Abstract 2658: The circadian clock modulates cancer immune checkpoint therapy through immune cell trafficking

Abstract Immune checkpoint inhibitor therapy (ICT) can provide durable remissions for cancer patients with previously incurable malignancies. However, ICT is ineffective for many cancer types, and even those who initially respond may develop ICT resistance and succumb to their cancer. Tumor cell extrinsic factors, termed host factors, have recently emerged as key mediators and biomarkers of ICT response. One intriguing host factor that may influence ICT response is the circadian clock, an evolutionarily conserved transcriptional-translational feedback loop that allows mammalian organisms to adapt to environmental exposures (e. g. light). However, whether “the clock” modulates the ICT anti-tumor immune response is unknown. Utilizing preclinical mouse models of cancer immunotherapy, we found that ICT efficacy is time-of-day dependent. ICT was most efficacious if ICT was administered at two hours after first light exposure (Zeitgeber time 2, ZT2) and least efficacious at ZT18. Utilizing flow cytometry, bulk cytokine analysis, and single cell RNA sequencing, we characterized the anti-tumor immune response after administering ICT at ZT2 and ZT18. There was an increase in effector granzyme B- and interferon-γ producing CD8+ T-cells in the tumor at ZT2 versus ZT18. This was accompanied by an increase in CD11c+ dendritic cells (DCs) and intratumoral chemokines (e. g. CXCL10) that promote DC/T-cell migration into the tumor microenvironment, and leads to enhanced DC-T-cell priming and anti-tumor immunity. Interestingly, these time-of-day dependent differences in tumor immune cell infiltration were present prior to the administration of ICT. To interrogate the role of the clock in mediating these time-of-day dependent differences, we characterized the response to ICT in mice that lack the core clock gene, BMAL1. Loss of BMAL1 in DCs (BMAL1fl/fl crossed with CD11c-cre) attenuated ICT efficacy, abrogated time-of-day dependent differences in ICT efficacy and dampened anti-tumor immunity. These findings highlight a role for a novel host factor, the circadian clock, in mediating the efficacy of cancer immune checkpoint therapy. Citation Format: Jake N. Lichterman, Tarun Srinivasan, Wenling Li, Parastoo Sabaeifard, Laura A. Coughlin, Nicole Poulides, Lora V. Hooper, Andrew Y. Koh. The circadian clock modulates cancer immune checkpoint therapy through immune cell trafficking abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2658.