In Vitro Study on the Effects of the Combined Use of a PD-L1 Silencing and Rituximab on Diffuse Large B-Cell Lymphoma

Background: The inhibitory immune checkpoint molecule programmed cell death ligand 1 (PD-L1) represents a promising therapeutic target for lymphoid malignancies. Moreover, PD-L1 expression in the tumor microenvironment correlates with tumor progression. Methods: This study used human diffuse large B cell lymphoma (DLBCL) cell lines SU-DHL-2 and SU-DHL-6. These cell lines were treated with either a PD-L1 smart silencer RNA (ssiPD-L1) or rituximab to evaluate antitumor effects by assessing cell viability, migration, and invasion. Flow cytometry was employed to assess cell apoptosis, and potential signaling pathways were examined using quantitative polymerase chain reaction (qPCR) and Western blot analyses. Results: Treatment with ssiPD-L1 significantly reduced PD-L1 expression, compared with the normal control smart silencer (ssiNC). Cell viability, migration, and invasion were significantly decreased after treatment with ssiPD-L1 or rituximab compared with control cells, with more pronounced effects observed after combination therapy. Administration of ssiPD-L1 or rituximab significantly increased the proportion of apoptotic and necrotic cells, while the proportion of proliferating cells was significantly reduced, again with stronger effects after combined treatment. Expression of PD-L1, the NF-κB, p-P65, C-X-C chemokine receptor type 4 (CXCR4), and B-cell lymphoma 2 (BCL-2) was significantly reduced after ssiPD-L1 or rituximab treatment. However, Bax expression, an apoptosis marker, was significantly increased in ssiPD-L1- and rituximab-treated cells, with the effect more pronounced in co-treated cells. Conclusion: Combined PD-L1 silencing and rituximab treatment inhibits DLBCL progression in vitro by promoting apoptosis and modulating NF-κB–related signaling pathways.