PD-L1/PD-L2 genetic profile in the molecular cytogenetic classification of classic Hodgkin lymphoma

Abstract

Genomic imbalances at 9p24.1 locus, the chromosome region encompassing PD-L1 and PD-L-2 (Programmed death 1 Ligand 1 and 2) genes, is a recurrent alteration in classical Hodgkin lymphoma (CHL). We analyzed 9p24.1 imbalance using fluorescence in situ hybridization (FISH) assay on formalin-fixed paraffin-embedded biopsies from 28 patients with newly diagnosed CHL to characterize the genetic profiles. Results were correlated with PD-L1 (H-score) and EBV (Epstein-Barr Virus)/LMP-1 (Latent membrane protein 1) protein expression by immunohistochemistry and clinical features. Genomic alterations in Hodgkin/Reed Sternberg (H/RS) cells were classified as amplification, copy gain and polysomy. Three molecular cytogenetic groups were defined based on the type and frequency of the copy number alteration: Group A (amplification) 32%, Group G (>50% cells with copy gains but no amplification) 36% and Group P (≥50% cells with polysomies but no amplification) 32%. Significant differences in the frequency of copy gains (p=0.02) and polysomies (p≤0.01) were observed among groups. A negative correlation was found between the percentage of H/RS cells with polysomy and PD-L1 protein expression (p≤0.01). Tumor microenvironmental cells showed chromosome 9 monosomy in 52.4% patients, particularly associated to Group P (100%). The highest mean H-score was observed in Group A (265.6), while Groups G and P showed mean H-scores of 123 and 60.3, respectively. Group P was associated with the highest mean age (p=0.036), increased frequency of advanced-stage disease, B symptoms, and extranodal involvement. In contrast, Groups A and G were linked to localized stages (p=0.035) and bulky masses, highlighting the relevance of 9p24.1 genomic imbalance profiling in the biological characterization of CHL.