Abstract P043

SPATIAL ORGANIZATION OF THE TUMOR MICROENVIRONMENT IN NODULAR LYMPHOCYTE-PREDOMINANT HODGKIN LYMPHOMA AND T-CELL/HISTIOCYTE-RICH LARGE B-CELL LYMPHOMA: INSIGHTS FROM A PILOT COHORT STUDY

Background: Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) and T-cell/histiocyte-rich large B-cell lymphoma (THRLBCL) are rare B-cell malignancies characterized by infrequent neoplastic cells embedded in an immunologically active tumor microenvironment (TME). NLPHL variants with T-cell infiltration, especially Fan pattern E, may resemble aggressive THRLBCL, to which NLPHL can transform. The cellular composition and spatial distribution of cells in the TME of NLPHL and THRLBCL have yet to be elucidated.

Design: In this initial pilot cohort, we collected comprehensive clinicopathological data from 11 patients with NLPHL Fan E/THRLBCL. A centralized review by an experienced hematopathologist (J.D.) ensured accurate diagnosis. We performed cyclic immunofluorescence (CycIF) on tissue microarrays (TMA) from diagnostic formalin-fixed paraffin-embedded (FFPE) tumor samples (lymph nodes). Our panel consisted of 31 markers focusing on immune cell subsets, immune checkpoint molecules, stroma, and blood vessels. We utilized the Scimap package (Python v.3.10) to enumerate the composition of tumor-infiltrating cells, with a particular emphasis on spatial distribution.

Results: All but one of the 11 patients had advanced-stage disease with bone marrow and liver or splenic involvement. All patients were treated with R-CHOP-like immunochemotherapy. We identified a total of 108597 single cells, with a median of 10127 cells per patient. The cellular composition between samples varied, with the most common cell type being helper T cells (Th; 48%), followed by cytotoxic T cells (Tc; 19%) and M2-like macrophages (M2; 11%). As expected, malignant B cells were rare, constituting only 0.7% of all cells. Th cells were closest to malignant B cells, followed by Tc cells, M2 macrophages, and nonmalignant B cells. In contrast, regulatory T cells, other malignant cells, and blood vessels were more frequently located at a greater distance. Interaction analyses revealed that Th cells especially avoided M2 macrophages, dendritic cells, and Tc cells, but not Treg cells or malignant B cells. M2 macrophages and Th cells were less often situated next to blood vessels.

Conclusions: In this pilot cohort, we identified an organized spatial distribution of cellular composition. Malignant B cells were rare, scattered, and surrounded by T cells, positioned far from blood vessels. We have performed CycIF on over 300 TMA cores from more than 100 NLPHL and THRLBCL patients, with analyses ongoing.

Authors

Ilja Kalashnikov, Kerttu Kalander, Ada Junquera, Matias Autio, Suvi-Katri Leivonen, Johannes Dunkel, Anniina Färkkilä, Sirpa M. Leppä