Classical Hodgkin Lymphoma with Reduced β2M/MHC Class I Expression Is Associated with Inferior Outcome Independent of 9p24.1 Status

In classical Hodgkin lymphoma (cHL), malignant Hodgkin Reed-Sternberg (HRS) cells evade antitumor immunity by multiple mechanisms, including perturbed antigen presentation and enhanced PD-1 signaling. HRS cell expression of the PD-1 ligands is attributable, in part, to copy number alterations of 9p24.1/CD274(PD-L1)/PDCD1LG2(PD-L2) Amplification of PD-L1/PD-L2 is associated with advanced clinical stage and inferior progression-free survival (PFS) following first-line (induction) therapy. The relationships between altered expression of β2-microglobulin (β2M), MHC class I, and MHC class II by HRS cells, PD-L1/PD-L2 amplification, and clinical outcome in cHL are poorly defined. We assessed these variables in diagnostic biopsy specimens from 108 patients with cHL who received uniform treatment and had long-term follow-up and found decreased/absent expression of β2M/MHC class I in 79% (85/108) and decreased/absent expression of MHC class II in 67% (72/108) of cases. Patients with decreased/absent β2M/MHC class I had shorter PFS, independent of PD-L1/PD-L2 amplification and advanced stage. Decreased or absent MHC class II was unrelated to outcome. These results suggest that MHC class I-mediated antigen presentation by HRS cells is an important component of the biological response to standard chemo/radiotherapy. The paucity of β2M/MHC class I expression on HRS cells also prompts speculation regarding alternative mechanisms of action of PD-1 blockade in cHL. Cancer Immunol Res; 4(11); 910-6. ©2016 AACR.