An IL-27/Stat3 axis induces expression of programmed cell death 1 ligands (PD-L1/2) on infiltrating macrophages in lymphoma

Summary

Immune escape and tolerance in the tumor microenvironment are closely involved in tumor progression, and are caused by T-cell exhaustion and mediated by the inhibitory signaling of immune checkpoint molecules including programmed death-1 (PD-1), cytotoxic T-lymphocyte associated protein 4, and T-cell immunoglobulin and mucin domain-containing molecule-3. In the present study, we investigated expression of the PD-1 ligand 1 (PD-L1) in a lymphoma microenvironment using paraffin embedded tissue samples, and subsequently studied the detailed mechanism of up-regulation of PD-L1 on macrophages using cultured human macrophages and lymphoma cell lines. We found that macrophages in lymphoma tissues of almost all cases of adult T-cell leukemia/lymphoma (ATLL), follicular lymphoma, and diffuse large B-cell lymphoma expressed PD-L1. Cell culture studies showed that the conditioned medium of ATL-T and SLVL cell lines induced increased expression of PD-L1/2 on macrophages, and that this PD-L1/2 overexpression was dependent on activation of signal transducer and activator of transcription 3 (Stat3). In vitro studies including cytokine array analysis showed that IL-27 (heterodimer of p28 and EBI3) induced overexpression of PD-L1/2 on macrophages via Stat3 activation. Since lymphoma cell lines produced IL-27B(EBI3) but not IL-27p28, it was proposed that the IL-27p28 derived from macrophages and the IL-27B(EBI3) derived from lymphoma cells formed an IL-27(heterodimer) that induced PD-L1/2 overexpression. Although the significance of PD-L1/2 expressions on macrophages in lymphoma progression has never been clarified, an IL-27-Stat3 axis might be a target for immunotherapy for lymphoma patients.

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