Kinetics and isotype profile of antibody responses in rhesus macaques induced following vaccination with HPV 6, 11, 16 and 18 L1-virus-like particles formulated with or without Merck aluminum adjuvant

Abstract

BACKGROUND: Human papillomaviruses (HPV) are the most common sexually transmitted viruses. Infection of the cervical epithelium by HPVs can lead to the development of cervical cancer. Recent advances in vaccine research have shown that immunization with papillomavirus-like particles (VLPs) containing the major structural viral protein, L1 from HPV 16 can provide protection from the establishment of a chronic HPV 16 infection and related cervical intraepithelial neoplasia (CIN) in baseline HPV 16 naive women. METHODS: To better understand the quantitative and qualitative effects of aluminum adjuvant on the immunogenic properties of an HPV 6, 11, 16 and 18L1 VLP vaccine, we used an HPV-specific, antibody isotyping assay and a competitive immunoassay that measures antibodies to neutralizing epitopes to profile sera from rhesus macaques immunized with the HPV L1 VLP vaccine formulated with or without aluminum adjuvant. RESULTS: Immunization with VLPs formulated with the aluminum adjuvant elicited a significantly stronger immune response with higher peak antibody titers both at four weeks post vaccination (12.7 to 41.9-fold higher) as well as in the persistent phase at week 52 (4.3 to 26.7-fold higher) than that of VLPs alone. Furthermore, the aluminum adjuvant formulated HPV VLP vaccine elicited a predominantly T helper type 2 response, with high levels of IgG1 and IgG4 and low levels of IgG2. The vaccine also elicited high levels of serum IgA, which may be important in providing mucosal immunity to impart protection in the anogenital tract. CONCLUSION: These results show that the HPV 6, 11, 16 and 18 L1-VLP vaccine formulated with Merck aluminum adjuvant elicits a robust and durable immune response and holds promise as a vaccine for preventing cervical cancer.

Figure 1

HPV 6, 11, 16 and 18 type-specific antibody titers measured in the competitive Luminex Immunoassay (cLIA). Sera from rhesus macaques immunized with 2 μg each of HPV 6, 11, 16 and 18L1-VLPs formulated with Merck Aluminum Adjuvant (MAA) (-◆-) or 2 μg each of HPV 6, 11, 16 and 18L1-VLPs alone (-◊ -) were collected a t the indicated time points and tested for Abs to neutralizing epitopes on HPV 6, 11, 16 and 18 using the HPV cLIA. Responses are reported as GMTs in milli-Merck Units per milliliter (mMU/mL) (n = 5 animals per group) for HPV 6, 11, 16 and 18 (Fig 1A, 1B. 1C. and 1D respectively). Arrows indicate vaccination boosts at weeks 8 and 24. A one-tailed, un-paired t-Test analysis was conducted on log-transformed antibody titers obtained from the cLIA. Error bars represent the standard error of the titers within each group.

Figure 2

HPV 6, 11, 16 and 18 L1 VLP-specific total IgG antibody titers. Sera from rhesus macaques immunized at week 0, 8 and 24 with 2 μg each of HPV 6, 11, 16 and 18L1-VLP formulated with Merck Aluminum Adjuvant (+MAA) (-◆-) or 2 μg each of HPV 6, 11, 16 and 18L1-VLPs alone (-MAA) (-◊ -) were collected at the indicated time points and tested for HPV 6, 11, 16 and 18 L1 VLP specific total IgG (-◆-, -◊ -) titers in a multiplexed detection assay. Responses are reported as the geometric means of end point dilution titers (n = 5 animals per group) for HPV 6, 11, 16 and 18 (2A, B, C, and D respectively). Arrows indicate vaccination boosts at weeks 8 and 24. The starting dilution for each sample was 1:10 and responses above an end point dilution of 10 were considered positive.

Figure 3

HPV L1-VLP specific IgM, IgA, IgG1 and IgG4 antibody titers. Sera from rhesus macaques immunized at week 0, 8 and 24 with 2 μg each of HPV 6, 11, 16 and 18 L1-VLPs formulated with Merck Aluminum Adjuvant (+MAA) (-◆-) or 2 μg each of HPV 6, 11, 16 and 18L1-VLPs alone (-MAA) (-◊ -) were collected at the indicated time points and tested for HPV L1 VLP specific (A) IgM, (B) IgA, (C) IgG1 and (D) IgG4 titers in a multiplexed detection assay. Responses are reported as GMTs (n = 5 monkeys per group) for HPV 16. Arrows indicate vaccination boosts at weeks 8 and 24. The starting dilution for each sample was 1:10 and responses above an end point dilution of 10 were considered above background. Graphs shown are for HPV 16 and are representative of HPV 6, 11, and 18.