High-grade B-cell lymphomas with MYC and BCL2 translocations lack tumor-associated macrophages and PD-L1 expression: A possible noninflamed subgroup

Abstract

We investigated the intratumoral source of PD-L1 expression and the infiltration of tumor-associated macrophages (TAMs) in large B-cell lymphomas (LBCLs) with or without MYC-translocation, as well as possible correlations to BCL2-and BCL6-translocations and cell of origin (COO). One-hundred and twenty-six patient samples were studied in a cohort enriched for MYC-translocated tumors with 34 samples carrying this translocation. Demonstration of intratumoral distribution and cellular source of PD-L1 was enabled by immunohistochemical (IHC) dual staining specifically highlighting PD-L1 expression in lymphoma B-cells with antibodies against PD-L1 and PAX5. Additional IHC with antibodies against CD68 and CD163 identified TAMs. We found that CD68-positive TAMs were the main source of PD-L1 protein expression in contrast to lymphoma B cells which rarely expressed PD-L1. Semiquantitative IHC demonstrated a significant correlation between CD68 and PD-L1 protein expression. Unsupervised hierarchical analysis of PD-L1, CD68, and CD163 IHC data subsequently demonstrated three potential clusters defined by expression of the three biomarkers. Cluster A consisted of patient samples with significantly lower expression of PD-L1, CD68, and CD163, but also significantly higher prevalence of BCL2-translocation and MYC-BCL2-double-hit (DH) compared to the other two clusters. In cluster C we found a significant accumulation of BCL6 translocated tumors. This cluster in contrast had the highest protein expression of PD-L1, CD68, and CD163. Cluster B tumors had an intermediate expression of the three biomarkers, but no accumulation of the specific genetic translocations. Our data, which were based on morphological analysis, immunophenotyping and genotyping by fluorescence in situ hybridization were in line with new concepts of LBCL taxonomy integrating genetic, phenotypical, and immunological characteristics with identification of new subgroups where MYC translocation and MYC-BCL2 DH may identify a noninflamed subtype. These findings may furthermore hold significant predictive value especially regarding immune checkpoint blockade therapy, but further molecular characterization should be done to substantiate this hypothesis.

Keywords: MYC; double-hit lymphoma; immune checkpoint blockade therapy; large B-cell lymphoma; programmed death ligand 1; tumor-associated macrophages.