T cells in chronic lymphocytic leukemia display dysregulated expression of immune checkpoints and activation markers.

Chronic lymphocytic leukemia is characterized by impaired immune functions largely due to profound T-cell defects. T-cell functions also depend on co-signaling receptors, inhibitory or stimulatory, known as immune checkpoints, including cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) and programmed death-1 (PD-1). Here we analyzed the T-cell phenotype focusing on immune checkpoints and activation markers in chronic lymphocytic leukemia patients (n=80) with different clinical characteristics and compared them to healthy controls. In general, patients had higher absolute numbers of CD3 cells and the CD8 subset was particularly expanded in previously treated patients. Progressive patients had higher numbers of CD4 and CD8 cells expressing PD-1 compared to healthy controls, which was more pronounced in previously treated patients (=0.0003 and =0.001, respectively). A significant increase in antigen-experienced T cells was observed in patients within both the CD4 and CD8 subsets, with a significantly higher PD-1 expression. Higher numbers of CD4 and CD8 cells with intracellular CTLA-4 were observed in patients, as well as high numbers of proliferating (Ki67) and activated (CD69) CD4 and CD8 cells, more pronounced in patients with active disease. The numbers of Th1, Th2, Th17 and regulatory T cells were substantially increased in patients compared to controls (<0.05), albeit decreasing to low levels in pre-treated patients. In conclusion, chronic lymphocytic leukemia T cells display increased expression of immune checkpoints, abnormal subset distribution, and a higher proportion of proliferating cells compared to healthy T cells. Disease activity and previous treatment shape the T-cell profile of chronic lymphocytic leukemia patients in different ways.