Salivary Molecular Screening For B7-H1/PDL-1 Expression Among Smokers

Objectives: The cell surface B7 homolog 1 or B7-H1 (also known as CD274 or the programmed death ligand PDL-1) binds to cytotoxic T-cell receptors to induce an inhibitory signal to down-regulate T-cell activation and proliferation when encountering normal somatic cells and tissues. Previous studies have demonstrated overexpression of the programmed death ligand (PDL-1) among oral squamous cell carcinoma samples, as well as other tumors including esophageal, lung, and colon, that may explain the ability to escape immune system detection. The main objective of this pilot study was to determine if dysregulation of B7-H1 could be observed among smokers.
Methods: Using an existing saliva sample repository, RNA was isolated from samples originally obtained from patients that self-identified as smokers (n=12) or non-smokers (n=11). RNA was extracted using a commercial isolation kit, resulting in 22 RNA samples with sufficient RNA quality and quantity for RT-PCR screening (yield = 22/23 or 95%).
Results: Molecular screening revealed B7-H1 expression among all of the normal, non-smoking patient samples screened but was absent or missing from all of the samples derived from smoking patients. Although B7-H1 dysregulation was observed among samples from smoking patients, the lack of expression was unexpected.
Conclusions: Although previous studies have found overexpression of B7-H1 in well-established tumors and oral cancers, little information is available regarding the expression among patients without a definitive diagnosis and virtually no information is available regarding expression in oral tissues comparing smokers and non-smokers. This study may be the first to observe down-regulation of B7-H1 among oral saliva-based samples from smokers, which may suggest an intermediate expression phase during oral carcinogenesis – although larger, prospective studies will be needed to verify these effects and observations.