Human papillomavirus DNA resides in surgical drain fluid exosomes from HPV+ oropharyngeal squamous cell carcinoma patients and can be spread to neighboring HPV-negative cells.

Abstract

e18050 Background: Human papillomavirus (HPV) is the primary driver of oropharyngeal squamous cell carcinoma (OPC) in the US. Previous studies have investigated the role of plasma and saliva-based cell-free HPV DNA in OPC, yet the pathophysiological impact of exosomes in HPV+ OPC remains unknown. Exosomes are nanometer-sized membrane vesicles of endocytic origin carrying DNA, RNA and proteins, and have been shown to exist in blood, plasma, and in urine. We hypothesize that serosanguinous fluid drained from the postoperative bed, which we call “surgical drain fluid” (SDF) also contains exosomes. We further hypothesize that exosomes derived from SDF in HPV+ OPC patients contain HPV DNA that can be directly transmitted into HPV-negative cells. Methods: Twenty-six 5-mL SDF samples were collected following surgical neck dissections directly from the surgical drain; 21 from HPV+ and 5 from HPV- OPC patients. Exosomes were isolated from SDF using the Qiagen exoEasy kit. Exosome structure was characterized by transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). Western blotting (WB) targeted known exosomal surface markers. Exosomes were pretreated with DNase (New England Biolabs) to cleave the surface DNA, then exosomal DNA was extracted using a cell-free DNA isolation kit (Sigma). TaqMan real-time PCR was employed to detect HPV16 copy numbers. Lastly, exosomes isolated from 3 HPV+ patients’ SDF and 1 HPV- patient’s SDF were incubated with HPV- cell lines, SCC22A and SCC25, in order to query exosome-mediated HPV transmission. Results: TEM identified exosomes as round/oval-shaped vesicles measuring between 70 and 150 nm. NTA enumerated an average of 1.5 x 1011 particles per mL of SDF. WB further confirmed exosomal identity with strong CD63, CD9, and TSG101 signal detected. Among SDF exosomes from HPV+ OPC, 81% (n = 17) had detectable HPV16 DNA by real-time PCR, while all HPV- SDF exosomes (n = 5) showed undetectable HPV16. Paired comparison of HPV16 levels within exosomes to total HPV16 in SDF revealed an average of 90% of HPV16 in SDF was contained within exosomes. In an in vitro assay, SCC22A and SCC25 cells treated with HPV16 + exosomes became real-time PCR-positive for HPV16, while cells treated with HPV16- exosomes remained HPV16 negative. Conclusions: This study demonstrates that SDF, a novel post-surgical biofluid analyte, is enriched for HPV-containing exosomes in HPV+ OPC patients. We also found that exosomes from HPV+ OPC patients can transmit HPV to HPV-negative cells, suggesting a novel mode of virus-mediated spread of disease.