Follicular Lymphoma Cell Niche: Identification of a Preeminent IL-4-Dependent T_FH- B Cell Axis.

Abstract 757

Follicular lymphoma (FL) B cells contract tight connections with their microenvironment, which governs the pathogenesis and progression of the disease. Indeed, specific immune response gene signatures, obtained on whole biopsy samples, have been associated with patient survival, independently of classical clinical features. In this study we performed, using Affymetrix U133 Plus 2.0 oligonucleotide microarrays, the gene expression profiling of purified CD19^pos B-cell and CD19^negCD22^neg non-B cell compartments, prospectively obtained from FL and reactive lymph nodes. Unsupervised analyses of B-cell compartment in one hand (n=21) and non-B cell compartment in the other hand (n=14) allowed to differentiate FL from reactive samples. We then identified 677 nonredundant genes defining the FL synapse, i.e. the list of genes involved in the crosstalk between B cells and their microenvironment in FL. Using Ingenuity pathway analysis we pointed out 26 FL-specific functional networks among this FL synapse, including an IL-4-centered pathway. Interestingly, whereas in tonsils and reactive lymph nodes only exceptional scattered phospho-STAT6^pos cells were observed, a high number of CD20^posphospho-STAT6^pos cells were evidenced within FL biopsies. In addition, several IL-4-target genes, including IL4I1 and HOXC4, were overexpressed in malignant B cells. Altogether, these results demonstrated that the upregulation of IL-4 within FL microenvironment was associated to a strong activation of FL B cells. In addition, FL microenvironment was characterized by a strong enrichment in follicular helper T cells (T_FH), as demonstrated through both Gene Set Enrichment Analysis (GSEA)-based transcriptomic approach and flow cytometry analysis of the CD4^posCXCR5^hiICOS^hi cell compartment. The majority of phospho-STAT6^pos B cells were located at the vicinity of cells expressing the PD-1 T_FH marker. Moreover, purified FL-derived T_FH, unlike non-T_FH T cells, expressed IL4. Finally, whereas chronically inflamed tonsils also exhibited an increase percentage of T_FH cells, tonsil-derived T_FH did not express IL4. Altogether, our study demonstrated that tumor-infiltrating T_FH specifically express functional IL-4 in FL, creating therefore an IL-4-dependent T_FH-B cell axis. This crosstalk could sustain FL pathogenesis and represent a new potential therapeutic target.