<p>Crystalline and Amorphous Preparation of Aluminum Hydroxide Nanoparticles Enhances Protective Antigen Domain 4 Specific Immunogenicity and Provides Protection Against Anthrax</p>

Abstract

Introduction: Aluminum salts, although they have been used as adjuvants in many vaccine formulations since 1926, exclusively induce a Th2-biased immune response, thereby limiting their use against intracellular pathogens like Mycobacterium tuberculosis. Methods and Results: Herein, we synthesized amorphous and crystalline forms of aluminum hydroxide nanoparticles (AH nps) of 150-200 nm size range. Using Bacillus anthracis protective antigen domain 4 (D4) as a model antigen, we demonstrated that both amorphous and crystalline forms of AH nps displayed enhanced antigen D4 uptake by THP1 cells as compared to commercial adjuvant aluminum hydroxide gel (AH gel). In a mouse model, both amorphous and crystalline AH nps triggered an enhanced D4-specific Th2-and Th1type immune response and conferred superior protection against anthrax spore challenge as compared to AH gel. Physicochemical characterization of crystalline and amorphous AH nps revealed stronger antigen D4 binding and release than AH gel. Conclusion: These results demonstrate that size and crystallinity of AH nps play important roles in mediating enhanced antigen presenting cells (APCs) activation and potentiating a strong antigen-specific immune response, and are critical parameters for the rational design of alum-based Th1-type adjuvant to induce a more balanced antigen-specific immune response.

Co-Administration of Aluminium Hydroxide Nanoparticles and Protective Antigen Domain 4 Encapsulated Non-Ionic Surfactant Vesicles Show Enhanced Immune Response and Superior Protection against Anthrax

“…However, AH np enhanced the IgG2a production against D4. This is in agreement with our previous results, where it was shown that AH np promotes IgG2a production against D4 [ 41 ]. Similarly, NISV-D4 promoted IgG2a production, which is in agreement with our previous results [ 40 ].…”

“…Alhydrogel had the slowest antigen release with around 15% antigen release by the 6 th day of analysis, followed by AH np with only around 15% antigen release. This can be correlated to the higher binding coefficient of D4 to alhydrogel and AH np, as was reported in our previous article and by other groups as well [ 41 , 56 , 57 ]. The D4 release kinetics from NISV-D4+ AH np and NISV-D4+ alhydrogel was almost similar.…”

“…D4 alone was unable to detect any significant antibody isotype, even after three immunisations. When administered with alhydrogel, D4 primarily elicited IgG1 antibody as reported in previous studies using D4 as antigen [ 41 ]. However, AH np enhanced the IgG2a production against D4.…”

“…However, particles of alhydrogel that are in the micron range do not typically offer a large area for binding, as it has been reported that only 1.7% of the area of alhydrogel is available for binding [ 61 ]. In our previous publication, we had shown that we can improve the available surface area for binding to antigens by synthesising aluminiujm hydroxide nanoparticles [ 41 ]. Moreover, APCs are more efficient in the phagocytosis of nanoparticulate adjuvants as compared to micron-range adjuvants [ 10 ].…”

“…In our previous publication [ 41 ], we have described the preparation and quantification of aluminium hydroxide nanoparticles. Briefly, equal volumes of 0.06 M AlCl 3 were mixed with 0.18 M NaOH with continuous stirring in a magnetic stirrer.…”