Next-generation sequencing fails to identify human virus sequences in cutaneous squamous cell carcinoma

Nonmelanoma skin cancer (NMSC) shows a strongly increased incidence in solid organ transplant recipients (OTRs) and AIDS patients, suggesting an infectious etiology. The role of certain viruses, i.e., cutaneous human papillomaviruses (HPVs), in NMSC in immunosuppressed patients remains controversial. Merkel cell polyomavirus (MCPyV), which was recently identified using high-throughput sequencing, has been linked to cutaneous proliferations. Here, we aimed to identify novel or known viral sequences at the transcript level in cutaneous squamous cell carcinomas (SCCs) from OTR by using 454 high-throughput pyrosequencing, which can produce long reads (~400 bp) and thus is better suited for the analysis of unknown sequences than other sequencing platforms. cDNA libraries from three OTR SCC biopsies were generated and submitted to next-generation sequencing using a 454 platform. Bioinformatic analysis included digital transcriptome subtraction and--in parallel-reference mapping as an alternative way for depleting human sequences. All control sequences introduced for bioinformatics analysis were recovered correctly. Among 717,029 454-sequenced transcripts, nearly all identified viral reads were derived from phages. Bacterial sequences originated from the skin flora or environmental sources. Our study did not reveal any transcripts of known oncogenic or related unknown human viruses. These findings suggest that there is no abundant expression of known human viruses, or viruses with a high degree of homology to known human viruses, in cutaneous SCCs of OTR. Further studies are required to exclude the presence of viruses in NMSC, which cannot easily be identified on the basis of sequence homology to known viruses.