(M1130-12-69) Release of Vaccine Nanoparticles from Hydrogels Intended for HIV Immunization

Purpose: Today about 37.9 Mio people are living with the human immunodeficiency virus (HIV) of which only about 65 % have access to combination antiretroviral therapy. An HIV-vaccine for prophylaxis would be the most effective approach to fight this global pandemic. The viral envelope protein (Env) of HIV plays a key role in broadly neutralizing antibody elicitation and therefore protection against infection. We and others have shown that the immobilization of Env on the surface of nanoparticles (NPs) is more effective compared to vaccination with the soluble protein (2). Another aspect is that a prolonged delivery of Env antigens (Ag) e.g. from mini-osmotic pumps mimicking the kinetics of natural infections, enhanced humoral responses compared to traditional bolus immunization as well (3). Our goal is to combine both principles namely the particulate and prolonged delivery of Env Ag. Hydrogels have been widely used to release proteins with different kinetics and preserve protein integrity. Therefore, Ag carrying silica nanoparticles (SiNPs) were incorporated into poly(ethylene glycol) (PEG) hydrogels for release over a prolonged period.

Methods: PEG hydrogels were made by cross linking furyl and maleimide functionalized 8armPEG40k via the Diels-Alder reaction. Env monomer as well as human serum albumin (HSA) as a model were used for immobilization on SiNPs (100 nm) (3). Hydrogels of varying polymer content with incorporated SiNPs were fabricated and characterized in terms of rheology, in vitro release, and physicochemical properties. The extent and impact of possible PEGylation of Env monomer during hydrogel formation was analyzed by HPLC and estimated by affinity to broadly neutralizing antibody (Ab) by microscale thermophoresis, respectively.

Results: To allow for the formation of hydrogels, we successfully functionalized 8armPEG40k with furyl and maleimide groups (conversion: 82% and 61%). By mixing HSA-SiNPs together with the polymer, hydrogels were successfully loaded with HSA-SiNPs and released in vitro over 17 days in a controlled manner. Investigating the impact of loaded SiNPs on hydrogel integrity, rheological experiments revealed that gelation time (t_gel=104 min; 10% (w/V)) and hydrogel strength were not negatively influenced. Despite some Ag PEGylation phenomena (34 to 60%) during gel formation, the Ab affinity to Env-monomer was not negatively affected (K_{d (-PEG)} = 9.04 nM vs K_{d (+PEG)} = 1.46 nM).

Conclusion: We believe that PEG hydrogels could serve as a controlled release system for vaccination with Ag carrying NPs. An important step will be to produce hydrogels that allow for release of NPs over different time periods and kinetics and to demonstrate biological activity of released Ag carrying SiNPs in vivo.

References: (1) Peterhoff, D. et al., Vaccines (Basel) 2021, 9 (6).
(2) Tam, H. H et al., P Natl Acad Sci USA 2016, 113 (43), E6639-E6648.
(3) Thalhauser, S. et al., Eur J Pharm Sci 2020, 155.

Acknowledgements: This work was supported by a grant from the German Federal Ministry of Education and Research (BMBF, Project HIVacToGC).