Poster Presentation Asia-Pacific Vaccine and Immunotherapy Congress 2024

Interferon regulatory factors 1 and 2 regulate expression of programmed cell death-ligand 1 in dendritic cells (#170)

Ashley M Firth 1 , Christophe Macri 1 , Annabelle Blum 1 , Cassandra Ouslinis 1 , Nishma Gupta 2 3 , Justine D Mintern 1
  1. Bio21 Institute of Molecular Science and Biotechnology, Department of Biochemistry and Pharmacology, The University of Melbourne, Parkville, Victoria, Australia
  2. Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia
  3. ACRF Chemical Biology Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, Australia

Background

Programmed cell death-ligand 1 (PD-L1) is a regulatory molecule which is overexpressed in many cancers and plays a major role in suppressing the immune system. As well as tumour cells, PD-L1 is expressed by all haematopoietic cells. In particular, the upregulation of PD-L1 on dendritic cells (DCs), one of the primary cells which presents antigen to T cells, can lead to T cell inhibition through binding to programmed cell death-1 (PD-1). Many immunotherapies have traditionally focussed on the T cell response to cancer, including blocking PD-1 expression by T cells. However, the importance of DCs in the immunological response to cancer is now better appreciated, and targeting of immunotherapies to DCs is an emerging area in cancer research. Still, the regulation of PD-L1 and other checkpoint inhibitor molecules expressed in DCs remains poorly understood.

Methods and results

A genome-wide CRISPR/Cas9 screen searching for regulators of PD-L1 in DCs identified the transcription factor, interferon regulatory factor 2 (IRF2), as a promotor of PD-L1 cell surface expression. Production of a single-gene knockout of IRF2 in the MuTu DC line (Irf2-/-) allowed confirmation that Irf2-/- DCs have lower cell surface expression of PD-L1 when compared to wild type, without affecting the DC’s ability to stimulate adaptive immunity. Reduced PD-L1 expression was also observed on Irf2-/- DCs following stimulation with a toll-like receptor agonist, CpG, which is a potent inducer of PD-L1 upregulation. In contrast, when Irf2-/-DCs were activated with interferon-γ, a major driver of PD-L1 expression in the tumour microenvironment, there was no discernible difference in PD-L1 expression relative to wild type cells. Instead, the upregulation of another interferon regulatory factor, IRF1, is observed. Production of a knockout of IRF1 in MuTu DCs confirmed that it is the main transcriptional driver of PD-L1 expression in interferon-γ-activated DCs. This mirrors the role of IRF1 as a known promoter of PD-L1 in tumour cells.

Conclusion

This study supports that in DCs, PD-L1 expression is regulated by the transcription factors IRF1 and IRF2, which play interchangeable roles dependent on the stimuli encountered in the microenvironment. Ongoing research aims to confirm the roles of IRF1 and IRF2 as PD-L1 regulators in primary DC cultures and mouse models. Further expansion on the roles of IRF1 and IRF2 will advance our understanding of the DC response to tumours and could lead to the generation of more effective immunotherapies.