Exploring the Function of MHC-II/Lag3 Axis in Brain Metastasis to Develop Novel Therapeutic Strategies

摘要 脑转移(BM)影响着数以百万计的癌症患者，是一个尚未得到满足的临床挑战。 靶向治疗和免疫治疗的进展通过更好地控制癌症患者的 原发癌症和颅外转移，但BM的发病率随着疾病的增加而稳步上升 复发。可悲的是，有症状的BMS患者对目前的治疗反应不佳， 幸存的人非常可怜。大脑具有独特的结构和生物学特征，因此BM的相互作用 肿瘤细胞与大脑的物理环境是独特的和未被探索的。对这些问题有更深的理解 独特的相互作用对于开发更好的BM疗法至关重要。最近，我们发现了小胶质细胞，它 脑中的髓系天然免疫细胞是在骨髓细胞渗入大脑时被激活的吗？ 薄壁组织。此外，小胶质细胞上的LAG3与BM癌的主要组织相容性复合体(MHC)-II结合 细胞，这种相互作用抑制早期骨髓的生长。有趣的是，MHC-II在 将人类和小鼠的BMS与其原发肿瘤进行比较。已知MHC-II基因被表观遗传沉默 对癌细胞的修饰，例如，EZH2诱导的3meK27H3，或增强组蛋白脱乙酰酶(HDAC)功能。 事实上，在癌细胞中敲除EZH2增加了BM细胞表面MHC-II分子并减少了BM的生长 用临床适用的EZH2和/或HDAC抑制剂处理癌细胞会增加MHC-II 表情。这些发现导致我们假设BM细胞上的MHC-II和小胶质细胞上的LAG3是动态的 相互作用控制早期骨髓生长，并使用表观遗传药物恢复骨髓MHC-II的表达可能 增强大脑的先天免疫反应，为治疗BM提供新的策略。我们将通过以下方式验证我们的假设 询问脑中独特的先天免疫成分小胶质细胞是如何与BM肿瘤细胞相互作用的 BM的时空递进。此外，早期的BM生物学研究严重不足，因为大多数 手术切除的患者的BMS是晚期病变。我们将探索BM和BM之间的互动 BM发育过程中独特的脑环境，并发现新的生物决定因素 早期BM的MRI增强成像精确定位早期BM病变，并根据空间基因 表情分析(目标1)。为了揭示在BM早期增强先天免疫反应的机制， 我们将评估肿瘤MHC-II/小胶质细胞LAG3相互作用如何在功能上控制BM的生长 将阐明骨髓细胞中MHC-II表达的表观遗传调控(目标2)。最后，我们将测试 临床适用的表观遗传药物治疗增加MHC-II增强免疫并抑制BM 临床前模型和测试表观遗传调节剂与现有免疫相结合的潜在协同作用 检查点疗法(目标3)。综上所述，我们建议的研究集中于揭示动态相互作用和 骨髓细胞与脑内天然免疫隔膜的串扰和新的早期发育 使用表观遗传药物增强免疫反应和治疗BMS的干预和治疗策略。

Summary Brain metastasis (BM) affects millions of cancer patients and represents an unmet clinical challenge. Advances in targeted- and immuno-therapies have prolonged cancer patients’ survival via better control of primary cancers and extracranial metastases, but the incidence of BM is increasing steadily upon disease recurrence. Sadly, patients having symptomatic BMs do not respond well to current treatments and have extremely poor survivals. The brain has unique structural and biological features, thus the interaction of BM tumor cells with the brain physical environment are distinctive and underexplored. Deeper understanding of these unique interactions is critical for developing better therapeutics for BM. Recently, we found that microglia, which are myeloid-derived innate immune cells in the brain, were activated upon BM cell extravasation into the brain parenchyma. Further, Lag3 on microglia binds to the major histocompatibility complex (MHC)-II on BM cancer cells, and this interaction inhibits early-stage BM outgrowth. Interestingly, MHC-II is severely downregulated in human and mice BMs compared to their primary tumors. MHC-II genes are known to be silenced by epigenetic modifications in cancer cells, e.g., EZH2-induced 3meK27H3, or increased histone deacetylase (HDAC) function. Indeed, knockout EZH2 in cancer cells increased BM cell surface MHC-II molecules and decreased BM growth in mice; and treating cancer cells with clinically-applicable EZH2- and/or HDAC-inhibitors increased MHC-II expression. These findings led us to hypothesize that MHC-II on BM cells and Lag3 on microglia dynamically interact to control early-stage BM outgrowth, and restoring MHC-II expression in BM using epigenetic drugs may boost brain innate immune responses and provide novel strategies to treat BM. We will test our hypothesis by interrogating how microglia, a unique innate immune component in the brain, interact with BM tumor cells along the temporo-spatial progression of BM. Also, early-stage BM biology is severely understudied, since most surgically resected patients’ BMs are late-stage lesions. We will explore the interaction between BM and the unique brain environment during BM development and discover novel biological determinants that are critical for early-stage BM using enhanced MRI imaging to precisely locate early stage BM lesions, and by spatial gene expression profiling (Aim 1). To uncover mechanisms that boost the innate immune response in early stage BM, we will assess how the tumoral MHC-II/microglial Lag3 interaction functionally controls BM outgrowth and we will elucidate the epigenetic regulation of MHC-II expression in BM cells (Aim 2). Lastly, we will test whether therapeutically increasing MHC-II with clinically-applicable epigenetic drugs boosts immunity and inhibits BM in preclinical models and test the potential synergy of combining epigenetic modulators with existing immune checkpoint therapies (Aim 3). In summary, our proposed studies focus on revealing the dynamic interactions and crosstalk of BM cells with the innate immune compartment within the brain and developing novel early intervention and therapeutic strategies using epigenetic drugs to enhance the immune response and treat BMs.