Stimuli-Responsive Polymers as Adjuvants and Carriers for Antigen Delivery

Stimuli-responsive polymers are gaining importance in immunology not only as carriers for delivering antigens to target tissues but also as immunologically inert adjuvants. Delivery of antigens in the presence or absence of a specific stimulus like pH, temperature and ionic strength offers a wide range of application possibilities to these smart polymers including vaccine formulations, implantation studies, targeted therapies and induction of autoimmunity. Other properties of polymers such as biocompatibility, biodegradability with different kinetics, nontoxicity, easy and defined chemical synthesis, and the ability to incorporate different types of antigens/immunostimulators make them promising candidates over other conventional materials for biomedical applications. Activation or suppression of antigen-specific immune responses and protection of antigens from in vivo degradation are some of the other advantages with these polymers. Changes in physical conformation of the polymers due to an environment stimulus provide an optimal release of an antigen. Varying the ratio of monomers and crosslinkers controls the release of antigens and degradation of polymer. In particulate form (as nano-sized) polymers can efficiently encapsulate the desired amount of antigens, which can easily cross across several biological barriers. However, adjuvant and carrier properties of these smart polymers depend not only on their intrinsic properties such as chain length, molecular weight, charge and a balance between hydrophobic and hydrophilic functional moieties, but also on extrinsic properties like format, shape and distribution of polymeric chains. In conclusion, further characterization of smart polymers could facilitate their direct application in humans.