Analysis of Butyrophilin-Mediated Activation of γδ T Cells from Human Spleen.

There is considerable interest in therapeutically engaging human γδ T cells. However, due to the unique TCRs of human γδ T cells, studies from animal models have provided limited directly applicable insights, and human γδ T cells from key immunological tissues remain poorly characterized. In this study, we investigated γδ T cells from human spleen tissue. Compared to blood, where Vδ2+Vγ9+ T cells are the dominant subset, splenic γδ T cells included a variety of TCR types, with Vδ1+ T cells typically being the most frequent. Intracellular cytokine staining revealed that IFN-γ was produced by a substantial fraction of splenic γδ T cells, IL-17A by a small fraction, and IL-4 was minimal. Primary splenic γδ T cells frequently expressed NKG2D (NK group 2 member D) and CD16, whereas expression of DNAM-1 (DNAX accessory molecule 1), CD28, PD-1, TIGIT, and CD94 varied according to subset, and there was generally little expression of natural cytotoxicity receptors, TIM-3, LAG-3, or killer Ig-like receptors. In vitro expansion was associated with marked changes in expression of these activating and inhibitory receptors. Analysis of functional responses of spleen-derived Vδ2+Vγ9+, Vδ1+Vγ9+, and Vδ1+Vγ9- T cell lines to recombinant butyrophilin BTN2A1 and BTN3A1 demonstrated that both Vδ2+Vγ9+ and Vδ1+Vγ9+ T cells were capable of responding to the extracellular domain of BTN2A1, whereas the addition of BTN3A1 only markedly enhanced the responses of Vδ2+Vγ9+ T cells. Conversely, Vδ1+Vγ9+ T cells appeared more responsive than Vδ2+Vγ9+ T cells to TCR-independent NKG2D stimulation. Thus, despite shared recognition of BTN2A1, differential effects of BTN3A1 and coreceptors may segregate target cell responses of Vδ2+Vγ9+ and Vδ1+Vγ9+ T cells.

Cutting Edge: Bispecific γδ T Cell Engager Containing Heterodimeric BTN2A1 and BTN3A1 Promotes Targeted Activation of Vγ9Vδ2+ T Cells in the Presence of Costimulation by CD28 or NKG2D.

Vγ9Vδ2+ T cell-targeted immunotherapy is of interest to harness its MHC-independent cytotoxic potential against a variety of cancers. Recent studies have identified heterodimeric butyrophilin (BTN) 2A1 and BTN3A1 as the molecular entity providing "signal 1" to the Vγ9Vδ2 TCR, but "signal 2" costimulatory requirements remain unclear. Using a tumor cell-free assay, we demonstrated that a BTN2A1/3A1 heterodimeric fusion protein activated human Vγ9Vδ2+ T cells, but only in the presence of costimulatory signal via CD28 or NK group 2 member D. Nonetheless, addition of a bispecific γδ T cell engager BTN2A1/3A1-Fc-CD19scFv alone enhanced granzyme B-mediated killing of human CD19+ lymphoma cells when cocultured with Vγ9Vδ2+ T cells, suggesting expression of costimulatory ligand(s) on tumor cells is sufficient to satisfy the "signal 2" requirement. These results highlight the parallels of signal 1 and signal 2 requirements in αß and γδ T cell activation and demonstrate the utility of heterodimeric BTNs to promote targeted activation of γδ T cells.

CDK4/6 inhibition enhances antitumor efficacy of chemotherapy and immune checkpoint inhibitor combinations in preclinical models and enhances T-cell activation in patients with SCLC receiving chemotherapy.

BACKGROUND: Combination treatment with chemotherapy and immune checkpoint inhibitors (ICIs) has demonstrated meaningful clinical benefit to patients. However, chemotherapy-induced damage to the immune system can potentially diminish the efficacy of chemotherapy/ICI combinations. Trilaciclib, a highly potent, selective and reversible cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor in development to preserve hematopoietic stem and progenitor cells and immune system function during chemotherapy, has demonstrated proof of concept in recent clinical trials. Furthermore, CDK4/6 inhibition has been shown to augment T-cell activation and antitumor immunity in preclinical settings. Therefore, addition of trilaciclib has the potential to further enhance the efficacy of chemotherapy and ICI combinations. METHODS: In murine syngeneic tumor models, a schedule of 3 weekly doses of trilaciclib was combined with chemotherapy/ICI regimens to assess the effect of transient CDK4/6 inhibition on antitumor response and intratumor T-cell proliferation and function. Peripheral T-cell status was also analyzed in patients with small cell lung cancer (SCLC) treated with chemotherapy with or without trilaciclib to gain insights into the effect of transient exposure of trilaciclib on T-cell activation. RESULTS: Preclinically, the addition of trilaciclib to chemotherapy/ICI regimens enhanced antitumor response and overall survival compared with chemotherapy and ICI combinations alone. This effect is associated with the modulation of the proliferation and composition of T-cell subsets in the tumor microenvironment and increased effector function. Transient exposure of trilaciclib in patients with SCLC during chemotherapy treatment both preserved and increased peripheral lymphocyte counts and enhanced T-cell activation, suggesting that trilaciclib not only preserved but also enhanced immune system function. CONCLUSIONS: Transient CDK4/6 inhibition by trilaciclib was sufficient to enhance and prolong the duration of the antitumor response by chemotherapy/ICI combinations, suggesting a role for the transient cell cycle arrest of tumor immune infiltrates in remodeling the tumor microenvironment. These results provide a rationale for combining trilaciclib with chemotherapy/ICI regimens to improve antitumor efficacy in patients with cancer.

Diethylstilbestrol (DES)-stimulated hormonal toxicity is mediated by ERα alteration of target gene methylation patterns and epigenetic modifiers (DNMT3A, MBD2, and HDAC2) in the mouse seminal vesicle.

BACKGROUND: Diethylstilbestrol (DES) is a synthetic estrogen associated with adverse effects on reproductive organs. DES-induced toxicity of the mouse seminal vesicle (SV) is mediated by estrogen receptor α (ERα), which alters expression of seminal vesicle secretory protein IV (Svs4) and lactoferrin (Ltf) genes. OBJECTIVES: We examined a role for nuclear receptor activity in association with DNA methylation and altered gene expression. METHODS: We used the neonatal DES exposure mouse model to examine DNA methylation patterns via bisulfite conversion sequencing in SVs of wild-type (WT) and ERα-knockout (αERKO) mice. RESULTS: The DNA methylation status at four specific CpGs (-160, -237, -306, and -367) in the Svs4 gene promoter changed during mouse development from methylated to unmethylated, and DES prevented this change at 10 weeks of age in WT SV. At two specific CpGs (-449 and -459) of the Ltf gene promoter, DES altered the methylation status from methylated to unmethylated. Alterations in DNA methylation of Svs4 and Ltf were not observed in αERKO SVs, suggesting that changes of methylation status at these CpGs are ERα dependent. The methylation status was associated with the level of gene expression. In addition, gene expression of three epigenetic modifiers-DNMT3A, MBD2, and HDAC2-increased in the SV of DES-exposed WT mice. CONCLUSION: DES-induced hormonal toxicity resulted from altered gene expression of Svs4 and Ltf associated with changes in DNA methylation that were mediated by ERα. Alterations in gene expression of DNMT3A, MBD2, and HDAC2 in DES-exposed male mice may be involved in mediating the changes in methylation status in the SV. CITATION: Li Y, Hamilton KJ, Lai AY, Burns KA, Li L, Wade PA, Korach KS. 2014. Diethylstilbestrol (DES)-stimulated hormonal toxicity is mediated by ERα alteration of target gene methylation patterns and epigenetic modifiers (DNMT3A, MBD2, and HDAC2) in the mouse seminal vesicle. Environ Health Perspect 122:262-268; http://dx.doi.org/10.1289/ehp.1307351.

DNA methylation profiling in human B cells reveals immune regulatory elements and epigenetic plasticity at Alu elements during B-cell activation.

Memory is a hallmark of adaptive immunity, wherein lymphocytes mount a superior response to a previously encountered antigen. It has been speculated that epigenetic alterations in memory lymphocytes contribute to their functional distinction from their naive counterparts. However, the nature and extent of epigenetic alterations in memory compartments remain poorly characterized. Here we profile the DNA methylome and the transcriptome of B-lymphocyte subsets representing stages of the humoral immune response before and after antigen exposure in vivo from multiple humans. A significant percentage of activation-induced losses of DNA methylation mapped to transcription factor binding sites. An additional class of demethylated loci mapped to Alu elements across the genome and accompanied repression of DNA methyltransferase 3A. The activation-dependent DNA methylation changes were largely retained in the progeny of activated B cells, generating a similar epigenetic signature in downstream memory B cells and plasma cells with distinct transcriptional programs. These findings provide insights into the methylation dynamics of the genome during cellular differentiation in an immune response.

Cancer biology and NuRD: a multifaceted chromatin remodelling complex.

The nucleosome remodelling and histone deacetylase (NuRD; also known as Mi-2) complex regulates gene expression at the level of chromatin. The NuRD complex has been identified - using both genetic and molecular analyses - as a key determinant of differentiation in mouse embryonic stem cells and during development in various model systems. Similar to other chromatin remodellers, such as SWI/SNF and Polycomb complexes, NuRD has also been implicated in the regulation of transcriptional events that are integral to oncogenesis and cancer progression. Emerging molecular details regarding the recruitment of NuRD to specific loci during development, and the modulation of these events in cancer, are used to illustrate how the inappropriate localization of the complex could contribute to tumour biology.

DNA methylation prevents CTCF-mediated silencing of the oncogene BCL6 in B cell lymphomas.

Aberrant DNA methylation commonly occurs in cancer cells where it has been implicated in the epigenetic silencing of tumor suppressor genes. Additional roles for DNA methylation, such as transcriptional activation, have been predicted but have yet to be clearly demonstrated. The BCL6 oncogene is implicated in the pathogenesis of germinal center-derived B cell lymphomas. We demonstrate that the intragenic CpG islands within the first intron of the human BCL6 locus were hypermethylated in lymphoma cells that expressed high amounts of BCL6 messenger RNA (mRNA). Inhibition of DNA methyltransferases decreased BCL6 mRNA abundance, suggesting a role for these methylated CpGs in positively regulating BCL6 transcription. The enhancer-blocking transcription factor CTCF bound to this intronic region in a methylation-sensitive manner. Depletion of CTCF by short hairpin RNA in neoplastic plasma cells that do not express BCL6 resulted in up-regulation of BCL6 transcription. These data indicate that BCL6 expression is maintained during lymphomagenesis in part through DNA methylation that prevents CTCF-mediated silencing.

Pertussis toxin-sensitive G proteins regulate lymphoid lineage specification in multipotent hematopoietic progenitors.

Lymphoid and myeloid lineage segregation is a major developmental step during early hematopoiesis from hematopoietic stem cells. It is not clear, however, whether multipotent progenitors (MPPs) adopt a lymphoid or myeloid fate through stochastic mechanisms, or whether this process can be regulated by extracellular stimuli. In this study, we show that lymphoid lineage specification occurs in MPPs before lymphoid lineage priming, during which MPPs migrate from the proximal to the distal region relative to the endosteum of the bone marrow. Lymphoid-specified MPPs have low myeloid differentiation potential in vivo, but potently differentiate into myeloid cells in vitro. When treated with pertussis toxin, an inhibitor of G protein-coupled receptor signaling, lymphoid-specified MPPs regain in vivo myeloid potential, and their localization is dispersed in the bone marrow. These results clearly demonstrate that specific microenvironments that favorably support lymphoid or myeloid lineage development exist at structurally distinct regions in the bone marrow.

T and B lymphocyte differentiation from hematopoietic stem cell.

Until the past few years, it has been thought that lymphoid and myeloid lineage segregation represents the first step of lineage restriction during hematopoiesis from hematopoietic stem cell. Recent investigation of the cell populations within multipotent progenitors in the bone marrow has led to new understanding of how hematopoietic stem cells diversify into different hematopoietic cell types. This review focuses on the recent advances in understanding the developmental events that occur during hematopoietic stem cell specification into the T and B lymphocyte lineages in adult mice.

IL-7 specifies B cell fate at the common lymphoid progenitor to pre-proB transition stage by maintaining early B cell factor expression.

IL-7 plays a critical role in B cell fate decision by regulating early B cell factor (EBF) expression. However, it was not clear when IL-7 stimulation is necessary in hemato-/lymphopoiesis in adult mice. Here we show that pre-proB cells derived from IL-7-/- mice have lost B cell potential, despite up-regulation of EBF expression following IL-7 stimulation. Pre-proB cells from wild-type mice can give rise to proB cells in the absence of IL-7. In this case, EBF up-regulation during the transition from the pre-proB to proB stages occurs normally. In contrast, EBF expression by IL-7-/- pre-proB cells after IL-7 stimulation is approximately 20 times lower than wild-type pre-proB cells. In addition, only multipotent progenitors with higher levels of ectopic EBF can give rise to proB cells in the absence of IL-7. Therefore, the primary function of IL-7 before the pre-proB stage in B cell development is to maintain the EBF expression level above a certain threshold, which is necessary for pre-proB cells to further transit to the proB stage.

Identification of a bone marrow precursor of the earliest thymocytes in adult mouse.

The thymus requires continuous replenishment of progenitors from the bone marrow (BM) to sustain T cell development. However, it remains unclear which hematopoietic progenitors downstream from hematopoietic stem cells in the BM home to the thymus in adult mice. In this work, we demonstrate that although multiple BM populations have intrinsic T lineage differentiation potential, a small subset of multipotent progenitors (MPPs) expressing CCR9 preferentially homes to the thymus. These CCR9(+) MPPs are phenotypically similar to the most immature early T lineage progenitors (ETPs) in the thymus and are present in the peripheral blood. Similar to ETPs, CCR9(+) MPPs undergo Notch signaling, as indicated by higher expression of Notch1 and downstream target Hes1 genes compared with other MPP subsets. Furthermore, CCR9(+) MPPs possess differentiation potential similar to that of ETPs, with very limited granulocyte/macrophage differentiation potential, but they can differentiate into T, B, and dendritic cells. These characteristics implicate CCR9(+) MPPs as the BM precursors of the earliest thymic progenitors. In addition, our data suggest that before transition from BM to thymus, MPPs are lymphoid-specified and primed for T lineage differentiation.

Asymmetrical lymphoid and myeloid lineage commitment in multipotent hematopoietic progenitors.

The mechanism of lineage commitment from hematopoietic stem cells (HSCs) is not well understood. Although commitment to either the lymphoid or the myeloid lineage is popularly viewed as the first step of lineage restriction from HSCs, this model of hematopoietic differentiation has recently been challenged. The previous identification of multipotent progenitors (MPPs) that can produce lymphocytes and granulocyte/macrophages (GMs) but lacks erythroid differentiation ability suggests the existence of an alternative HSC differentiation program. Contribution to different hematopoietic lineages by these MPPs under physiological conditions, however, has not been carefully examined. In this study, we performed a refined characterization of MPPs by subfractionating three distinct subsets based on Flt3 and vascular cell adhesion molecule 1 expression. These MPP subsets differ in their ability to give rise to erythroid and GM lineage cells but are equally potent in lymphoid lineage differentiation in vivo. The developmental hierarchy of these MPP subsets demonstrates the sequential loss of erythroid and then GM differentiation potential during early hematopoiesis. Our results suggest that the first step of lineage commitment from HSCs is not simply a selection between the lymphoid and the myeloid lineage.

Antagonistic effect of CCAAT enhancer-binding protein-alpha and Pax5 in myeloid or lymphoid lineage choice in common lymphoid progenitors.

Lymphoid lineage-committed progenitors, such as common lymphoid progenitors (CLPs), maintain a latent myeloid differentiation potential, which can be initiated by stimulation through exogenously expressed cytokine receptors, including IL-2 receptors. Here we show that the transcription factor CCAAT enhancer-binding protein-alpha (C/EBPalpha) is promptly up-regulated in CLPs upon ectopic IL-2 stimulation. Enforced C/EBPalpha expression is sufficient to initiate myeloid differentiation from CLPs, as well as from proT and proB cells, even though proB cells do not give rise to myeloid cells after ectopic IL-2 stimulation. Expression of Pax5, a B lymphoid-affiliated transcription factor, is completely suppressed by enforced C/EBPalpha but not by ectopic IL-2 stimulation in proB cells. Introduction of Pax5 blocks ectopic IL-2 receptor-mediated myeloid lineage conversion in CLPs. These data suggest that C/EBPalpha is a proximal target of cytokine-induced lineage conversion in lymphoid progenitors. Furthermore, complete loss of Pax5 expression triggered by up-regulation of C/EBPalpha is a critical event for lineage conversion from lymphoid to myeloid lineage in CLPs and proB cells.

Heterogeneity of Flt3-expressing multipotent progenitors in mouse bone marrow.

Mechanisms of lymphoid and myeloid lineage choice by hemopoietic stem cells remain unclear. In this study we show that the multipotent progenitor (MPP) population, which is immediately downstream of hemopoietic stem cells, is heterogeneous and can be subdivided in terms of VCAM-1 expression. VCAM-1(+) MPPs were fully capable of differentiating into both lymphoid and myeloid lineages. In contrast, VCAM-1(-) MPPs gave rise to lymphocytes predominately in vivo. T and B cell development from VCAM-1(-) MPPs was 1 wk faster than that from VCAM-1(+) MPPs. Furthermore, VCAM-1(+) MPPs gave rise to common myeloid progenitors and VCAM-1(-) MPPs in vivo, indicating that VCAM-1(-) MPPs are progenies of VCAM-1(+) MPPs. VCAM-1(-) MPPs, in turn, developed into lymphoid lineage-restricted common lymphoid progenitors. These results establish a hierarchy of developmental relationship between MPP subsets and lymphoid and myeloid progenitors. In addition, VCAM-1(+) MPPs may represent the branching point between the lymphoid and myeloid lineages.

IL-7 receptor signaling is necessary for stage transition in adult B cell development through up-regulation of EBF.

Cytokine receptor signals have been suggested to stimulate cell differentiation during hemato/lymphopoiesis. Such action, however, has not been clearly demonstrated. Here, we show that adult B cell development in IL-7(-/-) and IL-7R alpha(2/-) mice is arrested at the pre-pro-B cell stage due to insufficient expression of the B cell-specific transcription factor EBF and its target genes, which form a transcription factor network in determining B lineage specification. EBF expression is restored in IL-7(-/-) pre-pro-B cells upon IL-7 stimulation or in IL-7R alpha(-/-) pre-pro-B cells by activation of STAT5, a major signaling molecule downstream of the IL-7R signaling pathway. Furthermore, enforced EBF expression partially rescues B cell development in IL-7R alpha(-/-) mice. Thus, IL-7 receptor signaling is a participant in the formation of the transcription factor network during B lymphopoiesis by up-regulating EBF, allowing stage transition from the pre-pro-B to further maturational stages.