Investigation of Pre-clinical and Phase II clinical studies of VLP-58-1023- AL-K3-PII vaccine for Alpha variant

Abstract

In the late December of 2019, SARS-CoV-2, a new coronavirus, was discovered in Wuhan, China and described as the causative agent of Coronavirus Disease 2019 (COVID-19). The disease has spread rapidly across the world due to its high transmissibility and has been declared a pandemic by the World Health Organization (WHO). The development of an effective vaccine has become the most significant issue to constrain the pandemic. Several COVID-19 vaccines have been authorized for human use and others are in clinical trials. Although SARS-CoV-2 encodes four structural proteins, which are Spike (S), Nucleocapsid (N), Membrane (M) and Envelope (E), most of the current vaccines used only Spike as antigen in order to generate antibodies for preventing the virus entry and replication. However, concerns have raised about Spike-based vaccines with the emerging of variants as they can moderately escape from neutralizing antibodies. For these purposes, we developed Virus-like particle (VLP) vaccine which displays hexaproline prefusion-stabilized spike (S-6p), N, M, E proteins, and adjuvanted with Alum and K3-CpG ODN. Rather than using wild type, we preferred to use the sequence of Alpha variant because of its high mortality risk and selection advantages. At the beginning of the study, we designed three different vaccine formulations and based on the results of humoral immune response in mice we determined the optimal formulation and dosage for human use. Our pre-clinical studies revealed that the best vaccine combination was high dose antigen and low dose adjuvants. Next, we wondered whether a 3rd dose has an impact on long-lasting immunity or enhancing immunogenicity in mice so that its applicability to humans could be determined. It was found that 3rd dose injection increased the antibody levels much higher than 2nd dose administration and prevented humoral immunity from decreasing after a certain amount of time. Further, both humoral and cellular immunity were studied with serum and PBMC samples from 117 volunteers who participated in the Phase II clinical trial. All IgG ELISA experiments indicated that VLP-58-1023-AL-K3-PII vaccine induced great amount of humoral immune responses against S,N proteins and WT, Alpha, Delta RBDs. In terms of T cell responses, it is known that Alum-induced robust Th2 response can be redirected to the Th1 axis with the use of CpG ODN. So, we investigated whether Th1 or Th2 type of cell response was dominant after vaccination. All cytokine levels specific to SARS-CoV-2 peptides demonstrated that the vaccine elicited Th1-biased responses. Taken together, this study revealed that VLP-58-1023-AL-K3-PII vaccine for Alpha variant successfully elicited both humoral and cellular immune responses, its effectiveness against other variants was indicated and the efficiency of vaccine could be increased with the administration of 3rd dose, in terms of ensuring long-lasting immunity.