First computational design using lambda-superstrings and in vivo validation of SARS-CoV-2 vaccine

Coronavirus disease 2019 (COVID-19) is the greatest threat to global health at the present time, and considerable public and private effort is being devoted to fighting this recently emerged disease. Despite the undoubted advances in the development of vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, uncertainty remains about their future efficacy and the duration of the immunity induced. It is therefore prudent to continue designing and testing vaccines against this pathogen. In this article we computationally designed two candidate vaccines, one monopeptide and one multipeptide, using a technique involving optimizing lambda-superstrings, which was introduced and developed by our research group. We tested the monopeptide vaccine, thus establishing a proof of concept for the validity of the technique. We synthesized a peptide of 22 amino acids in length, corresponding to one of the candidate vaccines, and prepared a dendritic cell (DC) vaccine vector loaded with the 22 amino acids SARS-CoV-2 peptide (positions 50-71) contained in the NTD domain (DC-CoVPSA) of the Spike protein. Next, we tested the immunogenicity, the type of immune response elicited, and the cytokine profile induced by the vaccine, using a non-related bacterial peptide as negative control. Our results indicated that the CoVPSA peptide of the Spike protein elicits noticeable immunogenicity in vivo using a DC vaccine vector and remarkable cellular and humoral immune responses. This DC vaccine vector loaded with the NTD peptide of the Spike protein elicited a predominant Th1-Th17 cytokine profile, indicative of an effective anti-viral response. Finally, we performed a proof of concept experiment in humans that included the following groups: asymptomatic non-active COVID-19 patients, vaccinated volunteers, and control donors that tested negative for SARS-CoV-2. The positive control was the current receptor binding domain epitope of COVID-19 RNA-vaccines. We successfully developed a vaccine candidate technique involving optimizing lambda-superstrings and provided proof of concept in human subjects. We conclude that it is a valid method to decipher the best epitopes of the Spike protein of SARS-CoV-2 to prepare peptide-based vaccines for different vector platforms, including DC vaccines.Luis Martínez and Iker Malaina were supported by the Basque Government, grants IT974-16 and KK-2018/00090 and by the UPV/EHU and Basque Center of Applied Mathematics, grants US18/21 and US21/27. Carmen Alvarez-Dominguez was funded by the Instituto de Salud Carlos III, grants DTS18-00022 and PI19-01580, co-funded in part with European FEDER funds “A new way of making Europe”, the Instituto de Investigación Marqués de Valdecilla, grant INNVAL20/01, and the COST European action ENOVA CA-16231. David Salcines-Cuevas was supported by a predoctoral contract for the BioHealth research program of the Cantabria government. Hector Teran-Navarro salary was supported by the Instituto de Investigación Marqués de Valdecilla, grant INNVAL19/26. Andrea Zeoli was an Erasmus student from the University of Milan “La Statale” (Milan, Italy) performing a stay at IDIVAL.Peer reviewe