Insight into the cellular fate and toxicity of aluminium adjuvants used in clinically approved human vaccinations

Abstract

Aluminium adjuvants remain the most widely used and effective adjuvants in vaccination and immunotherapy. Herein, the particle size distribution (PSD) of aluminium oxyhydroxide and aluminium hydroxyphosphate adjuvants was elucidated in attempt to correlate these properties with the biological responses observed post vaccination. Heightened solubility and potentially the generation of Al3+ in the lysosomal environment were positively correlated with an increase in cell mortality in vitro, potentially generating a greater inflammatory response at the site of simulated injection. The cellular uptake of aluminium based adjuvants (ABAs) used in clinically approved vaccinations are compared to a commonly used experimental ABA, in an in vitro THP-1 cell model. Using lumogallion as a direct-fluorescent molecular probe for aluminium, complemented with transmission electron microscopy provides further insight into the morphology of internalised particulates, driven by the physicochemical variations of the ABAs investigated. We demonstrate that not all aluminium adjuvants are equal neither in terms of their physical properties nor their biological reactivity and potential toxicities both at the injection site and beyond. High loading of aluminium oxyhydroxide in the cytoplasm of THP-1 cells without immediate cytotoxicity might predispose this form of aluminium adjuvant to its subsequent transport throughout the body including access to the brain.

From Stock Bottle to Vaccine: Elucidating the Particle Size Distributions of Aluminum Adjuvants Using Dynamic Light Scattering

“…The latter may serve to optimize the recognition and uptake of these complexes as well as delivering a greater amount of antigen for cellular processing, which in turn improves the kinetics and efficacy of the immunological response (Mannhalter et al, 1985). In our recent communication, we demonstrated high levels of adjuvant loading within the cytoplasm of THP-1 cells exposed to the Alhydrogel®-BSA complexes formed through the exposure of the adjuvant to nutrient rich culture medium (Mold et al, 2016). This observation was attributed to the large number of particles falling within the optimal size range for macrophagic recognition, which is reportedly between 2 and 3 μm (Champion et al, 2008).…”

“…However, strong associative forces between adjuvant and antigen can also induce the formation of agglomerates exceeding 10 μm (Morefield et al, 2005) and weak adsorption coefficients have been associated with the generation of higher relative antibody titres (Iyer et al, 2003; Hansen et al, 2007, 2009; Noe et al, 2010). Such agglomerates prove challenging to engulf (Morefield et al, 2005; Mold et al, 2016) and their subsequent cellular translocation to the lymph nodes may be significantly impeded as a result. In addition, conformational changes induced upon the adsorption of protein are more frequently encountered at the low concentrations of antigen used herein and in clinical vaccines (Lassen and Malmsten, 1996; Rabe et al, 2011).…”

Non-linear dose-response of aluminium hydroxide adjuvant particles: Selective low dose neurotoxicity

“…Although further studies are clearly required to document the influence of Alhydrogel® agglomeration state on in vivo neurotoxic effects, such a finding would not be unprecedented in the field of particle toxicology since both cellular uptake and distribution in the body of other types of particles are influenced by the particle size (Buzea et al, 2007;Reddy et al, 2007;Landsiedel et al, 2012), and aggregation rate (Mühlfeld et al, 2008), two parameters that strongly determine particle toxicity (Bell et al, 2014;Leclerc et al, 2012;Nascarella and Calabrese, 2012;Mold et al, 2016). …”

“…Macrophages capture bacteria which are usually in the 1-4 µm size range (Kowalski et al, 1999). A previous report showed in vitro exposure of monocyte lineage THP1 cells to Alhydrogel® 200 µg Al/mL resulted in cellular incorporation of Alhydrogel® agglomerates, the size of which was 1.20 µm as measured by transmission electron microscopy after 24h (Mold et al, 2014;Mold et al, 2016).…”

A poly(beta-amino ester) activates macrophages independent of NF-κB signaling

“…Additionally, the intrinsic immunogenicity of polymers and other therapeutic delivery vehicles remains under studied, and the structure-function relationships of the most common clinically used adjuvants (e.g. alum) are still being established [44, 45]. Although these findings should not be immediately extrapolated to all immunogenic synthetic carriers, they suggest pathways to investigate the mechanisms by which new carriers may modulate immune cell interactions, transfection efficiency, in vivo trafficking, and vaccine efficacy [8, 9, 46].…”