Objectives: Head and neck squamous cell carcinoma (HNSCC) is the 6th most common cancer worldwide with a poor prognosis of ~40% at 5 years for HPV-negative disease. Recently, immune checkpoint inhibitors (specifically, anti-PD-1 checkpoint inhibitors that block the PD-L1/PD-1 immunosuppressive axis) have been approved as a treatment for patients with recurrent/metastatic HNSCC. However, most patients (>80%) fail to respond to checkpoint inhibitors. PD-L1 expression on tumors plays an important role in immune evasion and can also influence response to checkpoint inhibitors. Tumor PD-L1 expression has been shown to correlate with checkpoint response. Factors that might affect PDL1 expression in HNSCC remain unclear. In this study, we explored the effect of periodontal bacteria, which has been associated with oral cancer, on PD-L1 expression in oral cancer cells.

Materials and Methods: 303 HNSCC were compared to 37 adjacent control tissues in the TCGA mRNA expression database (RNASeq V2); the analysis was done based on tumor types. RT-PCR and flow cytometry were used to measure the base line expression of PD-L1 in seven head and neck cancer cell lines and human oral tissues. OQ01, an oral cancer cell line, was infected with four periodontal bacteria (Tanneralla forsynthia, Treponema denticola, Porphyromonas gingivalis, and Fusobacterium nucleatum). OQ01 and RPMI2650 cells were infected with two different strains of Fusobacteria (F. periodonticum, F. vincentii). The relative changes in expression of PLD1 was measured using RT-PCR in cell lysate after RNA isolation. PD-L1 protein level on the cell surface was measured using flow cytometry.

Results: TCGA data analysis revealed that PDL1 was significantly (P< 0.0005) elevated in total cancer tissues compared to total controls. In the same data analysis, PDL1 expression was significantly (P< 0.05) elevated in oral cavity tumor compared to normal control. Expression of PD-L1 was variable among head and neck cancer patients and cell lines. Both F. nucleatum and P. gingivalis were able to enhance PD-L1 expression in OQ01 cells (10 and 15 fold, respectively). Two strains of Fusobacteria tested (F. periodonticum, F. vincentii) were also able to induce PD-L1 both at the mRNA (P< 0.005 and P< 0.05 respectively) and protein level in OQ01 and RPMI 2650 cells. Interestingly, the same strains of Fusobacteria enhanced MYC expression in OQ01 and RPMI 2650 cells. As a transcription factor MYC has been reported to regulate PDL1 transcription. These data along with our results suggest that Fusobacterial upregulation of PD-L1 expression might be through MYC enhanced expression.

Conclusions: This study revealed that Fusobacteria enhance PD-L1 expression on HNSCC cancer cell lines, possibly through upregulation of MYC. This may have implications on cancer cell immune evasion and checkpoint inhibitor treatment response.

Note: This abstract was not presented at the conference.

Citation Format: Amani Harrandah, Rekha Rani Grag, Yuk Pheel Park, Sasanka S. Chukkapalli, Nikhita Yadlapalli, Edward K. L. Chan, Natalie Silver. Fusobacteria upregulates PD-L1 in head and neck cancer cell lines: Potential mechanism for immune evasion [abstract]. In: Proceedings of the AACR Special Conference on the Microbiome, Viruses, and Cancer; 2020 Feb 21-24; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2020;80(8 Suppl):Abstract nr A10.