Lipid conjugation of TLR7 agonist Resiquimod ensures co-delivery with the liposomal Cationic Adjuvant Formulation 01 (CAF01) but does not enhance immunopotentiation compared to non-conjugated Resiquimod+CAF01

Oct 7, 2018Journal of controlled release : official journal of the Controlled Release Society

Attaching fat to the immune activator Resiquimod helps deliver it with a liposomal booster but does not improve immune response compared to unmodified Resiquimod with the booster

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Abstract

The formulation of DDA:TDB-TLR7/8 liposomes retains both resiquimod and the TB subunit antigen, but does not significantly enhance immune responses.

Resiquimod is a water-soluble agonist targeting TLR7/8, which plays a role in activating immune responses.
This study chemically conjugated resiquimod to a lipid to create a new liposome formulation for immunization.
The DDA:TDB-TLR7/8 formulation has similar size and charge characteristics to the DDA:TDB liposomes.
Immunization with these liposomes resulted in the formation of a vaccine depot at the injection site.
Despite the successful co-delivery of resiquimod and antigen, there was no notable increase in antibody or Th1 responses.

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Pattern recognition receptors, including the Toll-like receptors (TLRs), are important in the induction and activation of two critical arms of the host defence to pathogens and microorganisms: the rapid innate immune response (as characterised by the production of Th1 promoting cytokines and type 1 interferons) and the adaptive immune response. Through this activation, ligands and agonists of TLRs can enhance immunotherapeutic efficacy. Resiquimod is a small (water-soluble) agonist of the endosome-located Toll-like receptors 7 and 8 (TLR7/8). However due to its molecular attributes it rapidly distributes throughout the body after injection. To circumvent this, these TLR agonists can be incorporated within delivery systems, such as liposomes, to promote the co-delivery of both antigen and agonists to antigen presenting cells. In this present study, resiquimod has been chemically conjugated to a lipid to form a lipid-TLR7/8 agonist conjugate which can be incorporated within immunogenic cationic liposomes composed of dimethyldioctadecylammonium bromide (DDA) and the immunostimulatory glycolipid trehalose 6,6' - dibehenate (TDB). This DDA:TDB-TLR7/8 formulation offers similar vesicle characteristics to DDA:TDB (size and charge) and offers high retention of both resiquimod and the electrostatically adsorbed TB subunit antigen Ag85B-ESAT6-Rv2660c (H56). Following immunisation through the intramuscular (i.m.) route, these cationic DDA:TDB-TLR7/8 liposomes form a vaccine depot at the injection site. However, immunisation studies have shown that this biodistribution does not translate into notably increased antibody nor Th1 responses at the spleen and draining popliteal lymph node compared to DDA:TDB liposomes. This work demonstrates that the conjugation of TLR7/8 agonists to cationic liposomes can promote co-delivery but the immune responses stimulated do not merit the added complexity considerations of the formulation.

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