Poly( d,l -lactide-co-glycolide) Nanoparticles as Delivery Platforms for TLR7/8 Agonist-Based Cancer Vaccine

Targeted drug delivery can significantly influence the efficacy of a drug. In the past decades, diverse drug-delivery technologies, including nano- and microparticles, co-crystals, and microneedles have been developed to maximize therapeutic efficacy and minimize undesired side effects of therapeutics. Nanoparticles—submicron-sized drug carriers—have been actively investigated for the delivery of antibiotics, nucleic acids, peptide/proteins, and chemotherapeutics. Recently, nanoparticles have gained attention as a vaccine delivery platform for tumor-associated antigens (TAAs) and/or vaccine adjuvants. Agonists of imidazoquinoline-based Toll-like receptor (TLR) 7/8 are potent cytokine inducers that are used as cancer vaccine adjuvants to elicit robust T-cell response by activating dendritic cells (DCs). Despite their in vitro potency, the translation of TLR7 agonists as cancer vaccine adjuvants in the clinic has been limited by their poor retention at the injection site. Therefore, a formulation that could improve the availability of TLR7/8 agonists to DCs via conventional vaccine administration routes (subcutaneous, intramuscular) can broaden the application of TLR7/8 agonists for cancer immunotherapy. Polymeric nanoparticles fabricated with poly( d,l -lactide- co -glycolide) (PLGA) can be an efficient TLR7/8 agonist delivery platform. PLGA is a biocompatible polymer, and nanoparticles prepared from this polymer are stable in saline and are small enough to be administered by subcutaneous or intramuscular injections. Furthermore, nanoparticulate TLR7/8 delivery can enhance DC uptake and facilitate lymphatic drainage, both of which can enhance the adjuvanticity of TLR7/8 agonists compared with soluble forms. In this review, we discuss the use of PLGA nanoparticles with TLR7/8 agonists for improving cancer immunotherapy.