The Expression of the Co-Inhibitory Molecule PD-1 and Its Ligand PD-L1 in Patients with MDS

Programmed death receptor 1 (PD-1) is an important immunosuppressive molecule and expresses on activated T cells, B cells and myeloid cells. PD-L1, a primary ligand PD-1, is mainly expressed on T cells and primary B cell surfaces and plays a role in the differentiation and apoptosis of these cells, induces a coinhibitory signal in activated T cells, promotes T cells apoptosis, incompetence and functional exhaustion. The expression of PD-1 is high in patients with hematologic malignancies and a high expression of PD-L1 is found on hematologic malignancies cells.

To further know the characteristics of PD-1 and PD-L1 in patients with MDS, we detected theexpression of PD-1 and PD-L1 in peripheral blood (PB) and bone marrow (BM) samples from 25 RAEB and 10 RARS patients using Real-time PCR. The PD1 and PD-L1 expression levels of 13 PB and 8 BM samples from normal individuals were as controls. The PD-1 levels of PB samples from 25 RAEB patients [42.40(4.5-173.96)%] were significantly higher than that from normal controls [32.32(19.45-41.38)%, P=0.026]. While the level of PD-1 in 10 RARS patients was comparable to that of normal controls and RAEB patients (P=0.401 and P=0.352). Compared to normal controls [23.72(3.23-39.2)%], the median PD-1 level of BM from 10 RAEB patients[36.81(12.14-151.52)%] showed an increasing tendency, but the difference was not statistically significant (P=0.062). PD-L1 expression levels of PB samples from RARS patients were significantly lower than that of normal controls (P=0.009). There were no significant difference between RAEB patients and normal controls about the PD-L1 expression level in PB and BM samples (P=0.248 and P=0.181) and between RAEB and RARS patients about PD-L1 expression level in PB samples (P=0.243). PD-1 level in BM samples from 11 RAEB patients with remission was (31.32±15.75)% and it was lower significantly than that before treatment [(59.94±47.44)%, P=0.034]. After progression or transformation, the expression level of PD1 (54.72±37.27)% increased again and was higher than that in remission (P=0.028).There were also no significant difference on PD-L1 expression among before treatment, bone marrow remission and progression or transformation (P>0.05). In 8 RAEB patients transformed to AML after treatment, PD-1 level has a decreasing tendency(P =0.05)and the change of PD-L1 has no significant difference (P>0.05).

In conclusion, PD1 mRNA level increased significantly in patients with RAEB and the changes of PD-1 was associated with the evolution of the disease after treatment with demethylating agents. The level of PD1 may be used as an indicator to determine the efficacy, but the changes of PD-L1 was not found regularity.