Restricted T cell receptor repertoire in CLL-like monoclonal B cell lymphocytosis and early stage CLL

Abstract

Analysis of the T cell receptor (TR) repertoire of chronic lymphocytic leukemia-like monoclonal B cell lymphocytosis (CLL-like MBL) and early stage CLL is relevant for understanding the dynamic interaction of expanded B cell clones with bystander T cells. Here we profiled the T cell receptor β chain (TRB) repertoire of the CD4⁺ and CD8⁺ T cell fractions from 16 CLL-like MBL and 13 untreated, Binet stage A/Rai stage 0 CLL patients using subcloning analysis followed by Sanger sequencing. The T cell subpopulations of both MBL and early stage CLL harbored restricted TRB gene repertoire, with CD4⁺ T cell clonal expansions whose frequency followed the numerical increase of clonal B cells. Longitudinal analysis in MBL cases revealed clonal persistence, alluding to persistent antigen stimulation. In addition, the identification of shared clonotypes among different MBL/early stage CLL cases pointed towards selection of the T cell clones by common antigenic elements. T cell clonotypes previously described in viral infections and immune disorders were also detected. Altogether, our findings evidence that antigen-mediated TR restriction occurs early in clonal evolution leading to CLL and may further increase together with B cell clonal expansion, possibly suggesting that the T cell selecting antigens are tumor-related.

Keywords: T cell receptor (TR); antigen restriction; chronic lymphocytic leukemia (CLL); clonotype; monoclonal B cell lymphocytosis (MBL).

Figure 1.

Clonality analysis. A, Percentage cumulative frequency of all expanded CD4⁺ and CD8⁺ T cell clonotypes in MBL subjects and CLL-A(0) patients. Horizontal lines correspond to the median value for each case. B, Correlation between the absolute count of malignant B cells and the percentage cumulative frequency of all expanded CD4⁺ T cell clonotypes per sample. ρ: Spearman's rho correlation coefficient.

Figure 2.

TRBV gene repertoire analysis of the CD4⁺ (A) and CD8⁺ (B) expanded T cell clonotypes in the MBL and CLL groups. The 15 most frequently detected genes within the expanded clonotypes of the MBL group are detailed in a decreasing order in the x-axis. Significant differences (P < 0.05) are shown with #. Variation of the data (range) is detailed in Tables S1 and S2.

Figure 3.

Longitudinal analysis in three selected MBL cases for the CD4⁺ and CD8⁺ T cell fractions. Gene frequencies (A) were assessed considering clonotypes whereas clonality (B) was measured considering rearrangements. A, TRBV gene repertoire dynamics over time. Only the five most frequent genes are represented. Sequential time points are indicated in the x-axis whereas the frequency (%) of each gene is shown in the y-axis. B, Clonal fluctuations over time. Each horizontal bar illustrates a different time point. White cylindrical parts of the bars account for the different clonotypes among the distinct time points whereas darker cubic parts represent persistent clonotypes. The frequency (%) of each clonotype is shown along the x-axis. Clonotypes shared by different time points, as well as their CDR3 amino acid sequence, are depicted in the same color.