Imaging mass spectrometry analysis enables in situ detection of HPV in FFPE tissues

Aim: Cutaneous warts are benign papillomas of the skin caused by infection with human papillomavirus (HPV). HPV comprise a family of more than 130 types. Most warts are associated with low-risk HPV strains, and harbour no or little potential for malignant progression. Warts typically continue to increase in size and distribution and may become more resistant to treatment. Diagnostic tests are required to detect high-risk but also low-risk HPV subtypes with high specificity and sensitivity. We developed a proteomic-based imaging mass spectrometry (IMS) approach to investigate HPV molecular signals directly from host specimens. Methods: Formalin-fixed paraffin-embedded (FFPE) tissue sections from skin warts were deparaffinized, antigen retrieved, in-situ trypsin digested and covered with alpha-cyano-4-hydroxycinnamic acid matrix for IMS analysis using a rapifleX MALDI Tissuetyper (Bruker Daltonik). Clinical examination of warts including appearance, size, consistency and distribution were recorded. Mass spectra were exported from regions of interest and compared with histopathological diagnosis. Results: IMS allowed to obtain several molecular signals directly from tissue sections in a spatially-targeted approach. Collected mass spectra from HPV infected and non-infected tissue regions were compared and evaluated. More than fifty peptide signals were identified in the HPV infected tissue regions. Interestingly, specific peptide signals correlated with the virus location moving from the lower to the top epidermis skin layers. Conclusion: We detected specific peptides related to HPV directly from the host specimens using IMS. The ability to rapidly identify signatures specific to microorganisms in tissue is a major advantage that greatly decrease both time and cost.