Poster Presentation 14th Lorne Infection and Immunity 2024

Interferon regulatory factors 1 and 2 regulate expression of programmed cell death-ligand 1 in dendritic cells (#135)

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

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 and virus-infected 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). Repeated and strong interactions between PD-L1 on DCs and PD-1 on T cells can further result in T cell exhaustion. Despite its importance, the regulation of PD-L1 in DCs remains largely uncharacterised.

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. Reduced PD-L1 expression was also observed on Irf2-/- DCs following stimulation with toll-like receptor agonists, which are potent inducers of PD-L1 upregulation. In contrast, when Irf2-/-DCs were activated with interferon-γ, another major inducer of PD-L1, 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.

Overall, 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. Further studies aim to reciprocate these results in primary models.