Page 204 - Haematologica Vol. 110 - January 2025

LETTER TO THE EDITOR
polarization of M2 macrophages (Figure 2B; Online Supple- mentary Figure S2B).
Membrane-bound GPNMB can be cleaved by metallo- proteinases, such as ADAM10, to generate the soluble isoform, sGPNMB.9 We next studied if sGPNMB could be released by macrophages polarized by HRS cells. We re- peated the co-culture experiments using macrophages differentiated from the blood monocytes of three new do- nors, but this time measuring sGPNMB in the supernatant by enzyme-linked immunosorbent assay. As before, CM was as effective as direct co-culture in inducing surface GPNMB expression (data not shown). However, sGPNMB
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levels in cell supernatants were substantially higher after co-culture compared with exposure of macrophages to CM alone (Figure 2C; Online Supplementary Figure S2C). Thus, while soluble factors released by HRS cells are effective in inducing GPNMB surface expression, optimal sGPNMB release is dependent upon cell-cell contact. One explanation for this result is that cell-cell contact triggers the activation and/or upregulation of proteases that cleave GPNMB.
We next assessed the influence of GPNMB on cytotoxic T-lymphocyte (CTL) recognition of EBV-derived epitopes in cHL cell lines. cHL cell lines have been shown to effi-
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