Priming of human papillomavirus type 11-specific humoral and cellular immune responses in college-aged women with a virus-like particle vaccine

Abstract

In this study, we evaluated the potency of a human papillomavirus (HPV) virus-like particle (VLP)-based vaccine at generating HPV type 11 (HPV-11)-specific cellular and humoral immune responses in seronegative women. The vaccine was administered by intramuscular immunizations at months 0, 2, and 6. A fourth immunization was administered to approximately half of the women at month 12. All vaccine recipients had positive HPV-11 VLP-specific lymphoproliferative responses at month 3 following the second immunization (geometric mean lymphoproliferative stimulation index [SI] = 28.4; 95% confidence interval [CI] = 16.9 to 48.0) and HPV-11 VLP-specific antibody titers following the first immunization at month 1 (geometric mean antibody titer = 53.9 milli-Merck units/ml, 95% CI, 34.8 to 83.7). In contrast, lymphoproliferative and antibody titer responses were never detected in the participants who received placebo. Relatively homogeneous lymphoproliferative responses were observed in all vaccinated women. The mean lymphoproliferative SI of the vaccinated group over the first 12 months of the study was 7.6-fold greater than that of the placebo group following the initial immunization. The cellular immune responses generated by VLP immunization were both Th1 and Th2, since peripheral blood mononuclear cells from vaccinees, but not placebo recipients, secreted interleukin 2 (IL-2), IL-5, and gamma interferon (IFN-gamma) in response to in vitro stimulation with HPV-11 VLP. The proliferation-based SI was moderately correlated with IFN-gamma production and significantly correlated with IL-2 production after the third immunization (P = 0.078 and 0.002, respectively). The robust lymphoproliferative responses were specific for HPV-11, since SIs generated against bovine papillomavirus and HPV-16 VLPs were not generally observed and when detected were similar pre- and postimmunization.

Figures

FIG. 1.

Lymphoproliferative responses and antibody titers in HPV-11 VLP vaccine participants. Women in both dose groups (50 and 100 μg) are represented separately, while placebo recipients from both dose groups are combined. The bars indicate the 95% CIs for the geometric mean SI and antibody titer. Arrows at months 0, 2, 6, and 12 represent when vaccine was administered. Top panel, T-cell proliferation was measured by standard lymphoproliferation assays at designated times throughout the vaccination regime. Lymphoproliferation results are presented as SIs. Participants who received a 50-μg HPV-11 VLP vaccine dose regime were not monitored for lymphoproliferation at months 2 and 18. Bottom panel, HPV-11 VLP-specific antibody titers were measured by standard RIA methods at designated times throughout the vaccination regime. The data were quantified against a serum standard and expressed in arbitrary mMU per milliliter.

FIG. 2.

HPV-11 VLP-specific antibody titer versus SI. Measurements of humoral and cellular immunity are presented at baseline (month 0) and after first, second, and third immunizations (months 1, 3, and 7, respectively) in vaccine and placebo recipients. Lymphoproliferation results are presented as SI, and antibody data are presented in mMU per milliliter.

FIG. 3.

Persistence of HPV-11-specific humoral and cellular immune responses. Lymphoproliferative responses and antibody titers in HPV-11 VLP-immunized women are presented for 36 months of the vaccine study. The left y axis represents the T-cell lymphoproliferative response (SI), while the right y axis represents antibody titers (mMU/milliliter). The bars indicate the 95% CIs for the geometric mean SI and antibody titer. Arrows at months 0, 2, 6, and 12 represent when vaccine was administered. SIs and antibody titers are not presented for the 24- and 36-month time points, respectively.

FIG. 4.

Specificity of lymphoproliferative responses: evaluation of multiple papillomavirus antigens. Proliferation assays were performed using multiple papillomavirus VLPs and control lysates of the respective VLP expression systems. Six virginal women and 12 vaccinated women (at month 0 and month 7 or 13) were analyzed for proliferative responses against the following antigen preparations: BPV, HPV-16 VLP prepared in yeast (VLP16 [yeast]), HPV-16 VLP expressed by baculovirus (VLP16 [bac]), HPV-11 VLP, and yeast and baculovirus (Bac) lysates. The bars indicate the 95% CI for the geometric mean SI. Statistical significance is indicated (∗) from a comparison of baseline measurements for lymphoproliferation against HPV-11 VLP in vaccine recipients (P = 0.001).