Screening for B7 or PDL-1 mRNA Expression Among Smokers

Objectives: The programmed death ligand (PDL-1) or B7 is a cell surface molecule (CD274) that is highly expressed in oral cancers and may be responsible, in part, for down-regulation of CD8 or cell-mediated immune activity against tumors. Recent evidence has suggested that PDL may be upregulated in established oral cancers, but no evidence can be found to demonstrate whether these effects can be observed among smokers that have not yet developed oral cancer. Based upon this evidence, the primary objective of this study was to evaluate whether oral cells collected from smokers exhibit any differential expression in PDL-1 or B7 compared with non-smoking samples.

Methods: Using an approved and established saliva collection protocol, saliva samples were collected from both smokers and non-smokers at a public dental school patient clinic over the course of four months (n=81). Cells were then isolated and RNA was successfully extracted from n=76/81 or 93.8% of these samples. The RNA was then screened for PDL-1/B7 mRNA expression using relative endpoint (RE) RT-PCR.
Results: Although the demographic analysis of these sample populations were not significantly different, the results of this screening revealed that n=16/37 or 43.2% of samples obtained from smokers had elevated mRNA expression of PDL-1/B7. In comparison, only 5.1% or n=2/39 of samples obtained from non-smokers exhibited any expression of mRNA for PDL-1/B7.

Conclusions: Although this pilot study was initially limited to a small subset of clinic patients, the results from this study strongly suggest that a significant difference may exist between smoking and non-smoking patients specific to the expression of this key immunomodulatory. Moreover, the paucity of evidence regarding mRNA expression of PDL-1/B7 among non-cancerous patients who smoke may further suggest this screening may be helpful to explain one mechanism that may enable oral tumors to evade immune detection prior to diagnosis and treatment.