Identification of broadly neutralizing antibodies against influenza A viruses has raised hopes for the development of monoclonal antibody-based immunotherapy and ‘universal’ vaccines for influenza. However, a significant part of the annual flu burden is caused by two cocirculating, antigenically distinct lineages of influenza B viruses. Here we report human monoclonal antibodies, CR8033, CR8071 and CR9114, which protect mice against lethal challenge from both lineages. Antibodies CR8033 and CR8071 recognize distinct conserved epitopes in the head region of the influenza B hemagglutinin (HA), whereas CR9114 binds a conserved epitope in the HA stem and protects against lethal challenge with influenza A and B viruses. These antibodies may inform on development of monoclonal antibody-based treatments and a universal flu vaccine for all influenza A and B viruses.

A safe and effective vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) may be required to end the coronavirus disease 2019 (COVID-19) pandemic 1 – 8 . For global deployment and pandemic control, a vaccine that requires only a single immunization would be optimal. Here we show the immunogenicity and protective efficacy of a single dose of adenovirus serotype 26 (Ad26) vector-based vaccines expressing the SARS-CoV-2 spike (S) protein in nonhuman primates. 52 rhesus macaques were immunized with Ad26 vectors encoding S variants or sham control and were challenged with SARS-CoV-2 by the intranasal and intratracheal routes 9 , 10 . The optimal Ad26 vaccine induced robust neutralizing antibody responses and provided complete or near-complete protection in bronchoalveolar lavage and nasal swabs following SARS-CoV-2 challenge. Vaccine-elicited neutralizing antibody titers correlated with protective efficacy, suggesting an immune correlate of protection. These data demonstrate robust single-shot vaccine protection against SARS-CoV-2 in nonhuman primates. The optimal Ad26 vector-based vaccine for SARS-CoV-2, termed Ad26.COV2.S, is currently being evaluated in clinical trials.

Replication-deficient human adenovirus type 5 (Ad5) can be produced to high titers in complementing cell lines, such as PER.C6, and is widely used as a vaccine and gene therapy vector. However, preexisting immunity against Ad5 hampers consistency of gene transfer, immunological responses, and vector-mediated toxicities. We report the identification of human Ad35 as a virus with low global prevalence and the generation of an Ad35 vector plasmid system for easy insertion of heterologous genes. In addition, we have identified the minimal sequence of the Ad35-E1B region (molecular weight, 55,000 [55K]), pivotal for complementation of fully E1-lacking Ad35 vector on PER.C6 cells. After stable insertion of the 55K sequence into PER.C6 cells a cell line was obtained (PER.C6/55K) that efficiently transcomplements both Ad5 and Ad35 vectors. We further demonstrate that transduction with Ad35 is not hampered by preexisting Ad5 immunity and that Ad35 efficiently infects dendritic cells, smooth muscle cells, and synoviocytes, in contrast to Ad5.It has been shown in diverse in vivo models that recombinant adenovirus type 5 (Ad5) has potential as a vehicle to transfer genes for treatment or prevention of disease (49, 52). Although encouraging, the extrapolation from animal models to humans faces at least one extra hurdle, i.e., the presence of anti-Ad5 neutralizing activity (NA) in sera from human individuals. The humoral response to Ad5 is strong and has been found to impede, depending on the administration route, the infection efficiency in animal models as well as in humans (7,9,18,29,30,35,37,42,45). Concomitant with the decrease in transduction, high NA against the vector also abolishes Ad5-mediated toxicity (8). Importantly, when very high vector doses were used in preimmunized nonhuman primates, new toxic effects were found that were not observed in naive animals (54). These findings show that preexisting immunity severely hampers accurate dose control, since human individuals differ in their NA against Ad5-based vectors. Strategies to bypass NA to Ad5 viruses include switching of adenovirus type (28,32,36) and use of animal adenoviruses (13,25,34). Animal adenoviruses have the advantage that NA is predicted to be absent in humans. Disadvantages of this strategy include the lack of knowledge regarding the biology of these viruses including tropism on human cells, potential difficulties in manufacturing, and the possibility of in vivo recombination with human types leading to unknown disease. Human adenoviruses on the other hand are better characterized and their subclinical disease association in humans is known (10,17,55). However, recent knowledge on the prevalence of NA towards human adenoviruses worldwide is not available and therefore it is difficult to predict which type would be the best alternative for Ad5. To identify human adenovirus types with low seroprevalence, an extensive screen was performed using most human adenovirus types and serum samples derived from healthy blood donors from 6 different geographica...

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-γ. 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).