Impact of the Immune Landscape in Follicular Lymphoma: Insights into Histological Transformation in the Rituximab Era

Follicular lymphoma (FL) presents significant clinical heterogeneity, with some patients experiencing transformation into aggressive disease, a key contributor to FL-related mortality. Based on gene expression profiles, this study aimed to provide insights into immunological differences associated with transformation. Gene expression analysis using the NanoString nCounter Tumor Signaling 360 Panel was performed on diagnostic lymphoma samples from 70 FL patients diagnosed in the rituximab era, either non-transforming FL (nt-FL, n=34) or subsequently-transforming FL (st-FL, n=36), with paired high-grade transformed FL (tFL, n=36) samples available. In silico immunophenotyping was performed to infer immune cell infiltration using the CIBERSORTx algorithm. The gene expression analysis revealed 164 significantly differentially expressed genes distinguishing st-FL from nt-FL, generally presenting upregulation of B cell-related genes (CD40, IRF4, RELB), immunosuppressive molecules (IL10, SOCS3), and immune checkpoint molecules (CD276, TIM3). Analysis of immune cell proportions indicated significant differences in infiltrates of M1-like macrophages (p=0.007) and neutrophils (p=0.012) in nt-FL versus st-FL samples. Transformation-free survival (TFS) was associated with high numbers of both these cellular subsets (p=0.006 and 0=0.002, respectively). This was even more evident when combined, with inferior TFS in lymphomas with high infiltrates of both cell types (p<0.001). After transformation, tFL samples showed a reduction in T follicular helper cells (p=0.008) and an increase in immunosuppressive M2-like macrophages and neutrophils (p<0.001 and p=0.028, respectively). By elucidating the distinct molecular and immune landscapes of FL at the time of diagnosis and transformation, this study underscores the importance of immune microenvironment in FL transformation and patient outcome.