A new adjuvant for vaccination
There is a great need to prevent infections through prophylactic vaccines or to use the immune system to modify pathogenic responses (therapeutic vaccines). Often, suboptimal vaccines require the use of adjuvants, compounds that can enhance the elicited immune response. Given the limited number of licensed adjuvants currently available in the EU and the United States, there is an urgent need to develop new adjuvants both for therapeutic and prophylactic vaccination. As a result, researchers of the EU-funded 'Viscogel - A chitosan based adjuvant for prophylactic and therapeutic vaccination' (VIVAC) project aimed to evaluate the safety and efficacy of a carbohydrate-based (chitosan) adjuvant known as ViscoGel. The Act-Hib vaccine for Heamophilus influenzae type b causing bacterial meningitis was used as a prophylactic vaccine model. For therapeutic vaccination, the major birch pollen allergen Bet v1 was chosen as a model. Scientists assessed the various ViscoGel formulations developed in terms of their physicochemical, adhesion and permeation properties. A toxicity evaluation of ViscoGel and ViscoGel–Act-Hib was carried out, followed by a pre-clinical evaluation. Enhanced humoral and cellular responses were noted on administering vaccines both subcutaneously and intramuscularly. Characterisation of the local response indicated a rapid infiltration of granulocytes that could be interacting with dendritic cells to give rise to the observed strong immune response. Testing of the ViscoGel–Act-Hib formulation in a clinical trial was subsequently performed to assess its efficacy in prophylactic vaccination. Intramuscularly administered ViscoGel was shown to be safe and well tolerated with a positive adjuvant effect of ViscoGel. Pre-clinical evaluation experiments of ViscoGel in therapeutic vaccines supported the successful subcutaneous use of the adjuvant in driving an enhanced immune response. However, when the experimental formulations were administered sublingually, scientists could not detect an improved uptake by antigen-presenting cells. VIVAC data support the use of ViscoGel as a simple, safe and versatile formulation- and adjuvant system in humans. Its implementation will resolve to an extent the current challenges faced in the development of effective prophylactic and therapeutic vaccines for infectious diseases and allergy/cancer, respectively.
