传统树突状细胞（cDCs）是促进免疫系统激活以抵御肿瘤的抗肿瘤免疫反应的先锋。Flt3L是DC发育所需的细胞因子，治疗时可以增加肿瘤内的DC数量。然而，Flt3L对肿瘤微环境中不同cDC亚群表型的影响仍然大部分未知。在本研究中，我们使用多组学单细胞分析方法，发现Flt3L治疗可以增加正交E0771和TS/A乳腺癌以及LLC肺癌模型中的所有cDC亚群，但这并没有导致任何模型中肿瘤生长的减少。有趣的是，在Flt3L治疗下，E0771肿瘤、TS/A乳腺癌和LLC肺癌中诱导出了表达CD81+的migcDC1亚群，很可能是来源于cDC1的。该CD81+migcDC1亚群表达了典型cDC1标记物以及迁移性cDC活化和调控标记物，并且具有诱导Treg的潜力。为了将cDC表型转向T细胞刺激表型，我们在携带E0771肿瘤的小鼠中联合应用了CD40激动剂疗法和Flt3L。然而，尽管αCD40减缓了肿瘤生长，Flt3L并未改善对αCD40疗法的治疗反应。有趣的是，Flt3L+αCD40联合疗法增加了促进Treg生成的CD81+migcDC1的数量。尽管如此，Treg消除和αCD40疗法具有协同作用，但加入Flt3L到该联合疗法中并没有带来任何额外的益处。总的来说，这些结果表明，仅通过Flt3L治疗增加肿瘤中的cDCs不能改善抗肿瘤反应，因此可能对癌症治疗没有益处，尽管仍可用于增加自体DC治疗中的cDC数量。版权所有 © 2023年Clappaert，Kancheva，Brughmans，Debraekeleer，Bardet，Elkrim，Lacroix，Živalj，Hamouda，Van Ginderachter，Deschoemaeker和Laoui。

Conventional dendritic cells (cDCs) are at the forefront of activating the immune system to mount an anti-tumor immune response. Flt3L is a cytokine required for DC development that can increase DC abundance in the tumor when administered therapeutically. However, the impact of Flt3L on the phenotype of distinct cDC subsets in the tumor microenvironment is still largely undetermined. Here, using multi-omic single-cell analysis, we show that Flt3L therapy increases all cDC subsets in orthotopic E0771 and TS/A breast cancer and LLC lung cancer models, but this did not result in a reduction of tumor growth in any of the models. Interestingly, a CD81+migcDC1 population, likely developing from cDC1, was induced upon Flt3L treatment in E0771 tumors as well as in TS/A breast and LLC lung tumors. This CD81+migcDC1 subset is characterized by the expression of both canonical cDC1 markers as well as migratory cDC activation and regulatory markers and displayed a Treg-inducing potential. To shift the cDC phenotype towards a T-cell stimulatory phenotype, CD40 agonist therapy was administered to E0771 tumor-bearing mice in combination with Flt3L. However, while αCD40 reduced tumor growth, Flt3L failed to improve the therapeutic response to αCD40 therapy. Interestingly, Flt3L+αCD40 combination therapy increased the abundance of Treg-promoting CD81+migcDC1. Nonetheless, while Treg-depletion and αCD40 therapy were synergistic, the addition of Flt3L to this combination did not result in any added benefit. Overall, these results indicate that merely increasing cDCs in the tumor by Flt3L treatment cannot improve anti-tumor responses and therefore might not be beneficial for the treatment of cancer, though could still be of use to increase cDC numbers for autologous DC-therapy.Copyright © 2023 Clappaert, Kancheva, Brughmans, Debraekeleer, Bardet, Elkrim, Lacroix, Živalj, Hamouda, Van Ginderachter, Deschoemaeker and Laoui.