Impact of molecular weight on the intrinsic immunogenic activity of poly(beta amino esters)

Abstract

Polymeric carriers are ubiquitously studied in vaccine and drug delivery to control the encapsulation, kinetics, and targeting of cargo. Recent research reveals many polymers can cause immunostimulatory and inflammatory responses, even in the absence of other immune signals. However, the extent to which this intrinsic immunogenicity evolves during degradation is understudied. Here we synthesized a small library of poly(beta amino esters) (PBAEs) that exhibit different starting molecular weights (MWs), but with similar and rapid degradation rates. Primary dendritic cells (DCs) treated with free PBAEs, either intact or degraded to form low MW fragments, were not activated. In contrast particles formed from PBAEs at different extents of degradation caused differential expression of classical DC activation markers (for example, CD40, CD80, CD86, MHCII), as well as antigen presentation. During degradation, activation levels changed with changing physicochemical properties (for example, MW, concentration, size, charge). Of note, irrespective of starting MW, immunogenicity peaked when the MW of degrading PBAEs decreased to a range of ∼1500-3000 Da. These findings could help inform design of future carriers that exploit the dynamic interactions with the immune system as materials degrade, leading to carriers that deliver cargo but also help direct the immune responses to vaccine or immunotherapy cargo. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1219-1229, 2017.

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

“…In our lab’s previous studies, free PBAE did not activate primary DCs, whereas PBAE particles did cause DC activation [10, 11]. Thus, we tested these same questions using macrophages.…”

“…that may affect intracellular delivery – i.e. transfection efficiency – and interactions with individual cell types [4, 6-11]. …”

“…Because nucleic acid cargos can have off-target effects including immune stimulation [12, 13] and because PBAEs can exhibit intrinsic immunogenicity in certain forms [10, 11], it is vital to understand the ability of these materials to either mitigate or enhance pro-inflammatory signaling. The immunogenic properties of a polymeric carrier can complicate vaccine design because the carrier itself impacts the response to the antigen – the biological target of the immune system – or to other vaccine components.…”

“…Our lab has previously used DCs isolated from mice to show that PBAEs exhibit intrinsic immune function when in particulate form following complexation with a polyanion, poly(sodium 4-styrenesulfonate); PBAE degradation [10] and molecular weight [11] played roles in the nature of the immune response to these particles. Because PBAEs were designed and characterized as nucleic acid delivery vehicles [4, 6], here we extend our studies to characterize the intrinsic immunogenicity of these polymers during delivery of siRNA in an in vitro model of immune activation, RAW264.7 mouse macrophages.…”

Improving Vaccine and Immunotherapy Design Using Biomaterials

“…In one example using a common class of degradable polymers, poly (β-amino esters), particle size and charge changed as molecular weight decreased. Regardless of the starting polymer structure, the material-driven immunogenicity peaked at a characteristic molecular weight range [27,28]. Thus, surface chemistry is important in rational design of biomaterials and presents new opportunities to tailor the types of responses elicited (Figure 2A, bottom).…”