Development of an edible vaccine candidate conferring protective efficacy against pneumococcal challenge using conserved PspA epitopes in a murine model

Streptococcus pneumoniae , also known as pneumococcus, is one of the leading causes of respiratory tract infections, meningitis, and septicemia in Bangladesh. In recent years, the pneumococcal surface protein A (PspA) has been suggested as a promising candidate, alone or with other immunogens, to be included in a future vaccine. Edible plant-based vaccines use recombinant antigens produced in plant tissues, providing an affordable and oral delivery option compared to traditional vaccines. This study applied a computational reverse vaccinology strategy to identify four potential B-cell epitope peptides from the PspA. Four epitope peptide sequences were found as the most potential B cell epitopes. Conservancy analysis was done using in silico tools. The sequences of S. pneumoniae epitope sequences were analyzed and placed in fusion with alpha zein. Agrobacterium tumefaciens strain LBA4404 containing the Ti plasmid was used for selection in all cases for the integration of the gene of interest. Antigens of S. pneumoniae fused to zein in Lycopersicon esculentum were generated using Agrobacterium -mediated genetic transformation protocols. The transformation through A. tumefaciens was confirmed by kanamycin selection and PCR analysis with the specific primers. Mice immunized with transgenic plant tissue and the control mice were challenged intraperitoneally with 10 times the LD 50 dose of the S. pneumoniae type 7F. The results demonstrated significant protection, with 83% of immunized mice surviving the live S. pneumoniae challenge compared to only 50% survival in control groups. These findings highlight the selected PspA epitope region as a promising target conferring protective efficacy in this murine model, supporting further development of an oral pneumococcal vaccine candidate.