STAT3 as a Candidate Shared Regulator of the CXCR4/CXCL12 and CXCR5/CXCL13 Homing Axes in Chronic Lymphocytic...

Chronic lymphocytic leukemia (CLL) is characterised by the dependence of malignant cells on specialised tissue microenvironments within the bone marrow (BM) and secondary lymphoid organs (SLOs), which provide essential survival and proliferative signals. The CXCR4/CXCL12 and CXCR5/CXCL13 chemokine axes direct the trafficking of CLL cells into these anatomically distinct compartments, where stromal-derived survival signals protect them from both spontaneous and therapy-induced apoptosis. Although each chemokine axis has been extensively studied individually, no previous review has integrated both pathways into a unified mechanistic framework. This review proposes that the signal transducer and activator of transcription 3 (STAT3) function as a shared molecular hub that integrates niche-derived cytokine signals, including interleukin-6 (IL-6), IL-10, and IL-21, and may transcriptionally upregulate both CXCR4 and CXCR5, and reinforce tissue homing through a positive feedback loop. This review seeks to evaluate the expression, signalling, and clinical significance of each axis, their points of convergence and divergence and the therapeutic strategies that disrupt these parallel homing pathways. Complementing this framework, recent clinical evidence indicates that circulating CXCL13 serves as a robust prognostic biomarker in CLL, and that STAT3 inhibition may overcome bone marrow stromal-mediated cytoprotection. The CXCL12-CXCR4-STAT3-IL-10 immunosuppressive axis further drives T-cell exhaustion. Together, these pathways form an integrated oncogenic network that supports CLL cell survival, drives immune dysfunction, and promotes therapy resistance. Several important knowledge gaps remain. These include the lack of direct validation of the STAT3-CXCR5 transcriptional axis in primary CLL cells and uncertainty regarding whether CXCR4/CXCR5 dominance represents a stable transcriptional programme or a dynamic, microenvironment-driven process. Addressing these questions through single-cell transcriptomics, spatial transcriptomics, proteomics, and functional validation studies will be essential for developing rational combination therapies capable of simultaneously disrupting both homing axes.