Absence of Antibody against Human Papillomavirus Type 16 E6 and E7 in Patients with Cervical Cancer Is Independent of Sequence Variations

It is not known whether the lack of antibody response against human papillomavirus (HPV) type 16 E6 and E7 among some cervical cancer patients is due to naturally existing sequence variations. In this study, naturally occurring HPV-16 E6 and E7 variants (including the prototype) were cloned, antigens were expressed by in vitro transcription and translation, and the humoral immune response of 34 HPV-16-positive cervical cancer patients was analyzed by radioimmunoprecipitation assay (RIPA). In addition, the RIPA results were compared with those of a sandwich-protein ELISA, to further substantiate antibody status. Sera lacking E6 reactivity by RIPA remained negative by protein ELISA. All E6 antigens (the prototype and the variants 350G¿L83V, 131G¿R10G/350G¿L83V, 335T¿H78Y/350G¿L83V, 345G¿Y81C/350G¿L83V, and African 2 ¿Af2) showed cross-reactivity by RIPA. The lack of HPV-16 E6 or E7 antibodies is independent of naturally occurring variants in cervical cancer patients. Thus, testing for HPV-16 E6 or E7 prototype antigens seems to be sufficient in serological assays.