Objective     To study the immunoregulatory effect of PD-L1 expressed by human cervical carcinoma cell line HeLa on activated human peripheral blood T lymphocytes in vitro.      Methods     HeLa cells were transfected with PD-L1

+

plasmid

and then the cells (PD-L1

+

HeLa cells) were co-c

ultured with PHA-activated human peripheral blood T lymphocytes. The proliferation level of T lymphocytes was determined by MTT assay. The apoptosis rate of T lymphocytes and the ratio of CD8

+

T lymphocytes to CD4

+

T lymphocytes (CD8

+

T/CD4

+

T) were analyzed by flow cytometry. The IFN-γ concentration in the culture supernatant of T lymphocytes was measured by ELISA.      Results     The optical density (OD) of T lymphocytes co-cultured with PD-L1

+

HeLa cells (0.31 ±0.02) was significantly lower than those of T lymphocytes co-cultured with HeLa cells free of PD-L1 (PD-L1

-

HeLa cells) (0.62±0.02) and T lymphocytes cultured alone (0.59±0.03) (P0.01). The apoptosis rate of T lymphocytes co-cultured with PD-L1

+

HeLa cells (32.7%) was significantly higher than those of T lymphocytes co-cultured with PD-L1

-

HeLa cells (17.9%) and T lymphocytes cultured alone (18.3%). The CD8

+

T/CD4

+

T ratio of T lymphocytes co-cultured with PD-L1

+

HeLa cells (0.86) was slightly lower than those of T lymphocytes co-culture with PD-L1

-

HeLa cells (0.91) and T lymphocytes cultured alone (0.89). The IFN-γ concentration in the culture supernatant of T lymphocytes co-cultured with PD-L1

+

HeLa cells (801.1±20.5 pg/ml) was significantly lower than those in the T lymphocytes co-cultured with PD-L1

-

HeLa cells (1006.2±30.2 pg/ml) and T lymphocytes cultured alone (1070.2±113.3 pg/ml) (P0.01).      Conclusion     PD-L1 significantly inhibits the proliferation in active peripheral blood T lymphocytes

promotes their apoptosis

and down-regulates their immune response.