Much focus has been on the interaction of programmed cell death ligand 1 (PD-L1) on malignant B cells with programmed cell death 1 (PD-1) on effector T cells in inhibiting antilymphoma immunity. We sought to establish the contribution of natural killer (NK) cells and inhibitory CD163⁺ monocytes/macrophages in Hodgkin lymphoma (cHL) and diffuse large B-cell lymphoma (DLBCL). Levels of PD-1 on NK cells were elevated in cHL relative to DLBCL. Notably, CD3^-CD56^hiCD16^-ve NK cells had substantially higher PD-1 expression relative to CD3^-CD56^dimCD16⁺ cells and were expanded in blood and tissue, more marked in patients with cHL than patients with DLBCL. There was also a raised population of PD-L1-expressing CD163⁺ monocytes that was more marked in patients with cHL compared with patients with DLBCL. The phenotype of NK cells and monocytes reverted back to normal once therapy (ABVD [doxorubicin 25 mg/m², bleomycin 10 000 IU/m², vinblastine 6 mg/m², dacarbazine 375 mg/m², all given days 1 and 15, repeated every 28 days] or R-CHOP [rituximab 375 mg/m², cyclophosphamide 750 mg/m² IV, doxorubicin 50 mg/m² IV, vincristine 1.4 mg/m² (2 mg maximum) IV, prednisone 100 mg/day by mouth days 1-5, pegfilgrastim 6 mg subcutaneously day 4, on a 14-day cycle]) had commenced. Tumor-associated macrophages (TAMs) expressed high levels of PD-L1/PD-L2 within diseased lymph nodes. Consistent with this, CD163/PD-L1/PD-L2 gene expression was also elevated in cHL relative to DLBCL tissues. An in vitro functional model of TAM-like monocytes suppressed activation of PD-1^hi NK cells, which was reversed by PD-1 blockade. In line with these findings, depletion of circulating monocytes from the blood of pretherapy patients with cHL and patients with DLBCL enhanced CD3^-CD56^hiCD16^-ve NK-cell activation. We describe a hitherto unrecognized immune evasion strategy mediated via skewing toward an exhausted PD-1-enriched CD3^-CD56^hiCD16^-ve NK-cell phenotype. In addition to direct inhibition of NK cells by the malignant B cell, suppression of NK cells can occur indirectly by PD-L1/PD-L2-expressing TAMs. The mechanism is more prominent in cHL than DLBCL, which may contribute to the clinical sensitivity of cHL to PD-1 blockade.

David Arpon

Publications