The advent of cancer immunotherapy (CIT) and its success in treating primary and metastatic cancer may offer substantially improved outcomes for patients. Despite recent advancements, many malignancies remain resistant to CIT, among which are brain metastases, a particularly virulent disease with no apparent cure. The immunologically unique niche of the brain has prompted compelling new questions in immuno-oncology such as the effects of tissue-specific differences in immune response, heterogeneity between primary tumors and distant metastases, and the role of spatiotemporal dynamics in shaping an effective anti-tumor immune response. Current methods to examine the immunobiology of metastases in the brain are constrained by tissue processing methods that limit spatial data collection, omit dynamic information, and cannot recapitulate the heterogeneity of the tumor microenvironment. In the current review, we describe how high-resolution, live imaging tools, particularly intravital microscopy (IVM), are instrumental in answering these questions. IVM of pre-clinical cancer models enables short- and long-term observations of critical immunobiology and metastatic growth phenomena to potentially generate revolutionary insights into the spatiotemporal dynamics of brain metastasis, interactions of CIT with immune elements therein, and influence of chemo- and radiotherapy. We describe the utility of IVM to study brain metastasis in mice by tracking the migration and growth of fluorescently-labeled cells, including cancer cells and immune subsets, while monitoring the physical environment within optical windows using imaging dyes and other signal generation mechanisms to illuminate angiogenesis, hypoxia, and/or CIT drug expression within the metastatic niche. Our review summarizes the current knowledge regarding brain metastases and the immune milieu, presents the current status of CIT and its prospects in targeting brain metastases to circumvent therapeutic resistance, and proposes avenues to utilize IVM to study CIT drug delivery and therapeutic efficacy in preclinical models that will ultimately facilitate novel drug discovery and innovative combination therapies.

癌症免疫疗法（CIT）的出现及其在治疗原发性和转移性癌症方面的成功可能会为患者带来显着改善的结果。尽管有最新进展，但许多恶性肿瘤仍对CIT具有抵抗力，其中包括脑转移瘤，这是一种特别致命的疾病，没有明显的治愈方法。大脑的免疫学独特地位已经在免疫肿瘤学中引发了新的疑问，例如免疫应答中组织特异性差异的影响，原发肿瘤和远处转移之间的异质性以及时空动力学在形成有效抗肿瘤中的作用。免疫反应。目前检查脑转移瘤免疫生物学的方法受到组织处理方法的限制，这些方法限制了空间数据的收集，省略了动态信息，并且无法概括肿瘤微环境的异质性。在当前的审查中，我们描述高分辨率的实时成像工具，尤其是活体显微镜（IVM），在回答这些问题方面的工具。临床前癌症模型的IVM可以对关键的免疫生物学和转移性生长现象进行短期和长期观察，从而潜在地产生关于脑转移的时空动态，CIT与其中免疫元件的相互作用以及化学和放射疗法影响的革命性见解。 。我们描述了IVM通过跟踪荧光标记的细胞（包括癌细胞和免疫亚群）的迁移和生长来研究小鼠脑转移的效用，同时使用成像染料和其他信号生成机制监控光学窗口内的物理环境，以阐明转移性利基中的血管生成，缺氧和/或CIT药物表达。我们的综述总结了有关脑转移和免疫环境的当前知识，介绍了CIT的现状及其在靶向脑转移以规避治疗耐药性方面的前景，并提出了利用IVM在临床前模型中研究CIT药物递送和治疗效果的途径，最终将促进新颖的药物发现和创新的联合疗法。