Clinical Significance Of The Expression Of Programmed Death Ligand 1(PD-L1) In Human Acute Leukemia

Background and objectiveAcute leukemia is the most common hematological malignancy. As the continuous improvement of combined chemotherapy regimens, the widely application of targeted therapeutic agents and hematopoietic stem cell transplation,the prognosis of the patients has been improved substantially. However, there are many patients who died from the resistance to chemotherapy and relapse. The studies about the tumor immune escape mechanisms has been more and more popular. As one of the members of B7 superfamily, PD-L1 is expressed on various solid tumors. When combined with the receptor PD-1, PD-L1 can transmit inhibitory signals and inhibit the anti-tumor immune response, thus participate in the immune escape of the tumor. The study explored the expression of PD-L1 in acute leukemia patients, and analysis the relationship between PD-L1 and the patients’ clinical characteristics and prognoses. MethodsWe detected the expression of PD-L1 on leukemia cells of 75 patients with acute leukemia who received final diagnosis by the Department of Hematology in the First Affiliated Hospital of Zhengzhou University between September 2014 and November 2014, by the means of flow cytometry. The 75 patients includes 39 males and 36 females with 59 as de novo patients and 16 as recurrent/refractory patients. Ages ranged from 14 to 77 years with a median age of 38 years. 62 were acute myeloid leukemia, included 1 with AML-M0, 4 with AML-M1, 25 with AMl-M2, 11 with AML-M3 and 16 with AML-M5.The remaining 13 patients are acute lymphocyte leukemia,comprised of 11 B-ALL and 3 T-ALL. Collecting the clinical information and monitoring the efficacy of treatment at the same time. Result1) PD-L1 was expressed in human acute leukemia, with the total expression rate of 32%, and the expression in AML-M5 was higher than that in the other subtypes(56.3% and 25.4% respectively)( P=0.019). The expression of PD-L1 in the recurrent/refractory group was higher than that in the de novo group(56.3% and 25.4% respectively)( P=0.019).2) There was no significant relationship between the expressions of PD-L1 and the clinical characteristics, including the patients’ age, gender,extramedullary infiltration, the percentage of blast cells in bone marrow, and peripheral hemogram( including WBC count, Hb level, Plt count).3) Curative effect analysis of the 59 de novo patients showed that the CR rate after the first course of chemotherapy in PD-L1 positive group is lower than that in PD-L1 negative group(66.7% and 71.4% respectively),as well as the CR rate after two courses of chemotherapy(70% and 88.6% respectively). The relapse rate after half a year’s treatment in the PD-L1 positive group was higher than that in the PD-L1 negative group(20% and 8.82% respectively),as well as the proportion of refractory patients(30% and 14.3% respectively).4) There was no significant relationship between the expressions of PD-L1 and the molecular biological features and cytogenetical characteristics of acute myeloid leukemia. ConclutionPD-L1 is expressed in human acute leukemia. The expression in the recurrent/refractory group is higher than the de novo group. The CR rate after the first course of chemotherapy in PD-L1 positive group is lower than that in PD-L1 negative group, as well as the CR rate after two courses of chemotherapy. The relapse rate after half a year’s treatment in the PD-L1 positive group was higher than that in the PD-L1 negative group, as well as the proportion of refractory patients. PD-L1 may involve in the immune escape and primary resistance mechanisms. It may be used as an indicator of the the patients’ prognosis and recurrence.