scholarly journals Tertiary lymphoid structures induced by CXCL13-producing CD4+ T cells increase tumor infiltrating CD8+ T cells and B cells in ovarian cancer

2021 ◽  
Author(s):  
Masayo Ukita ◽  
Junzo Hamanishi ◽  
Hiroyuki Yoshitomi ◽  
Koji Yamanoi ◽  
Shiro Takamatsu ◽  
...  
Keyword(s):  
Gene Expression ◽  
Ovarian Cancer ◽  
T Cells ◽  
B Cells ◽  
Tumor Microenvironment ◽  
Mouse Model ◽  
Tumor Infiltrating Lymphocytes ◽  
Tertiary Lymphoid Structures ◽  
Lymphoid Structures

Background: Tertiary lymphoid structures (TLSs) are transient ectopic lymphoid aggregates whose formation might be caused by chronic inflammation states, such as cancer. The presence of TLS is associated with a favorable prognosis in most solid malignancies. The recognition of the relevance of TLS to cancer has led to a growing interest in TLS as an immunomodulatory target to enhance tumor immunity, although how TLSs are induced in the tumor microenvironment (TME) and how they affect patient survival are not well understood. Methods: TLS distribution in relation to tumor infiltrating lymphocytes (TILs) and related gene expression were investigated in high grade serous ovarian cancer (HGSC) specimens. CXCL13 expression, which is strongly associated with TLS, and its localization in immune cells, were examined. We explored the tumor microenvironment for CXCL13 secretion by adding various inflammatory cytokines in vitro. The induction of TLS by CXCL13 was examined in a mouse model of ovarian cancer. Results: CXCL13 gene expression correlated with TLS formation and the infiltration of T cells and B cells, and was a favorable prognostic factor for HGSC patients. The coexistence of CD8+ T cells and B-cell lineages in the TME was associated with a better prognosis of HGSC and was closely related to the presence of TLSs. CXCL13 expression was predominantly coincident with CD4+ T cells in TLSs and CD8+ T cells in TILs, and shifted from CD4+ T cells to CD21+ follicular dendritic cells as the TLS matured. Although TGF-β was reported to stimulate CXCL13 production, our in vitro results revealed that CXCL13 secretion was promoted in CD4+ T cells under TGF-β + IL-2-restricted conditions and in CD8+ T cells under TGF-β + IL-12-rich conditions. In a mouse model of ovarian cancer, recombinant CXCL13 induced TLSs and enhanced survival by the infiltration of CD8+ T cells. Conclusions: TLS formation was promoted by CXCL13-producing CD4+ T cells and TLSs facilitated the coordinated antitumor responses of cellular and humoral immunity in ovarian cancer.

scholarly journals Tertiary Lymphoid Structures as a Predictive Biomarker of Response to Cancer Immunotherapies

2021 ◽  
Vol 12 ◽  
Author(s):  
Marta Trüb ◽  
Alfred Zippelius
Keyword(s):  
T Cells ◽  
B Cells ◽  
B Cell ◽  
Tumour Response ◽  
Predictive Biomarker ◽  
Exciting Field ◽  
Inflammatory Conditions ◽  
Tertiary Lymphoid Structures ◽  
Lymphoid Structures ◽  
Cancer Immunotherapies

Tertiary lymphoid structures (TLS) are ectopic lymphoid formations which are formed under long-lasting inflammatory conditions, including tumours. TLS are composed predominantly of B cells, T cells and dendritic cells, and display various levels of organisation, from locally concentrated aggregates of immune cells, through clearly defined B cell follicles to mature follicles containing germinal centres. Their presence has been strongly associated with improved survival and clinical outcome upon cancer immunotherapies for patients with solid tumours, indicating potential for TLS to be used as a prognostic and predictive factor. Although signals involved in TLS generation and main cellular components of TLS have been extensively characterised, the exact mechanism by which TLS contribute to the anti-tumour response remain unclear. Here, we summarise the most recent development in our understanding of their role in cancer and in particular in the response to cancer immunotherapy. Deciphering the relationship between B cells and T cells found in TLS is a highly exciting field of investigation, with the potential to lead to novel, B-cell focused immunotherapies.

scholarly journals Qualitative Analysis of Tumor-Infiltrating Lymphocytes across Human Tumor Types Reveals a Higher Proportion of Bystander CD8+ T Cells in Non-Melanoma Cancers Compared to Melanoma

Cancers ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3344
Author(s):  
Aishwarya Gokuldass ◽  
Arianna Draghi ◽  
Krisztian Papp ◽  
Troels Holz Borch ◽  
Morten Nielsen ◽  
...  
Keyword(s):  
Ovarian Cancer ◽  
T Cells ◽  
T Cell ◽  
Tumor Infiltrating Lymphocytes ◽  
Autologous Tumor ◽  
Epithelial Cancers ◽  
Single Cell Rna Sequencing ◽  
Tumor Types ◽  
Infiltrating Lymphocytes

Background: Human intratumoral T cell infiltrates can be defined by quantitative or qualitative features, such as their ability to recognize autologous tumor antigens. In this study, we reproduced the tumor-T cell interactions of individual patients to determine and compared the qualitative characteristics of intratumoral T cell infiltrates across multiple tumor types. Methods: We employed 187 pairs of unselected tumor-infiltrating lymphocytes (TILs) and autologous tumor cells from patients with melanoma, renal-, ovarian-cancer or sarcoma, and single-cell RNA sequencing data from a pooled cohort of 93 patients with melanoma or epithelial cancers. Measures of TIL quality including the proportion of tumor-reactive CD8+ and CD4+ TILs, and TIL response polyfunctionality were determined. Results: Tumor-specific CD8+ and CD4+ TIL responses were detected in over half of the patients in vitro, and greater CD8+ TIL responses were observed in melanoma, regardless of previous anti-PD-1 treatment, compared to renal cancer, ovarian cancer and sarcoma. The proportion of tumor-reactive CD4+ TILs was on average lower and the differences less pronounced across tumor types. Overall, the proportion of tumor-reactive TILs in vitro was remarkably low, implying a high fraction of TILs to be bystanders, and highly variable within the same tumor type. In situ analyses, based on eight single-cell RNA-sequencing datasets encompassing melanoma and five epithelial cancers types, corroborated the results obtained in vitro. Strikingly, no strong correlation between the proportion of CD8+ and CD4+ tumor-reactive TILs was detected, suggesting the accumulation of these responses in the tumor microenvironment to follow non-overlapping biological pathways. Additionally, no strong correlation between TIL responses and tumor mutational burden (TMB) in melanoma was observed, indicating that TMB was not a major driving force of response. No substantial differences in polyfunctionality across tumor types were observed. Conclusions: These analyses shed light on the functional features defining the quality of TIL infiltrates in cancer. A significant proportion of TILs across tumor types, especially non-melanoma, are bystander T cells. These results highlight the need to develop strategies focused on the tumor-reactive TIL subpopulation.

scholarly journals The relationship of the tertiary lymphoid structures with the tumor-infiltrating lymphocytes and its prognostic value in gastric cancer

2021 ◽  
Author(s):  
Nana Zhang ◽  
Guanjun Zhang ◽  
Depu Wang ◽  
Hao Liu ◽  
Yuchi Zhang ◽  
...  
Keyword(s):  
Gastric Cancer ◽  
T Cells ◽  
Prognostic Value ◽  
Tumor Infiltrating Lymphocytes ◽  
High Endothelial Venules ◽  
Tumor Center ◽  
Tertiary Lymphoid Structures ◽  
Lymphoid Structures ◽  
Infiltrating Lymphocytes ◽  
The Relationship

IntroductionTo explore the relationship between the tertiary lymphoid structures (TLSs) and tumor-infiltrating lymphocytes (TILs), and their distribution characteristics as well as the prognostic value in gastric cancer (GC).Material and methodsThe TLSs and four subtypes of TILs were assessed by immunohistochemistry (IHC) staining. The presence of MECA-79 positive high endothelial venules (HEVs) identified among the ectopic lymphocyte aggregation area in the GC tissue was defined as a valid TLSs.The number of labeled TILs were observed in 5 fields of the most positive cells in tumor center, invasive edge and within the TLSs, respectively, at a field of vision×40.ResultsThe TLSs distributed significantly higher in the tumor invasive edge than the tumor center (P <0.001). Similarly, the infiltrating density of CD8+T cells and GrB+T cells were highly distributed in the tumor infiltrating edge than the tumor center. While the total number of TILs and the FOXP3+T cells were on the contrary. There was a positive correlation between the density of TLSs and TILs either in the location or the immune phenotype. And a higher frequency of TILs and TLSs often associated with the favorable clinicopathologic parameters. Multivariate analysis revealed that the density of TILs (P= 0.019) and TLSs (P= 0.037) were the independent prognostic predictor for GC patients.ConclusionsThe formation of TLSs predicts an advantageous immune system function and can be considered as a novel biomarker to stratify the overall survival risk of untreated GC patients and as a marker of efficient immunotherapies.

scholarly journals Pattern of Tumor-Infiltrating Lymphocytes in Mixed Epithelial and Stromal Tumor of the Kidney: A Review of Five Cases

Cells ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 917
Author(s):  
Hye Won Lee ◽  
Hyunwoo Lee ◽  
Chanho Park ◽  
Won Joon Oh ◽  
Tae Jin Kim ◽  
...  
Keyword(s):  
T Cells ◽  
Flow Cytometric Analysis ◽  
Γδ T Cells ◽  
Tumor Infiltrating Lymphocytes ◽  
Stromal Tumor ◽  
Effector Memory ◽  
Mullerian Ducts ◽  
Tertiary Lymphoid Structures ◽  
Lymphoid Structures ◽  
Infiltrating Lymphocytes

Mixed epithelial and stromal tumor of the kidney (MESTK), a benign rare tumor with malignant transformation potential, is thought to be derived from fetal or immature cells originating from the mesonephric and Müllerian ducts. However, due to its rarity, little is known about the anti-tumor immune responses in MESTK. Herein, we present five cases of MESTK and evaluate the population of tumor-infiltrating lymphocytes (TILs) using a freshly obtained MESTK sample. Microscopically, TILs were scattered or clustered in large aggregates in the stroma in all five cases; furthermore, three cases exhibited heavy, large lymphocytic aggregates with no well-organized tertiary lymphoid structures with germinal centers. Flow cytometric analysis of TILs in one freshly obtained MESTK sample revealed that >40% of CD3+ T cells were effector memory Fas+CD28− γδ T cells expressing high levels of programmed cell death protein 1 and inducible T-cell co-stimulator, but low levels of CD44 and CD27. Most αß T cells exhibited a naïve phenotype. Additionally, we detected many activated class-switched CD21+CD27+ B cells as well as CD11chighIgMhigh marginal zone B-like and CD27−CD21−CD23− immunoglobulin (Ig)DhighIgMlow age-associated B-like cells. Collectively, for the first time, we report the immune microenvironment pattern of MESTK to oncogenic stress.

Neoadjuvant Chemotherapy Modulates the Tumor Microenvironment in High-Grade Serous Ovarian Cancer

2021 ◽  
Author(s):  
Zhongling Zhuo ◽  
Min Tang ◽  
Hexin Li ◽  
Lili Zhang ◽  
Bingqing Han ◽  
...  
Keyword(s):  
Gene Expression ◽  
Ovarian Cancer ◽  
T Cells ◽  
Survival Analysis ◽  
Tumor Microenvironment ◽  
Neoadjuvant Chemotherapy ◽  
Mapk Pathway ◽  
Treatment Options ◽  
High Grade ◽  
Serous Ovarian Cancer

Abstract Background While surgical reduction with adjuvant chemotherapy is the traditional treatment for high-grade serous ovarian cancer (HGSOC), neoadjuvant chemotherapy (NACT) has increasingly been applied. This work aims to investigate the expression profiles before and after NACT, explore changes in the tumor microenvironment, expand current treatments, and design a combination of treatment options for patients. Methods We downloaded 326 pre-NACT RNA sequencing data and 37 matched pre- and post-NACT samples from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. Differentially expressed genes (DEGs) were determined with EdgeR, and Gene Ontology analysis was performed to identify the clusters responsible for the biological processes and pathways of HGSOC. Immune infiltration was analyzed using Single-sample Gene Set Enrichment Analysis (ssGSEA) and CIBERSORT. Kaplan-Meier (KM) survival analysis was performed to assess prognosis, and the potential correlations between modules and phenotypes were explored using weighted gene co-expression network analysis (WGCNA). Results After NACT, a total of 352 genes showed significant changes in RNA expression, among which 180 genes were up-regulated and 172 down-regulated. The most influential pathway was the positive regulation of mitogen-activated protein kinase (MAPK) cascade. Correlation analysis and KM survival analysis showed that overexpression of MAPK cascade genes correlated with shorter survival time in HGSOC patients. ssGSEA results showed that the expressions of anti-tumor cells (central memory CD4+ T cell and central memory CD8+ T cell) and pro-tumor cells (neutrophil and dendritic cells) were significantly increased after NACT. CIBERSORT showed that the abundances of memory B cells, NK cells, and monocytes were increased and the abundance of plasma cells was decreased after NACT. WGCNA and KM survival analysis showed that a lower abundance of Regulatory T cells (Tregs) was correlated with a better prognosis. Conclusions Gene expression of the MAPK pathway is up-regulated and the abundance of CD4+ T regulation cell decreases after NACT. Thus, the MAPK pathway may promote the differentiation of CD4+ T cells into Th17 cells while inhibiting Tregs development. The inhibited Tregs' development can lead to a better prognosis. Therefore, it is speculated that Tregs inhibitors combined with platinum-based NACT are potential treatment options for HGSOC.

536 Divergent cancer etiologies drive distinct B cell signatures and tertiary lymphoid structures in head and neck cancer

2020 ◽  
Vol 8 (Suppl 3) ◽  
pp. A572-A572
Author(s):  
Ayana Ruffin ◽  
Anthony Cillo ◽  
Tracy Tabib ◽  
Angen Liu ◽  
Sayali Onkar ◽  
...  
Keyword(s):  
T Cells ◽  
B Cells ◽  
B Cell ◽  
Head And Neck ◽  
Germinal Center ◽  
Spectral Unmixing ◽  
Cell Phenotype ◽  
Primary Tumors ◽  
Tertiary Lymphoid Structures ◽  
Lymphoid Structures

BackgroundCurrent FDA-approved immunotherapies aim to reinvigorate CD8+ T cells, but the contribution of the humoral arm of the immune response in human cancer remains poorly understood. B cells within tissues can mediate anti-tumor immunity and regulate immune responses by presenting antigen and producing tumor-specific antibodies and immunomodulatory cytokines. Head and neck squamous cell carcinoma (HNSCC) can be induced by human papillomavirus (HPV+) and carcinogens such as tobacco and alcohol (HPV-), and the immune infiltrate is quite distinct in the two etiologies, in particular, increased B cells in HPV+ HNSCC patients. Further, increased B cells in HNSCC patients correlate with improved patient survival. Our study seeks to differentiate B cell phenotype, function and location in HPV+ and HPV- HNSCC to identify putative B cell-centric immunotherapeutic targets.MethodsWe utilized a multi-level approach to clearly categorize B cells in HNSCC patients. Single cell RNA sequencing (scRNAseq) was performed on CD45+ tumor infiltrating lymphocytes (TIL) from HPV+ and HPV- HNSCC patients. HNSCC TIL and PBL were stained via spectral cytometry (Cytek Aurora,25 parameters) for unbiased analysis of B cell subsets via computational spectral unmixing. Paraffin embedded slides from HNSCC primary tumors were utilized for multispectral immunofluorescence (mIF) to identify tertiary lymphoid structures (TLS) and identify differences in HPV+ and HPV- disease.ResultsWe demonstrated distinct trajectories for B cells in HPV+ and HPV- disease. HPV- HNSCC tumors mainly contained memory B cells and plasma cells, while the B cells in HPV+ HNSCC were naïve and germinal center (GC). Further, we quantified B cells and CD4+ T cells in TLS, and germinal center-like TLS were associated with improved outcome in HPV+ disease. We also observed that transcriptional and protein expression of Semaphorin A (SEMA4a) was restricted to GC B cells and increased on GC B cells in HNSCC patients compared to healthy tonsils. Additionally, we identified distinct waves of gene expression in GC B cells in HNSCC tumors, ultimately revealing a novel transitional state for GC B cells in the tumor microenvironment (TME).ConclusionsUnderstanding B cell function in human cancers and how different TMEs influence B cells and TLS are important for devising novel therapeutic options for cancer patients. Ultimately, development of therapeutics to enhance B cell responses in the TME should be prioritized as a compliment to T-cell mediated therapies.

scholarly journals CXCL13 shapes immunoactive tumor microenvironment and enhances the efficacy of PD-1 checkpoint blockade in high-grade serous ovarian cancer

2021 ◽  
Vol 9 (1) ◽  
pp. e001136
Author(s):  
Moran Yang ◽  
Jiaqi Lu ◽  
Guodong Zhang ◽  
Yiying Wang ◽  
Mengdi He ◽  
...  
Keyword(s):  
Ovarian Cancer ◽  
T Cells ◽  
B Cells ◽  
Tumor Microenvironment ◽  
Immune Checkpoint ◽  
Ex Vivo ◽  
Immune Checkpoint Blockade ◽  
Checkpoint Blockade ◽  
High Grade ◽  
Serous Ovarian Cancer

BackgroundMost patients with high-grade serous ovarian cancer (HGSC) lack an effective response to immune checkpoint blockade, highlighting the need for more knowledge about what is required for successful treatment. As follicular cytotoxic CXCR5+CD8+ T cells are maintained by reinvigoration by immune checkpoint blockade in tumors, we attempted to reveal the relationship between CXCR5+CD8+ T cells and the tumor microenvironment to predict immunotherapy responses in HGSC.Methods264 patients with HGSC from two cohorts and 340 HGSC cases from The Cancer Genome Atlas cohort were enrolled. Ex vivo and in vivo studies were conducted with human HGSC tumors and murine tumor models. The spatial correlation between CXC-chemokine ligand 13 (CXCL13), CXCR5, CD8, and CD20 was evaluated by immunohistochemistry and immunofluorescence. Survival was compared between different subsets of patients using Kaplan-Meier analysis. The therapeutic effect of CXCL13 and programmed cell death-1 (PD-1) blockade was validated using human HGSC tumors and murine models.ResultsHigh CXCL13 expression was associated with prolonged survival. Tumors with high CXCL13 expression exhibited increased infiltration of activated and CXCR5-expressing CD8+ T cells. Incubation with CXCL13 facilitated expansion and activation of CXCR5+CD8+ T cells ex vivo. CXCR5+CD8+ T cells appeared in closer proximity to CXCL13 in tumors and chemotaxis towards CXCL13 in vitro. The combination of CXCL13, CXCR5, and CD8+ T cells was an independent predictor for survival. In addition, CXCL13 was associated with clusters of CD20+ B cells. CD20+ B cells predicted better patient survival in the presence of CXCL13. Histological evaluation highlighted colocalization of CXCL13 with tertiary lymphoid structures (TLSs). TLSs carried prognostic benefit only in the presence of CXCL13. CXCL13 in combination with anti-PD-1 therapy retarded tumor growth in a CD8+ T-cell-dependent manner, resulting in increased infiltration of cytotoxic CD8+ T cells and CXCR5+CD8+ T cells.ConclusionsThese data define a critical role of CXCL13 in shaping antitumor microenvironment by facilitating the maintenance of CXCR5+CD8+ T cells in TLSs and support a clinical investigation for a combination of CXCL13 and PD-1 blockade therapy in HGSC.

scholarly journals 47 Tertiary lymphoid structures (TLS) in desmoplastic melanomas (DM) differ from non-DM-associated TLS by their intratumoral location and enhanced immune activity

2021 ◽  
Vol 9 (Suppl 3) ◽  
pp. A54-A54
Author(s):  
Ileana Mauldin ◽  
Anne Stowman ◽  
Alexandra Hickman ◽  
Adela Mahmutovic ◽  
Alejandro Gru ◽  
...  
Keyword(s):  
T Cells ◽  
B Cells ◽  
B Cell ◽  
Cell Function ◽  
Immune Activity ◽  
Close Proximity ◽  
Tertiary Lymphoid Structures ◽  
Lymphoid Structures ◽  
Maturation State ◽  
Immunologic Activity

BackgroundTertiary lymphoid structures (TLS) are ectopic lymphoid organs that are localized near tumors and other sites of inflammation, and are commonly believed to support antitumor immunity. We previously published studies that show that most desmoplastic melanomas contain TLS, and that TLS in cutaneous metastatic melanomas varied widely in maturation state, in proportions of proliferating T and B cells, and in markers of B cell function, including AID and CD21. Thus, we hypothesized that there may be diversity in TLS function, or immunologic activity, among melanomas. To address this hypothesis, we evaluated TLS in primary desmoplastic melanomas (DM), and non-desmoplastic melanomas (non-DM) for markers of cell proliferation which are indicative of early immune activity.MethodsDM and non-DM tumor specimens, which included primary melanomas (PM), and cutaneous metastatic melanomas (CMM), were evaluated for TLS by multiplex Immunofluorescence histology, by staining for CD20, CD8, PNAd, Ki67, FoxP3, and DAPI. Lymphoid aggregates were identified in 20x spectrally unmixed images by visual inspection and identified as TLS if possessing organized T-cell and B-cell regions in addition to high endothelial venule-like vasculature (PNAd+). TLS were identified in 30 out of 64 screened (48%) CMM, 4/4 non-DM PM, and 8 out of 11 screened (73%) DM. Immune cells localized in TLS were enumerated using Halo software (Indica Labs). Mann-Whitney tests were used for statistical assessments.ResultsDM commonly contain a dense network of fibroblasts and associated stroma, which are not typical for other non-DM (PM and CMM). TLS in DM are located throughout the tumors, intratumorally, in sharp distinction from the peritumoral location of TLS in non-DM. Furthermore, when compared to TLS of non-DM (PM and CMM), TLS of DM contain increased densities of CD20+ B cells (PM p=0.007; CMM p<0.0001) and CD8+ T cells (PM p=0.017; CMM p=0.0006), and a higher proportion of proliferating (Ki67+) CD20+ B cells (PM p=0.04; CMM p=0.009).ConclusionsRecently published studies have identified tumor-associated fibroblasts as the likely initiating cells for TLS formation in murine melanomas. The intratumoral location of TLS in DM puts them in close proximity to the dense fibroblasts and desmoplastic stroma in these tumors, which may be responsible for their intratumoral location. The increased density of B and T cells, and higher proportion of proliferating (Ki67+) B cells, in DM than in non-DM, suggests that there may be greater immune activation, increased germinal center maturation, or less regulation in TLS of DM.Ethics ApprovalApproval was obtained for these studies under IRB protocol #’s 10598 and 19694.

PU.1 Is a Critical Downstream Target of AML1.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 358-358 ◽  
Author(s):  
Gang Huang ◽  
Pu Zhang ◽  
Steffen Koschmieder ◽  
Joseph D. Growney ◽  
D. Gary Gilliland ◽  
...  
Keyword(s):  
Gene Expression ◽  
Bone Marrow ◽  
T Cells ◽  
B Cells ◽  
Fetal Liver ◽  
Proximal Region ◽  
Specific Gene ◽  
Hematopoietic Stem

Abstract PU.1 is expressed in hematopoietic stem cells (HSC), progenitors and differentiating blood cells except terminally differentiated T cells, erythrocytes and megakaryocytes. PU.1 is required for commitment of HSC to multiple lineages. PU.1 −/− embryos die perinatally and fail to generate myeloid and B cells. We previously reported that a DNase I hypersensitive site located 14 kb upstream of the PU.1 transcription start site (−14 DHS) confers myelomonocytic specific gene expression. Targeted deletion this DHS fragment in mice results in a decrease in PU.1 expression in bone marrow to 20% of wild type levels, subsequently leading to a profound decrease in macrophages and B cells. Within the DHS fragment is a “core” consisting of a distal (296bp) and a proximal (253bp) region, which are highly conserved among different species. The PU.1 promoter by itself cannot direct gene expression in vivo. However, −14 DHS confers to the promoter the ability to direct expression of a reporter gene in granulocytes, monocytes, and B-cells of transgenic mice. The proximal region can itself direct high-level gene expression. The proximal region contains 3 AML1 sites. These results, along with data indicating that PU.1 expression is selectively absent from Aml1 −/− embryos (Okada, et al, Oncogene. 1998), suggested that AML1 is likely to be upstream of PU.1. Electro-mobility gel shift assays and chromatin immunoprecipitation assays confirmed that AML1 binds to all 3 AML1 sites both in vitro and in vivo. Mutation of the 3 AML1 sites dramatically reduced the DHS activity of conferring gene expression. We used real time PCR to quantitatively measure PU.1 expression in both embryonic and adult hematopoiesis. We found that PU.1 expression was completely lost in the 9.5 dpc yolk sac, 10.5 dpc AGM and fetal liver of Aml1−/− embryos, suggesting that AML1 is required for PU.1 expression during embryonic hematopoiesis. To evaluate the effects of AML1 loss in the adult hematopoiesis, we employed a conditional Aml1 knockout allele in which LoxP flanked Aml1 (Aml1F/F) was excised by Mx1 promoter driven Cre expression following injection of pIpC. These mice show that Aml1 is not required for maturation of myeloid lineages in adult mice. However, these mice develop a mild myeloproliferative phenotype characterized by increasing in bone marrow and peripheral blood (PB) neutrophils, a 5 fold increasing in HSC, and 2–3 fold increasing myeloid progenitors. Spleen and liver contain infiltration by myeloid cells. These mice also display a dramatic decrease (~80%) in PB platelets and bone marrow megakaryocytes. Furthermore, there are significant blocks in lymphoid development, including reduced numbers of pre-B, pro-B and mature B cells, as well a block in T cell maturation at the DN2 (CD4−;CD8−;CD44+;CD25+) stage. We observed a 70% reduction of PU.1 expression in sorted HSC, progenitors, Gr1+/Mac1+ and B-cells from these mice relative to control mice. In contrast, upregulation of 3–5 fold expression in Ter119+, CD41+, and T cells in these mice compared to controls. Our data shows that PU.1 is a critical target gene of AML1, and AML1 regulates PU.1 in both positive and negative way. We are currently testing the ability of restoration of PU.1 expression to rescue specific defects in Aml1F/F; Tg (Mx1-cre) mice, as well as investigating the role of decreased PU.1 expression in human AML in which the function of AML1 is disrupted.

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