Identification of Distinct Unmutated Chronic Lymphocytic Leukemia Subsets in Mice Based on Their T Cell Dependency.

Chronic lymphocytic leukemia (CLL) can be divided into prognostically distinct subsets with stereotyped or non-stereotyped, mutated or unmutated B cell receptors (BCRs). Individual subsets vary in antigen specificity and origin, but the impact of antigenic pressure on the CLL BCR repertoire remains unknown. Here, we employed IgH.TE μ mice that spontaneously develop CLL, expressing mostly unmutated BCRs of which ~35% harbor VH 11-2/Vκ14-126 and recognize phosphatidylcholine. Proportions of VH 11/Vκ14-expressing CLL were increased in the absence of functional germinal centers in IgH.TE μ mice deficient for CD40L or activation-induced cytidine deaminase. Conversely, in vivo T cell-dependent immunization decreased the proportions of VH 11/Vκ14-expressing CLL. Furthermore, CLL onset was accelerated by enhanced BCR signaling in Siglec-G -/- mice or in mice expressing constitutively active Bruton's tyrosine kinase. Transcriptional profiling revealed that VH 11 and non-VH 11 CLL differed in the upregulation of specific pathways implicated in cell signaling and metabolism. Interestingly, principal component analyses using the 148 differentially expressed genes revealed that VH 11 and non-VH 11 CLL clustered with BCR-stimulated and anti-CD40-stimulated B cells, respectively. We identified an expression signature consisting of 13 genes that were differentially expressed in a larger panel of T cell-dependent non-VH 11 CLL compared with T cell-independent VH 11/Vκ14 or mutated IgH.TE μ CLL. Parallel differences in the expression of these 13 signature genes were observed between heterogeneous and stereotypic human unmutated CLL. Our findings provide evidence for two distinct unmutated CLL subsets with a specific transcriptional signature: one is T cell-independent and B-1 cell-derived while the other arises upon antigen stimulation in the context of T-cell help.