Abstract 6406: Conditional knockout of the aryl hydrocarbon receptor in macrophages and dendritic cells enhanced antigen presentation and T cell activation, thereby synergistically improving anti-cancer effects in combination with anti-PD-1

Abstract Background: The aryl hydrocarbon receptor plays a pivotal role in regulating cancer metabolism and is activated across various immune cell types. Its activation fosters immune suppression by enhancing the functions of regulatory cells within the tumor microenvironment. Methods: LysMCre or ItgaxCre/AhRLoxP transgenic (Tg) mice were generated to investigate AhR knockout in myeloid lineage and dendritic cell specifically. The antitumor effects were evaluated using mice engrafted TC1 lung cancer cells. Results: To evaluate the impact of AhR knock-out on systematic immune variation, we compared the proportion of total immune cells in splenocytes. Flow cytometry analysis was performed to compare the immune phenotypes, including Myeloid, M-MDSC, PMN-MDSC, Macrophages, Dendritic cells, NK cells, NKT cells, and T cells. The results showed that both of Tg mouse strains exhibited a significant reduction in PMN-MDSC compared to wild-type (WT) mice. Specifically, IFN-γ+ T cells and PD-1+ T cells were significantly increased in both transgenic (Tg) mouse strains compared to WT mice. Notably, PD-1+ T cells in ItgaxCre/AhRLoxP mice populations were found to be even more elevated than in LysMCre/AhRLoxP mice populations. In contrast, Tregs were significantly decreased. In the Myeloid panel, M1 macrophages and dendritic cells were significantly increased in ItgaxCre/AhRLoxP mice, while a significant increase in dendritic cells was observed in LysMCre/AhRLoxP mice. To evaluate the impact of immune cells on anti-tumor effects, we used mice implanted with TC1 mouse lung cancer cells. Additionally, to assess the synergistic effects with anti-PD-1 (aPD-1), we treated the mice with aPD-1 based on the increased presence of PD-1+ T cells. The most potent anti-tumor effect was observed in the ItgaxCre/AhRLoxP plus aPD-1 group, with significant tumor suppression compared to WT. In contrast, no significant decrease was observed in the LysMCre/AhRLoxPgroup compared to WT. To investigate the immune response within the tumors, we performed immune profiling through flow cytometry on tumor samples. IFN-γ+ CD4+ Tem was significantly increased in both ItgaxCre/AhRLoxP group and ItgaxCre/AhRLoxP + aPD-1 groups compared to WT, while proliferating CD4+ Tem showed a significant increase in the ItgaxCre/AhRLoxP plus aPD-1 group compared to both WT and WT plus aPD-1 groups. The novel AhR inhibitor DA-4505 was shown to enhance the antigen-presentation functions of dendritic cells and macrophages while increasing the expression of IFN-γ+ T cells and granzyme B across various tumor models. Taken together, AhR inhibition promotes immune system activation. Conclusion: Knocking out AhR in myeloid cells enhances immune responses, thereby increasing the anti-tumor efficacy of aPD-1 combination therapy. Citation Format: Dong Kwon Kim, Sujeong Baek, Young Taek Kim, Joon Yeon Hwang, Seung Min Yang, Seul Lee, Seong-san Kang, Mi Hyun Kim, Heekyung Han, Kwangmin Na, Chai Young Lee, Seongsu Jeong, Jongho Cho, Dajeong Kim, Jae Hwan Kim, Youngseon Byeon, Young Seob Kim, Mi Ran Yun, Jii Bum Lee, Min Hee Hong, Sun Min Lim, Kyoung-Ho Pyo, Byoung Chul Cho. Conditional knockout of the aryl hydrocarbon receptor in macrophages and dendritic cells enhanced antigen presentation and T cell activation, thereby synergistically improving anti-cancer effects in combination with anti-PD-1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6406.