Recent Advances in Nanovaccines Using Biomimetic Immunomodulatory Materials

Vijayan, Veena; Mohapatra, Adityanarayan; Uthaman, Saji; Park, In-Kyu

Adjuvants are ingredients used in vaccines to enable the body to produce a stronger immune response, and help vaccines work better. There are different mechanisms by which adjuvants elicit immune responses, which are as follows: 1) prolonged release of antigen at the site of injection, 2) cytokines and chemokine level gets upregulated, 3) recruitment of cells at the injection site, 4) antigen uptake and presentation to antigen-presenting cells increases, 5) APC activates and matures, resulting in the migration to draining lymph nodes, and 6) inflammasome activation [88] [89] [90] . Generally, adjuvants are classified based on their mechanism of action, physicochemical properties, and origin. Adjuvants can be classified as delivery systems or immune potentiators, depending on their action mechanism. Table 2 describes the partial list of adjuvants used in the abovementioned three categories. Champion et al. reported a vault NP vaccine for inducing protective immunity at distant mucosal surfaces. These vault NPs contain immunogenic proteins, and hence they are considered as adjuvants [81] . In another study, Riitho et al. [91] formulated a biomimetic vaccine by encapsulating a viral protein inside a polymeric shell, wherein the viral protein was known to have effective cross-presentation by MHC class I. These polymeric NPs were adjuvanted with polyinosinic: polycytidylic acid (poly(I:C)), and loaded with viral proteins that act as antigens. These nanovaccines exhibited significant virus-neutralizing activity, and they were effective against infections caused by the bovine virus diarrhea-virus [91] . Wang et al. [22] reported the use of a dual-functional nanomodulator to enhance CpG mediated cancer therapy. In their work, they synthesized manganese oxide nanosheets and conjugated anticancer drug doxorubicin (DOX) and CpG-silver nanoclusters as the adjuvant [22] . Yang et al. [52] reported the use of a lipid (DSPE-PEG-mannose) modified cancer cell membrane that was coated onto a polymeric NP loaded with adjuvant TLR 7 for an anticancer effect [52] . Recently, Le et al. [92] suggested an in situ nanoadjuvant as a tumor vaccine to prevent the long-term recurrence of tumors. In their study, polydopamine NPs were loaded with imiquimod, and then the NP surface was modified with programmed death-ligand 1 (PDL1) antibodies for the co-delivery of both antigen and adjuvants to the same antigen-presenting cells. This nanoadjuvant with PDL1 antibody could block PDL1 immune checkpoint in tumors, and it is expected to have combinational photothermal and immunotherapy effects [92] .