+) T cell differentiation is unknown. Here we showed that repetitive antigen stimulations induced accumulation of memory CD8(+) T cells with uniform effector memory characteristics. However, genome-wide microarray analyses revealed that each additional antigen challenge resulted in the differential regulation of several hundred new genes in the ensuing memory CD8(+) T cell populations and, therefore, in stepwise diversification of CD8(+) T cell transcriptomes. Thus, primary and repeatedly stimulated (secondary, tertiary, and quaternary) memory CD8(+) T cells differed substantially in their molecular signature while sharing expression of a small group of genes and biological pathways, which may constitute a core signature of memory differentiation. These results reveal the complex regulation of memory CD8(+) T cell differentiation and identify potential new molecular targets to dissect the function of memory cells generated by repeated antigen stimulation.

Defining CD8 + T cells that provide the proliferative burst after PD-1 therapy

Chronic viral infections are characterized by a state of CD8+ T-cell dysfunction that is associated with expression of the programmed cell death 1 (PD-1) inhibitory receptor. A better understanding of the mechanisms that regulate CD8+ T-cell responses during chronic infection is required to improve immunotherapies that restore function in exhausted CD8+ T cells. Here we identify a population of virus-specific CD8+ T cells that proliferate after blockade of the PD-1 inhibitory pathway in mice chronically infected with lymphocytic choriomeningitis virus (LCMV). These LCMV-specific CD8+ T cells expressed the PD-1 inhibitory receptor, but also expressed several costimulatory molecules such as ICOS and CD28. This CD8+ T-cell subset was characterized by a unique gene signature that was related to that of CD4+ T follicular helper (TFH) cells, CD8+ T cell memory precursors and haematopoietic stem cell progenitors, but that was distinct from that of CD4+ TH1 cells and CD8+ terminal effectors. This CD8+ T-cell population was found only in lymphoid tissues and resided predominantly in the T-cell zones along with naive CD8+ T cells. These PD-1+CD8+ T cells resembled stem cells during chronic LCMV infection, undergoing self-renewal and also differentiating into the terminally exhausted CD8+ T cells that were present in both lymphoid and non-lymphoid tissues. The proliferative burst after PD-1 blockade came almost exclusively from this CD8+ T-cell subset. Notably, the transcription factor TCF1 had a cell-intrinsic and essential role in the generation of this CD8+ T-cell subset. These findings provide a better understanding of T-cell exhaustion and have implications in the optimization of PD-1-directed immunotherapy in chronic infections and cancer.

IL-2 negatively regulates IL-7 receptor α chain expression in activated T lymphocytes

Interleukin (IL)-2 is a type I four-α-helical bundle cytokine that plays vital roles in antigen-mediated proliferation of peripheral blood T cells and also is critical for activation-induced cell death. We now demonstrate that IL-2 potently decreases expression of IL-7 receptor α chain (IL-7Rα) mRNA and protein. The fact that IL-7Rα is a component of the receptors for both IL-7 and thymic stromal lymphopoietin (TSLP) suggests that IL-2 can negatively regulate signals by each of these cytokines. Previously it was known that the IL-2 and IL-7 receptors shared the common cytokine receptor γ chain, γc, which suggested a possible competition between these cytokines for a receptor component. Our findings now suggest a previously unknown type of cross-talk between IL-2 and IL-7 signaling by showing that IL-2 signaling can diminish IL-7Rα expression via a phosphatidylinositol 3-kinase/Akt-dependent mechanism.

GA binding protein regulates interleukin 7 receptor |[alpha]|-chain gene expression in T cells

The interleukin 7 receptor α-chain (IL-7Rα) is essential for T cell development in both humans and mice and for B cell development in mice. Whereas the transcription factor PU.1 regulates IL-7Rα expression in mouse pro–B cells via a GGAA motif, we demonstrate here that GA binding protein (GABP) bound to this site and was essential in the regulation of IL-7Rα expression in T cells, where PU.1 is not expressed. Moreover, IL-7Rα expression was diminished substantially in thymocytes but was normal on B220+ fetal liver cells from mouse embryos with diminished expression of GABPα. Thus, GABP is essential for the regulation of IL-7Rα expression in T cells, and the differential regulation of IL-7Rα in distinct lymphoid lineages is achieved at least in part by differential recruitment of factors to the same GGAA motif.

TCF-1 upregulation identifies early innate lymphoid progenitors in the bone marrow.

The cellular and molecular events that drive the early development of innate lymphoid cells (ILCs) remain poorly understood. We show that the transcription factor TCF-1 is required for the efficient generation of all known adult ILC subsets and their precursors. Using novel reporter mice, we identified a new subset of early ILC progenitors (EILPs) expressing high amounts of TCF-1. EILPs lacked efficient T and B lymphocyte potential but efficiently gave rise to NK cells and all known adult helper ILC lineages, indicating that they are the earliest ILC-committed progenitors identified so far. Our results suggest that upregulation of TCF-1 expression denotes the earliest stage of ILC fate specification. The discovery of EILPs provides a basis for deciphering additional signals that specify ILC fate.

Constitutive activation of Wnt signaling favors generation of memory CD8 T cells

T cell factor-1 (TCF-1) and lymphoid enhancer-binding factor 1, the effector transcription factors of the canonical Wnt pathway, are known to be critical for normal thymocyte development. However, it is largely unknown if it has a role in regulating mature T cell activation and T cell-mediated immune responses. In this study, we demonstrate that, like IL-7Rα and CD62L, TCF-1 and lymphoid enhancer-binding factor 1 exhibit dynamic expression changes during T cell responses, being highly expressed in naive T cells, downregulated in effector T cells, and upregulated again in memory T cells. Enforced expression of a p45 TCF-1 isoform limited the expansion of Ag-specific CD8 T cells in response to Listeria monocytogenes infection. However, when the p45 transgene was coupled with ectopic expression of stabilized β-catenin, more Ag-specific memory CD8 T cells were generated, with enhanced ability to produce IL-2. Moreover, these memory CD8 T cells expanded to a larger number of secondary effectors and cleared bacteria faster when the immunized mice were rechallenged with virulent L. monocytogenes. Furthermore, in response to vaccinia virus or lymphocytic choriomeningitis virus infection, more Ag-specific memory CD8 T cells were generated in the presence of p45 and stabilized β-catenin transgenes. Although activated Wnt signaling also resulted in larger numbers of Ag-specific memory CD4 T cells, their functional attributes and expansion after the secondary infection were not improved. Thus, constitutive activation of the canonical Wnt pathway favors memory CD8 T cell formation during initial immunization, resulting in enhanced immunity upon second encounter with the same pathogen.

The TCF-1 and LEF-1 transcription factors have cooperative and opposing roles in T-cell development and malignancy

The TCF-1 and LEF-1 transcription factors are known to play critical roles in normal thymocyte development. Unexpectedly, we found that TCF-1-deficient (Tcf7(-/-)) mice developed aggressive T cell malignancy, resembling human T cell acute lymphoblastic leukemia (T-ALL). LEF-1 was aberrantly upregulated in premalignant Tcf7(-/-) early thymocytes and lymphoma cells. We further demonstrated that TCF-1 directly repressed LEF-1 expression in early thymocytes and that conditional inactivation of Lef1 greatly delayed or prevented T cell malignancy in Tcf7(-/-) mice. In human T-ALLs, an early thymic progenitor (ETP) subtype was associated with diminished TCF7 expression, and two of the ETP-ALL cases harbored TCF7 gene deletions. We also showed that TCF-1 and LEF-1 were dispensable for T cell lineage commitment but instead were required for early thymocytes to mature beyond the CD4(-)CD8(-) stage. TCF-1 thus has dual roles, i.e., acting cooperatively with LEF-1 to promote thymocyte maturation while restraining LEF-1 expression to prevent malignant transformation of developing thymocytes.

LEF-1 and TCF-1 orchestrate TFH differentiation by regulating differentiation circuits upstream of the transcriptional repressor Bcl6

Follicular helper T cells (TFH cells) are specialized effector CD4+ T cells that help B cells develop germinal centers (GCs) and memory. However, the transcription factors that regulate the differentiation of TFH cells remain incompletely understood. Here we report that selective loss of Lef1 or Tcf7 (which encode the transcription factor LEF-1 or TCF-1, respectively) resulted in TFH cell defects, while deletion of both Lef1 and Tcf7 severely impaired the differentiation of TFH cells and the formation of GCs. Forced expression of LEF-1 enhanced TFH differentiation. LEF-1 and TCF-1 coordinated such differentiation by two general mechanisms. First, they established the responsiveness of naive CD4+ T cells to TFH cell signals. Second, they promoted early TFH differentiation via the multipronged approach of sustaining expression of the cytokine receptors IL-6Rα and gp130, enhancing expression of the costimulatory receptor ICOS and promoting expression of the transcriptional repressor Bcl6.T follicular helper (TFH) cells are specialized effector CD4+ T cells that help B cells develop germinal centers and memory. However, the transcription factors that regulate TFH differentiation remain incompletely understood. Here we report that selective loss of either Lef1 (LEF-1) or Tcf7 (TCF-1) resulted in TFH defects, while deletion of Lef1 and Tcf7 severely impaired TFH differentiation and germinal centers. Forced expression of LEF-1 enhanced TFH differentiation. LEF-1 and TCF-1 coordinated TFH differentiation by two general mechanisms. First, they established the responsiveness of naïve CD4+ T cells to TFH signals. Second, they promoted early TFH differentiation via the multipronged approach of sustaining expression of IL-6Rα and gp130, enhancing ICOS expression, and promoting expression of Bcl6.

IL-12 and type I interferon prolong the division of activated CD8 T cells by maintaining high-affinity IL-2 signaling in vivo

The signal 3 cytokines interleukin-12 and type I interferon sustain CD8 T cell division by prolonging expression of CD25 in vivo.