This study was designed to describe the course of IgA/IgG responses in cervical secretions and in serum following intramuscular administration of the HPV-16/18 AS04-adjuvant vaccine.
The cervical samples for IgA and IgG antibody quantification were obtained by insertion and removal of 2 ml phosphate-buffered saline (PBS) in the cervical canal. Peripheral blood was collected by venipuncture. Blood was collected into tubes containing separating gel, coagulated at room temperature and then centrifuged at 3000xg to obtain serum. An ELISA for detection of IgA and IgG anti-HPV-VLP was developed for this purpose. The cut-off values were calculated using the median absorbance plus three times the standard deviation (SD) of the results obtained with negative serum or cervical mucus control obtained of healthy HPV negative women. Comparisons between median of absorbance for anti-VLP antibodies pre-vaccination and post-vaccination were performed using two-way analysis of variance (ANOVA) followed by Sidak's multiple comparisons test. All values were considered significantly at p<0.05. The software employed for analysis was GraphPad Prism software, version 6.0 (GraphPad Software Inc., EUA).
IgG seroconversion after the second dose was observed in 100% of the subjects and remained one month after the third dose. Regarding IgG reactivity in cervical secretions, conversion was observed in 85% of women after the final dose. IgA seroconversion was observed in 76.7% of women after the third dose. Lower levels of IgA were detected in the cervical mucus (28.3%) and decreased to 23.3% after the last dose. Comparing local and systemic IgG responses, positivity in both serum and cervical samples was observed in 85%, while in 15% only the serum was IgG antibody positive. A weak agreement between local and systemic IgA responses was observed. Only 18.3% of subjects were local and systemic IgA positive, 58.4% were positive only in serum, 5% were positive only in the cervix, and 18.3% were both local and systemic IgA antibody negative.
After the third vaccination, there is a strong agreement between cervical and systemic IgG antibody responses and a weak agreement between cervical and systemic IgA antibody responses. The induction of IgA antibodies appears to be secondary to that of IgG antibodies in response to HPV intramuscular vaccination. The similarity in antibody levels obtained after the second and third vaccination suggests that two vaccinations may be sufficient to protect against HPV infection.