Anti-CD20 monoclonal antibody (mAb) represents an effective strategy for the treatment of B cell malignancies that may involve complement activity, antibody dependent cellular cytotoxicity (ADCC) and phagocytosis (ADP). While ADP mediated by Kupffer cells is essential to deplete circulating tumors, the relative contribution of each mechanism to the elimination of non-circulating targets has yet to be clarified. Using intravital imaging in a model of MYC-driven B cell lymphoma, we establish here the dominance and limitations of ADP in the bone marrow (BM). We found that tumor cells were stably residing in the BM with little evidence for recirculation. To quantify the contribution of different cytotoxic mechanisms in situ, we designed a dual fluorescent reporter to track phagocytosis and apoptosis in real-time. ADP by BM-associated macrophages was the primary mode of tumor elimination but was no longer active after one hour, resulting only in partial depletion. Moreover, macrophage density was strongly reduced in tumor-rich regions. Given their sessile phenotype, macrophages primarily targeted neighboring tumors, resulting in a substantial spatial constraint. Overcoming spatiotemporal bottlenecks in tumor-targeting Ab therapy represents a critical path towards the design of optimized therapies.

中文翻译：

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体内抗CD20治疗机制的影像学揭示了抗体依赖性吞噬作用的时空瓶颈

抗CD20单克隆抗体（mAb）代表了一种治疗B细胞恶性肿瘤的有效策略，可能涉及补体活性，抗体依赖性细胞毒性（ADCC）和吞噬作用（ADP）。尽管由枯否细胞介导的ADP对消除循环肿瘤至关重要，但每种机制对消除非循环靶点的相对贡献尚待阐明。在MYC驱动的B细胞淋巴瘤模型中使用活体成像，我们在这里建立了ADP在骨髓（BM）中的优势和局限性。我们发现肿瘤细胞稳定地存在于BM中，几乎没有再循环证据。为了量化原位不同细胞毒性机制的贡献，我们设计了一个双重荧光报告基因来实时追踪吞噬作用和细胞凋亡。BM相关巨噬细胞的ADP是消除肿瘤的主要方式，但一小时后不再起作用，仅导致部分耗竭。而且，在肿瘤丰富的区域巨噬细胞密度大大降低。考虑到它们的无梗表型，巨噬细胞主要靶向邻近的肿瘤，导致实质性的空间限制。克服靶向肿瘤的Ab治疗中的时空瓶颈是设计最佳治疗方法的关键途径。