Prolonged delivery of HIV-1 vaccine nanoparticles from hydrogels.

Immunization is a straightforward concept but remains for some pathogens like HIV-1 a challenge. Thus, new approaches towards increasing the efficacy of vaccines are required to turn the tide. There is increasing evidence that antigen exposure over several days to weeks induces a much stronger and more sustained immune response compared to traditional bolus injection, which usually leads to antigen elimination from the body within a couple of days. Therefore, we developed a poly(ethylene) glycol (PEG) hydrogel platform to investigate the principal feasibility of a sustained release of antigens to mimic natural infection kinetics. Eight-and four-armed PEG macromonomers of different MWs (10, 20, and 40 kDa) were end-group functionalized to allow for hydrogel formation via covalent cross-linking. An HIV-1 envelope (Env) antigen in its trimeric (Envtri) or monomeric (Envmono) form was applied. The soluble Env antigen was compared to a formulation of Env attached to silica nanoparticles (Env-SiNPs). The latter are known to have a higher immunogenicity compared to their soluble counterparts. Hydrogels were tunable regarding the rheological behavior allowing for different degradation times and release timeframes of Env-SiNPs over two to up to 50 days. Affinity measurements of the VCR01 antibody which specifically recognizes the CD4 binding site of Env, revealed that neither the integrity nor the functionality of Envmono-SiNPs (Kd = 2.1 ± 0.9 nM) and Envtri-SiNPs (Kd = 1.5 ± 1.3 nM), respectively, were impaired after release from the hydrogel (Kd before release: 2.1 ± 0.1 and 7.8 ± 5.3 nM, respectively). Finally, soluble Env and Env-SiNPs which are two physico-chemically distinct compounds, were co-delivered and shown to be sequentially released from one hydrogel which could be beneficial in terms of heterologous immunization or single dose vaccination. In summary, this study presents a tunable, versatile applicable, and effective delivery platform that could improve vaccination effectiveness also for other infectious diseases than HIV-1.

In Situ Forming iEDDA Hydrogels with Tunable Gelation Time Release High-Molecular Weight Proteins in a Controlled Manner over an Extended Time.

Off-target interactions between reactive hydrogel moieties and drug cargo as well as slow reaction kinetics and the absence of controlled protein release over an extended period of time are major drawbacks of chemically cross-linked hydrogels for biomedical applications. In this study, the inverse electron demand Diels-Alder (iEDDA) reaction between norbornene- and tetrazine-functionalized eight-armed poly(ethylene glycol) (PEG) macromonomers was used to overcome these obstacles. Oscillatory shear experiments revealed that the gel point of a 15% (w/v) eight-armed PEG hydrogel with a molecular weight of 10 kDa was less than 15 s, suggesting the potential for fast in situ gelation. However, the high-speed reaction kinetics result in a risk of premature gel formation that complicates the injection process. Therefore, we investigated the effect of polymer concentration, temperature, and chemical structure on the gelation time. The cross-linking reaction was further characterized regarding bioorthogonality. Only 11% of the model protein lysozyme was found to be PEGylated by the iEDDA reaction, whereas 51% interacted with the classical Diels-Alder reaction. After determination of the mesh size, fluorescein isothiocyanate-dextran was used to examine the release behavior of the hydrogels. When glucose oxidase was embedded into 15% (w/v) hydrogels, a controlled release over more than 250 days was achieved. Overall, the PEG-based hydrogels cross-linked via the fast iEDDA reaction represent a promising material for the long-term administration of biologics.