Abstract A001: Epithelial cancers demonstrate IL34-associated dysfunction of Langerhans cells
Authors: Trinh Dang Thi Viet , Gillinder Kevin R. , Nguyen Quan , Mulay Onkar , Vo Tuan , Mehdi Ahmed M. , Zhou Chenhao , Brooks Andrew J. , Asplett Kiran , Leggatt Graham R. , Hume David A. , Frazer Ian H. , Chandra Janin 
Published: October 2024

Abstract
Background: Persistent human papillomavirus (HPV) infection of basal keratinocytes (KC) can lead to malignant transformation, often associated with local immune suppression. We previously observed in a murine model of HPV-induced dysplastic epithelium an association between decreased T cell activation upon intradermal immunisation and impaired antigen-presentation by Langerhans cells (LCs). This was correlated with reduced epithelial production of interleukin 34 (IL34), a cytokine critical for LC homeostasis. Low expression of IL34 is common in skin diseases associated with dysplastic epithelium and is correlated with poor prognosis in mucosal squamous cell cancers, including cervical cancers. Objectives: We aimed (I) to decipher why the expression of IL34 is suppressed, (II) how this may impact LC function, and (III) to develop tools to restore its expression in the hyperplastic epithelium. Methods: We employed the TNMplot database to analyze the RNA expression of IL34 in tumor tissues versus normal tissues. We used the K14E7 transgenic mouse model expressing the HPV16 E7 oncoprotein under the control of the Keratin 14 promoter in KCs, leading to hyperproliferation, and the Assay for Transposase-Accessible Chromatin sequencing (ATACseq) to elucidate chromatin accessibility in KCs and LCs. We further designed a gene therapy tool to restore IL34 expression in vivo. Results: IL34 mRNA expression was significantly reduced in epithelial cancers of the head and neck, cervix, lung, and oesophagus when compared to normal tissues. As with cervical cancer, head and neck squamous cell carcinoma patients exhibiting low IL34 expression had a poorer prognosis. ATACseq revealed more than 30,000 significant changes in chromatin accessibility between hyperproliferative and normal KCs. These changes included significantly reduced accessibility at multiple sites within the Il34 locus, including sites proximal to the skin-specific transcription start site and overlapping with Il34’s upstream enhancer. This reduced chromatin accessibility correlated with reductions of both Il34 mRNA and protein levels. Over 20,000 changes were detected in LCs residing in the hyperplastic epithelium, including increased accessibility of sites overlapping with enhancer and promoter regions of the Il34’s receptor - the colony-stimulating factor 1 receptor (Csf1r). Additionally, there was a significant decrease in chromatin accessibility at classical MHCII gene loci (H2-Aa, H2-Ab1, H2-Eb1, and Cd74), as well as genes related to antigen uptake (Cltc, Scarb2, Fcrl1, and Cd207). Furthermore, lentivirus-mediated delivery of Il34 to hyperplastic epithelium successfully restored IL34 expression to physiological levels. Conclusion: Reduced IL34 expression in hyperplastic epithelium may contribute to impaired function of Langerhans cells and progression of epithelial cancers.
Citation Format: Thi Viet Trinh Dang, Kevin R. Gillinder, Quan Nguyen, Onkar Mulay, Tuan Vo, Ahmed M. Mehdi, Chenhao Zhou, Andrew J. Brooks, Kiran Asplett, Graham R. Leggatt, David A. Hume, Ian H. Frazer, Janin Chandra. Epithelial cancers demonstrate IL34-associated dysfunction of Langerhans cells [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr A001.