Streptococcus pyogens known as group a streptococcus (GAS) is a gram-positive bacterium that causes more than 500 000 deaths annually over the world. Although primarily GAS causes mild symptoms such as fever and pharyngitis, but recurrent GAS infection may lead to severe diseases such as rheumatic heart disease and necrotizing fasciitis [1,2]. The development of vaccines is an effective approach to prevent GAS infection. Peptide-based subunit vaccines are safer than whole pathogen-based or protein-based vaccines. But peptide-based subunit vaccines are less immunogenic because they contain only the fragment of antigen [3]. So, the use of adjuvant is compulsory to improve the immune response. There is no available commercial safe universal vaccine adjuvant. Since the C-type lectin receptors (CLRs) are abundantly expressed in antigen presenting cells (APCs) and they can bind with the ligands bearing terminal sugar such as mannose and thus improve antigen uptake by APCs [3, 4]. So, the objective of this study is the development of mannosylated peptide-based vaccine against GAS.
Peptide antigen and a variety of mannosylated ligands were synthesized by microwave-assisted Fmoc and Boc-SPPS (solid-phase peptide synthesis) method. All compounds were purified and characterized using HPLC and mass spectrometry. Both antigen and targeting ligands were anchored to the liposome and liposomes were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Liposomes were injected subcutaneously (tail) to the C57BL/6 mice.
All liposomes composed of antigen and targeting ligands with purity >95% were less than 150 nm. The mannosylated liposomal vaccine formulations produced significant IgG titers compared to the negative control group upon immunization.
The most potential mannose ligand, able to improve immune response, has been chosen for future study. The effective mannose ligand can be used for the other vaccine formulation.