Calcium phosphate nanoparticle adjuvant

Abstract

Vaccination to protect against human infectious diseases may be enhanced by using adjuvants that can selectively stimulate immunoregulatory responses. In a murine model, a novel nanoparticulate adjuvant composed of calcium phosphate (CAP) was compared with the commonly used aluminum (alum) adjuvants for its ability to induce immunity to herpes simplex virus type 2 (HSV-2) and Epstein-Barr virus (EBV) infections. Results indicated that CAP was more potent as an adjuvant than alum, elicited little or no inflammation at the site of administration, induced high titers of immunoglobulin G2a (IgG2a) antibody and neutralizing antibody, and facilitated a high percentage of protection against HSV-2 infection. Additional benefits of CAP include (i) an insignificant IgE response, which is an important advantage over injection of alum compounds, and (ii) the fact that CAP is a natural constituent of the human body. Thus, CAP is very well tolerated and absorbed. These studies were performed with animal models. By virtue of the potency of this CAP adjuvant and the relative absence of side effects, we believe that this new CAP formulation has great potential for use as an adjuvant in humans.

FIG. 1

Anti-HSV-2 IgG and IgG2a antibody levels at 6 and 14 weeks after the initial immunization among different immunized groups of mice. The antigen concentration and the antibody dilution used in the IgG ELISA were 6 μg/ml and 1:800, respectively. The antigen concentration and the antibody dilution used in the IgG2a ELISA were 12 μg/ml and 1:400, respectively. □, control; ▧, CAP; ▤, HSV-2; ▥, HSV-2 plus alum; ■, HSV-2 plus CAP. ∗, P < 0.05 (HSV-2 plus CAP versus HSV-2 plus alum, HSV-2, and CAP).

FIG. 2

Anti-HSV-2 IgE and IgA antibody titers for mice immunized with HSV-2 alone, CAP alone, and HSV-2 containing CAP or alum at 6 and 14 weeks after the initial vaccination. The antigen concentration and the antibody dilution used in the IgE ELISA were 6 μg/ml and 1:800, respectively. The antigen concentration used in the IgA ELISA was 100 μg/ml. □, control; ▧, CAP; ▤, HSV-2; ▥, HSV-2 plus alum; ■, HSV-2 plus CAP. ∗, P < 0.05 (HSV-2 plus alum versus HSV-2 plus CAP, HSV-2, CAP, and control).

FIG. 3

Representative anti-EBV IgG and IgG2a antibody titers from mice immunized with EBV alone, CAP alone, EBV and CAP, and EBV and alum at 6 and 12 weeks after the initial immunization. The antigen concentration was 6 μg/ml, and the antibody titer was 1:800. □, control; ▧, CAP; ▤, EBV; ▥, EBV plus alum; ■, EBV plus CAP. ∗, P < 0.05 (EBV plus CAP versus EBV plus alum, EBV, CAP, and control).