T-cell/histiocyte-rich large B-cell lymphoma shows transcriptional features suggestive of a tolerogenic host immune response

Abstract

Background: Gene expression profiling has successfully identified the prognostic significance of the host response in lymphomas. The aggressive T-cell/histiocyte-rich large B-cell lymphoma and the indolent nodular lymphocyte-predominant Hodgkin's lymphoma are both characterized by a paucity of tumor cells embedded in an overwhelming background. The tumor cells of both lymphomas share several characteristics, while the cellular composition of their microenvironment is clearly different.

Design and methods: We collected 33 cases of T-cell/histiocyte-rich large B-cell lymphoma and 56 cases of nodular lymphocyte-predominant Hodgkin's lymphoma and performed microarray gene expression profiling on ten cases of each lymphoma, to obtain a better understanding of the lymphoma host response. By quantitative reverse transcriptase polymerase chain reaction we verified that these 20 selected cases were representative of the entire population of T-cell/histiocyte-rich large B-cell and nodular lymphocyte-predominant Hodgkin's lymphomas.

Results: We observed that the microenvironment in nodular lymphocyte-predominant Hodgkin's lymphoma is molecularly very similar to a lymph node characterized by follicular hyperplasia, while the microenvironment in T-cell/histiocyte-rich large B-cell lymphoma is clearly different. The T-cell/histiocyte-rich large B-cell lymphoma signature is hallmarked by up-regulation of CCL8, interferon-gamma, indoleamine 2,3 dioxygenase, VSIG4 and Toll-like receptors. These features may be responsible for the recruitment and activation of T cells, macrophages and dendritic cells, characterizing the stromal component of this lymphoma, and may point towards innate immunity and a tumor tolerogenic immune response in T-cell/histiocyte-rich large B-cell lymphoma.

Conclusions: The gene expression profile of T-cell/histiocyte-rich large B-cell lymphoma, in comparison with that of nodular lymphocyte-predominant Hodgkin's lymphoma, shows features suggestive of a distinct tolerogenic host immune response that may play a key role in the aggressive behavior of this lymphoma, and that may serve as a potential target for future therapy.

Figure 1.

Expression profiling of NLPHL and THRLBCL. (A) Principal component analysis, performed on the complete microarray data (54675 probe sets) of ten NLPHL cases, ten THRLBCL cases, and a reference pool of lymph nodes with follicular hyperplasia. Blue: NLPHL; red: THRLBCL; green: reactive lymph node pool. The first principal component (separating NLPHL from THRLBCL) captured 42% of the total variance. The second principal component captured 11% of the total variance. (B) Heat map of the 874 differentially expressed probesets (527 unique genes, Online Supplementary Table S1). Top: cluster dendrogram, showing the a priori expected separation between the THRLBCL and NLPHL samples, and confirming the similarity between NLPHL and the reactive lymph node reference; middle: identity of samples (colors as in A); bottom: graphical representation of gene expression (blue: high expression; red: low expression). (C) Expression of three selected genes, measured by real-time quantitative PCR, in 55 in-house (left) and 14 external (right) THRLBCL and NLPHL cases. Colors as in A.

Figure 2.

Representative pictures of the hematoxylin and eosin (A, E), CD20 (B, F), STAT1 (C, G) and IDO (D, H) stains on NLPHL (A–D) and THRLBCL (E–H), all taken with a 40X objective. (A) Atypical cells (popcorn cells) in NLPHL embedded in a background rich in small lymphocytes. (B) CD20 expression by a popcorn cell surrounded by CD20-negative lymphocytes, resulting in a T-cell rosette embedded in CD20-positive small B cells. (C) STAT1 is weakly expressed by most popcorn cells in the nucleus and in the cytoplasm, in some of the small lymphocytes and in large dendritic cells adjacent to the T-cell rosettes. (D) Popcorn cells, as well as surrounding lymphocytes do not express IDO, while some plasma cell-like, non-dendritic cells express IDO in their cytoplasm and in their nucleus. These IDO-positive cells might correspond to plasmacytoid monocytes/plasmacytoid dendritic cells. (E) The atypical cells of THRLBCL, embedded in a stroma rich in histiocytes and a limited number of small lymphocytes. (F) CD20 expression by the tumor cells, and absence of small CD20⁺ lymphocytes in the surrounding stroma. (G) Most of the stromal components of THRLBCL express STAT1, while the tumor cells are clearly negative. (H) IDO is expressed in small plasma cell-like cells in THRLBCL, assumed to correspond to plasmacytoid monocytes/plasmacytoid dendritic cells (as in NLPHL). In addition, large dendritic cells frequently located nearby tumor cells also clearly express IDO in all of the THRLBCL (and none of the NLPHL) cases.

Figure 3.

Schematic proposal of the host immune response in THRLBCL, based on our morphological and gene expression data, and on literature evidence. By morphology, the microenvironment of THRLBCL is hallmarked by the presence of histiocytes/macrophages. Gene expression profiling data confirm the central role of macrophages and/or dendritic cells and suggest that these cells may be recruited by CCL8., IFN-γ activates these cells to produce IDO., High levels of IDO, together with VSIG4, suppress the proliferation of effector T cells (such as CD8⁺ cytotoxic T cells), resulting in tumor tolerance., Macrophages and dendritic cells also express receptors involved in innate immunity, including scavenger and Toll-like receptors, and VSIG4 as a complement receptor. Blocking the production and/or the function of CCL8, IFN-γ, and in particular IDO and VSIG4 may abrogate the induction of tumor tolerance. It is encouraging to note that inhibitors to target IDO are available.