Cellular immune response to combined DNA-protein constructs carrying SARS-CoV-2 antigens

BACKGROUND: One approach that makes it possible to create vaccines relatively quickly and inexpensively is the creation of DNA vaccine constructs. They are of particular interest for the prevention of COVID-19, as they induce both types of immune response – humoral and T cell. Previously, we have created two DNA vaccines based on the pVAX vector: one encodes the full gene of the S protein of the SARS-CoV-2 virus, the second only encodes the receptor-binding domain (RBD) of the S protein of the SARS-CoV-2 virus. Next, the “naked” DNA was wrapped in a polycationic polyglucin-spermidine complex conjugated with the RBD protein. The resulting combined DNA-protein constructs were named CCV-RBD and CCV-S, respectively.

AIM: To investigate the induction of the T cell immune response of the developed combined DNA protein candidate vaccines in an animal model.

MATERIALS AND METHODS: BALB/c mice were immunized with constructs CCV-RBD and CCV-S, after which their spleens were removed from which splenocytes were isolated. The cellular response was assessed by the ability of splenocytes to secrete cytokines in response to stimulation with viral peptides. The intensity of the response was recorded using the intracellular cytokine staining (ICS) method using flow cytometry.

RESULTS: BALB/c mice were immunized twice with an interval of three weeks with a dose of 100 μg of DNA (8 animals per group): 1) CCV-RBD 2) CCV-S and 3) intact animals. It has been shown that both T helper lymphocytes (CD4⁺) and cytotoxic lymphocytes (CD8⁺) of animals immunized with CCV-S and CCV-RBD respond with the release of cytokines in response to stimulation with viral peptides.

CONCLUSIONS: In the case of CCV-RBD, a trend towards a higher response in both CD4⁺ and CD8⁺ was observed compared to the CCV-S group. Possibly, this difference may be due to more efficient synthesis of the RBD protein than the S protein, providing a DNA vaccine.