Access to Follicular Dendritic Cells Is a Pivotal Step in Murine Chronic Lymphocytic Leukemia B-cell Activation and Proliferation

In human chronic lymphocytic leukemia (CLL) pathogenesis, B-cell antigen receptor signaling seems important for leukemia B-cell ontogeny, whereas the microenvironment influences B-cell activation, tumor cell lodging, and provision of antigenic stimuli. Using the murine Eμ-Tcl1 CLL model, we demonstrate that CXCR5-controlled access to follicular dendritic cells confers proliferative stimuli to leukemia B cells. Intravital imaging revealed a marginal zone B cell–like leukemia cell trafficking route. Murine and human CLL cells reciprocally stimulated resident mesenchymal stromal cells through lymphotoxin–β-receptor activation, resulting in CXCL13 secretion and stromal compartment remodeling. Inhibition of lymphotoxin/lymphotoxin–β-receptor signaling or of CXCR5 signaling retards leukemia progression. Thus, CXCR5 activity links tumor cell homing, shaping a survival niche, and access to localized proliferation stimuli. Significance: CLL and other indolent lymphoma are not curable and usually relapse after treatment, a process in which the tumor microenvironment plays a pivotal role. We dissect the consecutive steps of CXCR5-dependent tumor cell lodging and LTβR-dependent stroma–leukemia cell interaction; moreover, we provide therapeutic solutions to interfere with this reciprocal tumor–stroma cross-talk. Cancer Discov; 4(12); 1448–65. ©2014 AACR. See related commentary by López-Guerra et al., p. 1374 This article is highlighted in the In This Issue feature, p. 1355