GENE EXPRESSION PROFILING OF T(14;18)‐NEGATIVE CD23+ FOLLICLE CENTER LYMPHOMA DEMONSTRATES ACTIVATION OF THE IL4/JAK/STAT6 PATHWAY AND A ROLE IN ITS PATHOGENESIS
2023-06-01

Introduction: t(14;18)-neg FL cases show similar copy number alterations and mutations as carried by t(14;18)-pos FL, but with different frequencies. STAT6 mutations are significantly more frequent in t(14;18)-neg FL than t(14;18)-pos FL and correlate with CD23 expression. The consequences of STAT6 mutations in t(14;18)-neg FL have not been investigated, and the impact of STAT6 pathway activation on the tumor microenvironment, which plays a central role in FL, are largely unknown. STAT6 pathway mutations (i.e., IL4R), have been demonstrated in primary mediastinal large B-cell lymphoma (PMBL), underlying the importance of STAT6 pathway activation in lymphomagenesis. The aim of this study was to perform gene expression profiling (GEP) on well-characterized t(14;18)-neg FL, with mutational analysis on STAT6 pathway associated genes. Methods: GEP was performed in 52 t(14;18)-neg FL including 39 cases with STAT6 or SOCS1 mutation (FLnegmut), and 13 cases with STAT6/SOCS1 wild type sequence (FLnegwt). Expression of 1392 genes associated with tumor/immune interaction was investigated using the HTG EdgeSeq Immuno-Oncology panel. DESeq2 algorithm was used to determine differentially expressed genes (p-adj < 0.05, fold change ≥1.5 and ≤−1.5). Gene set enrichment analysis (GSEA, Broad Institute) for STAT6 pathway genes was performed. An Ampliseq custom panel was used to explore STAT6 pathway genes (DUSP2, IL4R, IL13RA1, PTPN1, JAK1-3, STAT3, SOCS3, TYK2). Results: GEP of FLnegmut versus FLnegwt showed 32 differentially expressed genes. In FLnegmut a significant upregulation was detected in 23 genes (CD23, IL4R, CD83, ALOX5, ELL3, CD40, NCF1, GPR18, CD20, CD22, CD180, HLA-DOB, CIITA, HLA-DMB, LTB, PIK3CG, PAX5, CLEC4A, SELL, TNFRSF17, WASHC4, IL13RA1) and downregulation of 9 genes (SLAMF7, FCRLA, TNFRSF13B, CHIT1, FCGR1A_FCGR1B, MNDA, S100A8, IRF4, FCGR3A_3B). In FLnegmut, genes associated with germinal center (GC) and activated B cells (ABC) (CD23, IL4R, CD83, GPR18) were upregulated, whereas FLnegwt predominantly shows genes upregulated in post-GCB cells (SLAMF7, TNFRSF13B, IRF4), a transcriptional program supporting plasma cell differentiation. In contrast to PMBL, in t(14;18)-neg FL, no other mutations in the STAT6 pathway were identified. Conclusion: GEP identified two distinct groups within t(14;18)-neg FL, indicating different stages of differentiation of the neoplastic B cells. FLnegmut shows activation of STAT6 pathway through upregulation of CD23 and IL4R and by enrichment in GSEA and correlates with CD23 expression. Constitutive activation of STAT6 and consequent upregulation of CD23 prevent ongoing B cell differentiation in FLnegmut, precluding the cells from exiting the GC and adopting the state of activated B cell. In contrast, FLnegwt shows a transcriptional program supporting plasma cell differentiation suggesting that the COO is a late GC cell or a post-GCB cell. Keywords: indolent non-Hodgkin lymphoma, tumor biology and heterogeneity No conflicts of interests pertinent to the abstract.