Subunit Vaccine Design for Effective Immunity

So as to plan an appropriate vaccine candidate, it must have the ability to induce CTL and HTL immune response. In other words subunit vaccine must contain both CTL and HTL epitopes along with suitable linkers. Keeping in mind the end goal to effectively activate both innate and adaptive immune response, subunit vaccine must consist of a strong immunostimulatory adjuvant. In the previous decades, there is a huge headway in the adjuvant engineering, for instance, Toll-like receptor (TLR) agonists have made its contribution as a part of peptide-based subunit vaccine as a functional option for present-day immunotherapy^{45 (link)}. Recently, Junqueira et al. have shown that CpGs oligodeoxynucleotides (CpG ODNs) and Glycoinositolphospholipids (GIPL) gotten from Trypanosome cruzi having the ability to activate TLR-4 and TLR9 leads to actuate potent pro-inflammatory reaction^{46 (link)}. Secondly, proteo-glycolipid complex (P8GLC) derived from Leishmania parasite has shown its affinity for the TLR-4 receptor and recognized as ligand^{47 (link)}. Moreover, TLRs having the capability to recognize the Plasmodium ligands, for example, Plasmodium falciparum primes the human TLR-4 response towards high proinflammatory cytokine profile^{48 (link)}. Shanmugam A. et at. has reported that synthetic TLR-4 agonist namely RS-09 (Sequence: APPHALS) can be used as a novel class of adjuvant^{49 (link)}, therefore, it was added as an adjuvant and linked with epitopes (CTL and HTL) by using EAAAK linker^{50 (link)}. Linkers assume an imperative part in simulating the vaccine construct to work as an independent immunogen and producing higher antibody titer than that of single immunogen^{51 (link)}. Total three linkers namely EAAAK, AAY, and GPGPG, were used to construct the final vaccine. AAY and GPGPG linkers were added at the intra-epitope position to link the CTL and HTL epitopes, respectively.