Graded constitutive NF-κB signaling in B cells drives SLL/CLL-like lymphomagenesis and overcomes microenvironment dependence

Aberrant activation of NF-κB transcription factors is a hallmark of human lymphoma. Many lymphoma- as well as microenvironment-associated alterations mediating enhanced NF-κB signaling occur upstream of the IκB Kinase complex and its key kinase IKK2, therefore affecting additional pathways. Here, we specifically investigated the effects of graded canonical NF-κB activation in mouse B cells, induced through the expression of one or two copies of a constitutively active IKK2 variant (IKK2ca). Strong canonical NF-κB signaling drives an early expansion of B1a cells, culminating in lethal lymphomagenesis with complete penetrance. These B cell malignancies resemble human small lymphocytic lymphoma (SLL) and chronic lymphocytic leukemia (CLL) with respect to disease course, gene expression and stereotypic B cell receptor clonality. Mice with less pronounced canonical NF-κB activation presented delayed, more heterogeneous lymphomagenesis with lower penetrance, highlighting NF-κB dose-dependent effects. Mechanistically, we show that constitutive IKK2 signals provide a profound cell-intrinsic competitive advantage to B1a cells and strongly synergize with TCL1 overexpression, resulting in a severely accelerated and aggravated CLL-like disease. In addition, strong constitutive NF-κB activation overcomes the critical dependency of TC1tg lymphoma cells on obligate environmental maintenance signals. In conclusion, we provide direct in vivo proof for canonical NF-κB signals as an oncogenic driver in an animal model, and demonstrate reduced tumor microenvironment dependency as a key NF-κB-mediated mechanism in lymphomagenesis. Our findings underscore the pivotal role of this pathway in human SLL/CLL and its potential as a therapeutic target, particularly for aggressive/refractory disease.