Direct Identification of an HPV-16 Tumor Antigen from Cervical Cancer Biopsy Specimens

Abstract

Persistent infection with high-risk human papilloma viruses (HPV) is the worldwide cause of many cancers, including cervical, anal, vulval, vaginal, penile, and oropharyngeal. Since T cells naturally eliminate the majority of chronic HPV infections by recognizing epitopes displayed on virally altered epithelium, we exploited Poisson detection mass spectrometry (MS(^3)) to identify those epitopes and inform future T cell-based vaccine design. Nine cervical cancer biopsies from HPV-16 positive HLA-A02 patients were obtained, histopathology determined, and E7 oncogene PCR-amplified from tumor DNA and sequenced. Conservation of E7 oncogene coding segments was found in all tumors. MS(^3) analysis of HLA-A02 immunoprecipitates detected E7({11–19}) peptide (YMLDLQPET) in seven of the nine tumor biopsies. The remaining two samples were E7({11–19}) negative and lacked the HLA-A02 binding GILT thioreductase peptide despite possessing binding-competent HLA-A02 alleles. Thus, the conserved E7({11–19}) peptide is a dominant HLA-A02 binding tumor antigen in HPV-16 transformed cervical squamous and adenocarcinomas. Findings that a minority of HLA-A02:01 tumors lack expression of both E7({11–19}) and a peptide from a thioreductase important in processing of cysteine-rich proteins like E7 underscore the value of physical detection, define a potential additional tumor escape mechanism and have implications for therapeutic cancer vaccine development.