Background: Programmed death-1 (PD-1) and T-cell immunoglobulin- and mucin-domain-containing molecule-3 (Tim-3) are two major immune checkpoint receptors expressed on immune cells and their expression is related to the exhaustion phenotype. In the present in vitro study, blocking of PD-1 and Tim-3 molecules was performed on isolated natural killer (NK) cells from patients with chronic lymphocytic leukemia (CLL) to restore their functional properties.
Materials and methods: NK cells fraction was positively isolated from fresh peripheral blood of 18 CLL patients, treated with anti-PD-1 and anti-Tim-3 blocking monoclonal antibodies and co-cultured with K562 target cells to evaluate their apoptosis induction by Annexin V-PI method. Blocked NK cells were also incubated with anti-CD107a antibody to assess their degranulation properties by flow cytometry. The level of secreted tumor node factor-alpha (TNF-α) and interferon-gamma (IFN-γ) by NK cells was also measured by ELISA.
Results: Our results showed similar functional properties in terms of degranulation and apoptosis of K562 target cells by isolated NK cells from CLL patients in PD-1/Tim-3 blocked and control groups. It was also shown that blocking of PD-1 and Tim-3 could not improve the production of pro-inflammatory TNF-α and IFN-γ cytokines by isolated NK cells from CLL patients.
Conclusion: Altogether, our results indicated that pretreatment of NK cells with anti-PD-1 and anti-Tim-3 blocking antibodies in CLL patients at early clinical stages cannot improve their functional properties. Besides many other malignancies, the application of checkpoint inhibitors in CLL needs more investigations and complementary studies.
Keywords: Chronic lymphocytic leukemia; PD-1; Tim-3; immune checkpoint inhibitors; natural killer cells.