Frequency and functional characterization of exhausted CD8+ T cells in chronic lymphocytic leukemia

Objectives: The phenotypic and functional properties of Tim-3(+)/PD-1(+)/CD8(+) cells as exhausted T cells were investigated in chronic lymphocytic leukemia (CLL). Methods: Frequency of CD8(+)/Tim-3(+)/PD-1(+) exhausted cells was determined by flow cytometry. For functional analysis, magnetic beads-isolated CD8(+) T cells were stimulated with PHA and PMA/ionocymin to assess their proliferative responses and cytokine production by MTT and ELISA, respectively. Cytotoxic activity of isolated CD8(+) T cells was determined using CD107a degranulation assay. Results: The proportion of exhausted CD8(+) T cells was significantly higher in CLL compared to controls. Isolated CD8(+) T cells from CLL showed functional defects in proliferation, degranulation, and cytokines production. While IL-2, TNF-alpha, and IFN-gamma were significantly lower in CLL patients, IL-10 was higher in the patients group. Patients with progressive clinical stages showed higher frequency and dysfunction of exhausted CD8(+) T cells. Conclusion: Targeting immune inhibitory receptors to restore the function of tumor surrounding T cells could be helpful for immunotherapy of CLL.