Abstract T102

Malignant LP cells build a stroma-poor, avascular niche that concentrates IDO1+ macrophages and excludes regulatory T cells in NLPHL and THRLBCL

Background: Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is a rare B-cell malignancy in which infrequent neoplastic lymphocyte-predominant (LP) cells reside within an immunologically active tumor microenvironment (TME) typically surrounded by T-follicular helper (Tfh) rosettes. In contrast, THRLBCL loses these rosettes and shifts to a macrophage-rich TME. Whether the LP cell reprograms its neighbors remains unknown.

Design: We performed 20-marker cyclic immunofluorescence (CyCIF) on 1.53 million cells from 27 patients (16 NLPHL and 11 THRLBCL). Cells were segmented, scored for per-marker positivity with an in-house phenotyping pipeline, and assigned to 33 single-cell phenotypes using a fixed marker-rule scheme spanning lymphoid, myeloid, and functional states. We compared cellular composition across entities. For each phenotype, we quantified enrichment within 50 μm of LP cells relative to the tissue-wide background (per-patient log2 fold change, Wilcoxon vs tissue-wide, BH-FDR) and related spatial features to event-free survival (EFS).

Results: Median age was 53 years (range 16-75), and most patients were male (24/26). Over a median 17-year follow-up, 7 relapses (NLPHL 4, THRLBCL 3), 1 transformation (NLPHL), and 9 deaths (NLPHL 5, THRLBCL 4) occurred. From NLPHL to THRLBCL, bystander B cells were depleted (41% to 6%, q<0.001) and all macrophage subsets increased, most markedly IDO1+ macrophages (0.7% to 3.0%, q<0.01). Four phenotypes showed peri-LP enrichment or exclusion that was significant in both entities, defining a conserved niche. IDO1+ M1-like macrophages were enriched within 50 μm of LP cells, whereas regulatory T cells, myofibroblasts, and endothelial cells were excluded (q<0.05). In NLPHL, the niche was further enriched for PD1+ CD4+ Tfh rosettes, dendritic cells, and activated helper and cytotoxic T cells. In THRLBCL, these enrichments were absent, and the peri-LP niche was instead enriched for IDO1+ M2-like macrophages.

The disease entity was not prognostic (for EFS, P=0.62). Within NLPHL, peri-LP macrophage features showed a consistent but FDR-nonsignificant trend toward worse EFS (q=0.3).

Conclusion: Across NLPHL and THRLBCL, LP cells organize a conserved local niche by recruiting IDO1+ macrophages and excluding regulatory T cells and stroma. CD4+PD1+ rosettes also mark this niche in NLPHL and are replaced by an IDO1+ macrophage program toward THRLBCL. Spatial prognostic biomarkers will require larger cohorts.