Increased abundance of tumor-associated macrophages (TAMs) predicts shortened survival of patients with classical Hodgkin lymphoma (cHL). TAMs in cHL might support growth of the malignant, Reed-Sternberg (RS) cells and due to expression of PD-L1, contribute to T-cell exhaustion. In our previous studies, we identified almost universal expression of PIM-1/2/3 kinases (PIMs) in RS cells, but also noted that they are expressed in TAMs. In RS cells, PIMs support malignant cells survival and immune privilege. However, their role in the biology of cHL-TAMs remains to be explored. Herein, using an in vitro model of cHL-TAMs (RS-conditioned macrophages, RS-M) we characterize consequences of PIM inhibition for phenotype and functions of TAMs in cHL. THP1 cells and donor-derived monocytes were differentiated into macrophages (Mφ-0) using PMA and CSF-1 respectively. Mφ-0 were next cocultured with L428 or L1236 RS cells under conditions prohibiting direct contacts. Compared to Mφ-0, RS-M exhibited elevated expression of PIMs and genes involved in chemotaxis/immunomodulation (CCLs: 2, 5, 7, 8, 13, 17, 18 and 24), extracellular matrix organization (CD206, TGM2 and MMP-1, -7, -9 and -12), T cell exhaustion (PD-L1) and angiogenesis (VEGFA, PDGFB, CHI3L1/2). PIMs expression was also detected in primary cHL-TAMs. To assess role of PIMs in TAMs, RS-M were treated with a dual pan-PIM/FLT3 inhibitor, MEN1703, and subjected to transcriptional, biochemical and immunophenotype analyses. MEN1703 skewed gene expression profiles of RS-M toward pro-inflammatory (M1) macrophages and downregulated expression of genes associated with pro-tumoral (M2) macrophages. Consistently, PIM inhibition in RS-M downregulated expression or decreased activity of M2-associated molecules (CREB1, AKT, STAT3/6, CD163, CD206, CD209), and decreased PD-L1 levels by 32%. PIM inhibition hampered important functions of RS-M, including their ability to promote angiogenesis, matrix remodelling (collagen uptake), and eosinophil recruitment. In direct cocultures, RS-M decreased activity of T lymphocytes. This suppressive effect was alleviated in cocultures with the PIM inhibitor-treated RS-M. Our data suggest that PIMs support pro-tumoral and immunosuppressive phenotype of cHL-TAMs. Since PIM activity is required for RS cell survival and immune escape, these kinases are rational targets for therapy in cHL.
Grant support: National Science Centre, Poland 2017/26/D/NZ5/00561 and 2016/22/M/NZ5/00668