Response of Recombinant Protein Based on Epitopes of the Spike Protein SARS-CoV-2 Indonesian Isolate: Immune and Leucocytes

This study aimed to explore immune responses and analyze of leukocyte cells induced by the recombinant spike protein with epitope sequences FKNHTSPDV obtained from the Indonesian SARS-CoV-2 isolate. The recombinant spike protein is synthesized by PT. Genetic Science Indonesia with a purity of 95% before being injected subcutaneously into Wistar rats on days 1, 14, and 28. Blood sampling was done before mice had injections at week 0 and mice that had undergone 3 injections or in the sixth week to obtaining an overview of leukocyte cells. Sera were harvested 14 days after each injection to determine the titers of IgG, IgM and CD4+ cells using ELISA. The results revealed that the IgG titers and CD4+ cell concentrations were found to increase after injection. Statistical test results showed meaningful differences between the control and treatment groups for IgG and CD4+ cells (p=0.003 and p=0.001 respectively). The average number of leukocytes in the three treatments was not significantly different. Conclusively, recombinant spike proteins with epitopal sequences of FKNHTSPDV isolates of Indonesian SARS-CoV-2 not only can induce humoral and cellular immune responses, and also has no impact on increasing leucocytes. It is indicated that the recombinant spike protein is feasible as a COVID-19 vaccine candidate.