CD8^+ T-cells Co-expressing PD-1 and TIGIT Are Highly Frequent in Chronic Lymphocytic Leukemia

The role of immune checkpoint receptors in T-cell exhaustion has been demonstrated in several cancers. We investigated the co-expression of TIGIT/PD-1 and LAG-3/PD-1 cells in patients with chronic lymphocytic leukemia (CLL). The frequencies of TIGIT^+PD-1^+CD8^+and LAG-3^+PD-1^+CD8^+cells and relative mRNA expression of LSECtin and CD155 were examined in PBMCs from 33 CLL patients and 20 controls. The percentage of TIGIT^+PD-1^+CD8^+cells was significantly higher in CLL patients than in control subjects, with the preference in advanced-stage patients. However, LAG-3^+PD- 1^+CD8^+cell percentage was significantly lower in CLL patients than in the control subjects, and no significant differences were found between the early and advanced stages of the disease. An increase in the mRNA expression level of LSECtin, but not that of CD155, was observed in CLL patients compared to the control subjects. Collectively, a higher co-expression of PD-1 and TIGIT on CD8^+ T-cells in CLL compared to control subjects suggests an important role of TIGIT in T-cell exhaustion in CLL patients especially those with advanced disease