Mechanisms Underlying Functional Programs of Tumor-Associated Macrophages

描述（申请人提供）：尽管手术和全身治疗，许多乳腺癌患者因转移而复发。临床结果如此糟糕的一个原因与目前了解乳腺癌生物学的方法有关。目前的范例不成比例地集中在肿瘤发生的内在遗传和表观遗传变化上。然而，很明显，肿瘤细胞与宿主的相互作用促进了恶性进展。大量研究表明，乳腺肿瘤微环境的显性细胞外源性成分是巨噬细胞，称为肿瘤相关巨噬细胞（TAM）。虽然高TAM密度与较差的预后相关，但这并不表明TAM总是促肿瘤发生。事实上，与TAM浸润较少的患者相比，TAM密度高的患者的寿命明显延长。这种功能二分法引入了一个概念，即tam可以重新分类为M1（肿瘤抑制）或M2（肿瘤促进）亚型，让人想起CD4+ Th1-Th2范式。值得注意的是，目前人类tam的鉴定是基于单一表型标记CD68的表达，这不足以区分功能多样性。因此，我们将验证TAM表型反映M1和M2亚型的平衡的新假设，这是由IRF8的表达决定的，IRF8是一个关键的骨髓依赖性转录因子。与其他IRF成员不同，IRF8参与骨髓形成的不同阶段，是抗肿瘤免疫所必需的细胞因子/趋化因子（如IL-12， IL-18, CCL5）不可或缺的。研究IRF8在TAM生物学中的地位的另一个理由是基于我们最近在髓源性抑制细胞（MDSC）生物学方面的工作，这是一种新发现的促进肿瘤的髓系细胞群。在这里，我们发现IRF8的表达显著抑制MDSC的扩张，这与IRF8在骨髓形成中的作用模式一致。为了验证我们的中心假设，我们提出了三个目标：1)确定小鼠乳腺肿瘤模型中IRF8表达与TAM表型之间的因果关系；2)确定极化细胞因子信号如何阻碍或抑制IRF8的表达从而影响TAM表型；3)确定将人tam分层为表达IRF8hi和irf8lo亚型是否能提高乳腺癌的预后意义。总之，我们认为将tam分离为反映不同irf8反应性的亚型不仅可以为其功能多样性提供机制基础，还可以为跟踪患者预后提供新的方法。

DESCRIPTION (provided by applicant): Despite surgery and systemic treatment, many breast cancer patients relapse due to metastasis. One reason for such poor clinical outcomes concerns current approaches to understanding breast cancer biology. Current paradigms are disproportionately focused on intrinsic genetic and epigenetic changes underlying tumorigenesis. However, it has become clear that tumor cell interactions with the host facilitate malignant progression. Extensive studies reveal that a dominant cell-extrinsic element of the breast tumor microenvironment is the macrophage, termed tumor-associated macrophage (TAM). Although high TAM densities have been associated with a poorer prognosis, this does not indicate that TAMs are always pro-tumorigenic. In fact, proportions of patients with high TAM densities exhibit significant longevity compared to those with little TAM infiltration. This functional dichotomy introduces the notion that TAMs can be reclassified into M1 (tumor-suppressing) or M2 (tumor-promoting) subtypes reminiscent of the CD4+ Th1-Th2 paradigm. It is noteworthy that current identification of human TAMs is based on the expression of a single phenotypic marker, CD68, which is inadequate to distinguish functional diversity. Thus, we will test the novel hypothesis that TAM phenotype reflects the balance of M1 to M2 subtypes, which is determined by expression of IRF8, a key myeloid-dependent transcription factor. IRF8, unlike other IRF members is involved in diverse stages of myelopoiesis and is indispensable for cytokines/chemokines (e.g., IL-12, IL-18, CCL5) essential for antitumor immunity. Additional rationale for exploring IRF8 status in TAM biology is based on our recent work in myeloid-derived suppressor cells (MDSC) biology, a newly identified tumor-promoting myeloid population. Here, we showed that IRF8 expression significantly inhibited MDSC expansion, consistent with the mode of action of IRF8 in myelopoiesis. To test our central hypothesis, we propose three aims: 1) to determine the causal link between IRF8 expression and TAM phenotype in mouse mammary tumor models; 2) to determine how polarizing cytokine signals impede or repress IRF8 expression to impact TAM phenotype; and 3) to determine whether stratification of human TAMs into IRF8hi and IRF8lo-expressing subtypes improves prognostic significance in breast cancer. Altogether, we posit that separation of TAMs into subtypes reflecting distinct IRF8-reactivities will not only offer a mechanistic basis for their functional diversity, but also illuminate new ways to track patient outcomes.