Distinct signaling pathways and checkpoint molecule expression across histological subtypes of nodular lymphocyte-predominant Hodgkin lymphoma
Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is a rare B-cell malignancy characterized by infrequent neoplastic cells embedded in an immunologically active tumor microenvironment (TME). The composition of the TME is known to influence the outcomes; cases with a nodular B-cell rich TME (classical histology; Fan A-B) are generally indolent, whereas increased infiltration of T-cells or diffuse growth (variant histology; Fan C-F) is associated with a more aggressive clinical course. The molecular features underlying this association remain to be discovered. To gain further insights into disease biology, we recruited NLPHL cases as part of the Atlas of Blood Cancer Genomes (ABCG) initiative, a consortium consisting of 26 institutions.
We collected comprehensive clinicopathological data from 106 NLPHL patients, with centralized review performed by a panel of dedicated hematopathologists to ensure accurate diagnosis. We performed RNA sequencing on formalin-fixed paraffin-embedded (FFPE) diagnostic tumor samples (n=81) and enumerated tumor-infiltrating immune cell compositions using FARDEEP with signature matrix LM22 from CIBERSORT.
Patient demographics are shown in Table 1. Classical histology was associated with better survival compared to variant histology (Figure 1A-B). According to in silico immunophenotyping, NLPHLs with variant histology were characterized by a lower proportion of naïve B cells and increased proportions of CD8+ T cells and M1-macrophages compared to the classical histology (Figure 1C). Moreover, variant histology was associated with higher expression of checkpoint genes compared to classical histology (Figure 1D; P=0.019). Higher proportions of T cells and macrophages and increased expression of checkpoint genes were particularly prominent in cases with splenic involvement. Finally, we found a strong association between variant histology and gene expression related to inflammatory response (P<0.001), whereas genes related to cell cycle regulation through the E2F pathway were upregulated in NLPHLs with classical histology (P<0.001).
Our study represents the largest comprehensive clinical and transcriptomic analyses of NLPHL to-date. Our results indicate that TME is clinically meaningful and provide evidence for distinct signaling pathways and expression patterns of checkpoint genes across histological subtypes.