Antigen-Presenting Cell Control of CD8+ T Cell Exhaustion in Cancer

项目摘要 肿瘤反应性细胞毒性T淋巴细胞(CTL)通常进展为T细胞衰竭的功能障碍。 以程序性细胞死亡蛋白1(PD-1)的表达为标志，耗竭的T(TeX)细胞谱系是 PD-1低Tex祖细胞导致PD-1终末功能障碍的发育连续体 细胞。值得注意的是，免疫检查点阻断疗法能唤醒TeX祖细胞，但不能唤醒终末TeX细胞， 呼吁探索其分化机制和治疗干预手段。在小鼠身上 肿瘤模型，肿瘤发展诱导肿瘤相关巨噬细胞(TAMs)分化 与细胞的生成有关。转录组分析显示TAMS表现出共享 1型树突状细胞的特性，包括转录因子干扰素的表达 调节因子-8(IRF8)。IRF8促进将癌细胞抗原提呈给CD8+T细胞类似于 Dc1，但TAMs与Dc1在促进PD-1高表达方面有所不同。重要的是，巨噬细胞特异性缺失 IRF8抑制TeX细胞分化，抑制肿瘤生长。此外，人类的TAMS表达 的IRF8基因特征在多种癌症类型中追踪具有TeX细胞基因特征的特征。基于 这些发现，我们假设末端TeX细胞分化是由表达IRF8的TAMs和一个 耐受性抗原提呈细胞在肿瘤组织中的功能，以及这样一个-特克斯细胞调节轴 可作为新型癌症免疫治疗的靶点。为了验证这一假设，我们将首先确定IRF8是如何 TAMS的诱导，以及它如何促进的APC功能。通过进行染色质分析实验和 利用遗传小鼠模型，我们将评估丰富的转录因子BATF2是否使IRF8 通过+32KB IRF8增强子元件自动激活。IRF8基因缺陷的TAMs在获取癌细胞方面存在缺陷 抗原。利用巨噬细胞或癌细胞特异性缺失B2M基因的小鼠株系，我们将 研究IRF8是通过交叉呈现还是交叉穿戴促进获得抗原。 其次，我们将定义如何指定TAMS的致耐受功能，以及如何对其进行重新编程 接受治疗。与DC相比，TAM表达的白介素15水平更低，但表现出更高的水平 转化生长因子-b信号转导。通过产生巨噬细胞特异性的功能增减 在小鼠模型中，我们将探讨阻断转化生长因子-b信号是否逆转促血管生成素耐受的功能。 TAMS是否依赖IL-15，以及IL-15在巨噬细胞中的过度表达是否足以 在遗传模型和细胞治疗环境中诱导T细胞刺激的TAMs。与DC1相比，TAMs拥有 更小的单元格大小。我们将研究是否以及如何激活代谢调节因子哺乳动物靶标 雷帕霉素复合体1(MTORC1)将TAMs重新编程为免疫刺激APC。成功完成 该项目的实施不仅将产生对APC对癌症中Tex细胞分化的控制的机械性见解， 而且还指导了-TeX细胞调节轴的靶向，用于治疗广泛的恶性肿瘤。

Project Summary Tumor-reactive cytotoxic T lymphocytes (CTLs) often progress to dysfunction defined as T cell exhaustion. Marked by expression of the programmed cell death protein 1 (PD-1), the exhausted T (Tex) cell lineage is a developmental continuum wherein PD-1low Tex progenitors give rise to terminally dysfunctional PD-1high Tex cells. Notably, the immune checkpoint blockade therapy revives Tex progenitors, but not terminal Tex cells, calling for exploration of their differentiation mechanisms and means of therapeutic intervention. In a murine cancer model, tumor development induces differentiation of tumor-associated macrophages (TAMs) in association with generation of Tex cells. Transcriptome analysis revealed that TAMs exhibit shared characteristics with type 1 dendritic cells (DC1s) including expression of the transcription factor interferon regulatory factor-8 (IRF8). IRF8 promotes TAM presentation of cancer cell antigens to CD8+ T cells similar to DC1, but TAMs differ from DC1s in promoting high PD-1 expression. Importantly, macrophage-specific deletion of IRF8 attenuates Tex cell differentiation, and suppresses tumor growth. Furthermore, human TAMs express IRF8, and a TAM IRF8 gene signature tracks with a Tex cell gene signature in multiple cancer types. Based on these findings, we hypothesize that terminal Tex cell differentiation is driven by IRF8-expressing TAMs with a tolerogenic antigen-presenting cell (APC) function in the tumor tissue, and such a TAM-Tex cell regulation axis can be targeted for novel cancer immunotherapy. To test this hypothesis, we will first determine how IRF8 is induced in TAMs, and how it promotes TAM APC function. By performing chromatin profiling experiments and using genetic mouse models, we will assess whether the TAM-enriched transcription factor Batf2 enables IRF8 autoactivation via the +32kb Irf8 enhancer element. IRF8-deficient TAMs are defective in acquiring cancer cell antigens. Using mouse strains with macrophage- or cancer cell-specific deletion of the B2m gene, we will investigate whether IRF8 promotes TAM acquisition of antigens through cross-presentation or cross-dressing. Secondly, we will define how the tolerogenic function of TAMs is specified, and how it can be reprogrammed for therapy. Compared to DC1s, TAMs express lower levels of interleukin-15 (IL-15), but exhibit heightened transforming growth factor-b (TGF-b) signaling. By generating macrophage-specific gain- or loss-of-function mouse models, we will explore whether blockage of TGF-b signaling reverses the tolerogenic APC function of TAMs in an IL-15-dependent manner, and whether overexpression of IL-15 in macrophages is sufficient to induce T cell-stimulatory TAMs in genetic models and in a cell therapy setting. Compared to DC1s, TAMs have a smaller cell size. We will investigate whether and how activation of the metabolic regulator mammalian target of rapamycin complex 1 (mTORC1) reprogram TAMs to be immunostimulatory APCs. Successful completion of this project will not only generate mechanistic insights into APC control of Tex cell differentiation in cancer, but also guide the targeting of the TAM-Tex cell regulation axis for therapy of a wide range of malignancies.