The success of cancer immunotherapy can be limited by mechanisms that tumors develop to evade destruction by the immune system. Tumors can block the activation and obstruct the ability of immune cells (dendritic cells and T lymphocytes) to destroy the tumor, thereby creating an environment that is beneficial for cancer growth. Ascic et al. developed an approach to directly reprogram cancer cells into dendritic cells in vivo by delivering the transcription factors PU.1, IRF8, and BATF3 with an adenoviral vector (see the Perspective by Zhou and Wu). The transcription factors promoted dendritic cell–like functions and enabled the engineered tumor cells to present antigens and mount cancer-specific T cell immune responses. The tumor-to-immune cell “reprogramming” reshaped the tumor microenvironment, triggering tumor regressions and systemic immunity. —Priscilla N. Kelly
The success of cancer immunotherapy depends on the priming of tumor-specific T cells. However, tumor cells often down-regulate antigen presentation and mount an immunosuppressive microenvironment, which excludes immunogenic antigen-presenting cells from the tumor. These limitations hinder the broad success of cancer immunotherapies, including immune checkpoint blockade. Type 1 conventional dendritic cells (cDC1s), a rare subset of dendritic cells, are key for recruiting and activating cytotoxic T cells, and their presence in tumors correlates with improved survival. Previous studies showed that the transcription factors PU.1, IRF8, and BATF3 (PIB) can directly reprogram fibroblasts or tumor cells into antigen-presenting cDC1-like cells in vitro within 9 days. However, ex vivo cell manipulation and readministration of these reprogrammed cells pose significant challenges for clinical application.
We hypothesized that the reprogramming of tumor cells into cDC1-like cells could occur entirely in vivo within the tumor microenvironment. This approach would foster T cell activation by leveraging the unique functions of cDC1. Using a combination of syngeneic models, xenografts, and human cancer spheroids from multiple cancer types, we characterized local and systemic immune responses triggered by reprogramming and developed a viral platform for delivering PIB directly to tumors.
In vivo tumor cell reprogramming demonstrated faster kinetics and higher fidelity than in vitro approaches and resulted in tumor-resident cDC1-like cells showing a mature, immunogenic signature. Reprogramming efficiently progressed in human cancer spheroids despite the presence of immunosuppressive cancer-associated fibroblasts, myeloid-derived suppressor cells, or pericytes, leading to T cell activation and tumor cell elimination. In murine immune-competent models, reprogrammed tumor cells recruited and expanded polyclonal cytotoxic and memory T cells within the tumor while reducing exhausted and regulatory populations. The formation of tertiary lymphoid structures containing B, T, and stromal cells was observed, switching the immune response from “cold” to “hot.” Immune remodeling led to tumor regression independently of endogenous cDC1. CD4+ T cells were identified as critical mediators, because their depletion with antibodies abolished the therapeutic response. Furthermore, in vivo reprogramming established tumor-specific systemic immunity and immunological memory in melanoma models with varying profiles of immunogenicity and responsiveness to immune checkpoint blockade. In addition to the monotherapy effects, we observed a marked synergy with anti–programmed cell death protein 1 (anti–PD-1) or anti–cytotoxic T lymphocyte–associated protein 4 (anti–CTLA-4) immunotherapies. We further confirmed that reprogramming <2% of cells was sufficient to trigger tumor regression, supporting the intratumoral delivery of reprogramming factors.
Our study demonstrates that in situ delivery of PIB using adenoviral vectors induces the generation of cDC1-like cells within tumors, leading to remodeling of the tumor microenvironment, the formation of tertiary lymphoid structures, and the expansion of polyclonal cytotoxic and memory T cells. This work provides preclinical proof-of-concept for an off-the-shelf, tumor-specific immunotherapy that can orchestrate systemic and durable antitumor immunity.
Immunotherapy can lead to long-term survival for some cancer patients, yet generalized success has been hampered by insufficient antigen presentation and exclusion of immunogenic cells from the tumor microenvironment. Here, we developed an approach to reprogram tumor cells in vivo by adenoviral delivery of the transcription factors PU.1, IRF8, and BATF3, which enabled them to present antigens as type 1 conventional dendritic cells. Reprogrammed tumor cells remodeled their tumor microenvironment, recruited, and expanded polyclonal cytotoxic T cells; induced tumor regressions; and established long-term systemic immunity in multiple mouse melanoma models. In human tumor spheroids and xenografts, reprogramming to immunogenic dendritic-like cells progressed independently of immunosuppression, which usually limits immunotherapy. Our study paves the way for human clinical trials of in vivo immune cell reprogramming for cancer immunotherapy.
癌症免疫疗法的成功可能受到肿瘤发展出的、用于逃避免疫系统破坏的机制的限制。肿瘤可以阻断免疫细胞（树突状细胞和T淋巴细胞）的激活并阻碍其破坏肿瘤的能力，从而创造一个有利于癌症生长的环境。Ascic等人开发了一种方法，通过腺病毒载体递送转录因子PU.1、IRF8和BATF3，在体内直接将癌细胞重编程为树突状细胞（参见Zhou和Wu的观点文章）。这些转录因子促进了树突状细胞样功能，并使工程化的肿瘤细胞能够呈递抗原并引发癌症特异性的T细胞免疫反应。这种从肿瘤细胞到免疫细胞的“重编程”重塑了肿瘤微环境，引发了肿瘤消退和系统性免疫。—Priscilla N. Kelly
癌症免疫疗法的成功依赖于肿瘤特异性T细胞的启动。然而，肿瘤细胞通常会下调抗原呈递并建立免疫抑制微环境，从而将免疫原性的抗原呈递细胞排斥在肿瘤之外。这些限制阻碍了包括免疫检查点阻断在内的癌症免疫疗法的广泛成功。1型经典树突状细胞（cDC1s）是树突状细胞中一个罕见的亚群，对于募集和激活细胞毒性T细胞至关重要，它们在肿瘤中的存在与改善的生存率相关。先前的研究表明，转录因子PU.1、IRF8和BATF3（PIB）可以在体外9天内直接将成纤维细胞或肿瘤细胞重编程为抗原呈递的cDC1样细胞。然而，体外细胞操作以及这些重编程细胞的回输对临床应用构成了重大挑战。
我们假设，在肿瘤微环境中，将肿瘤细胞重编程为cDC1样细胞的过程可以完全在体内发生。这种方法将利用cDC1的独特功能来促进T细胞激活。我们使用同基因模型、异种移植模型和来自多种癌症类型的人类癌症球体模型的组合，表征了重编程引发的局部和系统性免疫反应，并开发了一种用于将PIB直接递送至肿瘤的病毒平台。
体内肿瘤细胞重编程比体外方法显示出更快的动力学和更高的保真度，并产生了显示成熟、免疫原性特征的肿瘤驻留cDC1样细胞。尽管存在免疫抑制性的癌症相关成纤维细胞、髓源性抑制细胞或周细胞，重编程在人类癌症球体中仍能有效进行，导致T细胞激活和肿瘤细胞清除。在具有免疫活性的小鼠模型中，重编程的肿瘤细胞在肿瘤内募集并扩增多克隆细胞毒性和记忆T细胞，同时减少了耗竭性和调节性T细胞群。观察到包含B细胞、T细胞和基质细胞的三级淋巴结构的形成，将免疫反应从“冷”转为“热”。免疫重塑导致了肿瘤消退，且不依赖于内源性cDC1。CD4+ T细胞被确定为关键介质，因为用抗体去除它们会消除治疗反应。此外，在具有不同免疫原性特征和对免疫检查点阻断反应性的黑色素瘤模型中，体内重编程建立了肿瘤特异性的系统性免疫和免疫记忆。除了单药治疗效果外，我们还观察到与抗程序性细胞死亡蛋白1（抗PD-1）或抗细胞毒性T淋巴细胞相关蛋白4（抗CTLA-4）免疫疗法存在显著的协同作用。我们进一步证实，重编程<2%的细胞足以引发肿瘤消退，这支持了重编程因子的瘤内递送策略。
我们的研究表明，使用腺病毒载体原位递送PIB可在肿瘤内诱导产生cDC1样细胞，从而重塑肿瘤微环境、形成三级淋巴结构并扩增多克隆细胞毒性和记忆T细胞。这项工作为一种现成的、肿瘤特异性的免疫疗法提供了临床前概念验证，该疗法能够协调全身性和持久的抗肿瘤免疫。
免疫疗法可以为一些癌症患者带来长期生存，但普遍的疗效因抗原呈递不足和免疫原性细胞被排斥在肿瘤微环境之外而受到阻碍。在此，我们开发了一种方法，通过腺病毒递送转录因子PU.1、IRF8和BATF3在体内重编程肿瘤细胞，使其能够像1型经典树突状细胞一样呈递抗原。重编程的肿瘤细胞重塑了其肿瘤微环境，募集并扩增多克隆细胞毒性T细胞；在多种小鼠黑色素瘤模型中诱导肿瘤消退；并建立了长期的系统性免疫。在人类肿瘤球体和异种移植模型中，向免疫原性树突状样细胞的重编程能够不受通常限制免疫疗法的免疫抑制影响而进行。我们的研究为开展人体内免疫细胞重编程用于癌症免疫治疗的临床试验铺平了道路。
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图：肿瘤细胞的体内重编程为树突状细胞。（1）通过腺病毒载体向肿瘤递送PIB可产生cDC1样细胞，其标志物包括XCR1、CLEC9A、MHC-I/II及CD40的表达。（2）重编程后的肿瘤细胞促进三级淋巴结构的形成、CD8+ T细胞的浸润以及多克隆细胞毒性CD4+ T细胞的生成，（3）从而实现肿瘤消退、形成免疫记忆，并有效控制远处肿瘤及肺转移灶。
In vivo dendritic cell reprogramming for cancer immunotherapy
肿瘤(癌症)患者之家