Evaluation of PD-1 / PD-L1 Expressions in Patients with Diffuse Large B Cell Lymphoma and Chronic Lymphocytic Leukemia

ABSTRACT
Aim: The programmed death 1 (PD-1) / PD-ligand (PDL) pathway is an important checkpoint for regulation of T cell mediated immune responses. Malignancies unfortunately also benefit from the immunosuppressive effects of the PD-1/PD-L1 pathway. There is not enough evidence regarding the importance of PD-1/ PD-L1 in Diffuse large B cell lymphoma (DLBCL) and Chronic lymphocytic leukemia (CLL). We aimed to evaluate the presence and prognostic significance of PD-1 / PD-L1 expression in DLBCL and CLL.
Materials and Methods: 26 DLBCL patients and 27 CLL patients aged between 18-80 years, who were followed up between January 2010 and September 2018 in Hematology Clinic, were included. For immunohistochemical staining, paraffin blocks belonging to the patients in the archive of Medical Pathology Department were used. Lymph node biopsy materials of DLBCL patients and bone marrow biopsy materials of CLL patients were evaluated. PD-1 was stained in non-neoplastic tissues and PD-L1 was stained in neoplastic cells. Those whose staining percentage was above 5% were considered positive. 
Results: PD-1; It was detected positive in 65.4% (n=17) of DLBCL cases and 14.8% (n=4) of CLL cases. PD-L1 was detected positive in 69.2% (n=18) of DLBCL cases, and PD-L1 was positive in 3.7% (n=1) of CLL cases. The frequency of PD-1 and PD-L1 expression and staining was found to be statistically significantly higher in DLBCL (p=<0.001). In PD-L1, a significant difference in expression was found between stages only in cases diagnosed with DLBCL (P=0,004). 
Conclusion: In our study, a higher rate of PD-1/ PD-L1 expression was detected in DLBCL than in the literature. A lower rate of PD-1/ PD-L1 expression was detected in CLL compared to other studies. It has been shown that PD-1/ PD-L1 expression is higher in DLBCL than in CLL. 
Keywords: Diffuse large B cell lymphoma, Chronic lymphocytic leukemia, PD-1, PD-L1.