NF-ΚB Activation as a Key Driver in Chronic Lymphocytic Leukemia Evolution to Richter’s Syndrome: Unraveling the Influence of Immune Microenvironment Dynamics

<b>Background/Objectives</b>: Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in Western countries and it can progress to Richter's syndrome (RS), a more aggressive condition. The NF-κB pathway is pivotal in CLL pathogenesis, driven mainly by B-cell receptor (BCR) signaling. However, recent evidence indicates that BCR signaling is reduced in RS, raising questions about whether and how NF-κB activity is maintained in RS. This study aims to elucidate the triggers and dynamics of NF-κB activation and the progression from CLL to RS. <b>Methods</b>: Integrated single-cell RNA sequencing data from peripheral blood samples of four CLL-RS patients were analyzed. NF-κB pathway activity and gene expression profiles were assessed to determine changes in NF-κB components and their targets. Tumor microenvironment composition and cell-cell communication patterns were inferred to explore NF-κB regulatory mechanisms. <b>Results</b>: RS samples showed increased proportions of malignant cells expressing NF-κB components, including <i>NFKB1</i>, <i>NFKB2</i>, <i>RELA</i>, <i>IKBKG</i>, <i>MAP3K14</i>, <i>CHUK</i>, and <i>IKBKB</i>, with significantly higher expression levels than in CLL. Enhanced NF-κB pathway activity in RS cells was associated with targets involved in immune modulation. The tumor microenvironment in RS displayed significant compositional changes, and signaling inference revealed enhanced cell-cell communication via BAFF and APRIL pathways, involving interactions with receptors such as BAFF-R and TACI on RS cells. <b>Conclusions</b>: The findings from this study reveal an active state of NF-κB in RS and suggest that this state plays a critical role in the evolution of CLL to RS, which is modulated by alternative signaling pathways and the influence of the tumor microenvironment.