[Characteristics of PD-L1 expression in tumor cells and tumor microenvironment of DLBCL with MYD88 L265P mutation]

Objective: To study the effect of MYD88 L265P mutation on the expression of PD-L1 in tumor cells and tumor microenvironment in diffuse large B-cell lymphoma (DLBCL), and to provide theoretical basis for immunotherapy for patients. Methods: Multiplex ligation-dependent probe amplification (MLPA) was used to detect the frequency of MYD88 L265P mutation in 72 cases of DLBCL diagnosed by pathologists in Cancer Hospital of Chinese Academy of Medical Sciences from August 2008 to May 2010. Expression of PD-L1 in tumor cells and tumor microenvironment in all samples was evaluated using PD-L1 (22C3) and PD-L1 (SP142) with Ventana automatic immunohistochemical (IHC) platform. The relationship between MYD88 L265P mutation and the expression of PD-L1 in DLBCL tumor cells and tumor microenvironment was assessed. Results: Of the 72 cases of DLBCL, MYD88 L265P mutation was detected in 15 (20.8%) cases. Nine cases with JAK2 amplification were excluded, and the remaining 63 cases of DLBCL were divided into MYD88 L265P mutant group (n=14) and MYD88 L265P wild-type group (n=49). IHC results showed that among the 14 cases of MYD88 L265P mutant groups, PD-L1 (22C3) was positive in 7 cases (7/14) of tumor cells and PD-L1 (SP142) was positive in 4 cases (4/14) of tumor microenvironment. Among the 49 cases of MYD88 L265P wild-type group, 9 cases (18.4%) were positive for PD-L1 (22C3) in tumor cells, and 38 cases (77.6%) were positive for PD-L1(SP142) in tumor microenvironment. In addition, among the 16 cases with PD-L1(22C3) expression in tumor cells, only 2 of the 7 cases with MYD88 L265P mutation were positive for PD-L1 (SP142) in tumor microenvironment. All 9 cases with wild-type MYD88 L265P were positive for PD-L1 (SP142) in tumor microenvironment. Statistical analysis showed that the expression level of PD-L1 (22C3) in tumor cells in the MYD88 L265P mutant group was significantly higher than that in the MYD88 L265P wild-type group (P=0.017). The expression level of PD-L1 (SP142) in tumor microenvironment in the MYD88 L265P mutant group was significantly lower than that in the MYD88 L265P wild-type group (P=0.001). Conclusions: MYD88 L265P mutation may play an important role in the regulation of PD-L1 expression in DLBCL tumor cells and tumor microenvironment. Further studies will provide a theoretical basis for immunotherapy of DLBCL patients with MYD88 L265P mutation.