Background: Oral squamous cell carcinoma (OSCC), with poor prognosis and high mortality rates, is one of the most diagnosed head and neck cancers. Cancer stem cells (CSCs) - epithelial-to-mesenchymal transition (EMT) loop is increasingly implicated in the therapy-resistance, relapse, and metastasis of OSCC patients. Accumulating evidence indicate that aberrantly expressed CD47 is associated with cell-death evasion, invasion and cancer metastasis; however, the role of CD47 in the modulation of CSCs-like phenotypes, including therapy-resistance and metastasis, with its underlying mechanism in OSCC remains largely underexplored. Methods: This study investigated the CSCs- modulating potential of CD47 in OSCC cell lines SAS, TW2.6, HSC-3 and FaDu using bioinformatics approach, immunoblotting, immunofluorescence staining, migration, invasion, colony and orosphere formation, as well as radiosensitivity assays. Results: We demonstrated that the characteristic ectopic expression of CD47 in OSCC patients was associated with ~ 20% 2-year survival disadvantage (p = 0.01) and positively correlated with the expression of pluripotency factors; while shRNA silencing of CD47 significantly suppressed cell viability and markedly inhibited orosphere formation, resulting in smaller and fewer orospheres, and downregulated CD133, SOX2, OCT4 and c-Myc mRNA and protein expression levels. We also showed that CD47 downregulation attenuates EMT, migration and clonogenicity of OSCC cells, with associated E-cadherin upregulation and suppression of Vimentin, Slug, Snail, and N-cadherin expression. Conclusion: Of therapeutic relevance, combined with radiotherapy, CD47 knockdown enhanced the anti-OSCC effect of radiotherapy. Thus, we demonstrate the therapeutic feasibility of a CD47-mediated anti-CSCs strategy, and suggest a role for CD47 suppression in potentiating the therapeutic efficacy of radiation therapy in OSCC patients.

Immune checkpoint inhibitors (ICIs), including anti-programmed cell death 1 ligand 1 (PD-L1) antibodies, are significantly changing treatment strategies for human malignant diseases including oral cancer. Cancer cells usually escape from immune system and acquire proliferative capacity and invasive/metastatic potential. We have focused on the two immune checkpoints, PD-1/PD-L1 and CD47/SIRPα in the tumor microenvironment of oral squamous cell carcinoma (OSCC), and performed a retrospective analysis of the expression of seven immune-related factors (PD-L1, PD-1, CD4, CD8, CD47, CD56 and CD11c), and examined their correlation with clinicopathological status. As a result, there were no significant findings relating seven immune-related factors and several clinicopathological statuses. However, the immune-checkpoint related factors (PD-1, PD-L1, CD47) were highly expressed in non-keratinized epithelium-originated tumors when compared to those in keratinized epithelium-originated tumors. It is of interest that immunoediting via immune checkpoint-related factors was facilitated in non-keratinized sites. Several researchers reported that keratinization of oral mucosal epithelia affected the immune response, but our present finding is the first study to show a difference of the tumor immunity in the originating-epithelium of OSCC, keratinized or non-keratinized. Tumor immunity, an immune escape status of OSCC might be different in the originating-epithelium, keratinized or non-keratinized.