Ad26 vector-based COVID-19 vaccine encoding a prefusion-stabilized SARS-CoV-2 Spike immunogen induces potent humoral and cellular immune responses

Development of effective preventative interventions against SARS-CoV-2, the etiologic agent of COVID-19 is urgently needed. The viral surface spike (S) protein of SARS-CoV-2 is a key target for prophylactic measures as it is critical for the viral replication cycle and the primary target of neutralizing antibodies. We evaluated design elements previously shown for other coronavirus S protein-based vaccines to be successful, e.g., prefusion-stabilizing substitutions and heterologous signal peptides, for selection of a S-based SARS-CoV-2 vaccine candidate. In vitro characterization demonstrated that the introduction of stabilizing substitutions (i.e., furin cleavage site mutations and two consecutive prolines in the hinge region of S2) increased the ratio of neutralizing versus non-neutralizing antibody binding, suggestive for a prefusion conformation of the S protein. Furthermore, the wild-type signal peptide was best suited for the correct cleavage needed for a natively folded protein. These observations translated into superior immunogenicity in mice where the Ad26 vector encoding for a membrane-bound stabilized S protein with a wild-type signal peptide elicited potent neutralizing humoral immunity and cellular immunity that was polarized towards Th1 IFN-gamma. This optimized Ad26 vector-based vaccine for SARS-CoV-2, termed Ad26.COV2.S, is currently being evaluated in a phase I clinical trial (ClinicalTrials.gov Identifier: NCT04436276).Molecular basis of virus replication, viral pathogenesis and antiviral strategie

Synthetic peptides for diagnostic use

Synthetic peptides representing relevant B-cell epitopes are, potentially, ideal antigens to be used in diagnostic assays because of their superior properties with respect to quality control as compared to those of biologically derived molecules and the much higher specificity that sometimes can be obtained. It is thus not a surprise than an increasing number of synthetic peptide based diagnostic assays are being developed or already are commercially available. In this report methods to define useful synthetic peptides, and diagnostic systems that are under development or on the market are discussed

Fine specificity of antibody recognition may predict amino acid substitution in the third variable region of gp 120 during HIV type 1 infection

To investigate how human immunodeficiency virus type 1 (HIV-1) escapes from antibodies directed against the neutralization domain in the third variable region (V3) of gp120, we examined precisely which amino acid contributed to antibody binding. From six HIV-1-infected individuals, sequential sera were tested for antibody binding to individually designed peptide panels. Each individual panel contained all V3 domain sequences of cloned HIV-1 variants obtained at several time points from the studied individual. We showed that the V3 domain is a major site for escape of the humoral immune response. We showed antibody binding was reduced by certain mutations in the V3 domain and sometimes concerted mutations rendered very distinct antigenic variants. The position and the number of the mutations that occurred during infection corresponded with the position and number of amino acids in the V3 domain that were important for binding to anti-V3 antibodies in the early immune response. The specificity of the antibody binding hardly changed during infection. Although mutations at several positions of the V3 domain reduced antibody binding, the mutations were limited to certain positions, probably because the function of the region has to be maintained. The amino acids that were important for binding in combination with the preference for changes at certain positions predicted to some extent the mutations that occurred later during infectio